Differential diagnosis of perioperative metabolic acidosis

Introduction Perioperatively, metabolic acidosis is commonly ascribed to lactic acidosis secondary to hypoperfusion. Our aim was to determine the exact nature of perioperative acidoses following elective, major surgery. Methods 935 consecutive, perioperative, heparinised arterial samples from adult and adolescent major elective orthopaedic cases were analysed using an ABL 700 series blood gas analyser (Radiometer, Copenhagen), also capable of measuring serum lactate and chloride levels. If acidotic samples had normal lactate and chloride levels, urine was tested for ketones using Multistix SG reagent strips(Bayer PLC). Abnormal values were as defined in the reference manual and package insert respectively. Blood biochemistry was examined for pre and postoperative renal or hepatic impairment. Results No patients had pre or postoperative renal or hepatic impairment. Metabolic acidosis (pH<7.35; SBE<-4) was present in 129(14%) of samples, the causes of which are listed in the table below. La refers to lactic only, La+Cla to mixed lactic and hyperchloraemic, Cla to hyperchloraemic only and Ka to ketoacidosis respectively. Discussion Not all blood gas analysers measure chloride and lactate levels, and whilst lactic acidosis was present in 48% of the samples, our results illustrate that it is not valid to assume this is the only explanation for a perioperative base defecit even in a population without acidosis secondary to renal or hepatic impairment. Perioperative chloride load and starvation seem to be significant factors in producing acidosis. Differential Diagnosis of Perioperative Metabolic Acidosis Type of Acidosis Number (%) La 7 (5%) L + Cla 55 (43%) Cla 47 (36%) Ka 20(6%).

Duke Scholars

Author Ian James Welsby Anesthesiology, Cardiothoracic