British journal of anaesthesia
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Physiological (VDphys) and anatomical (VDanat) deadspaces were measured in seven anaesthetized, paralysed and intubated adult patients ventilated at normal and high frequencies. To maintain a constant PaCO2 while increasing the ventilation frequency from 15 to 120 b.p.m., the mean VT was decreased from 454 +/- 62 ml (mean +/- SD) to 117 +/- 9 ml. ⋯ This study showed that the deadspace volume measured conventionally was not a constant factor, was mainly a function of VT and was a determinant of tidal and minute volume requirement even during high frequency ventilation. The variable VDphys showed a wide variation between subjects, and appeared to have a mean minimal value of approximately 1.1 ml kg-1 at 80 b.p.m. in adult human subjects with a tracheal tube in situ--a value about half the VDphys measured at conventional normal tidal volumes and ventilation frequencies.
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The problems of selection of tracheal tubes, and the need for a rationale, are outlined. Tracheal tubes of 7.5 mm and 8.5 mm i.d. are recommended for female and male patients, respectively. ⋯ To provide a seal with low pressure-high volume cuffed tubes, cuff sizes of 20.5 mm and 27.5 mm are recommended for female and male patients, respectively. The mechanism of sealing with low pressure-high volume cuffs is reviewed.
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The effects of frequency, tidal volume and added deadspace on carbon dioxide clearance were measured during high frequency jet ventilation at 1, 3 and 5 Hz in dogs. With a short, small volume deadspace, carbon dioxide clearance increased with minute volume at each frequency, but for a given minute volume the clearance decreased with increase in frequency. At 5 Hz, carbon dioxide clearance was less than carbon dioxide production. ⋯ At 5 Hz, an increased volume of added deadspace had little effect on carbon dioxide clearance, but increased length, without change in volume, decreased clearance. Carbon dioxide clearance was increased by placing the jet at the lung end of the tracheostomy tube. It is concluded that at 1 Hz, carbon dioxide elimination is governed by bulk flow, but at 5 Hz other mechanisms are important.
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Randomized Controlled Trial Comparative Study Clinical Trial
Comparison of four non-depolarizing neuromuscular blocking drugs in the suppression of the oculocardiac reflex during strabismus surgery in children.
Eighty children (aged 2-12 yr) undergoing strabismus surgery were randomly assigned to receive tubocurarine, alcuronium, pancuronium or vecuronium during anaesthesia with thiopentone, fentanyl and nitrous oxide in oxygen. Heart rate and rhythm were recorded before and after the induction of anaesthesia and before and during traction on an extraocular muscle. End-tidal carbon dioxide concentration and the degree of neuromuscular blockade were monitored. Alcuronium seemed to give more protection against the oculocardiac reflex (defined as a 20% decrease in heart rate) than did tubocurarine, pancuronium or vecuronium.