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Anesth Analg 1999;89:1482
© 1999 International Anesthesia Research Society

REGIONAL ANESTHESIA AND PAIN MANAGEMENT

Quantitative Comparison of Leakage Under the Tourniquet in Forearm Versus Conventional Intravenous Regional Anesthesia

Margaret M. Coleman, FFARCSI*, Philip W. Peng, FRCPC*, Joan M. Regan, FFARCSI*, Vincent W. S. Chan, FRCPC*, and Aaron L. Hendler, FRCPC{dagger}

*Department of Anesthesia and {dagger}Division of Nuclear Medicine, University of Toronto, The Toronto Hospital, Toronto, Canada

Address correspondence and reprint requests to Dr. Philip Peng, Department of Anesthesia, The Toronto Hospital, Western Division, 399 Bathurst St., Toronto M5T 2S8, Canada. Address e-mail to ppeng{at}torhosp.toronto.on.ca


   Abstract
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 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
We compared the quantitative leakage between forearm and conventional IV regional anesthesia (IVRA). Forearm IVRA remains unpopular because of the theoretical risk of local anesthetic leakage through the interosseous vessels. IVRA was simulated on the forearm or arm during two separate, randomized sessions using a double tourniquet in 14 volunteers. A radiolabeled substance, DISIDA (99m Tc-disofenin) with a structure similar to lidocaine, was injected instead of local anesthetic. Volumes of 0.4 mL/kg (maximum 25 mL), were used for forearm IVRA and 0.6 mL/kg (maximum 45 mL) for conventional IVRA. A {gamma} camera recorded radioactivity levels in the limb distal to the tourniquet every 30 s while the tourniquet was inflated (25 min) and for 20 min postdeflation. The leakage of radiolabeled substance during inflation was similar in both groups, 6% ± 12% (mean ± SD) from the forearm and 10% ± 20% from the upper arm. After deflation, mean loss of radioactivity was higher in conventional IVRA, 70% ± 7% vs 57% ± 11% and 82% ± 5% vs 69% ± 11% at 3 and 20 min, respectively (P < 0.001). We conclude that forearm IVRA results in tourniquet leakage comparable to conventional IVRA and is potentially safer because the required dose of local anesthetic is smaller.

Implications: Using a tourniquet on the forearm for IV regional anesthesia does not increase the risk of drug leakage. This is potentially a safer technique compared with conventional IV regional anesthesia because a much smaller dose of local anesthetic is required.


   Introduction
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 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
IV regional anesthesia (IVRA) or Bier’s block is one of the most popular methods of anesthesia for hand surgery used worldwide. It is safe, cost effective, and technically easy to perform. However, conventional IVRA has some disadvantages, including the potential for local anesthetic toxicity and lack of postoperative analgesia. Lidocaine, at a dose of 3 mg/kg often results in mild toxic symptoms after deflation of the tourniquet (1). Major toxic effects, albeit rare, can occur despite an adequate tourniquet time (2,3). Numerous adjuvant therapies have been studied (nonsteroidal antiinflammatory drugs, opioids, muscle relaxants) (4–6) in an attempt to minimize the potential for systemic toxicity, but the most reliable method appears to be minimizing the actual dose of local anesthetic.

Forearm IVRA allows the dose of local anesthetic to be decreased by up to 50% without affecting the quality of the analgesia (7–9). However, this technique was unpopular in the past because of the perceived leakage of local anesthetic into the circulation via the interosseous vessels (10). It is thought that these vessels may not be occluded by the tourniquet because of the biosseous structure of the forearm, thus increasing the possibility of local anesthetic toxicity and block failure. This theoretical leakage has not been substantiated in any study.

No quantitative analysis or comparison of leakage under a forearm tourniquet compared with the upper arm has been performed to date. The aim of our study was to quantify and compare the leakage of a radiolabeled substance under the tourniquet during simulated IVRA of the forearm and upper arm, in the same subjects.


   Methods
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 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
After institutional ethics committee approval and informed consent, a prospective randomized trial was conducted on 14 healthy volunteers, five women, and nine men, each volunteer acting as his or her own control.

