Abstract ID: A40
Abstract Title: Percutaneous electrode guidance for femoral nerve block in case of unperceivable artery pulsations.
Poster Type: Poster
ABSTRACT BODY
Introduction: Femoral nerve block is performed laterally to the femoral artery pulsation. In case of non perception of the artery, anatomical landmarks are difficult to determine. We present two cases in which such a difficulty is resolved by nerve prelocation (1-2) using percutaneous electrode guidance (PEG)
Case 1. A male patient 63 y/o,78 kg, 165 cm, ASA III was scheduled for large excision of necrosis on heel and ankle of the left foot involving sciatic and saphenous nerves. His past medical history was marked by chronic pancreatitis in relation with alcohol abuse, subsequent diabetes mellitus type I, complicated by neuropathy, vascular and renal insufficiency. Two weeks before he had undergone under general anesthesia a revision of infected nail plate on the right hip. For the surgery on his left foot the patient desired this time a regional technique. Lateral midfemoral sciatic nerve block was done with ropivacaine 0.5% 20 mL after stimulating plantar flexion of the foot at 1 mA (1Hz, 0.1ms). Absence of arterial pulsation of femoral artery was the surprise for the femoral nerve block. An attempt of prelocation of the femoral nerve through an electrode probe equipped with two stimulating bowls and coupled to the nerve stimulator (Multistim Vario, Pajunk, Geisingen, Germany) was carried out. The current (0.5 ms, 2Hz) was set initially at 5 mA as the probe was passing along on the inguinal crease from medial to lateral. As soon as electroshocks were perceived signalling the nerve underneath, PEG was immobilized and the operator indented the skin and increased quickly the amperage to evoke quadricipital contractions (7 mA in this case). The two points of indentation were then marked and a line indicating the nerve path was drawn between them. After disinfection and raise of a skin wheal with 2mL lidocaine 1% a stimulating needle was inserted on the line to a depth of 4 cm. Quadricipital contractions were stimulated at 1 mA (2Hz, 0.1ms). 10 mL of ropivacaine 0.5% were injected. This combined femoral and sciatic nerve block was successful for surgery.
Case 2. A female patient 52 y/o, 124 Kg, 160 cm was scheduled for total knee replacement under general anesthesia (GA). Before GA, regional techniques (combined femoral and sciatic nerve blocks) using neurostimulation were conducted to assure postoperative analgesia. The lateral midfemoral sciatic nerve block was performed without technical difficulty. For femoral nerve block there could be some difficulty as arterial pulsations were not perceived because of obesity. Fortunately, prelocation of the femoral nerve was rendered possible, thanks to the PEG probe following the pre-cited procedure. Quadriceps contractions were evoked at 8 mA (2Hz, 0.5 ms) with PEG. Similar motor responses were then elicited at 0.4mA (2Hz,0.1ms) by the stimulating needle inserted on the line determined by indentations and advanced to a depth of 6 cm. A stimulating catheter was successfully placed (0.6 mA at 12 cm of depth).
Discussion: These two cases show the interest of PEG in femoral nerve block when femoral arterial pulsations are unperceivable. The described electric features of neurostimulation chosen for PEG are based on “personal” experience with this technique of nerve prelocation as PEG was applied on one of the authors of these case reports. From 2 to 5 mA, electroshocks radiating along the femoral nerve are perceived with discomfort which disappears immediately when motor responses are elicited at a higher amperage. Similar sensations were experienced by the two patients.
1. Reg Anesth Pain Med 2002;27:261-267.
2. Reg Anesth Pain Med 2004; 29:206-211.
ATTACHED FILES
Reg Anesth Pain Med 2004; 29(2):A40