A Structured Approach for Investigating the Causes of Medical Device Adverse Events.

Aim. Medical device-related adverse events are often ascribed to "device" or "operator" failure although there are more complex causes. A structured approach, viewing the device in its clinical context, is developed to assist in-depth investigations of the causes.

Oscillometric sphygmomanometers: a critical appraisal of current technology.

Aim: Blood pressure (BP), a key vital sign, monitors general health. Oscillometric devices are increasingly used for measurement, although their accuracy continues to be critically debated. A functional block diagram is used to review the components that affect accuracy.

How important is the recommended slow cuff pressure deflation rate for blood pressure measurement?

Cuff pressure deflation rate influences blood pressure (BP) measurement. However, there is little quantitative clinical evidence on its effect. Oscillometric pulses recorded from 75 subjects at the recommended deflation rate of 2-3 mmHg per second were analyzed.

Estimation of mean arterial pressure from the oscillometric cuff pressure: comparison of different techniques.

Mean arterial pressure (MAP) is determined in most automated oscillometric blood pressure devices, but its derivation has been little studied. In this research, different techniques were studied and compared with the auscultatory technique. Auscultatory systolic and diastolic blood pressure (SBP and DBP) were obtained in 55 healthy subjects by two trained observers, and auscultatory MAP was estimated.

Best practice in the measurement of body temperature.

In the last two decades, there has been a significant change in the technology of clinical thermometry. Mercury-in-glass thermometers have been replaced with electronic devices that offer faster readings with minimal inconvenience to the patient. Each user should be aware of the characteristics and limitations of these devices to interpret correctly the temperature reading on the display.

Auditing the technology used to measure blood pressure.

Patient management requires accurate blood pressure measurement, but there is concern about the accuracy of the equipment. Makes and types of sphygmomanometers and sizes of their associated cuffs used in hospital wards and outpatient departments were recorded and calibration checked. Half the sphygmomanometers were oscillometric, 32% aneroid and 18% mercury.

Thermal- and light-induced spin crossover in a guest-dependent dinuclear iron(II) system.

We previously reported the dinuclear material [Fe(II) (2)(ddpp)(2)(NCS)(4)] x 4 CH(2)Cl(2) (1 x 4 CH(2)Cl(2); ddpp = 2,5-di(2',2''-dipyridylamino)pyridine) and its partially desolvated analogue (1 x CH(2)Cl(2)), which undergo two- and one-step spin-crossover (SCO) transitions, respectively. Here, we manipulate the type and degree of solvation in this system and find that either a one- or two-step spin transition can be specifically targeted. The chloroform clathrate 1 x 4 CHCl(3) undergoes a relatively abrupt one-step SCO, in which the two equivalent Fe(II) sites within the dinuclear molecule crossover simultaneously.

Automatic blood pressure measurement: the oscillometric waveform shape is a potential contributor to differences between oscillometric and auscultatory pressure measurements.

Objective: To explore the differences between oscillometric and auscultatory measurements.

Method: From a simulator evaluation of a non-invasive blood pressure (NIBP) device regenerating 242 oscillometric blood pressure waveforms from 124 subjects, 10 waveforms were selected based on the differences between the NIBP (oscillometric) and auscultatory pressure measurements. Two waveforms were selected for each of five criteria: systolic over and underestimation; diastolic over and underestimation; and close agreement for both systolic and diastolic pressures.

Effect of the shapes of the oscillometric pulse amplitude envelopes and their characteristic ratios on the differences between auscultatory and oscillometric blood pressure measurements.

Introduction: Oscillometric noninvasive blood pressure (NIBP) devices determine pressure by analysing the oscillometric waveform using empirical algorithms. Many algorithms analyse the waveform by calculating the systolic and diastolic characteristic ratios, which are the amplitudes of the oscillometric pulses in the cuff at, respectively, the systolic and diastolic pressures, divided by the peak pulse amplitude. A database of oscillometric waveforms was used to study the influences of the characteristic ratios on the differences between auscultatory and oscillometric measurements.

Validation of oscillometric noninvasive blood pressure measurement devices using simulators.

Oscillometric noninvasive blood pressure devices measure blood pressure using an indirect method and proprietary algorithms and hence require validation in clinical trials. Clinical trials are, however, expensive and give contradictory results, and validated devices are not accurate in all patient groups. Simulators that regenerate oscillometric waveforms promise an alternative to clinical trials provided they include sufficient physiological and pathological oscillometric waveforms.

Structural and magnetic resolution of a two-step full spin-crossover transition in a dinuclear iron(II) pyridyl-bridged compound.

A dinuclear iron(II) complex containing the new pyridyl bridging ligand, 2,5-di(2',2''-dipyridylamino)pyridine (ddpp) has been synthesised and characterised by single-crystal X-ray diffraction, magnetic susceptibility and Mössbauer spectral methods. This compound, [Fe(2)(ddpp)(2)(NCS)(4)]4 CH(2)Cl(2), undergoes a two-step full spin crossover. Structural analysis at each of the three plateau temperatures has revealed a dinuclear molecule with spin states HS-HS, HS-LS and LS-LS (HS: high spin, LS: low spin) for the two iron(II) centres.

Extracting oscillometric pulses from the cuff pressure: does it affect the pressures determined by oscillometric blood pressure monitors?

