[Barotrama during apnea testing for the determination of brain death]

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, O₂ catheters 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 O₂ catheter 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 PO₂ reduction (-59 vs. -32 mmHg, p = 0.72), rate of PCO₂ rise (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 PCO₂ rise (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).

CONCLUSION

Both methods of O₂ supplementation are associated with similar changes in arterial PO₂ and PCO₂. Performance of ABGs at regular intervals shortens apnea test duration and may avoid excessive pH reduction and consequent hemodynamic effects.

Pneumothorax as a Complication of Apnea Testing for Brain Death

BACKGROUND

Pneumothorax is an under-recognized complication of apnea testing performed as part of the neurological determination of death. It may result in hemodynamic instability or even cardiac arrest, compromising ability to declare brain death (BD) and viability of organs for transplantation. We report three cases of pneumothorax with apnea testing (PAT) and review the available literature of this phenomenon.

METHODS

Series of three cases supplemented with a systematic review of literature (including discussion of apnea testing in major brain death guidelines).

RESULTS

Two patients were diagnosed with PAT due to immediate hemodynamic compromise, while the third was diagnosed many hours after BD. An additional nine cases of PAT were found in the literature. Information regarding oxygen cannula diameter was available for nine patients (range 2.3-5.3 mm), and flow rate was available for ten patients (mean 11 L/min). Pneumothorax was treated to resolution in the majority of patients (n = 8), although only six completed apnea testing following diagnosis/treatment of pneumothorax and only three patients became organ donors afterward. Review of major BD guidelines showed that although use of low oxygen flow rate (usually ≤ 6 L/min) during apnea testing is suggested, the risk of PAT was explicitly mentioned in just one.

CONCLUSION

Development of PAT may adversely affect the process of BD determination and could limit the opportunity for organ donation. Each institution should have preventive measures in place.

EEG guidelines in the diagnosis of brain death

In France, for the determination and diagnostic validation of brain death the law requires either two EEG recordings separated by a 4-hour observation period, both showing electrocerebral inactivity; or cerebral angiography examination. Since EEG is available in most hospitals and clinics, it is often used in this indication, at the patient's bedside, especially in the context of organ donation. However, very precise methodology must be followed. The last French guidelines date back to 1989, before the development of digital EEG recording. We present the new guidelines from the Société de Neurophysiologie Clinique de Langue Française. Electrocerebral inactivity may be confirmed when a 30-minute good quality EEG recording shows complete electrocerebral silence, defined as no cerebral activity greater than 2 uV, having first ruled out the possible influence of sedative drugs, metabolic disorders or hypothermia. In the presence of sedative drugs, CT brain angiography will be the gold standard test for this diagnosis. In the newborn, the utmost caution is indicated since electrocerebral inactivity can be observed in the absence of cerebral death. In the infant, the criterion for the observation period to be respected between both EEG recordings needs to be more clearly refined.

[French guidelines on electroencephalogram]

Electroencephalography allows the functional analysis of electrical brain cortical activity and is the gold standard for analyzing electrophysiological processes involved in epilepsy but also in several other dysfunctions of the central nervous system. Morphological imaging yields complementary data, yet it cannot replace the essential functional analysis tool that is EEG. Furthermore, EEG has the great advantage of being non-invasive, easy to perform and allows control tests when follow-up is necessary, even at the patient's bedside. Faced with the advances in knowledge, techniques and indications, the Société de Neurophysiologie Clinique de Langue Française (SNCLF) and the Ligue Française Contre l'Épilepsie (LFCE) found it necessary to provide an update on EEG recommendations. This article will review the methodology applied to this work, refine the various topics detailed in the following chapters. It will go over the summary of recommendations for each of these chapters and underline proposals for writing an EEG report. Some questions could not be answered by the review of the literature; in those cases, an expert advice was given by the working and reading groups in addition to the guidelines.

A critique of the apneic oxygenation test for the diagnosis of "brain death"

OBJECTIVE

To determine the reliability and safety of the apneic oxygenation test to diagnose brain death for the purpose of organ donation.

