In our study, we compared four FAW systems for preventing hypothermia, and found that for patients undergoing elective laparoscopic radical resection of colorectal cancer under general anesthesia, all four types of FAW systems were able to prevent perioperative hypothermia, and the Group A system was most effective in maintaining normal body temperature compared with other FAW systems. The findings were also confirmed in manikin study, and the results revealed that the preferred product selected by EMTP is consistent with the preferred product selected in this study within a certain range of parameters. With the popularization of the enhanced recovery after surgery (ERAS) concept in recent years, perioperative body temperature protection has become more and more significant, and researchers have never stopped exploring thermal insulation measures, including active and passive warming[12]. Passive warming measures include sheet, surgical draping outside the operating field and so on[17]. FAW blanket is a common active warming measure, which is currently considered to be the most effective method for the prevention and treatment of hypothermia during the perioperative period according to the prior guidelines[18]. There are many manufacturers producing this product at domestic and foreign, and the prices of FAW blankets of different systems vary greatly. However, it is unclear whether there are differences in their clinical warming property. Elderly patients particularly, especially those over 65 years old, are at higher risk of hypothermia due to the low effective regulation ability of the central nervous system to body temperature, low basal metabolic rate, poor nutritional status and reduced subcutaneous adipose tissue[19, 20]. Therefore, the inclusion of elderly patients in this study is of great significance for the clinical guidance of perioperative body temperature protection.
The FAW system of group A was more effective than other systems in preventing hypothermia, the result was also confirmed in manikin study. This may be due to that group A FAW system has more holes per unit area than other FAW systems, and the more holes, the better the insulation effect. The heater outlet warming curve indicates that group C is still heating up despite reaching the equilibrium, this continued warming may lead to a risk such as skin empyrosis, so continuous temperature monitoring and early prevention of hyperthermia are very necessary during clinical warming blanket application. Although the pressure difference in group C was higher than that in the other groups in the manikin study, the patients were under anesthesia during surgery and there were no significant sensory differences. However, for awake patients such as cesarean delivery, prolonged operation with supine position may cause discomfort due to air pressure difference. In addition, no significant differences were found in our study among the four groups in terms of surgical site infections (SSI). There have been concerns that FAW system may increase the incidence of SSI by disrupting the operation room laminar airflow, and then transporting contaminants from the floor to the sterile surgical field[21]. Recently, a study by Shirozu K et al reported that FAW blanket would be less likely to cause surgical field contamination in the presence of sufficient laminar airflow, because the heated airflow produced by FAW system is well counteracted by downward laminar airflow from the ceiling, so there is little risk of SSI in the surgical area[22]. Furthermore, hole observation test showed that no fiber floated around the hole in group A FAW system, which may also reduce the incidence of SSI by preventing fiber from entering the surgical area. It is worth noting that the manufacturing process of FAW system is more standard and preventive measures (such as antibiotic application, sterile conditions, etc) against infection are more effective. A number of studies have also shown that FAW system may have beneficial effects against SSI by maintaining circulation and oxygen transport at the incision as well as preserving an effective immune response[23]. In a word, even if the four FAW systems can efficiently prevent perioperative hypothermia to a certain extent, more advantageous insulation systems tend to still have better performance details, group A FAW system had lower air pressure difference, greater number of holes per unit area and no fiber floated around the hole than other groups, so it can provide better heating effect.
At present, the working principles of inflatable insulation blankets on the market are basically similar, but their materials are different, and their stability in the process of use may not be the same. From the perspective of hospitals and medical insurance policies, cost-sensitive hospitals will give priority to FAW system according to the characteristic of economy, efficiency and convenience. According to the results of this study, all four FAW systems can meet the basic insulation requirements, which could well prevent the occurrence of hypothermia and postoperative shivering, has no significant impact on hemodynamics, so different types of surgery can be flexibly selected according to the actual situation to reduce hospital economic burden. When it is employed in various types of major operations with the planned long operation time, such as laparotomy, thoracotomy, critically ill patients and cardiac surgery, the Group A FAW system effect may be superior than the other three warming systems through reducing the heat loss perioperatively. For small and medium-sized surgery or surgery with less estimated operation time and less heat dissipation, interventions using other types of FAW systems (eg: group D) with relatively low price can be recommended to reduce the medical cost and socio-economic burden without affecting the thermal insulation effect of patients. Martindale abrasion resistance test showed that the durability of group D was similar to that of group A, and also had a good warming effect. Therefore, the group D FAW system for minor surgery can be employed repeatedly to reduce the medical fees.
The strength of our study is that it is the first in-depth multi-center research to investigate the effectiveness of different FAW systems on patient body temperature protection in laboratory manikin study and clinical practice. There were also several additional limitations to our study. Firstly, hypothermia still occurred in a small number of patients when sterile dressings, warm infusion fluid, abdominal lavage fluid and other measures were taken to prevent hypothermia during the perioperative period. Previous studies have confirmed that preoperative active FAW intervention can decrease the overall intraoperative hypothermic exposure[24], so further investigation into the effectiveness of preoperative combined with intraoperative FAW is warranted. Secondly, it is difficult to achieve a double-blind study due to the obvious differences in the appearance of FAW systems of different products. Lastly, this study is only applicable to patients undergoing laparoscopic radical resection of colorectal cancer, so the extrapolation of the results was limited.