Invasive Blood Pressure Monitoring During Mediastinoscopy: Which Side Are You On?

Case Report:

Adam A. Dalia, MD, MBA

Cardiothoracic Anesthesiology Fellow
Department of Anesthesia, Critical Care, and Pain Medicine
Massachusetts General Hospital
Boston, Massachusetts

Michael K. Essandoh, MD

Associate Director of Clinical Research
Associate Professor, Clinical Cardiovascular Anesthesiology
Department of Anesthesiology
The Ohio State University Medical Center
Columbus, Ohio

Routine mediastinoscopy can be a fairly low-risk procedure; however, the close proximity to vital cardiovascular structures in the chest may lead to unexpected dilemmas. Ischemic cerebrovascular accidents (CVAs) can occur during mediastinoscopy, and predominantly in the right hemisphere. This is secondary to prolonged compression of the innominate artery caused by the mediastinoscope, precipitating malperfusion to the head.

This case report discusses a patient who, while undergoing mediastinoscopy, experienced a precipitous drop in blood pressure as evidenced by a dampened arterial waveform that was readily diagnosed as a mechanical obstruction of flow caused by the mediastinoscope. The surgeon was notified immediately and the scope repositioned, relieving pressure of the right-sided vessel and restoring appropriate flow to the right upper extremity and right cerebral hemisphere. At our institution, it is standard practice to place all invasive arterial monitors in the right upper extremity as opposed to the left, since a right-sided monitor will more readily capture a mechanical compression of the innominate artery by the mediastinoscope.

Introduction

Although rare during routine mediastinoscopy, CVAs can occur in patients who are not adequately monitored. When cerebral ischemia occurs intraoperatively, it is generally located in the right hemisphere and likely secondary to innominate artery compression caused by mechanical compression of the mediastinoscope.

The head vessels off the aortic arch can vary anatomically, but the largest percentage of the population has 3 main vessels: innominate (brachiocephalic) with a right common carotid branch, the left common carotid, and the left subclavian artery supplying the left upper extremity. Presented here is a case of a patient who while undergoing mediastinoscopy experienced a sudden drop in perfusion pressure detected on a right-sided invasive arterial line, which prompted the anesthesiologist to alert the surgeon to reposition the scope. Of note, an arterial line was crucial in this speedy diagnosis, but the laterality of the invasive monitor—right-sided—proved decisive.

Case Description

A 64-year-old, 84.5-kg, 180-cm man with a recently diagnosed lung mass and mediastinal adenopathy was referred to the author’s institution for diagnostic staging. The patient’s medical history was relevant for chronic obstructive pulmonary disease, hypertension, and diabetes. The patient was scheduled for bronchoscopy, cervical mediastinoscopy, and lymph node biopsy under general anesthesia.

Intraoperatively, a right radial arterial catheter was placed for hemodynamic monitoring after the induction of general anesthesia and endotracheal intubation using standard American Society of Anesthesiologists monitors. In particular, the pulse oximeter probe was placed on the left hand for oxygenation and hemodynamic monitoring. During surgical biopsy of the lymph nodes, the patient developed acute arterial hypotension (Figure 1) with no airway pressure changes or alarms. What is the diagnosis?

The acute arterial hypotension, in the right radial artery, was concerning for compression of the innominate artery by the mediastinoscope due to dampening of the arterial waveform. Of note, the pulse oximeter (on the left) had a pulsatile waveform and an oxygen saturation of 100% during this event. Immediate repositioning of the mediastinoscope resulted in a rapid correction of the hypotension (Figure 2) without the need for vasopressor therapy.

A CVA is a rare but devastating complication that may occur in patients undergoing cervical mediastinoscopy.^1,2 Most CVAs occur in the right cerebral hemisphere secondary to prolonged compression of the innominate artery by the mediastinoscope, precipitating cerebral ischemia.

To prevent this potentially fatal complication, adequate perfusion of the right cerebral hemisphere should be monitored with a right-sided arterial catheter.¹ In most patients, the innominate artery is the first head vessel branching off the aortic arch that supplies blood to the head and right upper extremity; thus, due to its vast territorial coverage, it is crucial to maintain an adequate perfusion pressure in this critical vessel.

Although a pulse oximeter may be useful for monitoring, it fails to provide direct monitoring of innominate arterial pressure compared with a right radial arterial catheter, as described above. Failure to indirectly monitor the patient’s right cerebral perfusion with a right radial arterial line could have resulted in a delayed diagnosis of innominate artery compression, and could have further resulted in a CVA for this older patient. Hence, a right radial arterial catheter may be the best monitor for the timely detection of innominate artery compression, especially in older patients with atherosclerosis and possible poor circle of Willis collateral circulation.

Some may argue that a pulse oximeter on the right hand can achieve the same goal of detecting malperfusion, as a poorly perfused hand due to innominate artery compression can cause a decreased pulse oximeter reading. The benefit of an arterial line over a pulse oximeter is the speed with which a clinician can view the dampened hemodynamic tracing of an arterial line and promptly diagnose an innominate artery compression; by contrast, a dampened pulse oximeter may not present until prolonged malperfusion has occurred. To that point, the differential diagnosis of a dampened or poorly transduced pulse oximeter signal during mediastinoscopy is far more extensive than the sudden precipitous dampening of a right-sided arterial line, thus giving anesthesiologists the advantage of narrowing their differential diagnosis dramatically.

Conclusion

This report clearly demonstrates the benefits of right-sided perfusion monitoring during cervical mediastinoscopy, including the rapid diagnosis of mechanical compression of the innominate artery and the potential reduction in CVA risk.

References

1. Rami-Porta R, Call S. Invasive staging of mediastinal lymph nodes: mediastinoscopy and remediastinoscopy.Thorac Surg Clin. 2012;22(2):177-189.
2. Urschel JD, Vretenar DF, Dickout WJ, et al. Cerebrovascular accident complicating extended cervical mediastinoscopy.Ann Thorac Surg. 1994;57(3):740-741.