Clinical validation of electromyography and acceleromyography as sensors for muscle relaxation.

BACKGROUND AND OBJECTIVE: The aim of this study was to determine which of two clinically applied methods, electromyography or acceleromyography, was less affected by external disturbances, had a higher sensitivity and which would provide the better input signal for closed loop control of muscle relaxation. METHODS: In 14 adult patients, anaesthesia was induced with intravenous opioids and propofol. The response of the thumb to ulnar nerve stimulation was recorded on the same arm. Mivacurium was used for neuromuscular blockade. Under stable conditions of relaxation, the infusion-rate was decreased and the effects of turning the hand were investigated. RESULTS: Electromyography and acceleromyography both reflected the change of the infusion rate (P = 0.015 and P < 0.001, respectively). Electromyography was significantly less affected by the hand-turn (P = 0.008) than acceleromyography. While zero counts were detected with acceleromyography, electromyography could still detect at least one count in 51.1%. CONCLUSIONS: Electromyography is more reliable for use in daily practice as it is less influenced by external disturbances than acceleromyography.

Endothelin receptor blockade improves oxygenation in contralateral TRAM flap tissue in pigs.

Partial skin and fat necrosis is the most common complication occurring in TRAM flaps. It is related to disturbances of the microcirculation and oxygenation in the contralateral part of the flap. It may be hypothesised that the development of necrosis is promoted by the vasoconstrictor endothelin, the production of which is enhanced in ischaemic flap tissues. The purpose of this study was to evaluate the effect of tezosentan, a new endothelin receptor blocker, on microcirculation and oxygenation in experimental TRAM flaps. The administration of tezosentan began preoperatively (3 mg/kg body weight) and then continued at a rate of 1.5 mg/kg/h. A TRAM flap with a skin island measuring 16 x 8 cm was raised in the middle of the epigastrium in minipigs. The flap was pedicled on the right superior epigastric vessels. Microcirculatory blood flow was measured with laser Doppler flowmetry and tissue oxygen tension was measured with a Clark-type microprobe. Dominant subcutaneous veins were cannulated in both the ipsilateral and the contralateral parts of the flap. Subdermal tissue oxygen tension in the contralateral part of the flap was significantly reduced 4h after surgery to 5 mmHg (ca. 48 mmHg in normal tissue) in the control group, but to only 12 mmHg in the group that had been administered tezosentan (P< 0.05). Furthermore, tezosentan significantly attenuated venous hypertension (14 mmHg versus 24 mmHg), as well as lactate (4.0 mmol/l versus 5.6 mmol/l) and haemoglobin (10.2 g/dl versus 11.4 g/dl) concentrations in the venous effluent of the contralateral part of the flap, although microcirculatory blood flow remained virtually unchanged. Our findings suggest that tezosentan improves oxygenation and metabolism in the jeopardised contralateral flap tissue, probably as a result of a decrease in venous vascular resistance and fluid extravasation.

The effect of pedicle artery vasospasm on microhemodynamics in anatomically perfused and extended skin flap tissue.

The aim of this study was to evaluate quantitatively the influence of pedicle artery vasospasm on the microcirculation in skin flaps, particularly in the jeopardized extended portions. For this purpose, the hamster island skin flap model was used, which allowed for simultaneous assessment of hemodynamics in both the pedicle artery and the microvasculature of the flap by intravital microscopy. Vasospasm was induced by applying a V3 microvascular clamp for 30 seconds. Clamping resulted in a severe vasospasm, with the artery exhibiting a diameter of 7% +/- 2% (mean +/- standard error) of its original diameter (n = 10; p < 0.01), and with a reduction of total blood flow to the flap of 11% +/- 2% (p < 0.01). Diameter and blood flow recovered gradually to baseline levels after 25 and 15 minutes respectively. During recovery from severe pedicle artery vasospasm (moderate to mild vasospasm), the arterioles in the anatomically perfused flap tissue (n = 38) showed reactive vasodilation (p < 0.01), which was absent in the extended tissue (n = 49; p < 0.01 vs. anatomic). At a pedicle artery vasospasm of 50% of the original diameter, blood flow was restored to normal levels in the anatomically perfused arterioles, but remained below baseline in the extended part (partly p < 0.05 vs. baseline and anatomic). The findings suggest that the development of ischemic necrosis in extended flap portions may be promoted by prolonged, moderate vasospasm, which is well tolerated in the anatomically perfused tissue because of its high capacity for implementing compensatory local regulatory mechanisms.