Surgeons have long been highly concerned about various high-risk events in the perioperative period, among which perioperative respiratory complications are not uncommon and an important cause of increased morbidity and mortality and prolonged hospital stay in surgical patients, and even have a greater prognostic impact than cardiovascular complications in predicting long-term morbidity and mortality, especially in elderly patients.
The main perioperative respiratory complications include: pulmonary atelectasis, airway spasm, pulmonary edema, respiratory infections, respiratory failure, acute exacerbation of pre-existing respiratory disease, and various forms of airway obstruction. Among them, perioperative respiratory infection is one of the most common pulmonary complications, the vast majority of which occur in the postoperative period and can be divided into upper and lower respiratory tract infections by site. Upper respiratory tract infections refer to inflammation caused by biological factors between the nasal cavity and the throat, while lower respiratory tract infections mainly include tracheobronchitis and pneumonia. Postoperative pneumonia is the most common of the respiratory infections and has the greatest impact on prognosis. How to identify high-risk patients and take appropriate preventive measures in the perioperative period has become an important topic in today’s perioperative management. This article focuses on the issues related to postoperative pneumonia.
I. Epidemiology
The incidence of postoperative pneumonia varies widely with risk factors, ranging from 1.5% to 15.3% in high-risk groups; the 30-d postoperative mortality rate can be as high as 21%, depending on disease severity, complications, and pathogens. The timing of surgery also significantly affects the incidence of postoperative pneumonia, which has been reported in 11.1% of patients undergoing emergency abdominal surgery, compared with 2.9% of patients undergoing elective abdominal surgery. According to the literature, the incidence of perioperative hospital infection in general surgery is 2.9%, ranking 3rd among all surgical departments, lower than neurosurgery and thoracic surgery; and the lower respiratory tract is the site with the highest incidence of infection among all hospital infections, accounting for 38.3%.
Second, the respiratory physiology of general surgery after surgery
1, lung defense mechanism. The normal pulmonary defense mechanism is mainly composed of two aspects: the ciliary motor function of airway mucosal epithelial cells and the cough reflex, and the weakening of these two pulmonary defense mechanisms together determines that patients are more prone to respiratory infections after surgery.
(1) Ciliary motility of airway mucosal epithelial cells: factors such as tracheal intubation and general anesthesia not only increase airway secretions in surgical patients, but also damage the integrity of the airway mucosa, affecting the ciliary motility of airway epithelium and weakening the patient’s ability to clear airway secretions.
(2) Cough reflex: post-surgical pain, application of sedative and analgesic drugs will weaken the patient’s ability to cough autonomously and fail to expel airway secretions and trace regurgitant misabsorption from the oropharynx and gastrointestinal tract in time.
2. Changes in pulmonary function. Patients undergoing general surgery usually develop restrictive ventilation dysfunction, which is mainly manifested as a decrease in total lung capacity (TLC), spirometry (VC), maximum expiratory volume in the first second (FEV1), and functional residual volume (FRC). In particular, the decrease in FRC is more important for postoperative pulmonary complications, with a 30% decrease in postoperative FRC in patients undergoing upper abdominal surgery and a 10%-15% decrease in FRC in patients undergoing lower abdominal surgery. In addition, postoperative patients often have increased closure volume (CV). when FRC is reduced or CV is increased, the airway is prone to collapse, which can lead to pulmonary atelectasis, which is not conducive to the drainage of airway secretions and can easily develop into pneumonia and respiratory failure.
3. Changes in the function of the diaphragm. After abdominal surgery, the patient’s phrenic nerve is centrally stimulated and the transdiaphragmatic pressure is significantly reduced, resulting in diaphragm dysfunction. The weakened function of diaphragm inevitably causes the patient to use more auxiliary respiratory muscles to maintain adequate minute ventilation, when the patient’s respiratory rate increases, tidal volume decreases, and shallow fast breathing is the main form of breathing. This change in respiratory pattern will aggravate the impaired movement of airway epithelial cell cilia and inhibit the cough reflex, ultimately increasing the risk of postoperative pneumonia.
III. Pathogenesis of perioperative pneumonia
The airway below the tracheal ridge is normally a sterile environment. Regardless of the type of pneumonia that develops, it begins with the invasion of pathogens into the lower airways, and the pathogenesis depends on the pathogenicity, the number of pathogens, and the local and systemic immune status of the host. The pathogen invades the lower airways and produces pneumonia mainly through the following routes: aspiration of colonized bacteria from the upper respiratory and gastrointestinal tracts; dissemination from adjacent infection sites; and hematogenous dissemination. A variety of factors contribute to these pathways, such as tracheal intubation, application of acid-suppressive drugs, gastric retention, and fiberoptic bronchoscopy.
