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Endotracheal Tube Intracuff Pressure During Helicopter Transport
AIRWAY/BRIEF RESEARCH REPORT
Endotracheal Tube Intracuff Pressure During Helicopter Transport Marco Bassi, MD, Mathias Zuercher, MD, Jean-Jacques Erne, RN, Wolfgang Ummenhofer, MD From the Department of Anesthesia, University Hospital Basel, Basel, and the Swiss Air Rescue Organisation, Zurich, Switzerland.
Study objective: We evaluate changes in endotracheal tube intracuff pressures among intubated patients during aeromedical transport. We determine whether intracuff pressures exceed 30 cm H2O during aeromedical transport. Methods: During a 12-month period, a helicopter-based rescue team prospectively recorded intracuff pressures of mechanically ventilated patients before takeoff and as soon as the maximum flight level was reached. With a commercially available pressure manometer, intracuff pressure was adjusted to ⱕ25 cm H2O before loading of the patient. The endpoint of our investigation was the increase of endotracheal tube cuff pressure during helicopter transport. Results: Among 114 intubated patients, mean altitude increase was 2,260 feet (95% confidence interval [CI] 2,040 to 2,481 feet; median 2,085 feet; interquartile range [IQR] 1,477.5 to 2,900 feet). Mean flight time was 14.8 minutes (95% CI 13.1 to 16.4 minutes; median 13.5 minutes; IQR 10 to 16.1 minutes). Intracuff pressure increased from 28.7 cm H2O (95% CI 27.0 to 30.4 cm H2O [median 25 cm H2O; IQR 25 to 30 cm H2O]) to 62.6 cm H2O (95% CI 58.8 to 66.5 cm H2O; median 58; IQR 48 to 72 cm H2O). At cruising altitude, 98% of patients had intracuff pressures ⱖ30 cm H2O, 72% had intracuff pressures ⱖ50 cm H2O, and 20% even had intracuff pressures ⱖ80 cm H2O. Conclusion: Endotracheal cuff pressure during transport frequently exceeded 30 cm H2O during aeromedical transport. Hospital and out-of-hospital practitioners should measure and adjust endotracheal cuff pressures before and during flight. [Ann Emerg Med. 2010;56:89-93.] Please see page 90 for the Editor’s Capsule Summary of this article. 0196-0644/$-see front matter Copyright © 2009 by the American College of Emergency Physicians. doi:10.1016/j.annemergmed.2010.01.025
INTRODUCTION Background Cuffed endotracheal tubes are commonly used to allow positive-pressure ventilation. When adjusting the intracuff inflation volume and pressure, providers must weigh the need for a sufficient cuff seal with the risks of aspiration and tracheal injury from high intracuff pressures. Animal data suggest that high-volume, low-pressure cuffed tubes inflated to 30 cm H2O can induce mucosal lesions after as little as 15 minutes.1 For prolonged periods, especially during hypotension, significant reduction in tracheal blood flow may occur at even lower mucosal contact pressure.2 These findings were confirmed by human data showing mucosal blood flow impairment at lateral wall pressures ⱖ30 cm H2O and total mucosal blood flow obstruction at pressures ⱖ50 cm H2O.3 Importance High intracuff pressures can lead to severe tracheal injuries, including tracheal laceration, stenosis, or even rupture.4 Because gas in a closed space, such as an endotracheal tube cuff, will expand with increasing elevation (ie, decreased ambient Volume , . : August
barometric pressure), the intracuff pressure can increase substantially during aeromedical transport.5,6 Goals of This Investigation We evaluated intracuff pressure changes in tracheally intubated patients transported by a European helicopter transport system. Specifically, we determined the frequency of intracuff pressure increase to more than 30 cm H2O during air medical transport.
MATERIALS AND METHODS Theoretical Model of the Problem According to Boyle-Mariotte’s law, intracuff pressure during air evacuation can be calculated theoretically as Pcuff2⫽Pcuff1⫹ Patm1⫺Patm2, where Pcuff is intracuff pressure and Patm is atmospheric pressure at takeoff (Patm1) and during the flight (Patm2), respectively. Therefore, cuff pressure increases as atmospheric pressure decreases. For further details and an example, please refer to Appendix E1, available online at http:// www.annemergmed.com. Annals of Emergency Medicine 89
Endotracheal Tube Intracuff Pressure During Helicopter Transport
Editor’s Capsule Summary
What is already known on this topic High endotracheal tube cuff pressure may harm airway mucosa. What question this study addressed Does tracheal cuff pressure increase during air medical helicopter transport? What this study adds to our knowledge In this air medical series with a mean flight altitude of 2,260 feet, cuff pressure increased to harmful levels in 98% of patients. How this might change clinical practice Although the effect of transient increases in cuff pressure is unknown, it is prudent for out-ofhospital practitioners to adjust tracheal cuff pressure before and during air medical transport.
