Correspondence Table 7
81
Factors associated with need for information. Univariate analysis for various factors at T1, T2, and T3 *
Time points
Factors
More need
Less need
Odds ratio
P-value
95% CI
T1 (n = 201)
Previous surgery (no/yes) Anesthesia technique (general/regional) Education (≥/b12 yrs formal education) Education (≥/b12 yrs formal education) Age group (≤ 30 / N 30 yrs)
41/20 46/11 27/34 19/23 23/18
69/71 93/38 29/111 37/122 51/96
2.10 1.70 3.04 2.724 2.405
0.019 0.163 0.001 0.005 0.013
1.12 0.80 1.58 1.33 1.19
T2 (n = 201) T3 (n = 188)
3.95 3.64 5.82 5.54 4.86
Multivariate regression analysis for the factors at T1 Time points
Factors
Beta regression coefficient
Odds ratio
P-value
95% CI
T1 (n = 201)
Education (≥/b12 yrs formal education) Previous surgery (no/yes) Anesthesia technique (general/regional) constant
1.141 0.708 0.473 −1.644
3.13 2.03 1.60 0.193
0.001 0.041 0.242 0.000
1.57 1.02 0.72
6.22 4.01 3.54
⁎ This table is the corrected version of Table 7 from Pokharel K, Bhattarai B, Tripathi M, Khatiwada S, Subedi A. Nepalese patients’ anxiety and concerns before surgery. J Clin Anesth 2011;23: 372-8.
statement, “scores from 2 to 5 on the information scale: little or no information requirement”, should be corrected to “scores from 2 to 4 on the information scale: little or no information requirement” [1] (page 374). We apologize for this error. We reanalyzed our data. Now our interpretation in the Results section should say, “the number of patients with more need to know about anesthesia and surgery was significantly higher (P b 0.05) in the ward 61 (30.3%) compared to the holding area 42 (20.9%) and operating table 40 (21.8%) instead of “no statistically significant difference was noted between the frequencies of patients with more need to know about anesthesia or surgery at three time points [41 (19.9%), 35 (17.4%), and 31 (16.4%), respectively]”. Table 5 and Table 7 have been corrected accordingly. We stand by our statement, “the chi square test showed that the patients who desired more information also were more anxious (P b 0.001) at all three time points [Table 5].” Unfortunately, univariate analysis showed that more need for information in the ward did not correlate with general anesthesia as opposed to our previous result (page 376). However, it correlated with no previous exposure to surgery and higher educational status (≥ 12 yrs of formal education), as previously reported [1]. Among the correlating factors in the ward, multivariate logistic regression showed that higher education had the greatest impact on the need for information, followed by no previous surgery [Table 7]. The predictors for the more need for information in the preoperative holding area and operating room remain the same. In the Discussion, “general anesthesia” should be omitted from the list of independent factors for greater need to seek information about surgery and anesthesia in the preoperative period. Similarly, the statement, “over 80% of our patients in the ward were less eager to be informed about anesthesia or surgery”, should be corrected as “approximately 70% of our
patients in the ward were less eager to be informed about anesthesia or surgery”. With this analysis, our conclusions remain the same. Krishna Pokharel MD (Associate Professor) Mukesh Tripathi MD (Professor) Department of Anaesthesiology and Critical Care B.P. Koirala Institute of Health Sciences, Dharan, Nepal E-mail address: [email protected] http://dx.doi.org/10.1016/j.jclinane.2013.09.006
Reference [1] Pokharel K, Bhattarai B, Tripathi M, Khatiwada S, Subedi A. Nepalese patients’ anxiety and concerns before surgery. J Clin Anesth 2011;23: 372-8.
