The present multicenter study examined risk factors for the development of PC in patients after surgery for colorectal cancer. Patient age was greater, chronic obstructive pulmonary distress was more common, ASA-PS was poorer, BMI was lower, open surgery was more frequent, and volume of blood loss was more in the PC group. Multivariate analysis revealed male sex, high age, and poor ASA- PS as independent predictors for PC.
According to previous reports, the frequency of PC after abdominal surgery is 2–30% [1, 4, 5, 12, 14]. Abd El et al. used the multicenter database to examine 50,150 patients who underwent minimally invasive surgery for colorectal cancer between 2012 and 2017, identifying PC in 637 patients (1.3%) [12]. The incidence of PC in our multicenter database was relatively low, at 1.5%. In addition, approximately 20% of patients with PC die within 30 days, compared to 0.2–3% of patients without PC, representing a very high mortality rate [1]. In the present study, 1.5% of patients developed PC and 3.7% of those who developed PC died within 30 days. One reason for this low mortality rate may be that this study used relatively recent data, with improved perioperative management, a higher frequency of minimally invasive procedures (90.1%), and the active introduction of routine perioperative rehabilitation at all centers. In addition, 30-day mortality may have been lower because the facilities in which PC occurred in this study were equipped with intensive care units staffed by dedicated intensivists, who may have been able to achieve patient recovery using intensive care after complication onset. Of the 54 patients who developed PC, 10 (18.5%) developed intestinal obstruction and 8 (14.8%) experienced delirium. Vomiting and subsequent aspiration due to bowel obstruction after abdominal surgery is a major cause of pneumonia. Aspiration pneumonia is a life-threatening complication with a mortality rate of approximately 27% among high-risk patients [15]. Careful postoperative management of abdominal symptoms is important, as it can be prevented by immediate action, such as insertion of a nasogastric tube during vomiting [15].
Delirium is associated with a high risk of infection and an analysis of patients undergoing planned coronary artery bypass grafting found that patients who experienced delirium had infections significantly more frequently (22%) than those who did not (7.4%, p = 0.0037) [16]. Pneumonia and surgical site infection at the sternum were the most common. Delirium is usually reversible, but is associated with longer hospitalization, worse prognosis, and increased mortality [17]. PC and delirium may be caused by decreased activities of daily living due to trunk suppression caused by delirium or, conversely, by a cytokine upsurge caused by PC, which may impair optimal oxygenation of the brain.
In the present multivariate analysis of PC, male sex, older age, and poorer ASA-PS were independently associated with poor prognosis.
Notono et al. studied the perioperative outcomes of patients who underwent pneumonectomy, revealing that men were more likely to develop postoperative complications (OR 1.73, 95%CI 1.09–2.75; p = 0.01) and postoperative air leakage (OR 1.98, 95%CI 1.03). Schlager et al. reported that patients who underwent left-sided colon cancer surgery developed comorbidities more frequently (OR 1.59, 95%CI 1.10–2.54; p = 0.01) than those who underwent right-sided colon cancer surgery (OR 1.98, 95%CI 1.09–2.75; p = 0.01) and male sex (OR 1.47, 95%CI 1.21–2.98; P = 0.022) as independent risk factors for major complications [18]. One possible explanation is that men generally smoke more than women and have more comorbidities than women, which may significantly impact the occurrence of PC [19].
Bhowmick et al. found that age, smoking, BMI > 25 kg/m2, and bi- or unilateral neck dissection were independent predictors of PC after head and neck cancer surgery [20]. Aging is associated with altered immune response, which decreases alveolar macrophage function and increases cell apoptosis during sepsis, leading to more severe infection. In addition, the elderly generally have more fragile and weaker tissues, and blood supply and tissue healing are considered to deteriorate with age, representing a risk factor for infectious complications and supporting our results [21–23].
Laparoscopic surgery has become increasingly popular in recent years, and the pneumoperitoneum and body position applied have been reported to affect PC [7, 24]. The carbon dioxide used for insufflation increases intra-abdominal pressure and decreases both lung compliance and functional residual capacity [7]. The Trendelenburg position, used primarily in the approach to left-sided colorectal cancers, also worsens entry compliance and may cause upper airway edema, ventilatory blood flow imbalance, and increased airway pressure [24]. However, in the present study, the surgical approach was not associated with the occurrence of PC. One reason for this may be the fact that this study investigated relatively recent cases and that the time for insufflation and application of the Trendelenburg position were reduced due to improved anesthesia management and shortened operative time with the application of standardized laparoscopic techniques.
Several limitations to this study should be kept in mind. First, this was a retrospective study of a relatively small number of PC. Second, this study was based on a multicenter database and lacked information on factors that might be associated with the development of PC, such as smoking history, anesthesia method, and postoperative rehabilitation. A larger study with more information is therefore desirable.
Despite these limitations, our study revealed that male sex, greater age, and poorer ASA-PS are associated with greater risk of PC, and that pre- and postoperative rehabilitation and pneumonia control measures should be implemented for patients at high risk of PC.