Exclusion criteria included pregnancy, allergic reactions to dyes, and any coagulation disorder. Features such as height, weight, and arm circumference at midtourniquet level were measured. Blood pressure and heart rate were measured before beginning the study and every 5 min throughout the procedure. IVRA was simulated, once in the upper arm and once in the forearm, on two separate occasions. The sequence of the type of IVRA (upper arm or forearm) for each session was allocated randomly and separated by at least 1 wk.

For each session, a 22-gauge cannula was inserted into the dorsum of the nondominant hand. A 14-cm double tourniquet (Zimmer, Worthington, OH) was then placed either on the upper arm or 1 cm below the medial epicondyle on the forearm. Radiolabeled DISIDA (99m Tc-disofenin), a compound often used in biliary tract imaging, was used to simulate the local anesthetic drug (Figure 1) because it has a structure similar to lidocaine (11). A dose of 0.1 mg, labeled with 100 µCi of 99mTc was diluted with normal saline. The volume used was 0.6 mL/kg to a maximum of 45 mL for the upper-arm IVRA and 0.4 mL/kg, to a maximum of 25 mL for the forearm (7). The arm was elevated and a 10-cm Esmarch bandage was wrapped tightly around the hand and arm. After exsanguination, the tourniquet was inflated to 100 mm Hg greater than systolic blood pressure to a minimum of 250 mm Hg. The DISIDA solution was then administered slowly via the cannula over 3 min. Immediately after injection, a {gamma} camera began recording radioactivity levels in the limb at 30-s intervals for the 25 min of tourniquet inflation and for 20 min posttourniquet deflation (Figure 2).



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  		Figure 1. Molecular structure of 99mTc-disofenin (DISIDA).

 


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  		Figure 2. Gamma camera pictures of the radioactivity emitted throughout the study procedure in one subject (9). Frame A is taken immediately after injection of DISIDA (99mTc-disofenin) and frame B is at the end of the procedure. The tourniquet was released after frame Y.

 
Leakage was determined by measuring the amount of radioactivity that remained in the arm or forearm distal to the tourniquet; the percentage leak was calculated using the formula:


(the maximum being the radioactivity values obtained immediately postinjection and the minimal values those taken just before tourniquet deflation). Radioactivity levels were also assessed at 3 and 20 min after tourniquet deflation and the percentage of leakage was calculated. Leakage in this instance indicates the total amount of radiolabeled substance that has passed under the tourniquet at these two time points. All values were corrected for background radiation and natural decay.

The sample size was determined assuming a paired design in which forearm and arm tourniquets would be applied to each volunteer on two separate occasions. To have an 80% probability of detecting a difference between population means, as small as 15% of radioactive leakage, between the arm and forearm tourniquets (ß = 0.2), and testing at the 0.05 level ({alpha} = 0.05), the sample size was found to be 14 patients. The hypothesis was tested using a paired t-test. Data are presented as mean ± SD percent. Statistical significance was assumed to be achieved at P < 0.05.


   Results
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 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
All volunteers were ASA I–II, aged between 22 and 41 yr and weighing between 58 and 92 kg. The measured arm circumferences ranged from 26 to 33 cm and forearm circumferences ranged from 24 to 33 cm. The individual values of percentage leakage in each volunteer in both the upper-arm and forearm studies are shown in Figure 3. There is no significant difference between the leakage in the forearm, 6% ± 12% (mean ± SD), versus the upper arm, 10% ± 20%.



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  		Figure 3. Individual values for leakage of radiolabeled substance under the tourniquet in the forearm versus the upper arm in 14 volunteers.

 
Three minutes after tourniquet deflation, a mean leakage of 59% ± 11% was recorded when the forearm tourniquet was used and 70% ± 7% when the arm tourniquet was used, this difference being statistically significant (P < 0.001). Likewise at 20 min postdeflation, a leakage of 69% ± 11% and 82% ± 5% was noted in forearm and arm studies, respectively. Leakage under the tourniquet during inflation undertook a linear pattern with a sharp falloff once the pressure was released (Figure 4). There was no obvious correlation between arm circumference and percentage of leakage.



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  		Figure 4. Radioactivity counts emitted from the forearm, distal to the tourniquet, in one study subject (9). The point X denotes tourniquet deflation. The x axis represents time in seconds/10.

