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Experienced emergency medicine physicians cannot safely inflate or estimate endotracheal tube cuff pressure using standard techniques
American Journal of Emergency Medicine (2006) 24, 139 – 143
www.elsevier.com/locate/ajem
Original Contributions
Experienced emergency medicine physicians cannot safely inflate or estimate endotracheal tube cuff pressure using standard techniques Robert J. Hoffman MDa,*, Vivek Parwani MDb, In-Hei Hahn MDc a
Department of Emergency Medicine, Beth Israel Medical Center, New York, NY 10003, USA Section of Emergency Medicine, Department of Surgery, Yale University School of Medicine, New Haven, CT 06510, USA c Department of Emergency Medicine, St Luke’s–Roosevelt Hospital Center, New York, NY 10019, USA b
Received 14 June 2005; revised 27 July 2005; accepted 29 July 2005
Abstract Objective: Tracheal necrosis, stenosis, and rupture may result from overinflated endotracheal tube cuffs (ETTcs). We sought to determine the ability of faculty emergency medicine (EM) physicians to safely inflate ETTc as well as to estimate pressure of previously inflated ETTc. Methods: Using a previously tested tracheal simulation model, we assessed EM physician inflation of ETTc pilot balloons. Participants also palpated the pilot balloon of 9 ETTc inflated to pressures ranging from extremely low to extremely high in a random order and reported their estimate of pressure. Results: We sampled 41 faculty EM physicians from 5 EM residency programs. Using palpation, participants were only 22% sensitive detecting overinflated ETTc. The average ETTc pressure produced by inflation was more than 93 cm H2O (normal, 15-25 cm H2O). Conclusions: Participants were unable to inflate ETTc to safe pressures or estimate pressure of ETTc by palpation. Clinicians should consider using devices to facilitate safe inflation and accurate measurement of ETTc pressure. D 2006 Elsevier Inc. All rights reserved.
1. Introduction Endotracheal intubation is a life-saving procedure routinely necessary in the ED. Reported injuries from endotracheal intubation secondary to overinflated endotracheal tube cuffs (ETTcs) include tracheal rupture [1-3], tracheal This paper has been presented as an abstract at the Society for Academic Emergency Medicine 2004 Annual Meeting in Orlando, Fla. T Corresponding author. E-mail address: [email protected] (R.J. Hoffman). 0735-6757/$ – see front matter D 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.ajem.2005.07.016
necrosis [4], tracheal stenosis [5,6] as well as recurrent laryngeal nerve palsy [7]. Overinflation of an endotracheal tube (ETT) cuff may be prevented by use of a manometer to directly measure inflation pressure [1,8]. Use of such devices may prevent injuries from overinflated ETTc. We sought to determine the ability of faculty emergency medicine (EM) – attending physicians to both inflate an ETTc to an appropriate pressure using a standard syringe technique as well as their ability to assess the appropriateness of pressure in previously inflated ETTc by palpating the pilot balloon.
140
2. Methods 2.1. Study design This was a prospective, observational, cross-sectional study of faculty EM-attending physicians involving measurement of participant performance inflating ETTc and palpating ETTc pilot balloons. At the conclusion of the study, all participants completed a brief survey. This study was approved by the Institutional Review Board of the St Luke’s Roosevelt Hospital Center. Informed consent was obtained from all participants before the study.
2.2. Study setting and population The study population consisted of licensed faculty EMattending physicians from 5 accredited EM residency programs in New York City. Measurements and surveys were completed in their respective departments.
