Hypoxic respiratory failure due to phrenic nerve palsy from an interscalene brachial plexus block and previously asymptomatic pulmonary embolism
© Springer-Verlag 2011
Received: 23 May 2011
Accepted: 6 June 2011
Published: 21 June 2011
Interscalene brachial plexus block is a common regional anesthesia method for upper extremity surgery. A rare complication of this procedure is dyspnea secondary to phrenic nerve palsy and hemidiaphragm paralysis. In our case, this rare complication diagnosed using ultrasound led to the diagnosis of a previously asymptomatic pulmonary embolism. The use of ultrasonography was key in the diagnosis of the iatrogenic nerve palsy and was part of a multiple-modality diagnostic workup for her hypoxemia.
The use of brachial plexus blocks has been widely accepted as a safe and reliable method of anesthesia for upper extremity surgical procedures. Despite its relative safety, known complications can include seizure, pneumothorax, high cervical blocks, peripheral neuropathies, and cardiovascular collapse . Transient phrenic nerve palsy resulting in hemidiaphragm paralysis is a common side effect of the procedure that rarely produces symptoms . There have only been a small number of case reports on symptomatic dyspnea related to hemidiaphragm paralysis during interscalene blocks. While all these cases involved patients with symptomatic respiratory distress, clinical hypoxemia was reported only once . The acute hypoxemic respiratory failure observed in this case led to the further evaluation and diagnosis of an underlying, sub-acute pulmonary embolism.
A 63-year-old female with past medical history of hypertension, obesity, and obstructive sleep apnea, was transferred from an outpatient surgery center in acute respiratory distress after the placement of an interscalene brachial plexus block prior to right shoulder surgery. A previous traumatic injury had left her with chronic shoulder pain and paresthesias. These symptoms had led to a decrease in her normal level of activity in the time leading up to her surgery.
Preoperatively an interscalene brachial plexus block had been placed with the position confirmed by nerve stimulation testing. Adequate regional anesthesia was accomplished and no apparent complications were initially observed. When the patient was moved to the operating room, she experienced acute dyspnea and her oxygen saturation (SpO2) fell to 85% on room air. This improved with supplemental oxygen, but her dyspnea continued and breath sounds were noted as absent on the right side. Due to the concern for iatrogenic pneumothorax, the patient was urgently transferred to the emergency department (ED) for further evaluation.
Given the ultrasound diagnosis of hemidiaphragm paralysis and the patient’s clinical improvement, as the short acting component of the nerve block was wearing off, consideration was given to canceling the CT angiography. However, it was felt that the patient’s initial hypoxemia was difficult to attribute to an isolated hemidiaphragm paralysis in the absence of significant lobar atelectasis. With the persistent concern for coexistent pulmonary pathology, a CT angiography was obtained. A small, sub-acute, sub-segmental pulmonary embolus was found in the upper posterior right lung. Heparin was started in the ED, and the patient was admitted for observation and conversion to oral anticoagulation therapy.
While an elevated hemidiaphragm on chest radiography can be seen in the presence of pulmonary embolism, it must also raise the possibility of phrenic nerve palsy . The incidence of transient hemidiaphragm paralysis secondary to phrenic nerve palsy during the regional interscalene block has been well documented in previous studies. With the phrenic nerve running along the anterior scalene, local diffusion of the anesthetic from the intended injection site is difficult to avoid [7, 8]. Some studies have quoted the occurrence of phrenic nerve palsy and hemidiaphragm paralysis to be as high as 100% .
Despite the high incidence of hemidiaphragm paralysis, only a handful of case reports have ever described patients with symptomatic dyspnea and only one has described clinically significant hypoxemia [3, 7, 9, 10]. In our patient, a number of factors likely contributed to her respiratory distress. With limited lung compliance secondary to obesity and an unknown underlying pulmonary embolism, her functional reserve was clearly limited at baseline. The combination of these factors likely decreased her ability to compensate for the additional stress or hemidiaphragm paralysis.
The diagnosis of phrenic nerve palsy would have been missed in this patient if an ultrasound exam was not performed. The CT angiography study that found the pulmonary embolism would not have been able to diagnose the phrenic nerve palsy and paralysis of the hemidiaphragm. The elevated hemidiaphragm may have been attributed to the pulmonary embolism if not for the ultrasound examination.
This case report highlights the use of multiple imaging modalities to diagnose a complex presentation of dyspnea and hypoxia that would likely not have been diagnosed by any single method. The utilization of ultrasound provided key information in diagnosing the multi-factorial causes for the patient’s hypoxia and evaluating a common complication of perioperative neuronal blockade.
Conflicts of interest
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