Study Design After receiving approval from our regional ethics committee, we performed a prospective observational study in mechanically ventilated emergency and intensive care patients scheduled for aeromedical transport. Setting and Selection of Participants The study was performed at the Swiss Air-Rescue Organisation (REGA, Zurich, Switzerland), located at the EuroAirport Basel (900 feet above sea level) in the border region between Germany, France, and Switzerland. We studied patients transported in a Eurocopter EC 145 helicopter, which typically operates at altitudes between 2,500 and 4,000 feet above sea level. The crew consists of a pilot, a paramedic-flight assistant, and a board-certified anesthesiologist with a certificate in out-of-hospital emergency medicine. All mechanically ventilated patients were consecutively screened and enrolled in the study if they had a cuffed endotracheal tube and were transported by helicopter. Patients excluded were those with double lumen tubes, tracheotomy, safety concerns (heavy workload for the emergency physician because of cardiovascular or respiratory instability, resuscitation, or multiresistant infections), or incompatibility between the cuff connection and the cuff-pressure manometer. Methods of Measurement Pressure measurements were performed with a commercially available pressure manometer (Mallinckrodt, Hazelwood, MO). The manometer was attached to the cuff pilot before the patient was loaded into the helicopter. Per study protocol, intracuff pressure was adjusted to ⱕ25 cm H2O. If air leakage was audible, cuff pressure was increased until the leakage stopped. 90 Annals of Emergency Medicine
Bassi et al After helicopter takeoff, the pilot announced the maximum flight altitude, at which point the corresponding second intracuff pressure was recorded. Data Collection and Processing Cuff pressure and corresponding altitudes were noted on a special form and later entered into an Excel (Microsoft Inc., Redmond, WA) worksheet. Outcome Measures The endpoint of our investigation was the increase of endotracheal tube cuff pressure during helicopter transport. Because of the unclear clinical confounders and the wide range of potential receiving hospitals (10 major hospitals located in 3 countries), we decided a priori not to determine clinical outcomes; for example, hospital survival. Primary Data Analysis Data were analyzed with SPSS, version 15.0 (SPSS, Inc., Chicago, IL). Data are presented as descriptive statistics. Values are shown as means with 95% confidence intervals (CIs). Medians and interquartile ranges (IQRs) (25% to 75%) are given in parentheses. We determined the mean increase in intracuff pressure for each case. We also determined the proportion of cases in which intracuff pressure exceeded 30, 50, and 80 cm H2O. Flight time at maximum altitude was determined for each patient by using the individual flight profile provided by the pilot.
RESULTS Two hundred seven mechanically ventilated patients were transported by helicopter from January 1 to December 31, 2006. Ninety-three patients were excluded, 12 because of special tubes (eg, tracheotomy), 38 because of safety concerns, and 43 because of missing or incomplete data. Data from 114 patients were included for further analysis of flight-induced changes. Seventy-six patients were transports from an emergency department (ED) or out-of-hospital scene, and 38 were interhospital transports from an ICU. Most patients were men (85 men, 29 women). Mean age was 52.4 years (95% CI 48.6 to 56.2 years; range 10 to 85 years), mean estimated weight was 80.1 kg (95% CI 76.8 to 83.5 kg; range 30 to 150 kg), and mean tube depth was 22.9 cm (95% CI 22.5 to 23.2 cm; range 17 to 28 cm; n⫽111), measured at the front teeth. The tube size most commonly used was 8.0-mm (n⫽57) internal diameter (8.5 mm n⫽17; 7.5 mm n⫽21; 7.0 mm n⫽12, 6.5 mm n⫽2; 6.0 mm n⫽2). Per study protocol, intracuff pressure was reduced to 25 cm H2O before transport. Because of audible leaks, the cuff was inflated to higher pressure in 10 of 114 (9%) cases. One patient was omitted from the analysis because cuff pressure exceeded 120 cm H2O. This outlying measurement was judged as a technical failure. The mean increase in flight altitude (maximum flight altitude minus takeoff altitude) was 2,260 feet (95% CI 2,040 Volume , . : August
Bassi et al
Endotracheal Tube Intracuff Pressure During Helicopter Transport
Figure 2. Cuff pressure increase from takeoff (Pstart) to maximum flight level (Pmax). ⌬P⫽33.9 cm H2O; 95% CI 30.6 to 37.3 cm H2O (median 30 cm H2O; IQR 20.9 to 44 cm H2O).
