J Clin Monit Comput DOI 10.1007/s10877-014-9586-2
ORIGINAL RESEARCH
Continuous non-invasive monitoring improves blood pressure stability in upright position: randomized controlled trial Jan Benes • Alena Simanova • Tereza Tovarnicka • Silvie Sevcikova • Jakub Kletecka • Jan Zatloukal • Richard Pradl • Ivan Chytra • Eduard Kasal
Received: 4 February 2014 / Accepted: 14 May 2014 Ó Springer Science+Business Media New York 2014
Abstract Intermittent blood pressure (BP) monitoring is the standard-of-care during low and intermediate risk anaesthesia, yet it could lead to delayed recognition of BP fluctuations. Perioperative hypotension is known to be associated with postoperative complications. Continuous, non-invasive methods for BP monitoring have been developed recently. We have tested a novel non-invasive, continuous monitor (using the volume clamp method) to assist with maintaining BP in safe ranges for patients undergoing surgery in a beach chair position. Forty adult patients undergoing thyroid gland surgery in an upright position were included in this prospective randomised controlled trial. Patients were equally allocated to the group with continuous monitoring of BP using the CNAPÒ Monitor and to the control group managed using an intermittent oscillometric BP cuff. The absolute and proportional time spent outside the range of ±20 % of the target BP along with other hemodynamic and clinical parameters were evaluated. The continuous monitoring decreased the anaesthesia time spent below -20 % pressure range [absolute: 12 min (4–20) vs. 27 min (16–34); p = 0.001; relative to procedure length: 14 % (7–20) vs. 33.5 % (17.5–53); p = 0.003]. No significant differences were observed in postoperative morbidity or in hospital length of stay. Continuous non-invasive BP monitoring via the CNAPÒ Monitor allows for better BP management in Trial Registration: ACTRN12612001058864 (www.anzctr.org.au). J. Benes (&) A. Simanova T. Tovarnicka S. Sevcikova J. Kletecka J. Zatloukal R. Pradl I. Chytra E. Kasal Department of Anaesthesia and Intensive Care Medicine, Teaching Hospital and Faculty of Medicine in Plzen, Charles University Prague, Alej Svobody 80, 306 40 Plzenˇ, Czech Republic e-mail: [email protected]
patients undergoing surgery in a beach chair position. In our randomised trial the time spent in hypotension was significantly shorter using continuous monitoring. Keywords Arterial pressure General anaesthesia Hypotension Measurement techniques
1 Introduction Blood pressure (BP) measurement is an inevitable part of complex perioperative monitoring. Unlike other modalities (electrocardiography, pulse oxymetry), its non-invasive assessment had been possible only in an intermittent fashion using an interval which usually varies between 1 and 5 min. The available guidelines of the American Society of Anaesthesiologists [1] as well as the Czech Society of Anaesthesiology and Intensive Care [2] (authors’ national society) deem the 5 min interval as a minimum. In theory, this interval could lead to delayed recognition of deleterious hypotensive and hypertensive episodes. The arterial pressure waveform obtained by direct arterial catheterisation eliminates this problem and also contains important information about the cardiovascular system [3]. However, this technique is not without complications [4]. Also, catheterisation itself may be time consuming and not well tolerated by awake subjects. In high risk cases these ‘‘costs’’ of arterial cannulation are considered negligible [5], whereas low or intermediate risk procedures are monitored using intermittent BP readings as the standard-of-care. Chen et al. [6] hypothesized that 14 ± 3 min per hour of hypo- or hypertension could have been identified by continuous monitoring versus intermittent monitoring. Severe hypotension is associated with negative outcomes. This relationship was described
123
J Clin Monit Comput
recently [7–9]. Patients undergoing shoulder or thyroid gland surgery are often placed in a beach chair position after the induction of anaesthesia. These postural changes in anaesthetised subjects may induce severe BP fluctuations and sporadic life or health threatening complications [10, 11]. Hypotension was an independent predictor of diminished brain tissue perfusion measured by different methods in patients in the upright position [12, 13]. However, direct and continuous BP measurement is rarely performed. Novel devices adopted in clinical practice recently might overcome this problem by enabling continuous but non-invasive BP estimation. The CNAPÒ device (CNSystems, Graz, Austria) is based on the Penˇa´z ‘‘volume clamp’’ method, similar to the former Finapres monitor (FMS, Amsterdam, The Netherlands). The principle of the method is keeping the volume of the finger’s blood compartment constant (measured by photo-plethysmography) using an inflatable finger cuff. Pressure in the cuff equals under specific conditions (vascular unloading) the pressure inside the finger blood vessels and hence allows reconstructing of a typical arterial pressure curve. The values obtained at finger level are calibrated via brachial cuff measurement. Clinical evaluation was performed by some authors showing acceptable performance [14–16]; lower accuracy was found in certain situations only [14, 17]. Fig. 1 The CONSORT flow chart of the patients throughout the study
123
Recently, a benefit from continuous measurement using the CNAPÒ Monitor was observed in patients undergoing Caesarean section [18] and in patients admitted to the emergency department [19]. The goal of our controlled randomized study was to assess the effect of adding continuous non-invasive BP monitoring on the anaesthesiologist’s ability to reduce BP fluctuations in anaesthetised patients undergoing surgery in beach chair position. We hypothesized that use of the CNAP device would help to maintain better BP stability by quicker recognition of hypo-/hypertension and of the treatment response without the need for arterial catheterisation.
