European Journal of Pain

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1 European Journal of Pain 13 (2009) Contents lists available at ScienceDirect European Journal of Pain journal homepage: An audit of postoperative intravenous patient-controlled analgesia with morphine: Evolution over the last decade Chi Wai Cheung a, *, Chee Lun A. Ying a, Libby H.Y. Lee b, Suk Fung Tsang a, Siu Lun Tsui c, Michael G. Irwin a a Department of Anaesthesiology, The University of Hong Kong, Room 424, Block K, Queen Mary Hospital, 102 Pokfulam Road, Hong Kong b Department of Anaesthesiology, Queen Mary Hospital, Hong Kong c Pain Management Team, Department of Anaesthesiology, Queen Mary Hospital, Hong Kong article info abstract Article history: Received 12 August 2007 Received in revised form 24 April 2008 Accepted 21 May 2008 Available online 7 July 2008 Keywords: Analgesia Patient-controlled Medical audit Morphine Pain Post-operative The development and refinement of an acute pain service based on the increased availability of clinical evidence would be expected to improve the quality of postoperative pain control. This report reviews the application of postoperative patient-controlled analgesia (PCA) using intravenous morphine in a single institution between 2002 and More than 5000 patients were evaluated and the results were compared with a similar study performed 10 years ago. Prescription of PCA had increased by more than threefold. Morphine consumption from post-operative day 1 to day 3 (19.1 vs. 26.1, 8.6 vs and 4.5 vs lg/kg/h, respectively), demand-to-delivery ratio ( vs ) and the incidence of respiratory depression (0.06% vs. 2%) were significantly reduced (p < 0.001), but there was no improvement in pain relief. A substantial proportion of patients still experienced postoperative nausea (47%) and vomiting (18.5%) despite a reduction in morphine consumption. Most patients ranked PCA as good and only 0.3% were dissatisfied. We conclude that, in our institution over the last decade, PCA has become more popular for postoperative pain management but with no attendant improvement in pain relief or reduction in side effects. Using PCA alone may result in poorer quality postoperative analgesia. Our findings add to the growing body of evidence that postoperative pain management has not substantially improved despite increased adoption of acute pain services. Ó 2008 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Ltd. All rights reserved. 1. Introduction * Corresponding author. Tel.: ; fax: address: cheucw@hku.hk (C.W. Cheung). The concept of patient-controlled analgesia (PCA) was introduced in 1968, when it was used as a measure of analgesic response to intravenous (IV) morphine (Sechzer, 1968). The first PCA machine was developed in Its application to the management of postoperative pain increased rapidly thereafter, and it is now ubiquitous. It has been studied extensively and proven to be safe and reliable (Macintyre, 2001). Despite improvements in technology, the contribution from clinical research evidence and the advent of Acute Pain Services (APS), a national survey performed in the United States reported that post-operative pain remains undermanaged and the level of pain has not been reduced over the last decade (Apfelbaum et al., 2003). Therefore, we conducted this retrospective study of 5137 patients, who received post-operative PCA at our hospital between 2002 and Results were compared with a study performed 10 years ago at the same institution (Tsui et al., 1996). Over this period an APS has been introduced and developed as a multidisciplinary team involving anaesthetists, pain nurses, surgeons and ward nurses with the aim of improving postoperative pain management. We also stopped using a background morphine infusion in response to clinical evidence (Macintyre, 2001). The methodology in both studies was, otherwise, largely similar. The major outcomes compared include efficacy (morphine consumption and pain), tolerability (side effects), safety (respiratory depression) and patient satisfaction. 2. Methods This study was conducted at Queen Mary Hospital, a tertiary referral teaching hospital in Hong Kong, and was approved by the local Institutional Ethics Committee. Data were collected from patient records kept by the Acute Pain Service of the Department of Anaesthesiology. Retrieved patient records were those who had been prescribed postoperative PCA using IV morphine between January 1, 2002 and December 31, Patients were excluded from data analysis if (1) PCA had not been started after prescription, or did not start within the first day after surgery, e.g., patients who remained mechanically ventilated in the intensive care unit after surgery; (2) there was concomitant use of other acute pain /$36.00 Ó 2008 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Ltd. All rights reserved. doi: /j.ejpain