2.3. Study protocol We sought to determine the skill and precision of faculty EM-attending physicians to (1) inflate an ETTc to a safe pressure and (2) determine by pilot balloon palpation if pressure in a previously inflated ETTc exceeds safe pressure. Faculty EM-attending physicians were randomly recruited from the departments of EM of 5 accredited EM residency training programs in New York City. The study used a previously tested tracheal simulation model [9] with a 7.5 ETT with a high-volume low-pressure cuff (Mallinkrodt, St Louis, MO) fixed centrally within a rigid plastic cylinder 2.0 cm in diameter. Using their choice of a 5- or 10-mL syringe (Becton-Dickson, Franklin Lakes, NJ), participants inflated the ETTc by using the standard method of injecting air. This was accompanied by palpation of the pilot balloon to allow adjustment of air volume in the ETTc if the participant chose to use such palpation to estimate ETTc pressure. The intracuff pressure was subsequently measured using a sensitive and accurate analog manometer (Posey Company, Pasadena, CA). Participants then, in random order, palpated the pilot balloon of 9 ETTc previously inflated to pressures of 0, 4, 8, 16, 20, 22, 80, 100, and 120 cm H2O, and reported their assessment of pressure of each pilot balloon as appropriate, too low or too high. Study participants also completed a survey instrument to report (1) the number of years they have practiced as an EM-attending physician; (2) whether they typically inflate an ETTc by injecting a predetermined amount of air into the cuff, estimate the pressure by palpating the pilot balloon, or use another method; and (3) the approximate number of endotracheal intubations they perform yearly. Based on a previous studies of this phenomenon in EM residents and paramedics, a sample size of 5 was expected to be adequate to for statistical analysis with a 1% significance level (a) and 80% power (1 b). Rather than simply testing 5 study participants, which would be
R.J. Hoffman et al. one from each residency program, we sampled 6 to 8 participants from each program.
2.4. Measurements Endotracheal tube cuff pressure was measured using a sensitive and accurate analog manometer (Posey Company, Pasadena, CA). This manometer measures pressure in a range from 0 to 120 cm H2O in 2–cm H2O increments. Over an initial 1-month pilot period, measurements of intracuff pressures, and use of the survey instrument with participants not included in this study were performed. This was done to ensure investigator skill in making measurements and to assess for flaws in protocol design, implementation, or conduct of the study.
2.5. Data analysis Our null study hypothesis was that the maximal ETTc pressure generated by study participants would not exceed 25 cm H2O, the presumed maximal safe pressure in humans. A secondary hypothesis was that study participants would be able to detect overinflated ETTc by palpation. Fisher exact and v 2 tests were used for hypothesis testing where appropriate. Linear regression analysis was performed to assess for correlation between years of experience as an EM-attending physician and accuracy inflating ETTc or palpating previously inflated ETTc. Statistical analysis was performed using Intercooled Stata 8.2 statistical software (College Station, TX).
3. Results We sampled 41 participants. Their average career length as an EM-attending physician was 9.2 years (range, 2-30 years; 95% confidence interval, 7.1-11.3 years). Selfestimated frequency of performing endotracheal intubation with a cuffed ETT was 78% (n = 32), performed more than 25 times per year; 17% (n = 7), performed 11 to 25 times per year; 2.4% (n = 1), performed 4 to 10 times per year; and 2.4% (n = 1), performed less than 4 times per year. The average ETTc pressure produced cannot be precisely determined because 90% (n = 37) inflated to pressures greater than the upper limit of manometer sensitivity (N120 cm H2O). Using the available censored data, however, the average pressure generated was more than 93.2 cm H2O (range, 16-120 cm H2O; 95% confidence interval, 82.3-104.2 cm H2O). Using a 1-tailed hypothesis test with a of .01, the null hypothesis that the mean pressure generated by study participants would not exceed 25 cm H2O was rejected. The secondary hypothesis of participants’ ability to detect overinflated ETTc by palpation was also rejected. Participants were only 22% sensitive detecting overinflated ETTc. No participant correctly identified all overinflated ETTc. There was no correlation between years in practice or
Endotracheal tube cuff pressure
141
Table 1 Endotracheal tube cuff pressures generated by physicians using tracheal simulation model Pressure to which physician inflated ETTc (cm H2O)
No. of physician who inflated ETTc within this pressure range
V15 16-25 (appropriate pressure) 26-35 36-45 46-55 56-65 66-75 76-85 86-95 96-105 106-120 N120
0 3 2 1 1 2 1 7 0 1 1 22
number of endotracheal intubations performed yearly and ability to properly inflate ETTc or ability to detect overinflated ETTc (Table 1). Survey data revealed that 58% of participants (n = 24) inflated ETTc using a method of palpation of the pilot balloon to determine quantity of air to inject into the balloon. The other 48% (n = 17) inflated ETTc by injecting a predetermined quantity of air without any palpation of the pilot balloon.