Figure 1. Histograms of endotracheal cuff pressure A, at takeoff and B, when maximum flight altitude was reached.
to 2,481 feet; median 2,085 feet; IQR 1,477.5 to 2,900 feet). The mean flight time was 14.8 minutes (95% CI 13.1 to 16.4 minutes; median 13.5 minutes; IQR 10 to 16.1 minutes; range 4 to 61 minutes). Mean intracuff pressure at takeoff was 28.7 cm H2O (95% CI 27.0 to 30.4 cm H2O; median 25 cm H2O; IQR 25 to 30 cm H2O) (Figure 1). Mean intracuff pressure at maximum altitude was 62.6 cm H2O (95% CI 58.8 to 66.5 cm H2O; median 58 cm H2O; IQR 48 to 72 cm H2O) (Figure 1). Mean cuff pressure increase (Pmax⫺Pstart) was 33.9 cm H2O (95% CI 30.6 to 37.3 cm H2O; median 30 cm H2O; IQR 20.9 to 44 cm H2O) (Figure 2). At cruising altitude, 112 of 114 patients (98%) had an intracuff pressure ⱖ30 cm H2O, 82 of 114 (72%) had an intracuff pressure ⱖ50 cm H2O, and 23 of 114 (20%) had and intracuff pressure ⱖ80 cm H2O (Figure 2). The change in cuff pressure was associated with change in altitude (Figure 3). According to standard flight operation procedures, the time at cuff pressures ⬎30 cm H2O was calculated for each patient. An intracuff pressure of ⱖ30 cm H2O during 15 minutes or longer was reached for 49 patients (43%). Of those, 37 (32%) had intracuff pressures ⱖ50 cm H2O, and 15 (13%), ⱖ80 cm H2O.
LIMITATIONS This study has several limitations. The providers were not blinded. We used a commercial analogue cuff pressure Volume , . : August
Figure 3. Individual increase in endotracheal cuff pressure in relation to the corresponding change in flight altitude.
manometer not specifically calibrated for air transportation. Further variations in pressure might result from different physical properties of tubes supplied by different manufacturers.5 Because the patients included in this study were recruited from several hospitals or emergency medical services, we could not control for the type of tubing. Because data were incomplete for one third of cases, selection bias was possible. Although increased cuff pressure is presumably harmful, the long-term implications are unknown. Because of the heterogeneity of target hospitals located in 3 countries and involving different languages, we did not link to patient outcomes. We did not determine minor (eg, sore throat, hoarseness) or major complications (eg, tracheal rupture, stenosis). Select patients had intracuff pressures exceeding 25 cm H2O at the start of the flight. These instances resulted from cuff leaks Annals of Emergency Medicine 91
Endotracheal Tube Intracuff Pressure During Helicopter Transport requiring additional inflation (n⫽8) and spontaneous increases in pressure (n⫽47). In the operating room, we have observed similar spontaneous cuff pressure increases. When we excluded cases with starting pressure ⬎25 cm H2O, we observed cuff pressure increases of 35 cm H2O (95% CI 29.6 to 39.3 cm H2O).
DISCUSSION This large series of intubated air medical patients demonstrated intracuff pressure increases to ⱖ30 cm H2O for 98% of patients. Cuff pressures exceeded even higher levels (ⱖ50 cm H2O and ⱖ80 cm H2O) in a significant percentage of these cases (72% and 20%, respectively). According to flight times, 49 of 114 (43%) patients were exposed to excessive intracuff pressure (⬎30 cm H2O) for longer than 15 minutes. Our observations have important implications for both inhospital and out-of-hospital care, highlighting the need for intracuff pressure monitoring before and during aeromedical transport. Despite reducing intracuff pressure before flight, almost all cuffs exceeded 30 cm H2O, and nearly three fourths exceeded 50 cm H2O. Endotracheal tube intracuff pressures are known to be very high in the out-of-hospital and ED setting.7,8 If the intracuff pressures had not been adjusted before takeoff, an even higher percentage of patients would have experienced values greater than 50 cm H2O. Henning et al6 first described high intracuff pressures during aeromedical transports, observing a mean increase in pressure of 23 cm H2O for a 3,000-feet ascent. They also observed correlation between changes in altitude and intracuff pressure (0.78 cm H2O per 1,000 feet). Contrary to their data, ours exhibited a large variability of pressure increases at maximum flight level (Figures 2 and 3). These differences may be related to several major design differences. Their study was small (n⫽10), and they excluded patients with an audible air leak. In our study, patients were intubated with tubes from different manufacturers. An in vitro study5 reported differences in cuff pressure with altitude among different brands of commonly used endotracheal tubes. Furthermore, Henning et al6 measured cuff pressure with a pressure transducer, a more precise technique than the more clinically available cuff manometer that we used. Several strategies have been proposed to avoid excessive intracuff pressures, including the use of saline solution rather than air to seal the cuff,5,9 novel cuffs with a high-pressure relief system,10 automated control devices,11 or frequent manometry with titration of the pressure/volume. The use of saline solution is reasonable but lacks supporting data. Pressure relief valves would be helpful for ascending flights but bear the risk of insufficient sealing while descending. The use of automated control devices seems promising and merits testing during aeromedical transport. In our setting, periodical control of intracuff pressure with a manometer seems simple and feasible, and simple routine monitoring would alert providers to the problem of increased cuff pressures. 92 Annals of Emergency Medicine
Bassi et al In this series of aeromedical patients, endotracheal cuff pressure exceeded 30 cm H2O in almost all cases. Hospital and out-of-hospital practitioners should measure and adjust endotracheal cuff pressures before and during flight. The authors thank Robert A. Berg, MD, for critically reviewing the manuscript, and Allison Dwileski, BS, for expert editorial assistance. Supervising editor: Henry E. Wang, MD, MS Author contributions: MB and MZ were responsible for conception of the study. MB and J-JE designed the study. MB was responsible for statistical analysis of the data. MB, MZ, and WU interpreted the data and drafted the article. MZ was responsible for statistical consulting. MZ and WU revised the article critically for important intellectual content. J-JE was responsible for selection of patients and critical revision of the article. WU had final approval of the article. WU takes responsibility for the paper as a whole. Funding and support: By Annals policy, all authors are required to disclose any and all commercial, financial, and other relationships in any way related to the subject of this article that might create any potential conflict of interest. See the Manuscript Submission Agreement in this issue for examples of specific conflicts covered by this statement. Funding was provided by the Department of Anesthesia, University Hospital Basel. The Swiss Air-Rescue Organisation helped collect the data. Publication dates: Received for publication June 8, 2009. Revisions received July 7, 2009; December 4, 2009; and January 1, 2010. Accepted for publication January 25, 2010. Available online February 25, 2010. Reprints not available from the authors. Address for correspondence: Wolfgang Ummenhofer, MD, Department of Anesthesia, University Hospital Basel, CH-4031 Basel, Switzerland; 41-61-265-7258, fax 41-61-265-7320; E-mail [email protected].
