J Clin Monit Comput DOI 10.1007/s10877-014-9583-5
ORIGINAL RESEARCH
Detection of endobronchial intubation by monitoring the CO2 level above the endotracheal cuff Shai Efrati • Israel Deutsch • Nathan Weksler Gabriel M. Gurman
•
Received: 26 February 2014 / Accepted: 7 May 2014 Ó Springer Science+Business Media New York 2014
Abstract Early detection of accidental endobronchial intubation (EBI) is still an unsolved problem in anesthesia and critical care daily practice. The aim of this study was to evaluate the ability of monitoring above cuff CO2 to detect EBI (the working hypothesis was that the origin of CO2 is from the unventilated, but still perfused, lung). Six goats were intubated under general anesthesia and the ETT positioning was verified by a flexible bronchoscope. The AnapnoGuard system, already successfully used to detect air leak around the ETT cuff, was used for continuous monitoring of above-the-cuff CO2 level. When the ETT distal tip was located in the trachea, with an average cuff pressure of 15 mmHg, absence of CO2 above the cuff was observed. The ETT was then deliberately advanced into one of the main bronchi under flexible bronchoscopic vision. In all six cases the immediate presence of CO2 above the cuff was identified. Further automatic inflation of the cuff, up to a level of 27 mmHg, did not affect the above-the-cuff measured CO2 level. Withdrawal of the ETT and repositioning of its distal tip in mid-trachea caused the disappearance of CO2 above the cuff in a maximum of 3 min, confirming the absence of air leak and the correct positioning of the ETT. Our results suggest that S. Efrati (&) Research and Development Unit, Assaf Harofeh Medical Center, Affiliated with the Sackler School of Medicine, Tel-Aviv University, 70300 Zerifin, Israel e-mail: [email protected] I. Deutsch Hospitech Respiration Ltd., Petah Tikva, Israel N. Weksler G. M. Gurman Division of Anesthesiology and Critical Care, Myney Hayeshuah, Bnei Brak, Ben-Gurion University of the Negev, Beersheba, Israel
measurement of the above-the-cuff CO2 level could offer a reliable, on-line solution for early identification of accidental EBI. Further studies are planned to validate the efficacy of the method in a clinical setup. Keywords Endobronchial Intubation One lung CO2 Endotracheal tube
1 Introduction Intubation of a main bronchus, more frequently on the right, is a common incident during tracheal intubation for general anesthesia and/or prolonged mechanical ventilation [1–7]. The pathological consequences of one lung intubation are mainly reduction of blood oxygenation, appearance of tension pneumothorax (because of hyperinflation of the intubated lung), and an increase in the post-intubation pulmonary complications, including atelectasis and pneumonia. A report by the Australian Incident Monitoring Study (AIMS) on 2000 patients found endobronchial intubation (EBI) to be the most common incident involving tracheal intubation [1]. A second AIMS study [2], on 2,947 patients, found that accidental EBI accounted for 3.7 % of all incidents reported. The relatively high incidence is mainly due to the incertitude of the anatomical distance between the teeth and the carina. That is why relying on fixed measurement does not guarantee proper positioning in all patients, as Owen and Cheney proposed in their study [3], does not cover those patients who do not belong to the ‘‘normal range of height’’. Moreover, physical examination, including auscultation of the chest wall, is a nonobjective measure highly dependent on the physician’s
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experience. For example, in a study done by Sitzwohl et al., first year residents missed EBI by auscultation in 55 % of the cases, which was significantly worse than experienced anaesthetists [6]. Neither clinical auscultation [5, 8], monitoring of oxygen saturation [9], nor end-tidal CO2 [10, 11] offers an accurate and rapid method of identifying EBI. Furthermore, any change in the patient’s head or neck position can lead to migration of the ETT. Conrardy et al. reported that neck flexion can advance the tube up to 3.1 cm toward the carina, exposing the patients to higher risk of EBI [12]. Accordingly, there is a need for an objective, non-invasive method that identifies and alarms the medical staff early when the ETT is mal-positioned. The present study proposes a new method of early detection of bronchial location of the ETT distal tube, using a system that identifies the presence of CO2 just above the ETT cuff when there is no leak around the cuff. We hypothesized that the CO2 from the non-ventilated lung can be detected above the cuff once main stem intubation accidentally occurs.