4. Discussion When the ETTc intracuff pressure exceeds the capillary perfusion pressure of the tracheal mucosa, mucosal blood flow becomes obstructed. The precise pressure at which capillary perfusion is impaired certainly will vary from patient to patient, but it is reported that 25 cm H2O is a maximal safe pressure [10]. It is reported that, at pressures as low as 30 cm H2O, tracheal mucosal blood flow may be impaired, and at 45 cm H2O, tracheal mucosal blood flow is completely obstructed [11]. The precise pressure at which any individual will experience impaired or obstructed tracheal mucosal blood flow will be dependent upon numerous factors, most importantly their blood pressure. Severe overinflation of ETTc imparts risk for serious, even fatal, injury [1,12]. Overinflation of ETTc is also associated with less severe but significant adverse effects. Prospective evaluation of postoperative tracheal pain and its relationship to ETTc pressure found correlation between excessive ETTc pressure and the presence of tracheal pain 1 hour and 24 hours postextubation [13]. In addition, postextubation stridor has been associated with elevated ETTc pressure [14]. Other than the occurrence of major injuries such as tracheal rupture, the immediate effects of endotracheal intubation with excessive ETTc pressure or the effects of excessive ETTc pressure for brief periods of time are unknown. Prospective evaluation of patients whom
were endotracheally intubated for varying periods of time in an intensive care unit found 63% with early laryngeal lesions such as tracheal granulomas, 31% with ring-shaped tracheitis at the level of the ETTc, and 10% with tracheal stenosis [15]. The inability of clinicians to determine ETTc pressure by traditional standard method of palpation of the pilot balloon has been addressed by other investigators. Studies of faculty anesthesiologists and anesthesia residents [16] as well as critical care unit staff [17,18] have demonstrated a prevalent inability of these clinicians to accurately determine the intracuff pressure of ETTc by palpation of the pilot balloon. Study of endotracheally intubated intensive care unit and postanesthesia care unit patients has found that patients in these areas typically have excessively high ETTc pressure [19]. An inflated ETTc prevents air leak and allows appropriate air exchange during mechanical ventilation. Underinflation of an ETTc would present a distinct set of problems and risks. It also serves to protect against aspiration. Participants in this study could not detect ETTc that were underinflated by palpation. Although this may also be a concern, it is presumed that underinflation of an ETTc would typically be detected by an audible air leak during mechanical ventilation or excessive pressure or volume necessary during mechanical ventilation. There are certain circumstances such as manual ventilation in a noisy environment, as with ambulance or helicopter transport, when such an air leak would not be easily detected by audible clues. The risk for injury resulting from overinflated ETTc warrants evaluation of currently used endotracheal intubation practices. In particular, the practice of inflating ETTcs without precisely measuring such pressure should be closely scrutinized. Several improvised devices [20 -22] allowing for determination of ETTc pressure have been described. Use of improvised devices is unnecessary because inexpensive, approved, commercially available devices developed expressly for the purpose of measuring ETTc pressure exist. Duration of time that an ETTc is overly inflated is almost certainly a determinant of tracheal hypoperfusion injury. Specific lengths of time of hypoperfusion of tracheal tissue that pose a risk for injury are unknown. Therefore, it is unknown how much time, if any, is a safe duration during which excess ETTc pressure may be tolerated without injury. The device used in this study is actually a combination inflation device and manometer called a cufflator. When such a device is used, accurate cuff inflation pressure is known and achieved at the time of endotracheal intubation. No prospective study of the short-term benefits of measurement of ETTc pressure exist, but prospective study of cuff pressure in patients with inflated ETTc or tracheostomy tube cuffs has demonstrated that measurement of such cuff pressures 3 times daily serves to prevent tracheal stenosis and ischemic lesions of the trachea [23].
