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BJA Advance Access originally published online on October 28, 2005
British Journal of Anaesthesia 2006 96(1):111-117; doi:10.1093/bja/aei270
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© The Board of Management and Trustees of the British Journal of Anaesthesia 2005. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

PAIN

Evaluation of costs and effects of epidural analgesia and patient-controlled intravenous analgesia after major abdominal surgery

E. Bartha1,*, P. Carlsson2 and S. Kalman1

1 Department of Anaesthesiology, Linköping University Hospital. 2 Centre for Medical Technology Assessment, Linköping University, Linköping, Sweden

* Corresponding author. E-mail: elisabeth.bartha{at}lio.se

Accepted for publication October 3, 2005.


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
Background. The outcome of different treatment strategies for postoperative pain has been an issue of controversy. Apart from efficacy and effectiveness a policy decision should also consider cost-effectiveness. Since economic analyses on postoperative pain treatment are rare we developed a decision model in a pilot cost-effectiveness analysis (CEA) comparing epidural analgesia (EDA) and patient-controlled intravenous analgesia (PCIA) after major abdominal surgery in routine care.

Methods. Using a decision-tree model, treatment with EDA (ropivacaine and morphine) was compared with PCIA (morphine). Effects and costs of treatment were established. The number of pain-free days at rest (pain intensity <30 using visual analogue scale 1–100 mm) was the primary measure of effect. An incremental cost-effectiveness ratio (ICER) was calculated as the difference in direct costs divided by the difference in effect. A database on 644 patients collected for the purpose of quality control during the period of 1997 to 1999 was the main data source. Sensitivity analysis was used to test uncertain data.

Results. EDA was more effective in terms of pain-free days but more expensive. The additional cost for each pain-free day was 5652 Euros.

Conclusion. It is a judgement of value if the additional cost is reasonable. When the cost of around 55 000 Euros per gained life-year with full health for other interventions is debated, our result indicates poor cost-effectiveness for EDA. Before any conclusion can be drawn concerning policy recommendations the difference in costs has to be related to other outcome measures as length of hospital stay, morbidity and mortality are required.

Keywords: analgesia, postoperative; analgesia, patient-controlled; analgesic techniques, extradural; cost-effectiveness


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
Good postoperative pain control is a mandatory component of adequate postoperative care if accelerated recovery is aimed for.1 –3 The most common pain relief strategies after major abdominal surgery are epidural infusion of local anaesthetics and opiates (EDA) and/or patient-controlled administration of intravenous opiates (PCIA). According to the guidelines of the Swedish Society of Anaesthesiology both methods are accepted options following major surgery. In general when selecting different treatment strategies efficacy, effectiveness and costs should be taken into account. At the University Hospital in Linköping (Sweden) both EDA and PCIA have been used following major abdominal surgery. Assessment of the clinical effectiveness of EDA during the period of 1997 to 1999 revealed, in line with the findings of others,4 –7 that 10% of patients scheduled for epidural analgesia had their treatment discontinued because of technical problems, minor side-effects or insufficient pain relief. Hence costs and consequences of planned and discontinued treatment became of interest when comparing these two strategies. Moreover this decision-problem concerns a lot of patients. In the county of Östergötland in Sweden with 450 000 inhabitants, 930 postoperative patients received epidural analgesia and 800 PCIA during 2003. This would imply that in Sweden ~40 000 patients are treated with either EDA or PCIA every year.

Since there are few economic analyses of postoperative pain treatment a decision analytic model was developed8 to estimate the cost-effectiveness of epidural analgesia compared with patient-controlled intravenous analgesia (PCIA) after major abdominal surgery under ordinary clinical circumstances.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
Cost-effectiveness model
A decision tree was used to model the clinical pathways for estimating the effects (E) and costs (C) of treatment with EDA and PCIA. The measure of effect was expressed as number of pain-free days. The cost-effectiveness, the average cost for reaching a particular outcome for a given treatment, is expressed as cost-effectiveness ratio (CER) (Fig. 1).

When a decision has to be made to replace a treatment with a more expensive and more effective treatment, an estimate of the additional resources that have to be used to obtain the additional benefit is needed.9 That is the incremental cost-effectiveness ratio (ICER): the difference in direct cost ({Delta}C) divided by the difference in effect ({Delta}E) between the two alternatives (Fig. 1).