2 Methods A randomized controlled trial was performed at the Department of Anaesthesia and Intensive Care Medicine in Plzen—Charles University hospital—between October 2012 and April 2013. The study was approved by the institutional review board and registered in the primary WHO register (www.anzctr.org.au, ACTRN12612001058864). Patients signed an informed consent for study inclusion. During the study period all patients older than 18 years undergoing thyroid gland surgery in our surgical department were found eligible for inclusion. The study patients’
J Clin Monit Comput
distribution in adherence to the CONSORT statement [20] is given in Fig. 1. Patients included in the study were randomized into the Continuous and Intermittent measurement group using the sealed opaque envelopes technique at the start of anaesthesia by the treating anaesthesiologist (AS, TT). After randomization the information was concealed and all other study group members or treating staff were blinded to patients’ allocation. 2.1 Anaesthesia and blood pressure monitoring All procedures were performed under general anaesthesia induced by propofol (2 mg/kg) and sufentanil (0.5 lg/kg). The intubation was facilitated with muscle relaxants (rocuronium or atracurium, both 0.5 mg/kg according to decision of treating anaesthesiologist). Anesthesia maintenance was performed using an O2 ? Air gas mixture with Sevoflurane (MAC 0.8–1.2 adapted to patient’s age); analgesia and muscle relaxants were added when necessary. At the end of each procedure the patient was extubated and transferred to the postoperative care unit. Throughout the procedure standard monitoring of cardiovascular and respiratory functions was performed. BP was monitored continuously in both groups using the standalone CNAPÒ Monitor (software version 3.5), but device screen was displayed and visible to the treating anaesthesiologist only in the Continuous group. CNAPÒ monitoring was started before induction of anaesthesia in order to obtain a calibrated signal at the moment of intravenous anaesthetic administration. The induction of anaesthesia and the extubation were marked as the beginning and the end of the monitoring period (‘‘the length of anaesthesia’’). Every 15 min a recalibration of the CNAPÒ signal including a finger cuff change was done automatically according to the manufacturer’s recommendation. The recalibration is associated with 2–2.5 min interruption of the continuous monitoring (this time was subtracted from the calculated length of procedure to avoid bias). In order to avoid changes in pressure readings induced by change in position, the fingers and arm cuffs were all maintained at the level of the heart throughout the positioning. Intermittent arm pressure readings via a standard automatic oscillometric cuff (Ultraview SL2700, Spacelabs Healthcare, Washington, USA) were performed using a 5 min time protocol. The treating anaesthesiologist was allowed to increase the rate of pressure measurements (up to ‘‘once per minute’’) or make any additional measurements if necessary throughout the procedure. Throughout the procedure BP was maintained within ±20 % of patient’s target value (see later in methods section for the target systolic BP definition). In cases of hypotension, the following steps were performed according to presumed underlying cause: (1) if hypovolemia was suspected a bolus
of 250/500 ml of crystalloid solution was given, (2) 5–10 mg boluses of ephedrine were used repeatedly to a maximal dose of 100 mg per procedure (3) if hypotension was prolonged the infusion of norepinephrine was considered. In cases of hypertension and after exclusion of inadequate anaesthesia/analgesia, the infusion of nitrate donor (isosorbid dinitrate, nitroprusside) or other antihypertensive medication (urapidil, clonidine, esmolol, metoprolol) were started according to clinical conditions and presumed underlying cause. 2.2 Data analysis and outcome measures Patient demographic data regarding underlying thyroid gland disease, chronic comorbidities, presence of hypertonic disease, medication and usual BP were collected. Basal hemodynamic values (heart rate, BP) were collected before the anaesthesia induction and throughout the whole procedure. During the use of anaesthesia, starting with the administration of the i.v. anaesthetic until the extubation, continuous BP measurements were gathered by the CNAPÒ Monitor with 100 Hz frequency and stored on an external memory stick for off-line analysis. Medications given to manipulate the BP were collected via the anaesthesia procedure sheet. In the morning before surgery a clinical evaluation of cognitive functions was performed and the Short Memory Orientation Test (SMOT) questionnaire [21] was given by trained study personnel (JK, SS). Similar examinations were performed after the procedure within 40–60 min after arousal by the same member of the team (unaware of the patient’s group allocation). Postoperative care was provided by the treating staff of the relevant ward including clinical diagnosis of possible complications and their treatment. A study member unaware of treatment allocation performed a short clinical examination before patient discharge with retrospective morbidity assessment (JB, JZ, RP). As the hospital length of stay after thyroid gland surgery is very short no predefined criteria or readiness to discharge were evaluated. The off-line BP analysis was performed in a concealed fashion (JB) using the Task ForceÒ Monitor software (CNSystems, Graz, Austria). The software enables beat-tobeat transformation of the continuous pressure curve signal providing systolic and diastolic BP and beat length (in seconds). According to each patient’s target BP, time spent in each decile of BP (i.e. 70–79, 80–89 % of normal values etc.) was summed up and the percentage values during the whole monitoring period were calculated. The target systolic BP (TSBP) was defined as patient’s chronic value (reported by general practitioner in the preoperative assessment or known by the patient) increased by 10 mmHg in order to account for head perfusion level during upright position. The primary end point of the study was the time
123
J Clin Monit Comput
(absolute and proportional) spent outside the safe range of normal BP (-20 and ?20 % of TSBP). The number of hypotensive/hypertensive periods (±20 %), their length and number of interventions needed were also assessed. In addition, time spent in severe hypotension (-30 % TSBP), severe hypertension (?30 % TSBP), and with an absolute MAP value under 60 mmHg were also evaluated. The number and rate of postoperative complications including cognitive function assessment (using the SMOT test before and after procedure) were evaluated as safety outcomes.
Table 1 Baseline demographic characteristics
2.3 Statistical analysis In a previous study [6], comprising 25 patients, 23 ± 5 % of anaesthesia time (14 ± 3 min in hour) was spent in hypo/hypertension using the intermittent measurement. We decided to include a larger population (20 patients per group) as BP fluctuations in a beach chair position might be more frequent. Data presented in the paper are stated as median (interquartile range) for non-normally distributed and mean ± standard deviation for normally distributed values. The Kolmogorov–Smirnoff test was used to test the normal distribution of the data. For categorical variables the absolute number of cases and the percentage value were calculated. To evaluate the time spent in hypotension etc. the proportional time measure was calculated based on the percentage of the overall monitoring period. To test the statistical significance of the results between groups either unpaired t test or Mann–Whitney tests were used according to data normality. Change of SOMT in time was tested using the Wilcoxon test due to their non-normal distribution. Grouping variables were tested using Chi square test. A p value of \0.05 was considered to indicate statistical significance. All statistical calculations were performed using MedCalcÒ software, version 12.7.0.0 (Frank Schoonjans, MedCalc Software, Broekstraat 52, 9030 Mariakerke, Belgium).
3 Results During the study period (October 2012 to March 2013) 46 patients undergoing thyroid gland surgery were found eligible. In 4 cases the inclusion was not possible due to technical reasons (twice the CNAPÒ Monitor was in use at the same time, once it was out of function due to service and once the procedure was rescheduled to another operation theatre without possible change of personnel). In two cases exclusion criteria were met (once because of Raynaud’s syndrome and once because of finger deformities due to rheumatoid arthritis), both precluding a safe use of finger cuffs. All other patients were included and equally randomized. Baseline characteristics of patients included in
123
Continuous N = 20
Intermittent N = 20
p
Age (years)
56 ± 15
59 ± 12
0.431
Height (cm)
169 ± 6
169 ± 8
0.972
Weight (kg)
77 ± 15
86 ± 24
0.153
Sex (F/M)
18/2
15/5
0.405
ASA (1:2:3)
3/15/2
1/12/7
0.047
Chronic systolic blood pressure (mmHg)
121 ± 10
127 ± 11
0.079
Chronic diastolic blood pressure (mmHg)
76 ± 8
78 ± 6
0.209
Primary diagnosis (Hyperthyroidism/Goitre/ Hypothyroidism)
4/11/5
2/17/1
0.564
Procedure (Total/Partial resection)
16/4
17/3
1.000
Comorbidities Arterial hypertension
12 (60 %)
12 (60 %)
0.747
Ischemic heart disease
0 (0 %)
3 (15 %)
0.230
Chronic respiratory disease
1 (5 %)
3 (15 %)
0.598
Diabetes mellitus
1 (5 %)
3 (15 %)
0.598
Obesity
4 (20 %)
10 (50 %)
0.097
Data are presented as mean ± standard deviation or number (proportion) F Female, M Male, ASA Physical status classification system according to American Society of Anaesthesiologists