2 Methods The study included six healthy goats at the age of 2 years. The goats were not pregnant or lactating, and had a mean weight of 50 kg. The experiment was conducted in the Research and Development Unit of Assaf Harofeh Medical Center, Israel. All the animals included in the study were maintained according to the guidelines of the Local Ethics
Fig. 1 The three lumen endotracheal tube use for above cuff CO2 readings
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Committee for Animal Experimentation, and the experimental protocol was approved by the latter. Before anesthesia, the physiological parameters of each animal were measured and found to be within normal range: heart rate around 50/min, body temperature 38.0 °C, and respiratory rate around 20/min. Each goat was anesthetized using i.v. ketamine 10–11 mg/kg, midazolam 0.2 mg/kg, Lidocaine 0.2 mg/kg, and atropine 0.5 mg i.v. After tracheal intubation with an extended tube of 50 cm, especially prepared for this study, the animal was kept anesthetized with Isoflurane 1–2 % in oxygen, the head up 20 degrees and mechanically ventilated with a tidal volume of 7 ml/kg. 2.1 Endotracheal tubes and device used for above cuff CO2 reading A modified version of the AnapnoGuard system ETT (Hospitech Respiration Ltd., Petah Tikva, Israel) was used. As illustrated in Fig. 1, in order to enable successive CO2 readings (air samples taken from the space above the cuff and below the vocal cords to the AnapnoGuard system CO2 analyzer), the ETT has 2 additional lumens: one for CO2 readings (ventral lumen) while the other (dorsal lumen) is split into two at the distal end, used for suctioning of secretions. The lumens on both sides also serve as venting lumens, meaning that when the system is used for suctioning secretions, the ventral (CO2) lumen serves for venting while suctioning with the dorsal suction lumen and vice versa. The CO2 samples are pumped into the CO2 analyzer via the CO2/vent lumen or the suction lumen.
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3 Results
Fig. 2 Tracheal tube positioning and origin of CO2 during endobronchial intubation
Having this venting capability reduces the chances of lumen occlusion that usually happens with standard suction ETTs due to vacuum, and adherence to the tracheal wall is prevented. The AnapnoGuard system is an innovative respiratory guard system that automatically monitors and controls the ETT cuff pressure. The cuff pressure that seals off the trachea is set by measurement of CO2 levels above the cuff [13]. The optimal ETT cuff pressure is the minimal pressure needed to prevent CO2 leakage from the lungs to the oropharynx. 2.2 Tube positions After stabilizing the animal’s vital signs and verification of the perfect sealing off of the airways (no CO2 leak above the cuff, at a maximal cuff pressure of 15 mmHg), the tube was advanced into one of the main bronchi (the right one in four cases, the left in two cases) under flexible bronchoscopic vision. In this new ETT distal tip location, the cuff sealed off only the intubated main bronchus (Fig. 2). The above or below carina position of the ETT tip tube was verified using a flexible bronchoscope. The AnapnoGuard system upper limit of CO2 scale is 6 mmHg (consider to be a high significant leakage). After the ETT was positioned in the main bronchi, above cuff CO2 was continuously measured by the AnapnoGuard system for 4 min. If CO2 leakage was detected the cuff was inflated to a maximal preset cuff pressure of 27 mmHg and above cuff CO2 was re-measured in the next 4 min. Once it done, the ETT was repositioned to the trachea and in the following 3 min the cuff pressure was reduced by the AnapnoGuard system to the minimal pressure needed to prevent CO2 leakage.
All animals were hemodynamically stable and completed all study procedures. In each endobronchial ETT position the above-the-cuff CO2 was detected in each animal in less than 2 min; partial pressure was 6 mmHg in each of the 6 experiments (6 mmHg is the upper limit of the CO2 scale in the AnapnoGuard system, but most probably the true CO2 level at this stage of the experiment was much higher, closer to the arterial or alveolar level). Because of the system detection of CO2 above the cuff, the AnapnoGuard system automatically increased the cuff pressure to an average of 27 mmHg (range 22–29.5), but the system continued to detect significant CO2 levels above the cuff. Then the ETT distal tip was once again relocated above the carina and its position reconfirmed by flexible bronchoscopy; in the next 3 min the CO2 above the cuff disappeared and the automatic regulation of cuff pressure permitted its decrease to an average level of 13.6 mmHg. The sequence of procedures during the test is summarized in Table 1.
