The definitions of PPCs are wide and tend to depend on the objectives of individual studies and institutions. In Thailand, there is no incidence report of PPCs and their sequelae in a tertiary hospital. Identifying their incidence and the associated, modifiable, risk factors in high-risk patients might increase the quality of perioperative care and decrease the overall morbidity. To this end, we collected the data relating to 1,100 patients aged over 65 years who had either open or laparoscopic upper-abdominal surgery between January 2016 and December 2019.
In our study, the overall incidence of PPCs was 7.7%. That level was comparable with the incidence of PPCs after abdominal surgery (5.8%) found in an analysis of the National Surgical Quality Improvement Program by Yang et al.(13) Moreover, the incidence for those patients in the current investigation who underwent non-cardiac surgery (7.9%) was similar to the finding of an observational study entitled “Prospective Evaluation of a Risk Score for Postoperative Pulmonary Complications in Europe”.(12)
Our investigation revealed that the PPC with the highest incidence (36%) was pleural effusion, which was diagnosed from postoperative chest X-ray reports. Rossi and Bromberg also reported finding a high rate of pleural effusion through ultrasound examinations during the postoperative period following elective abdominal surgery (70.3%). Most of their cases were asymptomatic and self-limiting.(14) Pleural effusions might result from sodium and water retention, and they may be aggravated by the relative cardiac decompensation typically found in the elderly.(15) Subsequent to the performance of hepatectomies for the treatment of primary liver cancer, postoperative pleural effusions were found in a quarter of such cases. Subphrenic collection and operative injuries to the liver were found to be statistically related to those pleural effusions.(16)
Like other studies, older age was determined to be an independent risk factor for PPCs. Qaseem et al. reported that, compared with younger patients, the odds ratios of developing PPCs were 2.09 (95% CI, 1.70–2.58) for patients aged 60–69 years and 3.04 (95% CI, 2.11–4.39) for those aged 70–79 years. Although age cannot be modified, careful perioperative management might decrease the incidence or severity of complications in these patients.(17)
We also found that the incidence of PPCs rose in patients having an American Society of Anesthesiologists physical status > II, but it declined in those with a preoperative peripheral capillary oxygen saturation value of over 94% in room air. Our study showed that a high PPC incidence was not associated with gender; body mass index; or a history of asthma, chronic obstructive pulmonary disease, or obstructive sleep apnea. At the other end of the scale, a low PPC incidence was not associated with preoperative spirometer usage or deep-breathing exercises.
Unlike the findings of other studies, no correlations were found in the present work between PPCs and respiratory comorbidities (asthma, chronic obstructive pulmonary disease, and history of smoking).(18) This may be attributed to the fact that there were only 50 cases of respiratory-related patients, and they were all well controlled medically. Moreover, some of those 50 cases had been screened and treated by specialist staff at our Siriraj Pre-Anesthetic Clinic—with several achieving optimized medical conditions—at least 2 weeks prior to their surgeries. A retrospective review conducted at Pusan National University Yangsan Hospital, South Korea, found that the incidence of PPCs after non-cardiothoracic surgery with adult asthma patients was as high as 29.1%, with the most common PPCs being pneumonia (32.4%) and bronchospasm (24.3%). The significant risk factors identified by the South Korean study were age, the presence of preoperative respiratory symptoms, and a low forced expiratory volume in 1 second.(19)
In our study, patients who had a serum hemoglobin level of < 10 gm/dl had a threefold greater chance of experiencing at least 1 PPC than patients without anemia. Similar to the findings of earlier thoracic and lung resection studies, anemia in the present investigation demonstrated a two- to threefold increase in respiratory and infectious complications.(20, 21) Even at a mild degree (hemoglobin < 13 gm/dl in males and < 12 gm/dl in females), preoperative anemia has been reported to be independently related to a heightened risk of 30-day mortality and morbidities (cardiac, respiratory, CNS, urinary tract, wound, sepsis, and venous thromboembolism outcomes) in patients undergoing major non-cardiac surgery.