New Risk Tool for Opioid-Induced Respiratory Depression

Researchers are developing a tool they hope will quickly identify surgery patients at greatest risk for opioid-induced respiratory depression (OIRD).

With this tool, hospital staff will be better equipped to more closely monitor at-risk patients, which should reduce adverse events, increase patient safety, and improve patient satisfaction, said lead author Nicole Humbert, PharmD, Trinity Hospital, Livonia, Michigan.

She discussed the development of the preoperative OIRD risk index tool at a poster session during PAINWeek 2015.

Risk Factors

To define risk factors for OIRD that would form the basis of the tool, Dr Humbert and her colleagues carried out a retrospective observational single-center chart review at Saint Joseph Mercy. The study included patients aged 18 years and older admitted from October 1, 2012, to September 30, 2014, and who received an opioid within 24 hours of surgery.

The researchers defined respiratory depression as a respiratory condition requiring naloxone (multiple brands), an opioid antagonist that reverses the effects of opioids, including depression of the respiratory system.

The analysis included 114 patients who received naloxone and 13,724 patients who did not receive this agent.

Risk factors for OIRD fall into two categories: individual and iatrogenic, said Dr Humbert. For individual risk factors, researchers looked at age; airway obstruction; cardiac, hepatic, pulmonary, and renal function; and surgery type. For iatrogenic risk factors, they investigated such things as the percentage of patients receiving naloxone on postoperative day 0 vs postoperative days 1 and 2, the percentage of patients receiving intravenous opioids and sedatives within 12 hours of receiving naloxone, and the percentage of patients receiving long-acting opioids.

The researchers created weights (scores) for the different risk factors; the higher the score, the more likely the patient would require naloxone. They determined that surgery patients could be categorized according to the presence or absence of five risk factors: female sex, obstructive sleep apnea, renal dysfunction (glomerular filtration rate ≤ 29 ml/min), hepatic dysfunction (albumin level ≤ 3.0 g/dl), and upper abdominal surgical procedures. The factor associated with the highest risk (2.22) was hepatic dysfunction.

Excluded from the model were pulmonary and cardiac issues and age. The fact that age fell out of the model was somewhat surprising, said Dr Humbert. “If you have an 80-year-old patient, you’d expect that he or she would have more of an issue” with respiratory depression risks.

She said this could be explained by physicians ordering lower amounts of medications for these older patients.

On the basis of their weighted scores, patients fell into one of four categories: low, moderate, high, or very high.

The 7400 patients in the low-score category accounted for 53% of the patient population, but they accounted for only .32% of those receiving naloxone. In contrast, the 229 very-high-score patients accounted for only 1.65% of the patient population but 4.37% of patients who took naloxone.

Careful Monitoring

Patients in the very-high-risk or high-risk groups would need to be monitored more carefully for OIRD. This, said Dr Humbert, could include more frequent assessment of vital signs and pulse oximetry monitoring.

She and her colleagues will now look at performing a risk assessment preoperatively for all surgery patients and putting this on their initial profile. “We will also be looking at possible changes in their opioid therapy and looking at faster transitions from IV to oral,” said Dr Humbert.

She stressed the importance of transitioning from IV to oral opioids, because high peak levels following administration of IV opioids can contribute to OIRD risk.

Poster session co-chair Joseph Pergolizzi, Jr, MD, chief operating officer, NEMA Research, Bonita Springs, Florida, said the investigators have created a “novel risk stratification scheme” to help identify postsurgical patients who are more vulnerable to experiencing OIRD.

Identifying these patients is “very important” from a patient care perspective and from a hospital “quality metric” standpoint, he said.

“The information will be incorporated into the health system’s electronic medical record so that staff members can better predict who is at risk and then take the necessary measures to mitigate or even eliminate adverse events related to OIRD.”