Coloma, Margarita MD; Chiu, Jen W. MB, DEAA, MMed; White, Paul F. PhD, MD, FANZCA; Tongier, W. Kendall MD; Duffy, Larry L. MD; Armbruster, Steven C. MD
Controversy exists regarding the optimal anesthetic technique for extracorporeal shock wave lithotripsy (ESWL). As a result of the immobility required during these painful procedures, both regional and general anesthetic techniques have been recommended (1). Monitored anesthesia care (MAC) is also an effective technique for this minimally invasive procedure because its use is associated with a rapid recovery profile in the outpatient setting (2,3). The use of MAC techniques allows patients to routinely “bypass the postanesthesia care unit,” thereby facilitating the fast-tracking process (4,5).
Although it is commonly assumed that general anesthesia (GA) is associated with prolonged recovery times and increased side effects compared with epidural anesthesia or MAC, the use of newer, short-acting anesthetics and analgesics can provide for a rapid recovery from GA with few side effects (6,7). To date, no prospective study has compared GA using short-acting anesthetic and analgesic drugs with a MAC technique in outpatients undergoing ESWL procedures.
This study was designed to test the hypothesis that a desflurane-based GA technique using the cuffed oropharyngeal airway (COPA) device for airway management compares favorably to a propofol-based MAC technique with respect to requirements for opioid analgesic medication, cardiorespiratory stability, ability to bypass the postanesthesia care unit, side effects, and discharge times after immersion lithotripsy.
After we obtained institutional review board approval, 100 consenting, adult outpatients undergoing ESWL with an unmodified Dornier HM-3 lithotriptor (Kennessaw, GA) were randomly assigned to receive either MAC or GA in this prospective, randomized study. Exclusion criteria included age <18 yr or >75 yr, a history of allergic reaction to any of the study medications, clinically significant cardiovascular, respiratory, or neurologic diseases, a history of drug or alcohol abuse, chronic use of opioid analgesics, or a positive pregnancy test.
All patients received midazolam, 2 mg IV, for premedication before positioning themselves on the lithotripsy gantry. Standard monitors were used. In the MAC group, supplemental oxygen (2 L/min) was administered via a nasal cannula with a sampling side port to measure end-expiratory carbon dioxide and respiratory rate (RR). Propofol was infused at an initial rate of 50 μg · kg−1 · min−1 and was subsequently titrated between 50 and 100 μg · kg−1 · min−1 to maintain an observer’s assessment of alertness/sedation (OAA/S) score of 2 or 3 (with 5 = awake/alert; 4 =lethargic response to name spoken in normal tone; 3 = response only after name is called loudly and/or repeatedly; 2 = response only after mild prodding or shaking; and 1 = asleep) (8). Before the start of the ESWL procedure, an infusion of remifentanil (25 μg/mL dilution) was administered at a rate of 0.05 μg · kg−1 · min−1. In the GA group, anesthesia was induced with propofol 1.5 mg/kg IV and remifentanil 0.125 μg/kg IV. After loss of consciousness, a COPA device (Mallinckrodt Medical, Athlone, Ireland) was inserted and connected to the breathing circuit. Maintenance of anesthesia initially consisted of desflurane 2% (inspired) and nitrous oxide (N2O) 60% in oxygen. The desflurane concentration was subsequently varied between 2% and 4% (inspired) to maintain an adequate depth of anesthesia (i.e., absence of purposeful movements).
In both groups, remifentanil 0.125 μg/kg IV boluses were administered 1 min before the start of the procedure and when the patient complained of pain (MAC group only), displayed facial grimacing, or had a RR exceeding 20 breaths/min. Intraoperative cardiorespiratory variables were recorded at 5-min intervals. All episodes of respiratory depression (defined as RR < 8 breaths/min for >1 min or Spo2 <90% for 30 s) and disruptive movements necessitating transient discontinuation of the treatment were also noted. Respiratory depression was treated by decreasing the propofol infusion rate or inspired desflurane concentration by 50%. Atropine 0.5-mg IV boluses were administered to treat bradycardia (heart rate <60 bpm) in both groups. With 100 shocks remaining in the treatment, all anesthetic drugs were discontinued, and in the GA group, droperidol 0.625 mg IV was administered as a prophylactic antiemetic.
If patients achieved an OAA/S score (8) of 4 or 5 and a fast-track score (9) of 12 or higher on leaving the mobile lithotriptor, they were transported directly to the step-down (Phase II) recovery area. Recovery times were recorded from discontinuation of the anesthetic drugs until eye opening, achievement of an OAA/S score of 5, and discharge home. A 5-point rating scale (1 = poor, 2 = fair, 3 = good, 4 = very good, 5 = excellent) was used by the research fellow (MC) to assess the adequacy of the anesthetic technique.
Discharge criteria required that the patient be awake, alert, with stable vital signs on standing, and able to walk without assistance. A predischarge questionnaire was completed by all patients to assess their quality of recovery (QoR) score (10). Additionally, a global QoR assessment was performed before discharge home by using a 10-cm linear visual analog scale, with 0 = poor recovery and 10 = excellent recovery. Oral hydrocodone with acetaminophen was prescribed for pain control after discharge. Finally, a follow-up evaluation was performed via telephone at 24 h after surgery to assess patient satisfaction with the anesthetic technique by using a 5-point verbal rating scale (1 = poor, 2 = fair, 3 = good, 4 = very good, 5 = excellent). Patients were also queried regarding the incidence of side effects after the procedure (e.g., pain, nausea, vomiting, and pruritus).
