Postoperative pulmonary complications - Still room for improvement

This Invited Commentary accompanies the following original article: The investigators of the LAS VEGAS network. Epidemiology, practice of ventilation and outcome for patients at increased risk of postoperative pulmonary complications. LAS VEGAS - an observational study in 29 countries. Eur J Anaesthesiol 2017; 34:492–507. The intraoperative risks associated with anaesthesia care have significantly decreased over time.1 However, an increasing number of complications and adverse outcomes are identified during the postoperative period. A recent study using specific trigger tools identified an adverse event rate of 38.1% per 100 discharges from hospital between 2007 and 2011.2 A significant proportion (40.5%) of these events was associated with surgery and related procedures. These complications increase the likelihood of premature death, up to several years after surgery.3,4 Identifying patients at risk, and prevention and appropriate treatment of these complications during the perioperative period, are, therefore, crucial. The most common complications after surgery are postoperative bleeding, sepsis and cardiac and pulmonary complications.5 The last of these complications is particularly relevant to the anaesthetic community because ventilation is under the control of the anaesthetist during the intraoperative period. The large cross-sectional LAS VEGAS study, partially funded by the European Society of Anaesthesiology and published in this issue of the European Journal of Anaesthesiology,6 highlights a number of important aspects in this area: the incidence of postoperative pulmonary complications is high (19%); patients at increased risk of postoperative pulmonary complication have a longer duration of hospital stay (4 versus 1 day for low-risk patients); these patients have a higher mortality rate at 28 days (1.7 versus 0.2%); and modifying the intraoperative ventilation regimen, beyond modification of the intraoperative peak pressure, seems to be of limited benefit for these patients. Some aspects of the LAS VEGAS study deserve further comments. One is its large size. In all, 146 centres in and outside Europe participated in the study. Thus, our ability to generalise the study results is high. Another is the use of a validated risk score for assessment of the risk of pulmonary complications, the Assess Respiratory Risk in Surgical Patients in Catalonia score. It has a high predictive value (area under the curve 0.88).7–9 It includes straightforward and easily identifiable predictors such as age, preoperative peripherial oxygen saturation, respiratory infection in the last month, preoperative anaemia, site of surgical incision, duration of surgery and urgency of procedure. Thus, the study's findings have a high level of validity. Another aspect to be highlighted is that the LAS VEGAS study assessed outcomes that are important for perioperative healthcare management. The finding that 28% of all patients were at risk of postoperative pulmonary complications has consequences for the management of postoperative care. As 1.6% of patients are likely to develop postoperative respiratory failure, monitored and noninvasive ventilation should be planned before surgery in patients at highest risk to avoid unavailability of beds in intermediate or ICUs. Although highly valid and generally applicable, the results of the LAS VEGAS study should be interpreted with some caution. The secondary postoperative outcome of the LAS VEGAS study is a composite endpoint. It includes unplanned supplemental oxygen administration, respiratory failure, invasive mechanical ventilation, acute respiratory distress syndrome, pneumonia and pneumothorax. Some of these endpoints, such as pneumothorax, have clear definitions, whereas some others that relate to therapeutic interventions (e.g. supplemental oxygen administration) may include nonstandardised components such as local criteria to decide on the need for administration of additional oxygen. As a result, there is some variability in outcome definition that may add uncertainty around incidence measurement.10–12 Although the LAS VEGAS study identifies a number of pulmonary adverse outcomes, some are also missing. These are atelectasis, diaphragmatic dysfunction, retention of bronchial secretions, (micro) aspiration, pulmonary oedema and pleural effusion. Many of the included and not included postoperative pulmonary complications can be related to anaesthetic management, such as fluid or pain management, but some relate to unidentified acute cardiac dysfunction. These aspects could not be assessed in the study, which focused mainly on the ventilation regimen used. Biomarkers such as (pro)BNP and troponin could improve identification of pure pulmonary complications.13 Further studies investigating these covariates are required to provide the full picture of appropriate intraoperative patient management that can minimise the risk of postoperative pulmonary complications. The LAS VEGAS study nicely highlights the impact of pulmonary complications on length of hospital stay. Additional effects on health-related disability and quality of life should be also emphasised, as these can influence overall patient survival at 28 days and beyond. Patient-centred outcomes such as postoperative disability,14 recovery and health-related quality of life15 should be used increasingly in studies on perioperative care. The study also included patients who underwent surgery as part of palliative care with potential do not resuscitate orders. Although, this reinforces our ability to generalise the study results, the inclusion of this category of patients can increase the incidence of postoperative pulmonary complications, length of hospital stay and mortality rate of a study sample. Thus, the study results should be interpreted carefully, particularly as surgical approaches for palliative care may vary among centres and countries. Another noticeable aspect of the LAS VEGAS study is the small size effect of intraoperative peak pressure on postoperative complications. Tiny compared with large effect sizes are more likely to reflect bias than true intervention effects of clinical or public health importance.16 Thus, observational or nonrandomised studies with small intervention effects should be assessed with caution.17 Definitive conclusions on the optimal ventilation regimen for high-risk patients should not be drawn from this study. Nevertheless, the study's authors, contributors and the European Society of Anaesthesiology should all be congratulated for this significant scientific contribution to the understanding of the true incidence and risk factors of postoperative pulmonary complications. It contributes to opening the research agenda in this area and hopefully further large observational or randomised studies will emerge that should improve our knowledge on this critical topic. Acknowledgements relating to this article Assistance with the commentary: none. Financial support and sponsorship: none. Conflicts of interest: none. Comment from the Editor: this Invited Commentary was checked and accepted by the editors but was not sent for external peer review. BW is a Deputy Editor-in-Chief of the European Journal of Anaesthesiology.