การเปรียบเทียบความดันภายในถุงลมปลายท่อหายใจ ด้วยวิธีการเติมลมปริมาตรน้อยที่สุดที่สามารถอุดกั้น ลมรั่วในทางเดินหายใจ นรุตม์ เรือนอนุกูล พ.บ.*, กนกพร คุณาวิศรุต พ.บ.*, ปัญชิกา ลือตระกูล พ.บ.*, สุพิชฌา ฉันทะกุล พ.บ.* Abstract: Comparison of Endotracheal Tube Cuff Pressure with Minimal Occlusive Volume Techniques. Narut Ruananukun MD*, Kanokporn Kunawisarut MD*, Punchika Luetrakool MD*, Supitcha Chantakul MD*. *Department of Anesthesiology, Faculty of Medicine Ramathibodi Hospital, Mahidol University, Bangkok 10400, Thailand. Background: Inappropriate endotracheal tube cuff pressure causes various complications, such as sore throat, tracheitis, tracheal ischemia and aspiration. The recommendation is to inflate endotracheal tube cuff pressure to 25 - 30 cmH2O with cuff pressure manometer but it has not always been available especially in the operating theatres. Therefore, the minimal occlusive volume (MOV) technique has been widely suggested. There are two most common MOV techniques. First, incremental addition of air until the MOV is established (Technique A). Second, full cuff inflation followed by removal of 0.5 ml of air until a leak is detected then restore the cuff seal with 1 ml of air (Technique B). Objective: To compare the endotracheal tube cuff pressure inflated by two MOV techniques. Methods: A randomized crossover study was conducted in 40 patients who were scheduled for surgery under general anesthesia at Ramathibodi Hospital. We randomized patients into two groups, after oropharyngeal suction and fully endotracheal tube cuff deflation. In Group 1, the endotracheal tube cuff was inflated with the * ภาควิชาวิสัญญีวิทยา คณะแพทยศาสตร์โรงพยาบาลรามาธิบดี มหาวิทยาลัยมหิดล กรุงเทพฯ 10400 Volume 40 Number 2 April – June 2014 Thai Journal of Anesthesiology 117 MOV Technique A followed by Technique B while Group 2 used Technique B and was followed by Technique A. The inflated volume and pressure that was created in the closed system manometer by each MOV cuff inflation technique was recorded and then the differences between pressure and the reference pressure of 25 cmH 2O of two MOV techniques were calculated. Results: There was no significant differences of patients’ demographic data between two groups. The mean endotracheal tube cuff pressure created by the MOV Technique B was significantly higher than Technique A (21.53 + 5.94 and 19.05 + 4.07 cmH2O respectively; p < 0.05). The range from pressure observed to reference pressure of 25 cmH 2O between two groups were not significantly different (Technique A 6.15 + 3.75 and Technique B 5.83 + 3.59 cmH2O; p > 0.05). Conclusions: MOV technique is an alternative technique that does not create the pressure higher than the recommendation, but the mean pressures of both groups seem to be lower than reference pressure. Therefore, we recommend using cuff pressure manometer to optimize it. However, if necessary, MOV Technique B is more preferable. Introduction endotracheal tube cuff pressure that can prevent aspiration is 25 cmH 2O. Thus, the appropriate endotracheal tube cuff pressure should be 25 - 30 cmH2O2,3. Stewart SL et al compared pressure obtained from endotracheal tube cuff inflation techniques such as minimal occlusive volume (MOV) technique, minimal leak technique, predetermined volume technique, pilot balloon palpation technique and direct intracuff pressure measurement technique. The study showed that the estimation techniques were not accurate and using manometer was recommended as the standard endotracheal tube cuff inflation technique 4. However, there are limitations in general practice which impeded the use of manometer in all patients who are intubated especially in the operating theatres. If the endotracheal tube cuff pressure is too high, it may cause various complications such as sore throat, tracheitis, and tracheal ischemia. On the other hand, if the endotracheal tube pressure is too low, it may lead to pulmonary aspiration or leakage of tidal