Analytical calculation and acid-base analysis for detection of mixed disorders in critical care medicine.

ABSTRACT

Aim: The purpose of the study was to validate the systematic six-step arterial blood gas (ABG) analysis in critically ill patients to diagnose mixed ABG disorders. Materials and method: The study was conducted in the ICU of a tertiary care hospital (between 1 June and 30 September, 2007) for 4 months. A total of 560 ABG samples were evaluated from 183 patients. 50 samples were randomly picked and evaluated by single step, quick look method and six-step approaches for detecting mixed ABG disorders. Results: Single, quick and six-step methods when applied on same data, revealed higher number of mixed disorders with systematic six-step approach. Quick-step method revealed only 48% mixed disorders while six-step analysis confirmed 62% having mixed disorders, from the samples which initially appeared to be single disorder. Metabolic acidosis with respiratory acidosis (26%) was the commonest disorder. Metabolic acidosis with respiratory alkalosis (20%), respiratory alkalosis with metabolic alkalosis (6%), metabolic alkalosis with respiratory acidosis (4%), metabolic acidosis with NGMA (4%) and metabolic acidosis with metabolic alkalosis (2%) were the other mixed disorders seen. Conclusion: Mixed disorders as suspected on clinical grounds can only be validated after complete analysis by six-step approach in critically ill patients. pH, PaCO2, and HCO3 – allow determination of primary disorder, but it is only the inequality between predicted and actual compensatory response for simple acid-base disorders which reveals a mixed disorder.