 
No subject developed a rise in blood pressure >20% of their baseline level; however, one subject (Figure 3) was hypertensive at the commencement of the study, necessitating appropriate adjustment of the tourniquet pressures. This subject had an appearance of limb congestion during both study periods and analysis revealed a 46% and 76% leakage from the forearm and upper arm, respectively.


   Discussion
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 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
This study shows that venous leakage under the tourniquet in forearm IVRA is similar to that of conventional, upper-arm IVRA. This is in contrast to the generally held belief that forearm IVRA will result in greater leakage of local anesthetic into the systemic circulation via the interosseous vessels.

Assessment of leakage from conventional IVRA in previous studies may have been prone to certain pitfalls. Peripheral venous or arterial local anesthetic levels were measured during tourniquet inflation in conventional IVRA (12–14); however, studies like these do not account for the degree of drug metabolism, distribution, uptake, or elimination which may alter the final result. Likewise, multiple hemodynamic factors play a role in determining the rate of dilution of venous blood in the systemic blood flow. Similarly, when samples are taken from distal sites, e.g., the opposite arm, the drug levels attained may not accurately reflect the concentration of drug that reached the brain in the arterial system. It is this plasma level of drug in the cerebral circulation that best correlates with the severity of toxicity (13). Other studies measured the amount of labeled compound (15) or radiographic contrast (16,17) that leaked into the circulation during tourniquet inflation, but these were not quantitative.

Similar criticisms can be aimed at studies evaluating leakage under a forearm cuff because these have been performed in a similar manner. However, despite these pitfalls, serum venous lidocaine levels taken from the contralateral arm during forearm IVRA were very low—a mean of 0.26 µg/mL during tourniquet inflation and a maximal mean of 0.75 µg/mL, 15 minutes postdeflation (7). This is compared with levels recorded after conventional IVRA where, depending on the technique and assays used, the level of lidocaine in venous blood after tourniquet release varies from 1.2 to 6 µg/mL (1,18). Mild toxic effects are seen at 5 µg/mL, becoming more serious at 10 µg/mL (10). The perceived large leakage through the interosseous system has not been quantified or clinically substantiated (8,9).

Radiolabeled DISIDA, with its chemical structure similar to lidocaine, is well established in biliary tract imaging (11). Lillie et al. (19) used radiolabeled technetium pertechnetate, injected in upper-arm IVRA and measured the amount of radioactivity in the opposite arm. By direct measurement of the radioactivity in the arm undergoing IVRA, the leakage is quantified more precisely. To our knowledge, this is the first quantitative study comparing the leakage from the forearm with the upper arm. All results were controlled for background radiation and natural decay.

Studies involving the quantitative analysis of leakage are scant. Hoffmann et al. (20) compared the quantity of leakage from upper-arm IVRA and lower limb IVRA, using radiolabeled HIDA 123 N-(2,6 dimethylphenylcarbonylmethyl) imino-diacetic acid 125. This study revealed a mean leak of 15% ± 5% in the upper arm, comparable to our study with a leakage of 10% ± 12%. A leakage of 29% ± 8% occurred from under the lower limb tourniquet, positioned around the calf. The higher leakage from the lower limb was thought to be a result of the biosseous structure of the leg; a similar theory was popular regarding a possible large leakage from the forearm.

One possible criticism of our study is that it does not address arterial leakage that results in the inflow of blood into the limb. Arteries are perhaps less likely to be occluded by a tourniquet surrounding a biosseous structure such as the forearm. Arterial leakage, which can result in congestion and oozing, is relevant primarily for good surgical conditions. However, if the inflow of blood is substantial, the maximal venous pressure may be reached with resultant leakage of drug into the systemic circulation. Nevertheless, it is difficult to measure precisely this arterial leakage.

