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PubMed2003

[Impact of medical prescription computerisation on the incidence of adverse drug effects].

INTRODUCTION: Adverse drug effects are a significant public health problem. Prescription errors are responsible for a significant proportion of these adverse effects. METHODS: We have aimed to improve the link between generation of and interpretation of a prescription through computerisation. The prescription sheet, which is generated daily, was organised to allow care planning without the need to re-copy out treatments on the sheet. A prescription aid was available which was based on a core group of drugs commonly used in our respiratory service. The aim of the study was to compare the various types of errors observed during 6 weeks of computerized prescriptions (229 files) to a retrospective series of handwritten prescriptions of the service at an identical time (184 files) the previous year. The case-mix was identical for both analysed periods. RESULTS: The total number of technical prescribing errors in the 1,599 handwritten lines (49.27% error) was significantly higher (p<0.001) than the 1,805 computerized prescriptions lines (42.88% error). The errors of copying (p<0.001), eligibility (p<0.001) and incorrect spelling (p<0.05) were the main sources of error which were significantly reduced by computerisation. CONCLUSION: Computerised prescription is likely to reduce the incidence of prescribing errors and adverse drug effects.

Clinical Pharmacy Information Systems↗
PubMed1987

Activity measurements of calcium, sodium, potassium, and chloride after equilibrium dialysis used to show lack of evidence for protein interference with calcium electrodes.

We measured the activity of Ca2+, Na+, K+, and Cl- with ion-selective electrodes after equilibrium dialysis of solutions with different albumin concentrations. The calculated Donnan ratio was the same for all ions in the same solution and increased with the albumin concentration, as predicted by the Donnan theory. The Donnan distribution ratio for Ca2+ was similar, as determined with instruments from three different manufacturers. For healthy subjects and patients with renal stone disease, we did not find any correlation between serum concentrations of ionized calcium and albumin. The discordance between measured ionized calcium and albumin-corrected total calcium depended on the correction algorithm we utilized. The difficulties of absolutely proving or disproving a protein error in these measurements are discussed, but our data are not consistent with protein being a source of error in measurements of ionized calcium.

Adult↗
PubMed1994

[Early mortality in polytrauma. A critical analysis of preventable errors].

In order to assess the impact of errors on outcome and to identify the rate of preventable deaths we investigated 40 premature deaths that had occurred among polytraumatized patients (blunt trauma; average ISS 53 points) in a prospective study (years 1986-1992) in a level I trauma centre. On analysing the patients' course on the basis of a complete set of data we detected 41 management and timing errors, 15 mistakes in treatment and 8 diagnostic problems. According to the significance of the errors the patients could be divided into three groups: in group 1 (n = 12; 30%) no errors were found, in group 2 (n = 22; 45%) there were errors but these definitely had no influence on the outcome, and in group 3 (n = 6;15%) we ascertained errors with a possible influence on the deaths. In none of the 40 cases of premature death could it be definitely shown that the adverse outcome could have been avoided. In the care of polytraumatized patients there was a clear predominance of management and timing errors insofar as they accounted for 64% of all errors that occurred and had frequently preceded possibly preventable deaths (88% in group 3). To diminish sources of error in the management of polytraumatized patients we must demand that more accurate clinical standards and algorithms be developed and introduced into the treatment of such patients.

Adolescent↗
PubMed1997

Analyzing the sources of unreliability in fixed prosthodontics mock board examinations.

Mock board examinations in fixed prosthodontics were submitted to generalizability analysis in order to determine which sources of unwanted variance of measurement contribute to grade decisions and whether this lack of reliability is of practical significance. Students completed approximately three fixed prosthodontics test cases during their final year of clinic, and each case was scored by two faculty members. Of the subsamples of students where two test cases (trials) per student were graded by the same two raters, the subsamples with the highest and the lowest inter-rater reliability coefficients were chosen. Typical generalizability coefficients (reliability considering both raters and trials as sources of error) are much lower than the inter-rater reliability estimate, and the standard error of measurement is 80 percent of a grade interval on a five-point scale. In all analyses, the largest source of variance was the student-by-trial interaction, accounting for about 80 percent of the standard error of measurement or one-half a grade on a five-point scale. Even in the subsample with lowest inter-rater reliability, rater, rater-by-student interaction, and rater-by-trial interaction made no contribution to measurement error. Nor did students show evidence of improving over time. There is no possible improvement through the use of rater calibration or additional raters that would equal the improvement made by using two test cases rather than one. The concept of gradient of generalizability is introduced, and implications for initial licensure examinations are discussed.

