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Anesthesia & Analgesia:
doi: 10.1213/00000539-200208000-00020

Distal Nerve Blocks at the Wrist for Outpatient Carpal Tunnel Surgery Offer Intraoperative Cardiovascular Stability and Reduce Discharge Time

Gebhard, Ralf E. MD; Al-Samsam, Tameem MD; Greger, Jennifer MD; Khan, Ahmad MD; Chelly, Jacques E. MD, PhD, MBA

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Department of Anesthesiology and International Regional Research Center, The University of Texas Medical School at Houston, Houston, Texas

May 1, 2002.

Address correspondence and reprint requests to Jacques E. Chelly, MD, PhD, MBA, Department of Anesthesiology, University of Texas-Houston Medical School, 6431 Fannin MSB 5.020, Houston, TX 77030-1503. Address e-mail to

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Carpal tunnel release is often performed as an outpatient procedure. We designed this retrospective study to assess the effect of different anesthesia techniques on intraoperative cardiovascular stability and discharge time. According to the anesthesia technique received, 62 consecutive patients were categorized in Group BIER (IV regional anesthesia), Group BLOCK (distal nerve blocks), and Group GENERAL (general anesthesia). Incidences of intraoperative periods of tachycardia or bradycardia and hyper- or hypotension were studied, as were tourniquet, surgical, operating room, and discharge times. Cardiovascular stability was better achieved in Group BLOCK, as indicated by a significantly smaller incidence of periods of hypertension compared with Group BIER (5% vs 25%) and a significantly less frequent incidence of periods of hypotension compared with Group GENERAL (14% vs 42%). Patients in Group BLOCK spent significantly less time in the hospital after surgery than patients in Group BIER (65 vs 88 min) or patients in Group GENERAL (65 vs 133 min). We conclude that distal nerve blocks for outpatient carpal tunnel surgery are associated with greater intraoperative cardiovascular stability than general anesthesia. After surgery, patients in Group BLOCK could be discharged earlier than patients who received IV regional anesthesia or general anesthesia; this could be related to the superior postoperative analgesia provided by this technique.

Carpal tunnel release is often performed as an outpatient or even as an office procedure. Although general anesthesia is often still used in this setting (1), the search for increased efficiency and earlier discharge has led to consideration of alternative anesthesia techniques. In this respect, brachial plexus blocks (2,3), IV regional anesthesia (4), local infiltration (5,6), and distal blocks at the wrist (7,8) have been suggested. However, the extent of the anesthetized area achieved with brachial plexus blocks seems to be excessive for the rather small surgical trauma. IV regional anesthesia is easy to perform but has been associated with severe complications (9) and may not offer efficient postoperative pain control (10). Many surgeons performing carpal tunnel release as an office procedure have used local infiltration, but median nerve injury can occur (6), and the local anesthetic itself can make the procedure more difficult to perform, especially when endoscopic techniques are used (11). The efficacy of distal nerve blocks at the wrist has been demonstrated (7,8), but there are concerns of an increased risk of neurological complications by some authors (12), although the safety of this technique has been demonstrated by others (13). A “gold standard” anesthetic technique for carpal tunnel release surgery has not yet been developed, and the effect of the suggested anesthetic techniques on intraoperative complications and the duration of hospitalization has not been investigated.

Pavlin et al. (14) demonstrated that nerve blocks can reduce discharge time in outpatient surgery. Furthermore, several studies have recently shown that peripheral nerve blocks performed for major orthopedic surgery of the lower extremity have beneficial effects on outcome, length of hospital stay, and intraoperative side effects (15–17). However, continuous nerve block techniques were used, and procedures were not performed on outpatients. This retrospective study was designed to assess the effect of three different anesthetic techniques currently used in our institution—IV regional anesthesia (BIER), distal nerve blocks at the wrist, and general anesthesia—on the incidence of intraoperative episodes of tachycardia or bradycardia and hyper- or hypotension, as well as on the duration of postoperative hospitalization for patients undergoing ambulatory carpal tunnel release surgery.

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After approval by the Committee for the Protection of Human Subjects at The University of Texas Medical School at Houston, a retrospective study was performed. Sixty-two consecutive patients were included and divided into three groups according to the anesthetic technique used: Group BIER (n = 20), Group BLOCK (n = 21), and Group GENERAL (n = 21). After premedication with midazolam 1–2 mg IV, patients in Groups BIER and GENERAL were taken directly from the day surgery unit (DSU) to the operating room (OR), and standard ASA monitors (noninvasive blood pressure, electrocardiogram, and pulse oximetry) were attached.

In Group BIER, IV regional anesthesia was performed according to the following technique: additional IV access was established on the extremity scheduled for carpal tunnel release. A tourniquet with two cuffs was placed on the patient’s upper arm. After elevation of the extremity, an Esmarch bandage was used to produce exsanguination. The proximal tourniquet cuff was inflated to a pressure of 250 mm Hg, and 50 mL of lidocaine 0.5% was injected through the IV catheter. After 5 min, the distal tourniquet cuff was inflated to 250 mm Hg, and the proximal cuff was deflated. The quality of the block was evaluated, and when satisfactory analgesia was present, the patient was declared to be ready for surgery.