volume. So, the optimal pressure can protect airway from pulmonary aspiration without a decrease of capillary blood flow at tracheal mucosa. In 1984, Seegobin RD et al concluded that if the endotracheal tube cuff pressure is too high, it can cause a decrease tracheal mucosal blood flow. They found that at 25 cmH2O, the tracheal mucosa was normal, but at 30 cmH2O, the anterior part of the tracheal mucosa became pale1. Bernhard WN et al described in 1979 that the minimum 118 วิสัญญีสาร Keywords: Endotracheal tube cuff inflation, minimal occlusive volume technique, endotracheal tube cuff pressure ปีที่ 40 ฉบับที่ 2 เมษายน – มิถุนายน 2557 So, the estimate techniques are still used. MOV technique has been suggested widely and it is used more frequently compared with other techniques5,6. There are two MOV techniques in general practice. The first technique is incremental addition of air until the MOV is established (Technique A)4. The second technique is full cuff inflation followed by removal of 0.5 ml of air until a leak is detected, then restores the cuff seal with 1 ml of air (Technique B) 7. There is no current evidence deciding which technique is the best way to create the optimal endotracheal tube cuff pressure. Objective To compare the endotracheal tube cuff pressure inflated by two MOV techniques. Method After obtaining approval from the ethics committee and informed written consent, a randomized crossover study was conducted in 40 patients who were scheduled for surgery under general anesthesia. Sample size was calculated from the pilot study and the power is 0.95. Patients were enrolled as followed aged 18 - 80 years old, ASA physical status I-III, NPO 8 hours or clear liquid fluid 2 hours before the operation. The exclusion criteria were the patients who had risk of aspiration, airway trauma, airway obstruction, history of prolong intubation, history of intubation within 1 week, cough, sore throat before intubation or predicted difficult airway. The patients were randomized by the computer into 2 groups and sealed in opaque envelopes. In Group 1, the endotracheal tube cuff was inflated with MOV Volume 40 Number 2 April – June 2014 Technique A followed by Technique B (A first) and Group 2 used Technique B and was followed by Technique A (B first). General anesthesia was conducted and endotracheal tube (high volume, low pressure cuff endotracheal tube Curity® size ID 7.5 or 8 mm) was inserted. Content in oropharynx was cleared. The endotracheal tube cuff was fully deflated and connected to the closed system manometer which composed of pressure tubing size 6’’, stopcock, and manometer (cuff pressure gauge; VBM Medizintechnik GmbH) as in figure 1. The patients were ventilated with airway pressure at 20 cmH2O and the leakage was detected by palpation. The inflated volume and pressure that created by each MOV techniques were recorded. Finally, the endotracheal tube cuff was inflated until the pressure reached 25 cmH2O. Descriptive statistic was presented by mean + SD or frequency and independent t - test or Mann -Whitney test was used to compare it as appropriated. Normality of data was tested by Shapiro - Wilk test. Chi - square comparison for binary outcomes. Friedman’s ANOVA for within subjects analysis to find order effects. Statistical analyses were made with SPSS 20.0. The p - value of less than 0.05 was accepted as significant. Figure 1 Closed system manometer. Thai Journal of Anesthesiology 119 Protocol flow chart Enrolled patients aged 18 - 80 years old (n = 40) (n = 40) Randomized into 2 groups Clear content in oropharynx Deflate endotracheal tube cuff Connect endotracheal tube cuff with closed system manometer Group 1 (n = 20) Incremental addition of air until the MOV is established. (Technique A) Group 2 (n = 20) Full cuff inflation followed by removal of 0.5 ml of air until a leak is detected, then restoration the cuff seal with 1 ml of air. (Technique B) Group 2 (n = 20) Full cuff deflation, followed by