142
5. Limitations There are several limitations to our study. Foremost, a tracheal simulation model was used for this study. No model can perfectly simulate an endotracheal tube placed in a human trachea. It is possible that tracheal compliance, shape, or other factors are such that the physicians surveyed would have fared better if this study was conducted with live patients. The risk for injury to patients poses a significant ethical obstruction to conducting a prospective study involving experimental endotracheal intubation of human participants. Another limitation is that the pressure at which tracheal mucosal blood flow is impaired or obstructed will vary from patient to patient. We used a cutoff of 25 cm H2O as safe in our statistical analysis. It is possible that this number is very conservative and that higher pressures may be safe in many humans. However, our statistical findings are the same if the hypothesis test is performed with a cutoff of 75 cm H2O, which is certainly an unsafe pressure. An additional limitation to this study is lack of full understanding of the danger of placement of an ETTc with pressure in excess of capillary perfusion pressure. Although available evidence suggests that excessive pressure in an ETTc poses the risk for tracheal stenosis, necrosis, rupture, as well as recurrent laryngeal nerve palsy, the apparent rarity of these occurrences in clinical practice suggest that the risk may be less than currently suspected. Impaired perfusion of the tracheal mucosa might not typically be associated with injury or morbidity, and other factors preventing adverse outcomes from overinflated ETTc may be involved.
6. Conclusions Using the methods described in this study, faculty EMattending physicians detected overinflated ETTc with only 22% sensitivity. The average ETTc generated was high, 93 cm H2O, and 90% of participants inflated the ETTc to an extremely high pressure greater than 120 cm H2O. The inability to detect overinflated ETTc is not related to years of experience or self-reported frequency of performing endotracheal intubation. Prospective evaluation of endotracheal intubation practices in patients should be performed to determine if this in vitro phenomenon actually occurs in patients. The risk posed by overinflation of an ETTc coupled with the availability of inexpensive, easy-to-use devices for measurement of ETTc pressure warrants consideration of use of such devices in the ED. Endotracheal intubation with cuffed endotracheal tubes could easily be accompanied by objective measurement of the ETTc pressure. In medical specialties that involve frequent contact with endotracheally intubated patients, such as anesthesiology and respiratory therapy, use of such instruments to measure pressure in
R.J. Hoffman et al. ETTcs is often routine, standard practice. We believe that use of devices to prevent overinflation of ETTc, such as the use of pulse oximeters or capnometers, is a practice of anesthesiologists and intensivists that may be appropriate in the EM setting. Emergency medicine physicians should consider measuring the ETTc pressure in their endotracheally intubated patients.
References [1] Fan CM, Ko PC, Tsai K, Chiang W, Chang Y, Chen W, et al. Tracheal rupture complicating emergency endotracheal intubation. Am J Emerg Med 2004;22:289 - 93. [2] Harris R, Joseph A. Acute tracheal rupture related to endotracheal intubation: case report. J Emerg Med 2000;18:35 - 9. [3] Hofmann HS, Rettig G, Radke J, Neef H, Silber RE. Iatrogenic rupture of the tracheobronchial tree. Eur J Cardiothorac Surg 2002;21:649 - 52. [4] Deslee G, Brichet A, Lebuffe G, Copin MC, Ramon P, Marquette CH. Obstructive fibrinous tracheal pseudomembrane. A potentially fatal complication of tracheal intubation. Am J Respir Crit Care Med 2000;162:1169 - 71. [5] Shelly WM, Dawson RB, May IA. Cuffed tubes as a cause of tracheal stenosis. J Thorac Cardiovasc Surg 1969;57:623 - 7. [6] Weber AL, Grillo HC. Tracheal stenosis, an analysis of 151 cases. Radiol Clin North Am 1978;16:291 - 308. [7] Otani S, Fujii H, Ishizu T, et al. Recurrent nerve palsy after endotracheal intubation. Masui 1998;47:350 - 5. [8] Stewart S, Secrest J, Norwood B, Zachary R. A comparison of endotracheal tube cuff pressures using estimation techniques and direct intracuff measurement. AANA