(22) Therefore, anemia should be screened and corrected preoperatively, especially for reversible causes such as iron deficiency or nutritional deficiency anemia. Correcting anemia decreases the need for blood transfusions during abdominal surgery while concurrently shortening the length of hospital stay.(23, 24) Enhancing red blood cell production through the administration of erythropoietin should be considered for patients who have adequate iron levels or no evidence of other macronutrient deficiencies. However, transfusions are not recommended if the hemoglobin level is above 7 g/dL as they might cause immune modulation, volume overload, or transfusion reactions.(25) Preoperative blood transfusion is recommended only for patients with symptomatic anemia or hemoglobinopathy.(26, 27)
Although there was a statistical difference in the mean serum albumin levels of the non-PPC and PPC groups, neither mean was < 3.0 gm/dl, which Smetana and colleagues identified as a PPC predictor.(5, 28) Preoperative albumin has been reported to correlate inversely with complications such as reintubation, pneumonia, and failure to wean from a mechanical ventilator, especially after upper abdominal surgery.(29) Compared with colonic surgery, patients undergoing esophageal or pancreatic procedures have also been found to have significantly higher complication rates at any level of serum albumin < 3.25 gm/dl.(30) The relationship between serum albumin levels and mortality has also been demonstrated to be continuous when the levels were < 3.5 gm/dl.(31) Preoperative protein depletion might alter pulmonary dynamics and the respiratory muscle function, leading to a higher rate of pneumonia.(32) To reduce perioperative pulmonary complications, the American College of Physicians has recommended the strategy of measuring serum albumin in all patients clinically suspected of having hypoalbuminemia. The College has also suggested that the approach be considered for patients with one or more risk factors for perioperative pulmonary complications.(17)
Preoperative spirometry usage and deep breathing exercises showed no benefits in reducing the incidence of PPCs. This might be because the hospital’s high surgery volume and chronic shortage of healthcare staff had resulted in no individual having clear organizational responsibility for the consistent preoperative implementation and assessment of spirometry usage and deep breathing exercises. The preoperative physiotherapist consultations also varied, depending on the judgements of the attending surgeons, the operation type, and patient comorbidities.
Intraoperative and postoperative parameters
In the present work, strong relationships were demonstrated between PPCs and surgical duration (especially if longer than 3 hours) and open surgery, with at least a threefold increase in the incidence of complications. Patel et al. reported that the risk of PPCs increased with every additional minute of operating time.(33) Despite finding that laparoscopic and open cholecystectomies had similar PPC risk profiles in terms of their operative durations, Owen and colleagues demonstrated that open surgery had at least double the risk of PPCs than that of laparoscopic surgery.(34) A separate study comparing open and minimally invasive esophagectomies reported that there was a significant reduction in postoperative pneumonia when the minimal approach was employed.(35) Therefore, in identified high-risk patients, we should aim to limit the duration of surgery and a minimally invasive surgical technique should be considered. According to a study of the factors predicting mortality in emergency abdominal surgery of the elderly, the incidence of postoperative pneumonia was 12.8%, with over half of those occurrences being caused by aspiration. Furthermore, another 4.3% of the study cohort died from pneumonia. By comparison, our study revealed the incidence of patients having PPCs after emergency abdominal surgery was 16% (OR, 3.65; 95% CI, 1.93–6.91); however, there was no mortality.
During induction of general anesthesia, lung capacity decreases, resulting in a heightened possibility of atelectasis.(36) In patients undergoing abdominal surgery, epidural analgesia reduces the risk of postoperative pneumonia while improving the pulmonary function and arterial oxygenation.(37) However, in our study, the PPC incidence was not affected by the choice of anesthesia (general, versus a combination of general and regional anesthesia). There were also no statistical differences in the postoperative pain-rating scores or 72-hour opioid consumption levels of the non-PPC and PPC groups.
