Interscalene Brachial Plexus Block for Shoulder Surgery: A Proximal Paresthesia Is Effective James J. Roch, MD, Nigel E. Sharrock,
MB, ChB,
and Ludmilla Neudachin,
MB
Department of Anesthesiology, The Hospital for Special Surgery, Cornell University Medical College, New York, New York
This study was designed to determine whether the location of paresthesias is related to the success of interscaleneblocks in providing anesthesia for shoulder surgery. Interscaleneblocks were performed in 45 patients presenting for elective shoulder surgery. Interscalene injections of 33-55 mL of 1.5% mepivacaine with epinephrine were performed after the first elicited paresthesia to the shoulder, arm, forearm, or hand. In 20 patients (45%),the initial elicited paresthesia was to the shoulder, whereas in 25 patients (55%), the first parethesia was reported as distal to the shoulder. All patients developed brachial plexus anesthesia adequate for shoulder surgery. The
T
he interscalene brachial plexus block is a widely used anesthetic technique for surgery of the shoulder and upper arm. In our experience, when this block is performed at the level of C-6, the earliest elicited paresthesia is often to the shoulder. It has been recommended widely in texts of regional anesthesia that shoulder paresthesias not be accepted as an indication that the needle tip is near the plexus and that further needle probing should be performed until a more distal paresthesia is achieved (1-4). Prolonged needle exploration in the neck in search of a distal paresthesia not only delays completion of the block but also may add significantly to patient discomfort. This investigation was undertaken to prospectively evaluate the relative success of interscalene block for shoulder surgery by means of a shoulder versus a more distal first-reported paresthesia.
Methods After institutional approval, 45 unpremedicated patients (aged 17-79 yr) presenting for shoulder surgery Presented in part at the American Society of Anesthesiologists, Annual Meeting, Las Vegas, Nevada, October 1990. Accepted for publication March 31, 1992. Address correspondence to Dr. Roch, Department of Anesthesiology, The Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021.
386
Anesth Analg 1992;75:3W
time-course of onset of motor block as evaluated at the shoulder and elbow was not different between patients with shoulder paresthesias and those with more distal paresthesias. Handgrip strength was quantitatively evaluated with a dynamometer, and both paresthesia groups showed similar decrements in hand strength except at the end of the measurement period, when patients with distal paresthesias had a sigruficantly weaker handgrip than patients with shoulder paresthesias. We recommend that paresthesias to the shoulder be accepted in performing interscalene blocks for patients undergoing shoulder surgery. (Anesth Analg 1992;75:386-8)
were studied. Written, informed consent was obtained from all patients. Interscalene block was performed at the level of C-6 with a 23-gauge, 2.5-cm needle using a paresthetic technique described previously by Winnie (5). Patients were instructed to verbally identify the site of paresthesia as toward the shoulder, upper arm, elbow, forearm, or hand. At the first elicited paresthesia to the shoulder or more distally, patients received a standardized dose (10 mgikg) of bicarbonated 1.5% mepivacaine with epinephrine (3 pg/mL). A paresthesia to the shoulder was classified as “proximal,” whereas a paresthesia to the upper arm, elbow, forearm, or hand was classified as ”distal.” Motor block was assessed by evaluating the patient’s ability to elevate the upper arm at the shoulder, flex the forearm at the elbow, and perform a handgrip maneuver at baseline and every 2 min for 16 min after the interscalene injection. Motor block at the shoulder and elbow was qualitatively evaluated with a four-point scale: baseline motor ability was rated as grade 3; some demonstrable weakness was rated grade 2; marked weakness but with some retained antigravity ability was rated grade 1; and complete loss of antigravity ability was rated grade 0. Handgrip strength was quantitatively evaluated in all patients with a JAMAR dynamometer (JAMAR model 2A3, Asimow Engineering Co., Santa Monica, Calif.). 01992 by the International Anesthesia Research Society 0003-2999/92/$5.00
ANESTH ANALG 1992;75:386-8
REGIONAL ANESTHESIA AND PAIN MANAGEMENT ROCH ET AL. LOCATION OF PARESTHESIA AND INTERSCALENE BRACHIAL PLEXUS BLOCK
Table 1. Surgical Procedures Performed in 45 Patients Undergoing Elective Shoulder Surgery Proximal paresthesia group Open procedures Stabilization Rotator cuff repair Resection clavicular head Arthroscopic procedures Stabilization Acromioplasty Rotator cuff repair Debridement Total
5 2
1 5 3 0 4 20
Table 2. Onset of Motor Block After Interscalene Block Minutes until loss of movement against gravity
Distal paresthesia group 7 3 0 1 2 2 10 25
Elevation of arm at the shoulder
Flexion of forearm at the elbow
P value
Proximal paresthesia
4.4(k2.8) (range 2-10)
7.6 (k5.1)
P < 0.002
(range 2-16)
Distal paresthesia
(range 2-8)
6.5 (24.1) (range 2-16)
NS
NS
3.8 (22.0)
P < 0.001
NS, not significant. Values are mean (~sD); paired t-test.
