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ANESTHETIC PHARMACOLOGY

A Comparison of Patient-Controlled Sedation Using Either Remifentanil or Remifentanil-Propofol for Shock Wave Lithotripsy

Hwan S. Joo, MD FRCPC^*, William J. Perks, Phm, Mark T. Kataoka, MD FRCPC^*, Lee Errett, MD FRCSC, Kenneth Pace, MD FRCSC, and R. John Honey, MD FRCSC

Departments of *Anaesthesia and Pharmacy, Divisions of Cardiac Surgery and Urology, St. Michael’s Hospital, University of Toronto, Toronto, Ontario, Canada

Address correspondence to Hwan Joo, MD, Department of Anaesthesia, St. Michael’s Hospital, University of Toronto, 30 Bond St., Toronto, Ontario, Canada M5B 1W8. Address e-mail to hwanjoom{at}yahoo.com

	Abstract

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Patient-controlled sedation (PCS) has been used for extracorporeal shock wave lithotripsy (SWL) because it allows for rapid individualized titration of anesthetics. Because of its sedating effects, the addition of propofol to remifentanil may improve patient tolerance of SWL with PCS. One hundred twenty patients were randomly assigned to receive remifentanil 10 µg or remifentanil 10 µg plus propofol 5 mg for PCS with zero-lockout interval. Nine patients in the Remifentanil group and three patients in the Remifentanil-Propofol group required additional sedatives to complete their SWL (P = 0.128). Compared with the Remifentanil group, the Remifentanil-Propofol group required less remifentanil, had a decreased incidence of postoperative nausea and vomiting, and had a better overall satisfaction level. However, they had an increased incidence of transient apnea and oxygen desaturation. The incidence of apnea was 15% in the Remifentanil group and 52% in the Remifentanil-Propofol group (P < 0.001). All patients were able to move themselves to the stretcher at the end of SWL, and median time to home discharge was <70 min in both groups. Both remifentanil and remifentanil-propofol were useful for PCS during SWL.

IMPLICATIONS: The addition of propofol to remifentanil improves patient satisfaction and decreases postoperative nausea and vomiting. However, it causes more respiratory depression than remifentanil alone. When remifentanil-propofol is used with patient-controlled sedation, appropriate monitoring and a minimum 1–2 min lockout interval is required.

	Introduction

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Monitored anesthesia care has been used for extracorporeal shock wave lithotripsy (SWL), because it has been associated with rapid recovery and minimal postoperative sedation (1). A specific form of monitored anesthesia care, patient-controlled sedation (PCS), may be advantageous for SWL because it allows the patient to self-administer the exact amount of anesthetics required to treat varying degrees of pain and discomfort (2).

PCS with alfentanil has provided good conditions for SWL (2–4), and has been associated with significant patient satisfaction (5–7). The addition of propofol to alfentanil increases sedation, potentiates analgesia, and decreases postoperative nausea and vomiting (PONV), with no increase in respiratory depression (8). However, alfentanil may not be the ideal opioid to combine with propofol because of its relatively long half-life com-pared with propofol. Patient-controlled analgesia with remifentanil during labor has shown the advantages of using an ultra-short-acting opioid for reducing labor pains while allowing for minimal sedation after delivery (9,10). Remifentanil may have advantages over alfentanil because of its shorter half-life, comparative duration of effect to propofol, and lack of residual postoperative sedation (1). However, no study has been performed on the use of PCS using remifentanil or a combination of remifentanil and propofol for SWL. Remifentanil and propofol are stable as a mixture (11).

Our purpose for this study was to examine the efficacy of adding propofol to remifentanil for PCS during SWL. The primary hypothesis was that, because of the sedative and analgesic potentiating effects of propofol, more patients would successfully complete their SWL without the need for additional sedatives or analgesics administered by anesthesia staff. The addition of propofol should also decrease the amount of remifentanil used, increase patient satisfaction, and decrease PONV (12,13).