J 2003;71:443 - 7. [9] Patel V, Hahn IH, Preblick C, Hoffman RJ. Graduating paramedic students are unable to estimate endotracheal tube cuff pressure by standard palpation technique [abstract]. Prehosp Emerg Care 2004; 8:94. [10] Guyton DC. Endotracheal and tracheotomy tube cuff design: influence on tracheal damage. Crit Care Update 1990;1:1 - 10. [11] Somri M, Fradis M, Malatskey S, Vaida S, Gaitini L. Simple on-line endotracheal cuff pressure relief valve. Ann Otol Rhinol Laryngol 2002;111:190 - 2. [12] Guyton DC, Barlow MR, Besselievre TR. Influence of airway pressure on minimum occlusive endotracheal tube cuff pressure. Crit Care Med 1997;25:91 - 4. [13] Curiel Garcia JA, Guerrero-Romero F, Rodriguez-Moran M. Cuff pressure in endotracheal intubation: should it be routinely measured? Gac Med Mex 2001;137:179 - 82. [14] Efferen LS, Elsakr A. Post-extubation stridor; risk factors and outcome. J Assoc Acad Minor Phys 1998;9:65 - 8. [15] Kastanos N, Estopa MR, Marin Perez A, Xaubet Mir A, Agusti-Vidal A. Laryngotracheal injury due to endotracheal intubation: incidence, evolution, and predisposing factors. A prospective long-term study. Crit Care Med 1983;11:362 - 7. [16] Foroughi V, Sripada R. Sensitivity of tactile examination of endotracheal tube intra-cuff pressure. Anesthesiology 1997;87(3s): 965A [abstract]. [17] Ganner C. The accurate measurement of endotracheal tube cuff pressures. Br J Nurs 2001;10:1127 - 34. [18] Fernandez R, Blanch L, Mancebo J, Bonsoms N, Artigas A. Endotracheal tube cuff pressure assessment: pitfalls of finger estimation and need for objective measurement. Crit Care Med 1990;18:1423 - 6. [19] Braz JR, Navarro LH, Takata IH, Nascimento JP. Endotracheal tube cuff pressure: need for precise measurement. Sao Paulo Med J 1999; 117:243 - 7.
Endotracheal tube cuff pressure [20] Farre R, Rotger M, Ferre M, Torres A, Navajas D. Automatic regulation of the cuff pressure in endotracheally-intubated patients. Eur Respir J 2002;20:1010 - 3. [21] Komatsu H, Mitsuhata H, Hasegawa J, Matsumoto S. Evaluation of a pressure and volume-relief instrument (modified Brandt’s rediffusion system) to prevent increase in endotracheal tube cuff pressure. Masui 1993;42:296 - 9.
143 [22] Vitkn SA, Lagasse RS, Poppers PJ. Application of the Grieshaber air system to maintain endotracheal tube cuff pressure. J Clin Anesth 1990;2:45 - 7. [23] Granja C, Faraldo S, Laguna P, Gois L. Control of the endotracheal cuff balloon pressure as a method of preventing laryngotracheal lesions in critically ill intubated patients. Rev Esp Anestesiol Reanim 2002;49:137 - 40.
www.elsevier.com/locate/ajem
Original Contributions
Experienced emergency medicine physicians cannot safely inflate or estimate endotracheal tube cuff pressure using standard techniques Robert J. Hoffman MDa,*, Vivek Parwani MDb, In-Hei Hahn MDc a
Department of Emergency Medicine, Beth Israel Medical Center, New York, NY 10003, USA Section of Emergency Medicine, Department of Surgery, Yale University School of Medicine, New Haven, CT 06510, USA c Department of Emergency Medicine, St Luke’s–Roosevelt Hospital Center, New York, NY 10019, USA b
Received 14 June 2005; revised 27 July 2005; accepted 29 July 2005
Abstract Objective: Tracheal necrosis, stenosis, and rupture may result from overinflated endotracheal tube cuffs (ETTcs). We sought to determine the ability of faculty emergency medicine (EM) physicians to safely inflate ETTc as well as to estimate pressure of previously inflated ETTc. Methods: Using a previously tested tracheal simulation model, we assessed EM physician inflation of ETTc pilot balloons. Participants also palpated the pilot balloon of 9 ETTc inflated to pressures ranging from extremely low to extremely high in a random order and reported their estimate of pressure. Results: We sampled 41 faculty EM physicians from 5 EM residency programs. Using palpation, participants were only 22% sensitive detecting overinflated ETTc. The average ETTc pressure produced by inflation was more than 93 cm H2O (normal, 15-25 cm H2O). Conclusions: Participants were unable to inflate ETTc to safe pressures or estimate pressure of ETTc by palpation. Clinicians should consider using devices to facilitate safe inflation and accurate measurement of ETTc pressure. D 2006 Elsevier Inc. All rights reserved.