the study are given in Table 1. No significant differences were observed between study arms for most of these features. However, a trend towards higher rate of comorbidities and higher American Society of Anaesthesiology status (ASA) was observed among the Intermittent group patients. All patients were without clinical signs of hyper-/ hypothyroidism and their thyroid hormones were within normal levels. Neither differences in primary diagnosis (reason for the surgery) nor procedure performed were observed. The incidence of patients with chronic arterial hypertension was comparable based on their preadmission BP. The overall length of anaesthesia was similar. No monitoring-induced complications were observed among the study population. Patients in the Continuous group had a reduction of absolute time spent in hypertension (-20 % of TSBP) compared to the Intermittent group [12 min (4–20) vs. 27 min (16–34); p = 0.001]. The Continuous group also experienced a reduction in the relative proportion of time in hypotension versus the Intermittent group [14 % (7–20) vs. 33.5 % (17.5–53); p = 0.003]. Hypotensive periods were non-significantly less frequent in the Continuous arm but their duration was shorter. Interestingly, the number of interventions was comparable between both groups. The
J Clin Monit Comput Table 2 Primary and secondary outcome measures Continuous
Intermittent
p
70 [58–95]
81 [65–98]
0.387
Absolute time (min)
12 [4–20]
27 [16–34]
0.001
Proportional time (%)
14 [7–20] %
33.5 [17.5–53] %
0.003
Number of episodes per patient
2.5 [1.5–4]
3.5 [3–5.5]
0.053
Duration of episode (min)
4 [2–7]
8 [6–16]
0.014
Number of interventions
2 [1–3]
2 [1–4]
0.913
2 [0–4] 2.5 [0–4.5] %
8 [2–11] 10 [1.5–17.5] %
0.005 0.006
Absolute time (min)
0 [0–1]
0 [0–4]
0.897
Proportional time (%)
0 [0–1] %
0 [0–5] %
0.867
4 [1–6]
2 [0–4]
0.411
Anaesthesia duration (min) Hypotension -20 % of TSBP
-30 % of TSBP Absolute time (min) Proportional time (%) Fig. 2 Distribution of proportional time according to chronic systolic pressure deciles (bars show mean ± SD)
interventions were mostly performed using vasoactive drug (Ephedrine). In only three cases (two patients in Continuous group) volume expansion was performed. No significant hypovolemia was present in patients of either group according to the value of pulse pressure variation after induction [8 % (7–12) vs. 11 % (8–12) in Intermittent vs. Continuous groups; p = 0.15]. Similar difference between Continuous and Intermittent group was observed in time spent in severe hypotension [-30 % of TSBP: 2.5 % (0–4.5) vs. 10 % (1.5–17.5); p = 0.006]. There were no differences in time spent above the ?20 and ?30 % of TSBP threshold. Distribution of proportional time spent in BP deciles for patients of both groups is displayed in Fig. 2. The proportional time of MAP \ 60 mmHg was very short in both groups. In two cases (10 %) of the Continuous group no period of hypotension was observed and in a further three cases (15 %) only very short (1–2 min) periods of mild hypotension were observed. All patients in the intermittent group experienced at least one episode of hypotension and 18 patients (90 %) had more than one episode. The number and length of hypertensive periods was comparable between groups and only two interventions were initiated in the Continuous arm and one in the Intermittent. The results of primary and secondary outcome measures are summarised in Table 2. The hospital length of stay was comparable between groups, as well as number and rate of complications. The incidence of postoperative nausea and vomiting was also similar. In two patients (one per group) a revision for bleeding was necessary. One patient from the Intermittent group needed a short period (15 h) of postoperative
MAP \ 60 mmHg
Hypertension ?20 % of TSBP Absolute time (min) Proportional time (%)
5 [0.5–7] %
2 [0–4.5] %
0.210
Number of episodes per patient
1 [0–2.5]
1 [0–2]
0.966
Duration of episode (min)
2 [0–3]
2 [0–3]
0.889
Absolute time (min)
1 [0–2]
0 [0–3]
0.839
Proportional time (%)
1 [0–2] %
0 [0–3] %
0.897
?30 % of TSBP
Clinical endpoints SOMT Before anaesthesia
26 [26–28]
26 [24–28]
0.719
After anaesthesia
24 [20–26]#
24 [22–27]#
0.813
Postoperative nausea/ vomiting
3 (15 %)/3 (15 %)
3 (15 %)/4 (20 %)
0.831
Postoperative bleeding
1 (5 %)
1 (5 %)
0.468
Hospital length of stay (days)
3 [3–4]
3 [3–4]
0.479
Data are presented as median [interquartile range] or number (proportion) MAP Mean arterial pressure, SOMT Short Memory Orientation Test, TBSP target systolic blood pressure #
p \ 0.01—after versus before the anaesthesia (Wilcoxon test)
ventilation because of large goitre removal and resulting risk of airway oedema formation. No other complications were observed among our patients. No differences in the values of SMOT between groups (both before and after
123
J Clin Monit Comput
anaesthesia) were observed. After the procedure, there was a statistically, but not clinically, significant decay in SMOT in both groups compared to preoperative values (see Table 2). No overt cognitive dysfunction was observed in study patients throughout the postoperative stay.
4 Discussion In our prospective, controlled, randomized study the use of continuous, non-invasive BP monitoring decreased the time spent in hypotension and its magnitude compared to standard intermittent monitoring in patients undergoing thyroid gland surgery in a beach chair position. Maintaining BP stability is one of the major tasks of an anaesthesiologist during anaesthesia use. Although the safe margins of BP fluctuations are not exactly defined, the ±20 % range is usually recommended [22]. Perioperative BP lability is deemed to be a risk factor for complications development, most importantly myocardial ischemia, renal impairment [9, 11], cognitive dysfunction and in some extreme cases even brain damage [10]. The association between even mild BP fluctuations, the beach chair position and the cerebral perfusion assessed by tissue oxymetry was demonstrated by several groups [12, 13, 23, 24]. Whether these changes are associated with manifest neuronal loss is unresolved. In order to test for clinical correlate the SMOT test (similarly to the PINOCHIO trial [25]) was used in our study as a safety outcome. We have observed an early postoperative subclinical decline without showing any difference between groups. Expectedly, no apparent organ dysfunction developed in our rather low risk patients throughout the short period until discharge. Nevertheless, preventing prolonged hypotension might be important even in such patients. Based on general critical care experience, continuous monitoring enables faster recognition of BP changes and helps to reduce time spent outside declared safety margins. However, in low risk patients the monitoring-associated risks should be considered as well. Preventing arterial catheterisation by using non-invasive continuous BP monitors might offer a safe alternative. Previously Chen et al. [6] and Ilies et al. [18] used volume clamp based devices for assessing the risk of hypotension. In both trials the use of continuous, non-invasive BP monitoring was associated with lower hypotension occurrence, but the estimations were rather hypothetical given their observational nature. In our study we were able to directly quantify the effect of continuous non-invasive BP monitoring on the BP stability thanks to the controlled, randomized design. The absolute and relative time spent in hypotension was reduced to 50 % and severe hypotension to 25 % without increasing the monitoring-associated burden. This was in
123
large part due to shorter durations of these episodes, but they were also non-significantly less frequent. Both these facts support the hypothesis of faster recognition and shorter reaction times. This quantification of the therapeutic effect might be of importance for balancing the costs and benefits of monitoring escalation. Our study suffers from some important limitations which should be acknowledged. First the CNAPÒ device was used for continuous BP estimation. The use of arterial invasive pressure monitoring would offer more accurate results, especially in periods of sudden BP fluctuations. The radial artery catheterisation was considered during the study protocol preparation, but was strongly discouraged by the participating surgeons and review board as unnecessary escalation of invasiveness in low risk patients. Considerations still exist regarding the accuracy of the CNAP device. Several studies [14–16] showed a good agreement between BP monitored using the CNAPÒ in comparison to invasive pressure readings. The accuracy in absolute values seems to decrease after induction and during sudden and profound drops of BP [14, 17], without affecting the trending ability. Our results might be biased by underestimating the magnitude of observed fluctuations especially in the -30 % TBSP end-point. However, results published by Hahn with the newest software version—V3.5 (also used in our trial) showed clinically acceptable agreement [26]. Moreover, in low risk patients the BP monitoring via arterial cannulation is seldom performed and intermittent oscillometric method may be considered as a clinically relevant reference. The CNAP device uses the oscillometric cuff for calibration of continuous monitoring enabling comparison of both methods. Finally, our observations were done on a rather small, homogenous population of patients with presumably higher incidence of postural or operation-induced BP changes. Hence, generalizing our results to other clinical scenarios may not be straightforward. In addition, our small study sample of low risk patients precludes us from assessing the clinical relevance of our findings. Our results are potentially important for anaesthesia management itself, but the actual clinical benefit of better pressure stability remains unresolved.
