Opioid respiratory depression: sedation comes first
Table of contents
A 58-year-old man with obesity and loud snoring that his wife has described for years underwent abdominal surgery in the afternoon. He receives morphine through patient-controlled analgesia (PCA) and, as a precaution, oxygen through a nasal cannula. At 3 a.m., the nursing technician comes by for vital signs. Saturation is 97 percent, and the monitor has not alarmed. She calls the patient by name, and he takes a while to respond; he opens his eyes, mumbles something and falls back asleep mid-sentence. Counting calmly, the respiratory rate is 8 per minute. The scene is fictional and was written for teaching.
This text uses the scenario as a setting for clinical reasoning in nursing. Normal saturation is reassuring, and a patient sleeping at night looks like just a patient resting. Together, excessive drowsiness and slow breathing tell another story: opioid-induced respiratory depression, masked by oxygen. The text does not replace your institution's protocol or the medical prescription. If you play the case of the day on NEXO, you will recognize the challenge: distrusting the number that reassures.
Key points
- Opioid-induced respiratory depression usually appears in the first 24 hours after surgery.
- Sleep apnea, heart disease and lung disease increase the risk.
- Excessive sedation usually comes before the drop in breathing; the POSS scale helps measure it.
- With supplemental oxygen, saturation can stay normal while the patient hypoventilates.
- Capnography measures ventilation, not just oxygenation.
- Naloxone acts fast but lasts a short time; the patient must remain monitored.
Why this is a reasoning scenario
Opioid-induced respiratory depression is a known postoperative event, but it is usually recognized late. In a systematic review with more than 840,000 patients, the incidence was 5 events per 1,000 anesthetics, and 85 percent occurred in the first 24 hours after surgery (Gupta et al., 2018). In the international PRODIGY study, with continuous blinded monitoring of capnography and oximetry in 1,335 ward patients receiving parenteral opioids, 46 percent had at least one episode of respiratory depression over a median of 24 hours of monitoring (Khanna et al., 2020).
The scenario is good for training because routine numbers mislead. Saturation is good, and the patient seems to be sleeping. What changes the reading is the question about the quality of waking and breathing. The post on signs, symptoms and history shows how to read what the patient brings, and the post on clinical decision-making discusses how to choose the measure that changes management.
The cost of delay
The event is not only dangerous; it also prolongs the hospital stay. In PRODIGY, the stay was on average 3 days longer in those who had at least one episode (Khanna et al., 2020). In a cost analysis of the same study, patients with respiratory depression stayed 6.4 versus 5.0 days and had higher hospital costs, about 17 percent more in the weighted analysis (Khanna et al., 2021).
What the scene teaches
The scene trains four habits. The first is to assess sedation before counting breathing. The second is to count the respiratory rate with the patient unstimulated and for enough time. The third is to remember that saturation with oxygen does not measure ventilation. The fourth is to know the steps of the response, including the limits of naloxone.
Who is at higher risk
Not every patient on opioids has the same risk. The systematic review by Gupta et al. found more risk in patients with heart disease (odds ratio 1.7), lung disease (2.2) and obstructive sleep apnea (1.4); patients with the event also received higher daily opioid doses, in morphine equivalents (Gupta et al., 2018).
The PRODIGY score
PRODIGY derived a score with five variables: age 60 or older, male sex, no prior opioid use, sleep disorders and chronic heart failure (Khanna et al., 2020). Between the high and low risk groups, the odds ratio for respiratory depression was 6.07 (Khanna et al., 2020). The patient in the scene, a man with probable sleep apnea, adds up points.
Undiagnosed sleep apnea
The snoring described by his wife is a clue. In an analysis of PRODIGY, the nocturnal desaturation index (episodes of a 4 percent drop in saturation per hour) was strongly associated with respiratory depression; with 15 or more episodes per hour, the odds ratio was 4.71 (Liew et al., 2022). The authors suggest assessing the need for closer monitoring in these patients (Liew et al., 2022). Another study showed that simple measures of nocturnal oximetry before surgery performed similarly to the apnea-hypopnea index in assessing apnea severity and predicting postoperative respiratory depression (Assadi et al., 2024).
