October 2002 / Volume 47 / Number 10 / Page 1168
Accuracy of Oxygen Analyzers at Subatmospheric Concentrations Used in Treatment of Hypoplastic Left Heart Syndrome
Hypoplastic left heart syndrome (HLHS) is a potentially fatal congenital heart defect that occurs with failure of the systemic or left heart structures to develop adequately. HLHS describes a spectrum of cardiac abnormalities characterized by marked hypoplasia of the left ventricle and ascending aorta. HLHS affects 0.016-0.036% of live births and 1.4-3.8% of patients with congenital heart defect. Congenital heart defect is more prevalent in males than females, with a male predominance of 60-70%. Without surgical intervention, the majority of infants born with HLHS will die within a month of birth.
Infants born with HLHS have various degrees of hypo
Because of these complex congenital malformations, oxygen-saturated pulmonary venous blood returning to the left atrium cannot flow into the left ventricle. This intracardiac shunting results in pulmonary venous blood flowing across the atrial septum and mixing with desaturated, systemic venous blood in the right atrium. This desaturated, mixed blood gets pumped to both the pulmonary (via the branch pulmonary arteries) and systemic (via the ductus arteriosus and descending aorta) circulations in parallel by the right ventricle. Thus, blood flow into each circulation depends on the pulmonary or systemic vascular resistance.
Frequently, optimization of systemic oxygenation and perfusion is achieved with very little medical intervention other than intravenous administration of prostaglandins to maintain ductal patency. However, with clinical signs of poor perfusion, metabolic acidosis, or oliguria it becomes medically necessary to increase the pulmonary vascular resistance by active respiratory management.
In most neonatal intensive care units oxygen analyzers are routinely used with oxygen hoods and mechanical ventilators to measure concentrations of oxygen administered to acutely ill patients. Four types of oxygen analyzer are commonly available: polargraphic, galvanic cell, paramagnetic, and Wheatstone bridge. We chose to bench test 2 polargraphic analyzers because of their response time, design for continuous use, and the availability of both high and low oxygen concentration alarms. Commercially available oxygen analyzers are specified for use within the range of 0.21 to 1.0 fraction of inspired oxygen (FIO2). Within that FIO2 range both manufacturers of the analyzers we studied list an accuracy of ± 2%. With the accuracy of the analyzer uncertain we were unsure of our ability to adequately control a subatmospheric oxygen delivery system. The purpose of this bench study was to evaluate the accuracy of 2 oxygen analyzers below the measurement range specified by the manufacturer.