Apnea Test Safety in Brain Death: A Single-Center Retrospective Cohort Analysis

Abstract

Background: The apnea test, which is considered positive when no spontaneous breathing movements are observed following maximal hypercapnia (PaCO₂ > 55 mm Hg) respiratory center stimulation, was critically evaluated in this study by assessment of blood gas analyses performed during brain death protocols from 2010 to 2017, in the intensive care units of the Universidade Estadual de Campinas (UNICAMP).

Methods: A retrospective cohort analysis based on the intensive care unit and Transplant Organ Search Organization data banks. Blood gas analyses before (pre-first and -second apnea tests) as after (after-first and -second apnea tests) were assessed. Descriptive statistical analyses of the numerical variables (such as pH, PaO₂, PaCO₂, HCO_3, SatO₂) with mean values and standard deviation, medians, and quartiles were performed. The Student’s t-test was used for pairwise group comparisons. A P < 0.05 level was adopted for significance.

Results: Eighty-seven protocols were evaluated. The mean apnea test duration was 11 min. All of the patients were under vasoactive drugs. Only five apnea tests were interrupted before the end at 10 min due to rapid desaturation (SatO₂ < 90%), with no invalidated apnea test. Mean and standard deviation of blood gas tests assessed before the first apnea test were: pH 7.35(± 0.10), PaO₂ 252.15 mm Hg (± 114.11), PaCO₂ 42.78 mm Hg (± 10.84); after the first apnea test: pH 7.11(± 0.08), PaO₂ 208.39 mm Hg (± 112), PaCO₂ 82.43 mm Hg (± 16.91); before the second test: pH 7.33 (± 0.09), PaO₂ 253.56 mm Hg (± 105.36), PaCO₂ 43.76 mm Hg (± 9.67); following the second apnea test: pH 7.11 (± 0.10), PaO₂ 200.1 mm Hg (± 116.45), PaCO₂ 84.98 mm Hg (± 20.21). The pH, PaO₂, and PaCO₂ values before and after the first and second apnea tests have shown statistically significant differences (P < 0.0001).

Conclusions: The apnea test was safe, blood gas test results are similar to those described in the literature, severe hypoxemias were prevented by a quick reconnection to the mechanical ventilation; and marked hypercapnia and acidemia following the apnea test were found, but no test was invalidated.

J Neurol Res. 2021;11(1-2):14-19
doi: https://doi.org/10.14740/jnr646