Department of Anaesthesiology and Intensive Care, Hospital Bichat, 46 Rue Henri Huchard, F-75018 Paris, France*Corresponding author. E-mail: hawakeita@club-internet.fr
Supported in part by a research grant from Fondation de lAvenir pour la Recherche Médicale Appliquée. Some of this work was presented, at the annual meeting of the American Society of Anesthesiologists, Dallas, TX, USA October 913, 1999.
Accepted for publication: September 10, 2002
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Abstract |
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Methods. Forty patients older than 70 yr were randomly assigned to two different postoperative analgesic techniques for 48 h: i.v. PCA morphine (dose, 1 mg; lockout interval, 8 min; PCA group) or regular s.c. morphine injections (SC group). Postoperative pain was assessed at rest and when moving, using a visual analogue scale (VAS) every 4 h. A Mini Mental Status (MMS) examination was used to assess cognitive functions before surgery, at 2 h, 24 h and 48 h after surgery, and at hospital discharge. Side-effects were also recorded systematically during the first 48 h after surgery.
Results. The PCA group showed significantly lower pain scores than the SC group both at rest and during mobilization. However, the clinical significance of pain scores was weak. There was no intergroup difference in postoperative MMS scores. The incidence of side-effects was similar in both groups.
Conclusions. We conclude that in healthy elderly subjects undergoing THR, the flexibility of the analgesic regimen is more important than the route of administration with regard to efficacy, adverse effects and recovery of cognitive function.
Br J Anaesth 2003; 90: 537
Keywords: age factors; analgesia, patient-controlled; analgesics opioid, morphine; pain, postoperative; surgery, total hip replacement
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Introduction |
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Elderly patients comprise a large and rapidly increasing proportion of surgical patients. In this specific patient population, the best postoperative pain management technique remains to be determined. Egbert and colleagues4 reported that PCA was associated with superior analgesia and less confusion than intermittent i.m. morphine analgesia. However, this study was of a heterogeneous patient population as it was performed in elderly men undergoing various major surgical procedures (orthopaedic, thoracic or intra-abdominal surgery). In another study, a higher incidence of postoperative delirium in elderly patients was related to inadequate analgesia.5 To date, no study has compared the effects of PCA with subcutaneous (s.c.) morphine on postoperative pain in older patients undergoing a specific surgical procedure associated with moderate-to-severe postoperative pain. We therefore performed a prospective randomized study in elderly patients undergoing total hip replacement (THR), firstly to compare the efficacy and safety of PCA vs s.c. morphine used for postoperative analgesia and secondly to compare the time course of recovery of cognitive function, assessed by the Mini Mental Status (MMS), between the groups.
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Methods |
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Patients were randomly assigned using a random number table, to receive analgesia via either PCA (PCA group) or s.c. injections of morphine (SC group). All patients received instructions on how to use the visual analogue scale (VAS) (0 mm=no pain; 100 mm=worst imaginable pain) for pain assessment and patients in the PCA group received written and verbal instructions on the use of PCA. Patients were visited the day before surgery to obtain patient characteristics and baseline MMS score.
In both groups, oral premedication was hydroxyzine 1.5 mg kg1 1 h before surgery. General anaesthesia was induced with thiopental 3 mg kg1 and fentanyl l2 µg kg1. Tracheal intubation was facilitated by vecuronium 1 mg kg1. All patients underwent mechanical ventilation with an equal mixture of oxygen and nitrous oxide. Anaesthesia was maintained with desflurane. Additional fentanyl boluses (1 µg kg1) were given when necessary except during the last 30 min of anaesthesia.
After surgery, patients were transferred to the postanaesthesia care unit and asked every 10 min to rate their pain using the VAS. If a patient reported pain (VAS 30), the nursing staff administered boluses of i.v. morphine 2 mg every 10 min until the pain score was reported as <30 mm on the VAS. The study procedure was then started (time 0) and lasted for 48 h. Patients assigned to the PCA group were provided with an Abbott Pain Manager PCA pump (Abbot Laboratories, North Chicago, IL, USA), programmed to deliver morphine 1 mg i.v. with a lockout interval of 8 min. Patients assigned to the SC group received the first injection of morphine (0.1 mg kg1) 4 h after the study started or earlier if they reported inadequate pain relief (pain score
30). The injections could be repeated every 4 h if the patient reported pain (VAS
30). During the 48 h after surgery all patients received propacetamol (Pro-Dafalgan®, a prodrug of acetaminophen), 2 g infused i.v. over 15 min at 6-h intervals. In both groups, VAS scores were recorded at rest (VAS-R) and during mobilization (VAS-M; leg elevation at 30°) every 4 h. All pain evaluations were associated with the screening of side-effects of the analgesic procedure. These effects included arterial hypotension (systolic pressure <90 mm Hg), respiratory depression (ventilatory frequency
8 bpm), sedation score (0=awake, 1=sleepy but awakened by oral order, 2=sleepy but awakened by tactile stimulation, 3=not awakened), urinary retention (inability to urinate, requiring a urinary catheter to empty the bladder), nausea and vomiting (yes or no) and pruritus (yes or no). Nausea and vomiting were treated as necessary with ondansetron 4 mg i.v. The amount of morphine used was recorded at time 0, and 24 h and 48 h after surgery. The length of stay in hospital was also recorded. The postoperative MMS score was assessed at 2 h, 24 h, 48 h and at discharge from hospital by investigators not aware of the baseline MMS score.
