PubMed · 8131592
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M Servilla, S Q Simpson. 1994. Oximeter malfunction.. https://doi.org/10.1378/chest.105.3.975a
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UNLABELLED: Syringe drivers are used in anaesthetics, intensive care and emergency medicine to deliver small volumes of highly potent drugs with continuous, constant and reproducible flow. For early recognition of interruptions of the drug delivery caused by occlusion of the infusion system, an alarm is triggered as soon as the system pressure exceeds a certain limit. The sensitivity of this alarm depends on the flow rate, type-specific cut-off pressure and the elastic parameters of the infusion system. The sudden release of pressure built up in the system after occlusion occurred can cause delivery of an uncontrolled drug bolus and hence an additional hazard. METHODS: Six syringe drivers that are widely used in clinical practice were tested for alarm delay and bolus delivery in the event of an occlusion in the system. First, the alarm pressures at flow rates of 10, 50 and 100 ml/h were measured. Then the alarm delay time and bolus volumes post-occlusion were assessed, using a basic infusion system (syringe + single infusion set). Finally, several alterations to the system like extension, tap battery with germ filters or branching were made and their impact on alarm delay and bolus volume measured. RESULTS: Because of the great differences in alarm pressures between the devices tested, there were marked differences in the alarm delay at same flow rates. Predictably, there was an indirect proportional link between alarm delay and flow rate. Using the basic infusion system, alarm delays between 23 s and 143 min were measured. In two of the tested syringe drivers, a pressure-release mechanism is activated with the pressure alarm, which prevented bolus application. In the other devices, release of the pressure in the occluded system caused boli of 0.5-7 ml. Variations in the actual syringe volume and insertion of a second connection tube had no impact on alarm delay and bolus volume. Tap batteries, parallel running syringe drivers or trapped air in the system, however, caused marked increase in both alarm delay (107%) and bolus volume (+147%). DISCUSSION: Unidentified occlusions of the system cause grave malfunctioning of syringe drivers. While applying highly potent drugs, the discontinuation of drug delivery with subsequent bolus application can cause vital danger to the patient. As a result of the significant time delays in the pressure alarms, the devices tested do not provide sufficient protection against unrecognized system occlusion. Syringe drivers with adjustable alarm pressure can be set close to the actual infusion pressure. A further important point is that one should aim at a reduction in the elastic properties of the infusion set because of the great impact on alarm delay and bolus volume.
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An adequate respiratory protective device should keep the concentration of the pollutant inside the facepiece below the appropriate occupational exposure limit. Filtering respirators will not provide adequate protection if the device fails in an atmosphere which is immediately dangerous to life or health (IDLH). It has therefore been suggested that in contaminant concentrations above an IDLH level it is more appropriate to select breathing apparatus with an emergency breathing facility. In this paper IDLH levels published by the US National Institute of Occupational Safety and Health have been compared with UK occupational exposure limits. For some substances there was a relatively small difference between the IDLH level and the short-term occupational exposure limit (STEL). The median ratio of the IDLH level to the STEL was 10 for gases and vapours and 50 for aerosols. For almost half the substances with UK occupational exposure limits there is no IDLH value. It is concluded that the published IDLH concentrations are, on their own, an insufficient basis for selecting breathing apparatus over a filtering respirator. It is equally important to consider the likelihood that a filtering device may fail catastrophically since this determines the risk from wearing a respirator in an IDLH atmosphere. More emphasis should be placed on the control of potentially high exposure levels by means other than respiratory protection.