With the recent emphasis on treating postoperative pain aggressively, there is 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 data base 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 aircrafts 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 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 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 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 nalaxone. Patients over 65 years of age were also more likely to have bradypnea, whereas the morbidly obese and patients receiving continuous infusions were less likely to have bradypnea. The authors concluded that 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 early postoperative period to monitor patients receiving parenteral narcotics for postoperative pain.
 

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

It is quite possible that patients can drift into deep sleep, akin to MAC (monitored anesthesia care), consequent to judicious narcotic use during postoperative period. Patient variability can result in unexpected postoperative respiratory depression. American Society of Anesthesiologist (ASA) closed claims study demonstrated that MAC can result in hypoxia and brain damage (1), and the consequences 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 rises 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)

From Editorial [  the concerns are 1-3 ]   

["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 opioid 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 administered narcotic. If this respiratory depression is detected, it can be treated with naloxone. However, it is undetected respiratory depression that leads to hypoxic catastrophe. Well programmed PCA to some extent prevent adverse consequences of narcotic infusions, but do not prevent respiratory depression consequent to patient variability. in addition, programming errors, prescribing errors, PCA by proxy, 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 assessment 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 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 monitor of oxygenation, but does not forewarn impending hypoxia as a consequent 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 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<10, ETCO2 > 60 mm Hg, apnea alarm if no breathing>30 seconds). Pulse oximetry module alarms are set at 120<PR<50 and SPO2<90%. Having both infusion and monitoring on the same platform provides up to 24 hours of PCA dosing history with corresponding monitoring values from SPO2 and ETCO2. The data can be retrieved to survey events during the course of monitoring. The results of this study are promising as the device alerted the attention of care providers to several episodes of changes in ventilation that could have potentially resulted in hypoxia. These events could have gone unrecognized without the continuous capnography and pulse oximetry. In some instances, it was necessitated to discontinue PCA and physician notified.

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, postoperative monitoring are key elements to ensure 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 seems a promising new direction.


Further reading:

(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 a 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 lengthy 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 opioid 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.

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