Analysis of Variance↗
PubMed1998

[Analysis of variance of bacterial counts in milk. 1. Characterization of total variance and the components of variance random sampling error, methodologic error and variation between parallel errors during storage].

In contrast to the prevailing automatized chemical analytical methods, classical microbiological techniques are linked with considerable material- and human-dependent sources of errors. These effects must be objectively considered for assessing the reliability and representativeness of a test result. As an example for error analysis, the deviation of bacterial counts and the influence of the time of testing, bacterial species involved (total bacterial count, coliform count) and the detection method used (pour-/spread-plate) were determined in a repeated testing of parallel samples of pasteurized (stored for 8 days at 10 degrees C) and raw (stored for 3 days at 6 degrees C) milk. Separate characterization of deviation components, namely, unavoidable random sampling error as well as methodical error and variation between parallel samples, was made possible by means of a test design where variance analysis was applied. Based on the results of the study, the following conclusions can be drawn: 1. Immediately after filling, the total count deviation in milk mainly followed the POISSON-distribution model and allowed a reliable hygiene evaluation of lots even with few samples. Subsequently, regardless of the examination procedure used, the setting up of parallel dilution series can be disregarded. 2. With increasing storage period, bacterial multiplication especially of psychrotrophs leads to unpredictable changes in the bacterial profile and density. With the increase in errors between samples, it is common to find packages which have acceptable microbiological quality but are already spoiled by the time of the expiry date labeled. As a consequence, a uniform acceptance or rejection of the batch is seldom possible. 3. Because the contamination level of coliforms in certified raw milk mostly lies near the detection limit, coliform counts with high relative deviation are expected to be found in milk directly after filling. Since no bacterial multiplication takes place during storage, then error between samples always predominates the total variation. 4. The present results cannot be simply applied to other selective enumerations of microorganisms. Yet, a non-homogenous distribution should always be expected at microbial counts close to the detection limit. Technical errors arising from clustering as well as eugonic growth can additionally hamper the counting of colonies of such microorganisms. Effects of these observations in the decision-making process will be dealt with in the second communication.

Analysis of Variance↗
PubMed1988

Lack of necessity for corrections for pyloric losses and duodenogastric reflux in the performance of gastric secretory studies.

Gastric secretory studies are subject to considerable error owing to incomplete collections and to contamination by reflux of alkaline duodenal contents. Corrections for these sources of error have been defined, and they have been extensively applied in a research setting. In order to assess their utility in the performance of routine gastric secretory studies, the value of such corrections was assessed in 56 studies in patients with duodenal ulceration (10), previous surgical vagotomy (8), reflux oesophagitis (30) and primary oesophageal motility disorders (8). The effect of such corrections was small, and there were close correlations between uncorrected and corrected acid outputs in all four groups. The status of the vagal efferent gastric fibres was assessed by comparing the acid output after insulin hypoglycaemia with the maximal acid output after pentagastrin (insulin: pentagastrin ratio). The application of the corrections did not alter the conclusion regarding the assessment of vagal status in 55 of the 56 studies performed. It is concluded that such corrections are not necessary in the routine performance of gastric secretory studies.

Adult↗
PubMed1976

An examination of the xenon clearance method.

A definition of cortical and juxta-medullary regions is suggested based on a grouping of nephrons of common flow characteristics. A possible error is suggested in the xenon clearance method of measuring the regional flows. Experiments to test the source of error and its magnitude are described. It is concluded that while the error is present its effect on conventional component analysis is small.

Animals↗
PubMed1991

Accuracy of colour Doppler ultrasound velocity measurements in small vessels.

