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Selective Spinal Anesthesia Versus Desflurane Anesthesia in Short Duration Outpatient Gynecological Laparoscopy: A Pharmacoeconomic Comparison

Lennox, Pamela H., MB, MRCPI, FCARCSI; Chilvers, Colin, B MED DA (UK), FANZCA; Vaghadia, Himat, MB BS, MHSc, FRCPC, FFARCS

doi: 10.1097/00000539-200203000-00016
Ambulatory Anesthesia: Research Report
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We compared the cost and effectiveness of selective spinal anesthesia (SSA) with a desflurane-based general anesthetic (DES) for outpatient gynecological laparoscopy. A prospective analysis was undertaken of 10 patients randomized to receive SSA and compared with 10 patients randomized to receive DES. The groups were well matched in their demographic characteristics. The mean cost (in 2000 Canadian dollar values) of anesthesia supplies, drugs, and nursing for the SSA group of $62.31 was less than that for the DES group of $92.31 (P < 0.01). Recovery costs of both groups were similar. Time to administer anesthesia and time spent in the postanesthetic care unit were also similar. Postoperative analgesia was required by 50% of the DES group but in no patient receiving SSA (P < 0.01). SSA is a cost-effective alternative to DES in these patients.

Department of Anesthesia, Vancouver General Hospital, University of British Columbia, Vancouver, BC, Canada

October 24, 2001.

Address correspondence and reprint requests to Dr. Himat Vaghadia, Department of Anesthesia, JPP 2449, Vancouver General Hospital, 855 West 12th Avenue, Vancouver, BC, Canada V5Z 1M9. Address e-mail to hvaghadi@vanhosp.bc.ca.

Selective spinal anesthesia (SSA) is a technique that uses small-dose hypobaric lidocaine combined with a small dose of a shorter acting intrathecal opioid. This technique produces a brief sensory block of the abdomen with minimal motor and sympathetic blockade. A minimal motor block technique may be better suited in outpatients provided surgical conditions are acceptable. It is used at our surgical daycare center for short-duration laparoscopic procedures and has been refined and developed such that the small doses used can provide an anesthetic that is effective (1,2), acceptable to the patient (2), as well as being equally efficient to the shortest recovery profiles of a general anesthetic using desflurane (DES) (3).

Our aim was to analyze the direct hospital costs of anesthesia and recovery at our institution. We hypothesized that a SSA technique would be cheaper and more efficient than a desflurane-based general anesthetic (DES) technique for short-duration outpatient gynecological laparoscopic procedures.

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Methods

The analysis was conducted at our surgical daycare center, as part of a prospective, randomized, controlled trial that compared recovery profiles of female patients undergoing SSA and DES in short-duration outpatient gynecological laparoscopy. University ethics approval was obtained from the Clinical Screening Committee for Research and Others Studies Involving Human Subjects of the University of British Columbia, along with written informed consent from each patient recruited. There were 10 patients in each group and a standardized anesthetic was given to each patient. Sample size was chosen based on an anticipated sd of 0.3 in each group with respect to anesthesia costs and an expectation to show a difference between means of 1.0. With 10 patients per group, the power of the study would be more than 80%. A record of the supplies, drugs, and gases used in each case was recorded during the procedure from the preoperative phase through to their discharge from the postanesthetic care unit (PACU). Costs of anesthesia and recovery for each group were calculated in Canadian Dollars at 2000 values. Costs were constant throughout the 2-mo period of the study. All calculated values refer to the direct expense incurred to the hospital, not to what a patient would be charged.

“Supplies” consisted of all disposable materials used during the administration of anesthesia and in the postoperative period, including IV cannulae, tubing and oxygen masks. The Sterile Supply Department calculated sterilizing costs of airway and breathing equipment, including labor and repackaging.

Drug costing was based on certain assumptions: that one needle and one syringe of the appropriate size were used for each drug given and that there was wastage of residual drug left in an opened ampoule. “Gases” includes oxygen, nitrous oxide, and DES used. The cost of DES was calculated using the formula published by Dion (4). The concentration of DES administered was titrated with Bispectral Index electroencephalography (BIS-EEG Aspect Medical Systems, Natick, MA) and was recorded, as were all fresh gas flows (range, 1–2 L/min). The cost of the disposable EEG strip for BIS was included in the cost calculations. It was used to standardize administration of the volatile anesthetic but is not in routine use for this type of case in all institutions. Oxygen and nitrous oxide costs were calculated using the cost-per-liter of bulk supply to the hospital. The amount of oxygen used as the driving gas for the ventilator was derived from the product of the duration of the surgery and the manufacturer’s estimate of consumption. Oxygen flow rates and duration in the PACU were not recorded; therefore only the cost of the oxygen mask and tubing were included.

