39: Therapeutic Hypothermia

I. INDICATION

To reduce mortality in infants with perinatal hypoxia ischemia when initiated before 6 hours of age. It is indicated in the treatment of infants (36 0/7 weeks' gestation or greater, younger than 6 hours) who fulfill the criteria for the diagnosis of moderate to severe hypoxic ischemic encephalopathy (HIE). Cooling can be done by selective head (Olympic Cool-Cap System, Olympic Medical Corporation, Seattle, WA) or total-body cooling. This chapter discusses total body cooling.

II. ELIGIBILITY FOR HYPOTHERMIA

Infants should be evaluated for eligibility by (step A) clinical and physiological criteria followed by (step B) complete neurological examination. Infants have to meet both physiologic and neurologic criteria. Eligibility criteria are for either whole-body cooling by blanket or mattress or head cooling by a fitted cap. For head cooling a step C is required, which includes an amplitude-integrated electroencephalogram (aEEG) (recording at least 20 minutes duration) that shows either moderately or severely abnormal aEEG background activity or seizures.

1. Step A: clinical and physiological criteria. All infants should be evaluated as follows:

   1. Blood gas (a cord blood gas or an arterial [preferred] or venous/capillary blood gas within the first hour of life): pH <7 or base deficit >16, proceed to step B.

   2. No blood gas or arterial/venous/capillary blood gas pH 7–7.15 or base deficit of 10–15.9 with an acute perinatal event (cord prolapse, abruption placenta, severe fetal heart rate [FHR] abnormality, variable or late decelerations; maternal trauma, hemorrhage, or cardiac arrest) plus either a or b (below), then proceed to step B.

      1. 10-minute Apgar ≤5.

      2. Continued need for ventilation initiated at birth and continued for at least 10 minutes.

2. Step B: complete neurologic examination. Once infant meets step A clinical and physiological criteria, perform a complete standardized neurologic examination. Moderate to severe encephalopathy is defined as seizures or the presence of one or more signs in 3 of the 6 categories in staging of HIE (level of consciousness, spontaneous activity, posture, tone, primitive reflexes, and autonomic system). The number of moderate or severe signs will determine the extent of encephalopathy; if signs were equally distributed, the designation is based on the level of consciousness.

   1. If seizures are documented or are occuring, the infant is automatically eligible for cooling.

   2. No seizures are reported, the infant has to have at least 3 out of the 6 neurologic signs in moderate or severe encephalopathy (Table 39–1) to be eligible for cooling.

3. Infant is eligible for cooling once criteria in step A and B are met.