The result is presented both as CER and as ICER (Fig. 1). All costs are in 2005 price and are converted to Euros using the exchange rate: 1 Euro=9 Swedish crowns. Sensitivity analyses were performed to estimate the cost-effectiveness by testing data that were uncertain or debatable.



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  		Fig 1 Illustration of the cost-effectiveness ratio (CER) and the incremental cost-effectiveness ratio (ICER).10 The slopes of the lines from origin give the CER for the treatment with EDA and PCIA. The ICER (dotted line) is the slope of the line joining the points EDA and PCIA. CER=Cost/Effect and ICER=(CostEDA–CostPCIA)/(EffectEDA–EffectPCIA).

 
Data source
The main data source was an existing local database, started in 1997 for assessment of clinical effectiveness and by 1999 included 644 consecutive patients treated with EDA (n=602) or PCIA (n=42) following major abdominal surgery (Table 1). Patients were selected for treatment with PCIA in a non-systematic way if a shortage of resources existed on the PCU/ICU or if the patient refused epidural analgesia.


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  		Table 1 Patient characteristics of the epidural and the PCIA group. Age and weight are given in mean values (SD). The others are presented in percent

 
The data of the 42 patients treated with PCIA and of the 569 patients treated with EDA were used, but the data of 33 patients were incomplete. The Research Ethics Committee of the University Hospital in Linköping approved the use of the database as data source for analysis.

The treatment strategies
For the thoracic epidural analgesia a mixture of ropivacaine 2 mg ml–1 with morphine 0.03 mg ml–1 was delivered at a constant infusion rate of 5.5 ml h–1 (Baxter Infuser LV, Baxter Healthcare Corporation, Deerfield, IL). Rescue pain treatment was given according to an algorithm. The patients were observed on the Postoperative Care Unit/Intensive Care Unit (PCU/ICU) for at least 12 h according to actual guidelines.

For treatment with PCIA, morphine 5 mg ml–1 was used, and the pump (Smiths Medical, Deltec, Inc., St Paul, MN, USA) was programmed individually to meet requirements and delivery was on demand. The duration of the care on the PCU/ICU was shorter compared with the EDA group according to local instructions. The duration of the treatment was 3 days for both patient groups.

Estimation of probabilities
The structure of the decision tree was developed by the selection of the relevant events and pathways: complete treatment and change of treatment strategy; unsuccessful attempt to introduce epidural catheter; early dislocation of catheter; reinsertion of epidural catheter and need for additional pain treatment. The decision tree was supplemented with probabilities for different pathways using data from the database (Table 2 and Fig. 2). The structure of the model was simplified by one assumption: the costs and the number of pain-free days had a linear relationship.


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  		Table 2 The selected courses of treatment and the actual probabilities. Data are obtained from the database for the epidural and for the PCIA group.

 


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  		Fig 2 The decision tree illustrates the selected clinical pathways and probabilities for treatment with EDA and PCIA. The final branches show the effectiveness of treatment expressed as number of pain-free days with actual probabilities at rest and during activity. Finally the overall probability (product of the probabilities) for the actual branch is given using probabilities only at rest because of the limited space available.

 
Estimation of the effectiveness
The pain intensity was monitored every 3 h using a visual analogue scale both at rest and during activity (VAS 1–100 mm) and a representative value for each day was recorded in the database. The effectiveness of treatment—for the cost-effectiveness analysis—was expressed as the number of pain-free days at rest, as is shown in the decision tree. A pain-free day was defined as having a VAS≤30 a whole day. The analgesic effectiveness was 3 if the patient had 3 pain-free days, 2 in the case of 2 pain-free days, 1 in the case of 1 pain-free day, and 0 if the patient did not experience VAS≤30 at all (Fig. 2).

The number of pain-free days was weighted by the overall probabilities for each branch of the tree, and the sum of these resulted in the expected number of pain-free days for each treatment strategy (Fig. 2). The same procedure was done using probabilities at rest and at activity.

Estimation of the costs
The most relevant, direct medical costs were evaluated: the cost of human resources and also the costs of medical devices and drugs. The time used for the selected activities cannot be used for other simultaneous activities and hence represents a cost. Data on cost per hour for the staff and data on devices and drugs were obtained from the hospital administration and from the hospital pharmacy (Table 3). The time devoted to certain activities was measured or based on interviews with the staff. The cost of particular interventions related to problems with the epidural catheter at the insertion site (leakage, bleeding) or to minor side-effects (nausea, vomiting) was weighted based on the probabilities of these events. All calculated costs were based on 3-day long treatment periods. The cost of postoperative care was derived from official tariffs. The identified costs of the clinical pathways during treatment were weighted by the actual probabilities demonstrated on the decision tree.


