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Case Report

Dyspnea During Interscalene Block After Recent Coronary Bypass Surgery

Hashim, Mohamad S., MD; Shevde, Ketan, MD

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doi: 10.1213/00000539-199907000-00010
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Interscalene blocks are associated with ipsilateral diaphragmatic paresis in all cases. In healthy patients, no dire respiratory consequences ensue as a result of this, but in patients with predisposing factors, such as old age [1], obesity [2], pregnancy [3], and prior respiratory disease, this complication may become a significant concern. In this case report, we add one more predisposing factor, cardiac surgery, which is sometimes associated with diaphragmatic paresis.

Case Report

A 59-yr-old female patient was scheduled for arteriovenous graft placement in the right upper arm for hemodialysis 11 days after an aortocoronary bypass graft (CABG) and aortic valve replacement procedure. Her medical history included chronic renal failure, hypertension, diabetes mellitus, and a left-sided stroke. Hypertension was treated with propranolol and verapamil, and her diabetes was adequately controlled with neutral protamine Hagedorn insulin. She was 158 cm tall and weighed 75 kg. Her vital signs were within normal limits, with blood pressure 140/80 mm Hg, heart rate 74 bpm, and respiratory rate of 16 breaths/min. Recent laboratory data revealed hemoglobin 9.3 g/dL, hematocrit 27.9%, platelet count 161,000 mm3, Na+ 133 mEq/L, K+ 4.3 mEq/L, and blood glucose 194 mg/dL. A preoperative chest radiograph, which was performed after the CABG procedure, revealed minimal left-sided pleural effusion.

In the operating room, after applying ASA standard monitors and establishing IV access, a right interscalene plexus block was performed using a 22-gauge insulated needle and a nerve stimulator to accurately locate the brachial plexus. Lidocaine 1.5% and ropivacaine 0.5% in a 1:1 mixture 36 mL was injected slowly over 4 min. Fifteen minutes after the interscalene block had been performed, the patient complained of dyspnea. Her respiratory rate was 18-20 breaths/min and oxygen saturation was 95% while breathing 4 L/min of oxygen via a nasal cannula. On physical examination, she appeared to be using her intercostal and accessory muscles to breath, and breath sounds were clear to auscultation on both sides. The patient remained hemodynamically stable throughout the duration of the surgical procedure (2 h 40 min), during which she was reassured and given additional oxygen. Oxygen saturation was 97%-100% as measured by a pulse oximeter while breathing 6 L of oxygen via a face mask. pH was 7.42, PaCO2 was 38 mm Hg, and PaO2 was 101 mm Hg.

After surgery, the patient was transported to the postanesthesia care unit for observation. A chest radiograph taken with the patient in sitting position showed mild elevation of the right hemidiaphragm (the side on which the interscalene block was performed) and a minimal left pleural effusion. pH was 7.5, PaCO2 was 34 mm Hg, PaO2 was 89 mm Hg, and fraction of inspired oxygen was 0.2 with the head elevated 45[degree sign] to improve the respiratory mechanics. After 3 h in the postanesthesia care unit, the patient gradually became more comfortable, which coincided with the resolution of the interscalene block, and was soon transferred to the ward. The next day, a follow-up chest radiograph revealed a large left pleural effusion. Although the patient was asymptomatic, thoracocentesis was performed, and approximately 1000 mL of serous fluid was aspirated. The rest of the patient's hospital course was uncomplicated, and she was discharged home after a few days.

Discussion

Regional anesthesia is becoming increasingly popular because it provides very good operating conditions for patients who are awake and allows hospital discharge within a short period. It also allows prolonged postoperative pain relief, which may not be provided by general anesthesia. We presented a case in which regional anesthesia (interscalene block) was selected as the anesthetic of choice in consideration of the patient's medical problems, which included renal failure, coronary artery disease, diabetes mellitus, and hypertension. Interscalene block was performed to block the brachial and cervical plexus (C4-8) so that an arteriovenous shunt could be performed in the upper arm on the ipsilateral side. One of the complications of the interscalene block is paralysis of the diaphragm on the same side due to a phrenic nerve block (C3,4,5), which is in the path of the local anesthetic instilled for the block [4]. It is reported that the phrenic nerve is blocked in all cases of interscalene block [5]. Paresis of one hemidiaphragm is not usually associated with adverse clinical symptoms, although lung volume, pulmonary function tests, and arterial blood gas analyses are all negatively affected. The normal individual can compensate for these changes by using accessory and intercostal muscles and enhanced respiratory efforts. Intercostal and accessory muscles contribute 25%-50% of the total ventilatory effort. In addition, the respiratory rate increases by approximately 14% [6]. Pulmonary function tests simulate a picture that may be seen in restrictive lung disease. Forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) are both reduced, but the FEV1/FVC ratio remains unchanged [7,8]. Pulmonary atelectasis and shunting reduce PaO2 levels, but PaCO2 remains within normal limits [6].

Our patient had previously undergone CABG and an aortic valve procedure. These are associated with a small chance (7.2%) of phrenic nerve paralysis, most likely due to the infusion of ice-cold solution used for myocardial protection [9,10] in the left chest cavity, which is usually exposed for harvesting the left internal mammary artery. In most cases, the nerve injury is transient and is manifested by pleural effusion on the same side. Often the injury goes undiagnosed because the patient recovers fully without treatment. In retrospect, we presume that the pleural effusion on the opposite side of the interscalene block was due to left phrenic nerve involvement and went unnoticed. A more careful evaluation of this patient and the radiograph findings would have prevented this complication because another form of anesthesia would have been selected. It is our recommendation that, in postcardiac surgery patients, evidence of diaphragmatic paralysis, such as pleural effusion or diaphragmatic inactivity by chest radiograph or preferably by fluoroscopy, should be ruled out before initiation of an interscalene block to prevent bilateral diaphragmatic paresis. In view of the unexpected sudden changes in respiratory status after the interscalene block, this case emphasizes the need for emergency airway equipment to be available whenever regional anesthesia is used.

REFERENCES

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© 1999 International Anesthesia Research Society