Regional blood flow during severe hypoxemia and resuscitation with 21% or 100% O₂ in newborn pigs

Abstract

Our aim was to determine whether the use of room air or 100% oxygen has different effects on the peripheral circulation during resuscitation from severe hypoxemia. Twenty-four piglets, 2-to 5-days old, were anesthetized with pentobarbital and randomized to control (n = 5, surgery only) or hypoxemia. Hypoxemia (FiO2 = 0.08) was continued until base excess reached - 20 mml/L. Resuscitation was then performed with 21% (n = 10) or 100% O2 (n = 9) for 25 min followed by 21% O2 in both groups. Regional blood flow was measured with radioactive microspheres. Both hypoxic groups showed marked hyperemia during resuscitation in cardiac and skeletal muscle, a moderate hyperemia in intestine and pancreas while kidneys, liver, spleen and skin showed no hyperemic response. There were no significant differences between the two treatment groups in blood flow to any organ. Arterial oxygen content was significantly higher in the 100% O2 group than in the 21% O2 at 5 and 20 min after onset of resuscitation (11.6 +/- 0.7 and 11.2 +/- 0.6 vs 8.6 +/- 0.3 and 8.7 +/- 0.3 ml/100 ml, p < 0.01). Oxygen delivery was, however, significantly higher in the 100% O2 group than in the 21% O2 group only to the intestine and pancreas at 5 min of resuscitation. We conclude that resuscitation with 21% or 100% oxygen produces similar changes in peripheral blood flow in this porcine model of neonatal hypoxemia.

Dose Response of Intravenous Sildenafil on Systemic and Regional Hemodynamics in Hypoxic Neonatal Piglets

“…A left anterior thoracotomy in the third intercostal space was performed and a 6-mm flow probe (6SB906; Transonic Systems Inc) was placed around the main pulmonary artery to measure cardiac output. In our experience and in the experience of other authors (16), the patent ductus arteriosus in the piglets is functionally closed during normoxia and hypoxia. A 20G Insyte-W (Becton Dickinson Infusion Therapy Systems Inc, Sandy, Utah) was inserted and secured in the main pulmonary artery to measure PAP.…”

Resuscitation With 100% Oxygen Causes Intestinal Glutathione Oxidation and Reoxygenation Injury in Asphyxiated Newborn Piglets

“…Previous reports of intestinal blood flow during reoxygenation are contradic- tory, showing a hyperemic response during reoxygenation following hypoxia, 24 a return to prehypoxemic baseline blood flow, 38 or a decrease in mesenteric flow during the reoxygenation period. 39 While these studies 24,38,39 examined newborn piglets of similar maturity to our own, ranging from 0 to 5 days of age, the duration and severity of hypoxia varied, which may account for the different responses in SMA flow during reoxygenation. In our model, the degree and duration of hypoxia were clinically relevant, as indicated by the severity of hemodynamic changes and degree of asphyxia, which is similar to the clinical situation.…”

“…More severe hypoxia of shorter duration (57 Ϯ 6 minutes) resulting in similar clinically relevant hemodynamic and acid-base changes yielded similar changes in SMA flow upon reoxygenation, although no differences between 21% and 100% reoxygenation were reported. 24 This study, however, did not measure blood flow continuously and thus may have missed the differences seen between groups during early reoxygenation. Our study has further demonstrated that increased intestinal flow is a result of both decreased mesenteric vascular resistance and increased cardiac output during resuscitation.…”

“…This degree of hypoxemia was previously determined to consistently yield a clinically relevant degree of asphyxia, with severe hemodynamic changes in all piglets. 24 Following hypoxia, piglets were resuscitated with an F i O 2 of 0.21 (21% group), 0.50 (50% group), or 1.0 (100% group) for 1 hour, followed by 0.21 for 3 hours. A control group of piglets was ventilated and oxygenated at an F i O 2 of 0.21 for the 6 hours of study, with no period of hypoxia or reoxygenation.…”

“…Both human 22,23 and animal 24 studies have shown that the use of 21% oxygen is as effective or even better than 100% oxygen in the resuscitation of severely hypoxic newborns, in terms of recovery of cardiopulmonary function and organ perfusion. Furthermore, infants resuscitated with 100% oxygen had elevated blood markers of oxidative stress including an increased oxidized-to-reduced glutathione ratio, 23 which has been established as a marker for OFR-related cellular injury.…”