incremental addition of air until the MOV is established. (Technique A) Group 1 (n = 20) Full cuff deflation, followed by reinflation, removal of 0.5 ml of air until a leak is detected, then restoration the cuff seal with 1 ml of air. (Technique B) Inflate endotracheal tube cuff until the pressure reach 25 cmH2O. 120 วิสัญญีสาร ปีที่ 40 ฉบับที่ 2 เมษายน – มิถุนายน 2557 Result There was no statistically significant difference in patient’s demographic data between 2 groups as shown in table 1. The mean endotracheal tube cuff pressure created by the MOV Technique B (21.53 + 5.94 cmH2O) was significantly higher than Technique A (19.05 + 4.07 cmH2O) as shown in table 2 and figure 2. The range of pressure observed and reference pressure (25 cmH 2O) between Technique A and Technique B were not significantly different (Technique A 6.15 + 3.75 and Technique B 5.83 + 3.59 cmH2O; p > 0.05) as shown in figure 3. Table 1 Patient’s characteristics and perioperative value. Age (yr) Male/Female, n Body weight (kg) Height (cm) BMI (kg/m2) ETT size, n 7.5 8.0 Technique A first (N = 20) 43.60 + 14.02 7/13 55.45 + 8.13 158.45 + 6.44 22.10 + 3.07 Technique B first (N = 20) 48.80 + 14.16 4/16 58.75 + 11.02 156.35 + 6.29 24.14 + 4.78 14 6 15 5 P - value 0.251 0.288 0.287 0.303 0.116 > 0.999 Data are mean + SD unless otherwise stated. Table 2 Cuff volume used and range from absolute pressure value to reference value, between technique A and B. Cuff volume (ml) Pressure (cm H2O) Range from absolute pressure value to reference value† (cm H2O) Technique A (N = 40) 2.66 + 1.59 19.05 + 4.07 6.15 + 3.75 Technique B (N = 40) 3.11 + 1.56 21.53 + 5.94 5.83 + 3.59 P - value 0.072 0.048* 0.515 Data are mean + SD. † Reference value, 25 cm H2O * p < 0.05 Volume 40 Number 2 April – June 2014 Thai Journal of Anesthesiology 121 Figure 2 Correlation between cuff volume and pressure. This figure displays the correlation between cuff volume and pressure. A dotted line and straight line (not in bold) are trendlines of cut point between cuff volume and pressure in Technique A and B, respectively. × and o represents cut point between cuff volumes and pressures of Technique A and B in each patients, respectively. As in this figure, the straight line is closer to the bold line (represent 25 cmH2O) than the dotted line. This means that cuff pressures from Technique B is higher and tend to reach 25 cmH2O much more than Technique A. Figure 3 The range from absolute pressure to reference pressure Discussion In general practice, the endotracheal tube cuff is usually inflated by the estimated technique without concern about cuff pressure because some 122 วิสัญญีสาร clinicians think it is only short period. But no one knows when the complication will happen especially in the operating theater which takes long ปีที่ 40 ฉบับที่ 2 เมษายน – มิถุนายน 2557 operating time and nitrous oxide is used8. The minimum cuff pressure which can prevent complication is necessary. In our study, we used 25 cmH2O as the reference pressure, but some previous studies and guidelines suggested 20-30 cmH 2O 9,10. The mean pressure of both MOV techniques were around 20 cmH2O and no case had pressure over 30 cmH2O. So, MOV techniques are good to prevent over pressure complication and can decrease adverse effects from nitrous oxide that create further pressure. On the other hand, although the mean pressure was close to the minimum optimal pressure but there were several cases that had pressure which was lower than minimum optimal pressure. So, the aspiration should be concerned especially in patients with the risk of aspiration. In our study, all patients had no respiratory complicatons. When we changed the reference pressure to 20 cmH2O as recommended in some study by statistical technique, there was also no statistical difference in the range from absolute pressure to reference pressure between 2 techniques. The limitations of this study are the use of only one brand of endotracheal tube and