4 Discussion The AnapnoGuard system has already been clinically tried during general anesthesia and proven to be a reliable method of assuring the optimal cuff pressure that will avoid Table 1 Sequence of procedures, average cuff pressure, and CO2 level above the ETT cuff CO2 level above cuff (mmHg)
Average cuff pressure (mmHg)
Location of ETT distal tip
Procedure
Time (min)
Induction of general anesthesia
0
0
15 (Range 13–17)
Above carina
Tracheal intubation
3
6a
13.5 (Range 11–15)
Main bronchus (4 times Rt, 2 times Lt)
ETT advance under bronchoscope guidance
6
6a
27 (Range 22–29.5)
Main bronchus
Automatic inflation of the cuff to a preset maximal pressure
10
0 (in max. 3 min)
13.6 (Range 11–16)
Above carina
ETT repositioning
14
a
The current scale of the capnograph in the AnapnoGuard system is 0–6 mmHg. We speculate that the real CO2 level was much higher— probably close to the arterial or alveolar level
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air leak around the tube when its distal tip is located between the vocal cords and the carina [13]. In this experimental setup the only difference in comparison to any other anesthesia technique was the use of a special ETT, with side ports connected to a system that continuously measured the CO2 level above the cuff and automatically adjusted the cuff pressure to a level that avoided air leak. In addition, the length of the ETT used was greater than that in use for humans because of the anatomic conformation of goats. Our hypothesis for the present study was that once the ETT distal tip accidentally slips into one of the main bronchi, the AnapnoGuard system would react by identifying CO2 above the cuff. The origin of the CO2 in this case is expected to be the unventilated lung, which at least for the initial period of time is still perfused. Suggett et al. [14] have demonstrated, in their dog model, that even at the plateau phase, when the perfusion to the unventilated lung is significantly decreased, CO2 is still being diffused. Since during EBI, the malpositioned cuff cannot achieve complete sealing of the non-intubated lung, above cuff CO2 leak can be detected. The proposed method of early detection of accidental EBI has the advantage of being simple to use, noninvasive, and suitable for any intubated patient. It displays on-line the CO2 level above the cuff tube and thus can identify the endobronchial position of the distal tip after only a very short delay. Each of the already proposed techniques to be used for the purpose of identification of EBI has flaws and limitations. For instance, the Rapiscope technique [15] could not be used continuously. The reflectometry method [16] does not offer reliable results in the presence of bronchial secretions or a tracheobronchial tumor. Finally, the video imaging method [17] is limited in chest asymmetry; in addition, in the presence of air leak this method becomes unusable. Recently, two of the current investigators (NW, GMG) reported the use of a new monitoring method for detection of EBI by transforming the lung sounds recorded by four piezoelectric acoustic sensors into a processed electronic signal. These studies showed a good correlation between the real location of the ETT distal tip and the results of the signal analysis, in cases of both endotracheal tubes [18] and double lumen tubes [19], but the proposed method demanded the use of microphones and a complicated algorithm. We suggest that the AnapnoGuard system could detect accidental EBI at a very early stage and offers a valid alternative to the already proposed methods to be used for this purpose. It can be easily used by the average physician and its display is easy to understand. One possible incident during its use could be the accumulation of secretions around the cuff, but the ETT used with the AnapnoGuard
