Background: Maintenance of optimal Endotracheal Tube cuff Pressure (ETTcP) in anaesthetic practice reduces cuff pressure complications. Aneroid manometers for measurement of ETTcP are not widely available in Ghana, hence anaesthesia providers estimate ETTcP according to their experience. The study assessed ETTcP obtained from estimation techniques between anaesthesia providers at Korle-Bu Teaching Hospital (KBTH). It also evaluated the Volume of Air Required (VAR) to obtain an acceptable cuff inflation pressure for sizes 7.0 and 8.0 mm adult endotracheal tubes used at the hospital, and the effect of patient’s age, weight and height on this volume. Methods: Eighty-one patients who underwent general anaesthesia were recruited. ETTcP was measured using an aneroid manometer via a three-way tap. After full cuff deflation, the cuff was refilled with air until an ETTcP of 20 cm H 2O was obtained. Independent t-test was used to measure the statistical variations in the ETTcP using estimation techniques in relation to recommended levels as well as the significant difference of mean VAR to obtain a cuff pressure of 20 cm H 2O. Grouped t-test was used to determine significant differences in ETTcP between anaesthesia providers using estimation techniques. Results: Mean ETTcP obtained from estimation techniques was (61.87, 73.79) cm H 2O. The mean ETTcP measured for Physician and Nurse Anaesthetists were 65.36 cm H20 and 69.52 cm H 2O respectively. The mean VAR to achieve an ETTcP of 20 cm H 2O for endotracheal tube sizes 7.0 mm and 8.0 mm were 3.90 ± 1.13 mls and 4.55 ± 0.95 mls respectively. Age and weight significantly influenced the VAR to achieve a cuff pressure of 20 cm H 2O, however, height did not. Conclusions: This study demonstrated that cuff pressures obtained by estimation techniques were generally higher than the recommended average with no significant difference between anaesthesia providers. However, in the absence of an aneroid manometer, ETTcP of tube sizes 7.0 mm and 8.0 mm can be safely approximated to the recommended levels with predetermined inflation volumes.
General anaesthesia with endotracheal intubation and mechanical ventilation is utilized in many surgical procedures to maintain adequate ventilation for the patient. Large volume cuffs are ideal for generating low seal pressures [
However, these cuffs can also generate high intracuff and lateral tracheal wall pressures when inflated beyond the seal pressure. Cuff pressures greater than 30 cm H2O are known to obstruct tracheal capillary blood flow with total occlusion of flow occurring at pressures above 50 cm H2O [
Both excessive and under inflation of endotracheal tube cuffs have adverse complications [
Aneroid manometers for accurate measurement of endotracheal tube cuff pressure are not widely available in Ghana and most Ghanaian anaesthesia providers are inexperience in its use.
Various studies have been conducted with mixed results on experience-based estimation techniques with few of such studies conducted in Ghana. This study therefore seeks to measure the variations of endotracheal tube cuff pressure obtained by estimation techniques and determine its significance in respect to anaesthesia provider groups at Korle-Bu Teaching Hospital.
Endotracheal tube cuff pressures have been recommended to be between 20 - 30 cm H2O [
A lot of studies have been done concerning user experience and the method of inflation of endotracheal tube cuff in relation to the pressure obtained. There are conflicting results concerning the relation between user experience and the cuff pressure obtained in relation to the use of estimation techniques in cuff pressure measurement. Whilst some studies noted that the experience of a user had a significant effect on the endotracheal tube cuff pressure measured by estimation techniques, [
Wujtewicz et al. in 2002 and 2009 noted that errors in estimating endotracheal tube cuff pressure do not improve with experience and in fact tendency to over inflate endotracheal tube cuff is even more among highly experienced users [
Most of the studies on endotracheal tube cuff pressure estimations were situated within the health systems of the developed world, whilst Africa and Ghana in particular have little coverage in the experience of endotracheal tube cuff pressure practices and measurement.
The aim of the study was to assess whether cuff pressures obtained from estimation techniques at Korle-Bu Teaching Hospital differed significantly from the recommended levels of 20 - 30 cm H2O and whether it differed significantly between Physician and Nurse Anaesthetists at the Hospital. In addition, the study also sought to determine an estimated Volume of Air Required (VAR) for cuff inflation to obtain an acceptable cuff pressure for the commonest adult endotracheal tubes used at the hospital in the absence of an aneroid manometer. The study further sought to determine the influence of patients’ demographic characteristics on this VAR. Not only would this contribute to filling the gap in literature on endotracheal tube cuff pressure procedures in Ghana but also influence clinical policy to adopt mandatory monitoring of cuff pressures or its safe estimation in the absence of aneroid manometers.
