Respiratory compromise is a common, costly, deadly, and often preventable problem in hospitalized patients receiving opioids and across all hospital environments.

By Gregory K Spratt, BS, RRT, CPFT

Postoperative Respiratory Compromise

Respiratory compromise (RC), defined as respiratory decompensation through insufficiency, failure and/or arrest (see Figure 1), may be preventable through earlier identification and intervention.1-3 Respiratory conditions are the leading cause of ICU admissions, rescue calls, and code blues, and occur in nearly 1-of-8 elective surgery patients and 1-in-14 of all Medicare patients.4-8 It is projected that RC costs will reach $37 billion annually by 2019, and it ranks among the AHRQ “Top 5 Most Rapidly Increasing Hospital Costs.” 8-9

spratt_RC_figure1-500Patients that develop RC while on the general care floor (GCF) have a mortality rate 29 times that of GCF patients that do not develop RC.10 In light of these sobering statistics, the potential for prevention offers a ray of hope. In a review of primary respiratory arrests, 64% were classified as potentially avoidable, and, of these, all had inadequate treatment prior to the event, while 67% demonstrated clinicians failed to respond to abnormal findings.11 (See Figure 2, below.)

As respiratory therapists, we are uniquely positioned to be leaders within our institutions to improve both patient and economic outcomes for respiratory compromise. We possess a deep knowledge of the etiologies and pathophysiologies that lead to respiratory failure, understanding of monitoring modalities such as oximetry and capnography that can lead to early identification, and provide interventions that can halt or mitigate its progression.

spratt_RC_figure2-500

Several organizations, including The Joint Commission,12 the Anesthesia Patient Safety Foundation (APSF),13-14 the Society for Hospital Medicine,15 and the Association for the Advancement of Medical Instrumentation,16 have focused efforts on the problem of RC in post-operative patients secondary to opioid-induced respiratory depression (OIRD), but preventable RC can occur in patients across the hospital and the healthcare continuum via a variety of etiologies.3 Opportunities for improving outcomes exist in many patient populations.

Role of Continuous, Electronic Monitoring

Currently, the most common method of monitoring patients on the postoperative GCF is intermittent vital signs (eg, every 4-6 hours17), which the organizational recommendations referenced below state to be clearly inadequate. Nurses and other clinicians often face tremendous challenges in monitoring multiple patients simultaneously on the GCF.

A study of medical-surgical nurses in 36 hospitals showed that, on average, they spend only 7% of their time on patient assessment and reading vital signs.18 Manual vital sign monitoring is labor intensive and leaves patients unmonitored for 96% of the time.19 Spot-check entries may be inaccurate and not represent the patient’s true condition.19-20

Sun demonstrated that intermittent SpO2 spot checks missed 90% of hypoxemic episodes (recorded by blinded continuous oximetry) in which patients desaturated to less than 90% for at least one hour. He also points out that the patient with desaturations during sleep may be awake/awakened and even instructed to take deep breaths when SpO2 is low until a satisfactory vital sign is recorded, providing a false sense of normality.17

A review of opioid-related deaths and injuries resulting in litigation found that 97% of postoperative opioid-induced respiratory depression events (OIRDEs) on the ward were deemed preventable with better monitoring and response. Forty-two percent of OIRDEs in this analysis occurred within two hours of the last nursing check and 16% within 15 minutes.20 

spratt_RC_figure3-500

The organizations mentioned above, and several others, have recommended the use of continuous, electronic monitoring of oxygenation and ventilation to enable early identification. (See Figure 3). Several methods of monitoring are available, including pulse oximetry for oxygenation, capnography, RR, and tidal volume for quality of ventilation, each with its own inherent benefits and limitations.

Though a detailed comparison is beyond the scope of this paper, ideally, the monitoring should be continuous and noninvasive, with high reliability, sensitivity (ie, no false negatives), specificity (ie, minimal false or non-actionable alarms), and a fast response time to enable early clinician intervention as injury/death can ensue within minutes of an event occurring. An independent comparison of characteristics from several potential monitoring parameters is provided in Table 1, below.

spratt_RC_table1-500

There are several inherent challenges with broad implementation of continuous monitoring of all postoperative patients on the general care floor, known as “surveillance monitoring.” These include, but are not limited to:

  • Cost of the monitors and associated consumables/sensors for every bed/patient;
  • Unnecessary disruption to workflow due to false alarms, which are often the result of setting alarm thresholds too close to patient baseline; failure to customize the alarm settings to individual patient conditions; technical errors in application of sensors; and removal of sensors by patients (eg, noncompliance or removal to ambulate);24
  • Challenges in education of hospital personnel on interpreting monitoring parameters, waveforms, and trends, especially parameters less familiar to the primary bedside clinicians (eg, GCF nursing).

These challenges have led some hospitals to monitor only those patients deemed to be at higher risk based on a protocol or algorithmic assessment of risk factors, known as “conditional” or “risk monitoring.” 25 Some have suggested that risk cannot be adequately assessed at present and that monitoring only higher risk patients leaves unmonitored patients at risk; thus, surveillance monitoring of the entire population is preferred.13

Mechanisms and Risk Factors for Postoperative Respiratory Depression

A multitude of respiratory physiologic mechanisms are significantly compromised during and following anesthesia and exacerbated with administration of opioids and other respiratory depressant medications (eg, benzodiazepines, sleep aids, antihistamines, etc) used frequently across the hospital.

