The Science Journal of the American Association for Respiratory Care

1998 OPEN FORUM Abstracts

CONTINUOUS ARTERIAL BLOOD GAS MONITORING DURING CARINAL PEEP TITRATION AND INTRATRACHEAL PULMONARY VENTILATION IN A LUNG INJURY MODEL

Karl Hultquist BSRRT, Eills Hon MD, Balagangadhar Totapally MD, Dan Torbati PhD, Andre Raszynski MD, Jack Wolfsdorf MD. Division of Critical Care Medicine, Miami Children's Hospital, Miami, Fl. 33155.

Introduction: The primary objective of Intratracheal Pulmonary Ventilation (ITPV) is PaCO_{2} reduction. This effect may be assessed either by intermittent arterial blood gas analysis (IABG) or by continuous blood gas monitoring (CoABG); the latter is instantaneous and cost effective. The purpose of this study was to assess 1) the effect of PEEP titration on PaO_{2} and PaCO_{2} during ITPV; and 2) to compare the PaCO_{2} values obtained during CoABG with those of IABG in a rabbit lung injury model.

Methods: Five New Zealand dwarf rabbits (3-5 kg body weight) were anesthetized and tracheostomized (4.0 i.d. multi-lumen ET tube) and cannulated in one carotid artery and internal jugular vein. Conventional ventilation (CV) was instituted (FiO_{2} 1.0, frequency 80 bpm, carinal PEEP 2, flow 1L/kg/min). A normal range of IABG was established by adjusting I:E ratios. Lung injury was then instituted by repeated saline lavage. IABG and CoABG were measured during one hour of CV, followed by one hour on ITPV and return to CV (F_{i}O_{2}=1). ITPV was established using a reverse thruster catheter (Cook, Inc.) with a flow of 1 L/kg/min. The flow was delivered and humidified through an in-line, servo, pressure limited system (Hudson RCI). During both CV and ITPV, the frequency was set at 80 bpm. The blood gas effect of variable levels of PEEP from 2 to 8 cmH_{2}O was then assessed during a one hour continuation of ITPV (n=3). Arterial pressure, heart rate, and carinal pressures were continuously recorded. The IABG profiles were determined by a blood gas analyzer (ABL 30; Radiometer Copenhagen). The CoABG was continuously recorded by a fiberoptic sensor probe placed inside a 20G 1.5 inch carotid arterial catheter. The sensor was connected to a blood gas monitor (Paratrend 7; Diametrics Medical, Inc. St. Paul, MN). Extreme light triggers an internal safety discontinuation of CoABG monitoring. We utilized foil to shield the catheter and connecting wires from this effect. The continuous readings (pH, PaCO_{2} and PaO_{2}) were initially calibrated with the steady-state blood gas data and subsequently compared to the intermittent readings every 10-15 min. The arterial blood gas values obtained by both methods were analyzed with repeated measures ANOVA, followed by Tukey-Kramer, and precision for both methods were determined.

Results: The data showed lower PaCO_{2} during ITPV as measured both by IABG and CoABG. During ITPV, PaO_{2} increased significantly with a stepwise increase in PEEP from 2 to 8 cm H_{2}O (n=3; repeated ANOVA and Tukey Kramer); no significant changes occurred in PaCO_{2} with variable PEEP. Comparison of gas exchange parameters between IABG and CoABG showed matching values and a high precision for PaCO_{2} during both CV and ITPV. Stepwise changes in the blood gas values during the acute injury were demonstrated by the continuous monitoring.

Conclusions: During ITPV, increases in carinal PEEP were associated with higher PaO_{2} but had statistically insignificant effect on PaCO_{2}. Direct continuous monitoring of PaCO_{2}, to assess adequacy of ventilation during both ITPV and CV, is achievable and may be preferable to EtCO_{2} monitoring which is subject to inaccuracy (shunting, dead space ventilation, and low cardiac output state). Attention to external light effect is advisable when current CoABG monitoring is utilized. During lung injury, progressive hypoxia occurred with each lavage in a stepwise fashion. Continuous blood gas monitoring may be more appropriate for assessment of any acute experimental or clinical process that involves evolving hypoxia and hypercarbia.

The 44th International Respiratory Congress Abstracts-On-DiskĀ®, November 7 - 10, 1998, Atlanta, Georgia.

You are here: RCJournal.com » Past OPEN FORUM Abstracts » 1998 Abstracts » CONTINUOUS ARTERIAL BLOOD GAS MONITORING DURING CARINAL PEEP TITRATION AND INTRATRACHEAL PULMONARY VENTILATION IN A LUNG INJURY MODEL