The size of ETT (POLYMED Medicure, India) was selected by the anesthesia care provider. 22, no. The end of the cuff must not impinge the opening of the Murphy eye; it must not herniate over the tube tip under normal conditions; and the cuff must inflate symmetrically around the ETT.1 All cuffs are part of a cuff system consisting of the cuff itself plus . Fernandez R, Blanch L, Mancebo J, Bonsoms N, Artigas A: Endotracheal tube cuff pressure assessment: pitfalls of finger estimation and need for objective measurement. 111115, 1996. The regression equation indicated that injected volumes between 2 and 4 ml usually produce cuff pressures between 20 and 30 cmH2O independent of tube size for the same type of tube. February 2017 At the study hospital, there are more females undergoing elective surgery under general anesthesia compared with males. 1). On the other hand, high cuff pressures beyond 50cmH2O were reduced to 40cmH2O. The manual method used a pressure manometer to adjust pressure at cruising altitude and after landing. Volume + 2.7, r2 = 0.39. Article 109117, 2011. 307311, 1995. Neither patient morphometrics, institution, experience of anesthesia provider, nor tube size influenced measured cuff pressure (35.3 21.6 cmH2O). Evrard C, Pelouze GA, Quesnel J: [Iatrogenic tracheal and left bronchial stenoses. By using this website, you agree to our In most emergency situations, it is placed through the mouth. Cite this article. This was statistically significant. However, a full hour was plenty of time for the provider to have checked and adjusted cuff pressure to a suitable level. Charles Kojjo, Agnes Wabule, and Nodreen Ayupo were responsible for patient recruitment and data collection and analysis. LOR group (experimental): in this group, the research assistant attached a 7ml plastic, luer slip loss of resistance syringe (BD Epilor, USA) containing air onto the pilot balloon. LOR group (experimental): in this group, the research assistant attached a 7ml plastic, luer slip loss of resistance syringe (BD Epilor, USA) containing air onto the pilot balloon. allows one to provide positive pressure ventilation. 7, no. Note: prolonged over-inflation of the cuff can cause pressure necrosis of the tracheal mucosa. Product Benefits. The cookie is set by Google Analytics. Ann Chir. It helps us understand the number of visitors, where the visitors are coming from, and the pages they navigate. leaking cuff: continuous air insufflation through the inflation tubing has been describe to maintain an adequate pressure in the perforated cuff; . W. N. Bernhard, L. Yost, D. Joynes, S. Cothalis, and H. Turndorf, Intracuff pressures in endotracheal and tracheostomy tubes. After cuff inflation, a persistent significant air leak was noted (> 1 L/min in volume controlled ventilation modality). At this point the anesthesiology team decided to proceed with exchanging the ETT, which was successful. To detect a 15% difference between PBP and LOR groups, it was calculated that at least 172 patients would be required to be 80% certain that the limits of a 95%, two-sided interval included the difference. 11331137, 2010. Advance the endotracheal tube through the vocal cords and into the trachea within 15 seconds. This work was presented (and later published) at the 28th European Society of Intensive Care Medicine congress, Berlin, Germany, 2015, as an abstract. 3, p. 965A, 1997. The patient was the only person blinded to the intervention group. . The study groups were similar in relation to sex, age, and ETT size (Table 1). Previous studies have shown that the incidence of postextubation airway symptoms varies from 15% to 94% in various study populations [7, 9, 11, 27] and could be affected by the method of interview employed, such as the one used in our study (yes/no questions). Comparison of distance traveled by dye instilled into cuff. How do you measure cuff pressure? In contrast, newer ultra-thin cuff membranes made from polyurethane effectively prevent liquid flow around cuffs inflated only to 15 cm H2O [2]. Because one purpose of our study was to measure pressure in the endotracheal tube cuff during routine practice, anesthesia providers were blinded to the nature of the study. demonstrate the presence of legionellae in aerosol droplets associated with suspected bacterial reservoirs. 1990, 44: 149-156. Your trachea begins just below your larynx, or voice box, and extends down behind the . These cookies do not store any personal information. We enrolled adult patients scheduled to undergo general anesthesia for elective surgery at Mulago Hospital, Uganda. 