	Methods

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After ethics committee approval and informed consent, 120 patients were randomly assigned to receive either remifentanil PCS or remifentanil-propofol PCS. Randomization was performed by using computer-generated random numbers, kept in consecutively numbered closed envelopes. Double blinding was achieved by mixing remifentanil in 10% lipid emulsion. Patients of both sexes scheduled for SWL aged 18 to 90 yr were included in this study. Exclusion criteria included patients with allergies to the drugs being used, at risk for pulmonary aspiration, with increased intracranial pressure, who are heavier than 150% of their ideal body weight, with severe cardiovascular or respiratory diseases (ASA grade IV or higher), and patients who could not understand the concept of PCS.

No patients were premedicated with any sedatives. All patients received supplemental oxygen via facemask at 6 L/min. Standard monitors including electrocardiogram, pulse oximetry, and noninvasive blood pressure monitoring were used in all patients. Respiratory rate was derived by using end-tidal CO₂ monitoring via nasal prongs. All variables were recorded continuously except for blood pressure, which was measured every 2.5 min.

PCS was delivered using a Graseby 3300 patient-controlled analgesia pump (Sims Canada, Markham, Ontario) with zero lockout. One milliliter of solution was delivered over 18 s via the Grasby pump, making effective lockout 18 s. The study pharmacist mixed all medications immediately before the start of SWL. In the Remifentanil group, remifentanil was diluted in 10% lipid emulsion to a concentration of 10 µg/mL. In the Remifentanil-Propofol group, the solution contained 10 µg of remifentanil and 5 mg of propofol per milliliter. The PCS medications were delivered by a secondary infusion line, which was attached to a free-flowing IV, 15 cm from the IV skin insertion site.

All patients were instructed on the use of the PCS system in the preoperative area. In the lithotripsy unit, patients were instructed to give themselves three doses of their PCS medication before the start of SWL. SWL was performed by using a Dornier Lithotriptor MFL 5000 (Kennessaw, GA) at 17–26 kV. Patients were encouraged to press the PCS system when required, to treat the pain and discomfort associated with SWL. If the patient felt that they could not tolerate SWL with their PCS regimen, they were instructed to raise their hand. At this time, the attending anesthesiologist sedated the patient with midazolam 1 mg to a maximum dose of 4 mg. If the patient still could not tolerate SWL with additional midazolam, the anesthetic regimen was aborted and a light general anesthesia was induced with an infusion of propofol.

Apnea was defined as no detection of CO₂ for 20 s. If apnea persisted for >1 min or if SpO₂ decreased below 90%, patients were reminded to breathe more often. If the SpO₂ decreased below 85% at any time, a 1-min lockout was programmed into the PCS system. If a 1-min lockout did not prevent further desaturations to 85%, the study protocol was aborted and anesthesia was continued with a propofol infusion.

PCS was continued until the last shock was delivered. Time to reach an observer assessment of alertness and sedation (OAA/S) (14) score of 5 was recorded. The Aldrete score (15) was assessed at the end of SWL and every 10 min after arrival to a combined level I–II postoperative care unit. Before discharge, all patients were given a questionnaire regarding pain using a visual analog scale of 0 to 10 (10 worst) during the SWL and their overall satisfaction with their anesthetic technique. Patients were discharged home directly from the postoperative care unit.

Sample size for the study was derived to show a 20% difference in efficacy. Efficacy was defined as the ability of the patients to complete SWL with no additional anesthetic other than their study medications. Based on a 20% difference from 95% to 75%, 59 patients per group would be required using a power of 0.80 and = 0.05. To account for dropouts, we enrolled 60 patients per group.

Parametric measurements were analyzed by using unpaired t-tests. Nonparametric measurements were analyzed by using the rank-sum test. For categorical data, ² tests were used. For repeated measurements such as respiratory rates and oxygen saturation, two-way analysis of variance with Dunnett’s test for post hoc analysis was used. A value of P < 0.05 was considered statistically significant.

	Results

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The two groups had similar demographic background and stone localization (Table 1). Although time in the SWL suite, anesthetic time, and SWL procedure time were similar, the fluoroscopy time was longer in the Remifentanil-Propofol group (Table 2).

