Intraoperative Lung Injury During One-Lung Ventilation: Causes and Prevention

Introduction

The intraoperative period is critical for the patient undergoing thoracic surgery, frequently performed for resection of lung cancer. Both surgery and anesthesia are required to help the patient to overcome and survive a disease amenable to surgical treatment, however, both come at a cost to the patient. The cost of surgery is tissue destruction, bleeding, and ischemia-reperfusion injury which may lead to a varying degree of local and systemic inflammatory response in the perioperative period. The cost of undergoing anesthesia is among other problems, cardiovascular instability, and pulmonary injury. The cardiovascular consequences may include hypotension, sometimes aggravated by bleeding, which usually requires treatment with vasoactive substances and volume repletion, which when inappropriate, may lead to volume overload and its sequelae. Pulmonary injuries from positive pressure ventilation, even if protective lung ventilation strategy is applied, may lead to postoperative pulmonary complications (PPCs). Patients’ comorbidities, especially cardiovascular and pulmonary diseases or preoperative chemotherapy, may aggravate these problems.

This chapter will mainly review the ventilation strategies during thoracic surgery which when inappropriately applied may contribute to intraoperative lung injury. Although the inflammatory reaction of the lungs in response to ventilation or thoracic surgery may emerge and can be measured during one-lung ventilation, these do not predictably lead or correspond to the incidence of PPCs. ^, Therefore the relevant clinical hallmark of any intraoperative-inflicted lung injury is the increased incidence of PPC. Once present, PPCs contribute to an increased length of stay in high dependency units and may increase mortality and cost. ^,

Characterizing Postoperative Pulmonary Complication

Because PPCs are used as a measure of intraoperative lung injury, we need to better define them before reviewing the literature. Postoperative morbidities which are defined in clinical trials as PPCs, consist of atelectasis, pneumonia, lung edema, poor oxygenation, need for supplemental oxygen, postoperative invasive or noninvasive ventilation, reintubation, pleural effusion, pneumothorax, acute lung injury, acute respiratory distress syndrome (ARDS), pulmonary aspiration, postoperative fever over 38°C, bronchospasm, pulmonary embolism, radiologic consolidation, and more. Usually, a composite subset of these signs has been used to increase the chances of identifying complications and help evaluate the severity of respiratory complications. ^, In one major study in a general population of surgical patients, Canet et al. used a carefully chosen set of such signs with appropriate definitions ( Table 19.1 ), which was subsequently used in some studies to evaluate the incidence of postoperative lung injury after lung surgery. ^, There are some inherent problems in using the items of PPCs. Some of the items may have some degrees of overlap, that is, “pneumonia,” “consolidation,” and “atelectasis” or “respiratory failure” and “need for intubation.” Some of the complications, such as “need for oxygen” are considered a “minor” complication, whereas others such as acute lung injury or ARDS are “major” complications. Furthermore, the endpoints may or may not be appropriate depending on the clinical circumstances. For example, when evaluating the postoperative impact of intraoperative ventilation, endpoints such as atelectasis, pneumonia, need for oxygen, and pneumothorax may seem pathophysiologically linked to mechanical ventilation. Although aspiration pneumonitis or pulmonary embolism may contribute to PPCs as such, they may not necessarily be related to intraoperative ventilation. In general, linking specific intraoperative injurious interventions, such as mechanical ventilation, to PPCs may be difficult if they are not adequately controlled for unrelated intraoperative events (major bleeding, extent of tissue injury) or related to postoperative events (wound infections, anastomoses leakage, peritonitis), which may independently lead to PPCs. Thus consensual definitions of outcome measures in view of their pathophysiologic relevance have been attempted to standardize outcome measures for clinical studies.