The average cost of providing one hour of a registered nurse’s time in our daycare center in 2000 was $31.48. This figure takes into account leave and benefit entitlements but not personnel overhead costs. The time that the patient spent in the PACU and the average nurse-to-patient ratio were used to calculate the cost of nursing time in the PACU. The cost of nursing time in the operating room was not calculated, as this time is dependent on surgical rather than anesthetic factors and was approximately the same for both groups. Capital equipment depreciation was not included as all monitors and anesthetic machines were available to both groups. Physician reimbursement, maintenance of the center, and additional patient supplies (e.g., linen and catering) were also excluded.

To assess effectiveness of anesthesia, the time taken to administer anesthesia and the time in PACU until the patient’s discharge home were analyzed. “Time to administer anesthesia” assumes that the surgeon was ready to commence as soon as the anesthesiologist was satisfied that the patient was ready for the surgery to begin. While in the PACU, a record was kept of incidences of postoperative nausea and vomiting (PONV) and postoperative pain significant enough to require pharmacological treatment. All patients were evaluated in the PACU by nurses and anesthetic staff not intimately connected to the study. Blinding to patient grouping was not possible.

During the study period, anesthetic, surgical, and nursing staffs were the same. Discharge criteria and nursing protocols remained the same for the study period. All anesthetics were given by two of the investigators. Costs were calculated by an unblinded anesthesiologist who was not involved in the care of any of the study patients.

Data were entered into a spreadsheet program (Microsoft Excel). Parametric data were compared using the unpaired Students’t-test and nonparametric data were analyzed by using the χ2 test. A P value of <0.05 was considered significant.

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Results

In the SSA group, all patients had a spinal anesthetic administered using a midline approach at the L3-4 or L4-5 level injecting a hypobaric solution of lidocaine 10 mg and sufentanil 10 μg made up to a volume of 3 mL with sterile water through a 27-gauge Whitacre needle in the sitting position. No adjustment was made for height. No patient required conversion to general anesthesia, 3 patients required midazolam for anxiolysis (maximum 2 mg IV), and 2 patients required supplemental fentanyl for shoulder-tip discomfort (maximum 50 μg IV).

In the DES group, anesthesia was induced with fentanyl 2 μg/kg, propofol 2 mg/kg and tracheal intubation was facilitated with mivacurium 0.15 mg/kg and topical lidocaine 4% 160 mg. Anesthesia was maintained with DES 2%–6% in combination with 65% N2O in O2 titrated to keep BIS values between 45 and 65. The lungs were ventilated mechanically to maintain an end-tidal carbon dioxide concentration between 32 and 36 mm Hg. Supplemental doses of fentanyl 25–50 μg/kg IV were given to treat hemodynamic increases of more than 15% above preinduction baseline values. Three patients in this group required additional fentanyl for this reason.

All patients received acetaminophen 975 mg orally 30 min preoperatively and a diclofenac sodium 100 mg suppository and perphenazine 1 mg IV at the end of the procedure as prophylactic analgesic and antiemetic, respectively. All surgical sites were infiltrated with bupivacaine 0.25% to reduce incisional pain.

The two groups were well matched for demographic variables (Table 1). Costs for anesthesia and recovery are given in Table 2. The mean cost of anesthesia was significantly less in the SSA group ($62.31) than the DES group ($92.31, P < 0.01). This cost savings of $30 was attributable to lower cost of anesthetic supplies and sterilization in the SSA group, as well as lower cost of drugs and gases. The PACU costs, which included nursing and supplies/drug costs, were similar in both groups. Overall, the total cost of anesthesia and recovery was significantly less for patients given spinal anesthesia ($79.80) than desflurane general anesthesia ($107.80, P < 0.01). A cost savings of $30 with the SSA group represents approximately 30% of the total cost seen with the DES group.

Table 1

Table 1

Table 2

Table 2

Times to administer and to recover from anesthesia were similar in both groups (Table 3). Five patients in the DES group required postoperative analgesia, whereas none did in the SSA group (P < 0.01). Three patients in the SSA group had PONV requiring treatment with IV dolasetron compared with none of the DES group; however, this was not a significant difference.

Table 3

Table 3

Four patients in the SSA group had pruritus, none of which required treatment. No patient required overnight admission. However, none of the patients had urinary retention.

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Discussion

Our everyday practice should now consider the economically significant cost of a particular drug, new piece of equipment, or technique we intend to use. This study has demonstrated that a SSA technique is more cost effective than, and a good alternative to, a short-acting DES-based general anesthetic for outpatient gynecological laparoscopies at our hospital.

