Effects of hyperoxic ventilation on 6-h survival at the critical haemoglobin concentration aggravated by experimentally induced tachycardia in anaesthetized pigs.

Aim:  Administration of 100% oxygen [hyperoxic ventilation (HV)] has been proven to ameliorate oxygen transport, tissue oxygenation and survival in different models of extreme normovolemic and hypovolemic anaemia. However, up to date, it is unknown whether HV is also able to improve outcome of extreme anaemia if myocardial oxygen consumption is contemporaneously increased by tachycardia. Therefore, we investigated the influence of HV on the 6-h survival rate during extreme anaemia and aggravated by experimentally induced tachycardia in a prospective, randomized study in a pig model of critical anaemia. Methods:  After government approval, 14 anesthetized pigs mechanically ventilated on room air were haemodiluted by replacing a certain amount of whole blood with hydroxethyl starch 6% (200.000/0.5) until their individual critical haemoglobin concentration (Hbcrit) was achieved. At Hbcrit, tachycardia (180 bpm) was induced in all animals by atrial pacing. Thereafter, animals were observed for the next 6 h either at room air (FiO2 0.21; group NOX) or during HV (FiO2 1.0; group HOX) without further intervention. As primary outcome parameter of this study, the 6-h survival rate was selected. Results:  Hyperoxic ventilation increased the 6-h survival rate from 14 to 100%. In contrast to the NOX group, macrohaemodynamics and oxygen transport improved in the HOX group during the observation period without apparent adverse effects of HV. Conclusions:  Hyperoxic ventilation can be considered a safe and effective measure for the optimization of oxygen supply during extreme anaemia and despite concomitant tachycardia within 6 h. Whether HV can also be recommended beyond this period warrants further studies.