Other factors
In a Saudi hospital, among 15,753 patients who received opioids, 91 had respiratory depression; the risk was associated with daily doses of 150 morphine equivalents or more, the use of fentanyl and surgical admission (Almouaalamy et al., 2022). In a study of patients who received naloxone, age over 65 and surgery in the previous 24 hours were associated with respiratory depression (Savelloni et al., 2017). Hyland et al. note that avoiding associated sedatives, especially benzodiazepines, is an important modifiable risk factor, particularly in older, obese patients and patients with lung disease (Hyland et al., 2021).
| Factor | What nursing checks |
|---|---|
| Known or suspected sleep apnea | Snoring, observed pauses, CPAP use at home |
| Heart or lung disease | Diagnoses in the history, home oxygen |
| First 24 hours after surgery | Time the surgery ended |
| High dose of opioid or fentanyl | Prescription, PCA bolus, extra doses |
| Associated sedatives | Benzodiazepines, gabapentinoids, antihistamines |
| Advanced age, no prior opioid use | Age and history of opioid use |
Table sources: (Gupta et al., 2018), (Khanna et al., 2020), (Almouaalamy et al., 2022), (Savelloni et al., 2017) and (Hyland et al., 2021).
Sedation comes first: the POSS scale
Opioid-induced respiratory depression rarely appears out of nowhere. Usually the patient becomes increasingly drowsy before breathing drops. For this reason, assessing sedation is nursing's first line of defense. Hyland et al. recommend that institutional protocols include the Pasero Opioid-induced Sedation Scale (POSS) and capnography, in addition to conventional respiratory parameters and nursing assessment (Hyland et al., 2021).
How POSS works
In a study that used the scale, levels 1 and 2 were considered acceptable: the patient is awake and alert, or slightly drowsy and easy to arouse (Savelloni et al., 2017). Levels 3 and 4 indicate excessive sedation and risk of respiratory depression. At level 3, the patient is frequently drowsy, arouses easily but falls back asleep without constant stimulation; at level 4, the patient is drowsy, with minimal or no response to verbal and physical stimulation (Savelloni et al., 2017).
| Level | Description | Reading |
|---|---|---|
| 1 | Awake and alert | Acceptable |
| 2 | Slightly drowsy, easy to arouse | Acceptable |
| 3 | Frequently drowsy, arouses but falls back asleep without constant stimulation | Excessive sedation, risk of respiratory depression |
| 4 | Drowsy, minimal or no response to verbal and physical stimulation | Excessive sedation, risk of respiratory depression |
Table source: (Savelloni et al., 2017). Level S, normal sleep with easy arousal, appears in the original scale, which is not available in open full text; follow the version adopted by your service.
Applying it to the case
The patient in the scene opens his eyes when called, but falls back asleep mid-sentence. This corresponds to level 3: excessive sedation. Reading changes everything. A sleeping patient who wakes up and talks is resting; a patient who cannot stay awake while talking to the nurse is over-sedated.
PCA is not absolute protection
The idea of PCA is that the sedated patient stops pressing the button. This protection fails when a family member presses the button for the patient, when continuous infusion is programmed, or when another sedative is added. The question for nursing is simple: who pressed, how many times, and what else the patient received in the last hours.
Respiratory rate, oximetry and capnography
Respiratory rate seems like the simplest parameter, but it is one of the most poorly measured. Cheng and colleagues note that intermittent monitoring leaves intervals without surveillance, which can delay detection, and that interaction with nursing itself can temporarily increase the patient's attention and respiratory rate, masking the opioid effect (Cheng and colleagues, 2021).
Counting the right way
In practice, this suggests observing breathing before waking the patient and counting long enough to capture pauses, such as a full minute, according to the service protocol. Counting for 15 seconds and multiplying by four can miss long pauses. It also matters to look at depth and pattern: shallow breaths, snoring and pauses count as much as the number.