Detailed explanations are covered by other work and will not be repeated here but include depression of central respiratory drive resulting in alveolar hypoventilation, diminished compensatory responses to hypoxia and hypercarbia, respiratory/airway muscle tone reduction precipitating anatomic airway obstruction, diminished functional residual capacity, ventilation/perfusion mismatching, pulmonary shunt, diffusion impairment, increased oxygen extraction, diaphragmatic displacement, and atelectasis.26-27

In the postoperative period, response to hypoxia and hypercarbia can remain blunted secondary to residual effect of anesthesia and the use of opioids for acute pain which is exacerbated when used in combination with other potential respiratory depressants.  Atelectasis development may continue postoperatively secondary to low tidal volumes due to pain, especially during abdominal and thoracic surgery, which also makes clearing secretions from the airway difficult due to impaired cough. Functional residual capacity reaches a low point 1 to 2 days postoperatively and lung function may be diminished for days or even weeks postoperatively.26-27

spratt_RC_table2-500

Factors which may increase the risk of postoperative pulmonary complications have been referenced in several works on the topic and a few are summarized in Table 2, above. Risk factors can be classified in 3 groupings: 

  1. Patient factors (ie, conditions inherent to the patient, such as comorbidities, occult conditions such as undiagnosed or untreated OSA, obesity, age, etc)
  2. Treatment factors (ie, iatrogenic interventions provided to the patient, such as medications given, procedures performed, etc), and
  3. Area of care factors (ie, patient to nurse ratios, type/quality of monitoring, protocols in practice, knowledge of clinicians in responding to precursors to events, etc). 

It is often an interaction of several factors which creates the “perfect storm” scenario leading to catastrophic injuries and deaths. Furthermore, literature notes that the prevalence of certain patient factors, such as obesity, has dramatically increased in the US population, which may make this scenario more frequent.28

spratt_RC_figure4-500

Risk Assessment

Despite these known risk factors, because of the complexity and interactions of factors involved, reliable prediction of postoperative RC remains elusive. No standardized, validated tool to predict risk is available for determining which patients are at highest risk. In addition to the nearly ubiquitous use of opioids in postoperative patients, half of non-surgical (ie, medical GCF) patients receive opioids and there is little or no data available in the literature which can characterize the magnitude or risk factors of RC secondary to opioids in this population.30

There is a glaring need for a simple risk prediction tool to stratify risk of OIRD while on the GCF which has been emphasized in previous work on this issue.29 Such a tool could serve to guide which patients would benefit most from continuous monitoring (ie,‘risk monitoring’) when implementation challenges prevent surveillance monitoring of all patients.

Ideally, it should be automated and continuously updated as manual calculations based upon so many risk factors would be difficult, time consuming, and fail to reflect ongoing changes in risk factors. 

As the APSF suggests, such an approach might serve as an interim step toward a more ideal solution of surveillance monitoring all patients.13 Certainly, selective risk monitoring is preferred to current paradigms of intermittent vital sign monitoring and may help to demonstrate that improved patient outcomes (eg, reductions in reversals, admissions to ICU, rescue calls, code blues, LOS, etc) and the resultant reductions in the cost of care not only justify the investment made in monitoring those at highest risk but provide a basis of evidence which justifies broader application to all patients.

A survey of physicians and nurses revealed that 92% believe that continuous monitoring of patients who are at high risk or in early stages of respiratory compromise can lead to earlier interventions, preventing further deterioration, and 84% agree that RC monitoring can save money by preventing the need for more complex, more costly levels of care (eg, ICU admissions, intubation, ventilation, etc).31

Solutions on the Horizon

The PRODIGY trial is a multicenter, international, prospective study sponsored by Medtronic, designed with a primary objective to create and validate a risk prediction tool from continuous respiratory monitoring and patient electronic medical record data that can identify adult patients at risk of respiratory depression episodes when receiving parenteral opioid therapy on the medical and surgical general care floors. The study enrolled approximately 1,500 patients from 16 centers (US-9, EU-4, Asia-3) in seven different countries allowing potential comparisons across hospitals and geographical regions. The primary endpoints of PRODIGY will be respiratory depression (RD) as detected using blinded, non-alarming continuous capnography and oximetry monitoring on the GCF, RD being defined by one or more of the following:

  1. etCO2 ? 15 or ? 60 mmHg for ? 3 minutes;
  2. RR ? 5 breaths for ? 3 minutes;
  3. SpO2 ? 85% for ? 3 minutes;
  4. Apnea episode lasting > 30 seconds; or
  5. Any respiratory Opioid-related Adverse Drug Event.29,32

Secondary objectives of PRODIGY will include a comparison of RD risk subjects versus no-risk subjects in terms of incidence of adverse events and interventions, healthcare resource utilization, and subject mortality at 30 days. The predictive value of etCO2, RR, SpO2, and Medtronic’s Integrated Pulmonary Index algorithm will be correlated with the occurrence of RD and ORADEs. Data from two-thirds of study participants will be used to derive the risk assessment tool (Derivation Cohort).  Data from the remaining third will be used to validate the tool (Internal Validation Cohort).29,32

The recently released “PRODIGY: Seeking Answers” paper is the first publication from the trial discussing the rationale of this study and the methodology being used.29 Results from the trial, including primary and secondary objectives, will be published in subsequent papers to follow.

Summary

Respiratory compromise is a common, costly, deadly, and often preventable problem in hospitalized patients receiving opioids and across all hospital environments.  Continuous, electronic monitoring of oxygenation and quality of ventilation to aid in early identification and intervention in patients at risk has been identified as one mechanism to improve outcomes. Development of a risk prediction tool could be a significant step forward in understanding which patients would benefit most from prevention strategies, including continuous monitoring. RT

Gregory K Spratt, BS, RRT, CPFT is the director of Market Development, Medtronic. For more information, contact [email protected].

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