Hypothermia for newborns with hypoxic ischemic encephalopathy

Question 1

What is the mechanism of HIE?

Answer 1

Impaired cerebral blood flow in the setting of hypoxia
1. Decr blood flow, decr ATP/pump function, lactic acidosis, excitatory amino acids, necrosis
Following resusc/reperfusion, there is a latent period with normalization of oxidative metabolism lasting 6-12h = therapeutic window for neuroprotective interventions
2. 12-36 h, may last 7-14 days with initiation of apoptosis, mitochondrial failure, cytotoxic edema, accumulation of excitatory amino acids and ROS –> cell death.This secondary phase is assoc with worsening of HIE and correlates with poor outcomes

Question 2

What is the indication for hypothermia in neonates with HIE?

Answer 2

Standard of care for mod-severe HIE within 6 hours after birth, neuroprotective, decreased mortality and improved neurodevelopmental outcomes

Question 3

What are the criteria for hypothermia in neonates with HIE?

Answer 3

Cooling criteria: >=36wks 16 umb or w/n 1hr of birth

AND

Mod-severe encephalopathy (Sarnat 2-3) = seizures or 3/6 of decr LOC, decr activity, decr tone, posturing, decr primitive reflexes, ANS changes (pupils, decr HR, irregular resps)

Question 4

How much do you cool for HIE, and how do you rewarm?

Answer 4

Cool 34+/-0.5degC w/n 6hrs, for 48-72h. Rewarm 0.5degC q2h (~4hrs). NNT=9.

Question 5

What are the side effects of hypothermia?

Answer 5

Mild bradycardia, mild hypotension, arrhythmias, mild thrombocytopenia and sclerema/edema have been described