2 C.W. Cheung et al. / European Journal of Pain 13 (2009) control modalities, such as epidural anaesthesia, peripheral nerve block, or continuous morphine infusion; (3) essential data were missing, e.g., PCA machine configuration and morphine consumption; (4) PCA machine error resulted in resetting of the dosage count; (5) patients were found to have difficulties or were unfit to use PCA after surgery; (6) PCA was terminated due to deterioration of patient s condition, e.g., surgical complications requiring reoperation or intensive care; and (7) patients were participating in other pain-related research projects. All patients were monitored in the recovery area after surgery. Vital signs including blood pressure, oxygen saturation (SpO 2 ), electrocardiogram and numerical rating scale (NRS) of pain scores at rest and during cough (0 represents no pain and 10 indicates the most severe pain that patient could imagine) were assessed for at least 30 min before discharging back to the general ward. Morphine was given intravenously to patients by the attending anaesthetist until the NRS pain score was 3 or less. The PCA machine (Graseby 3300 Syringe Pump, Smiths Medical, London) was then connected to the patient via a dedicated IV line or a non-reflux valve. The PCA machine was placed at or below the patient s heart level to avoid siphoning. Patients were taught how to use PCA by the attending anaesthetist. A standard PCA IV morphine protocol was adopted throughout the studied period. The concentration of morphine prepared on the PCA machine was standardized to 1 mg/ml in normal saline. The PCA pump was programmed as follows: each IV bolus of morphine was 1 or 1.5 mg, taking age, body weight and health status into consideration; the lockout interval was 5 min; the 1-h-maximum dose limits were 0.1 mg/kg for patient less than 65 years old and mg/kg for 65 years or above. No basal infusion of morphine was given. The APS team would be informed if pain control was inadequate when hourly limit and bolus dose parameters could then be adjusted after assessment. Intramuscular pethidine (0.5 mg/kg) injection was prescribed as the rescue pain medication. More sophisticated alteration of the PCA configuration could only be made by the APS anaesthetists. All patients were closely monitored after transfer back to the general ward. SpO 2 was monitored continuously for at least 24 h after surgery. Respiratory rate and sedation score were observed hourly and then every 4 h when the patients were stable. Blood pressure, pulse, NRS pain score at rest and during cough, PCA demand and delivery counts, as well as cumulative dose were recorded every 4 h. Rescue pain medication and the use of antiemetics were also noted. All complications, including their severity and management were charted. Common minor complications were managed according to the guidelines. Anti-emetics were not routinely administered for prophylaxis. Metoclopramide 10 mg up to every 4 h was prescribed to be given intravenously for post-operative nausea and vomiting (PONV) on patient demand. Ondansetron was reserved for patients with PONV refractory to this treatment. The APS team or the on-call anaesthetist was informed if a severe adverse event occurred. These included loss of consciousness (unrousable and a sedation score of 3 or less, see Appendix 1), bradypnoea (respiratory rate less than 10 per minute), hypotension (systolic blood pressure less than 90 mmhg), hypercapnoea (Pa- CO 2 > 7 kpa), or oxygen desaturation (SpO 2 < 90%). When any of these events occurred, PCA was immediately suspended, and the patient was managed accordingly. Naloxone was given intravenously to patients with respiratory depression if necessary. PCA might be restarted when the clinical condition improved, after a thorough review of the patient, the drug dose and consumption, and the PCA setting by the APS team. Patients on PCA were followed up by the APS team everyday. Morphine consumption, NRS pain scores at rest and during cough, and side effects were assessed. If oral intake was allowed, adjuvant oral pain medications such as paracetamol, non-steroid antiinflammatory drugs (NSAIDs) and opioids (including dextropropoxyphene and dihydrocodine) might be prescribed at the discretion of the acute pain team anaesthetist. Per rectal adjuvant were also considered if the patient could not tolerate oral medication. Suitability for termination of PCA was also reviewed during the visit. PCA was stopped when the NRS pain score during cough was 3 or less, daily morphine consumption was less than 0.1 mg/ kg, or on patient s request. Rescue pain medication and oral adjuvant pain medication were usually continued after stopping PCA. Patients were asked by the APS to grade their satisfaction regarding the use of PCA as good, fair, or unsatisfactory