COMPARISON OF PH AND CARBON-DIOXIDE TENSION VALUES OF CENTRAL VENOUS AND INTRAOSSEOUS BLOOD DURING CHANGES IN CARDIAC-OUTPUT

Objective: To compare the pH and Pco(2) values determined from of simultaneously corrected samples of central venous and intraosseous blood during sequential changes in cardiac output. Design: Prospective, descriptive study. Setting: An animal laboratory in a university medical center. Subjects: Fourteen mixed breed 4-wk-old piglets. Interventions: Animals were anesthetized with ketamine hydrochloride and neuromuscular blockade was induced by the administration of pancuronium bromide. After endotracheal intubation and the institution of mechanical ventilation, a 4-Fr pulmonary artery catheter and a carotid artery cannula were inserted via a cutdown into the right neck of each piglet. A 16-gauge intraosseous needle was inserted into the anteromedial surface of the right tibia. Measurements and Main Results: Central venous and intraosseous blood gas samples were obtained simultaneously with thermodilution cardiac output measurements. Cardiac output measurements were as follows: during steady state (0.80 +/- 0.14 L/min), after volume loading of 15 mL/kg (1.00 +/- 0.25 L/min), after three successive bleeds of 15 mL/kg each at 30-min intervals (0.70 +/- 0.28, 0.54 +/- 0.22, and 0.43 +/- 0.16 L/min, respectively) and at exsanguination (unrecordable). Paired t-tests demonstrated no significant differences in pH and Pco(2) values between intraosseous and central venous samples under all study conditions. Limits of agreement for difference in Pco(2) between sites, within the range of cardiac outputs studied, were -12.86 to 11.38 torr (-1.71 to 1.46 kPa) and for pH were -0.09 to 0.15. Conclusions: Intraosseous blood samples can be obtained without difficulty even during extreme hypovolemia. The pH and Pco, values of intraosseous and central venous blood samples were similar under all study conditions. Intraosseous blood may be a useful alternative to central venous blood to assess tissue acid-base status during hemorrhagic shock and other low-flow states.