Anaesthesia
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Comparative Study
The effect of insufflation leaks upon ventilation. A quantified comparison of ventilators.
Some ventilator-dependent patients use uncuffed tracheostomy tubes, resulting in fluctuations in the minute volume of ventilation. Bedside measurement of ventilation is difficult because of the insufflation and exsufflation leaks. This laboratory study of five different ventilators measured the tidal volumes achieved with three insufflation leaks introduced in an increasing order of magnitude and at three levels of compliance. ⋯ The turbine-driven pressure-limited ventilator retained a peak pressure of 20.5 cmH2O and lost only 14% of the volume, whereas the volume ventilators lost 65% of the tidal volume. The loss of volume was 3% for every cmH2O decrease in airway pressure due to a leak, regardless of the ventilator or compliance. Using the Friedman test, the differences between the volume ventilators and the pressure ventilators were significant whilst the three pressure-limited ventilators did not perform significantly differently from each other.
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Randomized Controlled Trial Comparative Study Clinical Trial
Intra-ocular pressure during cardiopulmonary bypass--a comparison of crystalloid and colloid priming solutions.
Raised intra-ocular pressure secondary to alterations in plasma oncotic pressure has been implicated in the development of optic neuropathy after cardiopulmonary bypass. Patients presenting for open heart surgery received either crystalloid (n = 9) or colloid (n = 10) priming solutions for cardiopulmonary bypass. No differences in intra-ocular pressure or plasma oncotic pressure occurred between the groups before the onset of cardiopulmonary bypass. ⋯ At the same time plasma oncotic pressure decreased from approximately 20 mmHg in both groups to 10.6 mmHg with crystalloid and 15.7 mmHg with colloid primed cardiopulmonary bypass solutions (p < 0.05). Over the following hour of cardiopulmonary bypass, intra-ocular pressure and plasma oncotic pressure tended to return towards their pre-cardiopulmonary bypass values. Changes in plasma oncotic pressure, through fluid shifts, may have contributed towards this unexpected increase in intra-ocular pressure with crystalloid primed cardiopulmonary bypass.
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Randomized Controlled Trial Comparative Study Clinical Trial
Intra-operative patient-controlled sedation and patient attitude to control. A crossover comparison of patient preference for patient-controlled propofol and propofol by continuous infusion.
Intra-operative patient controlled sedation with propofol (bolus dose 18 mg over 5.4 s; lockout period 1 min) has been compared to continuous propofol infusion (3.6 mg.kg-1.h-1) in a randomised crossover study of 38 ASA 1 or 2 day surgery patients undergoing two-stage bilateral extraction of third molar teeth under local anaesthesia (76 procedures). Mean (SD) propofol used (mg.kg-1) was less with patient-controlled sedation (2.39 (1.28) than with the infusion (2.58 (0.84)) but the difference was not statistically significant. There were only minor differences between the methods in postoperative recovery of cognitive function and no differences for patient cooperation and surgeon's satisfaction with sedation. ⋯ Sedation was no deeper than eyelid closure with response to command in all 76 procedures. This level was reached in all 38 infusion cases but in only 26 cases with patient-controlled sedation, where 12 patients remained less sedated (p < 0.01). Patient-controlled sedation with propofol provided safe sedation and was strongly preferred over the infusion by a large proportion of patients.
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An investigation of end-tidal carbon dioxide tension changes was carried out in 19 healthy adult patients undergoing laparoscopic cholecystectomy. Following induction of anaesthesia, and throughout surgery, the end-tidal carbon dioxide tension was continuously monitored by capnography. ⋯ Correlation of the individual maximum end-tidal carbon dioxide tension during laparoscopy with the corresponding baseline value prior to carbon dioxide insufflation showed a positive linear relationship (correlation coefficient 0.86). The correlation showed that an end-tidal carbon dioxide tension of 5.32 kPa (40 mmHg) can be achieved during laparoscopy when the baseline value is adjusted to around 4.0 kPa (30 mmHg).