REFERENCES 1. Nordin U, Lindholm CE, Wolgast M. Blood flow in the rabbit tracheal mucosa under normal conditions and under the influence of tracheal intubation. Acta Anaesthesiol Scand. 1977;21:81-94. 2. Bunegin L, Albin MS, Smith RB. Canine tracheal blood flow after endotracheal tube cuff inflation during normotension and hypotension. Anesth Analg. 1993;76:1083-1090. 3. Seegobin RD, van Hasselt GL. Endotracheal cuff pressure and tracheal mucosal blood flow: endoscopic study of effects of four large volume cuffs. Br Med J. 1984;288:965-968. 4. Fan CM, Ko PC, Tsai KC, et al. Tracheal rupture complicating emergent endotracheal intubation. Am J Emerg Med. 2004;22: 289-293. 5. Smith RP, McArdle BH. Pressure in the cuffs of tracheal tubes at altitude. Anaesthesia. 2002;57:374-378.
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Bassi et al 6. Henning J, Sharley P, Young R. Pressures within air-filled tracheal cuffs at altitude: an in vivo study. Anaesthesia. 2004;59:252-254. 7. Galinski M, Treoux V, Garrigue B, et al. Intracuff pressures of endotracheal tubes in the management of airway emergencies: the need for pressure monitoring. Ann Emerg Med. 2006;47:545-547. 8. Svenson JE, Lindsay MB, O’Connor JE. Endotracheal intracuff pressures in the ED and prehospital setting: is there a problem? Am J Emerg Med. 2007;25:53-56.
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Endotracheal Tube Intracuff Pressure During Helicopter Transport 9. Kaye P. Effects of altitude on endotracheal tube cuff pressures. Emerg Med J. 2007;24:605. 10. Karasawa F, Takita A, Mori T, et al. The Brandt tube system attenuates the cuff deflationary phenomenon after anesthesia with nitrous oxide. Anesth Analg. 2003;96:606-610. 11. Weiss M, Doell C, Koepfer N, et al. Rapid pressure compensation by automated cuff pressure controllers worsens sealing in tracheal tubes. Br J Anaesth. 2009;102:273-278.
Annals of Emergency Medicine 93
Appendix E1.
PHYSICAL BACKGROUND Theoretical Considerations Boyle-Mariotte’s law states that pressure (P) times volume (V) is constant, if temperature remains unchanged. Therefore, the relationship between initial and final pressure and volume (P1 and V1, and P2 and V2, respectively) is expressed by the formula P1V1⫽P2V2. Because pressure within the system is equal to the sum of pressures, initial and final pressure can be expressed as (P⫽Pcuff⫹Patm). The equation relating these variables with respect to air evacuation is: (Pcuff1 ⫹Patm1)⫻V1 ⫽(Pcuff2 ⫹Patm2)⫻V2 Because the diameter of the trachea is of fixed proportion and any change in volume because of compression of soft tissues or proximal/
93.e1 Annals of Emergency Medicine
distal distortion of the cuff is so minor to be deemed negligible, the volume of an inflated cuff can be considered constant: V1 ⫽V2 Thus, the theoretically expected cuff pressure change during air transport is equivalent to final cuff pressure (Pcuff2), according to the calculation: Pcuff2 ⫽Pcuff1 ⫹Patm1 ⫺Patm2 Example: A helicopter takes off at sea level (Patm1⫽760 mm Hg) and cruises at an altitude of 2,000 feet (Patm2⫽704 mm Hg). Cuff pressure at takeoff is set to 25 cm H2O (Pcuff1⫽18 mm Hg). Expected cuff pressure at 2,000 feet is 100 cm H2O (Pcuff2⫽18⫹760⫺704⫽74 mm Hg).
