PLASMA OXYGEN DURING CARDIOPULMONARY BYPASS - A COMPARISON OF BLOOD-OXYGEN LEVELS WITH OXYGEN PRESENT IN PLASMA-LIPID

1. Although not often appreciated, it is a fact that molecular oxygen is more soluble in lipids than in aqueous solution, We have recently d eveloped a method to monitor oxygen within the lipid content of plasma , Monitoring plasma oxygen is one essential element during open heart surgery using a cardiopulmonary bypass pump and oxygenator, Currently oxygen is monitored electrochemically and is based upon monitoring the partial pressure of oxygen in a gas equilibrated with whole blood. 2. To determine the relative importance of lipid-associated oxygen in bl ood and assess the potential use of such a measurement we present comp arisons of changes in oxygen associated with whole blood and lipid con tent of plasma before, during and after cardiac surgery. 3. In a limit ed number of patients studied (n = 28), aged between 34 and 86 years, oxygen in lipid increased with decreased extracorporeal blood temperat ure during cardiopulmonary bypass, increased in proportion to oxygen s upplied and appeared to be a better monitor of oxygen than conventiona l electrochemical systems currently in use. Oxygen associated with who le blood and plasma lipid was markedly below normal on aortic declampi ng after cardiopulmonary bypass, suggesting an hypoxic episode at this point. Levels of oxygen in the lipid phase of plasma returned to norm al presurgical values 6-8 h after surgery. 4. Calculation of the conce ntration of lipid-associated oxygen present in plasma suggests that pl asma lipids contain up to 25% of that typically ascribed to haemoglobi n, Thus, we suggest that monitoring lipid-associated oxygen may prove a better alternative to current methods of measuring oxygen status, Fu rthermore, we suggest that plasma lipid is a hitherto unsuspected pool of circulating oxygen which may play a significant role in tissue oxy gen supply.