Methods
The study is a secondary analysis of a randomised controlled trial (RCT) published by Kastelik et al. (study registry: ClinicalTrials.gov, NCT03114306).[10] The background to the trial, methods and baseline characteristics of the randomized patients have been previously reported. Its objective was to evaluate the two analgesic methods in postoperative pain management for patients receiving total knee arthroplasty (TKA). Forty Patients receiving primary TKA under general anaesthesia were included between April and August 2017 and randomised 1:1 (20 LIA vs. 20 PNBA). Exclusion criteria were heart or liver insufficiency, evidence of diabetic polyneuropathy, severe obesity, chronic opioid therapy for more than 3 months before scheduled surgery and allergy to local anaesthetics. Patients either received a total intravenous anaesthesia (TIVA) with propofol or a balanced anaesthesia with sevoflurane. The primary endpoint for Kastelik et al. was time taken to postoperative mobilisation (walking in the ward), which was achieved in both study arms on the first postoperative day (LIA 24.0 h versus PNBA 27.1 h, 95% confidence interval of − 9.6–3.3 h).[10]
The main subject of the secondary analysis at hand was the difference in overall case costs between LIA and PNBA procedures.
All patients received postoperative analgesia following a standardised protocol of opioids (tilidine/naloxone retard), dipyrone and non-steroidal anti-inflammatory drugs (NSAIDs, i.e. ibuprofen). For additional analgesic treatment in case of acute pain scores on the numeric rating scale (NRS) > 6, patients received 10 mg of oral morphine.
During the LIA procedure the surgeon injects 150 ml Ropivacain 0.2% into the periarticular structures, thereby blocking the sensitive nerve endings of the knee. The targeted structures are the subcutaneous and periarticular soft tissues as well as the joint capsule. LIA is often administered during the orthopaedic implantation of endoprosthesis, immediately before suture.[10]
For PNBA, ultrasound-guided sub-gluteal block of the sciatic nerve as well as the adductor canal block with anaesthesia of the saphenous nerve were performed in the primary study.[10] Both nerve block procedures were administered just before induction of general anaesthesia.[10] In the calculations we considered the time taken to administer the PNBA as part of the anaesthesiological case costs (see below). For the blockage of the sciatic nerve 20 ml Ropivacain 0.75% were injected. The adductorial compartment was injected with 20 ml Prilocain 1% and a catheter was inserted for postoperative analgesia[10] via a patient controlled analgesia (PCA) system. Service life of the PCA was between 2 and 4 days (mean: 3.1 days). Patients with PNBA had regular visits by a pain nurse postoperatively.
Calculation of Costs
To calculate the overall case costs for each procedure we summed up the surgical case costs, anaesthesiological case costs, postoperative opioid requirements, material costs and costs of catheter review visits (only in PNBA procedure). The specification for the times used for the calculations was taken from Bauer et al. on perioperative process times and indicators[14] and is specified in brackets.
Surgical case costs were made up of the price per minute for personnel (doctor and surgical nurse), operational infrastructure and material (33.77€) and were multiplied by the incision to suture time (O8-O10[14]). The execution of the LIA was part of the incision to suture time as it was administered by the surgeon during the operation.
Anaesthesiological case costs consisted of the price per minute for personnel (doctor and anaesthesiology nurse), infrastructure and material (10.28€) and were multiplied by the total time of anaesthesia (beginning of the anaesthesiologist's presence with the patient until end of patient monitoring by the anaesthesiologist in the operating room (OR) or similar (A5-A9)[14]).
Material costs (Table 1 and Table 2) were extracted from the surgical and anesthesiological case costs and examined separately for better comparison.
Opioid costs for the treatment of acute postoperative pain included the individual and average dosages of tilidine/naloxone retard and oral morphine 10 mg tablets.[10] The prices for 100 mg tilidine/naloxone retard was 1.40€, 10 mg morphine were 0.61€ based on internal pharmacy prices.
Catheter review-visits for patients receiving the PNBA were calculated with 6.25€ per visit based on the assumption of a before-tax income of 25€/h of an anaesthesiological nurse and an average time per visit of 15 min.
Total costs were obtained by the summation of the above variables. All costs and prices were taken from the expenses of the Charité–Universitätsmedizin Berlin at the time the study was conducted.
Statistical Methods
The statistical analysis of our data was conducted in IBM SPSS 25. Descriptive data was summarised by mean and standard deviation or median depending on statistical distribution. The t-test for independent samples was used to test for statistical significance of parametric data. Data for opioid requirement for postoperative acute pain as well as for induction costs were analysed using the Mann-Whitney-U-Test. For all statistical analysis a 5% two-sided alpha level was applied. A case number analysis was not conducted for this secondary end-point as this was a descriptive non-confirmatory supporting analysis. The statistical graphic was originally produced with SPSS 25 revised as vector graphics using Affinity Designer 1.8.6. Images were designed to be accessible for people with anomalous trichromacy, dichromacy and monochromacy.
BMC Anesthesiol. 2022;22(80) © 2022 BioMed Central, Ltd.
