Brain Death

Published on 07/03/2015 by admin

Filed under Critical Care Medicine

Last modified 22/04/2025

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Chapter 60 Brain Death

10 How do you perform apnea testing?

Brain-dead patients must demonstrate an absence of respiratory drive. This is defined by an increase in PaCO2 and no discernible respiration. Prerequisites for apnea testing include the following:

See Box 60-3.

Box 60-3 Procedures for Apnea Testing

image Preoxygenate for at least 10 minutes with 100% oxygen to a PaO2 >200 mm Hg.

image Reduce ventilation frequency to 10 breaths per minute to eucapnia.

image Reduce positive end-expiratory pressure (PEEP) to 5 cm H2O (oxygen desaturation with decreasing PEEP may suggest difficulty with apnea testing).

image If pulse oximetry oxygen saturation remains >95%, obtain a baseline blood gas level (PaO2, PaCO2, pH, bicarbonate, base excess).

image Disconnect the patient from the ventilator.

image Preserve oxygenation (e.g., place an insufflation catheter through the endotracheal tube and close to the level of the carina and deliver 100% O2 at 6 L/min).

image Look closely for respiratory movements for 8 to 10 minutes. Respiration is defined as abdominal or chest excursions and may include a brief gasp.

image Abort if systolic blood pressure decreases to <90 mm Hg.

image Abort if oxygen saturation measured by pulse oximetry is <85% for >30 seconds.

image Retry procedure with T-piece, continuous positive airway pressure 10 cm H2O, and 100% O2 12 L/min.

image If no respiratory drive is observed, repeat blood gas analysis (PaO2, PaCO2, pH, bicarbonate, base excess) after approximately 8 minutes. If there is any reason to abort the test because of instability of the patient’s condition, draw an arterial blood gas sample immediately before reconnecting the ventilator.

image If respiratory movements are absent and arterial PaCO2 is ≥60 mm Hg (or 20 mm Hg increase in arterial PCO2 over a baseline normal arterial PCO2), the apnea test result is positive (i.e., supports the clinical diagnosis of brain death).

image If the test is inconclusive but the patient is hemodynamically stable during the procedure, it may be repeated for a longer period of time (10-15 minutes) after the patient is again adequately preoxygenated.

13 What ancillary tests can help with diagnosing brain death?

Testing can be divided into either cerebral arterial anatomic or flow studies versus studies of brain electrical activity.

image Flow studies

image Measures of brain electrical activity