Arteriovenous pH difference--a new index of perfusion

Measurement of the pH of arterial blood may not reflect early stages of anaerobic metabolism. Since a relationship exists between pH and cellular utilization of oxygen, this study sought to determine whether the difference between arterial and venous pH might serve as a more useful index for estimating the adequacy of tissue perfusion. Dogs were made hypovolemic, and hemodynamic profiles including thermodilution cardiac output were obtained while simultaneous arterial and central venous blood samples were analyzed for pH. Arteriovenous pH difference increased as cardiac index fell. Whenever the arteriovenous pH difference became greater than 0.05 pH units, the cardiac index had fallen below 65% of the baseline values. A difference of 0.05 pH units between arterial and venous blood predicted hypoperfusion in 90% of the animals. With deepening shock the gradient widened, and when resuscitation was effective the arteriovenous pH difference returned toward normal. These data suggest that arteriovenous pH difference may reliably predict clinically significant reductions in cardiac output and cellular perfusion. This finding could be useful in pediatric trauma and critical care settings in which invasive monitoring and direct determination of cardiac output are technically difficult.