PCS failed in one patient in each group because of inadequate analgesia. SWL was performed in these patients with a light, propofol infusion general anesthesia with spontaneous mask ventilation. The number of patients requiring additional midazolam and/or propofol infusion was nine (15%) in the Remifentanil group and three (5%) in the Remifentanil-Propofol group (P = 0.128). The Remifentanil-Propofol group had a more frequent incidence of apnea and oxygen desaturation <90% (P < 0.05). Six patients whose oxygen saturation decreased below 85% in the Remifentanil-Propofol group had a 1-min lockout instituted (effective lockout 78 s) into the PCS pump. No further oxygen desaturation occurred in these patients. The overall oxygen saturation was within normal limits for both groups (Fig. 1). However, the Remifentanil-Propofol group had a lower overall average respiratory rate during SWL (Fig. 2).

View larger version (12K): [in this window] [in a new window]   Figure 1. Graph of mean oxygen saturation with standard deviation versus time.

View larger version (13K): [in this window] [in a new window]   Figure 2. Graph of mean respiratory rate with standard deviation versus time.

No patient had intraoperative nausea or vomiting. The incidence of pruritus was infrequent and similar in both groups. PONV was more common in the Remifentanil group (P < 0.05) (Table 3). Willingness to try the same anesthetic regimen and overall patient satisfaction was high in both groups. However, patients in the Remifentanil-Propofol group had better satisfaction with their mode of anesthesia than the Remifentanil group (P < 0.05).

	Discussion

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Moderate-to-large doses of remifentanil have been associated with acute opioid tolerance (16), PONV (17), and pruritus (18). The total median dose of remifentanil was decreased by 37.5% in the Remifentanil-Propofol group compared with the remifentanil-only group. In the current study, PONV was decreased, patient satisfaction level was better, and there was a trend toward a decreased number of patients requiring additional postoperative analgesics in the Remifentanil-Propofol group compared with the Remifentanil group. This may have been caused by the sedating and remifentanil-sparing properties of propofol.

The remifentanil-propofol mixture caused more respiratory depression than remifentanil alone. The incidence of apnea (>20 seconds) was more frequent in the Remifentanil-Propofol group (52% versus 15%) (P < 0.001) as was the incidence of oxygen desaturation (14% versus 4%) (P = 0.02). Six patients in the Remifentanil-Propofol group had oxygen desaturation <85% and had a one-minute lockout instituted. The lockout prevented further desaturation. The frequent incidence of transient apnea and oxygen desaturation in the current study may have been prevented if an appropriate lockout had been instituted from the beginning of SWL. A limitation of the current study was the fixed bolus PCS dosing of medications in both groups. Each group received one milliliter of the study medication with zero lockout. The current protocol was designed to give the patients in both groups an equal amount of remifentanil per successful request while allowing the patients to rapidly titrate the amount of their medications to the level of their own satisfaction, with no upper limit. A lockout would have unfairly biased the study against the remifentanil group. Many of the patients who required large doses of remifentanil in the Remifentanil group would not have received an adequate amount of medication if a one-minute lockout had been instituted from the start of SWL. Unfortunately, the zero-lockout protocol also allowed the patients to temporarily overdose on their medications, causing apnea and oxygen desaturations. However, because of the short half-lives of both remifentanil (19) and propofol (20), these events were short and non-life-threatening. Oxygen desaturations were treated by either asking the patient to breathe more often or by instituting a one-minute lockout. Zero lockout may not be safe for clinical use with remifentanil and remifentanil-propofol PCS, because it allows the patient to receive a salvo of medications before the effects are felt. A lockout period of one to two minutes with individualized dosing of remifentanil or remifentanil-propofol may be more appropriate. Our current practice for SWL is to use midazolam 1–2 mg at the start of the procedure with remifentanil 10 µg and propofol 5 mg per mL solution. This solution is infused at 10–20 mL/h with a bolus dose of 1–2 mL and a lockout period of 1–2 minutes, depending on patient size and age.

Previous studies on volunteers with alfentanil and propofol combinations have shown only a mild decrease in minute ventilation with no change in the CO₂ response curve when compared with alfentanil alone (8). However, these subjects were minimally sedated, with a minimal decrease in level of consciousness. In clinical use, sedatives may induce a state of decreased level of consciousness, which abolishes the conscious effort to breathe, making the patient more susceptible to the respiratory depressant effect of opioids (21,22). When remifentanil was used in conjunction with midazolam for monitored anesthesia care, a frequent incidence of respiratory depression was also observed (23). Because the Remifentanil-Propofol group used less remifentanil, but had increased respiratory depression and a more frequent incidence of apnea, the results suggest that there are additive respiratory depressant effects when the two drugs are combined for clinical use.

