The findings of the present study suggest that the amount of blood loss is greater in patients with obstructive ventilatory impairment than in those with normal respiratory function undergoing laparoscopic hepatectomy, whereas obstructive ventilatory impairment has no impact on the amount of blood loss during open hepatectomy. To our knowledge, this is the first study to demonstrate the relationship between FEV1.0% and blood loss during laparoscopic hepatectomy in actual clinical practice; this topic has only been previously investigated in an experimental animal study . One advantage of the present study is that we assessed preoperative risk based on spirometry findings, which are simple to obtain and commonly determined in clinical practice. During hepatic dissection, if the hepatic venous pressure is high, bleeding will increase even by the minute hepatic vein injury. Under conditions of poor visual field, attempting to stop bleeding often results in further tearing of the hepatic veins and a rapid increase in bleeding. Even if hemostasis is achieved, manipulation under poor visual field may lead to Glisson injury, resulting in postoperative bile leak, which is still a common postoperative complication. In the present study, the median difference in blood loss between Obstructive group and Normal group in laparoscopic hepatectomy was slightly 22 mL, which seems rather small but has statistical significance because laparoscopic hepatectomy requires less blood loss by nature. However, liver surgeons are aware of the fear that small bleeding can lead to serious complications especially during laparoscopic hepatectomy, so it is extremely important to understand this as a preoperative risk.
The current study revealed two risk factors for massive blood loss during laparoscopic hepatectomy. One of these risk factors was low preoperative FEV1.0%. Previous studies have shown that low FEV1.0% is found in patients with COPD and/or obstructive ventilatory impairment and that AWP tends to be higher in such patients [14,15,18-20]. In the present study, the number of COPD patients in the Obstructive group was very low, only 6 (7.9%). This is reasonable because previous studies have shown that there is a discrepancy between the number of potential COPD patients and the number of patients who are actually diagnosed with COPD and receive respiratory rehabilitation and drug therapy . In this study, COPD patients may have been the most appropriate subjects for evaluation, but the sample size was so small that it was difficult to evaluate the study items using only these cases. Thus, we thought it would be desirable to obtain the actual spirometry measurements. As a countermeasure for patients with obstructive ventilatory impairment, preoperative respiratory rehabilitation or drug therapy was performed as is done for COPD patients in our study; however, re-measurement of spirometry was not performed after the intervention. Therefore, it could not be assessed to what extent the preoperative respiratory rehabilitation and pharmacotherapy improved respiratory function, and the effect was unknown. Additional research is needed determine the effectiveness of preoperative respiratory rehabilitation and pharmacotherapy in reducing intraoperative blood loss.
CVP is related to the amount of blood loss, and several methods for reducing CVP have thus been reported (e.g., positioning, fluid restriction, and inferior vena cava semi-clamping) [21-23]. During open hepatectomy, decreasing ventilation alone does not reduce bleeding from outflow, whereas setting the positive end-expiratory pressure to zero and decreasing ventilation reportedly reduces intraoperative blood loss [24, 25]. In an animal model, increases in pneumoperitoneal pressure led to increases in CVP under high-AWP conditions during laparoscopic hepatectomy . Thus, some researchers have suggested that in critical hemostatic situations during laparoscopic hepatectomy, lowering the CVP by lowering the AWP by 5 cm H2O should be the first intervention implemented; reducing the AWP to minimal levels by short periods of no ventilation is another reported option [2, 12, 26]. However, intraoperative respiratory acidosis and postoperative respiratory complications may occur more frequently if these measures are performed excessively. Currently, no data clearly indicate how best to reduce the AWP during laparoscopic hepatectomy. How to optimally change the AWP in accordance with the degree of obstructive ventilatory impairment requires further evaluation.
A system for scoring the difficulty of laparoscopic hepatectomy (which was another risk factor for massive blood loss during laparoscopic hepatectomy in the current study) was proposed in 2014, and subsequent studies confirmed this system’s validity and usefulness . However, this scoring system has some limitations and is therefore best combined with the four levels of difficulty of the IWATE criteria, which are significantly correlated with the operative time, blood loss, and complication rates [17, 28]. Surgery on patients with scores of ≥7 by the IWATE criteria has been classified as more difficult, and these patients reportedly differ significantly in intraoperative blood loss and operative time compared with patients who have scores of <7 . In our multivariate analysis, the OR of the IWATE criteria was higher than that of low FEV1.0%, suggesting that surgical difficulty may have an even greater impact on massive bleeding than respiratory function. In very difficult cases in daily clinical practice, patients with IWATE criteria scores of ≥7 who also have obstructive ventilatory impairment are candidates for hepatectomy, and the benefit of a laparoscopic approach should be carefully balanced against the increased risk of bleeding.
This study had some limitations. The first is its retrospective design and single-center setting. Although our sample size was not small, sample sizes differed between the laparoscopic and open hepatectomy groups. Further prospective multicenter studies are needed to validate our findings with matched patient background and sample size. Second, we could not assess fluctuations in intraoperative AWP and hemodynamics because intraoperative respiratory control and CVP were not recorded. Even if these records are to be obtained, the method of their measurement needs to be discussed in detail and the environment needs to be designed. In addition, although we requested the anesthesiology department to maintain a low CVP for intraoperative respiratory management, the actual adjustment was different in each case, so it was difficult to exactly match the conditions. In order to solve these problems, prospective multicenter studies are likely to be necessary. Third, this study did not include patients with diseases such as intrahepatic cholangiocarcinoma and benign tumors; only patients with hepatocellular carcinoma and metastatic liver cancer were included. Therefore, other types of diseases need to be studied.