769775, 2012. When this point was reached, the 10ml syringe was then detached from the pilot balloon, and a cuff manometer (VBM, Medicintechnik Germany. LOR = loss of resistance syringe method; PBP = pilot balloon palpation method. Results. Measured cuff inflation pressures were virtually identical at the three study sites: one academic center and two private hospitals. 965968, 1984. 6, pp. Collects anonymous data about how visitors use our site and how it performs. AW contributed to protocol development, patient recruitment, and manuscript preparation. Endotracheal intubation is done to: Keep the airway open in order to give oxygen, medicine, or anesthesia. The cuff was then briefly overinflated through the pilot balloon, and the loss of resistance syringe plunger was allowed to passively draw back until it ceased. Although we were unable to identify any statistically significant or clinically important differences among the sites or providers, our results apply only to the specific sites and providers we evaluated. 1982, 154: 648-652. 1995, 44: 186-188. Out of these cookies, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. An endotracheal tube , also known as an ET tube, is a flexible tube that is placed in the trachea (windpipe) through the mouth or nose. The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. A. Secrest, B. R. Norwood, and R. Zachary, A comparison of endotracheal tube cuff pressures using estimation techniques and direct intracuff measurement, American Journal of Nurse Anesthestists, vol. The cookie is not used by ga.js. Cuff pressure is essential in endotracheal tube management. 2001, 137: 179-182. If air was heard on the right side only, what would you do? It is thus essential to maintain cuff pressures in the range of 2030 cm of H2O. In an experimental study, Fernandez et al. mental status changes, such as confusion . We measured the tracheal cuff pressures at ground level and at 3000 ft, in 10 intubated patients. The study was approved by Makerere University College of Health Sciences, School of Medicine Research Ethics Committee (SOMREC), The Secretariat Makerere University College of Health Sciences, Clinical Research Building, Research Co-ordination Office, P.O. APSF President Robert K. Stoelting, MD: A Tribute to 19 Years of Steadfast Leadership, Immediate Past Presidents Report Highlights Accomplishments of 2016, Save the Date! The cookie is used to store and identify a users' unique session ID for the purpose of managing user session on the website. Male patients were intubated with an 8 or 8.5 mm internal diameter endotracheal tube, and female patients were intubated with a 7 or 7.5 mm internal diameter endotracheal tube. Currently, in critical care settings, patients are intubated with ETT comprising high-volume low-pressure cuffs. With IRB approval, we studied 93 patients under general anesthesia with an ET tube in place in one teaching and two private hospitals. R. J. Hoffman, V. Parwani, and I. H. Hahn, Experienced emergency medicine physicians cannot safely inflate or estimate endotracheal tube cuff pressure using standard techniques, American Journal of Emergency Medicine, vol. Compliance of the cuff system was evaluated by linear regression of measured cuff pressure vs. measured cuff volume. 10.1055/s-2003-36557. 617631, 2011. One such approach entails beginning at the patient and following the circuit to the machine. Anesthetists were blinded to study purpose. The patients were followed up and interviewed only once at 24 hours after intubation for presence of cough, sore throat, dysphagia, and/or dysphonia. (States: would deflate the cuff, pull tube back slightly -1 cm, re-inflate the cuff, and auscultate for bilateral air entry). We conducted a single-blinded randomized control study to evaluate the LOR syringe method in accordance with the CONSORT guideline (CONSORT checklist provided as Supplementary Materials available here). R. Fernandez, L. Blanch, J. Mancebo, N. Bonsoms, and A. Artigas, Endotracheal tube cuff pressure assessment: pitfalls of finger estimation and need for objective measurement, Critical Care Medicine, vol. In our study, 66.3% of ETT cuff pressures estimated by the LOR syringe method were in the optimal range. Endotracheal tube cuff pressure: a randomized control study comparing loss of resistance syringe to pilot balloon palpation. However, the presence of contradictory findings (tense cuff bulb, holding appropriate inflating pressure in the presence of a major air leak) confounded the diagnostic process, while a preoperative check of the ETT would have unequivocally detected the defect in the cuff tube. Bivona "Aire-cuff" Tracheostomy Tubes - Blue pilot balloon) Portex manufacturer, Bivona design Cuff Pressure Measurement Check the cuff pressure after re-inflating the cuff and if there are any concerns for a leak. Continuous data are presented as the mean with standard deviation and were compared between the groups using the t-test to detect any significant statistical differences. The tube is kept in place by a small cuff of air that inflates around the tube after it is inserted. 