Date Published: April 3, 2018
Author(s): Vidya K. Rao, Ashish K. Khanna.
Postoperative respiratory impairment occurs as a result of a combination of patient, surgical, and management factors and contributes to both surgical and anesthetic risk. This complication is challenging to predict and has been associated with an increase in mortality and hospital length of stay. There is mounting evidence to suggest that patients remain vulnerable to respiratory impairment well into the postoperative period, with the vast majority of adverse events occurring during the first 24 hours following discharge from anesthesia care. At present, preoperative risk stratification scores may be able to identify patients who are particularly prone to respiratory complications but cannot consistently and globally predict risk in an ongoing fashion as they do not incorporate the impact of intra- and postoperative events. Current postoperative monitoring strategies are not always continuous or comprehensive and do not dependably identify all cases of respiratory impairment or mitigate their sequelae, which may be severe and require the use of increasingly limited intensive care unit resources. As a result, postoperative respiratory impairment has the potential to cause significant downstream effects that can increase cost and adversely impact the care of other patients.
Respiratory impairment in the postoperative period is a significant contributor to morbidity and mortality following surgery and anesthesia . In 2015, the Agency for Healthcare Research and Quality rated postoperative respiratory failure as the 4th most common patient safety event, with other studies indicating an associated increase in mortality and hospital length of stay . There are significant data to suggest that the risk for respiratory compromise exists well beyond the duration of care in the postanesthesia care unit (PACU) and may be the highest in the first 4 to 6 hours following PACU discharge [3–6]. Up to 88% of respiratory events occur in the first 24 hours following the completion of anesthesia, and many of these cases appear to be preventable [3, 6]. While postoperative respiratory impairment can have tragic consequences for afflicted patients, there may be widespread downstream effects, particularly when critical care resources or unplanned intensive care unit (ICU) admission is required. The use of limited critical care resources can be financially burdensome, adversely impact the delivery of appropriate care to other patients, and affect the workflow and well-being of clinicians in critical care settings . The purpose of this review is to describe the problem of postoperative respiratory impairment, highlight its impact on the intensive care unit, and emphasize the role of anesthesiologists in mitigating this complication.
Postoperative pulmonary complications occur as a result of the interplay between modifiable and nonmodifiable comorbid conditions, surgical factors, persistence of intraoperative derangements in respiratory physiology, residual anesthetic effects, and the use of opioids and other sedating medications in the perioperative period. Despite the magnitude of this concern and the potential for catastrophic consequences in affected patients, no universal definition has been established. The published literature on this topic demonstrates significant variability in the characterization and identification of this complication, including hypoxemia, hypercarbia, hypoventilation, naloxone administration, or as part of a composite metric of postoperative pulmonary complications which include a wide variety of pathologies. Furthermore, the timing of what is classified as postoperative respiratory impairment varies considerably, ranging from the time spent in the postanesthesia care unit (PACU) to multiple days following surgery. The reported incidence ranges from 0.3 to 17% depending upon the metric evaluated [1, 8–10]. Institutional variability in anesthetic practice and postoperative monitoring strategies further precludes aggregation and generalizability of data. Thus, there is difficulty in accurately assessing the true incidence of postoperative respiratory impairment.
Respiratory physiology is dramatically altered with the initiation of anesthesia, particularly general anesthesia . There is notable depression of central respiratory drive, and even low anesthetic levels can diminish compensatory responses to hypoxia and hypercarbia. Respiratory muscle tone is also altered, precipitating anatomic airway obstruction , which can persist even with low levels of residual neuromuscular blockade. Functional residual capacity is also diminished , the diaphragm displaced, and many patients develop pulmonary atelectasis, which has been visualized on computed tomography studies in anesthetized patients .
In recent years, significant effort has been devoted to risk stratification and identification of patients with increased vulnerability for developing respiratory impairment. Multiple surgical subspecialties have evaluated their own patient populations to determine specific predictors of risk. While these investigations have some degree of interspecialty variability, there are commonalities among them, including age, American Society of Anesthesiologists classification of 3 or greater, congestive heart failure, obstructive sleep apnea, chronic obstructive pulmonary disease, obesity, preoperative anemia, and malnutrition [17–20]. Surgical factors that contribute to risk include surgical site, prolonged surgical duration, and emergency surgery [11, 18, 21].
Despite interest in multimodal analgesic therapy, opioids remain the cornerstone of pain management medication strategies. Over the past 2 decades, postoperative opioid use has escalated significantly in response to concerns regarding the undertreatment of pain and the resultant incorporation of pain scales into patient assessments . Studies performed subsequent to the institution of these measures reported an increase in over sedation and opioid-related adverse respiratory events, some with disastrous consequences [29, 30].
Given that prediction is an imperfect science, and with opioid therapy remaining the foundation of postoperative pain management, attention has also been directed toward optimization of postoperative monitoring. Multiple studies have demonstrated the inadequacies associated with intermittent assessment of vital signs. In one study, bedside nurses obtained intermittent vital signs while remaining blinded to continuous pulse oximetry monitoring. Notably, 38% of patients experienced hypoxemia (peripheral saturations <90%) for periods of greater than 1 hour, while 27% were hypoxemic for more than 2 hours. In contrast, only 5% of hypoxemic episodes were noted and documented during nursing assessments, which suggests an inadequacy of intermittent monitoring strategies to identify prolonged periods of postoperative hypoxemia . The previously mentioned closed claims analysis found that of the reported adverse respiratory events, respiratory monitoring was not utilized in 53% of cases, nursing assessments were inadequate in 31%, and 42% of respiratory events occurred within 2 hours of a nursing assessment . These investigations highlight the lack of adequate patient monitoring on surgical wards and expose an area of opportunity to improve patient safety. Critical care resources are often required in the management of patients with postoperative respiratory impairment. Audits of intensive care unit (ICU) admissions suggest that 17–47% of unplanned ICU admissions have a respiratory indication, and that the rate of unplanned ICU admissions is up to 91% higher in patients with postoperative pulmonary complications [34–37]. While some of these admissions may be unavoidable, there are published data to suggest that a significant percentage may be. All ICU admissions have the potential to create excessive demand on the limited supply of critical care resources, termed ICU capacity strain , but preventable admissions do so unnecessarily. Increasingly, ICUs are operating near capacity, with 90% unable to immediately provide a bed when required, and occupancy rates are projected to increase in the coming years [38–40]. There is ample evidence to suggest that the clinical consequences for patients with respiratory depression may be severe, which could translate into extended period of ICU care. Therefore, capacity strain may not be limited to the day of an unplanned or avoidable admission but could remain a persistent concern for the duration of the patient's stay. Postoperative respiratory impairment can have adverse consequences for afflicted patients as well as significant downstream effects that impact care delivery to others. Anesthesiologists, in an expanding role as perioperative physicians, have a multitiered responsibility in ensuring that patients safely transition into the postoperative period. This is particularly important during the highest risk period, which occurs as patients transfer from the PACU to the postoperative ward. Preoperatively, patients should be screened for respiratory vulnerability with the understanding that both intra- and postoperative events must also be considered in risk assessment. Intraoperative management, including medication administration, ventilatory strategies, and volume assessment should be optimized based on patients' comorbidities. Given limitations in risk prediction scores, appropriate vigilance and monitoring strategies should be employed, particularly during high-risk time periods, and anesthesiologists should take an active role in determining the optimal monitoring and acuity locations for patients upon PACU discharge. Source: http://doi.org/10.1155/2018/3215923