At least two consensus papers on the issue of PPC and its use in perioperative studies have been published with quite different results. In 2015, a European Society of Anaesthesiology and European Society of Intensive Care Medicine (ESA/ESICM) task force published outcome measures for postoperative outcomes which included PPCs. The ESA/ESAICM closely followed Canets’ items and definitions of PPC issued in 2010, ⁶ with minor changes (see Table 19.1 ). A more recent consensus statement by Abbott et al. used a systematic review and a three-stage Delphi process to choose appropriate items. Briefly, items were first procured from relevant available literature. Then, in three consecutive steps, investigators assessed and scored the items in terms of quality and validity, excluded items with low scores, and ultimately defined only four items: atelectasis , as detected with chest x-ray or chest computer tomography; pneumonia , using U.S. Centers for Disease Control and Prevention criteria; acute respiratory distress syndrome (ARDS) using the Berlin definition; and pulmonary aspiration using “clear clinical history and radiologic evidence.” Unfortunately, none of the two consensual agreements are used consistently among investigators studying PPCs. Despite the controversies on items included in endpoint of PPCs among studies, it would seem prudent to at least relate some of the intraoperative issues under assessment, that is, intraoperative lung ventilation to pathophysiologically related and well-defined postoperative complications.

The Incidence of Postoperative Morbidity and Mortality in Thoracic Surgery

The incidence of PPC following lung resection or thoracic surgery varies in accordance with the data surveyed and items used to define the entity of the pulmonary complication. Licker et al., as well as Serpa Neto et al. used the definitions of acute lung injury and ARDS as a measure of PPCs and found an incidence of 4.2% and 4.3%, respectively in thoracic surgical patients. Significantly, once a patient suffered from these complications, the mortality rate rose to 26%. In a study using a relevant clinical database, Blank and colleagues used postoperative events such as tracheostomy, empyema requiring treatment, pneumonia, reintubation, initial ventilator support greater than 48 hours, ARDS, bronchopleural fistula, pulmonary embolism, air leak greater than 5 days, atelectasis requiring bronchoscopy, and respiratory failure to define their primary outcome of “respiratory complications” and found an incidence of 18% among patients undergoing pneumonectomy. Adjusting for patient characteristics, such as age, gender, body mass index, and American Society of Anesthesiologists status, the length of hospital stay in patients who developed respiratory failure and respiratory complications was increased by a factor of 4.7 and 3.5 respectively ( Fig. 19.1 ). Alam et al. found an incidence of lung injury consisting of pneumonitis, acute lung injury, and ARDS of 5.3% after thoracic surgery; they report a 25% mortality rate in patients with PPC compared with 2.6% in those without. These studies show that postoperative pulmonary complications are highly relevant and, once developed, caused considerable increased in mortality.

Predisposing Condition for Postoperative Pulmonary Complication

Preoperative factors, such as age, preoperative peripheral oxygen saturation (SpO ₂ ), respiratory infection before surgery, and preoperative anemia have been identified as risk factors contributing significantly to the development of PPCs. Some of these factors (smoking, preoperative lung function, preoperative infections) are potentially amenable to preoperative improvement with proper preoperative rehabilitation, which, if pragmatically practicable, would be mandatory before surgery (see Chapter 9 ).

Intraoperative Lung Injury and Postoperative Pulmonary Complications

Intraoperative events which may injure or initiate injury in the lungs during the surgical procedure can be related to the surgery itself and/or to the anesthesiologic management. In the individual patient, both disciplines may contribute in a varying degree to PPCs. Some studies consistently show that both short- and long-term survival of lung cancer patients after surgery depend on the volume or number of operations performed at hospitals. Pezziet al. evaluated this issue in the National Cancer Database for major lung resections from 2007 to 2011. There were 124,418 major pulmonary resections identified in 1233 facilities. The 30-day and 90-day mortality rates were, respectively, 2.8% and 5.4%. Hospital volume of cases was significantly associated with 30-day mortality, with a ­mortality rate of 3.7% for an annual volume of cases less than 10, and 1.7% for a volume of 90 or more cases. The lowest volume centers had a 1.5- to 2-fold increase in 30-day and 90-day mortality in comparison to highest volume centers. This finding is significant considering that other improvements in care usually do not translate to a large difference in outcome.