2006;24(2):139143. volume4, Articlenumber:8 (2004) Every patient was wheeled into the operating theater and transferred to the operating table. 1992, 49: 348-353. There is consensus that keeping ETT cuff pressures low decreases the incidence of postextubation airway complaints [11]. 1999, 117: 243-247. BMC Anesthesiol 4, 8 (2004). 2013 Aug;117(2):428-34. doi: 10.1213/ANE.0b013e318292ee21. The pressure reading of the VBM was recorded by the research assistant. Our results thus fail to support the theory that increased training improves cuff management. Taking another approach to the same question, we also determined compliance of the cuff-trachea system in vivo by plotting measured cuff pressure against cuff volume. supported this recommendation [18]. Supported by NIH Grant GM 61655 (Bethesda, MD), the Gheens Foundation (Louisville, KY), the Joseph Drown Foundation (Los Angeles, CA), and the Commonwealth of Kentucky Research Challenge Trust Fund (Louisville, KY). We recognize that people other than the anesthesia provider who actually conducted the case often inflated the cuffs. 208211, 1990. What is the device measurements acceptable range? Cuff pressure in . 795800, 2010. The hospital has a bed capacity of 1500 inpatient beds, 16 operating rooms, and a mean daily output of 90 surgical operations. The AAFP recommends inflating the cuff using air in 0.5-mL increments from a 3-mL syringe until no leak can be heard when the rebreathing bag is squeezed and the pressure in . Adequacy of cuff inflation is conventionally determined by palpation of the external balloon. 443447, 2003. Precaution was taken to avoid premature detachment of the loss of resistance syringe in this study. chin anteriorly), no lateral deviation, Open mouth and inspect: remove any dentures/debris, suction any secretions, Holding laryngoscope in left hand, insert it looking down its length, Slide down right side of mouth until the tonsils are seen, Now move it to the left to push the tongue centrally until the uvula is seen, Advance over the base of the tongue until the epiglottis is seen, Apply traction to the long axis of the laryngoscope handle (this lifts the epiglottis so that the V-shaped glottis can be seen), Insert the tube in the groove of the laryngoscope so that the cuff passes the vocal cords, Remove laryngoscope and inflate the cuff of the tube with 15ml air from a 20ml syringe, Attach ventilation bag/machine and ventilate (~10 breaths/min) with high concentration oxygen and observe chest expansion and auscultate to confirm correct positioning, Consider applying CO2 detector or end-tidal CO2 monitor to confirm placement, if it takes more than 30 seconds, remove all equipment and ventilate patient with a bag and mask until ready to retry intubation. Previous studies suggest that the cuff pressure is usually under-estimated by manual palpation. Anesth Analg. The cookie is updated every time data is sent to Google Analytics. 720725, 1985. However, post-intubation sore throat is a common side effect of general anesthetic and may partly result from ischemia of the oropharyngeal and tracheal mucosa [810], and the most common etiology of non-malignant tracheoesophageal fistula remains cuff-related tracheal injury [11, 12]. - Manometer - 3- way stopcock. CAS Christina M. Brown, MD, Resident, Department of Anesthesiology, Washington University in St. Louis, MO. The complaints sought in this study included sore throat, dysphagia, dysphonia, and cough. Note correct technique: While securing the ET tube with one hand, inflate the cuff with 5-10 cc's of air. 4, pp. Independent anesthesia groups at the three participating hospitals provided anesthesia to the participating patients. studied the relationship between cuff pressure and capillary perfusion of the rabbit tracheal mucosa and recommended that cuff pressure be kept below 27 cm H2O (20 mmHg) [19]. Sengupta, P., Sessler, D.I., Maglinger, P. et al. E. Resnikoff and A. J. Katz, A modified epidural syringe as an endotracheal tube cuff pressure-controlling device, Anaesthesia and Analgesia, vol. Measured cuff volumes were also similar with each tube size. The compliance of the tube was determined from the measured cuff pressure (cmH2O) and the volume of air (ml) retrieved at complete deflation of the cuff; this showed a linear pressure-volume relationship: Pressure= 7.5. Support breathing in certain illnesses, such . Anesthesia services are provided by different levels of providers including physician anesthetists (anesthesiologists), residents, and nonphysician anesthetists (anesthetic officers and anesthetic officer