In the Remifentanil group, there was a 17.3-fold difference in the amount of remifentanil used between the patient requiring the largest and the patient requiring the smallest amount of remifentanil. This difference was 9.6 times in the Remifentanil-Propofol group. In fact, the patients with the least use stopped using the PCS after the initiation of SWL, because they stated that SWL was not painful to them. The high variability of remifentanil required to complete SWL in both groups may reflect differences in individual tolerance to pain and the variability of opioid requirements to treat pain. It may also reflect actual differences in pain levels depending on stone location, stone size, and kilovolt at the time of SWL. However, most methods of monitored anesthesia care rely on relatively rigid maximal and minimal analgesics and sedatives (24). With standard monitored anesthesia care, patients who require very little or no anesthetics will be overmedicated, and patients who require profound anesthesia will be undermedicated. The extreme range of remifentanil used during this study suggests that individualized patient-controlled dosing with PCS is beneficial to overcome this variability.

With PCS using either remifentanil or remifentanil-propofol, anesthetic induction time was rapid, because all patients were able to tolerate SWL after three PCS doses. Both groups had good conditions for outpatient SWL because the attending urologists felt that adequate surgical conditions were achieved in 98% of the patients in both groups. There were no complications in either group. All patients met the eligible criteria for discharge to a phase II recovery area at the end of SWL. For both groups, the median time to OAA/S score of 5 was 4 minutes and all patients were able to move themselves over to a stretcher without any help from attendants. The actual time to home discharge was short at 67 minutes for the Remifentanil group and 64 minutes for the Remifentanil-Propofol group. These results compare favorably to SWL performed under propofol monitored anesthesia care and desflurane general anesthesia. In a recent study on SWL, Coloma et al. (12) reported time to OAA/S score of 5 at 17 minutes with propofol monitored anesthesia care and 26 minutes with desflurane general anesthesia. They also reported home discharge time of 111 minutes and 114 minutes, respectively.

In conclusion, the addition of propofol to remifentanil increases patient comfort because the sedating effects of propofol result in decreased remifentanil usage, better patient satisfaction, and a decrease in the incidence of PONV. However, the addition of propofol to remifentanil for PCS results in increased respiratory depression compared with remifentanil alone. PCS should therefore be performed in a monitored setting with an appropriate lockout interval and individualized dosing for each patient, especially when propofol is added to remifentanil. Because both regimens are associated with good conditions for SWL, minimal postoperative sedation and early home discharge, both PCS with remifentanil or remifentanil-propofol may be useful for fast-track SWL.

	References

Top Abstract Introduction Methods Results Discussion References

 