Continuous monitoring
In the study by Cheng and colleagues, a wireless respiratory rate sensor showed satisfactory agreement with nursing measurement in women with PCA after gynecological surgery (Cheng and colleagues, 2021). In PRODIGY, respiratory depression was defined as a respiratory rate of 5 or less per minute, saturation of 85 percent or less, or exhaled carbon dioxide of 15 or less or 60 mm Hg or more for at least 3 minutes, apnea of more than 30 seconds, or any opioid-related respiratory event (Khanna and colleagues, 2020). These thresholds are for research; your service's alarms may be different.
Capnography
Capnography continuously measures exhaled carbon dioxide and allows identification of ventilation problems, such as hypoventilation, and apnea by audible alarm (Steele and colleagues, 2020). In a US tertiary hospital, the introduction of smart pumps integrated with capnography for all patients with PCA, with automatic pause of opioid infusion when breathing fell below defined limits, along with education and review of PCA policies, was associated with a 79.2 percent reduction in serious adverse events (from 3.08 to 0.64 per 10,000 patients treated with opioid) (Steele and colleagues, 2020).
Oxygen can hide hypoventilation
This is the central point of the scene. Supplemental oxygen improves oxygenation, but not ventilation. If the patient breathes slowly, carbon dioxide accumulates, even with good saturation.
What PRODIGY showed
In an analysis of PRODIGY, compared to periods in room air, periods with supplemental oxygen had a higher risk of episodes of respiratory depression (incidence rate ratio of 2.7), apnea (2.8) and bradypnea (3.0) (Doufas and colleagues, 2023). In patients with a high PRODIGY score, the ratio reached 4.5 (Doufas and colleagues, 2023). Desaturation episodes did not differ between groups (Doufas and colleagues, 2023). The authors explain that when continuous oximetry is the only monitor, the increase in oxygenation from supplemental oxygen can hide and delay detection of severe respiratory depression, which can progress quickly to frank apnea and hypoxemia (Doufas and colleagues, 2023).
Liew and colleagues make the same observation: since many postoperative patients receive oxygen, the severity of respiratory depression episodes can be masked (Liew and colleagues, 2022).
What this means in practice
Oxygen is not the villain. It remains indicated when there is hypoxemia. The mistake is using saturation as proof that breathing is fine in a patient on oxygen. In the patient in the scene, the 97 percent saturation says nothing about the 8 breaths per minute. Sedation and respiratory rate do.
What to do at the bedside
When the nurse finds a patient with POSS 3 or 4 and slow breathing, the exact sequence depends on the local protocol. The actions below follow the logic described in the sources: stop the opioid, stimulate, assess ventilation and call for help.
First minutes
Stimulate the patient, call them by name, ask them to breathe deeply. Stop the PCA and any opioid or sedative infusion. Position with the head of the bed raised and open the airway if needed. Call for help and notify the physician. Count the respiratory rate, check saturation, blood pressure and level of consciousness. If the patient is not breathing or does not respond, follow the emergency protocol and ventilate.
Communicate clearly
A structured message helps: "58-year-old patient, postoperative after abdominal surgery, on morphine via PCA and with probable sleep apnea. Now POSS 3, respiratory rate of 8, saturation of 97 percent on 2 liters of oxygen. I stopped the PCA, the head of the bed is raised. I request immediate evaluation and guidance on naloxone." This sentence covers sedation, ventilation and what has already been done.
Naloxone
Naloxone is an opioid receptor antagonist and restores breathing, but by the same mechanism it reduces or abolishes analgesia (van der Schier et al., 2014). In the hospital setting, it is given intravenously at a titrated dose to reverse respiratory depression while minimizing withdrawal symptoms; by this route, onset of action is usually the fastest, within 2 minutes (Dahan et al., 2024). The dose and dilution follow the prescription and the facility protocol. The goal is for the patient to breathe adequately again, not to wake up in severe pain.
