Hyperoxia Reduces Oxygen Consumption in Children with Pulmonary Hypertension

Abstract

High inspired oxygen concentration (FiO > 0.85) is administered to test pulmonary vascular reactivity in children with pulmonary hypertension (PH). It is difficult to measure oxygen consumption (VO) if the subject is breathing a hyperoxic gas mixture so the assumption is made that baseline VO does not change. We hypothesized that hyperoxia changes VO. We sought to compare the VO measured by a thermodilution catheter in room air and hyperoxia. A retrospective review of the hemodynamic data obtained in children with PH who underwent cardiac catheterization was conducted between 2009 and 2014. Cardiac index (CI) was measured by a thermodilution catheter in room air and hyperoxia. VO was calculated using the equation CI = VO/arterial-venous oxygen content difference. Data were available in 24 subjects (males = 10), with median age 8.3 years (0.8-17.6 years), weight 23.3 kg (7.5-95 kg), and body surface area 0.9 m (0.4-2.0 m). In hyperoxia compared with room air, we measured decreased VO (154 ± 38 to 136 ± 34 ml/min/m, p = 0.007), heart rate (91 [Formula: see text] 20 to 83 [Formula: see text] 21 beats/minute, p=0.005), mean pulmonary artery pressure (41 [Formula: see text] 16 to 35 [Formula: see text] 14 mmHg, p=0.024), CI (3.6 [Formula: see text] 0.8 to 3.3 [Formula: see text] 0.9 L/min/m, p = 0.03), pulmonary vascular resistance (9 [Formula: see text] 6 to 7 [Formula: see text] 3 WU m, p = 0.029), increased mean aortic (61 [Formula: see text] 11 to 67 [Formula: see text] 11 mmHg, p = 0.005), pulmonary artery wedge pressures (11 [Formula: see text] 8 to 13 [Formula: see text] 9 mmHg, p = 0.006), and systemic vascular resistance (12 [Formula: see text] 6 to 20 [Formula: see text] 7 WU m, p=0.001). Hyperoxia decreased VO and CI and caused pulmonary vasodilation and systemic vasoconstriction in children with PH. The assumption that VO remains unchanged in hyperoxia may be incorrect and, if the Fick equation is used, may lead to an overestimation of pulmonary blood flow and underestimation of PVRI.

Oxygen Therapy Lowers Right Ventricular Afterload in Experimental Acute Pulmonary Embolism

“…We showed that supplemental oxygen therapy lowered mPAP and PVR in PE to an extent similar to previous animal studies on acute, nonobstructive pulmonary hypertension (28,32), or chronic nonautologous PE (29). Similar effects have also been observed in patients with chronic pulmonary hypertension (11,12,30), whereas the effects of oxygen were less pronounced in patients with chronic thromboembolic pulmonary hypertension (13), where the degree of pulmonary vasoconstriction might be limited. Our study provides evidence that supplemental oxygen additionally unloads the RV in the setting of acute PE.…”

“…We observed an attenuated effect on HR (and thereby CO), which is in contrast to other animal models investigating oxygen therapy (28, 29). Human studies on pulmonary hypertension have observed reduced HR, although (13, 30). Oxygen may actually cause a minor fall in CO in PE patients (33).…”

“…Expected effect size of oxygen to lower mPAP or PVR was 20–30% based on animal and human studies (11, 12, 28–30). Our model has previously shown to increase PVR to 300 dynes after PE induction (22).…”

Pediatric Perioperative Pulmonary Arterial Hypertension: A Case-Based Primer

“…The focus is on decreasing oxygen demand and improving oxygen delivery, and supplemental oxygen can be used liberally in this case. There is, in fact, even evidence that in children with pulmonary hypertension, hyperoxia itself reduces oxygen consumption [ 19 ]. Noninvasive ventilatory measures can be considered, including high flow nasal cannula oxygen and continuous positive airway pressure (CPAP), particularly in the patient with lung disease and atelectasis.…”

Current understanding and perioperative management of pediatric pulmonary hypertension

“…Outside of the newborn/neonatal period, oxygen may be used liberally if acceptable for the procedure. Oxygenation will decrease PVR, mildly increase SVR, and may even reduce oxygen consumption and maintain higher mixed venous saturations in the event of right‐to‐left shunt physiology . When the child is breathing spontaneously, the child must be closely monitored for hypoventilation, atelectasis, and hypercapnia, with immediate measures to support ventilation as indicated.…”