British journal of anaesthesia
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Comparative Study
Midazolam versus propofol for reducing contractility of fatigued canine diaphragm.
The effects of midazolam and propofol on the contractility of fatigued canine diaphragm were examined. Diaphragmatic fatigue was induced by intermittent supramaximal bilateral electrophrenic stimulation at a frequency of 20 Hz applied for 30 min. After fatigue had been induced, group I (n=10) received no study drug, group II (n=10) was given a propofol infusion (0.1 mg kg(-1) loading dose plus 1.5 mg kg(-1) h(-1) maintenance dose) and group III (n=10) was given a midazolam infusion (0.1 mg kg(-1) loading dose plus 0.1 mg kg(-1) h(-1) maintenance dose). ⋯ Compared with group I, Pdi at 20 Hz stimulation was lower than fatigued values (P<0.05) during administration of the study drug in groups II and III. The decrease in Pdi was greater in group III than in group II (P<0.05). In conclusion, midazolam compared with propofol is associated with an inhibitory effect on contractility in the fatigued canine diaphragm.
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Reflex cardiovascular depression with vasodilation and bradycardia has been variously termed vasovagal syncope, the Bezold-Jarisch reflex and neurocardiogenic syncope. The circulatory response changes from the normal maintenance of arterial pressure, to parasympathetic activation and sympathetic inhibition, causing hypotension. This change is triggered by reduced cardiac venous return as well as through affective mechanisms such as pain or fear. ⋯ Treatment includes the restoration of venous return and correction of absolute blood volume deficits. Ephedrine is the most logical choice of single drug to correct the changes because of its combined action on the heart and peripheral blood vessels. Epinephrine must be used early in established cardiac arrest, especially after high regional anaesthesia.