Establishing Prolonged Hyperlactemia in Anesthetized Dogs

Abstract

Previously, we have shown that lactate (La-) infusates must be at pH 3.4-4.0 to maintain normal arterial blood pH when raising La- concentration to ≈10 mM. However, the time frame was short (< 2 h) and plasma ion concentrations were not measured. PURPOSE:To evaluate the impact of hyperlactemia (≥ 8 mM) on acid-base and ionic status over a prolonged period (i.e., 10 h) in an anesthetized canine model. METHODS:Six mongrel dogs were anesthetized with pentobarbital, intubated, and ventilated by respirator. Following the placement of sampling and infusion catheters, and baseline measurements of PO2, PCO2, O2 saturation, pH, La-, potassium (K+), calcium (Ca++), and glucose (Glu), the animal was infused with an aqueous solution (650 mM) of sodium lactate/lactic acid. The infusate pH was varied in an attempt to maintain arterial pH at ≈ 7.4. Once the blood La- reached 10 mM, the rate of infusion was decreased to maintain levels at 8-10 mM. RESULTS:Prior to lactate infusion the resting arterial blood lactate concentration was 0.6 ±0.2 mM. La- was elevated and maintained at 9.0 ± 0.6 mM for 10 h. In all cases, hyperlactatemia elicited declines in K+ and Ca++, requiring infusion of KCl and CaCl2 to maintain normal physiological levels. With low infusate pH, (2.2-3.4), hemolysis occurred. Therefore, infusate pH was increased to 4.6. Hemolysis was prevented, but in order to maintain arterial pH below 7.55, ventilation was decreased so that PCO2 rose to 52-55 mmHg. CONCLUSIONS:We were able to raise and maintain blood La- concentration in the 8mM range for 10 h; however, maintaining ion balance and pH required additional infusions and permissive hypercapnia.