Day surgery has evolved under continuing pressure to provide anaesthesia that is optimal for both the surgeon and patient with no awareness, short emergence times and cost-effectiveness. With the continuous introduction of both new drugs and equipment, impartial comparisons must be made with established techniques to allow clinicians to make informed choices, including costs. One such technique, the target controlled infusion (TCI) system, has been introduced to facilitate the use of propofol .
All the new, modern, anaesthetics are effective and safe and major differences in clinical outcome are not expected. However, even minor differences in clinical outcome or cost, or both, are of importance considering the large number of patients seen in ambulatory surgery. We have looked into an earlier series of studies of the consumption of anaesthetics associated with various standardized anaesthetic techniques used in day surgical procedures and found both clinical differences in emergence time and considerable differences in direct drug-related costs [2-4]. Direct comparisons of all three new anaesthetics are few. The present study compares the cost-effectiveness of propofol administered via a TCI-system with inhalation anaesthesia using either desflurane or sevoflurane in combination with nitrous oxide.
One hundred-and-two patients, ASA I-II, scheduled for elective knee arthroscopy were studied after approval from the hospital's Ethics Committee and informed consent. Cyclizine premedication 50 mg was given orally 30 min prior to anaesthesia. Routine monitoring included electrocardiography, pulse oximetry, heart rate and non-invasive systemic arterial pressure.
Induction study protocol
Patients were preoxygenated (FiO2 = 0.7) via a facemask for 3 min prior to induction. All patients received propofol for induction and a standardized bolus dose of fentanyl 0.1 mg. Patients who were to receive sevoflurane or desflurane were given a bolus of propofol 2.5 mg kg−1 to facilitate insertion of the laryngeal mask. In the group of patients which was to receive only propofol for maintenance, the propofol for induction was given by setting the TCI target concentration at 4 μg mL−1.
Additional propofol was given when found necessary to introduce the laryngeal mask airway. Muscle relaxants were not used and the laryngeal mask airway was placed in all patients and connected to a circle absorber system (Q-2 system®; Anmedic AB, Valentuna, Sweden). All patients received 10 mL intra-articular lidocaine (5 mg mL−1) with epinephrine at the start of surgery, and the same amount, together with 0.05 mg fentanyl, at the end of surgery.
Patients were randomized to three different types of maintenance anaesthesia after induction of anaesthesia. Group A used propofol TCI (Alaris Diprifusor®; Alaris Medical Systems Ltd, Hampshire, UK) and breathed oxygen in air in a ratio of 1:2. Group B received desflurane and Group C received sevoflurane. In addition both groups received oxygen and nitrous oxide, in a ratio of 1:2, with 3 L min−1 fresh gas flow. The anaesthetist (JJ) was not blinded to the drug used, and it was administered according to clinical need. Anaesthetic depth was considered adequate when heart rate and arterial pressure were within ± 15% from baseline and no movement was observed during noxious stimulation. No fixed end-tidal gas concentration or propofol concentration was predetermined because the depth of the anaesthetic was adjusted according to clinical needs throughout the surgical procedures in all three groups. At the end of surgery all anaesthetics were discontinued and a fresh oxygen flow of 6 L min−1 was given until removal of the laryngeal mask. Emergence, calculated as the time to removal of the laryngeal mask to when the patients could properly state their name and date of birth, were both defined from the cessation of anaesthetic.
Anaesthetic consumption determination
The desflurane and sevoflurane vaporizers were filled and weighed (scale type with a precision of 0.1 g in the range up to 16 000 g, Model BP-16000S®, Sartorius AG, Göttingen, Germany) prior to induction. When anaesthesia had been completed, the vaporizers were disconnected and re-weighed. The inhaled anaesthetic consumption per minute was calculated for each patient; propofol consumption was read from the TCI syringe pump display in milligrams.
All patients received lornoxicam 8 mg and paracetamol 2 g orally as postoperative analgesia. Pain was assessed at 30 and 60 min after emergence according to the visual analogue scale (VAS). Criteria for discharge were standard hospital routines: ability to drink, walk unassisted, void and VAS pain score <3. Official drug prices in Sweden (Tables 1 and 3) are converted to Euros (€1 = 9.1 Swedish crowns).
Data is presented as means and standard deviation unless otherwise stated. Range is occasionally shown in square brackets. Differences between groups, for weights before and after anaesthesia were studied using ANOVA. P < 0.05 was considered statistically significant. The sample size of 34 for each group was determined adequate by power analysis prior to the study to create a power of 80% at an α of 0.05. The power analysis assumed that (a) the emergence time in the sevoflurane group would be 5 min with an SD of 1.2, and (b) a change in emergence time of 30% would be considered a clinically valuable difference.
Patient data is shown in Table 2. The groups did not differ in age, weight, or duration of either surgery or anaesthesia. Arthroscopy indications did not differ among the groups with meniscus resection being the most common operation, followed by shaving of the synovia and diagnostic examination. All the surgery was uneventful. Haemodynamics were well controlled in all patients, there were no clinical signs of inadequate anaesthesia and no awareness was reported. Emergence (Table 2) was significantly faster for patients receiving sevoflurane or desflurane than for patients receiving propofol (P < 0.001).
Postoperative pain was low in all groups and VAS at 30 and 60 min postoperatively did not vary with anaesthetic technique (Table 2). Emesis was infrequent, and as with time to discharge did not differ between the groups.
The range of anaesthetic consumption was more pronounced in the inhalation groups than the propofol TCI group. Consumption rate for desflurane varied from 0.08 to 1.26 g min−1, for sevoflurane 0.13 to 0.5 g min−1, and for propofol 14.2 to 46.1 mg min−1.
