International journal of clinical monitoring and computing
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Int J Clin Monit Comput · Apr 1989
A microcomputer system for on-line monitoring of pulmonary function during artificial ventilation.
Standard monitoring of the artificially ventilated patient in the intensive care unit (ICU) and during anaesthesia includes repeated determinations of arterial blood gases, airway pressure and expired volume. However, there is a need for more extensive monitoring of the critically ill ventilator treated patient, and this is possible by better utilization of modern technology. Information on a variety of variables related to both pulmonary mechanics and gas exchange has long been accessible in the lung-function laboratory. ⋯ In studies of ten artificially ventilated patients the coefficients of variation (CV) were below 10% for directly obtained variables (tidal volume, airway pressure, end-tidal and mixed expired carbon dioxide, carbon dioxide production, airway dead space), whereas the derived variables (compliance, phase III carbon dioxide slope) were associated with greater variability, with CVs ranging from 1.3 to 24% (median 6.25% and 8.65% respectively). The accuracy in estimating dead space variations was checked in two ventilator-treated patients by adding known dead space volumes. Simple regression analysis yielded an r value of 0.98 indicating adequate correctness of measurements and calculations.
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Int J Clin Monit Comput · Jan 1989
The use of pulse oximetry in post-operative hypoxaemia in patients after propofol induction of anaesthesia.
Pulse oximetry was used to measure changes in oxygen saturation in the early post-operative phase in three groups of 50 patients in whom anaesthesia was induced with propofol. One group breathed room air during induction and anaesthesia was maintained with halothane whereas the other two groups both breathed oxygen during induction and anaesthesia was maintained with either halothane inhalation or a propofol infusion. In 59 patients distributed fairly evenly between the three groups the oxygen saturation fell below 90%; the mean minimum oxygen saturation was 91.7 +/- 0.3 and the mean time at which it occurred was 3.9 +/- 0.4 min after the anaesthetic was withdrawn. Neither the inhalation of oxygen during induction nor the anaesthetic technique affected the decrease in postoperative oxygen saturation but the infusion group took significantly longer to recover consciousness.
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Int J Clin Monit Comput · Jan 1988
Comparative StudyAn automated method of separating patient from ventilator work on the lungs.
This paper describes a method of determining the amount of work on the lungs done by the patient and the ventilator using various modes of ventilation. The method uses a pneumotachograph to measure air flow, and measures pressure from an esophageal balloon and at the airway. The patient's work is separated from the ventilator work by analysis of the esophageal pressure. ⋯ The studies of normal subjects show that in the assist mode with increased airway resistance, significant work by the subject is required to trigger the ventilator. Two patients are presented when the assist mode resulted in excessive amounts of work and fatal outcomes. Measurement of the mechanical work required of the patient can provide useful information for the control of ventilator therapy.
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Int J Clin Monit Comput · Jan 1988
'Anestheticography': on-line monitoring and documentation of inhalational anesthesia.
The safe practice of inhalational anesthesia requires control over the amount of volatile anesthetic delivered to the patient. With minimal fresh gas flow this is facilitated by continuous monitoring and recording of the agent's concentration ('Anestheticography'). Alterations brought about by routine clinical maneuvers become visible. ⋯ Initiating emergence by closing the vaporizer during minimal flow led to a slow decrease in concentration whilst at a flow of 61/min the inspiratory isoflurane concentration rapidly decreased to subanesthetic levels. Insertion of a charcoal filter into the inspiratory limb of the breathing circuit immediately dropped the inspiratory concentration to undetectable levels. 'Anestheticography' is a useful means of monitoring and documentation of inhalational anesthetic. With the use of a charcoal filter all advantages of minimal flow anesthesia can be realized throughout the entire anesthetic, including emergence.
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This computer program depicts the concentration-time curves for the nondepolarizing neuromuscular blocking agents. It simulates their administration by single and multiple iv injections, and with continuous infusion, alone and in combination. It provides the plasma concentrations related to 75% and 25% depression of the twitch response, using these to calculate clinically useful pharmacodynamic values, such as the duration of surgical relaxation, and the recovery index. These simulations allow the user to contrast the time-course of relaxation to be expected with various dosage regimens.