Acid-base disturbance during hemorrhage in rats: significant role of strong inorganic ions

The present study tests the hypothesis that changes in the strong inorganic ion concentrations contribute significantly to the acid-base disturbance t hat develops during hemorrhage in the arterial plasma of rats in addition t o lactate concentration ([Lac(-)]) increase. The physicochemical origins fo r this acid-base disorder were studied during acute, graded hemorrhage (10, 20, and 30% loss of blood volume) in three groups of rats: conscious, anes thetized with ketamine, and anesthetized with urethan. The results support the hypothesis examined: strong-ion difference (SID) decreased in the arter ial plasma of all groups studied because of an early imbalance in the main strong inorganic ions during initial hemorrhagic phase. Moreover, changes i n plasma [Lac-] contributed to SID decrease in a later hemorrhagic phase (a fter 10% hemorrhage in urethan-anesthetized, after 20% hemorrhage in ketami ne-anesthetized, and after 30% hemorrhage in conscious group). Inorganic io n changes were due to both dilution of the vascular compartment and ion exc hange with extravascular space and red blood cells, as compensation for blo od volume depletion and hypocapnia. Nevertheless, anesthetized rats were le ss able than conscious rats to preserve normal arterial pH during hemorrhag e, mainly because of an impaired peripheral tissue condition and incomplete ventilatory compensation.