Abstract
Objectives: Mild hypothermia has been shown to be neuroprotective for newborn infants with hypoxic ischemic encephalopathy (HIE). In this study, we examined the effects of deep hypothermia on systemic and brain temperature changes during whole-body or selective head cooling in an animal model of perinatal HIE.
Methods: Twelve piglets were studied under anesthesia and artificial ventilation. Five ultra-sensitive, flexible, titanium, thermocouple probes were used for continuous temperature recording from five brain regions, two kidney regions; the thoracic aorta, the wall of the small intestine, and the rectal lumen using single sensor probes for each. Changes in temperatures from the 10 sites were recorded continuously during baseline, 20 minutes of hypoxic-ischemic injury; 60 minutes whole-body cooling (n=6) or selectively the head cooling (n=6); and 60 minutes of re-warming.
Results: Deep hypothermia with whole-body cooling led to uniform drops in temperature in the five brain regions, maintaining a constant gradient across the superficial and deep brain regions. Deep hypothermia with selective head cooling led to larger drops in superficial than in the deep brain temperatures. Deep whole-body hypothermia led to sharp drops in core body, kidney and small intestinal temperatures; the latter dropping to −11.27°C ± 3.72°C below baseline compared to −3.32°C ± 1.52°C below the baseline with deep hypothermia for selective head cooling (P<0.001).
Conclusions: Deep hypothermia with whole-body cooling can lead to severe core hypothermia especially of the kidney and small intestines, which get cooled far in excess of the aortic blood. Reduced kidney and small intestinal blood flow, and a direct cooling effect from lying on the cooling mattress may be responsible for rapid cooling of the kidney and the intestines. These findings underscore the need to target the core temperatures to strict ranges, as specified in the published hypothermia trials, especially during the transportation of infants to centers providing therapeutic hypothermia.