It is hard to get a grip on it To the Editor: We read with great interest the recent article entitled, “Efficacy of facemask ventilation techniques in novice providers”, by Dr. Gerstein and colleagues [1]. For the reader to arrive at the same conclusion as the authors regarding the efficacy of the two-handed thenar eminence (TE) grip, more information is required. First, accurate recordings of exhaled tidal volumes (VT) are paramount to this study. A calibrated pneumotachograph at the interface of the facemask and the ventilator circuit, which is the gold standard for measuring flow and pressure delivery to the airway, was not used. Rather, flow and pressure were manually recorded from the anesthesia monitor. While the two
82
Correspondence
types of anesthesia machines used in this study employed piston-driven compliance-compensated ventilators, the ability to maintain a steady delivered volume is achieved when a breathing circuit compliance check is performed each time the circuit configuration changes. For example, when using “accordion-type” circuits, the delivered VTs can vary by as much as 25% if the circuit is extended after the compliance check. Importantly, the VTs reported by the ventilator’s display may not correlate with the volume realized by the airway under these circumstances [2]. Thus, the type of circuit (collapsible vs noncollapsible), when and how often compliance checks were performed, and some data regarding the accuracy of the values displayed on the monitor compared with similar measurements taken at the patient’s airway should be provided. Depth of anesthesia may increase over time, rendering ventilation by facemask more efficient. This is of particular importance in the absence of administered neuromuscular blocking drugs. Apnea induced by intravenous (IV) administration of fentanyl and propofol does not ensure adequate depth of anesthesia to blunt motor responses or upper airway reflex activation in response to a vigorous jaw thrust in all patients [3]. Further, it is unclear from the reported methods whether volatile anesthetic gas was started during mask ventilation, as would be done routinely following IV induction. If so, documentation and control by study design or statistical methodology of the end-tidal gas concentration would be an important factor for consideration. The fact that significant improvements in VTs occurred only when a patient started with the E-C clamp (EC) grip technique and crossed over to the TE grip technique, but did not worsen when going from TE to EC grip techniques, suggests that the outcome was dependent on other factors aside from the grip. This “sequence effect” was noted by the authors in their discussion, but no consideration was given to how these factors might have confounded their main results. Finally, the size, type, and management of the oropharyngeal airway were not described. Incorrectly inserted or malpositioned devices hinder mask ventilation. Progressive anterior displacement from a fully seated position with the proximal end deep in the hypopharynx may limit the efficiency of ventilation and be of particular importance in patients with obstructive sleep apnea [4]. In summary, it very well may be that the technique the authors propose is superior to the traditional E-C clamp technique, but their study, as described, limits the ability of the reader to agree with that conclusion. Aaron M. Joffe DO (Associate Professor of Anesthesiology) University of Washington Harborview Medical Center Seattle, WA 98104, USA E-mail address: [email protected]
Richard E. Galgon MD, MS (Assistant Professor of Anesthesiology) University of Wisconsin School of Medicine and Public Health, Madison, WI 53792, USA http://dx.doi.org/10.1016/j.jclinane.2013.07.010
References [1] Gerstein NS, Carey MC, Braude DA, et al. Efficacy of facemask ventilation techniques in novice providers. J Clin Anesth 2013;25:193-7. [2] Bachiller PR, McDonough JM, Feldman JM. Do new anesthesia ventilators deliver small tidal volumes accurately during volumecontrolled ventilation? Anesth Analg 2008;106:1392-400. [3] Townsend R, Brimacombe J, Keller C, Wenzel V, Herff H. Jaw thrust as a predictor of insertion conditions for the proseal laryngeal mask airway. Middle East J Anesthesiol 2009;20:59-62. [4] Hillman DR, Platt PR, Eastwood PR. The upper airway during anaesthesia. Br J Anaesth 2003;91:31-9.
Reply We welcome the interest and critique of Joffe and Galgon regarding our study, “Efficacy of facemask ventilation techniques in novice providers” [1]. They raise a number of insightful points and concerns regarding various facets of our study. We appreciate the opportunity to respond. Drs. Joffe and Galgon suggest that the use of a pneumotachograph (PNT) would increase the study validity and power (by decreasing random error), with reference to PNT as the gold standard for accurately measuring pressures and flows versus the use of the anesthesia machine’s sensors. However, due to the sequencing and crossover design, any error introduced by measurements would not be systematically biased in one direction. Any effect in measurements should affect both groups equally. There is no reason to suspect bias toward higher volumes in the thenar eminence (TE) group. There are a number of other contemporary mask ventilation studies that do not utilize a PNT or specify that a PNT is used for flow or volume measurements, as this does not represent the typical monitoring at many centers [2–5]. Using standard anesthesia machine-generated measurements lends face validity to our study, as this represents the manner in which ventilatory indices are typically assessed. The concern about increasing depth of anesthesia over time is similarly obviated by our crossover design and contradicted by the results themselves. Joffe and Galgon contend that an initially light anesthesia level may be responsible for the poor performance of the E-C clamp technique (EC) in the EC-first group. However, one would then need to explain why the TE technique was superior when used first, as shown in their Figure 4 and specifically tested in the Results and reiterated in the Discussion [1]. This makes it less likely that anesthesia depth was a confounder and perhaps progression of anesthesia depth may permit the EC grip as a fair reasonable second technique option.
