Prevention of Hypoxemia During Apnea Testing: A Comparison of Oxygen Insufflation And Continuous Positive Airway Pressure.
BACKGROUND
Apnea testing is an essential step in the clinical diagnosis of brain death. Current international guidelines recommend placement of an oxygen (O2) insufflation catheter into the endotracheal tube to prevent hypoxemia, but use of a continuous positive airway pressure (CPAP) valve may be more effective at limiting arterial partial pressure of O2(PO2) reduction.


METHODS
We performed a multicenter study assessing consecutive apnea tests in 14 intensive care units (ICUs) in two cities utilizing differing protocols. In one city, O2catheters are placed and arterial blood gases (ABGs) performed at intervals determined by the attending physician. In the other city, a resuscitation bag with CPAP valve is attached to the endotracheal tube, and ABGs performed every 3-5 min. We assessed arterial PO2, partial pressure of carbon dioxide (PCO2), pH, and blood pressure at the beginning and termination of each apnea test.


RESULTS
Thirty-six apnea tests were performed using an O2catheter and 50 with a CPAP valve. One test per group was aborted because of physiological instability. There were no significant differences in the degree of PO2reduction (-59 vs. -32 mmHg, p = 0.72), rate of PCO2rise (3.2 vs. 3.9 mmHg per min, p = 0.22), or pH decline (-0.02 vs. -0.03 per min, p = 0.06). Performance of ABGs at regular intervals was associated with shorter test duration (10 vs. 7 min, p < 0.0001), smaller PCO2rise (30 vs. 26 mmHg, p = 0.0007), and less pH reduction (-0.20 vs. -0.17, p = 0.0012). Lower pH at completion of the apnea test was associated with greater blood pressure decline (p = 0.006).


CONCLUSIONS
Both methods of O2supplementation are associated with similar changes in arterial PO2and PCO2. Performance of ABGs at regular intervals shortens apnea test duration and may avoid excessive pH reduction and consequent hemodynamic effects.
University of Calgary, Calgary, AB, Canada. andreas.kramer@albertahealthservices.ca.
Andreas H
AH
Kramer
University of Calgary, Calgary, AB, Canada.
Philippe
P
Couillard
Alberta Health Services, Calgary, Canada.
Ryan
R
Bader
Alberta Health Services, Calgary, Canada.
Peter
P
Dhillon
University of Alberta, Edmonton, Canada.
Demetrios J
DJ
Kutsogiannis
University of Calgary, Calgary, AB, Canada.
Christopher J
CJ
Doig
D000293:Adolescent; D000328:Adult; D001049:Apnea / Q000175:diagnosis*; D001784:Blood Gas Analysis / Q000379:methods* / Q000592:standards; D001926:Brain Death / Q000175:diagnosis*; D002245:Carbon Dioxide / Q000032:analysis; D002648:Child; D045422:Continuous Positive Airway Pressure / Q000379:methods* / Q000592:standards; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000517:prevention & control*; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000032:analysis
D002245:Carbon Dioxide; D010100:Oxygen
Apnea test; Brain death; Continuous positive airway pressure; Partial pressure of carbon dioxide; Partial pressure of oxygen