the moment PCA was stopped. They were also asked the reason(s) if they graded fair or unsatisfactory. The results from the present data were compared with a study conducted 10 years ago at the same institution (Tsui et al., 1996). Apart from the classification of operations, the methodologies of the two studies were similar. Operations were grouped according to anatomical location and organ system into more detailed categories than the previous study (Tsui et al., 1996). Among the large number of abdominopelvic operations, they were further categorized by organ system into five groups. Operations involving abdominal incisions but not involving the major organ systems were classified into other laparotomy. These operations mainly consisted of emergency laparotomy with extensive abdominal wound, such as open repair of abdominal aortic aneurysm, as well as abdominal exploration for haemoperitoneum and abscesses. Other procedures that did not fit into any of the groups belonged to miscellaneous. The outcomes compared included efficacy (pain relief and morphine consumption), tolerability (nausea and vomiting), safety (respiratory depression) and patient s satisfaction. Statistical analysis was performed using SPSS 14.0 for Windows (SPSS Inc., IL, USA). Pain scores, drug demand and delivery counts, and morphine consumption among groups were compared using Mann Whitney U or Kruskal Wallis test, as appropriate. Kaplan Meier survival analysis and log-rank test were used to compare the duration of PCA among types of operations. 3. Results During this 48-month period, 6023 post-surgical patients were prescribed PCA. Among them, 5137 patients were eligible for data analysis. The rest were excluded because PCA was not started within the first day after surgery (n = 473), patients had difficulties in using PCA (n = 59), PCA was terminated due to surgical complications (n = 101), concomitant morphine infusion was administered with PCA (n = 11), essential data was incomplete (n = 137), or patients were participated in other pain-related research projects (n = 127). Patients under 65 years old accounted for 63.8%. The duration of PCA use and the drop out rate were compared among different types of surgery in Table 1. Patients who received thoracic and oesophageal surgery had the longest duration of PCA use (median = 90 h, inter-quartile range (IQR) = 48 to 109 h), followed by the other laparotomy category (74 h, IQR = 64 to 94 h) and upper gastrointestinal surgery (68 h, IQR = 58 to 91 h). Over 90% of colorectal, thoracic and upper abdominal surgery patients continued the use of PCA on post-operative day 2. By day 3 after surgery, the lowest dropout rates were in upper gastrointestinal surgery (20%), thoracic and oesophageal surgery (31%), and colorectal surgery (32%). Since pain assessment was not recorded once PCA was taken off, data from post-operative days 2 and 3 were based on patients who were still using PCA. NRS pain scores at rest and during cough among different types of operation were shown in Table 2. Pain

3 466 C.W. Cheung et al. / European Journal of Pain 13 (2009) Table 1 Median duration of patient-controlled analgesia (PCA) use and the number of patients on PCA in the first 3 days after different types of operation Types of operation Duration (h) Day 1 Day 2 Day 3 n % n % n % All cases Head and neck Breast Upper gastrointestinal Hepatobiliary and pancreatic Colorectal Urological Gynaecological Other laparotomy Spine Limb Trunk Thoracic including oesophageal Miscellaneous Row percentages are shown. Log-rank test with Kaplan Meier analysis showed that the duration of use was significantly different among types of operation (P < 0.001). Table 2 Median pain scores (using numerical rating scale from 0 to 10) during the first, second and third 24 post-operative hours using PCA morphine Types of operation First 24 h Second 24 h Third 24 h n Rest Cough n Rest Cough n Rest Cough All cases Head and neck Breast Upper gastrointestinal Hepatobiliary and pancreatic Colorectal Urological Gynaecological Other laparotomy Spine Limb Trunk Thoracic including oesophageal Miscellaneous P <0.001 <0.001 <0.001 < Pain scores were compared among different types of operation using the Kruskal Wallis test. Table 3 Median morphine consumption (lg/kg/h) of patients receiving different types of operation Operation First 24 h Second 24 h Third 24 h Total n MC n MC n MC n MC All cases Emergency surgery? Yes No P <0.001 <0.001 <0.001 <0.001 Types of operation Head and neck Breast Upper gastrointestinal Hepatobiliary and pancreatic Colorectal Urological Gynaecological Other laparotomy Spine Limb Trunk Thoracic and oesophageal Miscellaneous P <0.001 <0.001 <0.001 <0.001 MC, morphine consumption. Results were compared using the Mann Whitney U test for emergency surgery and Kruskal Wallis test for types of operation.