Volume , . : August
Endotracheal Tube Intracuff Pressure During Helicopter Transport Marco Bassi, MD, Mathias Zuercher, MD, Jean-Jacques Erne, RN, Wolfgang Ummenhofer, MD From the Department of Anesthesia, University Hospital Basel, Basel, and the Swiss Air Rescue Organisation, Zurich, Switzerland.
Study objective: We evaluate changes in endotracheal tube intracuff pressures among intubated patients during aeromedical transport. We determine whether intracuff pressures exceed 30 cm H2O during aeromedical transport. Methods: During a 12-month period, a helicopter-based rescue team prospectively recorded intracuff pressures of mechanically ventilated patients before takeoff and as soon as the maximum flight level was reached. With a commercially available pressure manometer, intracuff pressure was adjusted to ⱕ25 cm H2O before loading of the patient. The endpoint of our investigation was the increase of endotracheal tube cuff pressure during helicopter transport. Results: Among 114 intubated patients, mean altitude increase was 2,260 feet (95% confidence interval [CI] 2,040 to 2,481 feet; median 2,085 feet; interquartile range [IQR] 1,477.5 to 2,900 feet). Mean flight time was 14.8 minutes (95% CI 13.1 to 16.4 minutes; median 13.5 minutes; IQR 10 to 16.1 minutes). Intracuff pressure increased from 28.7 cm H2O (95% CI 27.0 to 30.4 cm H2O [median 25 cm H2O; IQR 25 to 30 cm H2O]) to 62.6 cm H2O (95% CI 58.8 to 66.5 cm H2O; median 58; IQR 48 to 72 cm H2O). At cruising altitude, 98% of patients had intracuff pressures ⱖ30 cm H2O, 72% had intracuff pressures ⱖ50 cm H2O, and 20% even had intracuff pressures ⱖ80 cm H2O. Conclusion: Endotracheal cuff pressure during transport frequently exceeded 30 cm H2O during aeromedical transport. Hospital and out-of-hospital practitioners should measure and adjust endotracheal cuff pressures before and during flight. [Ann Emerg Med. 2010;56:89-93.] Please see page 90 for the Editor’s Capsule Summary of this article. 0196-0644/$-see front matter Copyright © 2009 by the American College of Emergency Physicians. doi:10.1016/j.annemergmed.2010.01.025
INTRODUCTION Background Cuffed endotracheal tubes are commonly used to allow positive-pressure ventilation. When adjusting the intracuff inflation volume and pressure, providers must weigh the need for a sufficient cuff seal with the risks of aspiration and tracheal injury from high intracuff pressures. Animal data suggest that high-volume, low-pressure cuffed tubes inflated to 30 cm H2O can induce mucosal lesions after as little as 15 minutes.1 For prolonged periods, especially during hypotension, significant reduction in tracheal blood flow may occur at even lower mucosal contact pressure.2 These findings were confirmed by human data showing mucosal blood flow impairment at lateral wall pressures ⱖ30 cm H2O and total mucosal blood flow obstruction at pressures ⱖ50 cm H2O.3 Importance High intracuff pressures can lead to severe tracheal injuries, including tracheal laceration, stenosis, or even rupture.4 Because gas in a closed space, such as an endotracheal tube cuff, will expand with increasing elevation (ie, decreased ambient Volume , . : August
barometric pressure), the intracuff pressure can increase substantially during aeromedical transport.5,6 Goals of This Investigation We evaluated intracuff pressure changes in tracheally intubated patients transported by a European helicopter transport system. Specifically, we determined the frequency of intracuff pressure increase to more than 30 cm H2O during air medical transport.
MATERIALS AND METHODS Theoretical Model of the Problem According to Boyle-Mariotte’s law, intracuff pressure during air evacuation can be calculated theoretically as Pcuff2⫽Pcuff1⫹ Patm1⫺Patm2, where Pcuff is intracuff pressure and Patm is atmospheric pressure at takeoff (Patm1) and during the flight (Patm2), respectively. Therefore, cuff pressure increases as atmospheric pressure decreases. For further details and an example, please refer to Appendix E1, available online at http:// www.annemergmed.com. Annals of Emergency Medicine 89
Endotracheal Tube Intracuff Pressure During Helicopter Transport
Editor’s Capsule Summary
What is already known on this topic High endotracheal tube cuff pressure may harm airway mucosa. What question this study addressed Does tracheal cuff pressure increase during air medical helicopter transport? What this study adds to our knowledge In this air medical series with a mean flight altitude of 2,260 feet, cuff pressure increased to harmful levels in 98% of patients. How this might change clinical practice Although the effect of transient increases in cuff pressure is unknown, it is prudent for out-ofhospital practitioners to adjust tracheal cuff pressure before and during air medical transport.