1. Introduction Endotracheal intubation is a life-saving procedure routinely necessary in the ED. Reported injuries from endotracheal intubation secondary to overinflated endotracheal tube cuffs (ETTcs) include tracheal rupture [1-3], tracheal This paper has been presented as an abstract at the Society for Academic Emergency Medicine 2004 Annual Meeting in Orlando, Fla. T Corresponding author. E-mail address: [email protected] (R.J. Hoffman). 0735-6757/$ – see front matter D 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.ajem.2005.07.016
necrosis [4], tracheal stenosis [5,6] as well as recurrent laryngeal nerve palsy [7]. Overinflation of an endotracheal tube (ETT) cuff may be prevented by use of a manometer to directly measure inflation pressure [1,8]. Use of such devices may prevent injuries from overinflated ETTc. We sought to determine the ability of faculty emergency medicine (EM) – attending physicians to both inflate an ETTc to an appropriate pressure using a standard syringe technique as well as their ability to assess the appropriateness of pressure in previously inflated ETTc by palpating the pilot balloon.
140
2. Methods 2.1. Study design This was a prospective, observational, cross-sectional study of faculty EM-attending physicians involving measurement of participant performance inflating ETTc and palpating ETTc pilot balloons. At the conclusion of the study, all participants completed a brief survey. This study was approved by the Institutional Review Board of the St Luke’s Roosevelt Hospital Center. Informed consent was obtained from all participants before the study.
2.2. Study setting and population The study population consisted of licensed faculty EMattending physicians from 5 accredited EM residency programs in New York City. Measurements and surveys were completed in their respective departments.
2.3. Study protocol We sought to determine the skill and precision of faculty EM-attending physicians to (1) inflate an ETTc to a safe pressure and (2) determine by pilot balloon palpation if pressure in a previously inflated ETTc exceeds safe pressure. Faculty EM-attending physicians were randomly recruited from the departments of EM of 5 accredited EM residency training programs in New York City. The study used a previously tested tracheal simulation model [9] with a 7.5 ETT with a high-volume low-pressure cuff (Mallinkrodt, St Louis, MO) fixed centrally within a rigid plastic cylinder 2.0 cm in diameter. Using their choice of a 5- or 10-mL syringe (Becton-Dickson, Franklin Lakes, NJ), participants inflated the ETTc by using the standard method of injecting air. This was accompanied by palpation of the pilot balloon to allow adjustment of air volume in the ETTc if the participant chose to use such palpation to estimate ETTc pressure. The intracuff pressure was subsequently measured using a sensitive and accurate analog manometer (Posey Company, Pasadena, CA). Participants then, in random order, palpated the pilot balloon of 9 ETTc previously inflated to pressures of 0, 4, 8, 16, 20, 22, 80, 100, and 120 cm H2O, and reported their assessment of pressure of each pilot balloon as appropriate, too low or too high. Study participants also completed a survey instrument to report (1) the number of years they have practiced as an EM-attending physician; (2) whether they typically inflate an ETTc by injecting a predetermined amount of air into the cuff, estimate the pressure by palpating the pilot balloon, or use another method; and (3) the approximate number of endotracheal intubations they perform yearly. Based on a previous studies of this phenomenon in EM residents and paramedics, a sample size of 5 was expected to be adequate to for statistical analysis with a 1% significance level (a) and 80% power (1 b). Rather than simply testing 5 study participants, which would be
R.J. Hoffman et al. one from each residency program, we sampled 6 to 8 participants from each program.
2.4. Measurements Endotracheal tube cuff pressure was measured using a sensitive and accurate analog manometer (Posey Company, Pasadena, CA). This manometer measures pressure in a range from 0 to 120 cm H2O in 2–cm H2O increments. Over an initial 1-month pilot period, measurements of intracuff pressures, and use of the survey instrument with participants not included in this study were performed. This was done to ensure investigator skill in making measurements and to assess for flaws in protocol design, implementation, or conduct of the study.
2.5. Data analysis Our null study hypothesis was that the maximal ETTc pressure generated by study participants would not exceed 25 cm H2O, the presumed maximal safe pressure in humans. A secondary hypothesis was that study participants would be able to detect overinflated ETTc by palpation. Fisher exact and v 2 tests were used for hypothesis testing where appropriate. Linear regression analysis was performed to assess for correlation between years of experience as an EM-attending physician and accuracy inflating ETTc or palpating previously inflated ETTc. Statistical analysis was performed using Intercooled Stata 8.2 statistical software (College Station, TX).
