EFFECTS OF EXOGENOUS LIPIDS ON BLOOD-GAS MEASUREMENTS

Objective. Numerous reports have appeared describing the effects of in travenous lipid administration on the pulmonary function of the critic ally ill patient. Our study was undertaken to determine whether the li pid content of an arterial blood gas specimen affects the measurement of arterial pH, PaO2, PaCO2, or arterial oxygen saturation. Design: Pr ospective, in vitro controlled study. Setting. Medical and cardiac int ensive care units. Patients: Critically ill patients undergoing clinic ally-directed blood gas sampling via indwelling arterial catheters. In terventions: None. Measurements: Arterial blood gas specimens were mod ified in vitro by dividing the sample and adding a known amount of lip id emulsion to half of the sample, resulting in a difference between t he plasma triglyceride concentrations of the two halves. Two series of experiments were run: one series was run with a predicted plasma trig lyceride difference of 400 mg/dL (4.5 mmol/L) between the two samples; the other series was run with a predicted plasma triglyceride differe nce of 800 mg/dL (9.0 mmol/L) between the two samples. Blood gas measu rements were performed on each half of a sample, and the results were compared. Because some studies have only noted changes in patients wit h the adult respiratory distress syndrome (ARDS), samples from these p atients were also analyzed as a separate group. Results: No significan t changes were found in arterial pH, PaO2, PaCO2, or arterial oxygen s aturation between the two halves of the sample. With 95% confidence, d ifferences as small as 1.5 torr (0.2 kPa) for PaO2 and PaCO2, 0.5% for arterial oxygen saturation, and 0.005 for pH, would have been detecte d. No differences were found in the ARDS subgroup. Conclusions: The ad dition of clinically relevant amounts of lipid to blood samples does n ot affect blood gas measurements. Any observed changes in blood gas va lues after lipid feeding are presumably due to products of lipid metab olism or alterations in pulmonary function.