81
Factors associated with need for information. Univariate analysis for various factors at T1, T2, and T3 *
Time points
Factors
More need
Less need
Odds ratio
P-value
95% CI
T1 (n = 201)
Previous surgery (no/yes) Anesthesia technique (general/regional) Education (≥/b12 yrs formal education) Education (≥/b12 yrs formal education) Age group (≤ 30 / N 30 yrs)
41/20 46/11 27/34 19/23 23/18
69/71 93/38 29/111 37/122 51/96
2.10 1.70 3.04 2.724 2.405
0.019 0.163 0.001 0.005 0.013
1.12 0.80 1.58 1.33 1.19
T2 (n = 201) T3 (n = 188)
3.95 3.64 5.82 5.54 4.86
Multivariate regression analysis for the factors at T1 Time points
Factors
Beta regression coefficient
Odds ratio
P-value
95% CI
T1 (n = 201)
Education (≥/b12 yrs formal education) Previous surgery (no/yes) Anesthesia technique (general/regional) constant
1.141 0.708 0.473 −1.644
3.13 2.03 1.60 0.193
0.001 0.041 0.242 0.000
1.57 1.02 0.72
6.22 4.01 3.54
⁎ This table is the corrected version of Table 7 from Pokharel K, Bhattarai B, Tripathi M, Khatiwada S, Subedi A. Nepalese patients’ anxiety and concerns before surgery. J Clin Anesth 2011;23: 372-8.
statement, “scores from 2 to 5 on the information scale: little or no information requirement”, should be corrected to “scores from 2 to 4 on the information scale: little or no information requirement” [1] (page 374). We apologize for this error. We reanalyzed our data. Now our interpretation in the Results section should say, “the number of patients with more need to know about anesthesia and surgery was significantly higher (P b 0.05) in the ward 61 (30.3%) compared to the holding area 42 (20.9%) and operating table 40 (21.8%) instead of “no statistically significant difference was noted between the frequencies of patients with more need to know about anesthesia or surgery at three time points [41 (19.9%), 35 (17.4%), and 31 (16.4%), respectively]”. Table 5 and Table 7 have been corrected accordingly. We stand by our statement, “the chi square test showed that the patients who desired more information also were more anxious (P b 0.001) at all three time points [Table 5].” Unfortunately, univariate analysis showed that more need for information in the ward did not correlate with general anesthesia as opposed to our previous result (page 376). However, it correlated with no previous exposure to surgery and higher educational status (≥ 12 yrs of formal education), as previously reported [1]. Among the correlating factors in the ward, multivariate logistic regression showed that higher education had the greatest impact on the need for information, followed by no previous surgery [Table 7]. The predictors for the more need for information in the preoperative holding area and operating room remain the same. In the Discussion, “general anesthesia” should be omitted from the list of independent factors for greater need to seek information about surgery and anesthesia in the preoperative period. Similarly, the statement, “over 80% of our patients in the ward were less eager to be informed about anesthesia or surgery”, should be corrected as “approximately 70% of our
patients in the ward were less eager to be informed about anesthesia or surgery”. With this analysis, our conclusions remain the same. Krishna Pokharel MD (Associate Professor) Mukesh Tripathi MD (Professor) Department of Anaesthesiology and Critical Care B.P. Koirala Institute of Health Sciences, Dharan, Nepal E-mail address: [email protected] http://dx.doi.org/10.1016/j.jclinane.2013.09.006
Reference [1] Pokharel K, Bhattarai B, Tripathi M, Khatiwada S, Subedi A. Nepalese patients’ anxiety and concerns before surgery. J Clin Anesth 2011;23: 372-8.
