Reversible hypophosphatemia during moderate hypothermia therapy for brain-injured patients

Objective: Because plasma potassium, which may similarly change as plasma phosphate (P), decreases during moderate hypothermia, plasma P, a requisite electrolyte for the cell function, may alter during therapeutic moderate hypothermia for brain-injured patients. In 22 such patients who underwent moderate hypothermia or were treated with normothermia, plasma concentrations of P and other chemicals were examined. Design: A prospective study. Setting: The intensive care unit of a medical university hospital. Patients and Interventions: In 15 consecutive patients with brain injury who underwent moderate hypothermia and 7 serial patients treated with normothermia, plasma concentrations of P, potassium, glucose, blood gas tension and pH, daily urine volume, and water balance were examined. Inequality in the numbers of patients of the two groups was the result of patient exclusion because of multiple trauma, aluminum hydroxide administrations, hyperventilation, preexisting diabetes mellitus, or administration of insulin. Daily blood sampling was done around 8 am. Inclusion criteria included a Glasgow Coma Scale score assessment less than or equal to8 at admission to the emergency room and evidence of injury on computerized tomography scanning of the brain. Measurement and Main Results: Hypothermia decreased plasma P levels as compared with those of normothermia within 4 days after the injury (this period was similar to the duration of the hypothermic phase in the hypothermia group). Such reduction related to changes in blood glucose levels, but not to any in the urine volume, or water balance. The P decrease occurred during the hypothermic phase, but subsequently there was a recovery of P after the rewarming phase. The changes in plasma potassium levels were similar to those in plasma P concentrations during the course. Such changes were accompanied by a recovery of decreased heart rate that occurred during the hypothermic phase. Conclusion. The results suggest that moderate hypothermia of 32-33 degreesC decreases plasma P levels. Further studies are required to examine whether P repletion may overcome certain hemodynamic derangements during moderate hypothermia in brain-injured patients.