High risk factors for perioperative pneumonia
A recent study from the US National Surgical Quality Improvement Program (NSQIP). The incidence of postoperative pneumonia was significantly higher in patients with a history of current smoking, and the higher the number of years of tobacco exposure, the higher the incidence of postoperative pneumonia. High-risk factors for postoperative pulmonary complications can be divided into patient-related and procedure-related. Patient-related risk factors include age, American Society of Anesthesiologists (ASA) classification ≥ grade II, chronic obstructive pulmonary disease (COPD), and congestive heart failure; surgery-related risk factors depend mainly on the site of surgery, and thoracic surgery, aortic surgery, and abdominal surgery are all high-risk factors for postoperative pneumonia. Multifactorial analysis showed that age ≥60 years, indwelling nasogastric tube, use of acid-suppressants or H2-blockers, systemic immunosuppression and severe underlying diseases were high-risk factors for postoperative pneumonia.
V. Prevention of perioperative pneumonia
In order to improve the prognosis of postoperative patients, the American Surgical Association proposed NSQIP in the mid-1980s, i.e., to establish a clinical database of postoperative patients in 133 hospitals, and then count the various complications and high-risk factors affecting the prognosis, and finally improve the treatment measures in a targeted manner so as to reduce the complications and mortality rate. Studies have shown that the implementation of NSQIP has achieved significant results, reducing postoperative mortality and complication rates by 27% and 45%, respectively. Among them, some scholars have even reduced the incidence of postoperative pneumonia from 1% to 0 through the implementation of a series of preventive measures, which is equivalent to a reduction of 2-3 cases of postoperative pneumonia in general surgery per month. The preventive measures mainly include: preoperative education, assist patients to exercise lung function; chlorhexidine oral care; postoperative elevation of the head of the bed; postoperative adhere to exercise lung function; early out of bed activities; regular testing and rinsing nasogastric tube, etc.
1.Preoperative prevention. The core of preoperative prevention is lung expansion technique, which mainly includes breathing exercise with induced pulmonary meters and chest physiotherapy, of which chest physiotherapy includes deep breathing, coughing, postural drainage, vibratory expectoration, intermittent positive pressure breathing and continuous positive airway pressure. Deep inspiratory training prevents alveolar atrophy and hypoxemia, and deep inspiratory training should be followed by effective coughing training, which makes it easier for the patient to expel airway secretions. In addition, oral care with chlorhexidine can reduce the occurrence of postoperative pneumonia by reducing the colonization of pathogenic bacteria in the oropharynx.
2. Intraoperative prevention. There are several measures to prevent the occurrence of postoperative pneumonia during surgery. Some studies have shown that epidural anesthesia can reduce the incidence of postoperative pneumonia compared with general anesthesia. In addition, the timing of inotropic drug use and the duration of surgery can affect the occurrence of respiratory complications. The incidence of postoperative pneumonia was 5% in patients using the medium-acting neuromuscular blocking agent atracurium, compared with 13% in patients using the long-acting pancuronium. The use of short- or medium-acting neuromuscular blocking agents is more likely to reduce the incidence of respiratory complications than long-acting ones.
3. Postoperative prophylaxis. The postoperative preventive measures mainly include: respiratory rehabilitation training, strengthening pain relief and preventing regurgitation misaspiration. Respiratory rehabilitation training is mainly to instruct the patient to perform deep inspiratory maneuvers to promote adequate expansion of the lungs. If the patient has sputum, he/she should be instructed to cough it up vigorously. Retention of a nasogastric tube is also one of the operations that contribute to the development of postoperative pneumonia. Therefore, routine indwelling nasogastric tube should be avoided unless the patient presents with severe postoperative nausea, vomiting or inability to tolerate transoral feeding, as well as severe abdominal distension.
VI. Anti-infective treatment of perioperative pneumonia
1. The pathogenic spectrum of perioperative pneumonia. Perioperative pneumonia is almost always a nosocomial acquired pneumonia (HAP), and no high-quality pathogenic investigation of perioperative pneumonia in general surgery has been seen. Therefore, the pathogenic spectrum of HAP is mainly referred to guide initial empirical anti-infective therapy. The common causative agents of HAP reported abroad are mainly aerobic gram-negative bacilli, including Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Bacillus spp.