Data were analysed using StatView version 5.0 software (SAS Institute Inc., Cary, NC, USA). From a previous study on postoperative analgesia,8 we considered a minimum of 20 mm reduction in VAS-R in the PCA group as a clinically significant result. A sample size of 20 in each group had an 80% power to detect a difference in mean VAS-R of 24 assuming that the common SD was 25.
Continuous variables are presented as the median (25th75th percentiles); categorical variables are presented as frequencies (percentage of patients).
Continuous variables in the two groups were compared using the MannWhitney U-test or by Wilcoxon matched paired test. The 2 or Fishers exact test were used to examine categorical variables. Scores for MMS in the two groups were compared using the MannWhitney U-test. Comparisons of VAS-R and VAS-M were performed using the MannWhitney U-test. Statistical significance was inferred for P
0.05.
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Results |
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Discussion |
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One aspect of the study design deserves comment. Evaluations during the days after surgery were not performed in a blinded fashion because of the clinical conditions of the study. It is technically difficult to achieve true double blinding in comparisons of PCA and conventional analgesia (i.m. or s.c. injections). Rayburn and colleagues9 abandoned a double-blind trial after finding that patients could distinguish placebo from genuine PCA infusions. However, the nurses in our surgical ward have good experience of both techniques and commonly use either PCA or s.c. morphine for analgesia after THR. For this reason, we did not think that an increased attentiveness of care in PCA group could have contributed to the apparent analgesic benefit of PCA. Furthermore, the lack of difference in opioid requirements and the comparable side-effects in both groups are in agreement with this hypothesis. The investigators were blinded for the baseline MMS scores when they performed the postoperative MMS evaluations.
The results of the current study confirm and extend data from previous studies suggesting that PCA provides effective management of postoperative pain in healthy elderly patients.10 11 Our data support the view that PCA is more effective than conventional morphine administration in reducing pain at rest and with movement.1214 Nevertheless, although the VAS scores were significantly different between the groups, the clinical relevance of these results has to be discussed. In fact, the difference in median VAS seems weak as it reached only 15 mm at rest. However, it could be argued that the median score in the PCA group was 30 mm or less at 24 h and 48 h, which is commonly considered as good and effective analgesia, in contrast to the SC group in which the median VAS scores were >30 mm. The clinical relevance is more questionable for the VAS scores with movement, as the scores remained in the moderate-to-severe intensity range in both groups and the difference between the two groups reached only 10 mm. Previous studies have reported that PCA is not sufficient and is less effective than other techniques like regional analgesia for postoperative pain relief during mobilization.15 16
Learning and acceptance of the PCA concept obviously requires a sufficient preoperative mental status.17 The MMS evaluation is a reliable, valid tool for screening acute confusion and dementia7 and has been found to be easy to use by elderly patients.6 Preoperative patient selection using MMS scores allowed us to identify patients with pre-existing cognitive impairment, who were subsequently excluded from the study. The normal MMS score of 26 obtained for the elderly patients6 18 was set as the cut-off criteria for acute confusion. As pre-existing cognitive dysfunction has been suggested to be a risk factor for postoperative confusion,19 the high preoperative MMS scores in the present study population may partially explain why we observed a very low incidence of cognitive impairment in the postoperative period. However, at 2 h after surgery there was a significant alteration of cognitive function in the two groups. These results are in agreement with previously reported MMS changes in the immediate postoperative period in elderly patients after general anaesthesia.20 Contrary to previous studies performed in elderly patients,4 5 11 21 we did not find evidence of clinically or statistically significant differences in mental status between the PCA and SC groups at any time, despite significant differences in pain intensity between the two groups. This result is possibly explained by the weak clinical significance regarding pain scores in our study.
The incidence of side-effects was similar in the PCA and SC groups. The literature concerning this point remains controversial. Choinière and colleagues2 observed no differences between two groups of patients (PCA compared with regular i.m. injections of morphine) after hysterectomy in terms of opioid side-effects and analgesia. Conversely, others have reported a lower incidence of side-effects with PCA.4 However, the most important side-effect, particularly in elderly patients, is respiratory depression.1 Comparison of the risk of respiratory depression with PCA and with conventional opioid analgesic techniques is difficult, as there is a lack of data relating to the latter methods. The incidence of respiratory depression with conventional methods of opioid administration is reported to be in the range of 0.20.9%,22 and an incidence of 0.10.8% has been reported with PCA.22 23 Increased incidences of 1.13.9% have been found when a concurrent background infusion is used.1 We did not use any background infusion with the PCA in our study, and we did not observe any respiratory depression in either group. Regardless of the route of administration of morphine, we reported a high incidence of nausea and vomiting (40% and 30% for the PCA and SC groups, respectively). Such results (or higher incidences) are frequently associated with opioid analgesia in the postoperative setting.2 11 In attempts to minimize these side-effects, an implementation of aggressive strategies to treat and even prevent opioid side-effects (e.g. prophylactic antiemetic therapy), regardless of the type of opioid regimen used, could be proposed. For example, adding an antiemetic such as droperidol to morphine PCA appears to be a good strategy.24 The similar incidence of side-effects in the two groups may be explained in part by the equal amounts of morphine required for pain relief.
Finally, there was no difference between the two groups in the length of hospital stay. However, as discharge criteria were not precisely defined before the study, we could not draw definite conclusions.
In summary, the current study indicates that PCA does not provide optimal dynamic pain relief after THR surgery in elderly patients. We suggest that in such patients the flexibility of analgesic regimen is more important than the route of administration with regard to efficacy, adverse effects and recovery of cognitive function.
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Acknowledgement |
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References |
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