3. Results We sampled 41 participants. Their average career length as an EM-attending physician was 9.2 years (range, 2-30 years; 95% confidence interval, 7.1-11.3 years). Selfestimated frequency of performing endotracheal intubation with a cuffed ETT was 78% (n = 32), performed more than 25 times per year; 17% (n = 7), performed 11 to 25 times per year; 2.4% (n = 1), performed 4 to 10 times per year; and 2.4% (n = 1), performed less than 4 times per year. The average ETTc pressure produced cannot be precisely determined because 90% (n = 37) inflated to pressures greater than the upper limit of manometer sensitivity (N120 cm H2O). Using the available censored data, however, the average pressure generated was more than 93.2 cm H2O (range, 16-120 cm H2O; 95% confidence interval, 82.3-104.2 cm H2O). Using a 1-tailed hypothesis test with a of .01, the null hypothesis that the mean pressure generated by study participants would not exceed 25 cm H2O was rejected. The secondary hypothesis of participants’ ability to detect overinflated ETTc by palpation was also rejected. Participants were only 22% sensitive detecting overinflated ETTc. No participant correctly identified all overinflated ETTc. There was no correlation between years in practice or
Endotracheal tube cuff pressure
141
Table 1 Endotracheal tube cuff pressures generated by physicians using tracheal simulation model Pressure to which physician inflated ETTc (cm H2O)
No. of physician who inflated ETTc within this pressure range
V15 16-25 (appropriate pressure) 26-35 36-45 46-55 56-65 66-75 76-85 86-95 96-105 106-120 N120
0 3 2 1 1 2 1 7 0 1 1 22
number of endotracheal intubations performed yearly and ability to properly inflate ETTc or ability to detect overinflated ETTc (Table 1). Survey data revealed that 58% of participants (n = 24) inflated ETTc using a method of palpation of the pilot balloon to determine quantity of air to inject into the balloon. The other 48% (n = 17) inflated ETTc by injecting a predetermined quantity of air without any palpation of the pilot balloon.
4. Discussion When the ETTc intracuff pressure exceeds the capillary perfusion pressure of the tracheal mucosa, mucosal blood flow becomes obstructed. The precise pressure at which capillary perfusion is impaired certainly will vary from patient to patient, but it is reported that 25 cm H2O is a maximal safe pressure [10]. It is reported that, at pressures as low as 30 cm H2O, tracheal mucosal blood flow may be impaired, and at 45 cm H2O, tracheal mucosal blood flow is completely obstructed [11]. The precise pressure at which any individual will experience impaired or obstructed tracheal mucosal blood flow will be dependent upon numerous factors, most importantly their blood pressure. Severe overinflation of ETTc imparts risk for serious, even fatal, injury [1,12]. Overinflation of ETTc is also associated with less severe but significant adverse effects. Prospective evaluation of postoperative tracheal pain and its relationship to ETTc pressure found correlation between excessive ETTc pressure and the presence of tracheal pain 1 hour and 24 hours postextubation [13]. In addition, postextubation stridor has been associated with elevated ETTc pressure [14]. Other than the occurrence of major injuries such as tracheal rupture, the immediate effects of endotracheal intubation with excessive ETTc pressure or the effects of excessive ETTc pressure for brief periods of time are unknown. Prospective evaluation of patients whom
were endotracheally intubated for varying periods of time in an intensive care unit found 63% with early laryngeal lesions such as tracheal granulomas, 31% with ring-shaped tracheitis at the level of the ETTc, and 10% with tracheal stenosis [15]. The inability of clinicians to determine ETTc pressure by traditional standard method of palpation of the pilot balloon has been addressed by other investigators. Studies of faculty anesthesiologists and anesthesia residents [16] as well as critical care unit staff [17,18] have demonstrated a prevalent inability of these clinicians to accurately determine the intracuff pressure of ETTc by palpation of the pilot balloon. Study of endotracheally intubated intensive care unit and postanesthesia care unit patients has found that patients in these areas typically have excessively high ETTc pressure [19]. An inflated ETTc prevents air leak and allows appropriate air exchange during mechanical ventilation. Underinflation of an ETTc would present a distinct set of problems and risks. It also serves to protect against aspiration. Participants in this study could not detect ETTc that were underinflated by palpation. Although this may also be a concern, it is presumed that underinflation of an ETTc would typically be detected by an audible air leak during mechanical ventilation or excessive pressure or volume necessary