Renarcotization
The elimination half-life of naloxone is 15 to 20 minutes; therefore, a single bolus can be followed by renarcotization, that is, the return of respiratory depression after a short period of adequate ventilation (van der Schier et al., 2014). Dahan et al. give the same warning for long-acting opioids such as fentanyl and its analogs (Dahan et al., 2024). In practice, after naloxone, vigilance continues: sedation and respiratory rate repeated at short intervals, as per protocol, and continuous monitoring when available.
After the episode
The episode is information. The team reviews the opioid prescription, the need for other opioid-sparing analgesics, the discontinuation of associated sedatives and the level of monitoring. Suspected sleep apnea goes into the record and the handover. The post on interprofessional clinical reasoning discusses how nursing, anesthesia and pharmacy decide together.
Step-by-step reasoning in the case
First, the risk: a man, obese, loud snoring, probable sleep apnea, first night after surgery, morphine via PCA. The PRODIGY score and the Gupta review point to increased risk (Khanna et al., 2020) (Gupta et al., 2018).
Second, sedation: he opens his eyes and falls back asleep mid-sentence. POSS 3 (Savelloni et al., 2017).
Third, ventilation: respiratory rate of 8, counted calmly. Saturation of 97 percent on oxygen does not rule out hypoventilation (Doufas et al., 2023).
Fourth, action: stop the PCA, stimulate, position, call for help, communicate with data.
Fifth, reversal: naloxone titrated as prescribed, if indicated (Dahan et al., 2024).
Sixth, vigilance: naloxone lasts less than many opioids, and depression can return (van der Schier et al., 2014).
Common mistakes
The first mistake is trusting the saturation of a patient on oxygen (Doufas et al., 2023).
The second mistake is waking the patient and only then counting the respiratory rate (Cheng et al., 2021).
The third mistake is recording "sleeping" without assessing whether the patient can stay awake.
The fourth mistake is treating snoring as a detail, without thinking of sleep apnea (Liew et al., 2022).
The fifth error is giving naloxone and not monitoring afterwards (van der Schier et al., 2014).
The sixth error is adding sedatives to the opioid without reassessing the risk (Hyland et al., 2021).
A pause before leaving the room
The night round is in a hurry. The post on diagnostic pause shows how to stop and review the picture before moving on. In the scene, the pause is concrete: before writing down 97 percent and leaving, ask whether the patient actually wakes up.
How NEXO helps train this reasoning
To use the case of the day as training, try three habits. Before the first guess, ask which medications the patient received in the last few hours. At each clue, ask whether it speaks of oxygenation or of ventilation. After the result, note the clue you ignored because it seemed reassuring.
Three exercises with cases
Classify the sedation. In each case with an opioid, state the POSS level and what it changes.
Separate oxygenation from ventilation. List which data speak of each one.
Plan the monitoring. State what you will measure, and when, after a dose of naloxone.
The post on differential diagnosis with clues shows how to organize hypotheses, the post on simulation of care shows how to train patient assessment, the post on case-based learning shows how cases help fix these habits, and the post on diagnostic uncertainty discusses how to decide when the data do not yet add up.
The limits of use of the game are described on the NEXO economy page. If you research the teaching of clinical reasoning, the page for researchers explains how to get in touch. Professionals who write or review cases find information in curation and in creators, and institutions can learn about the proposal on the partnerships page.
Frequently asked questions
Does a normal saturation rule out respiratory depression?
No, especially with supplemental oxygen, which can hide hypoventilation (Doufas et al., 2023).
When is respiratory depression more common?
In the first 24 hours after surgery, when 85 percent of the events occurred in Gupta's review (Gupta et al., 2018).
Which POSS level is concerning?
Levels 3 and 4 indicate excessive sedation and risk of respiratory depression (Savelloni et al., 2017).
What is the dose of naloxone?
