LAUSR

To the Editor: A 41-year-old woman (height: 163 cm; weight: 44 kg; and American Society of Anesthesiologists physical status I) visited the Gyeongsang National University Hospital with the chief complaint of warmth and pain in both ankles for 1 month. She had an unremarkable medical history. Cellulitis was diagnosed, and antibiotic treatment was provided. Nevertheless, surgery had to be performed because of worsened symptoms. Inflammation developed at the surgical site, so drainage under local anesthesia was planned. An orthopedist performed ultrasoundguided femoral and sciatic nerve blocks using 20 mL of 0.75% ropivacaine hydrochloride in the left leg and 15 mL of 0.75% ropivacaine hydrochloride in the right leg at an outpatient clinic. The initial nerve block was successful. However, the orthopedist started the operation 6 hours after the block because of an unexpected requirement for care of other patients. Owing to the possibility of decreased effect of the nerve block, the orthopedist injected additional 20 mL of 0.75% ropivacaine hydrochloride in the left leg and 15 mL of 0.75% ropivacaine hydrochloride in the right leg to obtain a long-lasting nerve block in the operation room. At the end of the additional ropivacaine administrations, the patient complained of severe dizziness, perioral numbness, and dysarthria. Immediately after, the orthopedist requested an anesthesiologist for treatment of suspected local anesthetic systemic toxicity (LAST). At the time, vital signs of the patient were as follows: blood pressure, 112/90 mm Hg; pulse rate, 98 beats/min; respiratory rate, 22 breaths/min; and arterial oxygen saturation, 100%. The electrocardiogram was unremarkable. Subsequently, 60 mL of 20% SMOFlipid (Fresenius Kabi Korea, Seoul, Korea) was intravenously injected over 1–2 minutes with 2 L/min of oxygen via a facial mask, and changes in the electrocardiogram were observed. The patient’s dizziness and slurred speech observed at the initial onset of LAST alleviated. Vital signs or the electrocardiogram of the patient at the time showed no changes. Subsequently, additional 100 mL of 20% SMOFlipid was intravenously infused over 30 minutes, and vital signs and symptoms suggested no further progression of LAST. The operation was cancelled because of LAST. Local anesthetics, which interrupt nerve impulses by blocking voltage-gated sodium channels, are widely used in various operations. They are safe drugs if injected at the appropriate dose and location in the body. However, LAST can occur when local anesthetics are administered at a dose higher than the doses recommended for infiltrations and nerve blocks or when local anesthetics are intravascularly administered.1 The following patient factors predispose to a high risk for LAST: low body weight, low muscle mass and fat mass, intracellular mitochondrial metabolic disorders, and reduced metabolic enzyme activity in the presence of liver diseases.2 LAST primarily involves the central nervous system (CNS) and cardiovascular system. The initial symptoms of local anesthetic-induced CNS toxicity are lingual and perioral numbness, paresthesia, restlessness, tinnitus, dizziness, visual and auditory disturbances, confusion, and facial muscle spasms.2 The initial excitatory phase of local anestheticinduced CNS toxicity causes tonic–clonic seizures, and the subsequent inhibitory phase causes unconsciousness, respiratory depression, and eventually, respiratory arrest.2 Although the pattern of clinical presentation of LAST varies, CNS symptoms typically precede cardiovascular symptoms in onset.1 The effect of local anesthetics on the cardiovascular system is dose-dependent and inhibits myocardial suppression, vasodilation, and cardiac conduction.1,2 The present patient had a low body mass index of 16.58 kg/m2 and reduced plasma volume because of drainage of the infection site, which may have increased the risk of LAST.1,2 The orthopedist used 262.5 mg of ropivacaine (5.96 mg/kg) and additional 262.5 mg ropivacaine (5.96 mg/kg) for nerve block, which exceeded the recommended dose of ropivacaine (3 mg/kg or a single maximum dose of 225 mg).3 Moreover, considering that the duration of action (sensory and motor block) of ropivacaine hydrochloride is 6 6 2 hours and plasma concentration 5 hours after bilateral intercostal nerve blocks is approximately 70% of the mean peak plasma concentration (approximately 1 mg/mL), we American Journal of Therapeutics 0, 1–3 (2020)