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  		Table 3 The calculated costs for staff and pharmacy charges, costs for material and drugs. The costs are calculated for each patient and for a 3-day treatment period

 
Sensitivity analysis
Sensitivity analysis was performed in order to test the robustness of the result. One approach was to test the most uncertain cost item in the model, the ‘tariff’, for postoperative care, as it was unclear how it was set in relation to real costs of resources used on the PCU/ICU. We have tested the model using the lowest reported tariff assuming that the EDA and the PCIA group had the same length (3–4 h) of care on the ICU/PCU. Another uncertainty was the effect, as it is a matter of dispute if the most valid measure of pain is estimated at rest or during activity. Therefore the model was tested by using the higher incremental effect of EDA over PCIA during activity. A second approach was the ‘scenario analysis’, when one optimal scenario of treatment was tested by reducing the probabilities of the technical difficulties related to EDA: catheter dislocation, unsuccessful attempt, reinsertion of catheter and the need for additional pain treatment (Table 4).


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  		Table 4 Probabilities used for optimal scenario. Both the probabilities from the database (base case) and the assumed probabilities (optimal scenario) for catheter dislocation, unsuccessful attempt, reinsertion of catheter and for change of treatment because of side effects or poor pain relief are given

 
At last we tested the influence of potential bias related to the data derived from a non-randomized population. Each patient treated with PCIA in the database was matched in pairs with one patient treated with EDA. First, the age (it was allowed to vary by 2 yr) and the type of surgical intervention and second, the gender and ASA-group were used in the matching procedure. Data of the matched subgroup of epidural patients was used as described in methods, and the ICER was also calculated.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
Analysis of the effectiveness
The number of the expected pain-free days at rest—for a patient in the model—treated with EDA was 2.36 and with PCIA 2.17, yielding an incremental effect of 0.19 day (E=EffectEDA–EffectPCIA). During activity the number of expected pain-free days was lower: 1.86 in the EDA and 1.27 in the PCIA group and the incremental effect was more than a half day, 0.59 (Table 5). The overall probabilities for different clinical pathways during treatment with EDA or PCIA can also be calculated using the decision tree (Fig. 2). For example, the probability of achieving 3 pain-free days without any additional pain treatment and without any problem with the epidural catheter was 0.49 at rest and 0.41 during activity with treatment with EDA. The corresponding values for the PCIA group were 0.56 at rest and 0.28 during activity.


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  		Table 5 The expected number of pain-free days, (rest and activity) and the costs of postoperative epidural analgesia and patient-controlled intravenous morphine analgesia. The incremental effect and cost is also demonstrated. The cost-effectiveness ratio (CER) and the incremental cost-effectiveness ratio (ICER) are calculated using the measure of effect at rest (base case result). CER=Cost/Effect and ICER=(CostEDA–CostPCIA)/(EffectEDA–EffectPCIA)

 
Cost analysis, calculation of the expected cost
The expected cost per patient in the EDA group was 1701 Euros and in the PCIA group 627 Euros. The difference in costs (C=CostEDA–CostPCIA) was 1074 Euros (Table 5).

The cost-effectiveness ratio (CER), incremental cost-effectiveness ratio (ICER)
The cost per pain-free day at rest was 721 Euros per patient for treatment with EDA and 289 Euros per patient for treatment with PCIA. The incremental cost-effectiveness ratio (ICER) at rest—base case result—was 5625 Euros (Table 5).

Sensitivity analysis
Using the lowest tariff, assuming the same length of care on the ICU/PCU, the base case ICER decreased by 66% from 5625 Euros to 1448 Euros (Table 6). When the influence of better pain relief of EDA was tested by using the measure of effect during activity, the ICER decreased by 67% from 5625 Euros to 1896 Euros (Table 6). The scenario analysis, when the probabilities in the model affected by the technical difficulties were optimized (Table 4), the cost of EDA decreased only by 2% to 1666 Euros; in contrast the incremental effect increased by 105% to 0.39 days which resulted in a decrease of ICER by 52% to 2664 Euros. The calculated ICER using data of the matched EDA group in the model was 4308 Euros. It deviated from the base case result (5625 Euros) by 23% due to differences in effect but the costs were unchanged (Table 6).


