Ian J. Gilmour

The effect of heated wire circuits on humidification of inspired gases

We performed this study to determine the effect of heated wire circuits on humidity delivered by several humidifiers commonly used during anesthesia. Humidifier bases from three manufacturers with several humidifying chambers for each base were tested using both heated and unheated circuits. Delivered humidity and circuit temperature were measured at the distal end of the circuit. Each chamber was tested under both continuous flow (CF) and intermittent flow (IF) conditions. IF was provided by a Servo 900 B ventilator. Adjustments of flow and volume were made for pediatric chambers. At 90 L/m CF, humidifier performance was unsatisfactory with both heated and unheated circuits. At 15 and 45 L/m CF, both distal circuit temperature (EXIT) and humidity were within acceptable limits; unheated circuits delivered more humidity than heated circuits (P < 0.05). Relative humidity was lower at 45 L/m CF than at 15 L/m (P < 0.05). During IF while all chambers provided satisfactory humidity, humidity was greater when unheated circuits were used. We conclude that when heated circuits are used, humidifying systems may fail to deliver 100% humidity to patients.

Low-frequency positive-pressure ventilation with extracorporeal carbon dioxide removal

Successful use of a new technique, low-frequency positive-pressure ventilation with extracorporeal CO2 removal (LFPPV-ECCR) is presented. The association of fulminant respiratory failure with CNS hemangio-blastoma, described in the present patient, has been reported only once before, in 1928. (Crit Care Med 1990; 18:218)

The effects of circuit and humidifier type on contamination potential during mechanical ventilation: A laboratory study

BACKGROUND This study was undertaken because of concerns that ventilator humidifiers could be exacerbating the problem of nosocomial pneumonia in patients receiving mechanical ventilation. METHODS Four different brands of humidifiers were used in conjunction with a siemens Servo 900B mechanical ventilator (Siemens Life Support Services, Solna, Sweden). In the first part, the ventilator was operated with humidifiers filled with contaminated water at room temperature. The viability of airborne particles and the effect of flow rates on the number of particles produced were assessed. In the second part, we measured the effect of time and temperature on bacterial survival in humidifier chambers. Because only bubble-through humidifiers were determined to produce infectious particles, the speed with which a contaminated bubble-through humidifier could infect circuit condensate was also determined. Aliquots of chamber water and circuit condensate, as well as air samples and distal circuit swabs, were cultured. RESULTS Humidifiers other than bubble-through humidifiers did not produce aerosols. Particle production by bubble-through humidifiers varied directly with flow rate (R2 = 0.91). Chamber temperatures did not affect chamber colony counts except in bubble-through humidifiers. Although chamber colony counts in bubble-through humidifiers decreased with time, organisms remained viable throughout the study. When bubble-through humidifiers were heated, both condensate and effluent gas became heavily contaminated within minutes of flow initiation. CONCLUSIONS Bubble-through humidifiers produce aerosols that readily contaminate both circuit condensate and effluent gas. Avoiding bubble-through humidifiers should improve patient safety while allowing changes in practice that can result in significant cost savings.

Preextubation ventilatory measurements in newborns and infants.

Maximum inspiratory pressure, inspiratory capacity, and minute ventilation were measured in a group of infants prior to extubation to determine whether these parameters predicted successful extubation. Data obtained suggested that maximum inspiratory pressure and inspiratory capacity more accurately assessed the patients ability to tolerate extubation than minute ventilation, pH, PCO2, or respiratory rate. A maximum inspiratory pressure of greater than 33 torr and an inspiratory capacity of greater than 150 ml/m2 were predictive of successful extubation.

Contamination of a hospital oxygen supply

There are a number of possible sites where difficulties might arise in hospital gas delivery systems (1). Sprague and Archer (2) list 14 different causes of hypoxic gas mixtures for anesthesia systems alone. Although problems with contamination of hospital central oxygen supplies have been known to occur, fortunately they are rare. In one reported instance, gross pollution of the oxygen supply with argon resulted in serious patient injury (3). We now describe an episode involving the central oxygen supply at a teaching hospital that illustrates another unreported manner by which contamination of oxygen supplies may occur. More important, this contamination was not detected by the usual oxygen monitoring systems.

Modular indirect calorimeter suitable for long-term measurements in multipatient intensive care units

ObjectiveThe construction of an indirect calorimeter capable of long-term automated sequential monitoring of multiple patients in adult and pediatric ICUs. DesignA prototype system utilizing modular engineering principles, including central respiratory mass spectrometer; validation by organic solvent combustion and nitrogen dilution methods, and Tissot spirometer. SettingSurgical and pediatric ICUs in a tertiary care university hospital. ResultsWhen expired minute volume was measured over a range of 4 to 28 L in six intubated patients, expired minute volume measured by the prototype system demonstrated a correlation coefficient of .998 compared with simultaneous expired minute volume measured by a Tissot spirometer. Organic solvent combustion demonstrated a maximum error of 3.8% for oxygen consumption (Vo2) and an average error of 1.73 ± 1.25% (SEM). The maximum error for the respiratory quotient was 3.0%, with an average error of 1.75 ± 1.07%. Vo2 (predicted) vs. Vo2 (measured) demonstrated a correlation coefficient of .997. Validation with the nitrogen dilution method over a range of Fio2 from 0.21 to 0.60 demonstrated a maximum error of 7.9%, with an average error of −1.72 ± 1.1% (n = 51). ConclusionsIndirect calorimetry by means of a shared system for measurements in multiple patients in ICUs is feasible and cost effective utilizing modular principles and a centralized respiratory gas analyzer. (Crit Care Med 1991; 19:963)

Safety and efficacy of a ventilator database interface

This report describes a ventilator dysfunction that arose during the mechanical ventilation of a lung transplant recipient. The problem was discovered because the data on the computer-based information management system (CIMS) was different from that on the ventilators dials. This incident is important because of the continued extensive use of analog mechanical ventilators, the increasing popularity of CIMS, and the patient safety implications of the incident.