In the present study, postoperative GDA was observed in 61 patients (47%), and the mean duration of GDA was 4.3 days (1–8 days). Furthermore, the multivariate analysis results indicated that the incidence of postoperative GDA correlated with the postoperative outcomes of the patients who underwent LLR in the left half lateral position. Thus, the incidence and duration of postoperative GDA are assumed to be useful predictors for postoperative complications, and these predictors should be assessed to improve the short-term outcomes of patients undergoing LLR.
In terms of the mechanism that causes GDA after surgery in the lateral position, Rheder et al was the first to suggest that there is a preferential distribution of tidal volume to the nondependent lung and preferential ventilation of the dependent lung in the lateral position . Furthermore, it has also been reported that not only increase in abdominal pressure by laparoscopic surgery but also relaxation of the diaphragm with the use of muscle relaxants elevate the diaphragm, further decreasing the functional residual capacity of the lower lungs . Regarding the increase in abdominal pressure, it is suggested that the pneumoperitoneum pressure in laparoscopic surgery may further raise the diaphragm and cause ventilation disorders. Furthermore, Kaneko et al showed that in subjects in the lateral position at lung volumes of less than 50% of total lung capacity, the nondependent regions of the lung receive a relatively large proportion of the inspired volume .
Long-term outcomes of LLR have been reported in some previous studies [7, 19, 20]. The results of these studies revealed that LLR was comparable to conventional open liver resection in terms of resection margins, recurrence rates, and long-term outcomes. However, the short-term outcomes of LLR have hardly been discussed until now. The reason for the lack of studies on short-term outcomes and risk factors for postoperative complications is that strict patient selection criteria for LLR were established by an international consensus on LLR . Tranchart et al first reported that the postoperative complication rate increases by 60% with each additional increment of time required for LLR . The potential relationship between operating time and risk of short-term outcomes was initially reported in 1960 [21, 22]. Nobili et al reported that operating time was identified by multivariate analysis as an independent risk factor for pulmonary and infectious complications after open hepatic resection .
According to our multivariate analysis, in addition to operating time, a GDA duration of 5 days was revealed to be an independent risk factor for LLR postoperative complications. Questions regarding the mechanisms by which the incidence of postoperative GDA potentially affects the postoperative outcomes of patients who undergo LLR remain unanswered. One potential hypothesis is related to the incidence rate of GDA being 47% and most of the cases having improved spontaneously by the 4th postoperative day. Conversely, it is suggested that patients with GDA lasting more than 5 days may develop severe pneumonia. In fact, mild-to-severe pneumonia was observed in all 4 patients with moderate or severe complications (Clavien-Dindo classification II to IV) in the present study. Furthermore, diabetes mellitus has been reported in the literature to be a risk factor for infectious complications, including pneumonia, after hepatic resection [23, 24]. Indeed, the present study showed that the proportion of patients with diabetes mellitus was higher in the with GDA group than in the without GDA group.
In conclusion, we found that a GDA duration of 5 days or more may be a useful predictor of postoperative complications, and this predictor should be assessed improve the short-term outcomes of patients undergoing LLR. Therefore, we assumed that the early termination of bed rest, including the start of respiratory rehabilitation, and early improvements in GDA are crucial for the prevention of complications, including pneumonia. The present study had limitations; it was a retrospective single-center study with a relatively small sample size. These results require confirmation by additional multicenter large-scale studies and prospective randomized controlled studies.