Thermal Preconditioning for Surgery: A Systematic Review

Preconditioning Strategies for Improving the Outcome of Fat Grafting

Autologous fat grafting is a common procedure in plastic, reconstructive, and aesthetic surgery. However, it is frequently associated with an unpredictable resorption rate of the graft depending on the engraftment kinetics. This, in turn, is determined by the interaction of the grafted adipose tissue with the tissue at the recipient site. Accordingly, preconditioning strategies have been developed following the principle of exposing these tissues in the pretransplantation phase to stimuli inducing endogenous protective and regenerative cellular adaptations, such as the upregulation of stress-response genes or the release of cytokines and growth factors. As summarized in the present review, these stimuli include hypoxia, dietary restriction, local mechanical stress, heat, and exposure to fractional carbon dioxide laser. Preclinical studies show that they promote cell viability, adipogenesis, and angiogenesis, while reducing inflammation, fibrosis, and cyst formation, resulting in a higher survival rate and quality of fat grafts in different experimental settings. Hence, preconditioning represents a promising approach to improve the outcome of fat grafting in future clinical practice. For this purpose, it is necessary to establish standardized preconditioning protocols for specific clinical applications that are efficient, safe, and easy to implement into routine procedures.

Agreement of zero-heat-flux thermometry with the oesophageal and tympanic core temperature measurement in patient receiving major surgery

To identify and prevent perioperative hypothermia, most surgical patients require a non-invasive, accurate, convenient, and continuous core temperature method, especially for patients undergoing major surgery. This study validated the precision and accuracy of a cutaneous zero-heat-flux thermometer and its performance in detecting intraoperative hypothermia. Adults undergoing major non-cardiac surgeries with general anaesthesia were enrolled in the study. Core temperatures were measured with a zero-heat-flux thermometer, infrared tympanic membrane thermometer, and oesophagal monitoring at 15-minute intervals. Taking the average value of temperature measured in the tympanic membrane and oesophagus as a reference, we assessed the agreement using the Bland-Altman analysis and linear regression methods. Sensitivity, specificity, and predictive values of detecting hypothermia were estimated. 103 patients and one thousand sixty-eight sets of paired temperatures were analyzed. The mean difference between zero-heat-flux and the referenced measurements was -0.03 ± 0.25 °C, with 95% limits of agreement (-0.52 °C, 0.47 °C) was narrow, with 94.5% of the differences within 0.5 °C. Lin's concordance correlation coefficient was 0.90 (95%CI 0.89-0.92). The zero-heat-flux thermometry detected hypothermia with a sensitivity of 82% and a specificity of 90%. The zero-heat-flux thermometer is in good agreement with the reference core temperature based on tympanic and oesophagal temperature monitoring in patients undergoing major surgeries, and appears high performance in detecting hypothermia.

Pinocembrin alleviates pyroptosis and apoptosis through ROS elimination in random skin flaps via activation of SIRT3

Random skin flap grafting is the most common skin grafting technique in reconstructive surgery. Despite progress in techniques, the incidence of distal flap necrosis still exceeds 3%, which limits its use in clinical practice. Current methods for treating distal flap necrosis are still lacking. Pinocembrin (Pino) can inhibit reactive oxygen species (ROS) and cell death in a variety of diseases, such as cardiovascular diseases, but the role of Pino in random flaps has not been explored. Therefore, we explore how Pino can enhance flap survival and its specific upstream mechanisms via macroscopic examination, Doppler, immunohistochemistry, and western blot. The results suggested that Pino can enhance the viability of random flaps by inhibiting ROS, pyroptosis and apoptosis. The above effects were reversed by co-administration of Pino with adeno-associated virus-silencing information regulator 2 homolog 3 (SIRT3) shRNA, proving the beneficial effect of Pino on the flaps relied on SIRT3. In addition, we also found that Pino up-regulates SIRT3 expression by activating the AMP-activated protein kinase (AMPK) pathway. This study proved that Pino can improve random flap viability by eliminating ROS, and ROS-induced cell death through the activation of SIRT3, which are triggered by the AMPK/PGC-1α signaling pathway.