Colour Doppler ultrasound offers the possibility of imaging small vessels not visible by B-mode alone. The colour Doppler image of velocities allows the course of small vessels to be imaged in the X-Y plane of the scan provided the Doppler frequency shift is of sufficient magnitude. This permits alignments of the Doppler cursor, allowing angle correction to provide true velocity measurements from the Doppler shift obtained. Before attempting to make velocity measurements, however, it is essential to be aware of the possible error in the Z plane caused by the thickness of the Doppler sample volume. To quantify this source of error, hydrophone and flow-rig measurements were performed on an Acuson 128 colour Doppler scanner with both 5 MHz linear-array and 3.5 MHz phased-array transducers. Measurements of the transmitted pulses using a point hydrophone showed that both probes employ approximately 3.5 MHz Doppler pulses (in both colour and pulsed Doppler modes). The two transducers have the same axial resolution. In colour Doppler mode the axial length of the sample volume increases automatically with depth by up to 0.5 mm. Measurements of colour and pulsed Doppler signal strength were obtained in a controlled flow rig. Both transducers produced accurate colour flow images of the phantom at their optimum depths; flow velocity errors due to Z-plane thickness are less than 5%. There was, however, substantial error outside these optimum conditions (up to 20%).

Arteries↗
PubMed2002

Precise image-receptor calibration and monitoring of beam quality with a step wedge.

OBJECTIVE: To describe an extended bootstrap calibration procedure that uses a step-wedge absorber and minimal equipment for rapid, accurate calibration of image receptors and simultaneous monitoring of beam quality. METHODS: Multiple radiographs of a step wedge are made at different exposures, with a precision dosimeter as a reference. An iterative least-squares minimization procedure is used to fit the data with a single calibration function. The calibration range can be extended by varying two exposure parameters in addition to stepwedge thickness. Small variations in beam quality and other experimental artifacts can be detected by testing redundant data for self-consistency. As a demonstration, two photostimulable phosphor (PSP) systems were calibrated, one with a well-regulated X-ray source and the other with a poorly regulated source. RESULTS: The first PSP system was calibrated over a range of 3.2 orders of magnitude with a relative standard deviation of the estimate of only 0.36%. The slope of the calibration curve agreed with the nominal, factory-set value within 0.8% (on a logarithmic scale). The second PSP system had a nearly linear response with a relative standard deviation of the estimate of 0.44% over the upper 97% of its range. Both X-ray sources showed easily detectable variations in tube potential. CONCLUSIONS: The new calibration method eliminates many of the sources of error of previous techniques such as inverse-square sensitometry. If a suitably precise X-ray source is available, the relative accuracy is limited only by the precision of the receptor system.

Absorption↗
PubMed2000

Mathematical theory of stereotactic coordinate transformation: elimination of rotational targeting error by addition of a third reference point. Technical note.

All frame-based stereotactic procedures require localization of an anatomical target within the coordinate system of the stereotactic frame. If the target is defined by its coordinates given in a stereotactic atlas (indirect localization), the neurosurgeon faces the mathematical task of transforming atlas coordinates into frame coordinates. In the method usually used, the frame coordinates of two reference points (the anterior and posterior commissures) are obtained from computerized tomography or magnetic resonance images, and serve as the basis for the coordinate transformation. This two-point algorithm relies on the additional assumption that the frame sits on the patient's head without exhibiting roll, that is, rotation about the anteroposterior axis (y axis). Usually this assumption is nearly, but not exactly, correct. An amount of roll as small as 3 degrees can cause a targeting error on the order of 1 mm when a two-point algorithm is used. This potential source of error can be eliminated by using a new method of coordinate transformation, the derivation of which is mathematically reported in this article. The new method requires a third reference point located in the midsagittal plane, in addition to the two commissural reference points.

Algorithms↗
PubMed1980

Methodological, technical, and ethical issues of a computerized data system.

This report examines some methodological, technical, and ethical issues which need to be addressed in designing and implementing a valid and reliable computerized clinical data base. The report focuses on the data collection system used by four residency based family health centers, affiliated with the University of Massachusetts Medical Center. It is suggested that data reliability and validity can be maximized by: (1) standardizing encounter forms at affiliated health centers to eliminate recording biases and ensure data comparability; (2) using forms with a diagnosis checklist to reduce coding errors and increase the number of diagnoses recorded per encounter; (3) developing uniform diagnostic criteria; (4) identifying sources of error, including discrepancies of clinical data as recorded in medical records, encounter forms, and the computer; and (5) improving provider cooperation in recording data by distributing data summaries which reinforce the data's applicability to service provision. Potential applications of the data for research purposes are restricted by personnel and computer costs, confidentiality considerations, programming related issues, and, most importantly, health center priorities, largely focused on patient care, not research.