4 C.W. Cheung et al. / European Journal of Pain 13 (2009) scores were significantly different among groups in the first 48 h, while resting pain scores on day 3 were similar. Patients who had upper gastrointestinal and colorectal surgeries reported the highest pain scores on post-operative day 1. Breast and trunk surgery patients reported higher pain scores on post-operative day 3 than day 1. Morphine consumptions among different types of operations were compared in Table 3. The morphine consumption was higher after emergency operations (p < 0.001). High morphine consumption (over 20 lg/kg/h) was observed among patients after upper gastrointestinal, thoracic and oesophageal surgeries, and other laparotomies. Table 4 showed morphine consumptions of patients with various characteristics. Morphine consumption was higher among patients younger than 65 years, males, smokers, alcohol drinkers and chronic drug users (p < 0.001). No difference was noted among the American Society of Anaesthesiologists physical statuses. Patients with hypertension used less morphine. Other common medical illnesses, such as chronic obstructive airway disease, ischemic heart disease and diabetes mellitus did not have an effect on morphine consumption. Table 4 Median morphine consumption (lg/kg/h) of patients with different characteristics Characteristics First 24 h Second 24 h Third 24 h Total n MC n MC n MC n MC All cases Age <65 years P65 years P < <0.001 Gender Male Female P <0.001 < <0.001 Ever smoker Yes No P <0.001 <0.001 <0.001 <0.001 Ever drinker Yes No P <0.001 < <0.001 Ever drug abuser Yes No P <0.001 <0.001 <0.001 <0.001 Hypertension Yes No P < <0.001 Diabetes mellitus Yes No P Ischaemic heart disease Yes No P Chronic obstructive airway disease Yes No P Asthma Yes No P Chronic renal failure Yes No P ASA PS ASA I ASA II ASA III ASA IV ASA V N/A 0 N/A P MC, morphine consumption; ASA PS, The American Society of Anesthesiologists physical status. Results were compared using the Mann Whitney U test for dichotomous factors and Kruskal Wallis tests for ASA PS.

5 468 C.W. Cheung et al. / European Journal of Pain 13 (2009) Table 5 Median morphine consumption (lg/kg/h) of patients who experienced various adverse effects Adverse effects First 24 h Second 24 h Third 24 h Total n % MC n % MC n % MC n % MC All cases Nauseated Yes No P Vomited Yes No P < <0.001 Dizziness Yes No P <0.001 Confusion Yes No P Pruritis Yes No P <0.001 MC, morphine consumption. Results were compared between groups using the Mann Whitney U test. Table 6 Patient-rated efficacy of PCA Types of operation Good Fair Unsatisfactory Unknown n % n % n % n % All cases Head and neck Breast Upper gastrointestinal Hepatobiliary and pancreatic Colorectal Urological Gynaecological Other laparotomy Spine Limb Trunk Thoracic and oesophageal Miscellaneous Row percentages are shown. The commonest side effects of PCA with IV morphine were nausea (47.4%) and vomiting (18.5%), dizziness (29.6%), and pruritis (8%) (Table 5). Patients suffered from vomiting had lower morphine consumption (p < 0.001). In spite of the high incidence of nausea and vomiting, only 5.1% used anti-emetic medication. Female sex and gynaecological surgeries were associated with higher risk of nausea and vomiting. Post-operative confusion developed in 25 patients (0.5%). Bradypnoea occurred in three patients (0.1%). One developed hypoxia but responded to oxygen therapy. No patient required naloxone. When the incidences of adverse events of excluded patients were analyzed, they were not higher than that of the included patients. The occurrence of nausea was lower among the excluded patients (p < 0.005), but there was no significant difference in other side effects. Satisfaction with PCA is shown in Table 6. Only 0.3% of patients reported unsatisfactory, while 79.8% reported good. Common reasons for dissatisfaction were nausea and vomiting, followed by inadequate pain control. 2.6% of patients required supplementary intramuscular pethidine when PCA with or without adjuvant oral analgesics could not control their pain. The rest complained that they were not happy with other side effects such as sedation and confusion. Patients who received adjuvant pain medications were compared with those who did not. The demand-to-delivery ratio of patients receiving adjuvant pain medications was higher on postoperative day 1 (p < 0.001). Both overall morphine consumption and pain scores were higher in patients receiving adjuvant pain medications from postoperative day 1 to day 3 (p < 0.001). Significant differences were noted when the present data were compared with that published 10 years ago (Tsui et al., 1996) as shown in Table 7. The demand-to-delivery ratios and morphine consumptions throughout post-operative days 1, 2, and 3 were significantly lower in the recent data (Table 7a and 7b, all p < 0.001). Generally, while resting pain scores were lower in the present data on days 1 and 2 (Table 8), scores during cough were significantly higher for most types of surgery (p < 0.001). Nausea and dizziness