Data were analyzed by using the Number Cruncher Statistical Systems version 6.0 (NCSS, Kaysville, UT). An a priori power analysis determined that a sample size of 50 patients in each group would be adequate to detect a 30% difference in remifentanil usage between the two groups with a power of 80% at the P ≤ 0.05 level of significance. Continuous data were analyzed by using the Student’s paired t-test. Nominal and ranked data were assessed by using the χ2 test and Wilcoxon’s ranked sum test, respectively. Data were presented as mean values ± sd, numbers, or percentages, with P values <0.05 considered statistically significant.
The two study groups were similar demographically (Table 1). Stone localization, number of shocks delivered, and the energy levels (kV) used were also comparable in both treatment groups. Although the duration of anesthesia and time spent in the lithotriptor suite (“room time”) did not differ significantly between the two groups, the ESWL procedural time was significantly shorter in the GA group (Table 2). Additionally, this group required significantly less remifentanil compared with the MAC group.
The mean arterial pressure values were significantly lower after the induction of anesthesia in the GA group, but the heart rate values were comparable in both treatment groups (Fig. 1). The RR was consistently slower during the procedure in the MAC group, and Spo2 values were also significantly decreased at 2 and 5 min after the start of the ESWL procedure in the MAC group (Fig. 2).
All the patients achieved the fast-track criteria before leaving the lithotriptor suite and were transferred directly to the step-down unit. However, a significantly larger percentage of patients in the GA group were rated as having excellent anesthetic conditions (Table 3). With respect to adverse events during the procedure, the MAC technique was associated with more disruptive movements and episodes of transient respiratory depression (Table 3). In the GA group, the incidences of blood on the COPA device and postoperative sore throat were 2% and 4%, respectively. There were no differences in the incidences of postoperative nausea, vomiting, or pruritus. Although the GA group required a significantly longer time interval to return to a fully alert state (OAA/S score of 5), the time to discharge home was similar for both anesthetic groups. Finally, patient satisfaction scores and QoR rating scores were similar with both anesthetic techniques.
A wide variety of general, regional, and MAC techniques has been used to facilitate immersion lithotripsy (1–3,6,11–15). Combinations of propofol and short-acting opioid analgesics have been associated with fast recovery profiles (4,16,17). Despite remifentanil’s short context-sensitive half-life, studies involving the use of a variable-rate infusion of remifentanil were associated with a high incidence of respiratory depression during MAC procedures (5,18). Thus, a small-dose “basal” infusion of remifentanil in combination with small bolus doses was used to supplement propofol sedation.
Richardson and Dooley (6) used an opioid-free GA technique consisting of propofol infusion 150–200 μg · kg−1 · min−1 IV and nitrous oxide 70% with a laryngeal mask airway (LMA) device for airway management. These investigators reported a faster recovery and smaller incidence of side effects compared with an epidural group. However, this GA technique has not been compared with a propofol-based MAC technique, which also has a superior recovery profile compared with epidural anesthesia (2). We chose to use desflurane rather than propofol because it preferentially facilitates fast-tracking in the ambulatory setting (7). This GA technique compared favorably with the propofol-remifentanil MAC technique with respect to the anesthetic conditions (including fewer oxygen desaturation episodes and disruptive movements), contributing to shorter ESWL procedural times. Not surprisingly, the anesthesiologist preferred the GA technique because fewer interventions were required during the ESWL procedure. Although the GA group required a longer time period to recover to “full” alertness after the procedure, this did not interfere with our ability to fast-track these patients or delay their discharge home.
When the COPA device was used as an alternative to the LMA device in spontaneously-breathing patients (19,20), it was associated with a high first-attempt success rate (21) and less pharyngeal trauma (19). The major advantage of the COPA over the LMA in this patient population is that the device can be more easily inserted after the patient has been positioned in the lithotripsy gantry. The ergonomic constraints imposed by the lithotripsy gantry (i.e., semisitting position with flexion at the neck, hips, and knees on an elevated platform) can make it difficult to insert the LMA device. In contrast to earlier studies (19–21), use of the COPA device in this position was not associated with the need for frequent airway manipulations.
The inability to blind patients and anesthesiologists is the primary deficiency of the study design. Although the urologists were not asked to assess the anesthetic technique, the use of GA allowed them to reach the maximum shock wave energy level more rapidly (unreported data), and there were fewer disruptions during the procedure because of patient movement. Not surprisingly, the urologists find the GA technique preferable for immersion lithotripsy. The use of a prophylactic antiemetic was helpful in minimizing postoperative emetic symptoms in the GA group (22). Importantly, patients experienced a high-quality recovery and expressed a high degree of satisfaction with both techniques.
In conclusion, a desflurane-based GA technique with the COPA device was an effective alternative to propofol-based MAC sedation for immersion ESWL. Future studies should address the cost effectiveness and cost utility of these two anesthetic techniques for outpatient immersion lithotripsy.
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