Apnea Testing Practice to Increase Baseline PaCO2 and Frequency of Blood Gas Analyses

Abstract

Objective: To study the influence of the initial partial pressure of carbon dioxide (PaCO₂) and frequency of blood gas analyses on the positivity rate and safety of apnea testing (AT).

Design: A prospective multicenter cohort study.

Setting: Seven teaching hospitals.

Participants: A total of 55 patients who underwent AT.

Interventions: Patients were divided into 2 groups according to their initial PaCO₂-the experimental group (≥40 mmHg, 27 patients) and the control group (<40 mmHg, 28 patients). Blood gas analysis was performed at 3, 5, and 8 minutes, and vital signs were taken. AT results and complications were compared between the groups.

Results: The initial PaCO₂ of the experimental group was 42.8 ± 2.2 mmHg v 36.4 ± 2.9 mmHg in the controls. The AT positivity rate was 100%. The experimental group needed less time to reach the target PaCO₂ than the control group (4.07 ± 1.27 minutes v 5.68 ± 2.06 minutes; p = 0.001). Twenty-six patients (96.3%) in the experimental group reached the target PaCO₂ in 5 minutes v 17 in the control group (60.7%) (p = 0.001). Seven patients (12.7%) were unable to complete 8-minute disconnection due to hypotension. The experimental group had a slightly lower incidence of hypotension than the control group, but there was no statistical difference (7.4% v 17.9%, p = 0.245).

Conclusion: Increasing the baseline PaCO₂ and doing more blood gas analyses can significantly shorten the time needed for AT and improve the AT positivity rate.

Keywords: apnea testing; brain death; multicenter study; positivity rate; safety.