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Year : 2004  |  Volume : 52  |  Issue : 3  |  Page : 342--345

Problems associated with the apnea test in the diagnosis of brain death

Gustavo Saposnik, Graciela Rizzo, Adriana Vega, Roberto Sabbatiello, Jorge L Deluca 
 Department of Organ and Tissue Procurement for transplantation. Garrahan Hospital, Buenos Aires University. Buenos Aires, Argentina

Correspondence Address:
Gustavo Saposnik
302-565 Talbot St. London, ON. Canada. N6A 2T1


Background: Brain death is the absence of all cortical functions, including the brainstem. The apnea test (AT) is a necessary requisite to complete this diagnosis. Anecdotal reports describing hypotension and acidosis due to apnea test have been reported. However, there are few studies that evaluate complications or difficulties related to this procedure. Objective: To analyze medical problems associated with the apnea test. Methods and Patients: We analyzed clinical features, potential risk conditions, and problems in 129 brain dead patients during the apnea test. The diagnosis of brain death was made according to the American Academy of Neurology recommendations. Results: Clinical problems during the apnea test were detected in more than two thirds of patients, including: arterial hypotension (12%), acidosis (68%), and hypoxemia (23%). Four patients developed major complications, including: pneumothorax, cardiac arrest, bradycardia, atrial fibrillation and myocardial infarction. Conclusion: The apnea test is not an innocuous procedure. Complications during the AT are more common than reported and limit organ procurement for transplantation. Guidelines for performing the AT should be followed in order to avoid clinical complications.

How to cite this article:
Saposnik G, Rizzo G, Vega A, Sabbatiello R, Deluca JL. Problems associated with the apnea test in the diagnosis of brain death.Neurol India 2004;52:342-345

How to cite this URL:
Saposnik G, Rizzo G, Vega A, Sabbatiello R, Deluca JL. Problems associated with the apnea test in the diagnosis of brain death. Neurol India [serial online] 2004 [cited 2020 Jul 2 ];52:342-345
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Brain Death (BD) has been subject of debate in the last decade.[1],[2] This diagnosis has a broad spectrum of legal, religious, philosophical, ethical, and medical implications. BD has been defined as the irreversible cessation of cerebral functions, including the brainstem. Definition of BD challenged according to the used criteria. Since 1981 several criteria's have been proposed to determine this diagnosis varying from one country to another. The most widely accepted criteria to de termine BD are the guidelines of the American Academy of Neurology (AAN), which include: unresponsiveness or coma, absence of brainstem reflexes, and apnea.[1] The apnea test (AT) is a mandatory criteria to establish the diagnosis of BD. The goal of this procedure is to document the absence of breath once pCO2 arise the appropriate level to stimulate the respiratory center. Nevertheless, this procedure is not innocuous since hypotension, hypoxia or acidosis may occur while performing this practice. As known, hemodynamic and metabolic changes limit the tissue perfusion, the condition of the potential donor, and subsequently, the organ procurement for transplantation.[3],[4],[5] The aim of this study was to analyze clinical problems related to the apnea test in the diagnosis of brain death.

 Materials and Methods

From April 1998 to September 1999, we retrospectively analyzed demographic factors, hemodynamic conditions, clinical features, and etiology of brain injury in a cohort of BD patients who were considered for organ donation. We looked into the presence of changes in the arterial blood pressure, pH, and pO2, before and at the end of the AT.

Diagnosis of BD was made according to the AAN guidelines; AAN Quality standards.[1] It included a sequence of diagnostic test such as a complete neurological examination, apnea test, routine lab, and EEG. The AT was performed following the recommendations of the AAN, which includes delivering 100% O2 (preoxygenate stage). If respiratory movements are absent and arterial pCO2 is >60 mmHg (or 20 mmHg increase of pCO2 over a baseline normal pCO2), the apnea test result is positive (i.e. it supports the diagnosis of BD). If arterial hypotension (systolic blood pressure 7.3, no patient developed pH reduction <7.10 ( p<0.001).

We looked for previous conditions or demographic data that could predispose to difficulties during the AT. There were no differences in sex, age, temperature, neurological examination, catecholamine use, or etiology of BD between patients with or without problems during to AT.

