Effects of potassium and lactic acid on ventilation in anaesthetized cats

Intravenous infusions of lactic acid alone, KCl alone and both together were administered to anaesthetized, spontaneously breathing cats. Ventilation (VI), end-tidal PO2 (PETO2), end-tidal PCO2 (PETCO2), arterial blood pressure and heart rate were recorded continuously. [K+]a and pHa were monitored using intravascular ion selective catheter electrodes. The increase in VI during infusion of KCl and lactic acid together was greater than that observed during infusion of lactic acid alone. The increment in VI produced by the addition of an infusion of KCl to the lactic acid infusion was greater than the increment produced by the addition of KCl to a control infusion of normal saline. The reduction in PaCO2 which occurred when KCl was added to the lactic acid infusion was similar to that when KCl was infused with NaCl. Thus the inhibition of respiration secondary to reduced PaCO2 was similar in both circumstances. These results suggest that the combined respiratory stimulant effect of elevation of [K+]a and acute lactic acidosis is more than additive.