+ Proximal Paresthesia
100
Patients received no sedation until completion of all measurements. Statistical analysis of data was done by analysis of variance, Scheffk F test, and paired or unpaired t-tests where appropriate.
387
"1
80 -
-El-
Distal Paresthesia
T
70 -
W50 40
-
30-
Results Forty-five interscalene blocks were performed. The first elicited paresthesia was observed to be proximal in 20 patients (45%) and distal in 25 patients (55%). There were no significant differences in age, height, weight, or gender between the proximal and distal paresthesia groups. After interscalene block, each patient developed adequate surgical anesthesia, and in no case was the block repeated or general anesthesia induced. The types of surgical procedures performed were similar in both groups (Table 1). All 45 patients demonstrated complete loss of ability to elevate the upper arm at the shoulder (grade 0 motor ability) by 10 min after the block was administered. The mean time to achieve this degree of motor block was not different between the proximal and distal paresthesia groups ( P > 0.05) (Table 2). Assessment of motor block at the elbow revealed that 44 of 45 patients had complete loss of ability to flex the forearm at the elbow against gravity by the end of the measurement period. The mean time to achieve this degree of motor block at the elbow was not different between the proximal and distal paresthesia groups (P > 0.05) (Table 2). The single patient who failed to achieve a complete motor block at the elbow by 16 min was in the proximal paresthesia group. By 2 min after the interscalene injection, this patient had a complete motor block at the shoulder and only grade 1 motor ability at the elbow; however, he retained weak antigravity motion at the elbow at the end of the measurement period. In both the proximal and distal paresthesia groups, motor block (grade 0
2010
-
0-10'
I
2
4
6
8
10
12
14
16
Time (minutes) Figure 1. The decline in handgrip strength after interscalene block. Both proximal and distal paresthesia groups demonstrated decreases in handgrip strength by 2 min after block ( P = 0.001), which continued to significantly decline through the measurement period ( P = 0.0001; analysis of variance for two-factor repeated measures). Proximal and distal paresthesia groups had similar decreases in handgrip except at 14 and 16 min after block, when the distal paresthesia group demonstrated a Significantly greater decrement in handgrip (P = 0.03; Scheff6 F test). *P < 0.02 vs proximal paresthesia.
motor ability) at the shoulder significantly preceded motor block at the elbow (Table 2). Handgrip strength was reliably reduced by 2 min after interscalene injection among all patients (P = 0.0001). The proximal and distal paresthesia groups showed similar reductions in handgrip strength throughout the measurement period except at 14 and 16 min after the injection, when the distal paresthesia group showed a significantly weaker handgrip than the proximal group ( P = 0.03) (Figure 1).
