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Abstract: There is much controversy about the optimal bloodgas management of hypothermic patients, whether the hypothermia is caused by accidents or induced before operations. The
surgeons and anesthesiologists have acquired more clinical experience in
recent years when operating on patients in hypothermia. The comparative physiology has given increased
information about the blood gas strategy of heterothermic endotherms and poikilothermic ectotherms during lowering of their core temperature. There are two types of strategies
which have been used in clinical medicine the last years in the blood gas management of patients in hypothermia: pH-stat method and alpha-stat method.
In the pH-stat method,
the arterial carbon dioxide tension (paCO2) is maintained at 5.3 kPa (40 mmHg) and the pH is maintained at 7.40 when measured at the actual temperature. It is then
necessary to add CO2 to the inspired gas.
In the alpha-method, the arterial carbon dioxide tension and the pH are maintained at 5.3 kPa and 7.40 when measured at +37
degrees C. When a patient is cooled down, the pH-value will increase and the
pCO2-value and the
pO2-value will decrease with lowering of the temperature if measured at the
Both the pH-stat and alpha-stat strategies have theoretical disadvantages. For
optimal myocardial function the alpha-stat method is the method of choice. The pH-stat method may result in loss of autoregulation in the brain (coupling of the cerebral blood flow with the metabolic rate in the brain). By increasing the cerebral
blood flow beyond the metabolic requirements, the pH-stat method may lead to cerebral microembolisation and intracranial hypertension. In Norway, the alpha-stat strategy is the
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Acid-base Management during Hypothermic Cardiopulmonary Bypass Does Not
Metabolism But Does Affect Cerebral Blood Flow and Neurological Outcome.
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