Apnea testing: the effects of insufflation catheter size and flow on pressure and volume in a test lung.

BACKGROUND

The apnea test is used to determine the absence of respiratory drive when determining brain death. Current guidelines for performing the apnea test do not specify the size of insufflation catheter (IC) to use with each endotracheal tube (ETT) size, despite case reports describing procedure-related complications with the use of various IC sizes. We studied the effect of the ratio of IC outer diameter to ETT inner diameter on the pressure and volume generated within the lungs during the apnea test.

METHODS

We tested ETTs with inner diameters of 6.0-10.0 mm, IC outer diameters of 10-16 French, and oxygen-supply tubing, at oxygen flows of 6-15 L/min, in an intubation manikin connected to a test lung.

RESULTS

The multivariate analysis of variance method identified significant differences in the pressures and volumes during the apnea test (P < .001), and the Tukey method identified significant differences in the pressures and volumes associated with IC/ETT ratios ≥ 0.7 and < 0.7 (P < .05).

CONCLUSIONS

An IC with an outer diameter < 70% of the ETT inner diameter, at 6 L/min, may prevent inappropriate lung pressure and volume during the apnea test. This recommendation, coupled with current American Academy of Neurology guidelines for the determination of brain death, may reduce the risk of procedure-related complications.