Discussion The most significant finding in our study is that each interscalene block performed after the elicitation of a shoulder paresthesia resulted in profound brachial
388
REGIONAL ANESTHESIA AND PAIN MANAGEMENT ROCH ET AL. LOCATION OF PARESTHESIA AND INTERSCALENE BRACHIAL PLEXUS BLOCK
plexus anesthesia. The explanation most commonly cited as to why shoulder paresthesias are unacceptable is that such a proximal paresthesia could theoretically result from needle stimulation of the suprascapular nerve after it has exited the fascial sheath that envelops the brachial plexus (4). If this occurs, any local anesthetic deposited would be expected to result in a selective block of the suprascapular nerve. Because the suprascapular nerve has no cutaneous innervation and provides motor innervation only to the supraspinous and infraspinous muscles, such a block would be easily discernible from a brachial plexus block. In the present study, when shoulder paresthesias were accepted such a selective blockade of the suprascapular nerve was never observed to occur. The observation that 45% of initial paresthesias were to the shoulder underscores the clinical relevance of evaluating the reliability of proximal paresthesias when interscalene blocks are performed. Because we looked solely at the initial elicited paresthesia, a necessary conclusion is that in our study, almost half of the interscalene blocks were successfully completed more quickly because we accepted a shoulder paresthesia rather than continuing to pursue a more distal paresthesia. In addition, because multiple needle insertions may possibly result in nerve trauma, one may speculate that by accepting a proximal paresthesia and avoiding prolonged needle probing, the patient may be exposed to a reduced risk of postinjection nerve damage. For this study, mepivacaine was used for interscalene blocks, because we have found this local anesthetic provides adequate duration of anesthesia for most shoulder procedures as well as rapid return of function after surgery. Because much of our shoulder surgery is performed on an ambulatory basis, this allows for early postoperative assessment of nerve function as well as determination of adequacy of pain relief before discharge. Although the dose of mepivacaine used was relatively large (10 mgkg), we have found this to be a safe and effective dose for brachial plexus blocks, as have other authors (6). In this study, we assessed brachial plexus block by evaluating the onset of motor rather than sensory blockade to allow us to use an objective measure of neural blockade (the dynamometer). In addition,
ANESTH ANALG 1992;75:386-8
because motor blockade often precedes sensory blockade (7), monitoring motor function allowed rapid completion of our measurements so as to minimize delay in preparation of patients for surgery. The observed sequential onset of motor blockade from proximal to more distal musculature has been described previously (8). The fact that there was little difference in the time-course of motor blockade between the proximal and distal paresthesia groups is compatible with the concept that in both situations, local anesthetic was deposited within the fascial sheath at approximately the same level (C-6). The slight difference in measured handgrip strength between the proximal and distal paresthesia groups near the end of the measurement period is not easily explained. It is possible that a more profound distal block results after a distal paresthesia and that this could have clinical implications when interscalene blocks are performed for more distal surgical procedures. In summary, it was observed that during the performance of interscalene brachial plexus blocks, almost half of the initial elicited paresthesias were toward the shoulder and that in all cases, use of these proximal paresthesias resulted in brachial plexus anesthesia, which was satisfactory for shoulder surgery. We therefore recommend that paresthesias toward the shoulder be accepted in the performance of interscalene blocks for surgical procedures involving the shoulder.
References 1. Raj PP. Practical management of pain. Chicago: Year Book, 1986:610. 2. Wildsmith JA, Armitage E. Principles and practice of regional anesthesia. New York Churchill-Livingstone,1987344. 3. Scott DB. Techniques of regional anaesthesia. East Nonvalk, Connecticut: Appleton & Lange, 1989:92. 4. Winnie AP. Plexus anesthesia. Philadelphia: WB Saunders, 1990:176. 5. Winnie AP. Interscalene brachial plexus block. Anesth Analg 1970;49:455-66. 6. Cockings E, Moore PL, Lewis RC. Transarterial brachial plexus blockade using high doses of 1.5% mepivacaine. Reg Anesth 1987;lZ:159-64. 7. Winnie AP, Tay CH, Pate1 KP, Ramamurthy S, Durrani Z. Pharmacokinetics of local anesthetics during plexus blocks. Anesth Analg 1977;56:852-61. 8. deJong RH. Local anesthetics. Springfield, Illinois: Charles C Thomas, 197765-71.
