Anesthesia and analgesia
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Anesthesia and analgesia · Jul 2002
Comparative StudyE-cylinder-powered mechanical ventilation may adversely impact anesthetic management and efficiency.
Anesthesiologists often administer care outside the operating room. These locations may depend on gas cylinders for their oxygen source more than the operating suites supplied by dedicated central pipelines. Using full E-cylinders, we determined the oxygen consumption of two often used, pneumatically driven anesthesia ventilators to answer three questions: How much time is available when mechanically ventilating patients in the setting of absent or malfunctioning central oxygen pipeline? How much oxygen is used by the ventilator to drive the bellows? How does changing the inspiratory to expiratory ratio and the inspiratory flow (Narkomed ventilator only) influence oxygen use? At a ventilation of 5 L/min, we found that mechanical ventilation consumes between 59% and 85% of the available oxygen in an E-cylinder to drive the ventilator at fresh gas flows ranging from 1 to 10 L/min. The time span until the low oxygen alarm sounded ranged from 38 to 99 min. Alteration of the inspiratory flow but not the inspiratory to expiratory ratio had a significant impact. Clinicians must recognize that mechanical ventilation using E-cylinders rapidly depletes this sole oxygen source and could jeopardize patient safety. Conversely, manual or spontaneous ventilation with low fresh gas flows minimizes oxygen depletion. ⋯ The time available to ventilate patients with an E-cylinder tank as the sole oxygen source was found to be as short as 38 min. Clinicians must recognize that mechanical ventilation using oxygen cylinders rapidly depletes oxygen and could jeopardize patient safety.
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Anesthesia and analgesia · Jul 2002
Modeling the effect of progressive endotracheal tube occlusion on tidal volume in pressure-control mode.
A recognized hazard of prolonged endotracheal intubation is progressive airway occlusion resulting from deposition of secretions on the inner surface of the endotracheal tube (ETT). When volume-controlled ventilation is used, progressive ETT occlusion may be detected by monitoring the difference between peak and plateau airway pressures. In pressure-controlled modes, however, inspiratory airway pressures are preset and thus cannot act as a warning indicator. Instead, changes in delivered tidal volumes may aid the diagnosis of ETT occlusion. To determine whether tidal volume monitoring effectively detects progressive ETT occlusion, we mathematically modeled the response of a ventilator operating in pressure-controlled mode to increasing airway resistance. To corroborate our model, we then bench-tested the Siemens 300 and Puritan-Bennett 7200 ventilators by using a test lung and a series of ETTs ranging in size from 9.0 to 3.5 mm inner diameter to simulate progressive occlusion. We found that when pressure-controlled mode was used, progressive ETT occlusion did not reduce delivered tidal volumes until occlusion was nearly complete. We conclude that prolonged use of pressure-controlled mode may allow significant ETT obstruction to build up undetected, risking complete ETT occlusion and complicating the perioperative care of patients ventilated with this mode. ⋯ Although increasing airway pressures during volume-controlled ventilation allow early recognition of endotracheal tube (ETT) obstruction, airway pressures with pressure-controlled ventilation are fixed. We found during tests of two intensive care unit ventilators that although ETT obstruction reduces delivered tidal volumes during pressure-controlled ventilation, reductions do not occur until occlusion is advanced.
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Anesthesia and analgesia · Jul 2002
Comparative Study Clinical TrialSensitivity to vecuronium in seropositive and seronegative patients with myasthenia gravis.
Patients with myasthenia gravis (MG) are hypersensitive to nondepolarizing neuromuscular blocking drugs. Although antibodies to the acetylcholine receptor (AChR) often are observed in MG patients, 10% to 30% of patients do not show an anti-AChR antibody. Little is known about differences in sensitivity to nondepolarizing neuromuscular blocking drugs between MG patients with and without anti-AChR antibody. Hypothesizing that seronegative patients are as sensitive to vecuronium as seropositive patients, we assessed sensitivity in seropositive and seronegative MG patients and in non-MG patients (n = 8 each). During anesthesia with sevoflurane (2.5%) and nitrous oxide (60%) in oxygen, neuromuscular transmission was monitored by measuring the twitch tension of the adductor pollicis muscle with supramaximal stimulation. After baseline measurements, 10 microg/kg IV dose increments of vecuronium were administered sequentially until blockade exceeded 90%. The degree of blockade and onset time after the initial 10 microg/kg of vecuronium were assessed, and doses required to exceed 90% blockade were recorded. In addition, effective doses of 50% and 95% for vecuronium were calculated from a single data point. Both types of MG patients showed increased sensitivity to vecuronium compared with non-MG patients. ⋯ Hypothesizing that seronegative patients are as sensitive to vecuronium as seropositive patients, we assessed sensitivity in seropositive and seronegative myasthenia gravis (MG) patients and in non-MG patients. They were, indeed, both equally sensitive to vecuronium.
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Anesthesia and analgesia · Jul 2002
Case ReportsThe resolution of ST segment depressions after high right thoracic paravertebral block during general anesthesia.
Thoracic epidural, stellate ganglion, and thoracic paravertebral blocks all relieve angina. We report a case of intraoperative resolution of ST segment depression after a right thoracic paravertebral block.
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Anesthesia and analgesia · Jul 2002
Sampling error can significantly affect measured hospital financial performance of surgeons and resulting operating room time allocations.
Hospitals with limited operating room (OR) hours, those with intensive care unit or ward beds that are always full, or those that have no incremental revenue for many patients need to choose which surgeons get the resources. Although such decisions are based on internal financial reports, whether the reports are statistically valid is not known. Random error may affect surgeons' measured financial performance and, thus, what cases the anesthesiologists get to do and which patients get to receive care. We tested whether one fiscal year of surgeon-specific financial data is sufficient for accurate financial accounting. We obtained accounting data for all outpatient or same-day-admit surgery cases during one fiscal year at an academic medical center. Linear programming was used to find the mix of surgeons' OR time allocations that would maximize the contribution margin or minimize variable costs. Confidence intervals were calculated on these end points by using Fieller's theorem and Monte-Carlo simulation. The 95% confidence intervals for increases in contribution margins or reductions in variable costs were 4.3% to 10.8% and 6.0% to 8.9%, respectively. As many as 22% of surgeons would have had OR time reduced because of sampling error. We recommend that physicians ask for and OR managers get confidence intervals of end points of financial analyses when making decisions based on them. ⋯ The common approach of using one fiscal year of perioperative accounting data can be insufficient to prevent random error from influencing important management decisions. When accounting data are used for hospital and operating room management decision making, confidence intervals should be calculated for the key financial variables (e.g., variable cost per hour of operating room time).