PULMONARY CLEARANCE OF HELIUM AS A NON-INVASIVE MEASURE OF COLON BLOOD FLOW IN POST-HEMORRHAGIC HYPOTENSION

Abstract

Ischemic bowel disease causes significant morbidity in the neonate. We have shown that pulmonary clearance of helium (CLHeμl/min/kg) reflects hypoxia induced change in colon blood flow. (Ped Res 19:1025) This study investigates the effects of acute (12 ml/kg) and incremental (4-28 mlAg) post-hemorrhagic hypotension in young New Zealand rabbits. The animals were cannulated and connected to a respirator with fixed minute ventilation and an in-line helium mass-spectrometer. Two rabbits had electromagnetic flow probes around their distal abdominal aortae as well. Following a 30 min. stabilization, 10 ml/kg helium was injected rectally and CLHe and aortic blood pressure (ABP) were continuously monitored for 90 mins. Group I (n=6) was the control group; Group II (n=5) had 12 ml/kg of acute blood loss followed by total reinfusion and Group III (n=8) had incremental (4 ml/kg) blood loss (total 28 ml/kg over 30 mins.) without reinfusion. In Grps II and III 12 ml/kg blood loss caused a 51% and 58% fall in mean ABP with a simultaneous and proportionate fall in CLHe which were highly correlated (p<.001). Reinfusion (Grp II) caused an initial parallel increase in mean ABP and CLHe followed by a disproportionate increase in CLHe indicating rebound hyperemia. In Grp III beyond 12 ml/kg of hemorrhage the ABP and aortic blood flow stabilized while CLHe continued to fall. This could represent the critical point at which intestinal blood flow is diverted to vital organs. Conclusion: pulmonary CLHe changes predictably and simultaneously with changes in ABP and could provide a non-invasive measure of colon blood flow in the neonate.