In the hospital, intravenous naloxone is titrated to restore breathing with minimal withdrawal (Dahan et al., 2024). The dose follows the prescription and the local protocol.
Why monitor after naloxone?
Because its half-life is 15 to 20 minutes, and the depression can return (van der Schier et al., 2014).
Final checklist
- I identified the risk factors, including suspected sleep apnea.
- I assessed sedation with the POSS before counting the breathing.
- I counted the rate without stimulating the patient and for enough time.
- I did not use oxygen saturation as proof of good ventilation.
- With POSS 3 or 4, I stopped the PCA, stimulated, positioned and called for help.
- I communicated sedation, rate, saturation and what has already been done.
- I prepared naloxone according to protocol and monitored after the dose.
- I reviewed associated sedatives and recorded the suspicion of sleep apnea.
Want to practice reasoning with progressive clues? Play the case of the day.
References
- Almouaalamy NA, Alshamrani M, Alnejadi WK, et al. Opioid-induced respiratory depression and risk factors in a tertiary hospital: A retrospective study. Saudi Pharm J. 2022. PMID 36164577.
- Assadi A, Chung F, Yadollahi A. Measures of overnight oxygen saturation to characterize sleep apnea severity and predict postoperative respiratory depression. Biomed Eng Online. 2024. PMID 38978075.
- Cheng SM, Chan JJI, Tan CW, et al. Use of wireless respiratory rate sensor monitoring during opioid patient-controlled analgesia after gynaecological surgery: A prospective cohort study. Indian J Anaesth. 2021. PMID 33776090.
- Dahan A, Franko TS, Carroll JW, et al. Fact vs. fiction: naloxone in the treatment of opioid-induced respiratory depression in the current era of synthetic opioids. Front Public Health. 2024. PMID 38481848.
- Doufas AG, Laporta ML, Driver CN, et al. Incidence of postoperative opioid-induced respiratory depression episodes in patients on room air or supplemental oxygen: a post-hoc analysis of the PRODIGY trial. BMC Anesthesiol. 2023. PMID 37794334.
- Gupta K, Nagappa M, Prasad A, et al. Risk factors for opioid-induced respiratory depression in surgical patients: a systematic review and meta-analyses. BMJ Open. 2018. PMID 30552274.
- Hyland SJ, Brockhaus KK, Vincent WR, et al. Perioperative Pain Management and Opioid Stewardship: A Practical Guide. Healthcare (Basel). 2021. PMID 33809571.
- Khanna AK, Bergese SD, Jungquist CR, et al. Prediction of Opioid-Induced Respiratory Depression on Inpatient Wards Using Continuous Capnography and Oximetry: An International Prospective, Observational Trial. Anesth Analg. 2020. PMID 32925318.
- Khanna AK, Saager L, Bergese SD, et al. Opioid-induced respiratory depression increases hospital costs and length of stay in patients recovering on the general care floor. BMC Anesthesiol. 2021. PMID 33743588.
- Liew LQN, Law LSC, Seet E, et al. Nocturnal Oxygen Desaturation Index Correlates with Respiratory Depression in Post-Surgical Patients Receiving Opioids - A Post-Hoc Analysis from the Prediction of Opioid-Induced Respiratory Depression in Patients Monitored by Capnography (PRODIGY) Study. Nat Sci Sleep. 2022. PMID 35510128.
- Savelloni J, Gunter H, Lee KC, et al. Risk of respiratory depression with opioids and concomitant gabapentinoids. J Pain Res. 2017. PMID 29180889.
- Steele T, Eidem L, Bond J. Impact of Adoption of Smart Pump System With Continuous Capnography Monitoring on Opioid-Related Adverse Event Rates: Experience From a Tertiary Care Hospital. J Patient Saf. 2020. PMID 30844891.
- van der Schier R, Roozekrans M, van Velzen M, et al. Opioid-induced respiratory depression: reversal by non-opioid drugs. F1000Prime Rep. 2014. PMID 25343036.