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 developed 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 blood and assess the potential use of such a measurement we present comparisons of changes in oxygen associated with whole blood and lipid content of plasma before, during and after cardiac surgery. 3. In a limited number of patients studied (n = 28), aged between 34 and 86 years, oxygen in lipid increased with decreased extracorporeal blood temperature during cardiopulmonary bypass, increased in proportion to oxygen supplied and appeared to be a better monitor of oxygen than conventional electrochemical systems currently in use. Oxygen associated with whole blood and plasma lipid was markedly below normal on aortic declamping after cardiopulmonary bypass, suggesting an hypoxic episode at this point. Levels of oxygen in the lipid phase of plasma returned to normal presurgical values 6-8 h after surgery. 4. Calculation of the concentration of lipid-associated oxygen present in plasma suggests that plasma lipids contain up to 25% of that typically ascribed to haemoglobin. Thus, we suggest that monitoring lipid-associated oxygen may prove a better alternative to current methods of measuring oxygen status. Furthermore, we suggest that plasma lipid is a hitherto unsuspected pool of circulating oxygen which may play a significant role in tissue oxygen supply.

Convective warming after hypothermic cardiopulmonary bypass.

In a randomized, controlled study, we found that convective warming after hypothermic cardiopulmonary bypass did not accelerate the rate of warming of the body core or the time to tracheal extubation. The relationship between body core and shell temperature, however, was affected. In all patients inadequate time spent rewarming on cardiopulmonary bypass prolonged body core warming time and time to tracheal extubation. Rate of warming of body core was inversely related to body mass index. Convective warming was delivered using BairHugger (Augustine Medical Inc., MN, USA) and Warm Touch (Mallinckrodt Medical UK Ltd, Northampton, UK) blankets. There was no difference between the performance of each blanket when powered by the BairHugger 500 power unit set at its medium setting of 38 degrees C, and when chest drain and radial artery cannulation sites were left exposed for observation.

Learning during general anaesthesia: implicit recall after methohexitone or propofol infusion.

Forty-four patients undergoing coronary artery surgery were allocated randomly to receive an infusion of propofol or methohexitone as a hypnotic supplement to a fentanyl-based anaesthetic technique. A taped message was played to the patients, consisting of 10 words associated with prompt sentences and a suggestion for a specific postoperative behavioural response. Twenty patients (10 propofol and 10 methohexitone) (perioperative group) were exposed to the taped message during surgery and in the immediate postoperative period and the other 24 patients (postoperative group) were exposed to the tape only in the postoperative period, after return to the intensive care unit (ICU). No patient had explicit recall of any events during the period when the tape was played. The patients in the propofol group who heard the tape during surgery had significant implicit recall of the word associations compared with the equivalent 10 methohexitone patients (P = 0.004), when tested 48 h after surgery. The patients who were played the tape whilst receiving identical infusion regimens for sedation in the ICU did not demonstrate implicit recall of the word associations in either the propofol or the methohexitone groups. There was no evidence of a response to the specific behavioural suggestion during the postoperative interview. The results confirm that auditory perception can occur during clinically adequate anaesthesia, and that suppression of auditory awareness or learning is a function of both the pharmacological degree of sedation and the degree of surgical stimulation.

Management of donors for heart and heart-lung transplantation.

The quality of donor organs will determine the quality of life for the recipient and the importance of optimal management of the multi-organ donor is that the organs may benefit up to five, critically ill, patients. The basic principle is to maintain sufficient preload to minimise the need for inotropic support and it is recommended that all multiple organ donors should have central venous and arterial pressure monitoring in addition to adequate venous access. The importance of the choice of fluid for volume expansion and the management of the hormonal disturbances which follow brain death are considered.

Vortex pumping for routine cardiac surgery: a comparative study.

Vortex pumping has become popular for mechanical assist applications, but has only recently received serious consideration for use as the arterial pump of choice for routine open-heart surgery. We report on a prospective randomized study designed to evaluate this pump in routine use. Sixteen patients undergoing routine coronary artery surgery were randomized into two groups in which the only difference in equipment and technique was the use of a Stockert roller pump in group S and a Biomedicus vortex pump in group B. The groups were compared with respect to haematology, perioperative fluid balance, transfusion requirements, complement activation, haemolysis and microbubble transmission. The groups were reasonably well matched, with slightly longer mean bypass and ischaemic times in group S (94.8 vs 105.5 minutes and 75.7 and 83.8 minutes respectively). Group B patients showed significant improvements over group S patients with respect to preservation of platelet numbers, decreased complement activation and reduced microbubble transmission. The afterload sensitivity of the vortex pump did not present the perfusionist with any practical problems although a different technique is required for initiating and terminating bypass. We conclude that vortex pumping would seem to offer better blood handling for routine use. More extensive testing is required to establish whether or not this would be reflected in clinically measurable improved patient outcome.

Storage and transport of heart and heart-lung donor organs with inflatable cushions and eutectoid cooling.

A system that uses a chemical method of cooling has been developed for the storage and transport of heart and heart-lung donor organs. This provides a precisely controlled environmental temperature without the use of ice, with its attendant problems of availability and potential contamination with pathogens. Storage and preservation solutions are transported to the donor hospital within the temperature-controlled polyurethane container, and the organs are returned in the same container, within an inflatable cushion. We have used this method for the distant procurement of over 260 hearts and for the most recent 30 heart-lung organ blocks. The mean ischemic time for hearts is 2.5 hours (1.5 to 4.2 hours) and for heart-lung blocks 2.2 hours (1.2 to 4.1 hours). Most donors give multiple organs such as kidney, liver, and pancreas. One patient received heart and kidney grafts from the same donor, and another received combined heart-lung and liver grafts. In relation to primary donor organ failure, there have been four deaths of patients who have had heart transplantations and no deaths of patients who received heart-lung organ blocks. We believe that the method offers advantages over the more conventional methods of organ storage with regard to convenience, temperature control, and sterility.

Medical services: nitrous oxide pollution in operating theatres.

The efficiency of facilities available for anaesthetic gas scavenging in East Anglian hospitals has been assessed using infrared spectrophotometry. Simple scavenging systems proved to be very effective and reduced the ambient nitrous oxide levels by a factor of ten. Sources of pollution outside of the influence of a scavenging system were due to damaged breathing systems, leaking ventilators and the anaesthetic technique. High levels could be further aggravated by poor maintenance of air conditioning equipment.

A comparison of five heat and moisture exchangers.

Five heat and moisture exchangers were investigated to compare their efficiency of humidification, their ability to filter bacterial spores and their various physical properties. The results are presented and the various mechanisms of heat and moisture exchange are reviewed. The Pall Ultipor BB50, because of its hydrophobic properties, has a slightly different action from heat and moisture exchangers already in use, The place of the Pall Ultipor BB50 in clinical practice is discussed.