Study Design After receiving approval from our regional ethics committee, we performed a prospective observational study in mechanically ventilated emergency and intensive care patients scheduled for aeromedical transport. Setting and Selection of Participants The study was performed at the Swiss Air-Rescue Organisation (REGA, Zurich, Switzerland), located at the EuroAirport Basel (900 feet above sea level) in the border region between Germany, France, and Switzerland. We studied patients transported in a Eurocopter EC 145 helicopter, which typically operates at altitudes between 2,500 and 4,000 feet above sea level. The crew consists of a pilot, a paramedic-flight assistant, and a board-certified anesthesiologist with a certificate in out-of-hospital emergency medicine. All mechanically ventilated patients were consecutively screened and enrolled in the study if they had a cuffed endotracheal tube and were transported by helicopter. Patients excluded were those with double lumen tubes, tracheotomy, safety concerns (heavy workload for the emergency physician because of cardiovascular or respiratory instability, resuscitation, or multiresistant infections), or incompatibility between the cuff connection and the cuff-pressure manometer. Methods of Measurement Pressure measurements were performed with a commercially available pressure manometer (Mallinckrodt, Hazelwood, MO). The manometer was attached to the cuff pilot before the patient was loaded into the helicopter. Per study protocol, intracuff pressure was adjusted to ⱕ25 cm H2O. If air leakage was audible, cuff pressure was increased until the leakage stopped. 90 Annals of Emergency Medicine
Bassi et al After helicopter takeoff, the pilot announced the maximum flight altitude, at which point the corresponding second intracuff pressure was recorded. Data Collection and Processing Cuff pressure and corresponding altitudes were noted on a special form and later entered into an Excel (Microsoft Inc., Redmond, WA) worksheet. Outcome Measures The endpoint of our investigation was the increase of endotracheal tube cuff pressure during helicopter transport. Because of the unclear clinical confounders and the wide range of potential receiving hospitals (10 major hospitals located in 3 countries), we decided a priori not to determine clinical outcomes; for example, hospital survival. Primary Data Analysis Data were analyzed with SPSS, version 15.0 (SPSS, Inc., Chicago, IL). Data are presented as descriptive statistics. Values are shown as means with 95% confidence intervals (CIs). Medians and interquartile ranges (IQRs) (25% to 75%) are given in parentheses. We determined the mean increase in intracuff pressure for each case. We also determined the proportion of cases in which intracuff pressure exceeded 30, 50, and 80 cm H2O. Flight time at maximum altitude was determined for each patient by using the individual flight profile provided by the pilot.
RESULTS Two hundred seven mechanically ventilated patients were transported by helicopter from January 1 to December 31, 2006. Ninety-three patients were excluded, 12 because of special tubes (eg, tracheotomy), 38 because of safety concerns, and 43 because of missing or incomplete data. Data from 114 patients were included for further analysis of flight-induced changes. Seventy-six patients were transports from an emergency department (ED) or out-of-hospital scene, and 38 were interhospital transports from an ICU. Most patients were men (85 men, 29 women). Mean age was 52.4 years (95% CI 48.6 to 56.2 years; range 10 to 85 years), mean estimated weight was 80.1 kg (95% CI 76.8 to 83.5 kg; range 30 to 150 kg), and mean tube depth was 22.9 cm (95% CI 22.5 to 23.2 cm; range 17 to 28 cm; n⫽111), measured at the front teeth. The tube size most commonly used was 8.0-mm (n⫽57) internal diameter (8.5 mm n⫽17; 7.5 mm n⫽21; 7.0 mm n⫽12, 6.5 mm n⫽2; 6.0 mm n⫽2). Per study protocol, intracuff pressure was reduced to 25 cm H2O before transport. Because of audible leaks, the cuff was inflated to higher pressure in 10 of 114 (9%) cases. One patient was omitted from the analysis because cuff pressure exceeded 120 cm H2O. This outlying measurement was judged as a technical failure. The mean increase in flight altitude (maximum flight altitude minus takeoff altitude) was 2,260 feet (95% CI 2,040 Volume , . : August
Bassi et al
Endotracheal Tube Intracuff Pressure During Helicopter Transport
Figure 2. Cuff pressure increase from takeoff (Pstart) to maximum flight level (Pmax). ⌬P⫽33.9 cm H2O; 95% CI 30.6 to 37.3 cm H2O (median 30 cm H2O; IQR 20.9 to 44 cm H2O).