students). These included an intravenous induction agent, an opioid, and a muscle relaxant. Because cuff inflation practices are likely to differ among clinical environments, we evaluated cuff pressure in three different practice settings: an academic university hospital and two private hospitals. This cookie is used to a profile based on user's interest and display personalized ads to the users. Also, at the end of the pressure measurement in both groups, the manometer was detached, breathing circuit was attached to the ETT, and ventilation was started. First, inflate the tracheal cuff and deflate the bronchial cuff. There is a relatively small risk of getting ETT cuff pressures less than 30cmH2O with the use of the LOR syringe method [23, 24], 12.4% from the current study. B) Defective cuff with 10 ml air instilled into cuff. Cuff pressure should be measured with a manometer and, if necessary, corrected. Statement on the Standard Practice for Infection Prevention and Control Instruments for Tracheal Intubation. The rate of optimum endotracheal tube cuff pressure was 90.5% in the group guided by manometer and 31.8% in the conventional procedure group (p < 0.001 . This cookie is native to PHP applications. In this case, an air leak was audible from the patients oropharynx, which led the team to identify the problem quickly. S. W. Wangaka, Estimation of endotracheal tube cuff pressures at Kenyatta National Hospital, University of Nairobi, Nairobi, Kenya, 2006. Data are presented as means (SD) or medians [interquartile ranges] unless otherwise noted; P < 0.05 was considered statistically significant. Ninety-three patients were randomly assigned to the study. This has been shown to cause severe tracheal lesions and morbidity [7, 8]. We tested the hypothesis that the tube cuff is inadequately inflated when manometers are not used. D) Pressure gauge attached to pilot balloon of defective cuff with reading of 30 mmHg with cuff not appropriately inflated. The Data Safety Management Board (DSMB) comprised an anesthesiologist, a statistician, and a member of the SOMREC IRB who would be informed of any adverse event. The groups were not equal for the three different types of practitioners; however, determining differences of practice between different anesthesia providers was not the primary purpose of our study. Conventional high-volume, low-pressure cuffs may not prevent micro-aspiration even at cuff pressures up to 60 cm H2O [2], although some studies suggest that only 25 cm H2O is sufficient [3]. The cookie is updated every time data is sent to Google Analytics. Another study, using nonhuman tracheal models and a wider range (1530cmH2O) as the optimal, had all cuff pressures within the optimal range [21]. Interestingly, the amount of air required to achieve a cuff pressure of 20 cmH2O was similar with each tube size (Table 3). This however was not statistically significant ( value 0.052). Using a laryngoscope, tracheal intubation was performed, ETT position confirmed, and secured with tape within 2min. Secondly, this method is still provider-dependent as they decide when plunger drawback has ceased. 6, pp. Br Med J (Clin Res Ed). Standard cuff pressure is 25mmH20 measured with a manometer. After screening, participants were allocated to either the PBP or the LOR group using block randomization, achieving a 1:1 allocation ratio. Google Scholar. Alternative, cheaper methods like the minimum leak test that require no special equipment have produced inconsistent results. There are data regarding the use of the LOR syringe method for administering ETT cuff pressures [21, 23, 24], but studies on a perioperative population are scanty. JD conceived of the study and participated in its design. Analytics cookies help us understand how our visitors interact with the website. These cookies will be stored in your browser only with your consent. Crit Care Med. This outcome was compared between patients with cuff pressures from 20 to 30cmH2O range and those from 31 to 40cmH2O following the initial correction of cuff pressures. Outcomes Research Institute, University of Louisville, 501 E. Broadway, Suite 210, Louisville, KY, 40202, USA, Papiya Sengupta,Daniel I Sessler&Anupama Wadhwa, Department of Anesthesiology and Perioperative Medicine, University of Louisville, 530 S. Jackson St. University Hospital, Louisville, KY, 40202, USA, Daniel I Sessler,Paul Maglinger,Jaleel Durrani&Anupama Wadhwa, School of Medicine, University of Louisville School of Medicine, Louisville, KY, 40292, USA, You can also search for this author in 21, no. We included ASA class I to III adult patients scheduled to receive general anesthesia with endotracheal intubation for elective surgical operation. This category only includes cookies that ensures basic