5 Conclusion In conclusion, our study shows that the use of continuous non-invasive arterial BP measurement might offer an improved monitoring solution in comparison to the standard intermittent measurement in patients undergoing operation in a beach chair position. Time spent in hypotension was significantly reduced using the continuous, non-invasive measurement.
J Clin Monit Comput Acknowledgments The study was supported by the Charles University Research Fund (Project number P36). The CNAPÒ Monitor and Task ForceÒ Monitor software were supplied by CNSystems, Graz, Austria. There were no additional payments depending on the results of the study. Conflict of interests JB received lecturing fees from Edwards Lifecsiences Inc., all other co-authors declare no competing interests.
References 1. ASA House of Delegates STANDARDS FOR BASIC ANESTHETIC MONITORING. http://www.asahq.org/For-Members/ */media/For%20Members/documents/Standards%20Guidelines% 20Stmts/Basic%20Anesthetic%20Monitoring%20201ashx. Accessed 12 July 2013 (2011). ´ SADY 2. Cvachovec K., Cˇerny´ V., Herold I., Kozlı´k P., Sˇturma J. ZA ˇ NE´ ANESTEZIOLOGICKE´ PE´CˇE. http://www.csarim. BEZPEC cz/Public/csim/22%20%20DP_safety_anesth_CSARIM_final_ approval_14021pdf. Accessed 12 Jul 2013 (2012). 3. Lamia B, Chemla D, Richard C, Teboul JL. Clinical review: interpretation of arterial pressure wave in shock states. Crit Care. 2005;9:601–6. 4. Scheer B, Perel A, Pfeiffer UJ. Clinical review: complications and risk factors of peripheral arterial catheters used for haemodynamic monitoring in anaesthesia and intensive care medicine. Crit Care. 2002;6:199–204. 5. Cannesson M, Pestel G, Ricks C, Hoeft A, Perel A. Hemodynamic monitoring and management in patients undergoing high risk surgery: a survey among North American and European anesthesiologists. Crit Care. 2011;15:R197. 6. Chen G, et al. Impact of non invasive and beat-to-beat arterial pressure monitoring on intraoperative hemodynamic management. J Clin Monit Comput. 2012;26:133–40. 7. Monk TG, Saini V, Weldon BC, Sigl JC. Anesthetic management and one-year mortality after noncardiac surgery. Anesth Analg. 2005;100:4–10. 8. Sessler DI, et al. Hospital stay and mortality are increased in patients having a ‘‘triple low’’ of low blood pressure, low bispectral index, and low minimum alveolar concentration of volatile anesthesia. Anesthesiology. 2012;116:1195–203. 9. Walsh M, et al. Relationship between intraoperative mean arterial pressure and clinical outcomes after noncardiac surgery: toward an empirical definition of hypotension. Anesthesiology. 2013;119:507–15. 10. Drummond JC, Lee RR, Howell JP. Focal cerebral ischemia after surgery in the ‘‘beach chair’’ position: the role of a congenital variation of circle of Willis anatomy. Anesth Analg. 2012;114:1301–3. 11. Pohl A, Cullen DJ. Cerebral ischemia during shoulder surgery in the upright position: a case series. J Clin Anesth. 2005;17:463–9.
12. Jeong H, et al. Haemodynamics and cerebral oxygenation during arthroscopic shoulder surgery in beach chair position under general anaesthesia. Acta Anaesthesiol Scand. 2012;56:872–9. 13. Tange K, et al. Cerebral oxygenation in the beach chair position before and during general anesthesia. Minerva Anestesiol. 2010;76:485–90. 14. Ilies C, et al. Investigation of the agreement of a continuous noninvasive arterial pressure device in comparison with invasive radial artery measurement. Br J Anaesth. 2012;108:202–10. 15. Jeleazcov C, et al. Precision and accuracy of a new device (CNAPTM) for continuous non-invasive arterial pressure monitoring: assessment during general anaesthesia. Br J Anaesth. 2010;105:264–72. 16. Biais M, et al. Continuous non-invasive arterial pressure measurement: evaluation of CNAP device during vascular surgery. Ann Fr Anesth Reanim. 2010;29:530–5. 17. Gayat E, et al. CNAP(Ò) does not reliably detect minimal or maximal arterial blood pressures during induction of anaesthesia and tracheal intubation. Acta Anaesthesiol Scand. 2013;57: 468–73. 18. Ilies C, et al. Detection of hypotension during Caesarean section with continuous non-invasive arterial pressure device or intermittent oscillometric arterial pressure measurement. Br J Anaesth. 2012;109:413–9. 19. Wagner JY, et al. Noninvasive continuous versus intermittent arterial pressure monitoring: evaluation of the vascular unloading technique (CNAP device) in the emergency department. Scand J Trauma Resusc Emerg Med. 2014;22:8. 20. Schulz KF, Altman DG, Moher D, CONSORT Group. CONSORT 2010 statement: updated guidelines for reporting parallel group randomised trials. BMC Med. 2010;8:18. 21. Katzman R, et al. Validation of a short orientation-memoryconcentration test of cognitive impairment. Am J Psychiatry. 1983;140:734–9. 22. Howell SJ, Sear JW, Foe¨x P. Hypertension, hypertensive heart disease and perioperative cardiac risk. Br J Anaesth. 2004;92:570–83. 23. Lee JH, Min KT, Chun YM, Kim EJ, Choi SH. Effects of beachchair position and induced hypotension on cerebral oxygen saturation in patients undergoing arthroscopic shoulder surgery. Arthroscopy. 2011;27:889–94. 24. Koh JL, Levin SD, Chehab EL, Murphy GS: Neer Award 2012: cerebral oxygenation in the beach chair position: a prospective study on the effect of general anesthesia compared with regional anesthesia and sedation. J Shoulder Elbow Surg. 2013;22: 1325–1331. 25. Bilotta F, et al. Early postoperative cognitive dysfunction and postoperative delirium after anaesthesia with various hypnotics: study protocol for a randomised controlled trial—the PINOCCHIO trial. Trials. 2011;12:170. 26. Hahn R, Rino¨sl H, Neuner M, Kettner SC. Clinical validation of a continuous non-invasive haemodynamic monitor (CNAP 500) during general anaesthesia. Br J Anaesth. 2012;108:581–5.