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system is provided with a special extra lumen, with two distal openings located just above the cuff, through which secretions are periodically aspirated. As detailed above, the primary intended use of the AnapnoGuard system is for ETT cuff pressure optimization by monitoring above cuff CO2 levels [16]. In addition, the AnapnoGuard system, by assuring optimal cuff sealing and continuous analysis of gradient pressure between the cuff and the ventilator, can detect the degree of intra-luminal ETT obstruction [20]. Moreover, the AnapnoGuard system with the special ETT enables effective suction of secretion from the subglottic space. Therefore, detection of EBI is an additional beneficial feature gained by monitoring above cuff CO2. The cost of the special ETT, with the extra 2 lumens, is similar to the costs of the other high end suction ETTs. However, the AnapnoGuard system is capital equipment that possessed additional cost. The special ETTs are FDA and CE (European) approved. The AnapnoGuard system has CE approval and is currently in the process of receiving FDA approval. There are certain situations in which the CO2 method may be misleading if not recognized appropriately. There are two conditions that may be associated with continued, unadjusted, above cuff CO2 readings even though it is not EBI (false positive) and two condition where CO2 will not be detected even though it is EBI (false negative). The first condition where CO2 will be continuously recorded is cuff rupture. That can be easily detected by the low non-filled cuff pressure. The second condition is proximal malposition of the ETT (cuff is within or above the vocal cords). The proximal malposition can be easily detected by looking at the insertion depth of the ETT at tooth line. On the other hand, if secretions are blocking the sampling lumen, there will be no CO2 reading. That can also be easily detected by the AnapnoGuard system since it will alert that the lumen is blocked (very unusual with the 3-lumen special ETTs). Another possible incident for misdiagnosis of EBI, false negative, could be when only the tip of the ETT is located the main-stem ventilating one lung, while the cuff is on the carina occluding both bronchi. In this case, it might be possible that CO2 will not leak and the ineffective ventilation will not be detected. Accordingly, since there is no single monitoring method that have 100 % accuracy, it is very important that as many signs as possible need to be frequently monitored in order to detect and prevent EBI. In conclusion, we propose a new method for early detection of accidental EBI by continuous measurement of CO2 level above the ETT cuff. This new use of the AnapnoGuard system could be added to the already proven indication of detection of air leak around the cuff in intubated patients, without any need to change any of the details of the proposed system for this task.
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We suggest that when using the proposed system, appearance of CO2 above the cuff, in the absence of an air leak (at high cuff pressures), might indicate the need to withdraw the ETT. However, this is a preliminary report and further studies are needed to evaluate the method in different clinical and experimental settings. Acknowledgments ration, Ltd.
The study was supported by Hospitech Respi-
Conflict of interest piration, Ltd.
SE and ID are shareholders in Hospitech Res-
References 1. Szekely SM, Webb RK, Williamson JA, Russell WJ. Problems related to the endotracheal tube. Anaesth Intensiv Care. 1992;21:611–6. 2. McCoy EP, Russell WJ, Webb RK. Accidental bronchial intubation. An analysis of AIMS incidents report from, 1988 to 1994 inclusive. Anaesthesia. 1997;52:24–31. 3. Owen TR, Cheney FW. Endobronchial intubation: a preventable complication. Anesthesiology. 1987;67:255–7. 4. Dornette WHL. Anatomy for the anesthesiologist. Springfield: Charles C. Thomas; 1963. p. 973–7. 5. Brunel W, Coleman DL, Schwartz DE, Peper E, Cohen NH. Assessment of routine chest roentgenograms and physical examination to confirm endotracheal tube position. Chest. 1989; 96:1043–5. 6. Sitzwohl C, Langheinrich A, Schober A, Krafft P, Sessler DI, Herkner H, Gonano C, Weinstabl C, Kettner SC. Endobronchial intubation detected by insertion depth of endotracheal tube, bilateral auscultation, or observation of chest movements: randomised trial. BMJ. 2010;341:c5943. 7. Efrati S, Deutsch I, Gurman GM. Endotracheal tube cuff–small important part of a big issue. J Clin Monit Comput. 2012; 26:53–60. 8. Alliaume B, Coddens J, Deloof T. Reliability of auscultation in positioning of double lumen endobronchial tube. Can J Anaesth. 1992;39:687–90.