A cross sectional study was conducted at the surgical theatre suite of the Korle-Bu Teaching Hospital (KBTH) between October 2012 and January 2013.
The survey site was the Korle-Bu Teaching Hospital, a tertiary health care facility in Ghana. It has a bed capacity of 2000 and over 3000 staff according to the annual report of the Korle-Bu Teaching Hospital, 2013. An average of 29, 757 clients are seen per month, average daily outpatient attendance is 1500 and average daily admission is 150.
The study population was elective surgical patients presenting for general surgical procedures (such as mastectomy, cholecystectomy, hernia repairs, excision of intra-abdominal tumours etc.) at the hospital and who gave their informed consent except:
1) Patients who had cough and sore throat before operation;
2) Patients with difficult endotracheal intubation and repeated endotracheal intubations;
3) Pregnant women;
4) Patients with known anatomical abnormalities of larynx and trachea;
5) Patients whose surgical procedures were done in the prone position;
6) Patients below the age of twelve years;
7) Emergency patients with full stomach;
8) Patients who were intubated with endotracheal tube sizes other than 7.0 mm and 8.0 mm RÜSCH Polyvinylchloride tube.
Using Open Epi 2010 and considering a standard deviation value of 21.6 [
After obtaining an ethical and protocol review approval, anaesthesia providers were not informed of the intention of determination of endotracheal tube cuff pressure measurement practices. This was done in order to protect possible manipulation of the results. To further avoid bias each anaesthesia provider anaesthetised only one of the sampled cases. General anaesthesia was induced by intravenous bolus of induction agent (thiopentone or propofol) and intubation and subsequent paralysis was achieved solely with vecuronium. Patients were intubated with RÜSCH high volume low pressure cuff endotracheal tube (7.0 mm for females and 8.0 mm for males). Anaesthesia providers insert the endotracheal tube and the cuff is either inflated by the provider himself or by the assistant. The anaesthesia provider always checks that the cuff is properly inflated using an estimation technique based on their experience. Cuff pressures obtained by estimation techniques were measured by the investigator directly using aneroid manometer (RÜSCH Endotest for low pressure cuffs, CE 0124, made in Germany) via a three way tap after 5 minutes of intubation (after securing the endotracheal tube). The estimation techniques used by the anaesthesia providers were also noted. The aneroid manometer measures pressures from 0 - 120 cm H2O. A syringe was then used to fully empty the cuff via the 3rd port of the three way tap. The cuff was then refilled with air in increments of 1.0 ml until a cuff pressure of 20.0 cm H2O was obtained. The Volume of Air Required to obtain a cuff pressure of 20 cm H2O was noted. The cuff pressure was maintained at 20 cm H2O thereafter. Anaesthesia was maintained with an inhalational agent (halothane or isoflurane) in an oxygen-air mixture. Nitrous oxide was not used in this study. The demographic characteristics of the patients (age, weight and height) were also documented.
Data was captured using Microsoft Excel 2007 Database. Analysis was done with Statistical Package for the Social Sciences (SPSS) software version 18.0. Survey data were analyzed by simple descriptive statistics (i.e. mean, proportions, ratios and percentages) and summarized in tables. An independent t-test was used to measure the statistical variations in the cuff pressures using estimation techniques in relation to recommended levels as well as the significant difference of mean volume of air required to achieve a cuff pressure of 20 cm H2O. Grouped t-test was used to determine the significant differences in cuff pressure among doctors and nurses using estimation techniques at the 95% confidence interval. A p-value of < 0.05 was judged as significant.
Ethical Approval for the survey was obtained from the Ethical and Protocol Review Committee of University of Ghana Medical School (Protocol Identification Number: MS-Et/M.3-P4.4/2012-2013). Clearance was also received from the Management of the Korle-Bu Teaching Hospital and Heads of Clinical units where survey was conducted.
Demographic Characteristics
The study involved eighty-one (81) patients made up of 49.4% males and 50.6% females. The mean age (years), weight (kg) and height (cm) of the patients was 45.4 years, 77.0 kg and 164.2 cm respectively (
Type of Anaesthetic Provider
The study involved 33 (40.7%) Physician Anaesthetists (PA) and 48 (59.3%) Nurse Anaesthetists (NA) who anaesthetised the patients.
Technique of cuff pressure measurement by anaesthesia providers
Out of the 33 physician anaesthetists, 32 used an estimation technique to measure the cuff pressure whilst one did not measure nor estimate the cuff pressure at all during general anaesthetic procedures.
All the 48 nurse anaesthetists measured the cuff pressure using an estimation technique (
Endotracheal Tube Logistics
The endotracheal tube sizes used for the study were 7.0 mm, 40 (49.4%) and 8.0 mm, 41 (50.6%).
