|Year : 2007 | Volume
| Issue : 1 | Page : 24-27
Endotracheal tube cuff pressures during general anaesthesia while using air versus a 50% mixture of nitrous oxide and oxygen as inflating agents
Jesni Joseph Manissery1, Vijaya Shenoy1, M Ambareesha2
1 M.D., Asso. Prof., Department of Anaesthesiology Kasturba Medical College, Mangalore, India
2 M.D., D.A., Prof. & Head, Deparment of Anaesthesiology Kasturba Medical College, Mangalore, India
|Date of Acceptance||16-Nov-2006|
|Date of Web Publication||20-Mar-2010|
M.D., D.A., Prof. & Head, Deparment of Anaesthesiology KasturbaMedicalCollege,Mangalore
Source of Support: None, Conflict of Interest: None
The present study was aimed at assessing the efficacy of filling a 50% mixture of nitrous oxide : oxygen (50%N 2 O:O 2 ) in the endotracheal tube cuff to provide stable cuff pressures during general anaesthesia with 67%N 2 O. The endotracheal tube cuff pressures with air (control) as the inflating agent in the tubes were found to have a total mean pressure of 62.60±12.33 at the end of one hour of general anaesthesia. When comparing the endotracheal tube cuff pressures in the Mallinckrodt tubes with that of the Portex tubes, with air as the inflating agent, the Portex tubes showed a significantly lower cuff pressures at the end of one hour. The endotracheal tube cuff pressures with 50%N 2 O:O 2 as the inflating agent showed a total mean pressure of 27.63 ± 3.221 at the end of one hour of general anaesthesia. This indicates that inflation of the cuff of the endotracheal tubes with a 50%N 2 O:O 2 rather than air maintains a stable intra cuff pressure. Therefore, the method of using a 50%N 2 O:O 2 for filling endotracheal tube cuff can be adopted for endotracheal tubes with high-volume, low-pressure cuffs to prevent both excessive cuff pressure and disruption of cuff seal, during general anaesthesia lasting up to one hour.
Keywords: : General anaesthesia, Endotracheal tube cuff pressure, Inflating agents, Air, 50%N 2 O:O 2
|How to cite this article:|
Manissery JJ, Shenoy V, Ambareesha M. Endotracheal tube cuff pressures during general anaesthesia while using air versus a 50% mixture of nitrous oxide and oxygen as inflating agents. Indian J Anaesth 2007;51:24-7
|How to cite this URL:|
Manissery JJ, Shenoy V, Ambareesha M. Endotracheal tube cuff pressures during general anaesthesia while using air versus a 50% mixture of nitrous oxide and oxygen as inflating agents. Indian J Anaesth [serial online] 2007 [cited 2019 Apr 18];51:24-7. Available from: http://www.ijaweb.org/text.asp?2007/51/1/24/61110
| Introduction|| |
Cuffed endotracheal tube,commonly used during general anaesthesia acts as a means of supplying oxygen (O 2 ) to the lungs and as a conduit for volatile anaesthetic agents. Keeping the cuff inflated for long time can result in ischemia and further complications such as postoperative sore throat, hoarseness of voice, tracheal ulceration, tracheal stenosis, trachaeo esophageal fistula etc. ,, N 2 O, an anaesthetic gas commonly used in conjunction with other volatile anaesthetic agents is known to diffuse into air filled cavities including endotracheal tube cuffs leading to an increase in cuff pressure, which is transmitted to the tracheal mucosa. Several workers have reported different concentrations of nitrous oxide (N 2 O) in the endotracheal tube cuff to provide stable cuff pressures during general anaesthesia with N 2 O. ,, This diffusion is maximum during the 1st hour of N 2 O anaesthesia. Several methods have been used to reduce the pressure exerted on the tracheal mucosa by decreasing the diffusion of N 2 O into the cuff. Checking of cuff volume and pressure regularly and cuff deflated if indicated, use of the same gas mixture inhaled by the patient to inflate the cuff and use of normal saline or distilled water to prevent increase in pressure are some of the methods recommended and followed. , Usage of special Brandt anaesthesia tubes or polyurethane foam cuff. ,, are also being practiced. The present study was carried out to assess the efficacy of filling air or 50%N 2 O:O 2 in the endotracheal tube cuff to provide stable cuff pressure during general anaesthesia with 67%N 2 O. Peri-operative complications were closely monitored for and the results are presented here.
