Aims: to determine the practicality and systemic effects of head cooling with mild or minimal systemic hypothermia in term neonates with moderate to severe hypoxic-ischemic encephalopathy.

Methods: Study Group: Infants ≥ 37 weeks gestation(mean 39±1 for all groups) with umbilical artery pH≤7.09 or Apgars≤6 at 5 min, plus evidence of encephalopathy. Infants with major congenital abnormalities were excluded. Trial Design: Infants were randomized to either no cooling (controls, rectal temp=37.2 to 36.8°C, n=10), minimal cooling (rectal temp 36.5 to 36.0°C, n=6) or mild cooling (rectal temp = 35.9 to 35.5°C, n=6). Head cooling was accomplished by circulating water at 10°C through a coil of tubing wrapped around the head, for up to 72 hours. All infants were warmed by servo-controlled overhead heaters to maintain allocated rectal temperature. Rectal, fontanelle and nasopharyngeal temperatures were continuously monitored.

Results: From Jan 1996 to Oct 1997, 22 term infants were randomized from 2 to 5 hours after birth. All infants had a metabolic acidosis at delivery, with a similar umbilical artery pH in the control mean±SD, 6.79±2.5), minimal (6.98±2.1) and mild groups(6.93±0.11), and depressed Apgar scores at 5 min in the control(4.5±2), minimal (4.7±2) and mild groups (6.0±1). No adverse effects due to cooling were observed. The mean rectal temperature for control infants was 37.0±0.2°C, for minimal cooling 36.3±0.2°C and for the mild cooling group 35.7±0.2°C during the cooling period. In the mild cooled infants, the naso-pharyngeal temperature was 34.5°C during cooling, 1.2°C lower than rectal. This gradient narrowed to 0.5°C after cooling was stopped. No infants developed cardiac arrhythmias, hypotension or bradycardia during cooling. Thrombocytopenia occurred in 2 controls, 2 minimal and 1 mild cooling infants. Hypoglycemia (glucose<2.6 mM) was seen on at least one occasion in 2 controls, 4 minimal and 1 mild infants. Acute renal failure occurred in all infants. The metabolic acidosis at the time of enrolment into the study progressively resolved even in the mild cooling group.

Conclusions: Selective head cooling combined with mild systemic hypothermia in term newborn infants following perinatal asphyxia is a safe and convenient method of quickly increasing the gradient between the surface of the scalp and core temperature, and thus reducing cerebral temperature without adverse effects. This safety study and the strong experimental evidence for improved cerebral outcome justify the planning of a therapeutic trial of selective head cooling for neonatal encephalopathy in term infants.