Hematological changes were measured in 14 dogs during partial heart-lung bypass procedures of 10 hr duration with an extracorporeal flow approximating 40% of the cardiac output. The changes occurring during the 1st hr of perfusion were identical to those previously reported for short periods of total heart-lung bypass, namely, thrombocytopenia and leukopenia. Later on, however, compensatory mechanisms were manifested by the appearance of a leukocytosis with a shift to the left, a leveling off of thrombocyte counts, and the appearance of nucleated red cells in the peripheral blood. Bone marrow studies revealed stimulation of myeloid tissues. These compensatory responses observed during perfusion were similar to changes which have been described as typical of the postperfusion period after shorter durations of extracorporeal circulation. The trauma inflicted on erythrocytes during extracorporeal blood handling became evident after perfusion as a marked anemia and an increased mechanical fragility of the red cells. Submitted on September 22, 1961

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Fluid and electrolyte balance was studied in 21 dogs after partial heart-lung bypass of 10 hr duration. Water retention was demonstrated by an increase in body weight and total body water, primarily due to an increase in extracellular fluid. Electrolyte retention was suggested by an increase in total extracellular sodium, potassium, and chloride. Urinary output was relatively normal but a progressive drop in urinary specific gravity was observed during bypass. Blood pH remained essentially unchanged. However, an increase in plasma lactate and a decrease in plasma bicarbonate suggested some degree of hypoxia and metabolic acidosis at the cellular level. Altered hormonal regulation of sodium and water excretion, hemolysis secondary to blood trauma, and the exchange of intracellular potassium for extracellular hydrogen ions were considered possible explanation for the fluid and electrolyte changes observed. assisted circulation; heart-lung bypass; acid-base balance; fluid balance; extracorporeal circulation; electrolyte changes with partial bypass; membrane oxygenator; disc oxygenator; bubble oxygenator Submitted on June 20, 1963

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