THE periodic paralyses are a group of familial abnormalities in membrane electrolyte conductance that cause patients to have episodes of flaccid weakness associated with alterations in serum potassium. Based upon potassium concentrations during the episodes of weakness, three distinct subgroups of this disorder have been described: hypokalemic, normokalemic, and hyperkalemic.
Numerous cases of patients with the hypokalemic and normokalemic forms of familial periodic paralysis undergoing both general and regional anesthesia have been reported, many of them complicated by exacerbations of weakness. Unfortunately, there is little data to guide the perioperative care of patients with the less-common hyperkalemic disorder. We believe that the case discussed below is the first detailed report of a regional anesthetic successfully performed for a patient with familial hyperkalemic periodic paralysis.
The patient was a 53-yr-old man who was seen at our Preoperative Evaluation Center the day prior to undergoing radical retropubic prostatectomy and right inguinal hernia repair. He described episodes of muscle weakness in association with upper respiratory infections beginning at age 6. Because his father carried the diagnosis of hyperkalemic periodic paralysis, the patient states that his symptoms were attributed to the same syndrome. At age 32, while in dental school, the patient underwent formal evaluation including electromyography but declined provocative and genetic testing. Since then, he has been followed at another institution by a neurologist familiar with his disorder. His past medical history was otherwise remarkable except for smoking, and his only medications were 250 mg acetazolamide orally per day and 5 g creatine orally per day. His father, brother, niece, and grandnephew also carried the diagnosis.
In 1999, the patient experienced his most severe and prolonged episode of weakness following a general anesthetic, which included succinylcholine for bilateral partial nasal turbinectomy. This episode lasted 4 days and was complicated by development of a deep venous thrombosis, requiring 6 months of warfarin therapy.
The patient fasted for 8 h prior to surgery. Resting electrocardiogram and admission laboratory values were within normal limits, including a QT interval of 0.40 s, serum potassium of 3.5 mEq/l, and serum glucose of 107 mg/dl. In the preoperative area, an 18-gauge peripheral IV was placed, and an infusion of 5% dextrose in normal saline was begun. The patient was taken to the operating room, where standard monitors, including continuous pulse oximetry, continuous electrocardiography, and noninvasive blood pressure cuff, were applied. The patient was sedated lightly with 2 mg intravenous midazolam. A subarachnoid block was performed at the level of L3–L4, with the patient in the sitting position, using 22.5 mg hyperbaric bupivacaine, 0.75% (3 ml), which produced a T4 sensory level bilaterally. The patient received an additional 2 mg midazolam during the case. He breathed spontaneously through a face mask. To prevent hypothermia, ambient temperature in the operating room was maintained at 72°F, an upper body forced-air warming blanket was applied, and all fluids were run through a blood-warming device; minimum rectal temperature was 35.8° centigrade. During the first 90 min of the case, 2,400 ml dextrose, 5%, in normal saline was administered, causing the patient's serum glucose to rise to 454 mg/dl. After receiving an additional 1,750 ml 9% normal saline, 0.9%, his serum glucose returned to 119 mg/dl within 2 h in the postanesthesia care unit. Serum potassium concentrations were measured hourly during the case and ranged from 3.3 to 3.6 mEq/l. The surgical procedure was completed 130 min after placement of the spinal. The patient was transferred to the postanesthesia care unit, where his subarachnoid block resolved completely. Postoperative pain management was provided by intravenous hydromorphone patient-controlled analgesia. He was discharged from the hospital on postoperative day 3, at which time he continued to show no evidence of muscle weakness.
The hyperkalemic form of familial periodic paralysis was first described by Gamstorp in 1956. The rarest of the dyskalemic periodic paralyses, the incidence of the hyperkalemic variety has been estimated at 1:500,000. 1It is inherited in an autosomal dominant fashion with a high degree of penetrance in both males and females. Attacks tend to be shorter in duration, but onset of the disease is earlier than in the hypokalemic variety, frequently in the first decade of life. Weakness is usually more pronounced in the proximal muscles of the extremities and trunk but may progress to affect facial and bulbar muscles. Muscles of respiration are generally spared. Electrocardiographic abnormalities frequently accompany episodes of paresis; T-wave peaking may precede the onset of clinical weakness. Dysrhythmias have been reported but are uncommon. Myotonia is a frequent symptom, leading some investigators to suggest that hyperkalemic periodic paralysis may be a part of the disease spectrum that includes paramyotonia congenita. Cold, infection, anesthesia, rest following exercise, and hunger have all been reported to precipitate attacks. Nonetheless, the paucity of literature and correlation among precipitating factors (cold and anesthesia) creates difficulty in evaluating the relative importance of individual factors. Acetazolamide and thiazide diuretics have been used chronically to decrease the frequency and severity of attacks, presumably via kaluresis. 2
The underlying defect in hyperkalemic periodic paralysis is a mutation of the α subunit of the skeletal muscle sodium channel located on chromosome 17. 3This mutation results in hypopolarization of the muscle membrane. During an attack, potassium moves out of muscle cells, causing serum potassium to rise. The average increase in serum potassium is just 20% and may even remain within normal limits; however, this relative hyperkalemia depolarizes the muscle membrane sufficiently to prevent activation of sodium channels and thus propagation of the action potential. 2
Just 2 yr after the syndrome was first described, Egan cited anesthesia as a precipitant of severe attacks of familial hyperkalemic periodic paralysis. He studied 41 affected members of three different families, each of which had at least one member who had received general anesthesia. Following each anesthetic, the patient experienced an attack of transient paralysis lasting from 2 to 5 h. Egan also commented that one of these patients later received a spinal anesthetic for childbirth without developing paralysis. Unfortunately, no further details regarding the anesthetic techniques, such as whether succinylcholine was used, are reported. 4In 1980, Flewellen reported the first safe use of general anesthesia without muscle relaxants in the management of a 10-yr-old girl with familial hyperkalemic periodic paralysis. 5Subsequent reports document the safe use of nondepolarizing muscle relaxants 6,7and propofol. 8
Despite finding only one prior allusion to regional anesthesia for a patient with hyperkalemic periodic paralysis, we could find no pathophysiologic reason why the use of a neuraxial technique should be contraindicated. In fact, there is some evidence that the inclusion of epinephrine in neuraxial local anesthesia causes moderate hypokalemia, a potential benefit in this patient population. 9In table 1, we outline some recommendations for anesthetic care of patients with hyperkalemic periodic paralysis.
In conclusion, we have provided a detailed report of a successful spinal anesthetic for the management of a patient with familial hyperkalemic periodic paralysis. We believe that neuraxial anesthesia is safe and in some cases may be the preferred option for this patient population.