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Designed, Produced, and maintained (Edition 12, 2022) by 

Bhavani Shankar Kodali MD

Updated September 2022

Postoperative Monitoring

Monitoring patients during the postoperative period 

'Avoid near misses'

     Bhavani Shankar Kodali MD


With the emphasis on treating postoperative pain aggressively, there is a substantial concern of narcotic-induced respiratory depression resulting in hypoxia in the immediate postoperative period. This is the time to think about this important phase of patient care. Intraoperative monitoring has become so rigorous in recent times and this has resulted in remarkable reductions in patient morbidity and mortality. However, as the patient moves from a stringent monitoring environment to a sparingly monitored area, the potential for unrecognized respiratory depression and hypoxia increases. We do not have a good database yet to determine the number of potentially life-threatening events in the postoperative area akin to the database of FAA's (Federal Aviation Authority) "near misses of aircraft collisions". Despite the lack of data, it is not uncommon to encounter patients with respiratory depression as a result of postoperative narcotic analgesics. This is the price tag that is associated with the diligent provision of postoperative analgesia.

Overdyk et al. recently (Anesthesia Analgesia 2007;105:2:412-8) monitored patients using patient-controlled analgesia (PCA) with pulse oximetry and side stream capnography providing a continuous record of heart rate, oxygen saturation, respiratory rate, and end-tidal CO2 from which they measured the incidence of respiratory depression (RD) using threshold criteria. In addition, nurses collected data on RD by rescue criteria and verified the proper placement of the transducers in response to audible monitor alarms. A total of 178 patients were included in the analysis. 12% and 41% of whom had episodes of desaturation (SPO2 <90%), and bradypnea (respiratory rate <10) lasting 3 minutes or more. One patient required 'rescue' with positive pressure ventilation, and none required naloxone. Patients over 65 years of age were also more likely to have bradypnea, whereas the morbidly obese patients receiving continuous infusions were less likely to have bradypnea. The authors concluded that the incidence of RD by bradypnea is significantly higher than the 1-2% incidence in the literature, using the same threshold criteria but more stringent duration criteria, while the incidence of RD based on desaturation is consistent with previous estimates. The higher incidence of bradypnea in this study could be due to greater emphasis in recent times on postoperative pain relief. There is potential for any RD events reported in this study, or otherwise, to progress to respiratory arrest if undetected.  

Clinical and technological efforts are being directed to focus on this newly emerging and recognized postoperative concern to enhance the safety of the patients during this vulnerable postoperative period. It is logical to be concerned, as the postoperative patients move from intensively monitored post-anesthesia care units to intermittently monitored or watched zones. Pulse oximetry and capnography have made operating room environments safe, which is reflected in lower operating room morbidity and mortality. This propelled enormous impetus into using capnography and pulse oximetry in cardiovascular and gastroenterology suits for procedural sedation to monitor ventilation and oxygenation. Several studies by gastroenterologists and emergency physicians endorsed the benefit of capnography in detecting changes in ventilation that were not detected by visual monitoring, or pulse oximetry. (see section 'procedural sedation of this website) There is growing interest to use capnography and pulse oximetry during the early postoperative period to monitor patients receiving parenteral narcotics for postoperative pain.

  Narcotics can result in respiratory depression in the postoperative period
  Respiratory depression can occur despite programmed PCA due to patient variability
  Intermittent nurse monitoring of postoperative patients may not pick up ventilatory depression that might occur during unattended periods.
 Continuous pulse oximetry can alert the hypoxic postoperative patient but does not give adequate forewarning of impending hypoxia due to ventilatory depression. The absence of forewarning can delay the deployment of corrective measures.
 There is a need to monitor ventilation during the early postoperative period that is vulnerable to respiratory depression consequent to narcotic administration for pain relief
 Technological innovations have integrated capnography and pulse oximetry modules into conventional PCA pumps. The initial observational case report study appears promising in detecting ventilatory depression occurring as a result of narcotics before alarming decreases in oxygenation in the patients.
 High-risk patients, who are likely to be vulnerable to respiratory depression by receiving parenteral narcotics in the postoperative period may be good candidates for considering the use multimodal PCA pumps. Favorable experience gained by the use of these pumps will augment future postoperative monitoring armamentarium to enhance patient safety in the vital early postoperative period.


Postoperative respiratory depression, A concern during the administration of parenteral narcotics for pain relief:

It is quite possible that patients can drift into a deep sleep, akin to MAC (monitored anesthesia care), consequent to judicious narcotic use during the postoperative period. Patient variability can result in unexpected postoperative respiratory depression. American Society of Anesthesiologists (ASA) closed claims study demonstrated that MAC can result in hypoxia and brain damage (1), and the consequences of poorly administered and monitored MAC are no different from complications of general anesthesia. A recently published editorial emphasizes that MAC should stand for 'Maximum Anesthesia Caution' and not 'Minimal Anesthesia Care.(2) The editorial also raises some important issues regarding analgesia sedation for patients outside of the operating room that are stated below. Some of these concerns expressed are quite valid during the use of postoperative narcotics.(2)

["Numerous malpractice claims and suits have been filed for drug-induced respiratory depression occurring after painful interventions. In addition, to the issues noted above (see details below), there are three other important considerations.
1. A surgeon or other interventionalist prescribing post-operative analgesic and sedative drugs should be cognizant of the residual effects of drugs administered during the procedure.
2. With the recent emphasis on treating pain aggressively the nurse caring for the patient does not experience significant pain, and an additional dose of opioids should not be administered even if the patient requests one during momentary arousal.
3. The evaluation of pain and suffering is purely subjective, and patient-controlled analgesia is a logical means of addressing variability and achieving effective and safe treatment."]

