The Science Journal of the American Association for Respiratory Care

2001 OPEN FORUM Abstracts

A PROSPECTIVE,RANDOMIZED TRIAL COMPARING HYPOXIA TO HYPERCARBIA IN PRE-OPERATIVE PATIENTSWITH HYPOPLASTIC LEFT HEART SYNDROME.

S. DurningBS, RRT, S. Tabbutt MD, PhD, SC Nicholson MD, L.M. Montenegro MD, C.RamamoorthyMB,BS, T.Schultz, RRT,RN

Background: An importantcomponent in the pre-operative management of patients with hypoplastic leftheart syndrome (HLHS) is maintaining a balance between pulmonary vascular resistance(PVR) and systemic vascular resistance. In some cases it is necessary to increasePVR in order to improve systemic blood flow. This may be accomplished via inducedhypoxic gas mixture with nitrogen to decrease the FiO2 to 15%-20%,or induced hypercarbia with inspired carbon dioxide of 7 torr-50 torr. We comparedoxygen delivery to pre-op patients with HLHS under the conditions of 17% FiO2and 20 torr carbon dioxide.1

Methods: This is a prospective,randomized trial comparing hypoxia (17% FiO2) to hypercarbia (20torr CO2) in pre-operative patients with the diagnosis of HLHS. Theinclusion criteria for this study were pre-operative HLHS, endotracheal intubation,no pulmonary pathology by CXR, central venous catheter with tip in SVC and IRBapproved consent from parents.

In this crossover design, the patientswere mechanically ventilated on room air to normocapnia at baseline and wererandomized to receive either 17% FiO2 or 20 torr CO2 first.All patients received both conditions. Each condition (hypoxia/hypercarbia)was maintained for 10 minutes with a 20 minute period in between to allow forreturn to baseline. Data collected at each condition included arterial and SVCblood gas with co-ox, heart rate, mean arterial pressure, SpO2 andexhaled minute ventilation. The CO2 was delivered at the outportof the ventilator and measured pre-humidifier via Nellcor Ultracap. The nitrogenwas delivered via the oxygen high pressure hose on the ventilator and FiO2was analyzed pre-humidifier via Ceramatec oxygen analyzer. The patients wereventilated via the Servo 300 ventilator in the PRVC mode.

Results:

BaselineHypoxiap ValueBaselineHypercarbiap Value
pH7.44 ± .027.46 ± .02 .0127.42 ± .027.32 ± 01.002
PO2 50.3 ± 1.942.2 ± 1.8<.0001 49.6 ± 1.650.8 ± 1.9 NS
pCO2 37.5 ± 1.835.7 ± 2 NS39.4 ± 1.653.7 ± 1.6.002
SpO2 93.2 ± 1.589.8 ± 2.8.004 92 ± 1.3 90.2 ± 1.8.04
Heart rate160 ± 6 153 ± 4NS150 ± 5149 ± 4NS
MAP45.3 ± 2.544.2 ± 2.4 NS42.8 ± 3.750.7 ± 2.8NS
Qp:Qs3.4 ± .52.6 ± .5 .0563.1 ± .52.2 ± .6.026
A-VO2 28.3 ± 3.228.8 ± 3.8NS28.5 ± 3.6 19.9 ± 3.8.005

Conclusion: Forpre-operative patients with HLHS who are anesthetized, paralyzed, and fullysupported on mechanical ventilation, hypoxia decreased oxygen delivery whilehypercarbia increased oxygen delivery.

1. Tabbutt S,et al. Impact of Inspired Gas Mixtures on Pre-Operative Infants with HypoplasticLeft Heart Syndrome During Controlled Ventilation. Circulation 2000; 102(supplII) II-469

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