Blood Gas Values During Hypothermia in Asphyxiated Term Neonates

Hypothermia has become an important novel neuroprotective strategy for asphyxiated term neonates.1 Most of these neonates will receive mechanical ventilation. Hypothermia affects blood gas parameters such as pH and Pco2. At lower temperatures pH increases and Pco2 decreases. This is relevant, because Paco2 is known to affect vascular tone and, hence, cerebral perfusion.2 In addition, cerebral blood flow decreases during hypothermia, which increases the risk of insufficient blood flow during hypocapnia.3 Most blood gas instruments, whether a central laboratory or point-of-care device, contain a temperature-controlled sample chamber specified to be 37°C. It is at that temperature that all measurements of pH and partial pressure of gases are performed. In the α-stat strategy, uncorrected values are used to keep the pH and Pco2 close to the 37°C reference value.4 However, most instruments can calculate and present temperature-corrected pH and Pco2 values. In the so-called pH-stat method, the measured pH is corrected to the actual body temperature of the patient. Ventilator settings can be adjusted to keep the actual pH as close to 7.4 as possible.4 At present, it is unclear whether the α-stat or pH-stat theory should be used in the neuroprotective strategy for asphyxiated term neonates. In the 2 large randomized, controlled trials on therapeutic hypothermia in term neonates with perinatal asphyxia, attending … Address correspondence to Floris Groenendaal, MD, PhD, Wilhelmina Children's Hospital, University Medical Center Utrecht, Department of Neonatology, Room KE 04.123.1, Lundlaan 6, 3584 EA Utrecht, Netherlands. E-mail: f.groenendaal{at}umcutrecht.nl