A comparative analysis was performed to determine whether the hemodynamic condition could predispose to problems during the TA by examine arterial blood pressure, pH, and pO2 before performing the AT and before the reconnection to the ventilator [Table:1]. The more common previous conditions were as follows: acidosis (pH<7.3) in 27 patients, hypotension in 13, and hypoxemia in 4 patients. Among 36 patients with one or more previous conditions, 15 (42%) had a reduction in the baseline pH greater than 0.2 points after to the AT. Individuals with previous conditions had higher frequency of problems during the AT than those patients without (80% vs 55%; p=0.03) [Table:1].

Complications during the AT were detected in four patients. All four had cerebral bleeding as the etiology of BD. They also had had previous risk conditions [Table:2]. Patient#4 developed acute changes in the cardiac rhythm (atrial fibrillation) during the apnea test, and subsequently, myocardial infarction.


BD patients may be suitable organ donors, and the apnea test is an essential procedure to establish this diagnosis. However, AT has not been validated in a large series of patients, and there are few studies on the predisposing conditions, nature, and frequency of complications during performing this procedure.[6],[7],[8],[9],[10],[11] Pitfalls in performing the apnea test can be encountered in clinical practice.[1],[12] Any complication during this procedure may limit organ perfusion, the diagnosis of BD, and subsequently the organ procurement for transplantation.

There are anecdotal reports of clinical problems or complications during or after the apnea test.[4],[5],[6],[12] However, prospective studies are lacking in the literature. Gad Bar and other authors reported patients that developed tension pneumothorax during the apnea test.[3],[4] All patients presented arterial hypotension and bradycardia, and finally had a cardiac arrest. Marks and Zisfein mentioned a patient with subcutaneous emphysema and thoracic insuflation during the apnea test.[5]

Wijdicks cautioned against the hypercarbia, acidosis, hypoxemia, and pulmonary edema during the AT.[6] He questioned the safety of this procedure, and suggested the AAN recommendations for performing this procedure be followed in order to avoid clinical complications.

Cardiovascular effects related to the apnea test have been reported in small series, including: a 30% decrease in systemic vascular resistance, an increased cardiac index, hypoxemia, arterial hypotension, and pulmonary hypertension.[9],[11],[12]

Effective tissue perfusion is the cardinal condition to preserve organ function. Prophylactic treatment with vasoreactive drugs has been suggested to prevent hemodynamic complications. However, there is no evidence favoring this intervention.

Several conditions may predispose to these complications, such as: a) Time between the BD diagnosis and performance of the apnea test, and b) Patientīs condition (e.g.: age, COPD, hypotension, hypothermia, acidosis, etc.). However, very few studies have specifically investigated the contribution of these conditions as risk factors when performing the AT.

Goudreau reviewed 145 apnea procedures in 121 patients to determine the frequency of complications and their predisposing factors.[13] Complications occurred in 26% of the procedures. Arterial hypotension was the most common complication (24%). Cardiac arrhythmia occurred in 4/145 (<3%) procedures. The most common predisposing conditions were inadequate preoxygenation, and acidosis. Complications were more common in individuals with inadequate precautions to perform the AT (39% vs 15%, p=0.01). The authors concluded that the AT is performed without adequate precautions or adherence to the AAN guidelines.[13]

We found relevant clinical problems during the AT in two third of the patients. The most frequent complications were acidosis, hypoxemia and arterial hypotension. Patients with pH <7.3, pO2 <90, or arterial blood pressure <100 mmHg had a higher frequency of hemodynamic changes limiting the organ perfusion. Four patients had complications related to the procedure, which implied a myocardium damage or cardiac arrest. In view of their clinico-physiological conditions may be these patients should not have undergone the apnea test.

Our findings are coincident with Goudreau results.[13] However, we found higher frequency of complications (68% vs. 26%) related to the AT. Differences in the predisposing conditions, following the AAN guidelines, and data analysis may explain this results.

In our country, as well as in others, the EEG is a legal requirement to determine the diagnosis of BD. The apnea test is usually performed at the end of the clinical exam and before the EEG. Thus, a cardiac arrest due to a complication during this procedure has legal implications because the BD diagnosis has not been established yet. In other words, the patient has to afford the risk of this test before the brain death is declared.

Because of the aforementioned complications during the apnea test, we believe that this practice is necessary, although not innocuous.

In summary, clinical problems and complications due to the apnea test are more frequent in patients with previous risk conditions (i.e.: arterial hypotension, acidosis) and when the AAN guidelines are not systematically followed. Prospective studies are necessary to establish risk factors and to define the entire spectrum and frequency of complications during this necessary practice.


The authors thank to Dr J.A. Bueri for the critical review and suggestions.


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