Peripheral oxygenation in hypotensive preterm babies

Monitoring oxygenation in peripheral tissues of preterm babies may be usefu l in understanding the redistribution of blood flow during hypotension. Hem oglobin flow and venous saturation were measured in the forearm using near infrared spectroscopy with venous occlusion and were used to calculate frac tional oxygen extraction, oxygen delivery, and oxygen consumption. Thirty v entilated preterm babies (median birth weight 976 g) were studied; 15 were hypotensive and 15 normotensive. Treatment for hypotension was dopamine alo ne (median dose 5 mu g/kg/min) in eight cases, 4.5% human albumin solution (20 mL/kg) with dopamine in five cases, and only a blood transfusion (20 mi packed cells/kg) in two cases. There was a weak correlation between hemogl obin flow and mean arterial blood pressure (r = 0.40, p = 0.03). In hypoten sive compared with normotensive babies, there was a significantly lower med ian hemoglobin flow (10.2 versus 20.2 mu mol/100 mL/min, p = 0.0006), forea rm oxygen delivery (37.8 versus 75.2 mu moL/100 mL/min, p = 0.0008), and ox ygen consumption (11.0 versus 23.9 mu mol/100 mL/min, p = 0.006), but the f ractional oxygen extraction (0.327 versus 0.306, p = 0.48) and the blood la ctate concentration (1.22 versus 1.20 mmol/L, p = 0.44) were similar. Follo wing treatment of hypotension, oxygen delivery (p = 0.02) and oxygen consum ption (p = 0.04) increased to 64.2 and 21.7 mu mol/100 mL/min, respectively , but fractional oxygen extraction (p = 0.81) and blood lactate concentrati on (p = 0.94) after treatment were unchanged. VO2 was Variable in the forea rm of human infants. It reduced when DO2 was low, and there was no evidence of tissue injury or switch to anaerobic metabolism. Measurements of periph eral tissue oxygenation seem to be of some value in understanding the patho physiologic changes that occur with hypotension.