123
ORIGINAL RESEARCH
Continuous non-invasive monitoring improves blood pressure stability in upright position: randomized controlled trial Jan Benes • Alena Simanova • Tereza Tovarnicka • Silvie Sevcikova • Jakub Kletecka • Jan Zatloukal • Richard Pradl • Ivan Chytra • Eduard Kasal
Received: 4 February 2014 / Accepted: 14 May 2014 Ó Springer Science+Business Media New York 2014
Abstract Intermittent blood pressure (BP) monitoring is the standard-of-care during low and intermediate risk anaesthesia, yet it could lead to delayed recognition of BP fluctuations. Perioperative hypotension is known to be associated with postoperative complications. Continuous, non-invasive methods for BP monitoring have been developed recently. We have tested a novel non-invasive, continuous monitor (using the volume clamp method) to assist with maintaining BP in safe ranges for patients undergoing surgery in a beach chair position. Forty adult patients undergoing thyroid gland surgery in an upright position were included in this prospective randomised controlled trial. Patients were equally allocated to the group with continuous monitoring of BP using the CNAPÒ Monitor and to the control group managed using an intermittent oscillometric BP cuff. The absolute and proportional time spent outside the range of ±20 % of the target BP along with other hemodynamic and clinical parameters were evaluated. The continuous monitoring decreased the anaesthesia time spent below -20 % pressure range [absolute: 12 min (4–20) vs. 27 min (16–34); p = 0.001; relative to procedure length: 14 % (7–20) vs. 33.5 % (17.5–53); p = 0.003]. No significant differences were observed in postoperative morbidity or in hospital length of stay. Continuous non-invasive BP monitoring via the CNAPÒ Monitor allows for better BP management in Trial Registration: ACTRN12612001058864 (www.anzctr.org.au). J. Benes (&) A. Simanova T. Tovarnicka S. Sevcikova J. Kletecka J. Zatloukal R. Pradl I. Chytra E. Kasal Department of Anaesthesia and Intensive Care Medicine, Teaching Hospital and Faculty of Medicine in Plzen, Charles University Prague, Alej Svobody 80, 306 40 Plzenˇ, Czech Republic e-mail: [email protected]
patients undergoing surgery in a beach chair position. In our randomised trial the time spent in hypotension was significantly shorter using continuous monitoring. Keywords Arterial pressure General anaesthesia Hypotension Measurement techniques
1 Introduction Blood pressure (BP) measurement is an inevitable part of complex perioperative monitoring. Unlike other modalities (electrocardiography, pulse oxymetry), its non-invasive assessment had been possible only in an intermittent fashion using an interval which usually varies between 1 and 5 min. The available guidelines of the American Society of Anaesthesiologists [1] as well as the Czech Society of Anaesthesiology and Intensive Care [2] (authors’ national society) deem the 5 min interval as a minimum. In theory, this interval could lead to delayed recognition of deleterious hypotensive and hypertensive episodes. The arterial pressure waveform obtained by direct arterial catheterisation eliminates this problem and also contains important information about the cardiovascular system [3]. However, this technique is not without complications [4]. Also, catheterisation itself may be time consuming and not well tolerated by awake subjects. In high risk cases these ‘‘costs’’ of arterial cannulation are considered negligible [5], whereas low or intermediate risk procedures are monitored using intermittent BP readings as the standard-of-care. Chen et al. [6] hypothesized that 14 ± 3 min per hour of hypo- or hypertension could have been identified by continuous monitoring versus intermittent monitoring. Severe hypotension is associated with negative outcomes. This relationship was described
123
J Clin Monit Comput
recently [7–9]. Patients undergoing shoulder or thyroid gland surgery are often placed in a beach chair position after the induction of anaesthesia. These postural changes in anaesthetised subjects may induce severe BP fluctuations and sporadic life or health threatening complications [10, 11]. Hypotension was an independent predictor of diminished brain tissue perfusion measured by different methods in patients in the upright position [12, 13]. However, direct and continuous BP measurement is rarely performed. Novel devices adopted in clinical practice recently might overcome this problem by enabling continuous but non-invasive BP estimation. The CNAPÒ device (CNSystems, Graz, Austria) is based on the Penˇa´z ‘‘volume clamp’’ method, similar to the former Finapres monitor (FMS, Amsterdam, The Netherlands). The principle of the method is keeping the volume of the finger’s blood compartment constant (measured by photo-plethysmography) using an inflatable finger cuff. Pressure in the cuff equals under specific conditions (vascular unloading) the pressure inside the finger blood vessels and hence allows reconstructing of a typical arterial pressure curve. The values obtained at finger level are calibrated via brachial cuff measurement. Clinical evaluation was performed by some authors showing acceptable performance [14–16]; lower accuracy was found in certain situations only [14, 17]. Fig. 1 The CONSORT flow chart of the patients throughout the study
123
Recently, a benefit from continuous measurement using the CNAPÒ Monitor was observed in patients undergoing Caesarean section [18] and in patients admitted to the emergency department [19]. The goal of our controlled randomized study was to assess the effect of adding continuous non-invasive BP monitoring on the anaesthesiologist’s ability to reduce BP fluctuations in anaesthetised patients undergoing surgery in beach chair position. We hypothesized that use of the CNAP device would help to maintain better BP stability by quicker recognition of hypo-/hypertension and of the treatment response without the need for arterial catheterisation.