Compared to conventional ventilation, a protective ventilation strategy reduces inflammation and improves oxygenation in patients undergoing esophagectomies. In a protective ventilation group, the incidence of pneumonia was demonstrated by 1 study to be lower than that for a conventional-ventilation group, although the difference was not significant. In our investigation, most of the ventilation parameters followed the lung-protective strategy; the mean tidal volume in both the PPC and non-PPC groups was almost 9 mL/kg, and all parameters of the groups were not statistically different. As to the anesthetic-risk factors, no relationship was apparent between the PPCs and airway equipment, inhalation agent, or anesthetic technique. We found an association between rocuronium and postoperative complications; the PPC-inducing action of rocuronium still remained even when used in conjunction with neostigmine or sugammadex. The observational study entitled “Post-Anaesthesia Pulmonary Complications After Use of Muscle Relaxants” showed that the administration of neuromuscular blocking drugs during general anesthesia was associated with an elevated risk of PPCs (OR, 1.86; 95% CI, 1.53–2.26). Furthermore, the usage of neuromuscular monitoring and reversal agents (sugammadex or neostigmine) were not associated with a decreased PPC risk.(38) However, in a multicenter, matched-cohort analysis (STRONGER), sugammadex administration was associated with a reduction in PPC risk (adjusted OR, 0.70 (95% CI, 0.63–0.77) as well as a 55% reduced risk of respiratory failure, compared with the administration of neostigmine.(39) In addition, a randomized controlled trial by Togioka and colleagues explored the effects of reversal agents on the PPC incidence of older adults undergoing prolonged surgery. Their work confirmed that sugammadex is superior to neostigmine in reducing the incidence of residual neuromuscular paralysis. Moreover, there was a threefold increase in the 30-day hospital readmission rate of the neostigmine group (15%) relative to that of the sugammadex group (5%).(40)
In recent years, our institution has been revising its perioperative management protocol for enhanced recovery (the Siriraj ERAS Protocol). Our observation has been that perioperative outcomes appear to be improved when a goal-directed therapy is employed as opposed to a liberal fluid therapy. An increased volume of fluid administration has been associated with an elevated risk of pulmonary complications, whereas goal-directed fluid administration has been reported to offer a 30% reduction in pulmonary complications following upper abdominal and major vascular surgery (OR, 0.7; 95% CI, 0.6–0.9).(41, 42) In the current work, although we were able to retrospectively collect and analyze the intraoperative fluid administration for each case, we were unable to identify which fluid strategy was used. Our results showed that the mean intraoperative crystalloid infusions of the PPC and non-PPC groups were 2,166 ± 1,689 ml and 1,198 ± 1,118 ml, respectively. No cut-off point has been established for the quantity of intraoperative fluid that might cause PPCs as many factors are involved in the administration of the fluid, for example, the presence of patient comorbidities, preoperative volume status, and perioperative fluid loss. The fluid administration, in terms of its volume and rate, should be performed cautiously, and anesthetists should always regard intravenous fluid as a kind of medication. Moreover, our statistical analysis revealed that an intraoperative crystalloid administration exceeding 1,000 ml was associated with a high PPC risk (OR, 4.06; 95% CI, 2.44–6.76).
A systematic review and meta-analysis focusing on the prevention of PPCs published in 2020 identified 7 perioperative interventions that probably reduce PPCs.
They were the use of enhanced recovery after surgery pathways; prophylactic mucolytics; postoperative, continuous positive airway pressure plus non-invasive ventilation; lung-protective intraoperative ventilation; prophylactic respiratory physiotherapy; epidural analgesia; and goal-directed hemodynamic therapy. However, some other factors might not be beneficial, namely, restrictive fluid administration strategies; postoperative, bi-level, non-invasive ventilation; postoperative, high-flow, nasal cannula oxygenation; smoking cessation therapy; inhaled β agonists; incentive spirometry; and variation of the intraoperative, fractional inspired oxygen concentration.(43)
The estimated blood loss in our study was 653 ± 735 ml for the PPC group, which was significantly higher than that for the non-PPC group (267 ± 655 ml). This result is consistent with the findings of a multivariate analysis conducted by Sah and colleagues of the gastric cancer treatments provided by a specialized center: if the blood loss volume exceeded 500 ml, it was associated with early postoperative complications (OR, 2.86; 95% CI, 1.67–4.92).(44)
Although the presence of a nasogastric (NG) tube has been reported by some studies to be a PPC risk factor(45), there were no significant differences between its use and non-use in terms of the PPC incidences in our study. One explanation is that nasogastric decompression was not a routine procedure at our hospital during the study period.