MB, ChB,
and Ludmilla Neudachin,
MB
Department of Anesthesiology, The Hospital for Special Surgery, Cornell University Medical College, New York, New York
This study was designed to determine whether the location of paresthesias is related to the success of interscaleneblocks in providing anesthesia for shoulder surgery. Interscaleneblocks were performed in 45 patients presenting for elective shoulder surgery. Interscalene injections of 33-55 mL of 1.5% mepivacaine with epinephrine were performed after the first elicited paresthesia to the shoulder, arm, forearm, or hand. In 20 patients (45%),the initial elicited paresthesia was to the shoulder, whereas in 25 patients (55%), the first parethesia was reported as distal to the shoulder. All patients developed brachial plexus anesthesia adequate for shoulder surgery. The
T
he interscalene brachial plexus block is a widely used anesthetic technique for surgery of the shoulder and upper arm. In our experience, when this block is performed at the level of C-6, the earliest elicited paresthesia is often to the shoulder. It has been recommended widely in texts of regional anesthesia that shoulder paresthesias not be accepted as an indication that the needle tip is near the plexus and that further needle probing should be performed until a more distal paresthesia is achieved (1-4). Prolonged needle exploration in the neck in search of a distal paresthesia not only delays completion of the block but also may add significantly to patient discomfort. This investigation was undertaken to prospectively evaluate the relative success of interscalene block for shoulder surgery by means of a shoulder versus a more distal first-reported paresthesia.
Methods After institutional approval, 45 unpremedicated patients (aged 17-79 yr) presenting for shoulder surgery Presented in part at the American Society of Anesthesiologists, Annual Meeting, Las Vegas, Nevada, October 1990. Accepted for publication March 31, 1992. Address correspondence to Dr. Roch, Department of Anesthesiology, The Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021.
386
Anesth Analg 1992;75:3W
time-course of onset of motor block as evaluated at the shoulder and elbow was not different between patients with shoulder paresthesias and those with more distal paresthesias. Handgrip strength was quantitatively evaluated with a dynamometer, and both paresthesia groups showed similar decrements in hand strength except at the end of the measurement period, when patients with distal paresthesias had a sigruficantly weaker handgrip than patients with shoulder paresthesias. We recommend that paresthesias to the shoulder be accepted in performing interscalene blocks for patients undergoing shoulder surgery. (Anesth Analg 1992;75:386-8)
were studied. Written, informed consent was obtained from all patients. Interscalene block was performed at the level of C-6 with a 23-gauge, 2.5-cm needle using a paresthetic technique described previously by Winnie (5). Patients were instructed to verbally identify the site of paresthesia as toward the shoulder, upper arm, elbow, forearm, or hand. At the first elicited paresthesia to the shoulder or more distally, patients received a standardized dose (10 mgikg) of bicarbonated 1.5% mepivacaine with epinephrine (3 pg/mL). A paresthesia to the shoulder was classified as “proximal,” whereas a paresthesia to the upper arm, elbow, forearm, or hand was classified as ”distal.” Motor block was assessed by evaluating the patient’s ability to elevate the upper arm at the shoulder, flex the forearm at the elbow, and perform a handgrip maneuver at baseline and every 2 min for 16 min after the interscalene injection. Motor block at the shoulder and elbow was qualitatively evaluated with a four-point scale: baseline motor ability was rated as grade 3; some demonstrable weakness was rated grade 2; marked weakness but with some retained antigravity ability was rated grade 1; and complete loss of antigravity ability was rated grade 0. Handgrip strength was quantitatively evaluated in all patients with a JAMAR dynamometer (JAMAR model 2A3, Asimow Engineering Co., Santa Monica, Calif.). 01992 by the International Anesthesia Research Society 0003-2999/92/$5.00
ANESTH ANALG 1992;75:386-8
REGIONAL ANESTHESIA AND PAIN MANAGEMENT ROCH ET AL. LOCATION OF PARESTHESIA AND INTERSCALENE BRACHIAL PLEXUS BLOCK
Table 1. Surgical Procedures Performed in 45 Patients Undergoing Elective Shoulder Surgery Proximal paresthesia group Open procedures Stabilization Rotator cuff repair Resection clavicular head Arthroscopic procedures Stabilization Acromioplasty Rotator cuff repair Debridement Total
5 2
1 5 3 0 4 20
Table 2. Onset of Motor Block After Interscalene Block Minutes until loss of movement against gravity
Distal paresthesia group 7 3 0 1 2 2 10 25
Elevation of arm at the shoulder
Flexion of forearm at the elbow
P value
Proximal paresthesia
4.4(k2.8) (range 2-10)
7.6 (k5.1)
P < 0.002
(range 2-16)
Distal paresthesia
(range 2-8)
6.5 (24.1) (range 2-16)
NS
NS
3.8 (22.0)
P < 0.001
NS, not significant. Values are mean (~sD); paired t-test.