One volunteer developed some limb congestion at both sessions. All precautions were taken throughout the study to minimize leakage: a distal IV cannula was used, thorough exsanguination was performed using an Esmarch bandage, and the drug was injected slowly over a three-minute period. Interestingly, in addition to limb congestion, this volunteer demonstrated an upper-arm leakage of 76% and a forearm leakage of 47%. It is our opinion that this occurred because the volunteer was hypertensive. We used a double tourniquet to simulate actual clinical practice, and by anatomic necessity, each cuff can only be five to six centimeters wide. The effective tourniquet pressure (i.e., the pressure transmitted to the underlying arteries and veins) with these narrow tourniquets can be as much as 80–100 mm Hg lower than tourniquet pressure (i.e., that registered on the tourniquet apparatus) (15). At the outset of both sessions, this volunteer was hypertensive, with systolic pressures ranging from 160–170 mm Hg. Tourniquet pressures wereadjusted accordingly at the commencement of each study; however, unrecorded surges of systolic hypertension throughout the period of tourniquet inflation may have resulted in the effective tourniquet pressure being exceeded with subsequent leakage.

Interestingly, in that same volunteer, the leakage was much higher from the upper arm than from the forearm. If this were a clinical scenario using lidocaine, the risk of local anesthetic toxicity from the upper arm would be quite high. Assuming the use of 40 milliliters of 0.5% lidocaine, a leakage of 76% may lead to toxicity, with the possibility of serious cardiovascular or central nervous system effects. Because only half the conventional dose of lidocaine is used in forearm IVRA, a leakage of 50% should be of little consequence. In hypertensive patients, the literature recommends caution in the use of all forms of IVRA, with consideration for the use of tourniquet pressures of 300 mm Hg, or use of a wider tourniquet, which eliminates blood flow at lower inflation pressures (21), or perhaps a single cuff which shows a discrepancy of only 10%–15% between the effective and registered tourniquet pressures (15).

Hoffmann et al. (20) found that three minutes after tourniquet release there was a very large decrease in radioactivity in the upper limb. In our study, the percentage loss of radiolabeled material in the three-minute period after tourniquet release was significantly higher in the upper arm than in the forearm, 70% ± 7% vs 57% ± 11%, respectively. When the total leakage at three minutes after deflation is corrected for the amount that leaked during the inflation period, the result remains the same. Peak levels of local anesthetic are reached in both arterial (22) and venous blood in the first three to five minutes after tourniquet release (10,23), decreasing rapidly thereafter (13,14,22). This is followed by a slower release of substance over a number of hours. Minimizing the release into the systemic circulation lowers the risk of toxicity if local anesthetic is used.

Similarly, 20 minutes after tourniquet release, a significantly higher percentage of substance had leaked from the upper arm than the forearm 82% ± 5% vs 69% ± 11%, respectively (P < 0.001). Although there is no satisfactory explanation to account for this phenomenon, this implies that drugs administered in IVRA will remain in the forearm tissues longer with this form of IVRA. If local anesthetic is used, this may result in a longer duration of pain relief.

Forearm IVRA is an effective method of anesthesia with success rates of 93% to 96% (7,9). The dose of local anesthetic necessary for successful blockade is approximately 50% smaller than in upper-arm IVRA. The ability to decrease the local anesthetic enables a larger safety margin in the use of local anesthetics. Lack of postoperative analgesia remains a problem in lidocaine-induced IVRA. Bupivacaine provided several hours of analgesia after tourniquet deflation; however, several deaths occurred secondary to its cardiotoxic effects (24). Ropivacaine, a newer long-acting local anesthetic, with a lower potential for cardiotoxicity, may be suitable for use in this setting and in preliminary studies has provided superior analgesia in conventional IVRA (25). The use of as small as 50% of the conventional dose for forearm IVRA should result in both an increased margin of safety and prolonged pain relief postoperatively.

In conclusion, leakage under the tourniquet from forearm and upper-arm IVRA is similar. A larger bolus of drug enters the circulation on tourniquet release in upper-arm IVRA than in forearm IVRA, both at 3 and 20 minutes after deflation. With lower dosage requirements, forearm IVRA increases the safety margin of this technique.


   Acknowledgments
 
We wish to thank Dr. H. El-Beheiry for his kind help in the preparation of this manuscript.


   Footnotes
 
Presented at the 56th Annual meeting of the Canadian Anesthesiologists’ Society, Calgary, Alberta, June 18–22, 1999.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

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Accepted for publication July 20, 1999.




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Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins and Stanford University Libraries' HighWire Press®. Copyright 1999 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press