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  		Table 6 Sensitivity analysis was performed to estimate the influence of uncertain items on cost and ICER. The model was tested by the lowest tarrif for PCU/ICU, by the higher incremental effect of EDA over PCIA at activity, by an optimized scenario and by a matching procedure. The used probabilities for the scenario analysis are demonstrated in Table 4

 

   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
We have modelled the most relevant clinical pathways for a patient treated for postoperative pain with epidural or patient-controlled intravenous analgesia. Based on a clinical database we have described how these two alternatives actually work under clinical circumstances and not how they ideally can work.

The approach to express the cost-effectiveness
In the health economic literature and methodological guidelines the costs per quality adjusted life year is recommended for use in CEA even if the gain is not a whole year. As we have analysed a very short effect duration of acute pain treatment and found that the cost per gained life year is inadequate, the cost per gained pain-free day was used.

An economic analysis in health care should describe a favourable improvement in patient's health or experience, and therefore the number of pain-free days is not optimal, e.g. number of pain-free days based on VAS do not capture the multidimensional experience of pain; it is an intermediate measure of outcome. As the influence of improved pain relief on the postoperative outcome is a mater of debate, other measures of outcome should also be considered. Using EDA, compared with PCIA, the length and cost of postoperative care was reported to be less,6 15 but the length of hospital stay was found to be the same12 13 16 or longer.14

Another limitation in our study is that only one representative value of the pain score was registered in the database; however the variability of the sampled pain scores was low. Besides these limitations the sensitivity analysis shows that the ICER was sensitive to some changes in critical input values in the model, but in all tested alternatives the PCIA was more cost-effective than EDA.

The higher cost of postoperative epidural analgesia compared with PCIA is in line with others6 11 –16 but the range of difference varies. In those studies other measures of outcome were used, and the results were not expressed in terms of cost-effectiveness making the comparison with our result difficult. Our result is based on real clinical data which allow some generalization, but use of more sophisticated methods for epidural analgesia or a separate analysis of low and high laparotomy may influence the result. However the probabilities of early discontinuation of treatment, accidental dislocation of catheter, minor side-effects or difficulties with catheter insertion are not likely to be affected by these.

Why a model analysis?
When alternative treatments are already established, ethical considerations may preclude randomized trials and consecutive patient selection may be preferred, as in a recent Swedish trial.17 Furthermore costs and effects evaluated in an RCT may be difficult to transform into clinical practice, because of the influence of controlled experimental settings, and the possible lack of clinical endpoints (e.g. effect-data of discontinued treatment) that are relevant for economic evaluation.18 The clinical endpoints for discontinued pathways of treatment with EDA were documented in our database, and therefore it was considered to be an important data source.

Implication of our results and conclusion
Bearing in mind the limitations of this study we conclude with reasonable degree of certainty that the cost of postoperative epidural analgesia is three times higher than that of PCIA but also that it gives better pain relief than PCIA, which shows that PCIA probably is the most cost-effective alternative under the actual circumstances. Decreasing the cost of the postoperative care and/or diminishing the technical difficulties related to epidural analgesia may cut the costs for EDA. A model (decision-tree) makes the different clinical pathways transparent, and it allows evaluation of assumed improvements. Moreover the structured analysis of the particular clinical pathways may give additional information, especially when the results of RCTs are difficult to summarize, and there is still doubt as to which technique is better in terms of analgesia, adverse effects and benefits.19 The better choice is not always the best one if resources are scarce, and it may be right to go for the second best alternative. According to Swedish law patients have the right to choose a more expensive treatment if the cost is reasonable in relation to the benefit. It is a judgement of value whether the additional cost of 5625 Euros per pain-free day is reasonable for society to pay for the obtained patient benefit. It is a question of opportunity costs, i.e. who else will suffer because of lack of health-care resources? In a broader health policy context, when the cost of around 55 500 Euros per extra life-year gained with full health (QALY) for other interventions are questioned, our results indicate a poor cost-effectiveness. We have to go for good control (for example tracing the clinical pathways with decision-tree) to be able to make improvements both in terms of costs and effects. Before any conclusion can be drawn concerning policy recommendations the difference in costs has to be related to other outcome measures such as length of hospital stay, morbidity, and mortality and also we need other outcome measures that reflect the improved experience or health state of patients due to better pain relief.