+ Proximal Paresthesia
100
Patients received no sedation until completion of all measurements. Statistical analysis of data was done by analysis of variance, Scheffk F test, and paired or unpaired t-tests where appropriate.
387
"1
80 -
-El-
Distal Paresthesia
T
70 -
W50 40
-
30-
Results Forty-five interscalene blocks were performed. The first elicited paresthesia was observed to be proximal in 20 patients (45%) and distal in 25 patients (55%). There were no significant differences in age, height, weight, or gender between the proximal and distal paresthesia groups. After interscalene block, each patient developed adequate surgical anesthesia, and in no case was the block repeated or general anesthesia induced. The types of surgical procedures performed were similar in both groups (Table 1). All 45 patients demonstrated complete loss of ability to elevate the upper arm at the shoulder (grade 0 motor ability) by 10 min after the block was administered. The mean time to achieve this degree of motor block was not different between the proximal and distal paresthesia groups ( P > 0.05) (Table 2). Assessment of motor block at the elbow revealed that 44 of 45 patients had complete loss of ability to flex the forearm at the elbow against gravity by the end of the measurement period. The mean time to achieve this degree of motor block at the elbow was not different between the proximal and distal paresthesia groups (P > 0.05) (Table 2). The single patient who failed to achieve a complete motor block at the elbow by 16 min was in the proximal paresthesia group. By 2 min after the interscalene injection, this patient had a complete motor block at the shoulder and only grade 1 motor ability at the elbow; however, he retained weak antigravity motion at the elbow at the end of the measurement period. In both the proximal and distal paresthesia groups, motor block (grade 0
2010
-
0-10'
I
2
4
6
8
10
12
14
16
Time (minutes) Figure 1. The decline in handgrip strength after interscalene block. Both proximal and distal paresthesia groups demonstrated decreases in handgrip strength by 2 min after block ( P = 0.001), which continued to significantly decline through the measurement period ( P = 0.0001; analysis of variance for two-factor repeated measures). Proximal and distal paresthesia groups had similar decreases in handgrip except at 14 and 16 min after block, when the distal paresthesia group demonstrated a Significantly greater decrement in handgrip (P = 0.03; Scheff6 F test). *P < 0.02 vs proximal paresthesia.
motor ability) at the shoulder significantly preceded motor block at the elbow (Table 2). Handgrip strength was reliably reduced by 2 min after interscalene injection among all patients (P = 0.0001). The proximal and distal paresthesia groups showed similar reductions in handgrip strength throughout the measurement period except at 14 and 16 min after the injection, when the distal paresthesia group showed a significantly weaker handgrip than the proximal group ( P = 0.03) (Figure 1).
