CARDIORESPIRATORY EFFECTS OF PERFLUOROCARBON-ASSOCIATED GAS-EXCHANGE AT REDUCED OXYGEN CONCENTRATIONS

Objective: To determine whether reducing FIO2 during perfluorocarbon-a ssociated gas exchange would cause deterioration of hemodynamics, lung mechanics, or gas exchange in normal piglets. Design: A prospective, controlled animal trial. Setting: Experimental animal laboratory in a university setting. Subjects: Twelve normal, anesthetized piglets, 7 t o 14 days old, and weighing 3.31 +/- 0.75 kg. Interventions: After the induction of anesthesia, tracheostomy and catheterization, piglets we re stabilized. They were mechanically ventilated with a tidal volume o f 15 mL/kg, inspiratory time of 25%, positive end-expiratory pressure of 4 cm H2O, and a respiratory rate of 20 to 28 breaths/min to obtain a baseline PaCO2 between 34 and 45 torr (4.7 and 6.0 kPa). Each animal was studied during continuous positive-pressure breathing, and during perfluorocarbon-associated gas exchange. They were ventilated at an F IO2 of 1.0 for 15 mins. FIO2 was randomly varied among 0.75, 0.5, and 0.3 every 15 mins, then returned to 1.0. At each FIO2, measurements of gas exchange, lung mechanics, and hemodynamics were made. After conti nuous positive-pressure breathing, perfluorocarbon-associated gas exch ange was instituted by replacing the gaseous functional residual capac ity of the lungs with perfluorooctylbromide. Animals were then ventila ted and measurements were taken. Measurements and Main Results: At eac h FIO2, measurements of gas exchange (arterial blood gases and saturat ion), lung mechanics (mean airway pressure, static end-inspiratory pre ssure, and peak inspiratory pressure), and hemodynamics (heart rate, a nd mean arterial, right atrial, pulmonary artery occlusion, and pulmon ary arterial pressures) were recorded. In six piglets, cardiac output was measured at each FIO2 by thermodilution. Cardiac index, indexed ox ygen delivery and consumption, and indexed pulmonary vascular resistan ce were derived using standard formulas. Piglets were well saturated a t all FIO2 settings during continuous positive-pressure breathing. How ever, during perfluorocarbon-associated gas exchange, arterial saturat ion decreased to 72% at an FIO2 of 0.3. Cardiac index and oxygen consu mption were not affected by reducing FIO2 during perfluorocarbon-assoc iated gas exchange, and were not significantly different than during c ontinuous positive-pressure breathing. Oxygen delivery was reduced at an FIO2 of 0.3 during perfluorocarbon-associated gas exchange, but oxy gen consumption remained in the now independent portion of the curve d espite arterial desaturation. Pulmonary arterial pressure was higher d uring perfluorocarbon-associated gas exchange than during continuous p ositive-pressure breathing. Pulmonary arterial pressure and indexed pu lmonary vascular resistance were significantly higher during perfluoro carbon-associated gas exchange at an FIO2 of 0.3 than at any other FIO 2 settings. Conclusions: Piglets showed no adverse effects on lung mec hanics during perfluorocarbon-associated gas exchange. Hemodynamics we re well supported at all FIO2 settings, and arterial blood was fully o xygenated during perfluorocarbon-associated gas exchange at an FIO2 of greater than or equal to 0.5.