6 C.W. Cheung et al. / European Journal of Pain 13 (2009) Table 7a Comparison of outcomes using PCA between data collected 10 years apart in the same institution Study First 24 h Second 24 h Third 24 h Mean demand-to-delivery ratios Tsui ( ) 2.8 ± ± ± 2.6 (n = 344) (n = 1233) (n = 1010) Cheung ( ) 1.76 ± 1.13 (n = 5095) 1.41 ± 0.95 (n = 3994) 1.35 ± 1.17 (n = 2364) P <0.001 <0.001 <0.001 Table 7b Overall mean morphine consumption (lg/kg/h) in the first, second and third 24 postoperative hours Study First 24 h Second 24 h Third 24 h Tsui ( ) 26.1 ± 20.0 (n = 1233) 18.1 ± 17.8 (n = 791) 19.0 ± 28.1 (n = 239) Cheung ( ) 19.9 ± 15.8 (n = 4680) 8.6 ± 8.6 (n = 3772) 4.5 ± 5.0 (n = 2242) P <0.001 <0.001 <0.001 Table 7c Common side effects Study Nausea Vomiting Dizziness Respiratory depression Tsui ( % 18.2% 17.4% 2% 1995) Cheung ( % (2395/ 18.2% (932/ 28.3% (1453/ 0.06% (3/5137) 2005) 5133) 5133) 5137) P < <0.001 <0.001 Table 7d Patient satisfaction Study Good Fair Unsatisfactory No comments Tsui ( ) (N = 1233) 76.7% (n = 946) 16.1% (n = 199) 1.4% (n = 17) 5.8% (n = 71) Cheung ( ) (N = 5137) 79.8% (n = 4100) 10.2% (n = 523) 0.3% (n = 16) 9.7% (n = 498) P <0.001 were more common in the recent group of patients (p < 0.001), but not vomiting (Table 7c), and the incidence of respiratory depression was lower (p < 0.001). For patient s satisfaction, more patients graded PCA as good (p = 0.016) and fewer found it unsatisfactory (p < 0.001) when compared to 10 years ago (Table 7d). 4. Discussion Intravenous opioid PCA is one of the most common techniques for postoperative pain control (Walder et al., 2001) since individual pharmacokinetic and pharmacogenetic variability allows individual titration(lehmann, 2005). At our centre, the number of patients receiving PCA after surgery had increased by more than three times over the last decade (Tsui et al., 1996). Despite much audit and research, controversy on efficacy, types of analgesic, pump settings, and patient outcomes still exists (Macintyre, 2001). To assess the advancement of an APS, continuous and regular audit is important (Rawal, 1999) and there are few articles that compare pain relief, morphine consumption and side effects of different types of operations. An APS should comprise both anaesthetists and pain nurses (Rawal, 1999). Such expert supervision can improve post-operative pain relief and minimise side effects through patient selection and education, training of nursing staff, as well as regular assessment of pain and treatment efficacy (Bardiau et al., 2003; Mann et al., 2005). Our centre has been evolving towards this direction in the last decade. In the early 1990s, there was no formal APS or specialized pain nurse. Patient education on the use of PCA was done briefly in the postoperative recovery area and ward staff did not have PCA training. In the late 90s, more resources were allocated for pain management, leading to the formal development of an APS team with specialised anaesthetists and nurses who also provide bedside teaching to ward nurses and patients. Detailed pain management guidelines and monitoring routines were made available to general ward staff and our APS is readily available. Regular meetings and continuous medical education are conducted among APS members and management guidelines are revised when necessary, in conjunction with continuous audit. Although there is a lack of evidence of patients benefit from an hourly upper dose limit (Macintyre, 2001), from personal experience we felt it could improve patient safety as some patients have mistaken the PCA demand button as a call button for nursing staff (Tsui et al., 1996). Adjuvant oral analgesics are considered once the patient could tolerate sips of water. The suitability and choice of adjuvant analgesics is decided by the APS. From the present data, patients on adjuvant oral medications had higher morphine consumption and pain scores, probably because medications were selectively prescribed to patients with higher pain intensity. Our present demand-to-delivery ratio has been significantly reduced from 1.95 to 1.19 (McCoy et al., 1993). The number of demands a patient makes, including the number of unsuccessful demands, is often used as an