Prevention and Treatment of Postoperative Pulmonary Complications

What Are Postoperative Pulmonary Complications (PPC)?

PPC have been defined in a variety of ways, reflecting the lack of consensus. At its broadest, PPC may refer to almost any pulmonary (respiratory) complication that follows surgery. Complications related to the airway that occur during or directly after surgery and anesthesia (such as laryngospasm) tend not to be included. Combining a diverse range of events into a single composite description or outcome (PPC) has many limitations.

Pneumonia, invasive mechanical ventilation, and severe hypoxemic respiratory failure could all be considered PPC yet they describe different things: in this case diagnosis, treatment, and severity, respectively. Equally unsatisfactory is combining diseases with totally different pathophysiologies into one composite outcome (e.g., pneumothorax and bronchospasm). This is particularly true if you want to evaluate the efficacy of an intervention at reducing PPC; for example, interventions that improve bronchospasm are unlikely to affect pneumothorax. Following cardiac surgery, the occurrence of an asymptomatic pleural effusion requiring no treatment is a PPC, but very different from an episode of acute respiratory distress syndrome (ARDS) requiring days of invasive mechanical ventilation. Considering both events equally does not seem sensible.

Recognizing that clinical outcome measures for clinical trials must be robust, clearly defined, and patient-relevant, the European Society for Anaesthesiology and the European Society of Intensive Care Medicine (ESA-ESICM) joint taskforce on perioperative outcome measures published some standardized lists of clearly defined clinical outcome measures, including PPC. This work was refined as part of the Core Outcomes Measures in Perioperative and Anaesthetic Care (COMPAC) initiative. Standardized Endpoints for Perioperative Medicine groups were convened with the aim of identifying a core outcome set for perioperative studies. One outcome of this endeavor was the recognition that none of the available definitions of PPC were suitable for use in clinical practice or as an endpoint in clinical trials. A novel definition was proposed ( Box 20.1 ) that combines four diagnoses potentially sharing common mechanisms and a separation of disease from severity of illness. It is not easy to separate severity of illness from receipt of therapy because these necessarily go hand-in-hand. These proposed definitions will require validation in future studies.

How Common Are Postoperative Pulmonary Complications?

In common with all questions about incidence, estimates depend upon the definition used, the population under consideration, and the method of data collection. In the decade since the last version of this book the availability of analyses of “big data” from electronic patient records (EPR) has grown substantially, providing us far greater ability to estimate outcomes, such as PPC.

The limitations of retrospective database analyses are well recognized and summarized succinctly in a recent editorial. One major limitation is that they rely on coding data, which does not always agree with the strict clinical definitions that might be used with prospective data collection as would be used in an interventional trial or prospective observational study. For example, a diagnosis of pneumonia according to the Centers for Disease Control and Prevention (CDC) classification (as you might use in a trial) has several specific requirements that exceed those that might be used in routine clinical practice. A postoperative patient with a cough, fever, and mildly impaired oxygenation might be given a diagnosis of pneumonia and treated as such by a clinician (and coded as such), but without the characteristic changes on a chest x-ray, they would not meet the CDC criteria.

An analysis of cardiac and pulmonary complications from 45,969 patients following bowel surgery in over 600 hospitals in the United States used a composite PPC that included pneumonia, tracheobronchitis, pulmonary failure, and mechanical ventilation more than 48 hours after surgery. Using this definition gave an incidence of 19% of PPC, with the commonest qualifying code being for pulmonary failure (60% of PPC). These results should be taken in the context of the coding for pulmonary failure being well recognized as being poorly defined, with variable reporting. Nonetheless, an interesting finding of this study was that PPC are considerably more common than postoperative cardiac complications.

Another analysis based on coding data from an EPR included over 109,000 heterogeneous patients who had undergone a diverse range of types of surgery in three hospitals in Massachusetts. Their primary question concerned the potential role of type of intraoperative ventilation (discussed later) but they also reported the incidence of PPC; using a different definition only 9.4% of patients were coded in the first 7 days postoperatively for a PPC (a composite of reintubation, pulmonary edema, pulmonary failure, or pneumonia).

A prospective multicenter observational study conducted at seven US academic institutions explored predictors of PPC and the association between incidence of PPC and clinical outcomes, specifically in 1202 high-risk patients with American Society of Anesthesiologists (ASA) physical status of 3 (indicates that these patients have preexisting severe systemic disease) undergoing noncardiac surgery. This study was able to avoid the problems of relying on coding data and formulated a precise and detailed (yet novel) composite PPC definition that explicitly included diagnoses (clinical and radiologic) and receipt of therapies, including supplemental oxygen administration. With such an inclusive definition and a high-risk group, it is not surprising that the incidence of PPC was 33.4%. A smaller prospective multicenter study from the UK looked for PPC (using a standard definition derived from a trial) in 286 patients having major elective abdominal surgery and reported a PPC incidence of 11.9%.

A highly influential prospective study (Assess Respiratory Risk in Surgical Patients in Catalonia: ARISCAT ) was conducted in 59 Spanish hospitals and led to the ARISCAT score (discussed more later), which was then validated in a second study (PERISCOPE ) conducted across 63 hospitals from across Europe. ARISCAT recruited a wide range of patients (including cardiac) and, using a composite definition later adopted by ESICM-ESA, found that 5% of the 2464 patients developed a PPC. PERISCOPE recruited 5099 patients and 7.9% developed a PPC.

What conclusions can be drawn from these various reports? The incidence of PPC (however defined) is highly related to the population under consideration—the type of surgery and associated anesthetic technique, and the risk characteristics of the patients. Considerable work has gone into predicting risk of PPC (described later in this chapter).

How Important?

Developing a PPC is associated with increased length of stay in hospital and associated health-care costs. Furthermore, the greater the number of PPC, the greater the effect on duration of stay and early mortality. PPC vary in their severity and consequent impact. Patients developing pneumonia that causes respiratory failure requiring invasive mechanical ventilation will have a far greater impact on recovery from surgery than if they had just developed uncomplicated pneumonia.

Longer-term outcomes are also worse in those who develop PPC. This was convincingly demonstrated by a landmark paper by Khuri et al. in 2005. The analysis combined data from the National Surgical Quality Improvement Program (NSQIP) and a database of vital outcomes in more than 100,000 patients who underwent eight major operations. Occurrence of a complication in the first 30 days after surgery was independently associated with a reduction in median survival, an effect that was present even having corrected for all known confounding variables. Considering PPC specifically (defined as pneumonia, reintubation, and failure to wean) this was associated with the greatest reduction in survival (apart from cardiac arrest) with median survival in those with a PPC being 2.2 years versus 17.3 years without PPC. These patients’ surgeries took place between 1991 and 1999 and the health-care landscape has changed very significantly since then. The authors concluded that events in the postoperative period are more important than preoperative patient risk factors in determining the survival after major surgery.

Prediction of Postoperative Pulmonary Complications

A range of tools exist to assist in risk stratification of individual patients. It is always important to appreciate that a risk prediction tool cannot accurately determine an individual’s risk but provides an indication of the risk for a population of similar patients.

Pathophysiology

The relationship between recent anesthesia and surgery with the development of a new pulmonary condition reflects the adverse effects of anesthesia and surgery on the respiratory system. These adverse effects are well described and can only be directly pathophysiologically related to a proportion of all possible pulmonary pathologies. Patients with comorbidities are at increased risk of PPC and the severity of illness resultant from the PPC is heavily influenced by their premorbid state.