The anaesthetic drug cost for both sevoflurane and desflurane was about 45% less than for the cost of consumed propofol (Table 3). If costs for wasted propofol are included (€16.50 per operation), inhalation gases per operation cost less than half that of propofol. These differences become somewhat less pronounced if non-prefilled propofol is used (15-17%).
Cost-effectiveness is a complex equation of many factors, of which drug cost is only one . Preparation and induction times, duration of anaesthesia/surgery, residence time in the operating theatre, time to discharge, and factors influencing personnel related costs are at least as important . Bach and colleagues have estimated that inhalation anaesthetic agents account for up to 5% of all the running expenses of an anaesthetic department .
This study has shown that inhalation anaesthesia with desflurane or sevoflurane in combination with nitrous oxide, results in identical direct drug-related costs and that these techniques are cost-effective for ambulatory elective knee arthroscopy. When compared with TCI propofol, these inhalation techniques reduced drug costs by about 45%. Furthermore, emergence time, the time to state name and date of birth, was reduced by 3 min.
Several previous studies have also demonstrated the benefits of inhalation anaesthesia. Rosenberg and colleagues showed in 1994 that desflurane is more cost-effective than propofol for various orthopaedic procedures . Boldt and colleagues studied more extensive surgery and found essentially identical costs for desflurane, sevoflurane and isoflurane, all of which were lower than anaesthesia with propofol . The same group also studied patients during laparoscopic cholecystectomy, and compared propofol TCI with both isoflurane/nitrous oxide and propofol using a standard infusion pump . They found that using propofol TCI resulted in faster emergence and earlier recovery compared with both isoflurane and standard delivery propofol, but at a considerably higher drug cost. Watson and colleagues compared propofol TCI with sevoflurane mono-anaesthesia and found that sevoflurane gave comparable but more predictable emergence times than propofol and at about half the cost . Smith and colleagues also documented lower direct costs for a sevoflurane-based anaesthetic as compared to propofol anaesthesia when both were combined with nitrous oxide . In a previous study for ambulatory surgery, we showed that sevoflurane/nitrous oxide is more cost-effective than propofol with either alfentanil or remifentanil .
In the present study we wanted to determine if the TCI system would improve the cost-effectiveness of propofol, where both drug consumption and emergence times should be considered drug-related costs. Interestingly, propofol consumption was the same as in our previous study . Emergence times were longer after propofol than after inhalation anaesthesia, a finding that we did not see in our previous study with propofol. In that study propofol was combined with a continuous infusion of alfentanil or remifentanil whereas in the present study fentanyl as a 0.1 mg bolus was given before induction. Vuyk and colleagues have shown that the dose and choice of the opioid which is combined with propofol is of great importance for emergence times . The concentration of main anaesthetic in the present study was adjusted according to clinical need and there was no blinding, a factor that may have had some impact. Blinding in anaesthesia is problematical, it may, however, have been of value to have used a more objective measure of anaesthetic depth, e.g. a bispectral index monitor. However, the favourable effects of sevoflurane and desflurane on emergence times as compared to propofol are consistent with two comparisons using meta analysis which have shown that anaesthesia with both sevoflurane and desflurane provide faster emergence than propofol [14,15].
We did see a tendency for a shorter time to discharge from the recovery room after inhalation anaesthesia (P < 0.068). In the context of the present comparison, this is a rather marginal factor both economically and for patient satisfaction. Of greater significance is the time each patient spends in the operating theatre. For example in the private Swedish hospital where this study was performed, the estimated theatre cost is €3.10 min−1. The shortening of time to removal of the laryngeal mask by 3 min in this study results in about 24 min saved during an eight-procedure day by using inhalation anaesthesia rather than propofol. Local costs and circumstances will determine whether or not this potential time saving can realistically be achieved by performing an extra procedure or decreasing overtime costs.
Comparisons of alternative methods are often complicated by advantages and disadvantages which cannot be compared on the same scale, such as if a more costly method is associated with greater patient preference. The economic discussion of the results of this study is simplified by the lack of any differences in either surgeon or patient preference. Even if patient preference as such could not be studied, the most sensitive factors, postoperative pain, nausea and the indirect measure of time to being 'street fit' and discharge, did not differ between groups. The independent role of the main anaesthetic on factors such as postoperative nausea and vomiting is fairly low, and it is therefore not surprising that no differences could be seen in the present study involving a low risk procedure .
To what extent the results of the present study are applicable to other types of surgery depend on a number of factors. In particular it is difficult to know whether the present findings are applicable to longer procedures. Boltd and colleagues did see similar results in longer procedures . A fresh gas flow of 3 L min−1 consisting of 33% oxygen in nitrous oxide was used in the present study and the sevoflurane saving effects of nitrous oxide are well known . Decreasing the fresh gas flow would further decrease the inhalation anaesthetic consumption and cost . For propofol the main variables are whether bulk (non-prefilled syringes) propofol at a low price can be used and how wasted propofol can be minimized.
The economic consequences of this study comparing TCI propofol with desflurane or sevoflurane inhalation anaesthesia are two-fold. First, inhalation anaesthesia reduced costs by €0.37 min−1, or about €5.50 per patient. Secondly, the total time occupying the operating room is reduced by approximately 3 min per procedure. In the context of a full surgical schedule and considering that postoperative characteristics were equal, these small savings of a few Euros and few minutes per patient using inhalation techniques can result in significant cost reductions.
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