Hypothermia

The clotting cascade and platelet function are both impaired by hypothermia; thus rewarming is important in restoring normal hemostasis. Fluid management

The aims of postoperative fluid management are to optimize preload and cardiac output, thus maintaining oxygen delivery to the tissues. Preload may change rapidly because of bleeding, spontaneous diuresis, vasodilatation during rewarming, and the effects of mechanical ventilation (with or without positive end-expiratory pressure). Pressure measurements commonly used as indicators of preload may not reflect end-diastolic volumes after cardiac surgery because ventricular compliance is altered, but are still valuable since a rise in left-sided pressure may precipitate myocardial ischemia or pulmonary edema. Preload is reduced if necessary with nitrates and diuretics.

Capillaries may be 'leaky' post-bypass and the patient receives a crystalloid load perioperatively (the pump prime, with or without cardioplegia), so that a diuresis is promoted, and crystalloid maintenance fluid is restricted to 1 ml/kg/h. Colloids are used to maintain preload. Opinions vary as to the threshold hematocrit for transfusion within the range 0.25 to 0.35. The hazards and expense of hemologous blood transfusion can be avoided to an extent by autotransfusion; the patient's shed blood is collected from the chest drains, filtered, and reinfused at a rate determined by hourly losses. Although this shed blood has a lower hematocrit, increased free hemoglobin, reduced clotting factors and platelets, and increased fibrinolytic breakdown products, the red cells are functional with a normal half-life. This technique is safe in volumes of up to 700 ml and can reduce hemologous blood usage. The risks include increased potential for infection and renal impairment.

Sleep Apnea

Sleep Apnea

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