Sympathetic innervation of the human leg arteries

Femoral artery block (FAB) attenuates thigh tourniquet-induced hypertension: a prospective randomized, double-blind, placebo-controlled trial

INTRODUCTION

Prolonged tourniquet inflation during surgery frequently leads to tourniquet hypertension (TH), which is thought to arise from compression of A-δ fibers leading to sympathetically mediated C fiber activation. In the lower extremity, C fibers and other sympathetic nerve fibers are carried along the femoral artery. We hypothesized that blockade of these fibers at the femoral artery would decrease the incidence of TH.

METHODS

Thirty American Society of Anesthesia 1-3 patients aged 18-75 undergoing total ankle arthroplasty were randomized to receive 15 mL of injectate (mepivacaine 1.5% or saline placebo) at the anteromedial aspect of the common femoral artery at the level of the inguinal crease under ultrasound guidance. Both groups received preoperative popliteal sciatic and saphenous nerve blocks for analgesia and a standardized general anesthetic. Esmolol was administered if systolic blood pressure rose >30% above baseline. Incidence of TH was the primary outcome.

RESULTS

TH was present in 93.3% of sham patients versus 33.3% of block patients. Mean systolic pressure at 120 min and 150 min of tourniquet time was significantly higher in the sham group compared with the block group. Esmolol requirement (95.3+107.6 v 8.0+14.2, p=<0.001) was also significantly higher in the sham group. No differences were noted in pain scores or opioid consumption, and no patient experienced sensory or motor block of the femoral nerve.

DISCUSSION

Under these experimental conditions, injection of local anesthetic around the femoral artery reduced the incidence of TH and intraoperative esmolol requirement.

TRIAL REGISTRATION NUMBER

www.clinicaltrials.gov (NCT03390426; December 28, 2017).

Assessment of captopril and nicardipine effects on chronic occlusive arterial disease of the lower extremity using Doppler ultrasound

The effects of two potent vasodilating drugs, captopril (C) (25 mg tid), nicardipine (N) (20 mg tid), and placebo (P) were evaluated and compared, in 10 men (mean age of sixty-five years) with intermittent claudication from moderate to severe multilevel chronic occlusive arterial disease (COAD) of the lower extremity, by use of the Doppler ultrasonic method, at rest and after Carter's exercise test. All the examined subjects were normotensive, without diabetes or cardiopathy; all have been smokers. The eight-week total protocol consisted of an initial two-week placebo run-in period followed by two active drug phases and a two-week placebo phase, according to a double-blind, randomized, crossover design. At the end of each two-week period, ankle-arm index (AAI) and, following exercise, onset of lower extremity discomfort time (ODT), duration of exercise (ET), decrease of ankle systolic pressure after test (APD), and recovery time (RT) were determined. Moreover, at rest, just after exercise, and after recovery, simultaneous common femoral artery velocity waves were recorded and analyzed by a quantitative approach to detect the peripheral vasomotor adjustments. None of the patients required the withdrawal of the active treatments. Compared with P, C significantly reduced APD and RT, and N reduced RT and AAI; furthermore N caused a significant decrease in ODT, whereas C showed a trend, although not statistically significant, to increase ODT. Neither active therapy modified ET. These results suggest that C and N have different short-term effects on peripheral circulation in COAD. During exercise, C induces hemodynamic improvement in the ischemic lower extremity probably by inhibition of the sympathetic system and consequent reduction in collateral vessel vasoconstriction.

Effect of intra-arterially induced alpha-receptor blockade upon resistance in collateral arteries in patients with occlusion of the superficial femoral artery

The effect of intra-arterially phentolamine inducing alpha-receptor blockade upon the resistance in collateral arteries bypassing an occlusion of the femoral artery was studied in five patients. The patients were placed on a tilt table and the measurements were performed with the patients in supine position and titled 40 degrees (head-up). Arterial blood pressure was measured directly in the brachial-common femoral-and popliteal artery. Relative blood flow was calculated as the relative change in arterio-venous oxygen saturation. Head-up tilt caused a decrease in blood flow of about 35% corresponding to an increase in total vascular resistance of 38%. Resistance in collateral arteries increased by 45%. In supine position alpha-receptor blockade reduced collateral resistance by 17%. However, the title-induced constriction of the collateral arteries was blocked by 87%. The results indicate that the constriction of the collateral arteries bypassing an occlusion of the superficial femoral artery is mainly mediated via sympathetic adrenergic vasoconstrictor fibres.

Histochemical studies on the autonomic innervation of the femoral artery and vein

The innervation of the femoral artery and vein in the dog was studied using: a) glyoxylic acid fluorescence (for the histochemical localization of adrenergic nerve fibers); b) acetylcholinesterase (for the histochemical localization of cholinergic nerve fibers). -Andrenergic nerve fibers and related terminals in both vessels are confined to the adventitial-medial transitional zone and the outer layers of the media. Acetylcholinesterase containing nerve fibers are localized in the adventitial-medial transitional zone of the femoral artery. These findings may indicate the presence of a cholinergic vasodilatator system in the control of the circulation in the femoral artery.