A systematic review of prophylactic nasogastric decompression after abdominal operations by Nelson et al. reported that patients with selective NG-tube usage after laparotomies developed pneumonia and atelectasis less often than patients using NG tubes until gastrointestinal motility returned.(46) With the presence of an NG tube, patients might not cough effectively, resulting in secretion retention and atelectasis. Furthermore, the tube can trigger silent aspiration and pneumonia as the lower esophageal sphincter cannot work as it should.(47)
The lengths of hospital and ICU stays are longer for PPC patients (Table 3), which inevitably leads to higher costs for the patients, their families, and the healthcare system. A multicenter study concluded that even mild PPC cases—such as atelectasis and the need for prolonged oxygen therapy—were related to increases in early postoperative mortality and extended ICU and hospital stays. The researchers opined that all such cases deserve attention and intervention.(48) There were no deaths during the perioperative period that were directly attributable to the PPCs in our study.
Our main concern with the upper abdominal operations was postoperative pain; this was because patients might avoid moving or breathing deeply when they felt uncomfortable, thereby possibly triggering a PPC. However, the average postoperative pain-rating scores for the PPC and non-PPC groups did not differ significantly. An analysis of the maximum postoperative pain ratings during the first 72 hours following surgery determined that the pain score was 5.92 for the PPC patients versus 5.25 for those without PPCs. Furthermore, the total opioid usage (morphine, pethidine, and fentanyl) of the 2 groups were not statistically different. However, our findings contrast with those of Roberta et al., who investigated PPCs experienced by the elderly after abdominal surgery. Those researchers concluded that pain is a contributing factor to the development of PPCs. This difference might result from the different assessment durations that were utilized. Specifically, the current investigation assessed the pain levels of both groups within 3 days postoperatively. By comparison, Roberta and colleagues assessed pain daily between postoperative Days 1 and 6, inclusive, and they found that their PPC patients experienced significant levels of pain at rest on postoperative Day 4.(49)
There are many predictive tools for PPCs, for example, the ARISCAT scoring system, the LAS VEGAS risk score, the Melbourne Risk Prediction Tool, and the Surgical Lung Injury Prediction model. However, only the ARISCAT system has a sufficient predictive power that has been confirmed by external validation. In Thailand, only 1 risk scoring system for the prediction of respiratory complications after thoracic surgery has been validated for the Thai population.(50) For our elderly patients undergoing upper abdominal surgery, we used the ARISCAT scoring system as a tool to predict PPCs. The mean ARISCAT scores for the non-PPC and PPC groups were 32 ± 13 and 43 ± 14, respectively (P value < 0.001). Although the means of both groups were categorized as an intermediate risk for PPCs, it can be seen that the higher the score, the greater the chance of developing PPCs. In addition, patients whose scores ranked in the intermediate-risk level had an odds ratio for pulmonary complications of 3.04 (95% CI, 1.53–6.03), while for those with scores in the high-risk level, the odds ratio was as high as 7.82 (95% CI, 3.90–15.70).
As only 85 cases out of the 1,100 patients in our study cohort developed PPCs, we could not establish a predictive score that would demonstrate an effective power as well as the ARISCAT scores presently do. However, the ARISCAT scores did help to predict PPCs in our high-risk patients and in our high-risk operations. Those scores could therefore be applied well to the general Thai population and might be used in other Southeast Asian countries.