DATE SOURCES

Published scientific literature in Medline database, organ donation guidelines and neurophysiological principles described in medical textbooks.

STUDY SELECTION

Articles on brain death, apnea testing, and radionuclide scintigraphy.

DATA EXTRACTION AND SYNTHESIS

Hypercarbia with a target Paco2 of 60 mm Hg (8.0 kPa) must be reached before apnea is deemed consistent with brain death in some clinical guidelines, whereas a level of 50 mm Hg (6.7 kPa) is required in another. However, the sensitivity and specificity of the test are doubtful because some patients have commenced spontaneous respiration >60 mm Hg (8.0 kPa) and high levels of Paco2 may cause CO2 narcosis. Furthermore, the test may be harmful if the brain stem is responsive because hypercarbia may also cause intracranial hypertension and contribute to brain damage. Although guidelines for organ donation recommend the test as an essential component of brain death diagnosis, it is often not performed or performed inadequately. Wide variation in conduct of the test has prompted calls for standardization.

CONCLUSIONS

: The apneic oxygenation test is unreliable in the diagnosis of brain death. It is scientifically flawed and hypothesized to cause brain death. In lieu of this test, a reliable test of brain perfusion should be mandatory, whereas the apneic oxygenation test, if performed at all, should be restricted to demonstration of apnea after brain perfusion has been shown to be absent.

Diagnosis of brain death

Brain death (BD) should be understood as the ultimate clinical expression of a brain catastrophe characterized by a complete and irreversible neurological stoppage, recognized by irreversible coma, absent brainstem reflexes, and apnea. The most common pattern is manifested by an elevation of intracranial pressure to a point beyond the mean arterial pressure, and hence cerebral perfusion pressure falls and, as a result, no net cerebral blood flow is present, in due course leading to permanent cytotoxic injury of the intracranial neuronal tissue. A second mechanism is an intrinsic injury affecting the nervous tissue at a cellular level which, if extensive and unremitting, can also lead to BD. We review here the methodology of diagnosing death, based on finding any of the signs of death. The irreversible loss of cardio-circulatory and respiratory functions can cause death only when ischemia and anoxia are prolonged enough to produce an irreversible destruction of the brain. The sign of such loss of brain functions, that is to say BD diagnosis, is fully reviewed.

[Barotrauma by Venturi effect during apnea testing for the determination of brain death. Should it change the terms of application of this test?]

The clinical diagnosis of brain death is based on three clinical criteria, one of them being the abolition of the spontaneous breathing shown by an apnoea testing [1,2]. During this manoeuvre, oxygen is administered by intratracheal way through oxygen supply tubing inserted into the endotracheal tube. Few cases of barotrauma with tension pneumothorax during this test have been described in the literature bringing to the loss of potential donor or grafts for transplantation. The authors report a new case of tension pneumothorax occurred during an apnoea testing despite the precautionary measures necessary to prevent such a catastrophic complication. In addition to the possible pathophysiologic explanation of the event advanced by the authors, it seems lawful to redefine the practical modalities of implementation of this test to avoid the loss of potential grafts.

The safe limits of mechanical factors in the apnea testing for the diagnosis of brain death

Apneic oxygenation is an apnea testing method in the diagnosis of brain death. In this method, oxygen (O2) is delivered into the trachea via an O2 catheter (O2C). However, barotrauma may develop during O2 insufflation into the trachea. Oxygen catheter diameters, O2 catheter tip position in the trachea, and O2 flow rate have been proposed as causes of barotrauma. This study was designed to highlight the airway pressure changes during apneic oxygenation in a model consisting of an anesthesia bag, which was connected to a pressure transducer and to an endotracheal tube (ETT). The pressure of the system was monitored while delivering O2 continuously to the system through O2C of different diameters, which were placed in the ETT. Tested variables were ETT/O2C ratio, O2C tip position in ETT (proximal 1/3 of the ETT, mid point of the ETT, and distal 1/3 of the ETT) and O2 flow rate (6, 8, and 10 L min(-1)). The increase in the airway pressure significantly correlated with O2C tip position in ETT (p = 0.017). ETT/O2C ratio smaller than 1.75 caused significantly high airway pressures (p < 0.05). The pressure was significantly higher at the flow rate of 10 L min(-1) O2 compared with the flow rate of 6 L min(-1) O2 (p < 0.01). Thus, ETT/O2C ratio, O2C tip position in ETT and O2 flow rate are the important factors that determine the airway pressure in the trachea during O2 insufflation. In conclusion, overlooked mechanical factors dangerously increase airway pressure during apnea testing.

