Hypothermia, defined as a core body temperature less than 36°C (96.8°F), is a relatively common occurrence in the unwarmed surgical patient . Hypothermia is associated with increased perioperative bleeding, a delay in wound healing, prolonged anesthesia extubation time, increased cardiac complications and even increased mortality . Even in mild hypothermia, a significant increase in cardiac complications is observed . In a previous study, the risk of hypothermia at the end of the operation was calculated as 77% in patients without perioperative heating. Many national and international guidelines have been published to reduce the risks of hypothermia ,,. However, the application of guidelines and the measures taken to prevent hypothermia seems to be insufficient. In a study, it was observed that anesthesiologists do not sufficiently follow hypothermia guides . Eventually, despite the precautions taken, it was seen that a significant proportion of patients were sent to the recovery room hypothermic after the operation. Complications from hypothermia result in prolonged hospitalization, mortality, morbidity, which justifies the importance of this issue on the agenda.
Apart from applying active heating methods in patients, the effectiveness of anesthesia in preventing hypothermia is a research topic. There are limited numbers of studies in the literature examining the effect of mechanical ventilation settings on core temperature . In a study comparing lung-protective ventilation and conventional high tidal volume ventilation, lung-protective ventilation did not have an advantage in maintaining the patient’s core temperature . It is critical to reaching the isothermal saturation limit to avoid damage to the mucosa and the ciliary epithelium . The excessive flow of fresh gas into the anesthesia circuit in high-flow anesthesia requires the air supplied to the patient to be reheated and humidified each time . This causes temperature loss in the patient through the airway. Also, better protection of mucociliary activity in LFA provides a benefit in maintaining temperature . In our results, it was seen that patients who underwent HFA had more temperature loss. Low fresh gas application is more effective in maintaining the patient's core temperature. Theoretically, this method may also reduce the costs associated with hypothermia complications and may be another cost effect of LFA.
The use of sevoflurane in low flow anesthesia started late compared to desflurane due to manufacturers' recommendations and renal side effect concerns. Nowadays, sevoflurane is a frequently preferred gas in low flow anesthesia . However, there are still some risks of low flow anesthesia. Some problems should be taken into consideration, such as increased risk of hypercarbia, early depletion of carbon dioxide absorption, the possibility of failing to achieve target oxygenation even with 100% oxygen delivered to the circuit in overweight patients . The need to calibrate flow meters for low flow will always be a must . Considering the results of our study; with all its benefits and limitations; As long as careful monitoring and control of concentrations and appropriate technology are performed, Low-flow anesthesia appears to be profitable for the hospital and advantageous for the patient in maintaining core temperature, with the potential to reduce complications and costs from hypothermia.
In our study, the mean duration of surgery was 185.6 ± 59.7 minutes, and our incidence of hypothermia was 32.5%. In a study conducted by Aksu et al, which included pediatric and geriatric patients, the incidence of postoperative hypothermia was found to be 45% . In another study conducted on geriatric patients, the incidence of hypothermia increased even in operations under 1 hour . The benefit of LFA application on reducing temperature loss may be more pronounced in procedures that take longer than one hour, and in hypothermia-sensitive groups such as pediatric and geriatric patients.
There are also studies showing that patients wake up faster after low flow anesthesia . Heiler et al. showed that plasma anesthetic concentrations were higher in hypothermic patients during recovery . Recovery times were not examined in our study. However, we determined that different flow rates affect the core temperature and we think that the reduction of temperature loss in low flow anesthesia may have an effective role on rapid recovery. An additional warming method was not applied to the patients in our study group. Operating room temperatures were in a constant range in each room. In our study, the operations were maintained in all three groups with fixed-range analgesic dose and neuromuscular blockers, and the depth of anesthesia was not followed during the operation. Many factors increase perioperative core temperature loss . Considering all these in the same study and the correlations of these factors with temperature loss may be the subject of a different study. Although low-flow anesthesia reduced core temperature loss, it was certainly not sufficient alone to reduce the incidence of hypothermia. Besides, in cases where the anesthesia method cannot be changed, changing the method of applying anesthetic gas (HFA or LFA) may be a method to reduce core temperature loss.
the most important limitation of our study is that it is a retrospective study. In addition, the low number of study patients can be considered as another important limitation. Undoubtedly, more operations were performed in the ENT room during the specified periods. However, the selection criteria for inclusion in our study and the exclusion of patients with incomplete information in their files caused a significant decrease in the number of patients. In practice, many factors can affect the patient's temperature. It may be necessary to work with a larger number of patients to understand the total effect of these factors. Since our study was conducted with retrospective data, we tried to keep other factors constant in order to focus only on the effect of fresh gas flow on core temperature. We believe that a larger patient cohort should be used in a prospective study. This study may also contribute to future studies as it shows that low flow anesthesia can contribute to the maintenance of core temperature as well as to reduce costs.