What is the time frame from cardiac arrest to dilation and fixation of pupils?

Time Frame from Cardiac Arrest to Pupillary Dilation and Fixation

Pupils typically become fixed and dilated approximately 72 hours after cardiac arrest in patients who have poor neurological outcomes, though this is not an absolute timeframe and can vary based on individual factors.

Pupillary Changes After Cardiac Arrest

Pupillary light reflex (PLR) is a critical neurological assessment tool in post-cardiac arrest patients. The timeline for pupillary changes following cardiac arrest follows a pattern:

Immediate Post-Arrest Period

• Immediately after cardiac arrest and during resuscitation, pupils may be reactive in patients who achieve return of spontaneous circulation (ROSC)
• Research shows that 97.5% of patients have reactive pupils within 1 hour after ROSC, even when they received epinephrine and/or atropine during resuscitation 1
• 100% of patients checked within 3 minutes of ROSC had reactive pupils 1

Early Post-Arrest Period (First 24-48 Hours)

• About 29% of patients may have nonreactive pupils on admission before therapeutic hypothermia 2
• Some patients (approximately 28% in one study) with initially nonreactive pupils may regain pupillary reactivity by day 3 2

72-Hour Mark - Critical Timepoint

• The absence of both pupillary light and corneal reflexes at 72 hours after cardiac arrest reliably predicts poor outcome in patients not treated with hypothermia 3
• This is considered a key timepoint for neurological prognostication in post-cardiac arrest patients

Important Clinical Considerations

Medications and Pupillary Response

• Contrary to common belief, standard doses of atropine (0.03 mg/kg) administered during CPR cause only slight pupillary dilation but do not abolish pupillary light reactivity 4
• Epinephrine administration during resuscitation does not abolish PLR in patients who achieve ROSC 1
• Nebulized ipratropium bromide can cause unilateral fixed dilated pupils that may take up to 24 hours to resolve 5

Prognostic Value of Pupillary Assessment

• Bilaterally absent pupillary light reflexes at 72-108 hours from ROSC predict poor outcome with only 1% false-positive rate 3
• Quantitative pupillometry as early as 6 hours post-ROSC can predict poor outcomes:
  • Neurological Pupil index (NPi) < 3 (sluggish) or 0 (nonreactive) strongly correlates with poor outcomes 6
  • All patients with nonreactive pupils (NPi = 0) within 6 hours after ROSC died in one study 6

Confounding Factors

• Hypothermia treatment may delay the timeline for reliable pupillary assessment
• For patients treated with therapeutic hypothermia, neurological examination for prognostication should be performed at least 72 hours after return to normothermia 3
• When fixed and dilated pupils are observed, they are not necessarily associated with large pupil size - 75% of nonreactive pupils were <5mm in diameter in one study 6

Clinical Implications

When evaluating a post-cardiac arrest patient:

1. Do not rely solely on pupillary assessment in the first 24-48 hours
2. Use a multimodal approach to neurological assessment
3. Recognize that fixed and dilated pupils at 72 hours post-arrest (or 72 hours post-rewarming in hypothermia-treated patients) strongly predict poor neurological outcome
4. Consider quantitative pupillometry when available, as it provides more objective assessment than visual examination

Remember that while pupillary changes are important prognostic indicators, they should be interpreted in the context of the patient's overall clinical picture and other neurological assessments.