Discussion The most significant finding in our study is that each interscalene block performed after the elicitation of a shoulder paresthesia resulted in profound brachial
388
REGIONAL ANESTHESIA AND PAIN MANAGEMENT ROCH ET AL. LOCATION OF PARESTHESIA AND INTERSCALENE BRACHIAL PLEXUS BLOCK
plexus anesthesia. The explanation most commonly cited as to why shoulder paresthesias are unacceptable is that such a proximal paresthesia could theoretically result from needle stimulation of the suprascapular nerve after it has exited the fascial sheath that envelops the brachial plexus (4). If this occurs, any local anesthetic deposited would be expected to result in a selective block of the suprascapular nerve. Because the suprascapular nerve has no cutaneous innervation and provides motor innervation only to the supraspinous and infraspinous muscles, such a block would be easily discernible from a brachial plexus block. In the present study, when shoulder paresthesias were accepted such a selective blockade of the suprascapular nerve was never observed to occur. The observation that 45% of initial paresthesias were to the shoulder underscores the clinical relevance of evaluating the reliability of proximal paresthesias when interscalene blocks are performed. Because we looked solely at the initial elicited paresthesia, a necessary conclusion is that in our study, almost half of the interscalene blocks were successfully completed more quickly because we accepted a shoulder paresthesia rather than continuing to pursue a more distal paresthesia. In addition, because multiple needle insertions may possibly result in nerve trauma, one may speculate that by accepting a proximal paresthesia and avoiding prolonged needle probing, the patient may be exposed to a reduced risk of postinjection nerve damage. For this study, mepivacaine was used for interscalene blocks, because we have found this local anesthetic provides adequate duration of anesthesia for most shoulder procedures as well as rapid return of function after surgery. Because much of our shoulder surgery is performed on an ambulatory basis, this allows for early postoperative assessment of nerve function as well as determination of adequacy of pain relief before discharge. Although the dose of mepivacaine used was relatively large (10 mgkg), we have found this to be a safe and effective dose for brachial plexus blocks, as have other authors (6). In this study, we assessed brachial plexus block by evaluating the onset of motor rather than sensory blockade to allow us to use an objective measure of neural blockade (the dynamometer). In addition,
ANESTH ANALG 1992;75:386-8
because motor blockade often precedes sensory blockade (7), monitoring motor function allowed rapid completion of our measurements so as to minimize delay in preparation of patients for surgery. The observed sequential onset of motor blockade from proximal to more distal musculature has been described previously (8). The fact that there was little difference in the time-course of motor blockade between the proximal and distal paresthesia groups is compatible with the concept that in both situations, local anesthetic was deposited within the fascial sheath at approximately the same level (C-6). The slight difference in measured handgrip strength between the proximal and distal paresthesia groups near the end of the measurement period is not easily explained. It is possible that a more profound distal block results after a distal paresthesia and that this could have clinical implications when interscalene blocks are performed for more distal surgical procedures. In summary, it was observed that during the performance of interscalene brachial plexus blocks, almost half of the initial elicited paresthesias were toward the shoulder and that in all cases, use of these proximal paresthesias resulted in brachial plexus anesthesia, which was satisfactory for shoulder surgery. We therefore recommend that paresthesias toward the shoulder be accepted in the performance of interscalene blocks for surgical procedures involving the shoulder.
References 1. Raj PP. Practical management of pain. Chicago: Year Book, 1986:610. 2. Wildsmith JA, Armitage E. Principles and practice of regional anesthesia. New York Churchill-Livingstone,1987344. 3. Scott DB. Techniques of regional anaesthesia. East Nonvalk, Connecticut: Appleton & Lange, 1989:92. 4. Winnie AP. Plexus anesthesia. Philadelphia: WB Saunders, 1990:176. 5. Winnie AP. Interscalene brachial plexus block. Anesth Analg 1970;49:455-66. 6. Cockings E, Moore PL, Lewis RC. Transarterial brachial plexus blockade using high doses of 1.5% mepivacaine. Reg Anesth 1987;lZ:159-64. 7. Winnie AP, Tay CH, Pate1 KP, Ramamurthy S, Durrani Z. Pharmacokinetics of local anesthetics during plexus blocks. Anesth Analg 1977;56:852-61. 8. deJong RH. Local anesthetics. Springfield, Illinois: Charles C Thomas, 197765-71.