two most common sizes of endotracheal tube uses in general anesthetic work in our hospital, especially the most used size which is 7.5. The different types or brands of endotracheal tube may have various contour, consistency and compliance of cuff. It may affect the outcome. In addition, the cuff leakage was detected by palpation which is subjective feeling. Some studies suggested auscultation with a Volume 40 Number 2 April – June 2014 stethoscope instead which is more sensitive or if some equipments are applied to detect it, it will be objective measurement2,4-7. This study shows that endotracheal tube cuff pressure created by MOV Technique B was significantly higher than Technique A. This is probably due to MOV Technique B which uses the restoration of cuff seal with 1 ml of air after leakage was detected. It may be better to create more optimal pressure with modified conventional MOV techniques such as incremental addition of air more than 1 ml after leakage was detected in Technique B or addition of air after leakage could not be detected in Technique A. However, the difference of cuff pressure between two techniques was borderline significant (p = 0.048) so it could hardly qualify as a precise indication. A further larger study is recommended to confirm this finding. Conclusion MOV technique is an alternative technique that does not create the pressure higher than the recommendation, but the mean pressures of both groups seem to be lower than the reference pressure. Therefore, we recommend using cuff pressure manometer to optimize it, but if necessary, MOV Technique B is more preferable. Acknowledgement The authors wish to thank the reviewers for their valuable comments and also appreciate the contribution of all colleagues and assistants Thai Journal of Anesthesiology 123 involved in the research. Miss Rojnarin Komonhirun is acknowledged for the statistical advice. References 1. Seegobin RD, van Hasselt GL. Endotracheal cuff pressure and tracheal mucosal blood flow: endoscopic study of effects of four large volume cuffs. BMJ. 1984;288:965-8. 2. Bernhard WN, Cottrell JE, Sivakumaran C, Patel K, Yost L, Turndorf H. Adjustment of intracuff pressure to prevent aspiration. Anesthesiology. 1979;50(4):363-6. 3. Chendrasekhar A, Timberlake GA. Endotracheal tube cuff pressure threshold for prevention of nosocomial pneumonia. The Journal of Applied Research. 2003;3(3):311-4. 4. Stewart SL, Secrest JA, Norwood BR, Zachary R. A comparison of endotracheal tube cuff pressure using estimation techniques and direct intracuff measurement. AANA Journal. 2003; 71(6):443-7. 5. Crimlisk JT, Horn MH, Wilson DJ, MarinoB. Artificial airways: a survey of cuff management practices. Heart Lung. 1996;25(3):225-35. 6. Al-metwalli RR, Al-Ghamdi AA, Mowafi HA, Sadek S, Abdulshafi M, Mousa WF. Is sealing 124 วิสัญญีสาร cuff pressure, easy, reliable and safe technique for endotracheal cuff inflation? :A comparative study. Saudi J Anaesth. 2011;5(2):185-9. 7. UTMB respiratory care services. PROCEDURE - Minimal Occluding Volume (MOV) or Minimal Leak Technique [Internet]. Texas: Galveston, 2005 [cited 2014 Jan 24]. Available from: http://www.utmb.edu/rcs/P & P/Clinical/ 7.3/7-3-49 - Minimal Occluding Volume (MOV).doc 8. Tu HN, Saidi N, Lieutaud T, Bensaid S, Menival V, Duvaldestin P. Nitrous oxide increases endotracheal cuff pressure and the incidence of tracheal lesions in anesthetized patients. Anesth Analg. 1999;89:187-90. 9. Sengupta P, Sessler DI, Maglinger P, Wells Spencer, Vogt A, Durrani J, et al. Endotracheal tube cuff pressure in three hospitals and the volume required to produce an appropriate cuff pressure. BMC Anesthesiology. 2004;4:8. 10. American Thoracic Society (ATS) and Infectious Diseases Society of America (IDSA). Guidelines for the management of adults with hospitalacquired, ventilator-associated, and healthcareassociated pneumonia. Am J Respir Crit Care Med. 2005; 171: 388-416. ปีที่ 40 ฉบับที่ 2 เมษายน – มิถุนายน 2557