Objective: Oscillometric noninvasive blood pressure measurement devices determine the pressures by analysing the relationship between the pressure in an occluding cuff and low-amplitude pressure pulses (oscillometric pulses) induced in the cuff by the arterial pressure wave. This paper examines the effects on the pulses and oscillometric pulse amplitude envelope of the filters that extract the pulses from the cuff pressure.

Methods: The cuff pressure and oscillometric pulses extracted by the filter were recorded from a Critikon DINAMAP and a Datex Cardiocap, chosen because of accessibility of the filtered and unfiltered signals.

Can a simulator that regenerates physiological waveforms evaluate oscillometric non-invasive blood pressure devices?

Introduction: A simulator has been developed that enables previously recorded clinical oscillometric waveforms to be regenerated for testing oscillometric non-invasive blood pressure measurement devices. Two non-invasive blood pressure devices were evaluated using the simulator with its database of 243 waveforms, to assess the value of a simulator for such evaluations.

Methods: Two oscillometric non-invasive blood pressure devices, both of which had previously been validated against auscultatory references, were selected.

Differences in oscillometric non-invasive blood pressure measurements recorded by different revisions of the Philips Component Monitoring System.

Objective: To investigate whether a simulator can detect differences in oscillometric noninvasive blood pressure measurements in different revisions of the Philips Component Monitoring System. Philips revised the intraarterial-based algorithm with software revision C.0, and added an auscultation-based algorithm in revision C.

Do SpaceLabs ambulatory non-invasive blood pressure recorders measure blood pressure consistently over several years use?

Objective: To assess the measurement consistency of SpaceLabs ambulatory recorders (Spacelabs, Washington, USA) that are in regular use.

Methods: A total of 14 SpaceLabs 90207 and one 90217 ambulatory recorders were tested for measurement consistency using the Dynatech CuffLink (Dynatech, Nevada, USA), a commercially available non-invasive blood pressure (NIBP) simulator. The NIBP recorders were tested at a range of pressures with 20 repeated determinations at a simulated 120/80 mmHg and five repeated determinations at simulated pressures of 80/50, 100/80, 150/100, 200/165 and 250/195 mmHg.

Learning from adverse incidents involving medical devices.

While an adverse event involving a medical device is often ascribed to either user error or device failure, the causes are typically multifactorial. A number of incidents involving medical devices are explored using this approach to investigate the various causes of the incident and the protective barriers that minimised or prevented adverse consequences. User factors, including mistakes, omissions and lack of training, conspired with background factors--device controls and device design, storage conditions, hidden device damage and physical layout of equipment when in use--to cause the adverse events.

Infusion devices: characteristics, limitations and risk management.

Safe administration of IV therapy requires skilled use of the equipment, knowledge of the associated risks and the prevention of adverse consequences. The authors outline the basic principles underpinning safe use of infusion devices.

Syringe pumps and start-up time: ensuring safe practice.

The start-up time is the delay between starting an infusion pump and the delivery of fluid at the set flow rate. Mechanical slack in syringe pumps can lead to start-up delays of an hour or more at low-flow rates. During this period no medication is delivered to the patient.

Quality improvement report: Learning from adverse incidents involving medical devices.

Problem: The NHS is perceived to have a poor record of learning from incidents. Despite efforts of the Medical Devices Agency, which issues safety warnings, adverse incidents with medical devices continue to occur, some of which result in serious injury or death through device failures, user errors, and organisational problems.

Design: Introduction of feedback notes on a supportive investigation that seeks to determine latent factors, immediate triggers, causes, and positive actions taken by staff that minimised adverse consequences.

Can simulators evaluate systematic differences between oscillometric non-invasive blood-pressure monitors?

Background: Oscillometric non-invasive blood-pressure (NIBP) monitors estimate the arterial pressure using model-specific signal processing and algorithms. Hence each model's accuracy must be clinically evaluated. Simulators may assist the evaluation, but their ability to do so has not been verified.

A simulation study of the consistency of oscillometric blood pressure measurements with and without artefacts.

Background: Oscillometric pressure is measured by analysing, in relation to the cuff pressure, low-amplitude cuff-pressure pulsations generated by each arterial pulse. The cuff pressure is sampled at the pulse rate, introducing measurement variations, which are compounded by artefactual pulses.

Objective: To study the consistency of measurements with and without artefacts using simulated waveforms.

Propaq Neonatal monitor used with its own single- or with Critikon twin-hose cuffs: does it matter?

Some oscillometric non-invasive blood pressure (NIBP) monitors use twin-hose cuffs, whereas others use single-hose cuffs. The incompatibility hinders the transfer of patients from monitors using a single-hose cuff to monitors using twin-hose cuffs and vice versa. In particular, the Propaq Encore uses a single-hose cuff, whereas the Critikon Dinamap uses a twin-hose single-bladder cuff.

A comparative evaluation of the DINAMAP 8100 and DINAMAP Compact TS using a non-invasive blood pressure simulator.

BACKGROUND: The Critikon DINAMAP 8100, although widely used in clinical practice, has been reported to measure the blood pressure with unacceptable systematic and non-systematic errors. The 8100 device has recently been succeeded by the Compact TS. OBJECTIVE: To evaluate two DINAMAP devices.