The results showed a significant decrease in the mean total calculated blood loss in the dexmedetomidine group compared to that in the control group. This may have been due to the hemodynamic effect of dexmedetomidine. Continuous infusion of dexmedetomidine led to decreased HR and BP, which was caused by a negative feedback loop of norepinephrine. Recent studies have also suggested that dexmedetomidine can decrease blood loss throughout several different surgical procedures [8, 16]. In previous studies, the surgical field of vision, which significantly affects blood loss, was considered to be directly related to decreased HR [17, 18]. There is evidence that decreasing MAP below 70 mmHg increases intraoperative bleeding due to local vasodilation , but decreased HR is strongly correlated with cardiac output, which is associated with operative field of vision . In contrast to α2 agonists, inhalational anaesthetics lead to vasodilatory effects and reflex tachycardia. Furthermore, opioids are less effective than dexmedetomidine in reducing HR. Decreased mean arterial pressure without controlled HR does not lead to improved visibility or lessened bleeding. In addition, the vasoconstrictive effect of intravenous dexmedetomidine has been demonstrated in animal models [20, 21]. Furthermore, studies have provided evidence that intravenous dexmedetomidine has similar vasoconstrictive effects on human arteries and veins . Contraction of the peripheral vessels caused by intravenous dexmedetomidine would further promote surgical site visualisation and reduction of bleeding. Improved surgical field of vision has been mentioned in other studies [23, 24]. This finding is important since it is closely related to blood loss and ease of operation for surgeons. Unfortunately, because this is a retrospective study, the intraoperative visual field could not be assessed using a numerical rating scale or other quantitative methods. Therefore, we could not verify whether the intraoperative field of vision in orthognathic surgery was improved as in other surgeries. Reduced bleeding will lead to fewer complications, such as hematoma, respiratory obstruction, and asphyxia, and will further promote the patient's postoperative recovery.
There was a significant increase in postoperative haemoglobin in patients treated with intraoperative dexmedetomidine. Patients who received allogeneic blood transfusions during operations were excluded because the level of postoperative haemoglobin would be affected. Reduced intraoperative blood loss increased levels of postoperative haemoglobin and improved postoperative safety. Postoperative anaemia is associated with dizziness, tinnitus, fatigue, hypoxia, and other side effects . Postoperative acute anaemia is correlated with an increased risk of injury to major organs, such as the brain, heart, and kidney , and elevated haemoglobin levels will help avoid these risks.
There was a significant decrease in the intraoperative HR of patients treated with intraoperative dexmedetomidine. The current study also revealed that deliberate hypotension with lower HR could reduce intraoperative blood loss and improve the surgical field [27, 28]. Dexmedetomidine decreases HR , specifically causing a 16–30% decrease from baseline at plasma drug concentrations > 1–3 ng/mL [30, 31]. There was a significant decrease in intraoperative BP at T1 in patients treated with intraoperative dexmedetomidine. The decreased BP may be caused by transient elevated plasma concentration, and it might further contribute to reduction of intraoperative blood loss in the early surgical procedure. There was no significant difference in the average arterial pressure at most time points due to human control. The anesthesiologist maintained the target BP level after the mean BP reached the target point. In addition, the requirement for esmolol was decreased because of the effect of reducing HR.
There was no difference in operation time between considered groups. Although the amount of blood loss was reduced by dexmedetomidine, the operation time was not shortened. Similar studies have also shown that dexmedetomidine improves the quality of the surgical field without significantly affecting operation time [8, 32]. No difference in the requirement of fentanyl was observed between the groups, but the remifentanil requirement in the dexmedetomidine group was significantly decreased. Studies have shown that long-term and high-dose use of opioids may produce some side effects, such as hyperalgesia, nausea and vomiting, and emergence agitation [33, 34]. The reduced dosage of remifentanil may help alleviate any hyperalgesia and reduce postoperative nausea and vomiting.
There was no significant difference in the incidence of allogeneic blood transfusion between the groups. This might be due to the low transfusion incidence of this surgical procedure. Most patients who undergo orthognathic surgeries do not need blood transfusion, with the exception of those who experience massive bleeding. Studies have also reported that ANH significantly reduces allogeneic blood transfusion [12, 35].
There was no significant difference in colloidal fluid volume. The decreased blood loss and HR, and intraoperative fluid management strategy led to significantly decreased crystalloid fluid volume. In addition, the dose of crystalloid fluids seemed to be large for an average 3.5-h duration of surgery. This may have been caused by heavy bleeding and ANH. Patients were required to be transfused with a large amount of crystalloid liquids after a predetermined amount of autologous blood was rapidly withdrawn to supplement blood volume and maintain stable vital signs . This protective measure increased crystalloid fluid dosage.
Although the results are promising, there are some limitations to this study. First, the retrospective nature of this study has inherent limitations and potential interference factors regarding data integrity and homogeneity. However, we have strictly followed the criteria for inclusion and exclusion and have used a rigorous statistical approach to avoid bias. Second, this study was a single-centre retrospective study, which may have led to selection bias. We expanded the sample size to minimise bias. Third, visualisation was pointed out, but it could not be assessed because of the retrospective nature of this study. We plan to conduct further studies to elaborate on this aspect. Fourth, different drugs, including propofol, remifentanil, and sevoflurane, were administered, and this may have affected the accuracy of our conclusions. We used various methods to ensure the reliability of the conclusions, such as expanding the sample size, PSM, and strict data management. Finally, different surgeons use different approaches; thus, the methodology of each operation are different. For example, some surgeons might think that preoperative ANH is necessary, while others might not.
The study showed dexmedetomidine decreases blood loss in orthognathic surgeries, and we plan to conduct a randomized controlled study in the future.