2 Methods A randomized controlled trial was performed at the Department of Anaesthesia and Intensive Care Medicine in Plzen—Charles University hospital—between October 2012 and April 2013. The study was approved by the institutional review board and registered in the primary WHO register (www.anzctr.org.au, ACTRN12612001058864). Patients signed an informed consent for study inclusion. During the study period all patients older than 18 years undergoing thyroid gland surgery in our surgical department were found eligible for inclusion. The study patients’
J Clin Monit Comput
distribution in adherence to the CONSORT statement [20] is given in Fig. 1. Patients included in the study were randomized into the Continuous and Intermittent measurement group using the sealed opaque envelopes technique at the start of anaesthesia by the treating anaesthesiologist (AS, TT). After randomization the information was concealed and all other study group members or treating staff were blinded to patients’ allocation. 2.1 Anaesthesia and blood pressure monitoring All procedures were performed under general anaesthesia induced by propofol (2 mg/kg) and sufentanil (0.5 lg/kg). The intubation was facilitated with muscle relaxants (rocuronium or atracurium, both 0.5 mg/kg according to decision of treating anaesthesiologist). Anesthesia maintenance was performed using an O2 ? Air gas mixture with Sevoflurane (MAC 0.8–1.2 adapted to patient’s age); analgesia and muscle relaxants were added when necessary. At the end of each procedure the patient was extubated and transferred to the postoperative care unit. Throughout the procedure standard monitoring of cardiovascular and respiratory functions was performed. BP was monitored continuously in both groups using the standalone CNAPÒ Monitor (software version 3.5), but device screen was displayed and visible to the treating anaesthesiologist only in the Continuous group. CNAPÒ monitoring was started before induction of anaesthesia in order to obtain a calibrated signal at the moment of intravenous anaesthetic administration. The induction of anaesthesia and the extubation were marked as the beginning and the end of the monitoring period (‘‘the length of anaesthesia’’). Every 15 min a recalibration of the CNAPÒ signal including a finger cuff change was done automatically according to the manufacturer’s recommendation. The recalibration is associated with 2–2.5 min interruption of the continuous monitoring (this time was subtracted from the calculated length of procedure to avoid bias). In order to avoid changes in pressure readings induced by change in position, the fingers and arm cuffs were all maintained at the level of the heart throughout the positioning. Intermittent arm pressure readings via a standard automatic oscillometric cuff (Ultraview SL2700, Spacelabs Healthcare, Washington, USA) were performed using a 5 min time protocol. The treating anaesthesiologist was allowed to increase the rate of pressure measurements (up to ‘‘once per minute’’) or make any additional measurements if necessary throughout the procedure. Throughout the procedure BP was maintained within ±20 % of patient’s target value (see later in methods section for the target systolic BP definition). In cases of hypotension, the following steps were performed according to presumed underlying cause: (1) if hypovolemia was suspected a bolus
of 250/500 ml of crystalloid solution was given, (2) 5–10 mg boluses of ephedrine were used repeatedly to a maximal dose of 100 mg per procedure (3) if hypotension was prolonged the infusion of norepinephrine was considered. In cases of hypertension and after exclusion of inadequate anaesthesia/analgesia, the infusion of nitrate donor (isosorbid dinitrate, nitroprusside) or other antihypertensive medication (urapidil, clonidine, esmolol, metoprolol) were started according to clinical conditions and presumed underlying cause. 2.2 Data analysis and outcome measures Patient demographic data regarding underlying thyroid gland disease, chronic comorbidities, presence of hypertonic disease, medication and usual BP were collected. Basal hemodynamic values (heart rate, BP) were collected before the anaesthesia induction and throughout the whole procedure. During the use of anaesthesia, starting with the administration of the i.v. anaesthetic until the extubation, continuous BP measurements were gathered by the CNAPÒ Monitor with 100 Hz frequency and stored on an external memory stick for off-line analysis. Medications given to manipulate the BP were collected via the anaesthesia procedure sheet. In the morning before surgery a clinical evaluation of cognitive functions was performed and the Short Memory Orientation Test (SMOT) questionnaire [21] was given by trained study personnel (JK, SS). Similar examinations were performed after the procedure within 40–60 min after arousal by the same member of the team (unaware of the patient’s group allocation). Postoperative care was provided by the treating staff of the relevant ward including clinical diagnosis of possible complications and their treatment. A study member unaware of treatment allocation performed a short clinical examination before patient discharge with retrospective morbidity assessment (JB, JZ, RP). As the hospital length of stay after thyroid gland surgery is very short no predefined criteria or readiness to discharge were evaluated. The off-line BP analysis was performed in a concealed fashion (JB) using the Task ForceÒ Monitor software (CNSystems, Graz, Austria). The software enables beat-tobeat transformation of the continuous pressure curve signal providing systolic and diastolic BP and beat length (in seconds). According to each patient’s target BP, time spent in each decile of BP (i.e. 70–79, 80–89 % of normal values etc.) was summed up and the percentage values during the whole monitoring period were calculated. The target systolic BP (TSBP) was defined as patient’s chronic value (reported by general practitioner in the preoperative assessment or known by the patient) increased by 10 mmHg in order to account for head perfusion level during upright position. The primary end point of the study was the time
123
J Clin Monit Comput
(absolute and proportional) spent outside the safe range of normal BP (-20 and ?20 % of TSBP). The number of hypotensive/hypertensive periods (±20 %), their length and number of interventions needed were also assessed. In addition, time spent in severe hypotension (-30 % TSBP), severe hypertension (?30 % TSBP), and with an absolute MAP value under 60 mmHg were also evaluated. The number and rate of postoperative complications including cognitive function assessment (using the SMOT test before and after procedure) were evaluated as safety outcomes.
Table 1 Baseline demographic characteristics
2.3 Statistical analysis In a previous study [6], comprising 25 patients, 23 ± 5 % of anaesthesia time (14 ± 3 min in hour) was spent in hypo/hypertension using the intermittent measurement. We decided to include a larger population (20 patients per group) as BP fluctuations in a beach chair position might be more frequent. Data presented in the paper are stated as median (interquartile range) for non-normally distributed and mean ± standard deviation for normally distributed values. The Kolmogorov–Smirnoff test was used to test the normal distribution of the data. For categorical variables the absolute number of cases and the percentage value were calculated. To evaluate the time spent in hypotension etc. the proportional time measure was calculated based on the percentage of the overall monitoring period. To test the statistical significance of the results between groups either unpaired t test or Mann–Whitney tests were used according to data normality. Change of SOMT in time was tested using the Wilcoxon test due to their non-normal distribution. Grouping variables were tested using Chi square test. A p value of \0.05 was considered to indicate statistical significance. All statistical calculations were performed using MedCalcÒ software, version 12.7.0.0 (Frank Schoonjans, MedCalc Software, Broekstraat 52, 9030 Mariakerke, Belgium).
3 Results During the study period (October 2012 to March 2013) 46 patients undergoing thyroid gland surgery were found eligible. In 4 cases the inclusion was not possible due to technical reasons (twice the CNAPÒ Monitor was in use at the same time, once it was out of function due to service and once the procedure was rescheduled to another operation theatre without possible change of personnel). In two cases exclusion criteria were met (once because of Raynaud’s syndrome and once because of finger deformities due to rheumatoid arthritis), both precluding a safe use of finger cuffs. All other patients were included and equally randomized. Baseline characteristics of patients included in
123
Continuous N = 20
Intermittent N = 20
p
Age (years)
56 ± 15
59 ± 12
0.431
Height (cm)
169 ± 6
169 ± 8
0.972
Weight (kg)
77 ± 15
86 ± 24
0.153
Sex (F/M)
18/2
15/5
0.405
ASA (1:2:3)
3/15/2
1/12/7
0.047
Chronic systolic blood pressure (mmHg)
121 ± 10
127 ± 11
0.079
Chronic diastolic blood pressure (mmHg)
76 ± 8
78 ± 6
0.209
Primary diagnosis (Hyperthyroidism/Goitre/ Hypothyroidism)
4/11/5
2/17/1
0.564
Procedure (Total/Partial resection)
16/4
17/3
1.000
Comorbidities Arterial hypertension
12 (60 %)
12 (60 %)
0.747
Ischemic heart disease
0 (0 %)
3 (15 %)
0.230
Chronic respiratory disease
1 (5 %)
3 (15 %)
0.598
Diabetes mellitus
1 (5 %)
3 (15 %)
0.598
Obesity
4 (20 %)
10 (50 %)
0.097
Data are presented as mean ± standard deviation or number (proportion) F Female, M Male, ASA Physical status classification system according to American Society of Anaesthesiologists
