2007 OPEN FORUM Abstracts
AN ALTERNATE APNEA TEST TO DETERMINE BRAIN DEATH: CAPNOGRAPHY WITH CARBOGEN ADMINISTRATION
M. Couture1, R. T. Pylant1, C. A. Fancella 1
Background: According to the American Academy of Neurology (AAN) practice guidelines, brain death is the irreversible loss of function of the brain and brainstem. Apnea testing is a primary test in determining brain death, usually by disconnecting the patient's ventilator for up to 10 minutes with supplemental O2 via a catheter inserted into the trachea. Criteria for confirming brain death includes a PaCO2 minimum increase of 20 mm Hg or > 55 mm Hg, and pH < 7.20 with absent respiratory movements. It is possible that the test could compromise viability of organs destined for transplantation. Adverse effects may include pneumothorax, hypoxemia, arrhythmia, hypotension, and cardiac arrest.
OBJECTIVE: This interim study assesses an alternative procedure to determine brain death by administration of carbogen (3% CO2/97% O2) with capnography.1 It is hypothesized that target pH and CO2 can be predicted by adding carbogen to the oxygen inlet of a ventilator.
Methods: Testing occurred after patients met AAN clinical criteria. Pre-oxygenation was not required. An end-tidal (ETCO2) carbon dioxide monitor (NICO, Respironics, Wallingford, CT) was placed close to the endotracheal tube in the ventilator circuit (Puritan Bennett 840, Tyco Healthcare, Pleasanton, CA). An ABG was obtained to calculate a post-apnea test target pH and PaCO2 using the following formula: final pH = (initial pH – 7.20)/ 0.006. The ventilator oxygen hose was attached to a carbogen gas cylinder. Ventilator settings were changed to FIO2 of 100%, pressure sensitivity of -2 cm H2O, and IMV of 4, which was gradually reduced to 1 breath. Ventilator flow patterns were observed for spontaneous breathing. When the target ETCO2 was reached, a post test ABG was obtained. Data were extracted from a retrospective review of 15 patients whose organs were harvested after brain death determination between January 2006 and January 2007.
Results: Multiple regression analysis showed a significant relationship between predicted PaCO2 and post test PaCO2 r = 0.854, r2 = 0.729. p < 0.001 (n=14). One outlier overshot the target PaCO2 and 1 test was stopped at 5 minutes due to systolic blood pressure < 70 mm Hg.
Conclusion: End-point PaCO2 may be predicted using a computational formula with carbogen and capnography in apnea testing.
1. Sharpe MD, Bryan Young G, Harris C. The apnea test for brain death determination: An alternative approach. Neurocritical Care. 2004; 1(3): 363-6.
|Parameter (n=)||Pre-apnea||Post-apnea||Pre-post gradient||p|
|ETCO2 (4)||32.5 ± 5.2||58 ± 12.9||26 ± 9.8||0.013|
(Target = 67.4 ± 10.5)
|38.1 ± 4.49||72.2 ± 13.2||34.1± 12.4||<0.001|
|pH (15)||7.40 ± 0.05||7.17 ± 0.05||0.23 ± 0.06||<0.001|
|PaO2 (15)||164 ± 97.4||341 ± 82.8||177 ± 131.7||<0.001|
A paired student t-test compared pre-apnea and post-apnea variables. Summary data were as follows: mean ± SD, p < 0.05 was considered significant.