Patient-controlled analgesia, although effective, the response to opioids varies greatly among individuals, and significant hazards are associated with PCA.(3,4) Even when PCA pumps are correctly programmed, therapeutic doses of opioids can suppress respiration and decrease heart rate and blood pressure.(3) Food and Drug Administration Manufacturer and User Facility Device Experience (MAUDE) database, a voluntary database for reporting problems with devices, implicates 106 adverse drug events that included 22 deaths.(5) The most serious adverse event associated with opioid analgesics is respiratory depression resulting from patients' variability to administer narcotics. If this respiratory depression is detected, it can be treated with naloxone. However, it is undetected respiratory depression that leads to hypoxic catastrophes. Well-programmed PCA to some extent prevents adverse consequences of narcotic infusions but do not prevent respiratory depression consequent to patient variability. in addition, programming errors, prescribing errors, PCA by proxy, and inadequate patient education and selection can result in over-sedation.(6,7) it is logical to conclude from the foregoing discussion that unmonitored PCA may not be all that safe, as has been perceived by many.

In most hospitals, patients on PCA typically are monitored by frequent intermittent assessments by clinicians and nurses. Assessment may include blood pressure, respiratory rate, degree of sedation, cognition, pain scores, and intermittent pulse oximetry. Patient assessments may be conducted hourly for the first several hours after initiating PCA therapy and then once every few hours until PCA is discontinued. However, it is possible that clinicians with multiple patient work-loads may not be able to monitor a patient as frequently as deemed ideal, particularly during the first 24 hours and at night, when nocturnal hypoxia can occur. The current nursing shortage likely increases the danger that vulnerable events suggesting overmedication may not be detected.

Change in respiratory status is a leading indicator of adverse patient response to opioid infusion.(3) A nurse’s intermittent assessment can stimulate an over-sedated patient to a higher level of consciousness and increased respiratory rate thereby masking the true opioid depressed level. Once the stimulus is removed, a patient can drift to an over-sedated state.(3,6) In many hospitals, pulse oximetry is used on a continuous or intermittent “spot check” option to measure oxygen saturation. However, it should be noted that even at a low respiratory rate, SPO2 usually is maintained, particularly in patients receiving supplemental oxygen. In one case, an elderly patient on PCA, whose SPO2 was 96%, had a respiratory rate of 4 breaths/min.(3,6) The important message here is that supplemental oxygen can simply delay the detection of hypoventilation if too much reliance is placed on pulse oximetry. Furthermore, when hypoxia ultimately occurs, there may not be adequate time to undertake corrective measures before causing harm. Pulse oximetry is good to monitor oxygenation, but does not forewarn impending hypoxia as a consequence of hypoventilation. Therefore, some form of ventilation monitoring is obligatory, which could give warning of changes in ventilation that may lead to hypoxia, if uncorrected.

Capnography has been successfully shown to detect hypoventilation during procedural sedation (see the section on procedural sedation of the website). Sensing a growing need for intensified monitoring to enhance safety during the vulnerable period of postoperative pain management, technologically innovative medical groups have integrated the monitoring modules into a traditional PCA pump, which simultaneously monitors ventilation and oxygenation, to augment patient monitoring during PCA narcotic administration.

Maddox et al (3) have used one such device (Alaris PCA pump with capnography/pulse oximetry) in a case series study to evaluate the potential benefits in patients receiving parenteral narcotics. The PCA pump portion of the Alaris device has software to prevent programming and dosage errors, while the capnography module is programmed to issue an alert whenever preestablished limits are exceeded (RR 60 mm Hg, apnea alarm if no breathing>30 seconds). Pulse oximetry module alarms are set at 120
In conclusion, with increasing emphasis on pain control following surgery, there is a strong need to evaluate how the patients are going to be monitored to safeguard against respiratory depression. PCA is an excellent option. However respiratory depression can occur due to patient variability. Physician and nursing education, patient selection, and postoperative monitoring are key elements to ensuring the safety of the patients during this vulnerable period. Multi-modality PCA pumps that can monitor oxygenation (pulse oximetry) and ventilation (capnography) during parenteral administration of narcotics seem promising new directions.