the study are given in Table 1. No significant differences were observed between study arms for most of these features. However, a trend towards higher rate of comorbidities and higher American Society of Anaesthesiology status (ASA) was observed among the Intermittent group patients. All patients were without clinical signs of hyper-/ hypothyroidism and their thyroid hormones were within normal levels. Neither differences in primary diagnosis (reason for the surgery) nor procedure performed were observed. The incidence of patients with chronic arterial hypertension was comparable based on their preadmission BP. The overall length of anaesthesia was similar. No monitoring-induced complications were observed among the study population. Patients in the Continuous group had a reduction of absolute time spent in hypertension (-20 % of TSBP) compared to the Intermittent group [12 min (4–20) vs. 27 min (16–34); p = 0.001]. The Continuous group also experienced a reduction in the relative proportion of time in hypotension versus the Intermittent group [14 % (7–20) vs. 33.5 % (17.5–53); p = 0.003]. Hypotensive periods were non-significantly less frequent in the Continuous arm but their duration was shorter. Interestingly, the number of interventions was comparable between both groups. The
J Clin Monit Comput Table 2 Primary and secondary outcome measures Continuous
Intermittent
p
70 [58–95]
81 [65–98]
0.387
Absolute time (min)
12 [4–20]
27 [16–34]
0.001
Proportional time (%)
14 [7–20] %
33.5 [17.5–53] %
0.003
Number of episodes per patient
2.5 [1.5–4]
3.5 [3–5.5]
0.053
Duration of episode (min)
4 [2–7]
8 [6–16]
0.014
Number of interventions
2 [1–3]
2 [1–4]
0.913
2 [0–4] 2.5 [0–4.5] %
8 [2–11] 10 [1.5–17.5] %
0.005 0.006
Absolute time (min)
0 [0–1]
0 [0–4]
0.897
Proportional time (%)
0 [0–1] %
0 [0–5] %
0.867
4 [1–6]
2 [0–4]
0.411
Anaesthesia duration (min) Hypotension -20 % of TSBP
-30 % of TSBP Absolute time (min) Proportional time (%) Fig. 2 Distribution of proportional time according to chronic systolic pressure deciles (bars show mean ± SD)
interventions were mostly performed using vasoactive drug (Ephedrine). In only three cases (two patients in Continuous group) volume expansion was performed. No significant hypovolemia was present in patients of either group according to the value of pulse pressure variation after induction [8 % (7–12) vs. 11 % (8–12) in Intermittent vs. Continuous groups; p = 0.15]. Similar difference between Continuous and Intermittent group was observed in time spent in severe hypotension [-30 % of TSBP: 2.5 % (0–4.5) vs. 10 % (1.5–17.5); p = 0.006]. There were no differences in time spent above the ?20 and ?30 % of TSBP threshold. Distribution of proportional time spent in BP deciles for patients of both groups is displayed in Fig. 2. The proportional time of MAP \ 60 mmHg was very short in both groups. In two cases (10 %) of the Continuous group no period of hypotension was observed and in a further three cases (15 %) only very short (1–2 min) periods of mild hypotension were observed. All patients in the intermittent group experienced at least one episode of hypotension and 18 patients (90 %) had more than one episode. The number and length of hypertensive periods was comparable between groups and only two interventions were initiated in the Continuous arm and one in the Intermittent. The results of primary and secondary outcome measures are summarised in Table 2. The hospital length of stay was comparable between groups, as well as number and rate of complications. The incidence of postoperative nausea and vomiting was also similar. In two patients (one per group) a revision for bleeding was necessary. One patient from the Intermittent group needed a short period (15 h) of postoperative
MAP \ 60 mmHg
Hypertension ?20 % of TSBP Absolute time (min) Proportional time (%)
5 [0.5–7] %
2 [0–4.5] %
0.210
Number of episodes per patient
1 [0–2.5]
1 [0–2]
0.966
Duration of episode (min)
2 [0–3]
2 [0–3]
0.889
Absolute time (min)
1 [0–2]
0 [0–3]
0.839
Proportional time (%)
1 [0–2] %
0 [0–3] %
0.897
?30 % of TSBP
Clinical endpoints SOMT Before anaesthesia
26 [26–28]
26 [24–28]
0.719
After anaesthesia
24 [20–26]#
24 [22–27]#
0.813
Postoperative nausea/ vomiting
3 (15 %)/3 (15 %)
3 (15 %)/4 (20 %)
0.831
Postoperative bleeding
1 (5 %)
1 (5 %)
0.468
Hospital length of stay (days)
3 [3–4]
3 [3–4]
0.479
Data are presented as median [interquartile range] or number (proportion) MAP Mean arterial pressure, SOMT Short Memory Orientation Test, TBSP target systolic blood pressure #
p \ 0.01—after versus before the anaesthesia (Wilcoxon test)
ventilation because of large goitre removal and resulting risk of airway oedema formation. No other complications were observed among our patients. No differences in the values of SMOT between groups (both before and after
123
J Clin Monit Comput
anaesthesia) were observed. After the procedure, there was a statistically, but not clinically, significant decay in SMOT in both groups compared to preoperative values (see Table 2). No overt cognitive dysfunction was observed in study patients throughout the postoperative stay.
4 Discussion In our prospective, controlled, randomized study the use of continuous, non-invasive BP monitoring decreased the time spent in hypotension and its magnitude compared to standard intermittent monitoring in patients undergoing thyroid gland surgery in a beach chair position. Maintaining BP stability is one of the major tasks of an anaesthesiologist during anaesthesia use. Although the safe margins of BP fluctuations are not exactly defined, the ±20 % range is usually recommended [22]. Perioperative BP lability is deemed to be a risk factor for complications development, most importantly myocardial ischemia, renal impairment [9, 11], cognitive dysfunction and in some extreme cases even brain damage [10]. The association between even mild BP fluctuations, the beach chair position and the cerebral perfusion assessed by tissue oxymetry was demonstrated by several groups [12, 13, 23, 24]. Whether these changes are associated with manifest neuronal loss is unresolved. In order to test for clinical correlate the SMOT test (similarly to the PINOCHIO trial [25]) was used in our study as a safety outcome. We have observed an early postoperative subclinical decline without showing any difference between groups. Expectedly, no apparent organ dysfunction developed in our rather low risk patients throughout the short period until discharge. Nevertheless, preventing prolonged hypotension might be important even in such patients. Based on general critical care experience, continuous monitoring enables faster recognition of BP changes and helps to reduce time spent outside declared safety margins. However, in low risk patients the monitoring-associated risks should be considered as well. Preventing arterial catheterisation by using non-invasive continuous BP monitors might offer a safe alternative. Previously Chen et al. [6] and Ilies et al. [18] used volume clamp based devices for assessing the risk of hypotension. In both trials the use of continuous, non-invasive BP monitoring was associated with lower hypotension occurrence, but the estimations were rather hypothetical given their observational nature. In our study we were able to directly quantify the effect of continuous non-invasive BP monitoring on the BP stability thanks to the controlled, randomized design. The absolute and relative time spent in hypotension was reduced to 50 % and severe hypotension to 25 % without increasing the monitoring-associated burden. This was in
123
large part due to shorter durations of these episodes, but they were also non-significantly less frequent. Both these facts support the hypothesis of faster recognition and shorter reaction times. This quantification of the therapeutic effect might be of importance for balancing the costs and benefits of monitoring escalation. Our study suffers from some important limitations which should be acknowledged. First the CNAPÒ device was used for continuous BP estimation. The use of arterial invasive pressure monitoring would offer more accurate results, especially in periods of sudden BP fluctuations. The radial artery catheterisation was considered during the study protocol preparation, but was strongly discouraged by the participating surgeons and review board as unnecessary escalation of invasiveness in low risk patients. Considerations still exist regarding the accuracy of the CNAP device. Several studies [14–16] showed a good agreement between BP monitored using the CNAPÒ in comparison to invasive pressure readings. The accuracy in absolute values seems to decrease after induction and during sudden and profound drops of BP [14, 17], without affecting the trending ability. Our results might be biased by underestimating the magnitude of observed fluctuations especially in the -30 % TBSP end-point. However, results published by Hahn with the newest software version—V3.5 (also used in our trial) showed clinically acceptable agreement [26]. Moreover, in low risk patients the BP monitoring via arterial cannulation is seldom performed and intermittent oscillometric method may be considered as a clinically relevant reference. The CNAP device uses the oscillometric cuff for calibration of continuous monitoring enabling comparison of both methods. Finally, our observations were done on a rather small, homogenous population of patients with presumably higher incidence of postural or operation-induced BP changes. Hence, generalizing our results to other clinical scenarios may not be straightforward. In addition, our small study sample of low risk patients precludes us from assessing the clinical relevance of our findings. Our results are potentially important for anaesthesia management itself, but the actual clinical benefit of better pressure stability remains unresolved.