Figure 1. Histograms of endotracheal cuff pressure A, at takeoff and B, when maximum flight altitude was reached.
to 2,481 feet; median 2,085 feet; IQR 1,477.5 to 2,900 feet). The mean flight time was 14.8 minutes (95% CI 13.1 to 16.4 minutes; median 13.5 minutes; IQR 10 to 16.1 minutes; range 4 to 61 minutes). Mean intracuff pressure at takeoff was 28.7 cm H2O (95% CI 27.0 to 30.4 cm H2O; median 25 cm H2O; IQR 25 to 30 cm H2O) (Figure 1). Mean intracuff pressure at maximum altitude was 62.6 cm H2O (95% CI 58.8 to 66.5 cm H2O; median 58 cm H2O; IQR 48 to 72 cm H2O) (Figure 1). Mean cuff pressure increase (Pmax⫺Pstart) was 33.9 cm H2O (95% CI 30.6 to 37.3 cm H2O; median 30 cm H2O; IQR 20.9 to 44 cm H2O) (Figure 2). At cruising altitude, 112 of 114 patients (98%) had an intracuff pressure ⱖ30 cm H2O, 82 of 114 (72%) had an intracuff pressure ⱖ50 cm H2O, and 23 of 114 (20%) had and intracuff pressure ⱖ80 cm H2O (Figure 2). The change in cuff pressure was associated with change in altitude (Figure 3). According to standard flight operation procedures, the time at cuff pressures ⬎30 cm H2O was calculated for each patient. An intracuff pressure of ⱖ30 cm H2O during 15 minutes or longer was reached for 49 patients (43%). Of those, 37 (32%) had intracuff pressures ⱖ50 cm H2O, and 15 (13%), ⱖ80 cm H2O.
LIMITATIONS This study has several limitations. The providers were not blinded. We used a commercial analogue cuff pressure Volume , . : August
Figure 3. Individual increase in endotracheal cuff pressure in relation to the corresponding change in flight altitude.
manometer not specifically calibrated for air transportation. Further variations in pressure might result from different physical properties of tubes supplied by different manufacturers.5 Because the patients included in this study were recruited from several hospitals or emergency medical services, we could not control for the type of tubing. Because data were incomplete for one third of cases, selection bias was possible. Although increased cuff pressure is presumably harmful, the long-term implications are unknown. Because of the heterogeneity of target hospitals located in 3 countries and involving different languages, we did not link to patient outcomes. We did not determine minor (eg, sore throat, hoarseness) or major complications (eg, tracheal rupture, stenosis). Select patients had intracuff pressures exceeding 25 cm H2O at the start of the flight. These instances resulted from cuff leaks Annals of Emergency Medicine 91
Endotracheal Tube Intracuff Pressure During Helicopter Transport requiring additional inflation (n⫽8) and spontaneous increases in pressure (n⫽47). In the operating room, we have observed similar spontaneous cuff pressure increases. When we excluded cases with starting pressure ⬎25 cm H2O, we observed cuff pressure increases of 35 cm H2O (95% CI 29.6 to 39.3 cm H2O).
DISCUSSION This large series of intubated air medical patients demonstrated intracuff pressure increases to ⱖ30 cm H2O for 98% of patients. Cuff pressures exceeded even higher levels (ⱖ50 cm H2O and ⱖ80 cm H2O) in a significant percentage of these cases (72% and 20%, respectively). According to flight times, 49 of 114 (43%) patients were exposed to excessive intracuff pressure (⬎30 cm H2O) for longer than 15 minutes. Our observations have important implications for both inhospital and out-of-hospital care, highlighting the need for intracuff pressure monitoring before and during aeromedical transport. Despite reducing intracuff pressure before flight, almost all cuffs exceeded 30 cm H2O, and nearly three fourths exceeded 50 cm H2O. Endotracheal tube intracuff pressures are known to be very high in the out-of-hospital and ED setting.7,8 If the intracuff pressures had not been adjusted before takeoff, an even higher percentage of patients would have experienced values greater than 50 cm H2O. Henning et al6 first described high intracuff pressures during aeromedical transports, observing a mean increase in pressure of 23 cm H2O for a 3,000-feet ascent. They also observed correlation between changes in altitude and intracuff pressure (0.78 cm H2O per 1,000 feet). Contrary to their data, ours exhibited a large variability of pressure increases at maximum flight level (Figures 2 and 3). These differences may be related to several major design differences. Their study was small (n⫽10), and they excluded patients with an audible air leak. In our study, patients were intubated with tubes from different manufacturers. An in vitro study5 reported differences in cuff pressure with altitude among different brands of commonly used endotracheal tubes. Furthermore, Henning et al6 measured cuff pressure with a pressure transducer, a more precise technique than the more clinically available cuff manometer that we used. Several strategies have been proposed to avoid excessive intracuff pressures, including the use of saline solution rather than air to seal the cuff,5,9 novel cuffs with a high-pressure relief system,10 automated control devices,11 or frequent manometry with titration of the pressure/volume. The use of saline solution is reasonable but lacks supporting data. Pressure relief valves would be helpful for ascending flights but bear the risk of insufficient sealing while descending. The use of automated control devices seems promising and merits testing during aeromedical transport. In our setting, periodical control of intracuff pressure with a manometer seems simple and feasible, and simple routine monitoring would alert providers to the problem of increased cuff pressures. 92 Annals of Emergency Medicine
Bassi et al In this series of aeromedical patients, endotracheal cuff pressure exceeded 30 cm H2O in almost all cases. Hospital and out-of-hospital practitioners should measure and adjust endotracheal cuff pressures before and during flight. The authors thank Robert A. Berg, MD, for critically reviewing the manuscript, and Allison Dwileski, BS, for expert editorial assistance. Supervising editor: Henry E. Wang, MD, MS Author contributions: MB and MZ were responsible for conception of the study. MB and J-JE designed the study. MB was responsible for statistical analysis of the data. MB, MZ, and WU interpreted the data and drafted the article. MZ was responsible for statistical consulting. MZ and WU revised the article critically for important intellectual content. J-JE was responsible for selection of patients and critical revision of the article. WU had final approval of the article. WU takes responsibility for the paper as a whole. Funding and support: By Annals policy, all authors are required to disclose any and all commercial, financial, and other relationships in any way related to the subject of this article that might create any potential conflict of interest. See the Manuscript Submission Agreement in this issue for examples of specific conflicts covered by this statement. Funding was provided by the Department of Anesthesia, University Hospital Basel. The Swiss Air-Rescue Organisation helped collect the data. Publication dates: Received for publication June 8, 2009. Revisions received July 7, 2009; December 4, 2009; and January 1, 2010. Accepted for publication January 25, 2010. Available online February 25, 2010. Reprints not available from the authors. Address for correspondence: Wolfgang Ummenhofer, MD, Department of Anesthesia, University Hospital Basel, CH-4031 Basel, Switzerland; 41-61-265-7258, fax 41-61-265-7320; E-mail [email protected].
