Abstract
Introduction
The use of continuous positive airway pressure has been shown to improve the tolerance of the apnea test, a critical component of brain death evaluation. The ability to deactivate the apnea backup setting has made apnea testing possible using several conventional mechanical ventilators. Our goal was to evaluate the safety and efficacy of apnea testing performed on mechanical ventilation, compared with the oxygen insufflation technique, for the determination of brain death.
Methods
This was a retrospective study. In 2016, our institution approved a change in policy to permit apnea testing on conventional mechanical ventilation. We examined the records of consecutive adults who underwent apnea testing as part of the brain death evaluation process between 2016 and 2022. Using an apnea test technique was decided at the discretion of the attending physician. Outcomes were successful apnea test and the occurrence of patient instability during the test. This included oxygen desaturation (SpO2) < 90%, hypotension (mean arterial pressure < 65 mm Hg despite titration of vasopressor), cardiac arrhythmia, pneumothorax, and cardiac arrest.
Results
Ninety-two adult patients underwent apnea testing during the study period: 58 (63%) with mechanical ventilation, 32 (35%) with oxygen insufflation, and 2 (2%) lacked documentation of technique. Apnea tests could not be completed successfully in 3 of 92 (3%) patients—two patients undergoing the oxygen insufflation technique (one patient with hypoxemia and one patient with hypotension) and one patient on mechanical ventilation (aborted for hemodynamic instability). Hypoxemia occurred in 4 of 32 (12.5%) patients with oxygen insufflation and in zero patients on mechanical ventilation (p = 0.01). Hypotension occurred during 3 of 58 (5%) tests with mechanical ventilation and 4 of 32 (12.5%) tests with oxygen insufflation (p = 0.24). In multivariate analysis, the use of oxygen insufflation was an independent predictor of patient instability during the apnea test (odds ratio 37.74, 95% confidence interval 2.74–520.14).
Conclusions
Apnea testing on conventional mechanical ventilation is feasible and offers several potential advantages over other techniques.
Key Points:
- Study Objective: Evaluates the feasibility and safety of using conventional mechanical ventilation for apnea testing in brain death diagnosis.
- Patient Population: Included 92 adult patients; 63% tested with mechanical ventilation, and 35% with oxygen insufflation.
- Key Findings: Hypoxemia occurred in 12.5% of patients tested with oxygen insufflation but in none tested with mechanical ventilation.
- ARDS and ECMO Patients: Mechanical ventilation showed superior safety in high-risk patients, including those with ARDS or on ECMO.
- Cardiopulmonary Stability: Mechanical ventilation was associated with significantly fewer episodes of overall instability (5.2% vs. 22% with oxygen insufflation).
- Testing Success Rate: Apnea testing on mechanical ventilation was successfully completed in all but one case, whereas two oxygen insufflation cases failed due to hypoxemia or hypotension.
- Practical Advantages: Mechanical ventilators allowed precise PEEP control, avoided disconnections, and enabled detection of subtle respiratory efforts via ventilator scalar waveforms.
- Guideline Integration: Findings align with recent recommendations endorsing ventilator-based apnea testing for better safety and efficacy.
- Statistical Insights: Multivariate analysis identified oxygen insufflation as an independent predictor of patient instability (OR 37.74).
- Limitations: Retrospective design, small sample size, and lack of progressive oxygenation and CO2 monitoring data during tests.
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