Anesthesia

Need for assessing postoperative nerve status or compartment syndrome.

A successful block hinders motor and sensory conduction and negates nerve testing in the immediate postoperative period. Therefore, if an immediate postoperative assessment of nerve function is required, a regional block should not be used. Distal blocks do not, however, preclude hand function. Distal peripheral nerve blocks have the advantage of greater preservation of upper extremity motor function compared with a brachial plexus block and can be considered if the goal is early hand mobilization.

Fear of masking postoperative compartment syndrome is another relative contraindication to regional anesthesia. Compartment syndrome is diagnosed from both subjective and objective findings including compartment pressure measurements. Excessive pain is the hallmark of a compartment syndrome. Pain in the postoperative period is estimated to precede neurovascular changes by 7.3 hours and can theoretically be masked by the use of nerve blockade provided for analgesia. Ischemic pain, however, is largely unaffected by regional anesthesia. Nonetheless, concern for the development of compartment syndrome should be conveyed prior to surgery and an appropriate pain management plan determined at that time. Appropriate vigilance is required and compartment pressures measurements mandatory if there is a suspicion for compartment syndrome, whether or not a nerve block has been performed.

Aggravating a preexisting nerve injury.

Another concern is the possibility that regional nerve blockade will incite further nerve injury (double-crush phenomenon) in patients with preexisting nerve injury or paresthesias. ^, While this is an understandable theoretical concern, experience has shown that regional nerve blockade remains an appropriate option for patients undergoing uncomplicated procedures such as ulnar nerve transposition and the vast majority of elective upper extremity operations.

At our institution, most surgeons and anesthesiologists, in consultation with the patient, opt for the use of regional nerve blockade in cases of existing nerve injury or dysfunction. The demonstrated safety of newer techniques and benefit of pain control outweigh the unlikely risk of further nerve injury. It is important to discuss the advantages and disadvantages with the patient, allowing him or her to participate in decision making, especially when nerve dysfunction preexists. For patients who appear to fear further nerve injury, we often opt to use general anesthesia with local anesthesia at the surgical site to avoid adding a perceived risk and fear to an already anxious patient.

Anticoagulation therapy.

A relative concern among regional anesthesiologists is performing regional blockade in patients on anticoagulation therapy. More and more patients presenting for surgery are taking anticoagulants for treatment of underlying coronary artery disease, atrial fibrillation, or cerebrovascular disease or for prevention or treatment of deep venous thrombosis.

Regional neuraxial (spinal or epidural) anesthesia does not contribute to venous thrombosis in patients. In fact, regional anesthesia has been shown to reduce the rate of blood clots following lower extremity and abdominal surgery, though this advantage has been lessened in recent years with the advent of timely thromboprophylaxis. Postulated mechanisms include sympathetic blockade leading to improved blood flow and decreased sympathetic stimulation, as well as a direct antithrombotic effect of the local anesthetic solution. However, neuraxial regional anesthesia is contraindicated in the fully anticoagulated patient, given the risk of epidural hematoma and subsequent devastating neural injury. Performance of deep plexus blocks in this setting, though, remains practitioner-dependent. There are case reports of retroperitoneal hematoma following deep lumbar plexus blockade in anticoagulated patients; however, the relative safety of this technique was confirmed in a large study of 670 patients who underwent continuous lumbar plexus blockade while anticoagulated with warfarin.

In the anticoagulated patient, a perivascular brachial plexus nerve block has the potential to cause excessive bleeding. Yet several case reports document the safety of peripheral nerve blocks in the anticoagulated patient, particularly when the block is placed under ultrasound guidance. Despite these reassuring findings, the most recent published regional anesthesia guidelines advocate applying the same recommendations for neuraxial anesthesia to anticoagulated patients undergoing deep perivascular nerve blocks, while performance of superficial nerve blocks should be managed based on site compressibility, vascularity, and consequences of bleeding. Patients who have incomplete reversal of their anticoagulation with mild derangements of their coagulation panel must be approached on a case-by-case basis with ample discussion of the risks and benefits.

Bilateral procedures.

There may be instances in which regional anesthesia could be used for bilateral procedures; however, there are many risks, and bilateral regional anesthesia should be avoided. The risk of drug toxicity is higher as the dose is nearly doubled. Using a lower amount to avoid toxicity raises the probability of block failure. The type of block also influences the risk. Interscalene nerve block commonly results in phrenic nerve paralysis, so bilateral interscalene nerve block is absolutely contraindicated due to the risk of respiratory failure. Even supraclavicular blockade has an estimated associated risk of transient diaphragmatic paralysis of around 50%. This risk combined with the associated risk of pneumothorax and the necessary high minimum effective dose makes bilateral supraclavicular blockade unreasonable. A safer alternative may be utilization of distal peripheral nerve blockade or performing the blocks using low-volume, short-acting local anesthetics in sequence (i.e., performing the block on the second limb only upon completion of operation on the first limb). ^,