during mechanical ventilation. There are certain circumstances such as manual ventilation in a noisy environment, as with ambulance or helicopter transport, when such an air leak would not be easily detected by audible clues. The risk for injury resulting from overinflated ETTc warrants evaluation of currently used endotracheal intubation practices. In particular, the practice of inflating ETTcs without precisely measuring such pressure should be closely scrutinized. Several improvised devices [20 -22] allowing for determination of ETTc pressure have been described. Use of improvised devices is unnecessary because inexpensive, approved, commercially available devices developed expressly for the purpose of measuring ETTc pressure exist. Duration of time that an ETTc is overly inflated is almost certainly a determinant of tracheal hypoperfusion injury. Specific lengths of time of hypoperfusion of tracheal tissue that pose a risk for injury are unknown. Therefore, it is unknown how much time, if any, is a safe duration during which excess ETTc pressure may be tolerated without injury. The device used in this study is actually a combination inflation device and manometer called a cufflator. When such a device is used, accurate cuff inflation pressure is known and achieved at the time of endotracheal intubation. No prospective study of the short-term benefits of measurement of ETTc pressure exist, but prospective study of cuff pressure in patients with inflated ETTc or tracheostomy tube cuffs has demonstrated that measurement of such cuff pressures 3 times daily serves to prevent tracheal stenosis and ischemic lesions of the trachea [23].
142
5. Limitations There are several limitations to our study. Foremost, a tracheal simulation model was used for this study. No model can perfectly simulate an endotracheal tube placed in a human trachea. It is possible that tracheal compliance, shape, or other factors are such that the physicians surveyed would have fared better if this study was conducted with live patients. The risk for injury to patients poses a significant ethical obstruction to conducting a prospective study involving experimental endotracheal intubation of human participants. Another limitation is that the pressure at which tracheal mucosal blood flow is impaired or obstructed will vary from patient to patient. We used a cutoff of 25 cm H2O as safe in our statistical analysis. It is possible that this number is very conservative and that higher pressures may be safe in many humans. However, our statistical findings are the same if the hypothesis test is performed with a cutoff of 75 cm H2O, which is certainly an unsafe pressure. An additional limitation to this study is lack of full understanding of the danger of placement of an ETTc with pressure in excess of capillary perfusion pressure. Although available evidence suggests that excessive pressure in an ETTc poses the risk for tracheal stenosis, necrosis, rupture, as well as recurrent laryngeal nerve palsy, the apparent rarity of these occurrences in clinical practice suggest that the risk may be less than currently suspected. Impaired perfusion of the tracheal mucosa might not typically be associated with injury or morbidity, and other factors preventing adverse outcomes from overinflated ETTc may be involved.
6. Conclusions Using the methods described in this study, faculty EMattending physicians detected overinflated ETTc with only 22% sensitivity. The average ETTc generated was high, 93 cm H2O, and 90% of participants inflated the ETTc to an extremely high pressure greater than 120 cm H2O. The inability to detect overinflated ETTc is not related to years of experience or self-reported frequency of performing endotracheal intubation. Prospective evaluation of endotracheal intubation practices in patients should be performed to determine if this in vitro phenomenon actually occurs in patients. The risk posed by overinflation of an ETTc coupled with the availability of inexpensive, easy-to-use devices for measurement of ETTc pressure warrants consideration of use of such devices in the ED. Endotracheal intubation with cuffed endotracheal tubes could easily be accompanied by objective measurement of the ETTc pressure. In medical specialties that involve frequent contact with endotracheally intubated patients, such as anesthesiology and respiratory therapy, use of such instruments to measure pressure in
R.J. Hoffman et al. ETTcs is often routine, standard practice. We believe that use of devices to prevent overinflation of ETTc, such as the use of pulse oximeters or capnometers, is a practice of anesthesiologists and intensivists that may be appropriate in the EM setting. Emergency medicine physicians should consider measuring the ETTc pressure in their endotracheally intubated patients.
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