indication that the patient is in pain and this has been suggested as a measure of the quality of analgesia (McCoy et al., 1993) and a more objective method of analgesic assessment than verbal methods of assessment. However, there may be a number of reasons accounting for this such as anxiety, patient confusion or inappropriate patient use (Macintyre, 2001). We believe that overuse of PCA can be prevented by providing information and education to patients. At the same time, we encourage them to use PCA when pain control is not adequate. Compared to 10 years ago, lower morphine consumption was observed, but there was no improvement in pain scores, and even more reported pain on cough. This may pose a great impact on patients after abdominal and thoracic surgeries, as it impairs clearance of sputum from the airways and affects ventilation due to muscle splinting, which could result in pulmonary complications. Patients receiving upper abdominal and thoracic surgery are known to have intense postoperative pain, which is reflected by the long duration of PCA, low dropout rate, and high morphine consumption in our data. The incisions for colorectal surgery are often located in the lower abdomen and might be thought to have less effect on painful respiratory movements, but our study shows that their pain scores (during cough = 7) were as high as that of upper gastrointestinal surgery on post-operative day 1. They also had a low drop-out rate (32%) by post-operative day 3 and high total morphine consumption (13.8 lg/kg/h) when compared with other types of operations. Similar results have been reported elsewhere (Steinberg et al., 2002). The high pain scores might be due to the extensive wounds of colorectal surgery and abdominal strain during cough. Gynaecological operations also involve lower abdominal incisions but these patients had lower pain scores and morphine consumption than the colorectal group, probably because these procedures are comparatively clean and less extensive. Patients in the breast and trunk groups had increased pain scores on postoperative days 2 and 3, while their cessation rate was comparatively high. This suggests that, while a small proportion of these patients may need special attention, pain control is very good in general.

7 470 C.W. Cheung et al. / European Journal of Pain 13 (2009) Table 8 Median PCA pain scores (using numerical rating scale from 0 to 10) during the first, second and third 24 posto-perative hours Types of operation Study First 24 h Second 24 h Third 24 h n Rest Cough n Rest Cough n Rest Cough All cases Tsui Cheung P <0.001 b <0.001 a <0.001 b <0.001 a <0.001 a <0.001 a Head and neck Tsui Cheung P a a a a Breast Tsui Cheung P Upper gastrointestinal Tsui Cheung P b b Hepatobiliary and pancreatic Tsui Cheung P b <0.001 a <0.001 a <0.001 a Colorectal Tsui Cheung P <0.001 b <0.001 a <0.001 a a Urological Tsui Cheung P <0.001 b <0.001 b a a Gynaecological Tsui Cheung P <0.001 b a <0.001 b <0.001 a a Other laparotomy Tsui Cheung P Spine Tsui Cheung P b b a b Limb Tsui Cheung P a a a Trunk Tsui Cheung P a a a NA NA Thoracic including oesophageal Tsui Cheung P a a a Miscellaneous Tsui Cheung P a a a Pain scores were compared between the two studies using the Mann Whitney U test. a Pain scores between 2002 and 2005 (Cheung et al.) were significantly higher than those between 1992 and 1995 (Tsui et al., 1996). b Pain scores between 1992 and 1995 (Tsui et al., 1996) were significantly higher than between 2002 and 2005 (Cheung et al.). The effects of gender and age on opioid analgesia is controversial (Kest et al., 2000). There has been reports that women require more morphine (Aubrun et al., 2005; Cepeda and Carr, 2003), while others showed women used less morphine in the first three postoperative days (Chia et al., 2002). Chia et al. found no difference in morphine consumption with age, unlike Macintyre and colleagues who found that older patients use less morphine (Macintyre and Jarvis, 1996). Our data suggest that morphine consumption is higher among men and younger patients. Higher morphine consumption was also observed in smokers, alcohol drinkers, and chronic drug users, possibly because of post-operative withdrawal and perhaps drug tolerance or enzyme induction. Smokers usually cough more and have more pain is associated with cough after surgery. Patients with hypertension used less morphine probably because of the diminished pain sensitivity (Ghione, 1996) and the exaggerated opioid analgesic response (McCubbin et al., 2006). Side effects of PCA are an important concern for both patients and medical staff (Dolin and Cashman, 2005). Despite