General anesthesia was induced in patients assigned to Group GENERAL with IV thiopental 3–5 mg/kg or propofol 2 mg/kg combined with fentanyl 1.5–2 μg/kg. After the ability to ventilate was confirmed, the patient received 0.6 mg/kg of rocuronium, and the trachea was intubated. Anesthesia was maintained with isoflurane, fentanyl, and a mixture of nitrous oxide and oxygen (7:3).

Patients assigned to Group BLOCK were taken before surgery to a block room, where they received 1–2 mg of IV midazolam. The median nerve, ulnar nerve, and branches of the musculocutaneous nerve were blocked according to the following technique. To block the median nerve, located lateral to the palmaris longus tendon and medial to the flexor carpi radialis tendon, a 25-mm insulated needle was inserted 6 cm above the wrist crease medial to the flexor carpi radialis tendon, and 8 mL of a mixture of 2% lidocaine and 0.5% bupivacaine (vol/vol) was injected at a depth of approximately 16 mm. To block the ulnar nerve, found medial to the ulnar artery and below the flexor carpi ulnaris tendon, the same needle, this time connected to a nerve stimulator (Stimuplex-DIG; B-Braun Medical, Bethlehem, PA) set up to deliver 1.5 mA, was inserted 6 cm above the wrist crease under the flexor carpi ulnaris tendon. After localization of the ulnar nerve with motor response present at <0.6 mA, 8 mL of the same local anesthetic mixture was injected. Finally, the musculocutaneous nerve branches were blocked by using a subcutaneous injection of 2 mL of the same local anesthetic mixture just proximal to the wrist crease. The quality of the distal nerve blocks at the wrist was assessed with ice. When it was found to be satisfactory, patients were taken to the OR. If required, the surgeon, using 1% lidocaine for local infiltration of the surgical site, completed the analgesia. During surgery, sedation was available for patients in Groups BIER and BLOCK with IV increments of 1 mg of midazolam or 20 mg of propofol. Intraoperative periods of tachycardia, bradycardia, hypertension, and hypotension were documented.

Tachycardia was defined as a heart rate (HR) >130% of baseline or >110 bpm, whereas bradycardia was defined as an HR <70% from baseline or <45 bpm. Hypertension was defined as a systolic arterial blood pressure of >130% from baseline or >160 mm Hg, whereas hypotension was defined as a systolic arterial blood pressure <70% from baseline or <90 mm Hg.

After surgery, awake and oriented patients with sufficient pain control and an uneventful intraoperative course were admitted directly from the OR to the DSU. Patients who could not be directly admitted from the OR to the DSU were admitted to the postoperative anesthesia care unit (PACU) first. As soon as the above-mentioned criteria were fulfilled, the patients were transferred from the PACU to the DSU. Intravenous morphine and oral Vicodin (acetaminophen and hydrocodone) were available in both units for postoperative pain control. OR, surgical, tourniquet, and recovery times were recorded. Recovery time was divided between time spent in the PACU and time spent in the DSU until patients were discharged. The need for postoperative pain treatment with either IV morphine or oral Vicodin was also evaluated.

Differences in demographics among groups were analyzed with a one-way analysis of variance. A Kruskal-Wallis test was used to analyze between-group differences for surgery time, tourniquet time, and recovery time. A Mann-Whitney U-test for paired comparison was performed for significant differences. The percentage differences among groups were analyzed with a χ2 test; α was considered significant at <0.05. Demographics; OR, surgical, tourniquet, and recovery times; and the amount of postoperative morphine consumption are expressed as mean ± sd. The incidences of complications during surgery and recovery time in the PACU, DSU, or both are presented as percentages.

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All patients underwent open carpal tunnel release surgery by one of seven different surgeons. Eighteen anesthesiologists provided general anesthesia in Group GENERAL, IV regional anesthesia in Group BIER, and intraoperative anesthesia care for patients in Group BLOCK. Surgeons and anesthesiologists were distributed equally among groups. Two anesthesiologists experienced in regional anesthesia techniques, using the same standardized approach as described previously, performed the peripheral nerve blocks before surgery. No significant differences in age, weight, sex, or ASA class were observed among the three groups (Table 1). Patients in Group BLOCK had hypertension significantly more often as a preexisting medical condition than patients in both the other groups (Table 1).

