Changes in Blood Oxygen Transport Function and Body Energy Expenditure During Anaesthesia During Cardiac Surgery in Adults: a Randomized Clinical Trial

Introduction Anaesthetic support for various types of cardiac surgery, such as coronary artery bypass grafting (CABG), heart valve repair or replacement, ascending aorta surgery, heart transplantation and surgical treatment of congenital heart disease, share many principles. Indirect calorimetry can be an indicator of homeostatic changes during surgery. Stress increases oxygen consumption (VO2) and during anaesthesia there is a decrease in VO2.

Cardiac surgery in adults is associated with the occurrence of postoperative complications [1]. Even minor complications, can increase the cost of their treatment. Given the potentially preventable nature of a number of these postoperative complications, preventive methods should be used to improve outcomes after cardiac surgery. One of them, is the choice of anaesthetic technique [2].

Tissues vary considerably in their sensitivity to hypoxia. Neurons tolerate hypoxia for only a few minutes, whereas the smooth muscles of the bladder go several days without oxygen. This has important implications for oxygen transport and monitoring of tissue hypoxia in patients. The mechanisms controlling the distribution of oxygen in the body are not fully understood (3). Increased oxygen extraction, the ratio of consumption to transport, has been associated with poor outcome after surgery. The authors note [4] a -65 ml decrease in oxygen consumption after general anaesthesia. Researchers [5,6] found that surgery and anaesthesia did not significantly affect oxygen consumption and energy expenditure during anaesthesia. However, Julia Jakobsson et al (2021) state that general anaesthesia reduced VO2 by approximately one third in elderly patients undergoing major abdominal surgery. These changes require further evaluation in relation to outcomes and surgery (7). Cerebral blood flow was reduced by 27.6% and cerebral vascular resistance by 51% at moderate propofol concentrations. Brain oxygen consumption was reduced by 18.2% [8]. Oxygen delivery (DO2) is an important marker of O2 transport than arterial blood oxygen saturation (SaO2). Anaesthetics (propofol or sevoflurane) had no significant effect on DO2 . In addition, no correlation was found between SaO2 and DO2. DO2 data may provide useful additional information about the patient's condition, especially with low SaO2 [9]. A decrease in metabolic rate during anaesthesia has been noted in patients with hypothermia, but this did not alter DO2. A significant decrease in O2ER might be partly due to a shift to the left of the oxyhemoglobin dissociation curve, as indicated by a decrease in P50 [10]. Oxygen consumption during general anaesthesia was independent of the type of anaesthetics. General anaesthesia leads to a marked decrease in oxygen consumption, but during recovery the O2 uptake can increase dramatically. Meperidine can suppress and reduce postoperative VO2 to the level observed after TIA [11]. Indirect calorimetry can be an indicator of homeostatic changes during surgery. Stress increases oxygen consumption and during anaesthesia there is a decrease in VO2 due to lack of kinetic energy as a cellular metabolic response to surgical trauma and anaesthesia. More research is needed to find out which oxygen consumption measurement system is the most appropriate for anaesthesia and what the VO2 limit values might be [12].

In view of the above opinion of the authors and the lack of studies that have shown the effects of sevoflurane, isoflurane and propofol on energy expenditure, blood oxygen and oxygen transport function, this needs to be further investigated.

Objectives: To evaluate the effects of sevoflurane, isoflurane and propofol on blood oxygen transport function and body energy expenditure during cardiac surgery in adults.