Place de l’EEG dans le diagnostic de mort encéphalique

Brain death diagnosis is based upon several clinical and paraclinical criteria that have been legally defined. There is a medico-legal protocol when brain death diagnosis is made in order to allow organ removal for a possible transplantation. In France, EEG or cerebral arteriography must legally be used to confirm a clinical brain death suspicion. There is a specific procedure to perform an EEG to confirm the diagnosis of brain death. However all the criteria have been made using conventional paper EEG, while numerized is now used. The comparison of EEG recording using both analogical and numerised acquisition allow us to report several recommendations to use EEG for brain death diagnosis.

Efficacy of a T-piece system and a continuous positive airway pressure system for apnea testing in the diagnosis of brain death*

OBJECTIVE

To prospectively compare three methods of apnea testing for the confirmation of brain death.

DESIGN

Prospective, randomized, crossover study.

SETTING

Intensive care unit of a tertiary care university hospital.

PATIENTS

Twenty adult patients requiring apnea testing for confirmation of brain death.

INTERVENTIONS

Ten minute apnea testing was repeated in random order for every patient with the three oxygenation systems: oxygen catheter inserted through the endotracheal tube (oxygen 6 L/min), T-piece system (oxygen 12 L/min), and continuous positive airway pressure (CPAP) system 10 cm H2O (oxygen 12 L/min).

MEASUREMENTS AND MAIN RESULTS

Arterial blood was drawn at 0, 2, 5, and 10 mins of each test. Compared with baseline, Paco2 increased by 30.6 +/- 7.4, 30.0 +/- 7.3 and 30.2 +/- 7.5 mm Hg during the apnea period (p = .96), reaching 73.3 +/- 8.3, 71.6 +/- 11.1, and 72.7 +/- 9.0 mm Hg at the end of the apnea test (p = .73) for the oxygen catheter, the T-piece, and the CPAP, respectively. Pao2 decreased less with the CPAP compared with the oxygen catheter or the T-piece (-22.4 +/- 76, -99.1 +/- 158, and -91.6 +/- 133 mm Hg, respectively, p < .01). In two patients, apnea testing could not be completed with the oxygen catheter and the T-piece because of desaturation, although it could be completed with the CPAP.

CONCLUSIONS

The T-piece and the CPAP systems are effective alternatives to the standard oxygen catheter technique for apnea testing. Oxygenation was best maintained with the CPAP system, which can be useful in some patients.

Apnea testing for the diagnosis of brain death

OBJECTIVES

A review is given on various methods, preconditions and pitfalls of apnea testing for the diagnosis of brain death.

MATERIALS AND METHODS

An extensive medical data base search was implemented by information gathered from books and our own experience with more than 2000 apnea tests.

RESULTS

While testing for apnea (AT) is considered indispensable worldwide, recommendations and handling differ. Rather than relying on elapsed time, a specific target value for the partial arterial pressure of carbon dioxide (PaCO2) should be aimed at being the maximum physiological stimulus for respiration. Methodological points are elaborated upon in detail for apneic oxygenation and hypoventilation.

CONCLUSION

AT is an indispensable element of diagnosing brain death. Although with proper handling and adequate precautions AT is safe, it should be performed as a last resort. An international agreement on target values for the PaCO2 is desirable.