9. Barker SJ, Tremper KK, Hyatt J, Heitzman H. Comparison of three oxygen monitors in detecting endobronchial intubation. J Clin Monit. 1988;4:240–3. 10. Johnson DH, Chang PC, Hurst TS, Reynolds FB, Lang SA, Mayers I. Changes in PETCO2 and pulmonary blood flow after bronchial occlusion in dogs. Can J Anaesth. 1992;39:184–91. 11. Heaneghan CPH, Scallan MJ, Branthwaite MA. End-tidal carbon dioxide during thoracotomy. Anaesthesia. 1981;36:1017–21. 12. Conrardy PA, Goodman LR, Lainge F, Singer MM. Alteration of endotracheal tube position. Flexion and extension of the neck. Crit Care Med. 1976;4:7–12. 13. Efrati S, Leonov Y, Oron A, Siman-Tov Y, Averbukh M, Lavrushevich A, Golik A. Optimization of endotracheal tube cuff filling by continuous upper airway carbon dioxide monitoring. Anesth Analg. 2005;101:1081–8. 14. Suggett AJ, Barer GR, Mohammed FH, Gill GW. The effects of localized hypoventilation on ventilation/perfusion (V/Q) ratios and gas exchange in the dog lung. Clin Sci. 1982;63:497–503. 15. Ezri T, Khazin V, Szmuk P, Medalion B, Shechter P, Priel I, Loberboim M, Weibroum AA. Use of the Rapiscope vs chest auscultation for detection of accidental bronchial intubation in non-obese patients undergoing laparoscopic cholecystectomy. J Clin Anesth. 2006;18:118–23. 16. Raphael DT, Benbassat M, Arnaudov D, Bohorquez A, Nasseri B. Validation study of two-microphone acoustic reflectometry for determination of breathing tube placement in 200 adult patients. Anesthesiology. 2002;97:1371–7. 17. Jean S, Cinel I, Gratz I, Tay C, Lotano V, Deal E, Parillo JE, Dellinger RP. Image-based monitoring of one-lung intubation. Eur J Anaesthesiol. 2008;25:995–1001. 18. Tejman-Yarden S, Lederman D, Eilig I, Zlotnik A, Weksler N, Cohen A, Gurman GM. Acoustic monitoring of double-lumen ventilated lungs for the detection of selective unilateral lung ventilation. Anesth Analg. 2006;103:1489–93. 19. Tejman-Yarden S, Zlotnik A, Weizman L, Tabrikian J, Cohen A, Weksler N, Gurman GM. Acoustic monitoring of lung sounds for the detection of one-lung intubation. Anesth Analg. 2007;105: 397–404. 20. Efrati S, Deutsch I, Gurman GM, Noff M, Conti G. Tracheal pressure and endotracheal tube obstruction can be detected by continuous cuff pressure monitoring: in vitro pilot study. Intensive Care Med. 2010;36:984–90.
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ORIGINAL RESEARCH
Detection of endobronchial intubation by monitoring the CO2 level above the endotracheal cuff Shai Efrati • Israel Deutsch • Nathan Weksler Gabriel M. Gurman
•
Received: 26 February 2014 / Accepted: 7 May 2014 Ó Springer Science+Business Media New York 2014
Abstract Early detection of accidental endobronchial intubation (EBI) is still an unsolved problem in anesthesia and critical care daily practice. The aim of this study was to evaluate the ability of monitoring above cuff CO2 to detect EBI (the working hypothesis was that the origin of CO2 is from the unventilated, but still perfused, lung). Six goats were intubated under general anesthesia and the ETT positioning was verified by a flexible bronchoscope. The AnapnoGuard system, already successfully used to detect air leak around the ETT cuff, was used for continuous monitoring of above-the-cuff CO2 level. When the ETT distal tip was located in the trachea, with an average cuff pressure of 15 mmHg, absence of CO2 above the cuff was observed. The ETT was then deliberately advanced into one of the main bronchi under flexible bronchoscopic vision. In all six cases the immediate presence of CO2 above the cuff was identified. Further automatic inflation of the cuff, up to a level of 27 mmHg, did not affect the above-the-cuff measured CO2 level. Withdrawal of the ETT and repositioning of its distal tip in mid-trachea caused the disappearance of CO2 above the cuff in a maximum of 3 min, confirming the absence of air leak and the correct positioning of the ETT. Our results suggest that S. Efrati (&) Research and Development Unit, Assaf Harofeh Medical Center, Affiliated with the Sackler School of Medicine, Tel-Aviv University, 70300 Zerifin, Israel e-mail: [email protected] I. Deutsch Hospitech Respiration Ltd., Petah Tikva, Israel N. Weksler G. M. Gurman Division of Anesthesiology and Critical Care, Myney Hayeshuah, Bnei Brak, Ben-Gurion University of the Negev, Beersheba, Israel
measurement of the above-the-cuff CO2 level could offer a reliable, on-line solution for early identification of accidental EBI. Further studies are planned to validate the efficacy of the method in a clinical setup. Keywords Endobronchial Intubation One lung CO2 Endotracheal tube
