THE EFFECT OF ISOFLURANE (1MAC) ON THE NORMAL AV CONDUCTION SYSTEM AND ACCESSORY PATHWAYS

Alfentanil-midazolam anaesthesia has no electrophysiological effects upon the normal conduction system or accessory pathways in patients with Wolff-Parkinson-White syndrome

The effects of alfentanil-midazolam anaesthesia upon the electrophysiologic (EP) properties of normal atrioventricular (A-V) and accessory pathway (AP) conduction were studied in eight patients with Wolff-Parkinson-White syndrome during accessory pathway surgical ablation. The presence of an AP was confirmed by preoperative EP studies. Anaesthesia was induced with alfentanil (50 micrograms.kg-1) and midazolam (0.15 mg.kg-1) and maintained with an alfentanil infusion (2 micrograms.kg-1.min-1) and intermittent boluses of midazolam (1-2 mg q 15 min, PRN). Following sternotomy, a baseline EP study was performed which consisted of effective refractory period (ERP) and shortest cycle length (SCC) measurement during antegrade conduction in the AV and AP, as well as during retrograde conduction in the AP. Comparison with preoperative EP studies indicated that the administration of alfentanil-midazolam anaesthesia had no effect upon conduction or ERP in either pathway. Haemodynamic stability occurred throughout the surgical procedure with no tachyarrhythmias. We conclude that a combination of alfentanil-midazolam is suitable for general anaesthesia in patients undergoing ablative procedures for accessory pathways.

Duration of action of supplemental doses of vecuronium is related to the duration after the initial dose

Vecuronium was administered in an initial dose of 0.1 approximately 0.3 mg.kg(-1) and in supplemental doses of 0.03 mg.kg(-1) or 0.05 mg.kg(-1) in 74 patients (ASA class 1 or 2) scheduled for abdominal surgery. The duration of the neuromuscular blockade provided by vecuronium after both the initial and supplemental doses was determined using the evoked integrated electromyographic device. A statistically significant positive correlation (correlation coefficient: 0.83 approximately 0.91) was found between the duration of action of the initial dose and that of the first to fourth supplemental doses. The regression lines of each of the first four supplemental doses to the initial dose were very similar to each other. These results suggest that, since the duration of action of supplemental doses of vecuronium was prolonged in patients showing a long duration of action of the initial dose, it would be wise to avoid blind adherence to a predetermined schedule for supplemental administration. Rather, anesthesiologists should take into account the patient's response to the initial dose and then decide the most appropriate timing for supplemental doses. Moreover, since vecuronium shows little cumulative effect even after 4 supplemental administrations in clinical-range doses, it can be concluded that vecuronium can be safely used in a wide dose range.

VO2 and VCO2 following tourniquet deflation

We examined changes in O2 uptake, CO2 output, blood pressure and heart rate following tourniquet deflation in 23 patients undergoing orthopaedic surgery of the lower extremities. A pneumatic tourniquet was applied for periods ranging from 21 to 106 min (mean 51 min). Prerelease values of VO2 (O2 uptake at each min) and VCO2 (CO2 output at each min) were 201 (37) and 174 (38) (mean (SD)) ml.min-1, respectively. Significantly, VO2 and VCO2 increased by 55% and 80%, respectively, at 2 min after tourniquet release and returned to prerelease values within 8 min. The blood pressure fell significantly and the heart rate rose significantly. The increases in CO2 output and O2 uptake were dependent on the length of tourniquet inflation time; Y = 4.7 x (tourniquet time) + 54, r = 0.88, (p less than 0.001) for CO2, and Y = 1.3 x (tourniquet time) + 99, r = 0.52, (p less than 0.05) for O2. The slope of the increase in CO2 output as a function in inflation time was 3.6 times greater than that of O2 uptake. In conclusion, CO2 output and O2 uptake increased transiently after tourniquet deflation and the extent of the increase in CO2 output is more than threefold as compared with that in O2 uptake.