The core body temperature better represents the temperature of the human body than the body surface temperature.1 When the core body temperature of a patient is less than 36°C due to various perioperative factors, this is known as perioperative hypothermia, a common phenomenon in patients undergoing surgery, especially under general anesthesia.2,3 Perioperative hypothermia can lead to many adverse outcomes, including perioperative adverse cardiovascular events (normal vs hypothermia was 1.4% vs 6.3%),4 surgical site infection (normal vs hypothermia was 6% vs 19%),5 coagulation dysfunction and increased blood transfusion requirements,6 decreased anesthetic efficacy, metabolic changes, delayed awakening times, and increased chills and discomfort,7,8 which can seriously affect the safety of surgical patients and decrease recovery quality.
For surgical patients under general anesthesia, hypothermia can result as a loss of consciousness, a lack of behavioral adjustment, and pharmacological inhibition of the central thermoregulatory responses as well as the chill response.9 All general anesthetics tested thus far markedly and briefly impair normal autonomic thermoregulatory control and can reduce thermoregulatory responses. As a result, the thermoregulatory response threshold range increased from 0.2 ℃ to 4 ℃. Furthermore, narcotic drugs can directly dilate blood vessels, and muscle relaxants affect chill response inhibition. Patients under general anesthesia are more likely to experience hypothermia than those who are not,10 especially those who undergo open operations with large areas or body cavities exposed. Both the new prevention guidelines for perioperative hypothermia in Germany11 and the national clinical guidelines in Britain12 stress the importance and necessity of perioperative hypothermia prevention. In addition, perioperative hyperthermia caused by fever or malignant hyperthermia, though not common, is often severe when it occurs. With some exceptions, anesthesiologists and operating room nurses are advised to maintain the patient’s temperature within the normal range.13 Therefore, it is necessary to monitor core body temperature throughout the operation, and an accurate measurement of core body temperature, even when in the normal range, is particularly important for surgical patients. Although the effective monitoring of intraoperative temperature changes is a prerequisite for maintaining constant and normal patient temperatures, it is difficult to manage the temperature of surgical patients.
Different methods of intraoperative core temperature monitoring have been developed and utilized. Core body temperature can be monitored intraoperatively at many sites, and a variety of devices are available. However, the most accurate measurements of core body temperature are also the most invasive and involve the pulmonary artery, esophagus, nasopharynx and eardrum.14 In many cases, invasive methods are not appropriate to measure core body temperature, and noninvasive methods are usually used instead. Minimally invasive and non-core body temperature measurements can usually replace invasive core body temperature measurements and include “deep” temperatures of the bladder, mouth and rectum.15 Other commonly used methods include oral temperature measurement, infrared ear temperature measurement, underarm temperature measurement, temporal artery thermometry and liquid crystal frontal temperature stripping. These methods are convenient, rapid, painless, and basically safe and risk free. However, the accuracy of intraoperative body temperature varies with different collection devices and sites. In addition, whether intraoperative core temperature can be continuously monitored throughout the whole course is an issue worthy of discussion.
The blood temperature of the axillary artery reaches or is near core body temperature. In a warm environment, as in a hospital, the temperature measured near the axillary artery after a period of adduction and clamping of the arm can be used to approximate core body temperature.16 In contrast, the randomly measured axillary temperature can be used to approximate skin temperature and is often 3°C lower than core body temperature. With the traditional method, even the axillary temperature obtained by careful measurement does not better reflect core body temperature.17 A meta-analysis also confirmed considerable variability.18 The relationship between axillary temperature and core body temperature therefore depends largely on the measurement technology and clinical environment. A novel wireless temperature sensor (iThermonitor, CW100X) was used in conjunction with a temperature monitoring device that provides better core temperature estimation than traditional axillary thermometers. This improvement is due to the continuous temperature measurement and recording of the iThermonitor temperature sensor at a frequency of once every 4 seconds and the use of a patented algorithm to compensate for the temperature error of the ambient temperature and the change in the measurement position. The accuracy of the iThermonitor in the intraoperative monitoring of core temperature in adult noncardiac surgery was confirmed, and the difference between the core temperature reflected by using the iThermonitor temperature sensor to monitor the body surface temperature and esophageal core temperature is only 0.14°C ± 0.26°C.19 Our previous study was conducted on 3621 pairs of body temperatures measured, which showed that the temperatures measured with the iThermonitor agreed with those measured with the mercury thermometers overall, with a mean difference of 0.03°C ± 0.35℃ and a moderate correlation (r = 0.755, P < 0.001),20 implying that the iThermonitor is promising for continuous, remote, noninvasive, wireless and intelligent temperature monitoring in surgical patients.
To our knowledge, there is currently a lack of research on monitoring core body temperature via the body surface using noninvasive and wireless body temperature sensors in patients undergoing lung cancer surgery. The changes in intraoperative core body temperature and the influence of hypothermia on rapid recovery indicators of patients undergoing lung cancer surgery remain unclear. These limitations of existing results can, to some extent, be addressed by analyzing the feasibility and significance of core temperature monitoring. Therefore, it is necessary to explore a feasible and reliable method to monitor and investigate changes in core body temperature of the patients undergoing lung cancer surgery to effectively manage their body temperature and prevent hypothermia. Thereafter, we used research data from a registry to examine the feasibility and effectiveness of wireless and noninvasive body surface monitoring (using the iThermonitor® temperature sensor) of core body temperature in patients undergoing lung cancer surgery and the contribution of hypothermia exposure to prolonged hospital stays and increased medical costs.