1. Sa RM, Inagaki Y, White PF. Remifentanil administration during monitored anesthesia care: are intermittent boluses an effective alternative to a continuous infusion? Anesth Analg 1999; 88: 518–22.[Abstract/Free Full Text]
2. Kortis HI, Amory DW, Wagner BK, et al. Use of patient-controlled analgesia with alfentanil for extracorporeal shock wave lithotripsy. J Clin Anesth 1995; 7: 205–10.[ISI][Medline]
3. Chin CM, Tay KP, NG FC, et al. Use of patient-controlled analgesia in extracorporeal shockwave lithotripsy. Br J Urol 1997; 79: 848–51.[ISI][Medline]
4. Irwin MG, Campbell RC, Lun TS, Yang JC. Patient maintained alfentanil target-controlled infusion for analgesia during extracorporeal shock wave lithotripsy. Can J Anaesth 1996; 43: 919–24.[Abstract/Free Full Text]
5. Osborne GA, Rudkin GE, Jarvis DA, et al. Intra-operative patient-controlled sedation and patient attitude to control: a crossover comparison of patient preference for patient-controlled propofol and propofol by continuous infusion. Anaesthesia 1994; 49: 287–92.[ISI][Medline]
6. Schelling G, Mendl G, Weber W, et al. Patient controlled analgesia for extracorporeal shock wave lithotripsy of gallstones. Pain 1992; 48: 355–9.[ISI][Medline]
7. Uyar M, Ugur G, Bilge S, et al. Patient-controlled sedation and analgesia during SWL. J Endourol 1996; 10: 407–10.[ISI][Medline]
8. Pavlin DJ, Coda B, Shen DD, et al. Effects of combining propofol and alfentanil on ventilation, analgesia, sedation, and emesis in human volunteers. Anesthesiology 1996; 84: 23–37.[ISI][Medline]
9. Thurlow JA, Waterhouse P. Patient-controlled analgesia in labour using remifentanil in two parturients with platelet abnormalities. Br J Anaesth 2000; 84: 411–3.[Abstract/Free Full Text]
10. Jones R, Pegrum A, Stacey RG. Patient-controlled analgesia using remifentanil in the parturient with thrombocytopaenia. Anaesthesia 1999; 54: 461–5.[ISI][Medline]
11. Stewart JT, Warren FW, Maddox FC, et al. The stability of remifentanil hydrochloride and propofol mixtures in polypropylene syringes and polyvinylchloride bags at 22°–24°C. Anesth Analg 2000; 90: 1450–1.[Abstract/Free Full Text]
12. Coloma M, Chiu JW, White PF, et al. Fast-tracking after immersion lithotripsy: general anesthesia versus monitored anesthesia care. Anesth Analg 2000; 91: 92–6.[Abstract/Free Full Text]
13. Tramer M, Moore A, McQuay H. Propofol anaesthesia and postoperative nausea and vomiting: quantitative systematic review of randomized controlled studies. Br J Anaesth 1997; 78: 247–55.[Abstract/Free Full Text]
14. Chernik DA, Gillings D, Laine H, et al. Validity and reliability of the Observer’s Assessment of Alertness/Sedation Scale: study with intravenous midazolam. J Clin Psychopharmacol 1990; 10: 244–51.[ISI][Medline]
15. Aldrete JA. Modifications to the postanesthesia score for use in ambulatory surgery. J Perianesth Nurs 1998; 13: 148–55.[Medline]
16. Guignard B, Bossard AE, Coste C, et al. Acute opioid tolerance: intraoperative remifentanil increases postoperative pain and morphine requirement. Anesthesiology 2000; 93: 409–17.[ISI][Medline]
17. Bekker AY, Berklayd P, Osborn I, et al. The recovery of cognitive function after remifentanil-nitrous oxide anesthesia is faster than after an isoflurane-nitrous oxide-fentanyl combination in elderly patients. Anesth Analg 2000; 91: 117–22.[Abstract/Free Full Text]
18. Avramov MN, Smith I, White PF. Interactions between midazolam and remifentanil during monitored anesthesia care. Anesthesiology 1996; 85: 1283–9.[ISI][Medline]
19. Babenco HD, Conard PF, Gross JB. The pharmacodynamic effect of a remifentanil bolus on ventilatory control. Anesthesiology 2000; 92: 393–8.[ISI][Medline]
20. Cockshott ID, Briggs LP, Douglas EJ, White M. Pharmacokinetics of propofol in female patients: studies using single bolus injections. Br J Anaesth 1987; 59: 1103–10.[Abstract/Free Full Text]
21. Henson LC, Ward DS. Effects of anaesthetics and sedatives on the control of breathing. Ann Acad Med Singapore 1994; 23: 125–9.[Medline]
22. Luebbe N, Walz R, Walz K, et al. Clonidine prolongs fentanyl-induced ventilatory depression. Eur J Anaesthesiol 1998; 15: 292–6.[ISI][Medline]
23. Litman RS. Conscious sedation with remifentanil and midazolam during brief painful procedures in children. Arch Pediatr Adolesc Med 1999; 153: 1085–8.[Abstract/Free Full Text]
24. Hosking MP, Morris SA, Klein FA, et al. Anesthetic management of patients receiving calculus therapy with a third-generation extracorporeal lithotripsy machine. J Endourol 1997; 11: 309–11.[ISI][Medline]

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (17) Citing Articles via Google Scholar Google Scholar Articles by Joo, H. S. Articles by Honey, R. J. Search for Related Content PubMed PubMed Citation Articles by Joo, H. S. Articles by Honey, R. J. Related Collections Pain Pharmacology

Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999