Thermal preconditioning can reduce the incidence of intraoperatively acquired pressure injuries

Intraoperatively acquired pressure injuries (IAPIs) occur frequently among patients who undergo surgical procedures that last longer than 3 h. Several studies indicated that heat shock proteins (HSPs) play an important role in the protection of stress-induced damages in skin tissues. Hence, the aim of this study was to investigate the potential preventive effect of thermal preconditioning (TPC) on IAPIs in surgical patients and rats and to identify the differentially expressed HSP genes in response to the above treatment. TPC was performed on one group of hairless rats before the model of pressure injuries was established. Subsequently, the size of skin lesions was measured and the expression levels of mRNA and protein of HSPs of the pressured skin were detected by real-time polymerase chain reaction (RT-PCR), western blot, and immunohistochemical staining. For human studies, 118 surgical patients were randomly divided into the TPC group (n = 59) and the control group (n = 59), respectively. The temperature and pressure of sacral skin, as well as the incidence of pressure injury (PI) were detected and compared. In animal studies, TPC significantly reduced both the size and incidence of PI in rats on the second, third and fourth days post treatment. In addition, the expression levels of both mRNA and protein of HSP27 were increased in the TPC group, compared with the control group. Immunohistochemical staining showed that HSP27 was distributed in various types of dermal cells and increased in basal cells. In human studies, a significant reduction (75%) of IAPIs was observed among the patients in the TPC group. TPC can reduce the incidence of PI in rats and humans, and the upregulation of HSP27 may play an important role in this biological progress. Further studies are warranted to explore the molecular mechanism of the preventive effect in PI mediated by HSP27.

The effects of prolonged intraoperative hypothermia on patient outcomes in immediate implant-based breast reconstruction

BACKGROUND

The importance of thermoregulation in surgical procedures has become a recent focus for anesthesiologists and surgeons to improve patient outcomes. In breast surgery, maintenance of normothermia has been shown to reduce surgical-site infections. However, there is a paucity of information evaluating the relationship between intraoperative core body temperatures and reconstructive surgical outcomes.

METHODS

A retrospective review of patients who underwent immediate breast reconstruction following mastectomy from 2015 to 2020 was performed. Patients were classified into a majority normothermic (NT) group if patients spent greater than half of the operative time ≥36 °C or a majority hypothermic (HT) group if patients spent greater than or equal to half of the operative time <36 °C. Patient demographics, comorbidities, surgical techniques, and postoperative complications were recorded. Complications were classified according to the Clavien-Dindo Classification. Univariate and multivariate statistics were used to assess significant relationships.

RESULTS

A total of 329 patients met inclusion criteria, of which 174 were in the NT group and 155 were in the HT group, yielding 302 and 264 total breasts, respectively. There was no significant difference in rates of infection (p = 1.0), seroma (p = 0.27), hematoma (p = 0.61), or wound dehiscence (p = 1.0). However, patients in the HT group had significantly more overall ischemic complications (p = 0.009) and, specifically, grade IIIb ischemic complications (p = 0.04). After controlling for tobacco use, body mass index, mastectomy pattern, radiation, operating surgeon, and mastectomy weight, multivariate analysis showed increased ischemic complications in the HT group (p = 0.04).

CONCLUSION

Prolonged intraoperative hypothermia can increase the risk for the development of ischemic wounds such as tissue necrosis or eschar formation that require operative intervention. This presents reconstructive complications that increase both patient and health system burdens that could be addressed through the maintenance of normothermia. Further studies using real-time flap temperature would provide more accurate insight into the relationship between temperature and implant-based breast reconstruction.

Heme oxygenase‑1 improves the survival of ischemic skin flaps (Review)

Heat shock protein 32 (Hsp32), also known as heme oxygenase‑1 (HO‑1), is an enzyme that exists in microsomes. HO‑1 can be induced by a variety of stimuli, including heavy metals, heat shock, inflammatory stimuli, heme and its derivatives, stress, hypoxia, and biological hormones. HO‑1 is the rate‑limiting enzyme of heme catabolism, which splits heme into biliverdin, carbon monoxide (CO) and iron. The metabolites of HO‑1 have anti‑inflammatory and anti‑oxidant effects, and provide protection to the cardiovascular system and transplanted organs. This review summarizes the biological characteristics of HO‑1 and the functional significance of its products, and specifically elaborates on its protective effect on skin flaps. HO‑1 improves the survival rate of ischemic skin flaps through anti‑inflammatory, anti‑oxidant and vasodilatory effects of enzymatic reaction products. In particular, this review focuses on the role of carbon monoxide (CO), one of the primary metabolites of HO‑1, in flap survival and discusses the feasibility and existing challenges of HO‑1 in flap surgery.