| Material and Methods|| |
After the institutional ethical committee approval, 60 adult patients undergoing elective surgical procedures were selected. The sample size chosen for the study was based on a pilot study of five cases done in the preliminary stage, following which the results were discussed with the statistician. The out come of the pilot study indicated that a sample size of 60 would give enough power of more than 85% (However the results of the pilot study are not included in the results of the main study). In this randomised prospective controlled, double blind, crossover study, the selection criteria followed include; adult patients of either gender between 18 and 70 years, belonging to ASA physical status I and II, scheduled for elective surgery requiring general anaesthesia with endotracheal intubation and controlled ventilation and scheduled for surgery lasting more than two hours. Patients undergoing surgery in any position other than supine, surgery of head and neck region, higher risk of pulmonary aspiration and with history of hyperactive airway disease were rejected. The selected patients were randomly distributed in four groups designated as M1, M2, P1 and P2 with 15 patients each. Mallinckrodt tubes were used to intubate the patients under groups M1 and M2 while patients under P1 and P2 Portex tubes were used. Air was used to inflate the cuff for the 1st one hour followed by 50%N 2 O:O 2 for the 2nd hour in groups M1 and P1, while this schedule was reversed (crossover) in groups M2 and P2. Polyvinyl chloride tubes with high-volume, low-pressure cuffs of the brand 'Mallinckrodt Hi contour TM' which has smaller pilot balloon and 'Portex Profile soft-seal cuff' which has a large pilot balloon were the two tubes used in this study. Endotracheal tube size selection was based on the sex, build and clinical judgement of the anaesthesiologist administering anaesthesia. Prior to intubation, the tubes selected for the study were checked for any leaks in the cuff system. The source of air was room air and the 50%N 2 O:O 2 was aspirated from the common gas outlet of an anaesthetic machine.
The control-inflator device, Endotest TM, used in this study measures the cuff pressure at the pilot balloon. Marquette TM monitor with a multiple gas analyser was used to analyse the concentration of N 2 O in the aspirated gas samples from the cuffs of the endotracheal tube. Syringes of 10ml capacity were used to collect and fill the gases and to aspirate and analyze the gas samples. General anaesthesia for the subjects in the study was standardized after appropriate pre medication. The brand of the tube was randomly allotted to the patients and trachea intubated with the appropriate size of the tube selected. Five minutes after settling the patient, oral suctioning was done and the endotracheal tube cuff was aspirated completely. The cuff was then refilled with 6-8 ml of a gas (G1, either air or 50%N 2 O:O 2 ) to achieve a pressure approximately greater than 30 cm H 2 O, subsequently the control inflator device was used to accurately set the pressure at 30 cm H 2 O. Then time was noted as zero minute and pressures were monitored continuously and recorded every 10 minutes. At the end of one hour the cuff was deflated completely after doing an oral suction and the gas aspirated was analyzed for the concentration of N 2 O. The cuff was again refilled with 6-8ml of a gas (G2, either air or 50%N 2 O:O 2 ) as part of the crossover study. Air was used as a control to compare it with 50%N 2 O:O 2 . The data required for this study was collected using the aid of a designed proforma. Patients were followed up post-operatively to monitor for any adverse effects of general anaesthesia, especially with regard to sore throat for 24 hours after the procedure. Sore throat when occurred was graded into four grades depending on the severity, no sore throat at grade 0 and severe sore throat at grade . ,
| Results|| |
The minimum age of the patient was 18 and the maximum was 62 years with the mean age in M1, M2, P1 and P2 being 37.73, 40.47, 31.8 and 34.4 respectively. The total sex distribution in all four groups consisted of 46.7% male and 53.3% female as shown in [Table 1]. The maximum number of endotracheal tubes used were of 7.5 mm ID in all the four groups which constituted 40% of the total tubes. No cuff seal leak was detected on auscultation over the neck in any of the 60 patients in this study. No sore throat was recorded for 57.6% of the patients. While the remaining 22, 18.6 and 1.75 % patients had grade 1, 2 and 3 sore throat respectively.
| Cuff pressure|| |
The mean cuff pressures measured in Mallinckrodt and Portex tubes with air or 50%N 2 O:O 2 mixture as inflating agents initially and their cross over are given in [Table 2]. Cuff pressure measured with air as inflating agent, from 10 to 60 min, showed statistically significant difference for every 10 min measurements in all the four groups (F=312.059, P<0.0001) and between the four groups (F=33.462, P<0.0001). However, comparison using multiple comparison criterion, it was found that groups M1& M2 and P1& P2 did not show statistically significant difference. Whereas group M1 showed significant difference with groups P1& P2 (P<0.001) and group M2 with groups P1& P2 (P<0.001).
Cuff pressure measured with 50%N 2 O:O 2 as inflating agent, from 10 to 60 min, showed statistically significant difference for every 10 min measurements in all the four groups (F= 51. 195, P<0.0001) and between the four groups (F=32.013, P < 0.0001). However, comparison using multiple comparison criterion, it was found that groups M1& M2 and groups P1& P2 did not show statistically significant difference. But, group M1 showed statistically significant difference with groups P1& P2 (P<0.05& P<0.001) and group M2 with groups P1& P2 (P<0.05& P<0.001).