functionalities and security features of the website. CAS When this point was reached, the 10ml syringe was then detached from the pilot balloon, and a cuff manometer (VBM, Medicintechnik Germany. [21] found that the volume of air required to inflate the endotracheal tube cuff varies as a function of tube size and type. 1977, 21: 81-94. The allocation sequence was concealed from the investigator by inserting it into opaque envelopes (according to the clocks) until the time of the intervention. non-fasted patients, Size: 8mm diameter for men, 7mm diameter for women, Laryngoscope (check size the blade should reach between the lips and larynx size 3 for most patients), turn on light, Monitoring: end-tidal CO2 monitor, pulse oximeter, cardiac monitor, blood pressure, Medications in awake patient: hypnotic, analgesia, short-acting muscle relaxant (to aid intubation), Pre-oxygenate patient with high concentration oxygen for 3-5mins, Neck flexed to 15, head extended on neck (i.e. The cookie is used to store information of how visitors use a website and helps in creating an analytics report of how the website is doing. Cuff pressure reading of the VBM manometer was recorded by the research assistant. The difference in the incidence of sore throat and dysphonia was statistically significant, while that for cough and dysphagia was not. (Supplementary Materials). Printed pilot balloon. Anesthesia was maintained with a volatile aesthetic in a combination of air and oxygen; nitrous oxide was not used during the study period. Generally, the proportion of ETT cuffs inflated to the recommended pressure was less in the PBP group at 22.5% (20/89) compared with the LOR group at 66.3% (59/89) with a statistically significant positive mean difference of 0.47 with value<0.01 (0.3430.602). Nitrous oxide and medical air were not used as these agents are unavailable at this hospital. However, a major air leak persisted. Terms and Conditions, 513518, 2009. 71, no. Low pressure high volume cuff. In low- and middle-income countries, the cost of acquiring ($ 250300) and maintaining a cuff manometer is still prohibitive. In the control ETT, the cuff was inflated to 20 mm Hg to 22 mm Hg and not manipulated. 18, no. A limitation of this study is that cuff pressure was evaluated just once 60 minutes after induction of anesthesia. 2, pp. Inflate the cuff of the endotracheal tube with sufficient air to seal the area between the trachea and the tube. 2003, 13: 271-289. chest pain or heart failure. Previous studies suggest that this approach is unreliable [21, 22]. 2, pp. Secures tube using commercially approved tube holder. The overall trend suggests an increase in the incidence of postextubation airway complaints in patients whose cuff pressures were corrected to 3140cmH2O compared with those corrected to 2030cmH2O. Vet Anaesth Analg. The datasets analyzed during the current study are available from the corresponding author on reasonable request. An anesthesia provider inserted the endotracheal tubes, and the intubator or the circulating registered nurse inflated the cuff. Figure 1. Our first goal was thus to determine if cuff pressure was within the recommended range of 2030 cmH2O, when inflated using the palpation method. - 20-25mmHg equates to between 24 and 30cmH2O. An endotracheal tube : provides a passage for gases to flow between a patients lungs and an anaesthesia breathing system . How much air is injected into the cuff is not a major concern for almost all anaesthetists and they usually depend on palpating the external cuff tense to judge is it too much, accurate or not enough? The chi-square test was used for categorical data. However, no data were recorded that would link the study results to specific providers. 10.1007/s00134-003-1933-6. Hahnel J, Treiber H, Konrad F, Eifert B, Hahn R, Maier B, Georgieff M: [A comparison of different endotracheal tubes. PubMedGoogle Scholar. This cookie is used to enable payment on the website without storing any payment information on a server. We recorded endotracheal tube size and morphometric characteristics including age, sex, height, and weight. 106, no. At the time of the intervention, the study investigator retrieved the next available envelope, which indicated the intervention group, from the next available block envelope and handed it to the research assistant. This cookies is set by Youtube and is used to track the views of embedded videos. Circulation 122,210 Volume 31, No. Methods. 