Table 1
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As indicated in Figure 1, periods of intraoperative hypotension occurred significantly more often in patients undergoing general anesthesia compared with patients with IV regional anesthesia or distal nerve block. In contrast, the incidence of intraoperative hypertension was significantly more frequent in Group BIER than in the two other groups. No significant difference was observed regarding intraoperative episodes of tachycardia or bradycardia. Overall, there was a significantly less frequent incidence of cardiovascular complications in Group BLOCK compared with Groups BIER and GENERAL (29% vs 50% and 29% vs 67%, respectively). Tourniquet time was significantly shorter in Group BLOCK and Group GENERAL than in Group BIER. In contrast, the surgical time in Group BIER was significantly decreased compared with Group GENERAL, and OR time was significantly shorter in Group BIER than in Groups BLOCK and GENERAL (Fig. 2). Recovery time in the PACU was not necessary in 90% of patients in Group BLOCK and 65% of patients in Group BIER (Fig. 3). These patients were admitted to the DSU immediately after surgery. In contrast, all patients in Group GENERAL were recovered in both units (P < 0.05). Patients in Group BLOCK spent significantly less time in the DSU compared with those in Group GENERAL and spent less time in the hospital after their surgery compared with patients in Groups BIER and GENERAL (Fig. 4). Postoperative pain control was better achieved with IV regional anesthesia (Group BIER) and with distal nerve blocks at the wrist (Group BLOCK) compared with Group GENERAL, as indicated by a significant reduction in the amount of morphine consumed by patients during recovery (1 ± 1 mg versus 6 ± 4 mg and 0 vs 6 ± 4 mg, respectively) and the need for Vicodin after surgery (30% vs 62% and 19% vs 62%, respectively).

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We reviewed three anesthesia techniques used for outpatient carpal tunnel release in our facility. Distal nerve blocks at the wrist allowed for earlier discharge than general anesthesia or IV regional anesthesia. In addition, this approach was also associated with better cardiovascular stability and offered good pain control during recovery.

The use of peripheral nerve blocks has beneficial effects for postoperative outcome after major orthopedic surgery of the lower extremity. Capdevilla et al. (15) reported an 8% reduction in the duration of rehabilitation after total knee replacement, and Singelyn and Gouverneur (16) demonstrated a 19% reduction in the length of hospital stay when femoral nerve blocks were used for perioperative analgesia after total hip replacement. In addition, our own data (17) showed a 20% reduction in length of hospital stay and earlier mobilization with the same technique for patients undergoing total knee replacement. Carpal tunnel release is a short, simple procedure associated with minor surgical trauma. Many different techniques of intraoperative anesthetic management have been suggested, but until now the effect of different techniques on the duration of recovery, length of hospital stay, or incidence of intraoperative complications has not been investigated. Our data indicate that distal nerve blocks reduced the overall time patients spent in our facility to recover after carpal tunnel release surgery by almost one hour compared with patients who received general anesthesia and by 25 minutes compared with patients who had IV regional anesthesia. At first, these reductions may not appear to be remarkable when compared with the days of hospitalization saved after major joint replacement when continuous nerve block techniques are used. However, in a busy day surgery center, one hour can make an appreciable difference, especially at times of nursing staff shortages and cutbacks in hospital budgets. Moreover, 90% of patients with distal nerve blocks did not require admission to the PACU but could be directly admitted to the DSU, whereas 100% of patients undergoing general anesthesia and 35% of patients with IV regional anesthesia recovered in both units. In our institution, the first 90 minutes in the PACU cost more than US$400.00. Under managed care conditions, our data suggest that US$360.00 per patient could be saved if distal nerve blocks at the wrist were used instead of general anesthesia.

Postoperative pain is an important factor influencing length of hospital stay after ambulatory surgery (14). As indicated by the demand for morphine and Vicodin during recovery, IV opioids given during general anesthesia did not provide effective postoperative analgesia for carpal tunnel release surgery. The need for postoperative pain therapy with IV morphine might explain our observation of increased recovery time in these patients. No significant difference was observed in postoperative morphine or Vicodin consumption between those patients with peripheral nerve blocks and those with IV regional anesthesia. However, Atanassoff et al. (10) have shown that IV regional anesthesia provides limited postoperative analgesia when lidocaine is used. The increased incidence of Vicodin consumption with IV regional anesthesia may indicate a trend to superior postoperative analgesia provided by the distal nerve blocks.

Individuals with hypertension as a preexisting medical condition have a more frequent incidence of periods of intraoperative hypotension (18). Therefore, the less frequent incidence of intraoperative hypotension in Group BLOCK when compared with Group GENERAL was a surprising result, given the significantly increased prevalence of hypertension as a preexisting medical condition in Group BLOCK. In our opinion, this result underlines the beneficial effects of the peripheral nerve block technique on intraoperative cardiovascular stability. Rapid changes in blood pressure and HR are risk factors for events of intraoperative myocardial ischemia (19) and postoperative renal and cardial complications (18). Although we did not experience such a severe complication in our patients, individuals at risk would probably benefit from the intraoperative cardiovascular stability offered by the nerve block technique.

In conclusion, we believe that improved cardiovascular stability and reduced duration of postoperative hospitalization are important advantages of using distal nerve blocks for outpatient carpal tunnel release. Therefore, distal nerve blocks at the wrist appear to be a superior anesthetic technique for outpatient carpal tunnel release compared with general or IV regional anesthesia.

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