A multicenter, prospective survey of HAP conducted in 13 teaching hospitals in different cities in China in 2012 showed that among 610 HAP patients with isolated bacteria, the top 4 pathogens were Acinetobacter baumannii (30%), Pseudomonas aeruginosa (22%), Staphylococcus aureus (13.4%), and Klebsiella pneumoniae (9.7%). The pathogenic spectrum of HAP occurred at different times, with early-onset HAP (≤5 d of admission) often dominated by less resistant Streptococcus pneumoniae and Haemophilus influenzae, while late-onset HAP (>5 d of admission) was dominated by highly resistant Klebsiella pneumoniae with ultra broad-spectrum β-lactamase (ESBL), Pseudomonas aeruginosa, Bacteroides immobilis, methicillin-resistant Staphylococcus aureus (MRSA) are predominant. It must be emphasized that patients with perioperative pneumonia in general surgery are often combined with abdominal organ infections, and anti-infective therapy needs to cover not only the above common HAP causative organisms, but also anaerobes, enterococci, Enterobacteriaceae, etc.
2. Initial empirical anti-infective therapy. Once the diagnosis of pneumonia is established in postoperative patients, anti-infective therapy should be started as early as possible. Preferably, specimens should be retained for microbiological examination before starting the application of anti-infective drugs. For the early postoperative period (≤5 d) when pneumonia develops or when there are no risk factors for multi-drug resistant organisms (MDR), antimicrobial drug selection needs to cover anaerobes in addition to the usual common Streptococcus pneumoniae, Haemophilus influenzae, antimicrobial-sensitive Gram-negative enterobacteria, and Staphylococcus aureus. 2nd or 3rd generation cephalosporins, penicillins, β-lactamase inhibitors or quinolones can be used. For patients who develop pneumonia in the late postoperative period (>5 d) or have high-risk factors for MDR (previous antimicrobial use within 90 d; hospitalization longer than 5 d; residence in a community with a high prevalence of drug-resistant bacteria or in a special healthcare facility; being treated with immunosuppressive therapy or immune dysfunction), coverage of Pseudomonas aeruginosa, ESBL-producing Enterobacteriaceae (such as Klebsiella pneumoniae β-lactams or β-lactamase inhibitor combination agents (e.g. cefoperazone-sulbactam, piperacillin-tazobactam) or carbapenems (e.g. imipenem, meropenem) can be used; Gram-negative resistant bacterial infections can be considered in combination with quinolones (e.g. ciprofloxacin, levofloxacin) or aminoglycosides (e.g. amikacin, gentamicin); if Gram-positive resistant bacterial infections can be combined with linezolid or glycopeptides (e.g. vancomycin, teicoplanin).
There are fewer studies on whether monotherapy or combination therapy should be chosen for initial empiric treatment of patients with postoperative pneumonia, and the current study from ventilator-associated pneumonia (VAP) suggests that for certain mixed infections and MDR infections, combination strategies are more justified in initial empiric anti-infective therapy, but the differences in morbidity and mortality and clinical cure rates are not statistically significant compared with monotherapy. Therefore, for patients with postoperative pneumonia, initial empirical treatment generally selects monotherapy anti-infective therapy with an appropriate antimicrobial spectrum, and selects combination therapy only when patients with mixed or MDR infections are considered.
3. Targeted anti-infective therapy. Targeted anti-infective therapy refers to the treatment strategy of giving the appropriate antimicrobial drugs according to the drug sensitivity results of the causative organism on the premise of fully assessing the clinical characteristics of the patient and obtaining the pathogenic culture and drug sensitivity results. The perioperative postoperative pneumonia in surgical patients is similar to HAP and VAP, and should be promptly converted to targeted treatment once the pathogenic basis is obtained.
4. The course of anti-infective therapy. The course of anti-infective therapy for perioperative pneumonia should be considered in the context of the severity of the patient’s disease, the causative organism, and the clinical efficacy.
VII. Other treatment of perioperative pneumonia
In addition to early application of anti-infective drugs, perioperative respiratory infections in general surgery require active search for other sources of infection at the same time, especially when initial empirical anti-infective therapy is ineffective. Pay attention to exclude common general surgery diseases such as intestinal perforation, acute purulent cholangitis, abdominal abscess, and subphrenic abscess, etc. When the above-mentioned other sites of infection appear, timely and adequate drainage or even surgical intervention is needed to effectively control the primary disease in order to improve the cure rate and survival of pneumonia.