5 Conclusion In conclusion, our study shows that the use of continuous non-invasive arterial BP measurement might offer an improved monitoring solution in comparison to the standard intermittent measurement in patients undergoing operation in a beach chair position. Time spent in hypotension was significantly reduced using the continuous, non-invasive measurement.
J Clin Monit Comput Acknowledgments The study was supported by the Charles University Research Fund (Project number P36). The CNAPÒ Monitor and Task ForceÒ Monitor software were supplied by CNSystems, Graz, Austria. There were no additional payments depending on the results of the study. Conflict of interests JB received lecturing fees from Edwards Lifecsiences Inc., all other co-authors declare no competing interests.
References 1. ASA House of Delegates STANDARDS FOR BASIC ANESTHETIC MONITORING. http://www.asahq.org/For-Members/ */media/For%20Members/documents/Standards%20Guidelines% 20Stmts/Basic%20Anesthetic%20Monitoring%20201ashx. Accessed 12 July 2013 (2011). ´ SADY 2. Cvachovec K., Cˇerny´ V., Herold I., Kozlı´k P., Sˇturma J. ZA ˇ NE´ ANESTEZIOLOGICKE´ PE´CˇE. http://www.csarim. BEZPEC cz/Public/csim/22%20%20DP_safety_anesth_CSARIM_final_ approval_14021pdf. Accessed 12 Jul 2013 (2012). 3. Lamia B, Chemla D, Richard C, Teboul JL. Clinical review: interpretation of arterial pressure wave in shock states. Crit Care. 2005;9:601–6. 4. Scheer B, Perel A, Pfeiffer UJ. Clinical review: complications and risk factors of peripheral arterial catheters used for haemodynamic monitoring in anaesthesia and intensive care medicine. Crit Care. 2002;6:199–204. 5. Cannesson M, Pestel G, Ricks C, Hoeft A, Perel A. Hemodynamic monitoring and management in patients undergoing high risk surgery: a survey among North American and European anesthesiologists. Crit Care. 2011;15:R197. 6. Chen G, et al. Impact of non invasive and beat-to-beat arterial pressure monitoring on intraoperative hemodynamic management. J Clin Monit Comput. 2012;26:133–40. 7. Monk TG, Saini V, Weldon BC, Sigl JC. Anesthetic management and one-year mortality after noncardiac surgery. Anesth Analg. 2005;100:4–10. 8. Sessler DI, et al. Hospital stay and mortality are increased in patients having a ‘‘triple low’’ of low blood pressure, low bispectral index, and low minimum alveolar concentration of volatile anesthesia. Anesthesiology. 2012;116:1195–203. 9. Walsh M, et al. Relationship between intraoperative mean arterial pressure and clinical outcomes after noncardiac surgery: toward an empirical definition of hypotension. Anesthesiology. 2013;119:507–15. 10. Drummond JC, Lee RR, Howell JP. Focal cerebral ischemia after surgery in the ‘‘beach chair’’ position: the role of a congenital variation of circle of Willis anatomy. Anesth Analg. 2012;114:1301–3. 11. Pohl A, Cullen DJ. Cerebral ischemia during shoulder surgery in the upright position: a case series. J Clin Anesth. 2005;17:463–9.
12. Jeong H, et al. Haemodynamics and cerebral oxygenation during arthroscopic shoulder surgery in beach chair position under general anaesthesia. Acta Anaesthesiol Scand. 2012;56:872–9. 13. Tange K, et al. Cerebral oxygenation in the beach chair position before and during general anesthesia. Minerva Anestesiol. 2010;76:485–90. 14. Ilies C, et al. Investigation of the agreement of a continuous noninvasive arterial pressure device in comparison with invasive radial artery measurement. Br J Anaesth. 2012;108:202–10. 15. Jeleazcov C, et al. Precision and accuracy of a new device (CNAPTM) for continuous non-invasive arterial pressure monitoring: assessment during general anaesthesia. Br J Anaesth. 2010;105:264–72. 16. Biais M, et al. Continuous non-invasive arterial pressure measurement: evaluation of CNAP device during vascular surgery. Ann Fr Anesth Reanim. 2010;29:530–5. 17. Gayat E, et al. CNAP(Ò) does not reliably detect minimal or maximal arterial blood pressures during induction of anaesthesia and tracheal intubation. Acta Anaesthesiol Scand. 2013;57: 468–73. 18. Ilies C, et al. Detection of hypotension during Caesarean section with continuous non-invasive arterial pressure device or intermittent oscillometric arterial pressure measurement. Br J Anaesth. 2012;109:413–9. 19. Wagner JY, et al. Noninvasive continuous versus intermittent arterial pressure monitoring: evaluation of the vascular unloading technique (CNAP device) in the emergency department. Scand J Trauma Resusc Emerg Med. 2014;22:8. 20. Schulz KF, Altman DG, Moher D, CONSORT Group. CONSORT 2010 statement: updated guidelines for reporting parallel group randomised trials. BMC Med. 2010;8:18. 21. Katzman R, et al. Validation of a short orientation-memoryconcentration test of cognitive impairment. Am J Psychiatry. 1983;140:734–9. 22. Howell SJ, Sear JW, Foe¨x P. Hypertension, hypertensive heart disease and perioperative cardiac risk. Br J Anaesth. 2004;92:570–83. 23. Lee JH, Min KT, Chun YM, Kim EJ, Choi SH. Effects of beachchair position and induced hypotension on cerebral oxygen saturation in patients undergoing arthroscopic shoulder surgery. Arthroscopy. 2011;27:889–94. 24. Koh JL, Levin SD, Chehab EL, Murphy GS: Neer Award 2012: cerebral oxygenation in the beach chair position: a prospective study on the effect of general anesthesia compared with regional anesthesia and sedation. J Shoulder Elbow Surg. 2013;22: 1325–1331. 25. Bilotta F, et al. Early postoperative cognitive dysfunction and postoperative delirium after anaesthesia with various hypnotics: study protocol for a randomised controlled trial—the PINOCCHIO trial. Trials. 2011;12:170. 26. Hahn R, Rino¨sl H, Neuner M, Kettner SC. Clinical validation of a continuous non-invasive haemodynamic monitor (CNAP 500) during general anaesthesia. Br J Anaesth. 2012;108:581–5.
123