 A PRODIGY (PRediction of Opioid-induced respiratory Depression In patients monitored by capnoGraphY) risk prediction model, derived from continuous oximetry and capnography, accurately predicted respiratory depression episodes in patients receiving opioids on the general care floor. Implementation of the PRODIGY score to determine the need for continuous monitoring may be a good step toward reducing the incidence and consequences of respiratory compromise in patients receiving opioids on the general care floor.(8) 

In a systematic review of pulse oximetry and capnography monitoring for postoperative respiratory depression and adverse events, continuous pulse oximetry was associated with significant improvement in the detection of oxygen desaturation. The addition of capnography identified 8.6% more postoperative respiratory events versus pulse oximetry alone monitoring group. (9)

Capnography was successfully to monitor women who underwent cesarean delivery after receiving intrathecal morphine. Though continuous capnography detected apnea alert events, these were nonsignificant thereby showing intrathecal morphine is safe in pregnant women following cesarean delivery. (10)

Further reading:

See the Lecture section on monitoring patients receiving narcotics for postoperative pain control.


(1) Bhanankar S, Posner KL, Cheney FW, Caplan RA, Lee LA, Domino KB. Injury and Liability Associated with Monitored Anesthesia Care.
Anesthesiology 2006;104:228-34.
The authors assessed the patterns of injury and liability associated with monitored anesthesia care (MAC) compared with general and regional anesthesia. The data was obtained from closed claims malpractice claims in the American Society of Anesthesiologists Closed Claims Database since 1990.
121 surgical anesthesia claims associated with MAC claims were compared to 1519 general anesthesia and 312 regional anesthesia claims. A detailed analysis of MAC claims was performed to identify causative mechanisms and liability patterns.
MAC group claims involved older and sicker patients compared with general anesthesia claims (P<0.025), often undergoing elective eye surgery (21%) or facial plastic surgery (26%). More than 40% claims involved death or permanent brain damage, similar to general anesthesia claims. In contrast, the proportion of regional anesthesia claims with death or permanent brain damage was less (P<0.01). Respiratory depression, after absolute or relative overdose of sedative or opioid drugs, was the most common (21%, n=25) specific damage mechanism in MAC group claims. Nearly half of these claims were judged preventable by better monitoring, including capnography improved vigilance, or audible alarms. On-the-patient operating room fires, from the use of electrocautery, in the presence of supplemental oxygen during facial surgery, resulted in burn injuries in 20 MAC claims (17%).

2. Hug CC Jr. MAC should stand for maximum anesthesia caution, not minimal anesthesiology care. Anesthesiology 2006;104:221-3.
Hug CC Jr, in an editorial accompanying this paper (Anesthesiology 2006;104:221-3), gave an appropriate title to MAC. MAC should stand for 'Maximum Anesthesia Caution', not 'Minimal Anesthesiology Care'. The most striking conclusion from the above study, as per the editorial, is that MAC is no less risky than general anesthesia in terms of occurrences of permanent brain injury and death for patients undergoing predominantly elective operations mostly in outpatient settings. Several factors could contribute to MAC-related morbidity and mortality, and they include attitudes of anesthesia and surgical personnel (being less diligent due to long history of prior safety), operating conditions being less than ideal, inadequate monitoring, deliberately turned down alarms volumes, much sicker patients, variability in patient response, and use of potent respiratory depressant drugs, etc.
"Numerous malpractice claims and suits have been filed for drug-induced respiratory depression occurring after painful interventions. In addition, to the issues noted above, there are three other important considerations. (1). A surgeon or other interventionalist prescribing post-operative analgesic and sedative drugs should be cognizant of the residual effects of drugs administered during the procedure. (2) With the recent emphasis on treating pain aggressively the nurse caring for the patient does not experience significant pain, and an additional dose of opioids should not be administered even if the patient requests one during momentary arousal. (3). The evaluation of pain and suffering is purely subjective, and patient-controlled analgesia is a logical means of addressing variability and achieving effective and safe treatment."


3. Maddox RR, Williams CK, Oglesby H, Butler B, Colclasure B. Clinical experience with patient-controlled analgesia using continuous respiratory monitoring and a smart infusion system. Am J Health-Syst Pharm 2006;63:157-64.

4. Eitches RC. Respiratory depression associated with patient-controlled analgesia: a review of eight cases. Can J Anaesth 1994;41(2):125-32.

5. Manufacturer and User Facility Device Experience Database (MAUDE). Rockville, MD: Food and Drug Administration 2004;Jan-Dec.

6. Nurse advise-ERR. Safety issues with patient-controlled analgesia. ISMP Med Saf Alert 2005;3(1):1-3.

7. Safety issues with patient-controlled analgesia. Part I-how errors occur. ISMP Med Saf Alert 2003;Jul 10.

8. Khanna et al. Prediction of Opioid-Induced Respiratory Depression on Inpatient Wards Using Continuous Capnography and Oximetry: An International Prospective, Observational Trial. Anesth Analg 2020;131(4):1012-25.

9. Lam et al. Continuous Pulse Oximetry and Capnography Monitoring for Postoperative Respiratory Depression and Adverse Events: A Systematic Review and Meta-analysis. Anesth Analg 2017;125(6):2019-29.

10. Weiniger et al. Prospective Observational Investigation of Capnography and Pulse Oximetry Monitoring After Cesarean Delivery With Intrathecal Morphine. Anesth Analg 2019;1128(3):513-22.