Abstract

Perioperative radial nerve injury is a rare anesthetic complication, and is rarely seen in association with the use of an automatic blood pressure monitor. As far as we know, only one case has been reported. Here, we report a 26-year-old healthy, lean female who sustained acute radial nerve palsy after appendectomy. A dropped wrist improved 5 days later. The cause of the radial neuropathy is discussed. We recommend that when an automatically cycling blood pressure monitor is used on a lean patient, caution should be taken against such a complication.

Keywords

blood pressure monitors; postoperative complications; radial neuropathy;

1. Introduction

The incidence of peripheral nerve injury during anesthesia is rare. The most common peripheral neuropathy is ulnar nerve injury.¹ Male sex, extremes of body habitus, and prolonged hospitalization are important risk factors for perioperative ulnar neuropathy.² Most cases with acute radial nerve injury occurring intraoperatively are usually subjected to malpositioning of the arm with consequent stretching or compression of the nerve.³ The American Society of Anesthesiologists Task Force on Prevention of Perioperative Peripheral Neuropathies advised that prolonged pressure on the radial nerve in the spiral groove of the humerus should be avoided.⁴ Here, we report a case of acute radial neuropathy,possibly as a result of compression by the automatic blood pressure cuff during surgery.

2. Case Report

A 26-year-old woman, with a height of 160 cm and weight of 45 kg, received emergency appendectomy for a ruptured appendix. The patient was in good health and had no previous neuropathy. In the operating room, standard monitoring, including electrocardiography, pulse oximetry (SpO₂), noninvasive blood pressure monitoring, capnography and measurement of body temperature was performed. A standard sized adult blood pressure cuff was affixed to the patient’s right arm with the sleeve of the surgical dress on and connected to a SpaceLab 91496 monitor module (SpaceLabs Medical Inc., Issaquah, WA, USA). The blood pressure monitor was set to cycle automatically every 5 minutes. The preoperative blood pressure, heart rate, and SpO₂ were 110/73 mmHg, 90 beats/min, and 100%, respectively. General anesthesia was induced with fentanyl 100 μg, thiamylal 250 mg and rocuronium 30 mg, following sufficient preoxygenation. After tracheal intubation, general anesthesia was maintained with 3% sevoflurane in oxygen and rocuronium 0.2 mg/kg/ hr was given intravenously for surgical relaxation. During the 2-hour operation, the blood pressure cuff was observed to be subjected to repeated inflation in response to the inability of the device to determine the patient’s blood pressure. The “insufficient data” alarm was shown on the monitor. Measurement of blood pressure was then performed manually instead of automatically. The patient’s systolic blood pressure as measured was within the normal range of 95−140 mmHg. The operation was uneventful and the patient was extubated after the residual effect of muscle relaxant had been reversed.

One day after the operation, the patient complained of numbness over the dorsal aspect of the right hand and a dropped right wrist. The scale of muscle power of the wrist and finger extensor muscles showed 0/5 and 1/5, respectively. Acute radial nerve palsy was diagnosed. The patient received conservative treatment with a corticosteroid and physical therapy. The right hand numbness and weakness improved 5 days later and a nerve conduction velocity test was within normal limits. The patient was discharged 10 days after surgery.

3. Discussion

The anatomy of the radial nerve can explain how an automatic blood pressure monitor can cause injury of the radial nerve. The radial nerve lies over the lateral aspect of the humerus in the lower third of the arm, where the nerve courses from the posterior compartment to the anterior compartment of the arm immediately superior to the lateral epicondyle.⁵ The motor fibers to the triceps and brachioradialis leave the radial nerve more proximally, and the superficial branch (containing sensory fibers) leaves the nerve as it crosses the lateral epicondyle.³ It was in this region that the distal edge of the pneumatic cuff was located.

Numerous factors have been observed to coincide with perioperative nerve injury, including surgical positioning during anesthesia, prolonged hypotension, hypothermia, prolonged application of a tourniquet (usually longer than 3 hours), type of surgery (cardiac surgery), coexisting medical illness (diabetes mellitus, vitamin deficiency, alcoholism), and extremes of body habitus.⁶ The cause of the radial nerve damage from the use of an automatic blood pressure cuff in this case was possibly the prolonged inflation in response to undetected pulsation. In our review of previous reports about radial nerve injury, we only found one case caused by prolonged inflation of an automatic blood pressure cuff, which was reported in 1990 by Bickler et al.³ The cause of prolonged inflation of the pressure cuff in that case report was the result of interference from movement of the patient during childbirth.

The exact mechanism of the peripheral nerve injury is unclear. Nerve ischemia is suspected to be the principal cause of the nerve injury, although some evidence showed that 45−60 minutes compression at a pressure of 250 mmHg directly onto a nerve is required to cause irreversible block of nerve conduction.⁷ In our case, the maximum systolic pressure during surgery was 140 mmHg, making the sealoff inflating pressure unlikely to approach or exceed 250 mmHg. The duration of inflation of the blood pressure cuff was around 100−150 seconds. The high compression pressure is one of the predisposing factors; the patient’s body habitus should be taken into account. The patient was 45 kg in weight and 160 cm in height, and her body mass index (BMI) was 17.75 kg/m² , which is considered underweight. The patient illustrated in the previous case report was also underweight (BMI, 17.3 kg/m² ). Therefore, we believe that in an underweight patient, the radial nerve might be relatively deprived of protection from the cushioning effect of subcutaneous fat and thus the patient would be vulnerable to radial nerve injury. After the incident, we re-checked the SpaceLab medical monitor and confirmed that it was correctly calibrated and functioning normally. No object that could cause compression was placed near the patient’s arm and there was no manipulation from the surgeons or from the instrument which would have caused compression of the nerve. We also contemplated the possibility of nontraumatic paralysis of the radial nerve.⁸ However, the signs and symptoms of our case were not compatible with those of nontraumatic paralysis of the radial nerve.

In summary, we report a rare complication from the use of an automatically cycling blood pressure machine. Although the injury is extremely rare, it could occur in a lean and underweight patient when repeated inflation of the pressure cuff takes place in response to erroneous signals from outside interference. Ischemic neuropathy cannot be ruled out. Placing the pressure cuff higher on the arm, to allow sufficient distance from the elbow joint at which the radial nerve crosses superficially, may prevent this rare injury. Caution should also be taken in the use of an automatically cycling blood pressure monitor in extremely lean patients, and monitoring on demand rather than automatically is essential.