Protective effect of sevoflurane preconditioning on ischemia-reperfusion injury in patients undergoing reconstructive plastic surgery with microsurgical flap, a randomized controlled trial

In our study, we tried to assess the damage from ischemia reperfusion in two groups of patients undergoing DIEP flap for breast reconstruction.

As a marker of ischemia reperfusion, regional tissue O2 saturation in the 24 h following surgery was evaluated, along with blood levels of lactate, transaminases, lactic dehydrogenase and creatine phosphokinase. Conversely, the failure of the microsurgical flap was not considered a valid outcome to assess the damage from ischemia reperfusion since it is influenced by numerous technical variables (proper surgical technique, involvement of more than one microvascular surgeon, intraoperative fluid administration). However, the incidence of surgical site infection and surgical re-exploration were recorded.

The regional tissue oximetry is based on blood chromophores’ different characteristics of absorption of the near infrared light, in particular hemoglobin and deoxyhemoglobin’s absorption. This system, reflecting the balance between oxygen supply and demand, is a validated non-invasive and reproducible [12] method for continuous surveillance of oxygenation and perfusion of the analyzed tissue. In plastic surgery this technology is already widely used to monitor free tissue transfers [13, 14], not only for breast free flaps, but also in head, neck [15, 16] and lower extremity flaps [17].

Our results show that there is a significant increase of the average value of rSO2 measured according to INVOS at 4 h after surgery in the BAL group. It was also increased in other time frames and compared to average values, but not in a statistically significant manner. The CPK at the end of the surgery is also significantly lower in the sevoflurane group, but the difference in the two groups tends to disappear in later times.

From the results obtained, we can assert that there is an improvement of flap oxygenation with sevoflurane preconditioning, but this effect seems to be limited in time, and as hours pass the level of tissue oxygenation returns comparable to the one of not preconditioned tissue.

Congruent with our results, Balzan and colleagues [18] in their study on animals subjected to hepatic preconditioning with sevoflurane, found lower levels of C-reactive protein after ischemia, which increased in following time frames, and they concluded that the protective effect is mainly circumscribed to the initial phase of injury whereas it lessens as time elapses.

In a recent review, Swyers [19] described two possible phases of sevoflurane protection in ischemia reperfusion injury, with a mechanism similar to the protective effect of ischemic preconditioning. Swyers attributed the protective effect of volatile anesthetics to their ability to interact with the multi-signaling pathway of mitochondrial K-ATP channels. The action mechanism proposed was to hinder the entry of calcium ions in the mitochondria, allowing the functionality of the mitochondrial membrane to remain unaltered, mimicking the early phase of ischemic preconditioning. Most of studies in literature have focused on the early phase of protection, but the duration of the beneficial effects of preconditioning with volatile anesthetics remains uncertain. The early phase protection appears immediately after ischemic stimuli, but disappears within 2–4 h. The late phase protection emerges around 12 to 24 h after the initial ischemic preconditioning and lasts for 2 or 3 days [20, 21]. Some studies [22, 23] have identified adenosine and nitric oxide as the vasoactive mediators that begin a complex signal transduction cascade involving the activation of transcription factors which results in the synthesis of effector proteins. These effector proteins may confer cytoprotection in the second phase of prolonged ischemic stress. Our results may indicate a slight decrease in the protective action of sevoflurane during this phase of late protection.

The main factors that could explain our dissonant results compared to current literature are the administration of sevoflurane and the examined population.

Isofluorano studies have shown a dose-dependent protective effect of anesthetic preconditioning, reveling that higher concentrations of volatile anesthetic are more protective than lower concentrations [24‐26]. On the other hand, many studies show benefits of preconditioning only after prolonged pre ischemic administration of sevoflurane [27, 28]. It is possible that a protective effect would have occurred if we had planned higher concentrations or a longer administration of sevoflurane in our study.

Further considerations regard the female population under examination. Many studies on animals and on humans have reported that female hearts have higher tolerance for ischemic injury compared to males’ [29, 30]. This difference seems to be determined by the effects of female hormones. Estrogen contributes to a natural cardioprotection in adult women by reducing oxidative stress, acting on inflammation factors and improving coronary flow [31, 32].

In his study on rabbits, Wang [33] speculates that isoflurane’s late phase protection is only active for males, not for females. This gender specificity would be due to the high baseline levels of endothelial nitric oxide synthase (eNOS) expressed in females, due to estrogen, which naturally give additional protection against myocardial infarction, but do not grant the benefit of preconditioning effects of volatile anesthetics in females, through a mechanism that has not yet completely been understood.

Another animal study [34] indicated that anesthetic postconditioning could also lead to gender differences in cardioprotection. In this case, the protective effect on males is expressed through the key role of the phosphatidylinositol-3-kinase (PI3K / Akt) pathway. Due to estrogen influence, in female rats the PI3K/Akt pathway was already markedly overexpressed and was not activated any further by postconditioning with sevoflurane.

Sevoflurane preconditioning has been widely investigated in the context of cardiac surgery and clinical studies have shown that sevoflurane is cardio-protective in cardiac surgery patients [35], but this effect is ambiguous on other tissues and organs in different surgical fields [6]. Some studies on patients undergoing liver resection [36, 37] did not show significant differences in hepatocyte and endothelial dysfunction markers, nor in postoperative outcomes between the groups. In addition, results on kidney function are controversial, and they were unable to report definitive improvements in the degree of kidney injury [38, 39].

About microvascular breast flap surgery, there are no studies that have investigated the protective effect of sevoflurane on ischemia reperfusion injury, also due to the lack of highly specific blood markers. In our case, we considered regional O2 inflow measured by NIRS technology and common markers of cellular damage valid indicators to assess the damage from IR. Although we excluded patients with vascular or bleeding pathologies from the study, the relation between tissue perfusion and management is complex and multifactorial, so we tried to minimize counfunding factors by using strict protocols. Mean arterial pressure was maintained in established limits using opioids and hypnotic drugs, fluid therapy was also used to regulated ABP and to replace loss, the temperature was also maintained constant in the operating room.

Regarding the weaknesses of our study, this is a multicentric trial, so the surgery was conducted by two different equipes, this obviously determined a margin of procedure variability. To minimize this inter-instituitonal gap we standardized the anesthesiological management while the surgical procedure was discussed and decided out of accorded with the two operative teams. Other limits: the number of patients was relatively small and we used a single preconditioning protocol; our study may represent a starting point for future studies, which will also consider different volatile anesthetic concentrations and different preconditioning timings.