| Crossover analysis|| |
The crossover analysis was used to test the effect of cross over on the cuff pressure between groups M1& M2 for, using air initially followed by 50%N 2 O:O 2 in group M1, compared to, using 50%N 2 O:O 2 initially followed by air in group M2. Similar studies between groups P1& P2 revealed no statistically significant difference (T=0.0966& P=0.4921 and T=0.8074& P=0.2131 respectively). Comparison of cuff pressures for every 10 min intervals when air or 50%N 2 O:O 2 were used as inflating agents was done by applying paired 't' test and showed significant (P<0.0001) difference for each of the 10 min intervals from 10 min onwards for all the four groups taken together. Application of paired 't' test for each of the individual groups M1, M2, P1 and P2 showed similar significant difference (P<0.0001) between the two inflating agents in all the four groups, for each of the 10 min intervals from 10 min onwards.
| N 2 O concentration in cuff|| |
The mean concentration of N 2 O in the cuff expressed as percentage when air and 50%N 2 O:O 2 were used as cuff inflating agents at the end of one hour of anaesthesia were 49.47 and 48 in M1, 49.13 and 49.87 in M2, 49.07 and 49.47 in P1 and 48.8 and 50.6 in P2 respectively. There was no significant difference between the four groups with respect to N 2 O concentration in the cuff with air as inflating agent (P=0.969) or 50%N 2 O:O 2 as inflating agent (P=0.330). Paired 't' test done to compare the N 2 O concentration within each group also did not show any statistical significance.
| Discussion|| |
The rise in cuff pressures with air as inflating agent recorded in this study is comparable to the previous reports. ,, The endotracheal tube cuff pressures with air as inflating agent in the tube cuffs were found to have a total mean pressure of 62.60±12.33 at the end of one hour of general anaesthesia. With pressure just greater than 30 cm H 2 O (22 mmHg) objective evidence of compromise to the tracheal mucosal capillary perfusion has been reported.  Also at this pressure, which is above 50 cm H 2 O (37 mmHg) (critical perfusion pressure), there is cessation of flow to the mucosa over the tracheal rings and posterior wall. 
The significantly lower cuff pressures in the Portex tubes compared to the Mallinckrodt tubes could be due to the larger pilot balloon of the Portex tube. The larger pilot balloon with larger surface area could facilitate efflux of nitrous oxide into air more easily and therefore limit the increase in the cuff pressures. Also, the larger pilot balloon being more compliant could accommodate for the increased volume and thus limiting the cuff pressures. , The endotracheal tube cuff pressures with 50%N 2 O:O 2 as the inflating agent were found to have a total mean pressure of 27.63±3.221 at the end of one hour of general anaesthesia. This pressure was not only statistically significant as compared to the control group but also below 30 cm H 2 O above which compromise to the tracheal mucosal capillary perfusion occurs. Though the fall in endotracheal tube cuff pressures from the initial set pressures of 30 cm H 2 O was statistically significant, clinically none of the tubes showed any evidence of leak around the cuff, maintaining adequate cuff seal.
This indicates that inflation of the cuff of the endotracheal tubes with 50%N 2 O:O 2 rather than air during anaesthesia with 67% N 2 O maintains a stable and safe intra cuff pressure. The results are consistent with that of an earlier study in achieving stable intra cuff pressures with 50%N 2 O:O 2 . However, with respect to leak around the cuff our finding is inconsistent, as a leak was detected in 2 out of 25 patients in their study. 5 No leak was detected in any of the 60 patients in our study.
The concentration of N 2 O analysed in the endotracheal tubes at the end of one hour of general anaesthesia were similar in all the groups and equilibrated at a concentration less than that administered for general anaesthesia. This is in agreement with with the findings of the earlier studies reported. ,
The incidence of sore throat in the present study could not be compared between the groups as all the 60 patients in the study were exposed to both air and 50%N 2 O:O 2 and inflating agents in the cuff during their course of general anaesthesia. There are many factors affecting morbidity associated with tracheal intubation, which include tube size, lateral wall pressure, movement, orotracheal suction and the lubricant used. Cuff related tracheal damage is influenced mostly by both lateral wall pressure and the duration of intubation and among these two factors, pressure is much more important.  Therefore, inhibition of excessive intracuff pressure can reduce severity of post operative sore throat by 50%.  On the other hand, the pressure exerted against the tracheal wall by the cuff of a tracheal tube should be high enough to avoid gas leaks and aspiration of regurgitated gastric contents. To control changes in intracuff pressure, automated devices ,, to prevent gas diffusion into the cuff, and cuffs made of new materials with high gas barrier properties  have been developed, which are effective but expensive. The methods used in the present study, however, require no extra cost because 50% N 2 O is available from a common outlet of every anaesthetic machine.
| Conclusion|| |
The practice of using 50%N 2 O:O 2 for filling endotracheal tube cuff facilitates an inexpensive method for providing safe and stable cuff pressures during anaesthesia. Therefore this method can be adopted for endotracheal tubes with high-volume, low-pressure cuffs similar to that used in the present study to prevent both excessive cuff pressure and disruption of cuff seal, during general anaesthesia with 67% nitrous oxide and lasting up to one hour.
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[Table 1], [Table 2]