   Acknowledgments
 
The authors are grateful to Mona Lindblad and Lilian Adamson, Department of Anaesthesiology, University Hospital Linköping, Sweden for help with data acquisition and Martin Henriksson CMT/HIS Linköping University for valuable comments on the manuscript.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Brodner G, Van Aken H, Hertle L, et al. Multimodal perioperative management—combining thoracic epidural analgesia, forced mobilization, and oral nutrition—reduces hormonal and metabolic stress and improves convalescence after major urologic surgery. Anesth Analg 2001; 92: 1594–600[Abstract/Free Full Text]

Kehlet H. Acute pain control and accelerated postoperative surgical recovery. Surg Clin North Am 1999; 79: 431–43[CrossRef][Web of Science][Medline]

Kehlet H, Mogensen T. Hospital stay of 2 days after open sigmoidectomy with a multimodal rehabilitation programme. Br J Surg 1999; 86: 227–30[CrossRef][Web of Science][Medline]

McLeod G, Davies H, Munnoch N, et al. Postoperative pain relief using thoracic epidural analgesia: outstanding success and disappointing failures. Anaesthesia 2001; 56: 75–81[CrossRef][Web of Science][Medline]

Andersen G, Rasmussen H, Rosenstock C, et al. Postoperative pain control by epidural analgesia after transabdominal surgery. Efficacy and problems encountered in daily routine. Acta Anaesthesiol Scand 2000; 44: 296–301[CrossRef][Web of Science][Medline]

Brodner G, Mertes N, Buerkle H, et al. Acute pain management: analysis, implications and consequences after prospective experience with 6349 surgical patients. Eur J Anaesthesiol 2000; 17: 566–75[CrossRef][Web of Science][Medline]

Wigfull J, Welchew E. Survey of 1057 patients receiving postoperative patient-controlled epidural analgesia. Anaesthesia 2001; 56: 70–5[CrossRef][Web of Science][Medline]

Drummond MF, O'Brien BJ, Stoddart GL, Torrance GW. Methods for the Economical Evaluation of Health Care Programmes, 2nd edn. New York, Oxford: Oxford University Press, 1997; 117, 120, 242, 276, 281–3

Karlsson G, Johannesson M. The decision rules of cost-effectiveness analysis. Pharmaeconomics 1996; 9: 113–20

Drummond MF, O'Brien BJ, Stoddart GL, Torrance GW. Methods for the Economical Evaluation of Health Care Programmes, 2nd edn. New York, Oxford: Oxford University Press, 1997; 41

Rockemann MG, Seeling W, Goertz AW, et al. Effectiveness, side effects and costs of postoperative pain therapy: intravenous and epidural patient-controlled analgesia (PCA). Anasthesiol Intensivmed Notfallmed Schmerzther 1997; 32: 414–9[Web of Science][Medline]

Paulsen EK, Porter MG, Helmer SD, et al. Thoracic epidural versus patient-controlled analgesia in elective bowel resections. Am J Surg 2001; 182: 570–7[Medline]

Cohen BE, Hartman MB, Wade JT, et al. Postoperative pain control after lumbar spine fusion. Patient-controlled analgesia versus continuous epidural analgesia. Spine 1997; 22: 1892–6; discussion 1896–7[Web of Science][Medline]

Ammar AD. Postoperative epidural analgesia following abdominal aortic surgery: do the benefits justify the costs? Ann Vasc Surg 1998; 12: 359–63[CrossRef][Medline]

de Leon-Casasola OA, Parker BM, Lema MJ, et al. Epidural analgesia versus intravenous patient-controlled analgesia. Differences in the postoperative course of cancer patients. Reg Anesth 1994; 19: 307–15[Medline]

Norris EJ, Beattie C, Perler BA, et al. Double-masked randomized trial comparing alternate combinations of intraoperative anesthesia and postoperative analgesia in abdominal aortic surgery. Anesthesiology 2001; 95: 1054–67[CrossRef][Web of Science][Medline]

Flisberg P, Rudin A, Linner R, et al. Pain relief and safety after major surgery. A prospective study of epidural and intravenous analgesia in 2696 patients. Acta Anaesthesiol Scand 2003; 47: 457–65[CrossRef][Web of Science][Medline]

Drummond MF, O'Brien BJ, Stoddart GL, Torrance GW. Methods for the Economical Evaluation of Health Care Programmes, 2nd edn. New York, Oxford: Oxford University Press, 1997; 233–44

Werawatganon T, Charuluxanun S. Patient controlled intravenous opioid analgesia versus continuous epidural analgesia for pain after intra-abdominal surgery. Cochrane Database Syst Rev 2005; 1: CD004088


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This Article
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