Apnea Test

Norm of Apnea Test

Negative test (absence of brain death).
Spontaneous respiratory effort occurs after mechanical ventilation is stopped.
Positive test (presence of brain death).
Absence of spontaneous respiratory effort throughout test (up to 8 minutes for adults and up to 15 minutes for pediatrics), Paco2 ≥60 mm Hg or 20 mm Hg higher than baseline value.

 

Usage of Apnea Test

Determination of the absence (or presence) of spontaneous breathing when one is testing for brain death; evaluation of the intracranial hemodynamic status in carotid occlusive disease.

 

Description of Apnea Test

The apnea test is part of a neurologic evaluation that tests for the respiratory reflex in clients suspected of having brain death. It is performed with a full neurologic examination, clinical history that includes a central nervous system event, and other confirmatory tests to determine brain death. Brain death is the term used when the entire brain, including the brainstem, has irreversibly stopped functioning. Brain death cannot be determined in clients receiving neuromuscular blockers, or with low core-body temperatures (such as ≤32.2 degrees C).

 

Professional Considerations of Apnea Test

Consent form recommended from spokesperson for the client.

Risks
Cardiac arrest, pneumoperitoneum, pneumothorax.
Contraindications
Use for purposes other than those described in the previous discussion is contraindicated.

 

Preparation

1. Obtain and document baseline Paco2 value.
2. Determine if client meets requirements for apnea testing:
   • Pco2 = 40 mm Hg
   • Mean arterial pressure (MAP) >54 mm Hg
   • Positive fluid balance in previous 6 hours
   • Absence of the possibility of acute drug or alcohol intoxication
   • Absence of the presence of any centrally acting drugs that could depress respiration
3. Obtain a pulse oximeter, ice, oxygen T-piece, and arterial blood gas kit.

 

Procedure

1. Position pulse oximetry probe on client. Set heart rate, blood pressure, and respiratory rate alarms. Monitor all throughout the test.
2. Preoxygenate client with 100% oxygen for 10 minutes.
3. Remove client's gown or clothing from the chest and abdominal area to allow visualization of respiratory muscle efforts.
4. Discontinue mechanical ventilation. Apply oxygen through a T-piece at 6 L/min. Monitor for spontaneous respiratory effort.
   • If no respiratory effort is noted after 5–8 minutes, obtain an arterial blood gas sample and restart mechanical ventilation.
   • Observe chest for spontaneous respirations or any respiratory effort.
   • Discontinue the test if any of the following occur:
     1. Presence of spontaneous respiratory effort
     2. Hemodynamic instability
5. Test is repeated at least 6–12 hours later.

 

Postprocedure Care

1. Document procedure, including methodology, length of apneic time, baseline and ending Paco2 values, stability of vital signs, and apneic status.
2. For positive tests, request organ donation, as and when appropriate.

 

Client and Family Teaching

1. Organ and tissue donation rates are higher when families or significant others receive a careful and thorough explanation of the concept of brain death.

 

Factors That Affect Results

1. Paco2 rises approximately 3 mm Hg each minute while the client is apneic and not receiving mechanical ventilation.
2. Results must be interpreted with extreme caution in clients with brain injury. Caution should be used in determining brain death when the cause of the brain injury is not known and in high cervical spine fracture in which there is damage to the spinal cord.
3. Posturing may make detection of respiratory effort impossible.

 

Other Data

1. The neurologic examination in brain death reveals the absence of spontaneous reflexes, absence of response to pain, and absence of brainstem reflexes, including the respiratory reflex.