1 Introduction Intubation of a main bronchus, more frequently on the right, is a common incident during tracheal intubation for general anesthesia and/or prolonged mechanical ventilation [1–7]. The pathological consequences of one lung intubation are mainly reduction of blood oxygenation, appearance of tension pneumothorax (because of hyperinflation of the intubated lung), and an increase in the post-intubation pulmonary complications, including atelectasis and pneumonia. A report by the Australian Incident Monitoring Study (AIMS) on 2000 patients found endobronchial intubation (EBI) to be the most common incident involving tracheal intubation [1]. A second AIMS study [2], on 2,947 patients, found that accidental EBI accounted for 3.7 % of all incidents reported. The relatively high incidence is mainly due to the incertitude of the anatomical distance between the teeth and the carina. That is why relying on fixed measurement does not guarantee proper positioning in all patients, as Owen and Cheney proposed in their study [3], does not cover those patients who do not belong to the ‘‘normal range of height’’. Moreover, physical examination, including auscultation of the chest wall, is a nonobjective measure highly dependent on the physician’s
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experience. For example, in a study done by Sitzwohl et al., first year residents missed EBI by auscultation in 55 % of the cases, which was significantly worse than experienced anaesthetists [6]. Neither clinical auscultation [5, 8], monitoring of oxygen saturation [9], nor end-tidal CO2 [10, 11] offers an accurate and rapid method of identifying EBI. Furthermore, any change in the patient’s head or neck position can lead to migration of the ETT. Conrardy et al. reported that neck flexion can advance the tube up to 3.1 cm toward the carina, exposing the patients to higher risk of EBI [12]. Accordingly, there is a need for an objective, non-invasive method that identifies and alarms the medical staff early when the ETT is mal-positioned. The present study proposes a new method of early detection of bronchial location of the ETT distal tube, using a system that identifies the presence of CO2 just above the ETT cuff when there is no leak around the cuff. We hypothesized that the CO2 from the non-ventilated lung can be detected above the cuff once main stem intubation accidentally occurs.
2 Methods The study included six healthy goats at the age of 2 years. The goats were not pregnant or lactating, and had a mean weight of 50 kg. The experiment was conducted in the Research and Development Unit of Assaf Harofeh Medical Center, Israel. All the animals included in the study were maintained according to the guidelines of the Local Ethics
Fig. 1 The three lumen endotracheal tube use for above cuff CO2 readings
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Committee for Animal Experimentation, and the experimental protocol was approved by the latter. Before anesthesia, the physiological parameters of each animal were measured and found to be within normal range: heart rate around 50/min, body temperature 38.0 °C, and respiratory rate around 20/min. Each goat was anesthetized using i.v. ketamine 10–11 mg/kg, midazolam 0.2 mg/kg, Lidocaine 0.2 mg/kg, and atropine 0.5 mg i.v. After tracheal intubation with an extended tube of 50 cm, especially prepared for this study, the animal was kept anesthetized with Isoflurane 1–2 % in oxygen, the head up 20 degrees and mechanically ventilated with a tidal volume of 7 ml/kg. 2.1 Endotracheal tubes and device used for above cuff CO2 reading A modified version of the AnapnoGuard system ETT (Hospitech Respiration Ltd., Petah Tikva, Israel) was used. As illustrated in Fig. 1, in order to enable successive CO2 readings (air samples taken from the space above the cuff and below the vocal cords to the AnapnoGuard system CO2 analyzer), the ETT has 2 additional lumens: one for CO2 readings (ventral lumen) while the other (dorsal lumen) is split into two at the distal end, used for suctioning of secretions. The lumens on both sides also serve as venting lumens, meaning that when the system is used for suctioning secretions, the ventral (CO2) lumen serves for venting while suctioning with the dorsal suction lumen and vice versa. The CO2 samples are pumped into the CO2 analyzer via the CO2/vent lumen or the suction lumen.