a reduction in morphine consumption, the incidence of nausea and vomiting remained high when compared with our previous study (Tsui et al., 1996). Patients who vomit commonly use less morphine to avoid further vomiting, which in turn limits effective analgesia. Effective anti-emetic medication could help this condition but, unfortunately, many of these drugs have poor efficacy particularly once PONV is established. Consensus guidelines have been published for the management of PONV (Gan et al., 2003). Patients at high risk of PONV should be identified, so that medications and anaesthesia techniques with less emetic potential, such as propofol based intravenous anaesthesia should be employed. Ondansetron is an effective prophylactic agent for PONV, but unfortunately was not a first line medication at our centre because of its cost. We have not used droperidol since the US Food and Drug Administration issued a black box warning(grass, 2005). A potential

8 C.W. Cheung et al. / European Journal of Pain 13 (2009) improvement in our protocol would be to use this information for early identification of high risk patients and treat them prophylactically. Nevertheless, if patients underuse PCA leading to poor pain control, nausea and vomiting can paradoxically ensue despite lower opioid consumption. The incidence of respiratory depression while using IV opioid PCA has been reported as 0.25% (Grass, 2005). Our figure was 0.06%, but this could have been under reported as the respiratory rate was only charted at an hourly intervals. Moreover, some of the high risk patients were ventilated postoperatively in the intensive care unit, and were, therefore, excluded from analysis. Thus, we believe that safety can be enhanced by better patient selection, so that patients at high risk of respiratory depression should receive regional analgesia rather than opioid PCA (Cashman and Dolin, 2004). Overall patient satisfaction was more favourable when compared to our previous report, but the magnitude was clinically insignificant. High satisfaction ratings may not directly reflect better pain control (Chumbley et al., 1998; Coleman and Booker- Milburn, 1996). Patients are often reluctant to criticize their treatment after surgery (Chumbley et al., 1998), especially when directly asked by the APS staff as in this study. Patient s satisfaction is also affected by their preferences and expectation of pain relief, as well as the communication skills and empathy expressed by the health care providers (Egan and Ready, 1994; Etches, 1999). Despite our efforts to refine PCA over the last decade, the quality of our postoperative pain management has not been improved. In 1997, it was boldly proposed that by 2002 less than 5% of patients should experience pain after surgery (Audit Commission for Local Authorities and the National Health Service in England and Wales, 1997), encouraging health care centres worldwide to raise their standard of care. However, recent national surveys report that may still be as high as 80% and the figure has not improved over the last decade (Apfelbaum et al., 2003). The use of PCA alone is probably inadequate and multimodal acute pain management may be a better approach (Grass, 2005). For example, adjuvant pain medications (NSAIDs, coxibs), local wound infiltration and peripheral regional block, applied in conjunction with PCA, can help to improve analgesia and reduce opioid related side effects. The concept of pre-emptive and preventive analgesia (e.g., intraoperative low dose ketamine, dexamethasone and NSAIDs) may also be considered in spite of the controversial clinical evidence (Pogatzki-Zahn and Zahn, 2006). It is likely that the future development of PCA will be directed to the use of alternative routes and drugs (Grass, 2005). Innovative drug delivery methods such as the transdermal iontophoresis may also become suitable for PCA and hopefully close the analgesic gap resulting in more effective acute pain control (Carr et al., 2005). Appendix 1 Sedation score: 0 = awake, spontaneous eye opening 1 = drowsy 2 = sleeping but rousable 3 = unconscious and unrousable References Apfelbaum JL, Chen C, Mehta SS, Gan TJ. Postoperative pain experience: results from a national survey suggest postoperative pain continues to be undermanaged. Anesth Analg 2003;97: Aubrun F, Salvi N, Coriat P, Riou B. Sex- and age-related differences in morphine requirements for postoperative pain relief. Anesthesiology 2005;103: Audit Commission for Local Authorities and the National Health Service in England and Wales Anaesthesia Under Examination. 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