Application of the Pneumatic Tourniquet
Apply the double pneumatic tourniquet (Figure 127-2). Place one cuff high on the upper arm. Place the second cuff above the angiocatheter and just below the proximal cuff. Elevate the arm. Tightly apply a rubber Esmarch bandage spirally around the arm, starting at the hand and terminating at the distal cuff of the double tourniquet (Figure 127-3). The process of arm elevation followed by the application of an Esmarch bandage exsanguinates the arm. Place the tourniquets about the elbow and proximal forearm for procedures of the hand, wrist, and distal forearm (Figure 127-4).
Preparatory steps. An angiocatheter is inserted into a dorsal hand vein. The double tourniquet is applied to the upper arm after the application of protective padding.
Exsanguination of the arm. The patient's arm is elevated and an Esmarch bandage is tightly applied.
A modified setup for procedures involving the hand, wrist, and distal forearm.
Apply digital pressure to occlude the axillary artery. Inflate the proximal cuff of the double tourniquet to 50 to 100 mmHg above the patient's systolic blood pressure. Wrap tape around the tourniquet to ensure there is not failure of the Velcro and it spontaneously opens, allowing the local anesthetic solution to access the central circulation. It is important to compress the axillary artery both before and during the inflation of the pneumatic tourniquet. Venous outflow is prevented before arterial inflow is occluded as the pressure in the tourniquet rises. Exsanguination of the extremity may be incomplete without occlusion of the arterial inflow before the tourniquet is inflated. Remove the Esmarch bandage.
Injection of the Local Anesthetic Agent
Slowly inject 30 to 50 mL, maximum 3 mg/kg, of 0.5% lidocaine hydrochloride. The precise volume depends upon the size of the arm being anesthetized and the maximal anesthetic dose based upon the patient's weight (Table 123-1). Slow and controlled injection rates are an absolute necessity to avoid the development of elevated venous pressures. The onset of anesthesia should begin in approximately 5 to 7 minutes. Inflate the distal cuff to 50 to 100 mmHg above the patient's systolic blood pressure approximately 25 to 30 minutes after the onset of anesthesia. Wrap tape around the tourniquet to ensure there is not failure of the Velcro and it spontaneously opens, allowing the local anesthetic solution to access the central circulation. Remove the tape on the proximal cuff. Slowly deflate the proximal cuff to prevent a rush of local anesthetic solution back into the central circulation. Deflation of the proximal cuff will minimize the development of tourniquet pain. Begin the procedure for which the IVRA was performed.
The usual dose of lidocaine to administer is approximately 3 mg/kg. This is a relatively large dose in terms of potential systemic toxicity. Systemic toxic reactions can and do occur due to leakage past the tourniquet, sudden accidental deflation of the tourniquet during the procedure, or intentional deflation following brief surgical procedures.8,9 Opiate receptors have been discovered in the peripheral nervous system.10,11 It has been demonstrated that opioids may produce effective, long-lasting analgesia when injected with local anesthetics for brachial plexus blockade.12–16 Several investigators have attempted to decrease the potential for lidocaine toxicity by adding opioids in order to reduce the volume of lidocaine. Although it has not been proven, it appears that the addition of fentanyl to lidocaine for IVRA results in improved analgesia while reducing the risks of lidocaine toxicity.17,18 Other investigators have found that adding an opioid and a muscle relaxant to 0.25% lidocaine provides the same analgesia and muscular relaxation as 0.5% lidocaine alone and reduces the likelihood of systemic toxicity.
Adjuvants added to 0.25% lidocaine have included 50 μg of fentanyl plus 0.5 mg of pancuronium, fentanyl plus rocuronium, and fentanyl plus D-tubocurarine.19–22 The authors reported outstanding operating conditions in each of these cases. The lidocaine concentration was reduced in half to 0.25% and the potential for systemic toxicity was also halved. A small dose of any nondepolarizing muscle relaxant may be chosen as an adjunct to the local anesthetic. Avoid using D-tubocurarine as it releases histamine, even in small doses.
Other agents used in an attempt to improve IVRA have included ketorolac, clonidine, dexmedetomidine, dexamethasone, and bicarbonate. Adding ketorolac to the IVRA leads to less tourniquet pain and improved postoperative analgesia.23–25 Clonidine and dexmedetomidine, both α-2-adrenoceptors agonists, have shown some benefit in decreasing tourniquet pain and in improving postoperative analgesia.26,27 However, both have the possible side effects of sedation and hypotension upon cuff deflation. This may limit their clinical use. In limited studies, dexamethasone (8 mg IV) has shown some efficacy in improved postoperative analgesia.25,28 Alkalization of the local anesthetic with bicarbonate may improve pain upon injection.29,30 This has not been demonstrated to hasten the onset or prolong the duration of anesthesia. Of all the agents described above, ketorolac (20 to 60 mg IV) seems to have the largest clinical benefit with the least side effects.
Lidocaine is the most commonly utilized local anesthetic agent for IVRA in the United States. Prilocaine (0.5%) is more routinely chosen in Europe. Prilocaine is metabolized to orthotoluidine, an oxidizing compound capable of converting hemoglobin to methemoglobin. This is usually only of concern when the dose of prilocaine is greater than 600 mg, which, even for lower extremity IVRA and volumes as high as 100 mL, should not be attained.
Deflation of the Pneumatic Tourniquet
Deflation of the tourniquet, after the procedure has been performed, is a critical step to minimizing the possibility of toxicity associated with IVRA. It is absolutely mandatory that the tourniquet not be deflated unless at least 30 minutes have elapsed since the injection of the local anesthetic agent, even if the duration of surgery or manipulation has been very brief. At least one case of cardiac arrest has been reported when the tourniquet was released soon after the injection of the local anesthetic solution and the duration of surgery was extremely short.31
It is absolutely mandatory to deflate the tourniquet in a cyclical fashion. Remove the tape from the cuff. Deflate the cuff and immediately reinflate it to 50 to 100 mmHg above the patient's systolic blood pressure. Observe the patient for 1 minute and question them carefully for the occurrence of symptoms associated with local anesthetic toxicity such as tinnitus, lightheadedness, and a metallic taste in their mouth. Obvious signs of central nervous system stimulation may also represent local anesthetic toxicity. If there are no such signs or symptoms after approximately 1 minute, deflate the cuff and once again immediately reinflate the cuff. Observe the patient for a period of approximately 1 to 2 minutes and question them again for the symptoms associated with local anesthetic toxicity. Repeat this process a third time. The tourniquet may be safely deflated and removed if there are no signs and symptoms of local anesthetic toxicity after three cycles of deflation and reinflation of the cuff. The safety of the cycled deflation/reinflation allows only a small fraction of the administered (and unbound) local anesthetic agent to enter the systemic circulation each time.32 This minimizes the possibility of a sudden sustained increase in the blood level of the local anesthetic agent.32