Computers↗
PubMed1993

Measurement of respiratory mechanics using the Puritan-Bennett 7200a ventilator.

This study was designed in order to validate the respiratory mechanical variables measured by the Puritan-Bennett 7200a ventilator equipped with the 30/40 module. Two ventilators were connected to a lung model and submitted to several breathing patterns by modifying the respiratory rate, the tidal volume, the inspiratory flow-rate and the model resistance. The inspiratory flow-rate (V), tidal volume (VT), peak inspiratory pressure (Pmax), plateau pressure (Pplat) and PEEP measured by the ventilators were compared with the same variables measured at the connection between the breathing circuit and the lung model. The compliance (C30/40) and the resistance (R30/40) calculated by the 30/40 module were compared with those calculated by using the variables measured by the reference equipment. Both ventilators made a constant underestimation of V by 2.8 and 3.7 L.min-1, respectively. The VT was measured with a mean error of less than 10 ml but did not reflect the preselected values in the presence of an intrinsic PEEP. The Pplat was overestimated by 7 and 10%, respectively. The same calibration error was observed with Pmax which was also affected by a pressure gradient due to the resistance of the breathing circuit. Even in the absence of intrinsic PEEP, C30/40 presented an error due to the combination of the measurement errors on VT, Pplat and PEEP. Finally, R30/40 presented a high percentage of error due to the combination of the measurement errors on V, Pmax, and Pplat, and to a sporadic aberrant selection of V. Due to these numerous sources of error, the two ventilators studied did not give reliable estimates of resistance and compliance.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1994

Reliability of passive wrist flexion and extension goniometric measurements: a multicenter study.

BACKGROUND AND PURPOSE: The purpose of this study was twofold: (1) to determine whether passive wrist flexion and extension goniometric measurements using ulnar alignment, radial alignment, and volar/dorsal alignment were similar or dissimilar and (2) to examine which of these three techniques had the greatest intratester and intertester reliability. SUBJECTS: One hundred forty patients (141 wrists) were measured. The testers were 32 therapists from eight different hand/upper-extremity clinical sites around the United States. METHODS: Randomly paired testers measured passive wrist flexion and extension. The intraclass correlation coefficient (ICC) was used as an estimate of agreement for both intratherapist (model 3.1) and intertherapist (model 2.1) reliability. RESULTS: Six of the eight clinics showed significant differences among the various goniometric techniques. Flexion intratherapist mean ICCs for the radial, ulnar, and dorsal alignment techniques were .86, .87, and .92, respectively. Extension intratherapist mean ICCs were .80, .80, and .84 for the three techniques. Intertherapist flexion mean ICCs were .88, .89, and .93 for the radial, ulnar, and volar alignment techniques, respectively. Extension intertherapist mean ICCs were .80, .80, and .84 for the three techniques. The standard error of measurement was also used to quantify reliability, with the volar/dorsal alignment technique consistently producing less error than the ulnar and radial alignment techniques. The generalizability theory statistical model was utilized to identify the sources of error. The patient contributed to variance the most, although inherent error within the study, diagnostic category, therapeutic approach, and goniometric technique also contributed. CONCLUSION AND DISCUSSION: The overall results indicated there were differences among the three goniometric techniques. The volar/dorsal alignment technique is the goniometric technique of choice, as it consistently had the greatest reliability.

Adolescent↗
PubMed1990

Errors of measurement affecting the reliability and validity of data acquired from self-assessed quality of life.

Research often uses self-assessed quality of life. Quality of life cannot be observed directly; other variables have to serve as its indicators. In the case of self-assessed quality of life, the researcher has to rely upon the individual's own statement as to how she/he feels. The subjective nature of the term creates problems in the matter of reliability and validity of the data thus collected. Random and systematic errors of measurement are liable to influence the result of the investigations. The researcher must know the possible sources of error and make allowances for them if research into quality of life is to be a worthwhile contribution to a greater understanding of what is meant by having a good life, and of the means to achieve it.

