Evaluation of Relationship Between Arterial and Venous Blood Gas Values in the Patients with Tricyclic Antidepressant Poisoning

Abstract

Introduction. Determination of arterial blood gas (ABG) values is essential in the evaluation of patients with TCA poisoning. The relationship between arterial and venous blood gas pH has not been established in TCA poisoning. In TCA poisoning, blood vessels vasodilatation due to antidepressant-induced α-blockade and also metabolic acidosis may lead to arterialization of venous blood, which in turn enhances the relationship between ABG and VBG parameters. Therefore this study was designed to evaluate the relationship between ABG and VBG pH values in TCA poisoned patients. Methods. This prospective study was performed in the Poisoning Emergency Department of Noor Hospital, Isfahan, Iran. Samples for arterial and venous blood gas analysis were obtained during initial evaluation of TCA-poisoned patients and 30 min after treatment with sodium bicarbonate. The venous blood gas samples were collected with samples for other blood tests at the time of intravenous line insertion. Laboratory data were recorded on a database form initiated in the emergency department and analyzed by paired student t-test. The degree of agreement between the arterial and venous pH measurements was evaluated by Bland and Altman method. Results. Data from 50 TCA-poisoned patients were analyzed. There were significant differences between mean differences of ABG and VBG parameter values on the initial evaluation. There was also a relationship between arterial and venous pH on the initial evaluation. Conclusion. In TCA poisoning, the peripheral venous pH measurement is a valid and reliable substitute for arterial pH.