Local lower extremity hyperkalemia during robotic prostatectomy: A case report

Abstract

Robotic urologic surgery often requires patients to be placed in the steep Trendelenburg position with upper extremities tucked, limiting access for vascular lines and laboratory samples. A case of lower extremity hyperkalemia due to Trendelenburg positioning is presented. This case emphasizes that localized hyperkalemia, secondary to lower extremity hypoperfusion in the context of prolonged Trendelenburg positioning during robotic surgery, may not respond to systemic therapies, which could lead to systemic hyperkalemia upon return to the supine position.

1 Introduction

Robotic prostatectomy often requires patients in the steep Trendelenburg position with the upper extremities tucked to facilitate surgical access. However, this position also restricts vascular line placement and makes collecting laboratory samples difficult. Lower extremity hypoperfusion is a known consequence of this position, but the concomitant electrolyte abnormalities have been underreported. This case describes localized hyperkalemia in the lower extremity during robotic prostatectomy and highlights the limitations of interpreting blood gas values taken from the lower extremity under these conditions. The importance of recognizing positional effects on laboratory values during robotic surgery is critical since systemic therapies may be futile. The patient has provided written consent as well as written Health Insurance Portability and Accountability Act (HIPAA) authorization for the publication of this case report.

2 Case description

A 72-year-old man presented for robotic prostatectomy for benign prostatic hyperplasia. Additional past medical history included foley-dependent urinary retention, chronic obstructive pulmonary disease (COPD), hypertension, and hepatitis C virus infection. Chronic medications included oxybutynin and Flomax. Past surgical history was notable for transurethral resection of bladder tumor in 2011 and umbilical hernia repair in 2006. The patient reported no relevant social history.

Induction of general anesthesia and endotracheal intubation proceeded uneventfully. The patient was placed in the lithotomy position then steep Trendelenburg prior to docking the robot. Approximately two hours following surgical incision, 600 ml of blood loss was noted. Systolic and diastolic blood pressures were within 15 % of the patient’s baseline values on low-dose (0.01–0.02 mcg/kg/min) norepinephrine and intravenous fluid totaled 1 L of Ringers lactate. Given that 600 ml of blood had been lost and the patient was requiring a vasoactive infusion to maintain appropriate blood pressure, additional intravenous access was sought. Because the upper extremities were tucked, an 18-gauge Angio catheter was inserted in the left saphenous vein and the first venous blood gas (VBG) was drawn at 1913 (approximately 2 hours after surgical incision) .

Approximately 1 h and 30 min later (at 2047), another VBG from the left saphenous vein revealed severe hyperkalemia at 7.6 mmol/L. Albuterol was administered, along with 1 g of calcium gluconate, 10 units of insulin, and 25 g of dextrose. Peaked T waves were not appreciated, and the patient remained in normal sinus rhythm at a normal rate without ectopy. Approximately one hour later (at 2144), another VBG from the left saphenous vein again revealed hyperkalemia at 7.4 mmol/L. An additional 10 units of insulin were administered.

Because the hyperkalemia did not change with standard corrective measures, hypoperfusion of the left lower extremity yielding local hyperkalemia from ischemia was suspected. We considered the physiologic and metabolic consequences of the steep Trendelenburg position to be similar to the pneumatic tourniquet for lower extremity surgery, where cellular ischemia leads to accumulation of metabolic byproducts, such as hyperkalemia. At the conclusion of surgery, the patient returned to the supine position. A VBG collected from the right upper extremity revealed mild hyperkalemia and lactic acidosis, presumably from return of blood from the lower extremities. Table 1 presents the results of each of the blood gases obtained in this case. We had no reason to mistrust the venous blood gas values, thus a confirmatory basic metabolic panel was not collected.

Table 1

Venous blood gas values by time and location.

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