Percentages of endotracheal tube cuff pressure measured after intubation by anaesthesia providers for various ranges.
Of the eighty-one (81) cases, 6.25% of the cuff pressures measured were within the recommended range of 20 - 30 cm H2O, 15% of cuff pressures measured were between 30 - 40 cm H2O and 78.75% of measured cuff
Factor | N | Minimum | Maximum | Mean | Std. Deviation |
---|---|---|---|---|---|
Age of patients | 81 | 15 | 78 | 45.4 | 14.7 |
Height of patients | 81 | 148 | 187 | 164.2 | 8.5 |
Weight of patients | 81 | 42 | 126 | 77.0 | 18.1 |
Source: research survey.
pressures were above 40 cm H2O. None of the measured cuff pressure were below 20 cm H2O (
Assessment of Recommended Mean Interval
The study sought to assess whether endotracheal tube cuff pressures obtained after intubation by anaesthesia providers differed significantly from the recommended range of 20 - 30 cm H2O. A confidence interval measure was used to determine the mean interval of the sampled observations within a 95% confidence. The results indicated a mean endotracheal tube cuff pressure of 67.83 cm H2O with a 95% Confidence Interval of (61.87, 73.79;
Endotracheal Tube Cuff Pressure per Anaesthetic Provider Group
An independent t-test was used to measure the mean differences in endotracheal tube cuff pressure per anaesthesia provider group at a significance level of 5%. The results indicated that the mean endotracheal tube cuff pressure obtained after intubation by Physician Anaesthetists and Nurse Anaesthetists were 65.36 cm H2O and 69.52 cm H2O respectively (
Method of measuring endotracheal tube cuff pressure | Physician Anaesthetist | Nurse Anaesthetist |
---|---|---|
Use of Aneroid Manometer | 0 | 0 |
Estimation Methods | ||
Minimal Leak Technique | 7 | 8 |
Palpation of pilot balloon cuff | 20 | 28 |
Minimal Occlusive Technique | 2 | 3 |
Use of Predetermined Volume Technique | 3 | 9 |
None | 1 | 0 |
Total | 33 | 48 |
Source: research survey.
t | df | Sig. (2-tailed) | Mean difference | 95% Confidence interval of the difference | ||
---|---|---|---|---|---|---|
Lower | Upper | |||||
Endo tube cuff pressure (cm H2O) | 22.65 | 80 | 0.000 | 67.827 | 61.87 | 73.79 |
Source: research survey.
pressures were ranged between 25 - 120 cm H2O (95 cm H2O) for Physician Anaesthetists and 30 - 120 cm H2O (90 cm H2O) for Nurse Anaesthetists.
Assessment of VAR (ml) to achieve a cuff pressure of 20 cm H2O
An Independent t-test was used to measure the significant difference of mean volume of air required to achieve a cuff pressure of 20 cm H2O for each size of endotracheal tube at 95% Confidence level. The results indicated that the mean volume of air required for endotracheal tube size 7.0 mm was 3.90 ml whilst that for size 8.0 mm was 4.55 ml (
Influence of Demographic Characteristics on VAR to achieve a Cuff Pressure of 20 cm H2O
The study adopted Classical Multiple Regression to measure the relationship between demographic variables such as age, weight and height on the volume of air required to obtain a cuff pressure of 20 cm H2O.
On regression analysis, the model
Y = β0 + β1X1 + β2X2 (1)
where β0 = −0.089;
β1 = 0.031;
β2 = −0.016;
X1 = Age (years);
X2 = Weight (Kg).
Thus
Y = −0.089 + 0.031 (age in years) − 0.016 (weight in kilograms)
where Y = VAR to achieve a cuff pressure of 20 cm H2O.
The results indicated that age and weight of patients were statistically significant at 95% Confidence level in explaining volume of air required. In contrast, height did not have a statistically significant effect on volume of air required to obtain a cuff pressure 20 cm H2O (
Group of anaesthesia provider | N | Mean | Std. deviation | Std. error mean | p-value | |
---|---|---|---|---|---|---|
Endotracheal tube cuff pressure (cm H2O) | Physician Anaesthetist | 33 | 65.36 | 28.073 | 4.887 | |
Nurse Anaesthetist | 48 | 69.52 | 26.313 | 3.798 | 0.499 |
Source: research survey.
Size of endotracheal tube | N | Mean | Std. deviation | p-value | |
---|---|---|---|---|---|
Volume of air required to obtain a cuff pressure of 20 cm H2O | 7.0 mm | 40 | 3.90 | 1.13 | |
8.0 mm | 41 | 4.55 | 0.95 | 0.006 |
Source: research survey.