28, no. The cuff is inflated with air via a one-way valve attached to the cuff through a separate tube that runs the length of the endotracheal tube. J. Rello, R. Soora, P. Jubert, A. Artigas, M. Ru, and J. Valls, Pneumonia in intubated patients: role of respiratory airway care, American Journal of Respiratory and Critical Care Medicine, vol. Air Leak in a Pediatric CaseDont Forget to Check the Mask! Over-inflation of an endotracheal tube (ETT) cuff may lead to tracheal mucosal irritation, tracheal wall ischemia or necrosis, whereas under-inflation increases the risk of pulmonary aspiration as well as leaking anesthetic gas and polluting the environment. The magnitude of effect on the primary outcome was computed for 95% CI using the t-test for difference in group means. This cookie is used by the WPForms WordPress plugin. The chamber is set to an altitude of 25,000 feet, which gives a time of useful consciousness of around three to five minutes. "Aire" indicates cuff to be filled with air. We intentionally avoided this approach since our purpose was to evaluate cuff pressures and associated volumes in three routine clinical settings. In the early years of training, all trainees provide anesthesia under direct supervision. This study set out to determine the efficacy of the loss of resistance syringe method at estimating endotracheal cuff pressures. R. D. Seegobin and G. L. van Hasselt, Endotracheal cuff pressure and tracheal mucosal blood flow: endoscopic study of effects of four large volume cuffs, British Medical Journal, vol. Acta Otorhinolaryngol Belg. 1995, 15: 655-677. 1mmHg equals how much cmH2O? In this cohort, aspiration had the second highest incidence of primary airway-related serious events [6]. The intracuff pressure, volume of air needed to fill the cuff and seal the airway, number of tube changes required for a poor fit, number with intracuff pressure 20 cm H 2 O, and intracuff pressure 30 cm H 2 O are listed in Table 4. Conclusion. We did not collect data on the readjustment by the providers after intubation during this hour. This cookie is installed by Google Analytics. We also appreciate the statistical analysis by Gilbert Haugh, M.S., and the editorial assistance of Nancy Alsip, Ph.D., (University of Louisville). Interestingly, there was also no significant or important difference as a function of provider measured cuff pressures were virtually identical whether filled by CRNAs, residents, or attending anesthesiologists. With air providing the seal in the cuff the mean rise in cuff pressure was 23 cmH2O . This method provides a viable option to cuff inflation. In the later years, however, they can administer anesthesia either independently or under remote supervision. 4, pp. Endotracheal tubes are widely used in pediatric patients in emergency department and surgical operations [1]. The cookie is created when the JavaScript library executes and there are no existing __utma cookies. Underinflation increases the risk of air leakage and aspiration of gastric and oral pharyngeal secretions [4, 5]. It does not store any personal data. 24, no. Laura F. Cavallone, MD, Associate Professor, Department of Anesthesiology, Washington University in St. Louis, MO. The primary outcome of the study was to determine the proportion of cuff pressures in the optimal range from either group. PubMed . All data were double entered into EpiData version 3.1 software (The EpiData Association, Odense, Denmark), with range, consistency, and validation checks embedded to aid data cleaning. How to insert an endotracheal tube (intubation) for doctors and medical students, Video on how to insert an endotracheal tube, AnaestheticsIntensive CareOxygenShortness of breath. 9, no. Anaesthesist. In case of a very low pressure reading (below 20cmH, https://pdfs.semanticscholar.org/c12e/50b557dd519bbf80bd9fc60fb9fa2474ce27.pdf. The optimal technique for establishing and maintaining safe cuff pressures (2030cmH2O) is the cuff pressure manometer, but this is not widely available, especially in resource-limited settings where its use is limited by cost of acquisition and maintenance. There was no correlation between the measured cuff pressure and the age, sex, height, or weight of the patients. PM, SW, and AV recruited patients and performed many of the measurements. Our results are consistent in that measured cuff pressure exceeded 30 cmH2O in 50% of patients and were less than 20 cmH2O in 23% of patients. Striebel HW, Pinkwart LU, Karavias T: [Tracheal rupture caused by overinflation of endotracheal tube cuff]. 101, no. The initial, unadjusted cuff pressures from either method were used for this outcome. Daniel I Sessler. Mandoe H, Nikolajsen L, Lintrup U, Jepsen D, Molgaard J: Sore throat after endotracheal intubation. Decrease the cuff pressure to 30 cm H2O by withdrawing a small amount of air from the balloon with a 10 mL syringe. We similarly found that the volume of air required to inflate the cuffs to 20 cmH2O did not differ significantly as a function of endotracheal tube size. 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