It is hard to get a grip on it To the Editor: We read with great interest the recent article entitled, “Efficacy of facemask ventilation techniques in novice providers”, by Dr. Gerstein and colleagues [1]. For the reader to arrive at the same conclusion as the authors regarding the efficacy of the two-handed thenar eminence (TE) grip, more information is required. First, accurate recordings of exhaled tidal volumes (VT) are paramount to this study. A calibrated pneumotachograph at the interface of the facemask and the ventilator circuit, which is the gold standard for measuring flow and pressure delivery to the airway, was not used. Rather, flow and pressure were manually recorded from the anesthesia monitor. While the two
82
Correspondence
types of anesthesia machines used in this study employed piston-driven compliance-compensated ventilators, the ability to maintain a steady delivered volume is achieved when a breathing circuit compliance check is performed each time the circuit configuration changes. For example, when using “accordion-type” circuits, the delivered VTs can vary by as much as 25% if the circuit is extended after the compliance check. Importantly, the VTs reported by the ventilator’s display may not correlate with the volume realized by the airway under these circumstances [2]. Thus, the type of circuit (collapsible vs noncollapsible), when and how often compliance checks were performed, and some data regarding the accuracy of the values displayed on the monitor compared with similar measurements taken at the patient’s airway should be provided. Depth of anesthesia may increase over time, rendering ventilation by facemask more efficient. This is of particular importance in the absence of administered neuromuscular blocking drugs. Apnea induced by intravenous (IV) administration of fentanyl and propofol does not ensure adequate depth of anesthesia to blunt motor responses or upper airway reflex activation in response to a vigorous jaw thrust in all patients [3]. Further, it is unclear from the reported methods whether volatile anesthetic gas was started during mask ventilation, as would be done routinely following IV induction. If so, documentation and control by study design or statistical methodology of the end-tidal gas concentration would be an important factor for consideration. The fact that significant improvements in VTs occurred only when a patient started with the E-C clamp (EC) grip technique and crossed over to the TE grip technique, but did not worsen when going from TE to EC grip techniques, suggests that the outcome was dependent on other factors aside from the grip. This “sequence effect” was noted by the authors in their discussion, but no consideration was given to how these factors might have confounded their main results. Finally, the size, type, and management of the oropharyngeal airway were not described. Incorrectly inserted or malpositioned devices hinder mask ventilation. Progressive anterior displacement from a fully seated position with the proximal end deep in the hypopharynx may limit the efficiency of ventilation and be of particular importance in patients with obstructive sleep apnea [4]. In summary, it very well may be that the technique the authors propose is superior to the traditional E-C clamp technique, but their study, as described, limits the ability of the reader to agree with that conclusion. Aaron M. Joffe DO (Associate Professor of Anesthesiology) University of Washington Harborview Medical Center Seattle, WA 98104, USA E-mail address: [email protected]
Richard E. Galgon MD, MS (Assistant Professor of Anesthesiology) University of Wisconsin School of Medicine and Public Health, Madison, WI 53792, USA http://dx.doi.org/10.1016/j.jclinane.2013.07.010
References [1] Gerstein NS, Carey MC, Braude DA, et al. Efficacy of facemask ventilation techniques in novice providers. J Clin Anesth 2013;25:193-7. [2] Bachiller PR, McDonough JM, Feldman JM. Do new anesthesia ventilators deliver small tidal volumes accurately during volumecontrolled ventilation? Anesth Analg 2008;106:1392-400. [3] Townsend R, Brimacombe J, Keller C, Wenzel V, Herff H. Jaw thrust as a predictor of insertion conditions for the proseal laryngeal mask airway. Middle East J Anesthesiol 2009;20:59-62. [4] Hillman DR, Platt PR, Eastwood PR. The upper airway during anaesthesia. Br J Anaesth 2003;91:31-9.
Reply We welcome the interest and critique of Joffe and Galgon regarding our study, “Efficacy of facemask ventilation techniques in novice providers” [1]. They raise a number of insightful points and concerns regarding various facets of our study. We appreciate the opportunity to respond. Drs. Joffe and Galgon suggest that the use of a pneumotachograph (PNT) would increase the study validity and power (by decreasing random error), with reference to PNT as the gold standard for accurately measuring pressures and flows versus the use of the anesthesia machine’s sensors. However, due to the sequencing and crossover design, any error introduced by measurements would not be systematically biased in one direction. Any effect in measurements should affect both groups equally. There is no reason to suspect bias toward higher volumes in the thenar eminence (TE) group. There are a number of other contemporary mask ventilation studies that do not utilize a PNT or specify that a PNT is used for flow or volume measurements, as this does not represent the typical monitoring at many centers [2–5]. Using standard anesthesia machine-generated measurements lends face validity to our study, as this represents the manner in which ventilatory indices are typically assessed. The concern about increasing depth of anesthesia over time is similarly obviated by our crossover design and contradicted by the results themselves. Joffe and Galgon contend that an initially light anesthesia level may be responsible for the poor performance of the E-C clamp technique (EC) in the EC-first group. However, one would then need to explain why the TE technique was superior when used first, as shown in their Figure 4 and specifically tested in the Results and reiterated in the Discussion [1]. This makes it less likely that anesthesia depth was a confounder and perhaps progression of anesthesia depth may permit the EC grip as a fair reasonable second technique option.