REFERENCES 1. Nordin U, Lindholm CE, Wolgast M. Blood flow in the rabbit tracheal mucosa under normal conditions and under the influence of tracheal intubation. Acta Anaesthesiol Scand. 1977;21:81-94. 2. Bunegin L, Albin MS, Smith RB. Canine tracheal blood flow after endotracheal tube cuff inflation during normotension and hypotension. Anesth Analg. 1993;76:1083-1090. 3. Seegobin RD, van Hasselt GL. Endotracheal cuff pressure and tracheal mucosal blood flow: endoscopic study of effects of four large volume cuffs. Br Med J. 1984;288:965-968. 4. Fan CM, Ko PC, Tsai KC, et al. Tracheal rupture complicating emergent endotracheal intubation. Am J Emerg Med. 2004;22: 289-293. 5. Smith RP, McArdle BH. Pressure in the cuffs of tracheal tubes at altitude. Anaesthesia. 2002;57:374-378.
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Bassi et al 6. Henning J, Sharley P, Young R. Pressures within air-filled tracheal cuffs at altitude: an in vivo study. Anaesthesia. 2004;59:252-254. 7. Galinski M, Treoux V, Garrigue B, et al. Intracuff pressures of endotracheal tubes in the management of airway emergencies: the need for pressure monitoring. Ann Emerg Med. 2006;47:545-547. 8. Svenson JE, Lindsay MB, O’Connor JE. Endotracheal intracuff pressures in the ED and prehospital setting: is there a problem? Am J Emerg Med. 2007;25:53-56.
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Endotracheal Tube Intracuff Pressure During Helicopter Transport 9. Kaye P. Effects of altitude on endotracheal tube cuff pressures. Emerg Med J. 2007;24:605. 10. Karasawa F, Takita A, Mori T, et al. The Brandt tube system attenuates the cuff deflationary phenomenon after anesthesia with nitrous oxide. Anesth Analg. 2003;96:606-610. 11. Weiss M, Doell C, Koepfer N, et al. Rapid pressure compensation by automated cuff pressure controllers worsens sealing in tracheal tubes. Br J Anaesth. 2009;102:273-278.
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Appendix E1.
PHYSICAL BACKGROUND Theoretical Considerations Boyle-Mariotte’s law states that pressure (P) times volume (V) is constant, if temperature remains unchanged. Therefore, the relationship between initial and final pressure and volume (P1 and V1, and P2 and V2, respectively) is expressed by the formula P1V1⫽P2V2. Because pressure within the system is equal to the sum of pressures, initial and final pressure can be expressed as (P⫽Pcuff⫹Patm). The equation relating these variables with respect to air evacuation is: (Pcuff1 ⫹Patm1)⫻V1 ⫽(Pcuff2 ⫹Patm2)⫻V2 Because the diameter of the trachea is of fixed proportion and any change in volume because of compression of soft tissues or proximal/
93.e1 Annals of Emergency Medicine
distal distortion of the cuff is so minor to be deemed negligible, the volume of an inflated cuff can be considered constant: V1 ⫽V2 Thus, the theoretically expected cuff pressure change during air transport is equivalent to final cuff pressure (Pcuff2), according to the calculation: Pcuff2 ⫽Pcuff1 ⫹Patm1 ⫺Patm2 Example: A helicopter takes off at sea level (Patm1⫽760 mm Hg) and cruises at an altitude of 2,000 feet (Patm2⫽704 mm Hg). Cuff pressure at takeoff is set to 25 cm H2O (Pcuff1⫽18 mm Hg). Expected cuff pressure at 2,000 feet is 100 cm H2O (Pcuff2⫽18⫹760⫺704⫽74 mm Hg).
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