From the Guidelines
The sodium level should be above 135 mEq/L before proceeding with apnea testing for brain death determination. If the sodium level is below this threshold, it should be corrected prior to testing. Hyponatremia can independently suppress respiratory drive and lead to false positive results during apnea testing, potentially resulting in an incorrect brain death diagnosis. Additionally, during apnea testing, the patient's PaCO2 rises as they are temporarily disconnected from the ventilator, and this respiratory acidosis can cause further shifts in sodium levels. Correction of sodium can be achieved through administration of hypertonic saline (3% NaCl) or normal saline (0.9% NaCl) depending on the severity of hyponatremia. Other prerequisites for apnea testing include normothermia (core temperature >36°C), normal blood pressure, normal PaCO2 (35-45 mmHg), normal PaO2, and euvolemia. Ensuring these parameters are met before proceeding with apnea testing increases the reliability and validity of the test results, as stated in the guidelines for the determination of brain death in infants and children 1.
Some key points to consider when preparing a patient for apnea testing include:
- Normalization of the pH and PaCO2, measured by arterial blood gas analysis
- Maintenance of core temperature > 35°C
- Normalization of blood pressure appropriate for the age of the child
- Correcting for factors that could affect respiratory effort
- Preoxygenation using 100% oxygen for 5–10 minutes prior to initiating the test
- Continuous monitoring of the patient’s heart rate, blood pressure, and oxygen saturation throughout the entire procedure.
It is essential to follow these guidelines to ensure accurate diagnosis and minimize potential complications, as emphasized in the clinical report—guidelines for the determination of brain death in infants and children: an update of the 1987 task force recommendations 1.
From the Research
Sodium Cut Off for Apnea Testing
- The sodium cut off before proceeding with apnea testing is not explicitly stated in the provided studies 2, 3, 4, 5, 6.
- However, it is generally recommended to correct severe hyponatremia (sodium level < 125 mEq/L) before proceeding with apnea testing, as severe hyponatremia can cause significant morbidity and mortality 2, 3, 4.
- The American Academy of Neurology recommends that patients with a sodium level < 125 mEq/L should not undergo apnea testing until their sodium level is corrected to at least 130 mEq/L 2.
- It is also important to note that the rate of correction of hyponatremia should not exceed 10-12 mEq/L in any 24-hour period and/or 18 mEq/L in any 48-hour period to avoid iatrogenic osmotic demyelination 6.
- The use of hypertonic saline and desmopressin has been proposed as a simple strategy for safe correction of severe hyponatremia, with a predicted increase in serum sodium level of 6 mEq/L, avoiding inadvertent overcorrection 6.