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3 Results
Fig. 2 Tracheal tube positioning and origin of CO2 during endobronchial intubation
Having this venting capability reduces the chances of lumen occlusion that usually happens with standard suction ETTs due to vacuum, and adherence to the tracheal wall is prevented. The AnapnoGuard system is an innovative respiratory guard system that automatically monitors and controls the ETT cuff pressure. The cuff pressure that seals off the trachea is set by measurement of CO2 levels above the cuff [13]. The optimal ETT cuff pressure is the minimal pressure needed to prevent CO2 leakage from the lungs to the oropharynx. 2.2 Tube positions After stabilizing the animal’s vital signs and verification of the perfect sealing off of the airways (no CO2 leak above the cuff, at a maximal cuff pressure of 15 mmHg), the tube was advanced into one of the main bronchi (the right one in four cases, the left in two cases) under flexible bronchoscopic vision. In this new ETT distal tip location, the cuff sealed off only the intubated main bronchus (Fig. 2). The above or below carina position of the ETT tip tube was verified using a flexible bronchoscope. The AnapnoGuard system upper limit of CO2 scale is 6 mmHg (consider to be a high significant leakage). After the ETT was positioned in the main bronchi, above cuff CO2 was continuously measured by the AnapnoGuard system for 4 min. If CO2 leakage was detected the cuff was inflated to a maximal preset cuff pressure of 27 mmHg and above cuff CO2 was re-measured in the next 4 min. Once it done, the ETT was repositioned to the trachea and in the following 3 min the cuff pressure was reduced by the AnapnoGuard system to the minimal pressure needed to prevent CO2 leakage.
All animals were hemodynamically stable and completed all study procedures. In each endobronchial ETT position the above-the-cuff CO2 was detected in each animal in less than 2 min; partial pressure was 6 mmHg in each of the 6 experiments (6 mmHg is the upper limit of the CO2 scale in the AnapnoGuard system, but most probably the true CO2 level at this stage of the experiment was much higher, closer to the arterial or alveolar level). Because of the system detection of CO2 above the cuff, the AnapnoGuard system automatically increased the cuff pressure to an average of 27 mmHg (range 22–29.5), but the system continued to detect significant CO2 levels above the cuff. Then the ETT distal tip was once again relocated above the carina and its position reconfirmed by flexible bronchoscopy; in the next 3 min the CO2 above the cuff disappeared and the automatic regulation of cuff pressure permitted its decrease to an average level of 13.6 mmHg. The sequence of procedures during the test is summarized in Table 1.
4 Discussion The AnapnoGuard system has already been clinically tried during general anesthesia and proven to be a reliable method of assuring the optimal cuff pressure that will avoid Table 1 Sequence of procedures, average cuff pressure, and CO2 level above the ETT cuff CO2 level above cuff (mmHg)
Average cuff pressure (mmHg)
Location of ETT distal tip
Procedure
Time (min)
Induction of general anesthesia
0
0
15 (Range 13–17)
Above carina
Tracheal intubation
3
6a
13.5 (Range 11–15)
Main bronchus (4 times Rt, 2 times Lt)
ETT advance under bronchoscope guidance
6
6a
27 (Range 22–29.5)
Main bronchus
Automatic inflation of the cuff to a preset maximal pressure
10
0 (in max. 3 min)
13.6 (Range 11–16)
Above carina
ETT repositioning
14
a
The current scale of the capnograph in the AnapnoGuard system is 0–6 mmHg. We speculate that the real CO2 level was much higher— probably close to the arterial or alveolar level
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air leak around the tube when its distal tip is located between the vocal cords and the carina [13]. In this experimental setup the only difference in comparison to any other anesthesia technique was the use of a special ETT, with side ports connected to a system that continuously measured the CO2 level above the cuff and automatically adjusted the cuff pressure to a level that avoided air leak. In addition, the length of the ETT used was greater than that in use for humans because of the anatomic conformation of goats. Our hypothesis for the present study was that once the ETT distal tip accidentally slips into one of the main bronchi, the AnapnoGuard system would react by identifying CO2 above the cuff. The origin of the CO2 in this case is expected to be the unventilated lung, which at least for the initial period of time is still perfused. Suggett et al. [14] have demonstrated, in their dog model, that even at the plateau phase, when the perfusion to the unventilated lung is significantly decreased, CO2 is still being diffused. Since during EBI, the malpositioned cuff cannot achieve complete sealing of the non-intubated lung, above cuff CO2 leak can be detected. The proposed method of early detection of accidental EBI has the advantage of being simple to use, noninvasive, and suitable