Previous studies have found delayed recovery with spinal anesthesia and hence increased cost (5,6). This delay has mainly been an issue because of motor blockade. Indeed, many surgical procedures require a motor block; however, a short-duration laparoscopy does not. Subsequently, ambulation occurs as soon as the procedure is completed. More recently, we have demonstrated equivalent recovery profiles in patients undergoing outpatient gynecological laparoscopy under spinal anesthesia compared with general anesthesia (2,7). Because patients can usually move themselves from the operating table to a stretcher after SSA, motor block becomes a nonissue in PACU stay. In fact, discharge criteria requiring resolution of sensory block is now the limiting factor in keeping SSA patients in the PACU.

In this study, a BIS monitor was used to provide a more objective measure of anesthetic depth in the DES group to avoid excessive administration of anesthesia (8). Even though a BIS monitor is not a standard of care in all institutions, in research studies and when endeavoring to fast-track patients, it is a very useful tool to standardize anesthetic protocols and to limit excess volatile anesthetic use. For this reason, we thought it necessary to include it in the overall coat of DES. It costs $30 to our institution; excluding this, the costs of the two techniques are similar. The time to administer anesthesia was similar in both groups. There was no time delay in administration of the spinal anesthetic or in waiting for adequate block. This is partly attributable to the rapid onset of the solution used. This is in contrast to what is popularly expected with “conventional spinal techniques.”

None of the patients in the SSA group required postoperative analgesia, whereas half of the patients in the DES group did. This may be a result of the analgesic properties of intrathecal sufentanil or perhaps residual sensory block. An unexpected finding was that three patients in the Spinal group had PONV, compared with none in the DES group. Each of these patients had severe PONV after previous surgery. Some of the patients in this study were at high risk for PONV and were happy to have a spinal anesthetic to avoid recurrence of PONV experienced with previous general anesthesia. We assume that intrathecal sufentanil was the reason for this adverse effect, although the other risk factors of being a female and undergoing gynecological surgery would also contribute toward this. Even though none of our patients experienced a postdural puncture headache, it should be considered as a potential adverse effect requiring further treatment, including hospital admission. Just one postdural puncture headache would have significantly altered our cost findings in this small study. Transient neurological symptoms have a very infrequent incidence in small-dose spinal anesthesia and their cost impact would be unclear (9).

This was a controlled, randomized, prospective cost analysis study. Even though it is not possible to compare a spinal technique with a general anesthetic technique in a blinded manner, this study is more precise than a larger-scale retrospective study despite the small sample size because it has adequate statistical power. As with most pharmacoeconomic studies we were still required to make some assumptions in our analysis. The costs calculated for each group represent the direct cost to the hospital and reflect the actual cost of the anesthetic technique, excluding physician fees. Even though nurses are employed to work on a shift basis, it is important to prorate their hourly cost into the analysis of PACU costs to arrive at a meaningful comparison of the two techniques. The examination of direct costs is a better method of comparing economic advantages between two techniques (10). The study perspective is purely institutional. Although it is not appropriate to apply the actual dollar values to other institutions, the significant difference in cost between the two techniques could be translated to others using similar anesthetic techniques.

A previous study at our institution retrospectively looked at the costs between regional anesthesia and an isoflurane based general anesthetic. In terms of cost, it found that the total cost of anesthesia and recovery was similar and that analgesic requirements were less in the regional group than in the isoflurane group. However, in terms of effectiveness, the regional group was less efficient in relation to anesthetic time as well as duration of patient stay in the PACU (11). These results are at odds with our current findings of an anesthetic cost reduction in the Spinal group and comparable recovery profiles in both groups. The improvements in cost effectiveness of spinal anesthesia might be explained by the following: a) prospective study design with protocols limiting use (and thus cost) of supplementary drugs, whose use is perhaps more likely in patients under spinal anesthesia; b) greater cost of desflurane than isoflurane despite the use of a BIS monitor, without a concomitant improvement in overall recovery time in these patients; c) the increased operator experience and thus faster SSA administration; d) a reduction in dose of the drugs used for SSA resulting in more rapid block resolution. SSA is used in our institution for laparoscopy and is gaining acceptance for a wider range of surgical procedures (9,12). Operator comfort with this technique is acquired through experience without which conversion to general anesthesia is more likely. This would then negate any cost savings associated with SSA.

In conclusion, we found the cost of materials, drugs and PACU nursing for SSA was at least 25% less than a DES-based general anesthetic for short-duration outpatient gynecological laparoscopy. In terms of effectiveness, SSA is equal to DES in time to administer and recover from anesthesia and provides markedly better postoperative analgesia while the patient is in the hospital. SSA for outpatient laparoscopy can now be listed among many other regional techniques demonstrated to be more cost effective than general anesthesia (13,14). Overall, neither technique increases the costs excessively, particularly when operating room times are not prolonged.

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References

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© 2002 International Anesthesia Research Society