1Department of Anaesthesia and Intensive Care, Cairns Base Hospital, The Esplanade, Cairns 4870, Australia 2Department of Anaesthesia and Intensive Care Medicine, Leopold-Franzens University, A-6020 Innsbruck, Austria*Corresponding author
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Accepted for publication: September 7, 2001
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Abstract |
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Methods. A 16FG gastric tube was positioned with the tip in the mid-oesophagus with the proximal end attached to an injection port with a one-way valve. Four observers participated in the study. Observers were paired and each pair studied 15 patients. Each patient underwent four test sequences in random order, two by each observer. Each test sequence comprised one observer injecting different volumes of air (0.25 ml, 0.5 ml, 1 ml, 2 ml, 3 ml, 4 ml, 5 ml, 10 ml, 15 ml and 0 ml as a control) in random order whilst the second blinded observer listened with a stethoscope over the epigastrium. Each randomized volume was injected rapidly at 5 s intervals for 1 min. The number of injections required to detect air entering the stomach was recorded. The stomach was deflated between each test sequence.
Results. To detect air entering the stomach with 95% confidence, 11 injections were required for 0.25 ml; 7 for 0.5 ml; 3 for 1 ml; 2 for 2 ml and 3 ml, and 1 for 4 ml. The mean (range) inter- and intraobserver reliability was 0.73 (0.710.75) and 0.76 (0.760.89), respectively. The incidence of false positives was 21% (25/120) and the incidence of false negatives was 10% (103/1080), making the specificity and sensitivity 79% and 91%, respectively.
Conclusions. We conclude that epigastric auscultation can detect gastric insufflation of 0.25 ml air after 11 breaths and 4 ml air after one breath with 95% confidence. Inter- and intraobserver reliability is moderate to excellent. Epigastric auscultation should be repeated to reduce the risk of false positives.
Br J Anaesth 2002; 88: 1279
Keywords: complications, gastric insufflation; ventilation, positive pressure
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Introduction |
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Methods and results |
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Sample size (n=30) was based on data from a pilot study with eight patients with an injected volume of 0.5 ml (reporting a difference of the mean of 1.5 and a SD of 2.7) for a type I error of 0.05 and a power of 0.9. The distribution of data was determined using KolmogoroffSmirnov analysis.5 Inter- and intraobserver reliability was analysed using intraclass correlation coefficient (ICC).6 Scores for statistical measurements with the ICC range from 0 to 1 where 0 shows no reliability and 1 shows perfect reliability. A score 0.75 is graded as excellent reliability, 0.410.74 as moderate reliability and <0.40 as poor reliability.7
The mean (range) age, height and weight were 38 (1881) yr, 172 (151193) cm and 69 (48110) kg, respectively. The male:female ratio was 16:14. There were no missing data points. To detect air entering the stomach with 95% confidence, 11 injections were required for 0.25 ml; 7 for 0.5 ml; 3 for 1 ml; 2 for 2 ml and 3 ml; and 1 for 4 ml. The interobserver reliability between A and B was 0.71 and between C and D was 0.75, with an overall reliability of 0.73. The intraobserver reliability was 0.89, 0.76, 0,76 and 0.76 for observer A, B, C and D, respectively, with an overall value of 0.76. The incidence of false positives was 21% (25/120) and the incidence of false negatives was 10% (103/1080), making the specificity and sensitivity 79% and 91%, respectively. The incidence of false negatives for volumes
4 ml after one breath was 4% (16/360) and 0% after four breaths. No oropharyngeal leaks were detected.
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Comment |
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Our experimental model does not precisely mimic the clinical situation in which gastric insufflation occurs because patients were intubated and a gastric tube was in situ. However, tracheal intubation was necessary for airway protection and to ensure that no additional air leaked into the oesophagus, as might have occurred if a face mask or LMA was used. The gastric tube was necessary to allow known volumes of air to be injected into the oesophagus. Although unlikely, it is also possible that the gastric tube may have interfered with the dynamics of the lower oesophageal sphincter and thus influenced the quality of sound generated as air passed across it into the stomach.
We found a false-positive rate of 21% and a false-negative rate of 10%. This implies that in approximately one in five occasions the clinician will hear air entering the stomach when in fact it is not, and in approximately 1 in 10 occasions will not hear air entering the stomach when in fact it is. Repeated auscultation is likely to reduce the false-positive rate. The clinical importance of small volumes of air entering the stomach with every breath is unknown. We speculate that the healthy stomach will be able to cope with some gas load without insufflation through absorption and movement of the gas into the small bowel. Cricoid pressure is an effective method of preventing gastric insufflation during ventilation with the face mask and probably with other extraglottic airway devices.1
We conclude that epigastric auscultation can detect gastric insufflation of 0.25 ml air after 11 breaths and 4 ml air after one breath with 95% confidence. Inter- and intraobserver reliability is moderate to excellent. Epigastric auscultation should be repeated to reduce the false-positive rate.
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References |
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