for any intubated patient. It displays on-line the CO2 level above the cuff tube and thus can identify the endobronchial position of the distal tip after only a very short delay. Each of the already proposed techniques to be used for the purpose of identification of EBI has flaws and limitations. For instance, the Rapiscope technique [15] could not be used continuously. The reflectometry method [16] does not offer reliable results in the presence of bronchial secretions or a tracheobronchial tumor. Finally, the video imaging method [17] is limited in chest asymmetry; in addition, in the presence of air leak this method becomes unusable. Recently, two of the current investigators (NW, GMG) reported the use of a new monitoring method for detection of EBI by transforming the lung sounds recorded by four piezoelectric acoustic sensors into a processed electronic signal. These studies showed a good correlation between the real location of the ETT distal tip and the results of the signal analysis, in cases of both endotracheal tubes [18] and double lumen tubes [19], but the proposed method demanded the use of microphones and a complicated algorithm. We suggest that the AnapnoGuard system could detect accidental EBI at a very early stage and offers a valid alternative to the already proposed methods to be used for this purpose. It can be easily used by the average physician and its display is easy to understand. One possible incident during its use could be the accumulation of secretions around the cuff, but the ETT used with the AnapnoGuard
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system is provided with a special extra lumen, with two distal openings located just above the cuff, through which secretions are periodically aspirated. As detailed above, the primary intended use of the AnapnoGuard system is for ETT cuff pressure optimization by monitoring above cuff CO2 levels [16]. In addition, the AnapnoGuard system, by assuring optimal cuff sealing and continuous analysis of gradient pressure between the cuff and the ventilator, can detect the degree of intra-luminal ETT obstruction [20]. Moreover, the AnapnoGuard system with the special ETT enables effective suction of secretion from the subglottic space. Therefore, detection of EBI is an additional beneficial feature gained by monitoring above cuff CO2. The cost of the special ETT, with the extra 2 lumens, is similar to the costs of the other high end suction ETTs. However, the AnapnoGuard system is capital equipment that possessed additional cost. The special ETTs are FDA and CE (European) approved. The AnapnoGuard system has CE approval and is currently in the process of receiving FDA approval. There are certain situations in which the CO2 method may be misleading if not recognized appropriately. There are two conditions that may be associated with continued, unadjusted, above cuff CO2 readings even though it is not EBI (false positive) and two condition where CO2 will not be detected even though it is EBI (false negative). The first condition where CO2 will be continuously recorded is cuff rupture. That can be easily detected by the low non-filled cuff pressure. The second condition is proximal malposition of the ETT (cuff is within or above the vocal cords). The proximal malposition can be easily detected by looking at the insertion depth of the ETT at tooth line. On the other hand, if secretions are blocking the sampling lumen, there will be no CO2 reading. That can also be easily detected by the AnapnoGuard system since it will alert that the lumen is blocked (very unusual with the 3-lumen special ETTs). Another possible incident for misdiagnosis of EBI, false negative, could be when only the tip of the ETT is located the main-stem ventilating one lung, while the cuff is on the carina occluding both bronchi. In this case, it might be possible that CO2 will not leak and the ineffective ventilation will not be detected. Accordingly, since there is no single monitoring method that have 100 % accuracy, it is very important that as many signs as possible need to be frequently monitored in order to detect and prevent EBI. In conclusion, we propose a new method for early detection of accidental EBI by continuous measurement of CO2 level above the ETT cuff. This new use of the AnapnoGuard system could be added to the already proven indication of detection of air leak around the cuff in intubated patients, without any need to change any of the details of the proposed system for this task.
J Clin Monit Comput
We suggest that when using the proposed system, appearance of CO2 above the cuff, in the absence of an air leak (at high cuff pressures), might indicate the need to withdraw the ETT. However, this is a preliminary report and further studies are needed to evaluate the method in different clinical and experimental settings. Acknowledgments ration, Ltd.
The study was supported by Hospitech Respi-
Conflict of interest piration, Ltd.
SE and ID are shareholders in Hospitech Res-
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