Demographic characteristic of patients | Coefficients | t-value | p-value. | |
---|---|---|---|---|
(β) | Std. error | |||
Age | 0.031 | 0.008 | 3.799 | 0.000 |
Weight | −0.016 | 0.007 | −2.420 | 0.018 |
Height | 0.025 | 0.014 | 1.843 | 0.069 |
Source: research survey.
The mean endotracheal tube cuff pressure obtained from this study was 67.83 cm H2O (
In addition, 6.3% of the cuff pressures measured were within the recommended range of 20 - 30 cm H2O (
None of the cuff pressures measured was below the recommended range (
Experienced anaesthesia providers are expected to properly manage endotracheal tube cuff pressures. In this study, it was noted that there was no statistically significant difference in cuff pressures measured between the two groups of anaesthesia providers studied namely Physician anaesthetist and Nurse anaesthetist (p-value = 0.499). This shows that experience does not necessarily confer proper cuff pressure management in the absence of an aneroid manometer. This finding is similar to other comparable studies [
Although there was no statistically significant difference in cuff pressures between the anaesthesia providers studied, these results reflect the management of endotracheal tube cuff pressure at Korle-Bu Teaching Hospital and the anaesthesia providers studied. This finding might be fairly representative countrywide but variations could exist due to institutional differences in anaesthesia practice.
In this study (
Patient’s age and weight had a statistically significant influence in explaining the volume of air required to attain a cuff pressure of 20 cm H2O (
From
Coefficient | Std. error | t-value | p-value | |
---|---|---|---|---|
Constant | −0.089 | 2.291 | −0.039 | 0.969 |
Source: research survey. R2 = 0.182.
pressure of 20 cm H2O was:
Y = −0.089 + 0.031(age in years) − 0.016 (weight in kilograms)
where Y = volume of air required to achieve a cuff pressure of 20 cm H2O.
Although a significant regression equation for the model was obtained, it was not useful for prediction of the volume needed to achieve a cuff pressure of 20 cm H2O as the associated R squared for the model was 0.182. This implies that the prediction of the volume of air required contributed by the age and weight of a patient is only 18.2%.
Anaesthesia providers can however appropriately estimate volume of air required to approximate cuff pressure to 20 cm H2O for size 7.0 mm tube for females and size 8.0 mm tube for males using the predetermined volumes obtained from
The results of this study should be viewed in light of the following limitations. Data for the study was collected at one institution over a period of time, and therefore it is possible that the anaesthesia providers may have changed their endotracheal tube cuff inflation practices because their patients could be included in the study. It was also noticed that the endotracheal tube cuff was mostly inflated by the anaesthetic assistants, and therefore failure on the part of the anaesthetic providers to check the endotracheal tube cuff pressure may wrongly implicate them in poor endotracheal tube cuff pressure management. The aneroid manometer used in the study measured cuff pressures from 0 - 120 cm H2O hence cuff pressures above 120 cm H2O could not be measured.
This study revealed that cuff pressures measured by estimation techniques were higher than the recommended range between anaesthesia providers at Korle-Bu Teaching Hospital. Cuff pressures should be routinely measured using a standard manometer so as to reduce complications of high cuff pressures.
The study also revealed no statistically significant difference in the measured cuff pressures between Physician anaesthetist and Nurse anaesthetist at Korle-Bu Teaching Hospital; therefore cuff pressure optimisation has no association with experience of anaesthesia provider. In a large teaching hospital such as the study site, efforts should be made to use aneroid manometers for accurate monitoring of endotracheal tube cuff pressure for optimum patient care. However, in a resource limited setting, endotracheal tube cuff pressures of tube sizes 7.0 mm and 8.0 mm can safely be approximated to the recommended levels with predetermined inflation volumes.
The authors have no conflicts of interest to declare, financial or otherwise.
We are thankful to all health workers and patients in the Surgical Department of the Korle-Bu Teaching Hospital who participated in the study and for the support received from staff of the Department of Anaesthesia, University of Ghana School of Medicine and Dentistry, College of Health Sciences, University of Ghana.
Ebenezer OwusuDarkwa,FrankBoni,EugeniaLamptey,YawAdu-Gyamfi,ChristianOwoo,RobertDjagbletey,Alfred EdwinYawson,EdmundAyesu,Daniel AkwanfoYaw Sottie, (2015) Estimation of Endotracheal Tube Cuff Pressure in a Large Teaching Hospital in Ghana. Open Journal of Anesthesiology,05,233-241. doi: 10.4236/ojanes.2015.512042