Affect↗
PubMed1986

Health risks and air pollution--error analysis for a cross-sectional mortality study.

An attempt is made to analyze in quantitative terms the uncertainties in multiple regression estimates of the effects of air pollution on death rates. A range of factors--statistical fluctuations in numbers of deaths, differences in local age distribution, differences in smoking habits, errors in estimated pollution levels, migration, and variability of the characterization of socioeconomic effects--are assessed as potential sources of error. Both the precision and the robustness of the regression calculation are shown to be poor. Examples and illustrative calculations are given based on a study of U. K. death rates around the 1971 Census.

Air Pollution↗
PubMed1995

Medicolegal alcohol determination: variability of the blood- to breath-alcohol ratio and its effect on reported breath-alcohol concentrations.

There is substantial agreement among scientists that the variability of a person's blood- to breath-alcohol ratio contributes significantly to the experimental error in results from breath-alcohol analysis. Some have argued that the need to correct for this source of error can be eliminated by reporting breath test results in units of breath-alcohol concentration rather than blood-alcohol concentration. A simple mathematical proof is presented to demonstrate that this is not the case. Moreover, the scientific and legal flaws of this argument are discussed, and recommendations are offered for dealing with the problems that have developed from adoption of this view.

Alcoholism↗
PubMed1999

Accidental iatrogenic intoxications by cytotoxic drugs: error analysis and practical preventive strategies.

OBJECTIVES: Drug errors are quite common. Many of them become harmful only if they remain undetected, ultimately resulting in injury to the patient. Errors with cytotoxic drugs are especially dangerous because of the highly toxic potential of the drugs involved. For medico-legal reasons, only 1 case of accidental iatrogenic intoxication by cytotoxic drugs tends to be investigated at a time, because the focus is placed on individual responsibility rather than on system errors. The aim of our study was to investigate whether accidental iatrogenic intoxications by cytotoxic drugs are faults of either the individual or the system. The statistical analysis of distribution and quality of such errors, and the in-depth analysis of contributing factors delivered a rational basis for the development of practical preventive strategies. METHODS: A total of 134 cases of accidental iatrogenic intoxication by a cytotoxic drug (from literature reports since 1966 identified by an electronic literature survey, as well as our own unpublished cases) underwent a systematic error analysis based on a 2-dimensional model of error generation. Incidents were classified by error characteristics and point in time of occurrence, and their distribution was statistically evaluated. The theories of error research, informatics, sensory physiology, cognitive psychology, occupational medicine and management have helped to classify and depict potential sources of error as well as reveal clues for error prevention. RESULTS: Monocausal errors were the exception. In the majority of cases, a confluence of unfavourable circumstances either brought about the error, or prevented its timely interception. Most cases with a fatal outcome involved erroneous drug administration. Object-inherent factors were the predominant causes. A lack of expert as well as general knowledge was a contributing element. In error detection and prevention of error sequelae, supervision and back-checking are essential. Improvement of both the individual training and work environment, enhanced object identification by manufacturers and hospitals, increased redundancy, proper usage of technical aids, and restructuring of systems are the hallmarks for error prevention. CONCLUSIONS: Errors follow general patterns even in oncology. Complex interdependencies of contributing factors are the rule. Thus, system changes of the working environment are most promising with regard to error prevention. Effective error control involves adapting a set of basic principles to the specific work environment. The work environment should allow for rectification of errors without penalty. Regular and ongoing intra-organisational error analysis needs to be an integral part of any error prevention strategy. However, it seems impossible to totally eliminate errors. Instead, if the environment guarantees timely error interception, most sequelae are avoided, and errors transform into a system-wide learning tool.

Antineoplastic Agents↗
PubMed1999

Plasma and interstitial glucose dynamics after intravenous glucose injection: evaluation of the single-compartment glucose distribution assumption in the minimal models.

Recent experimental evidence suggests that estimates of glucose effectiveness (S(G)) from the minimal model of unlabeled glucose disappearance (Cold-MM) are in error. The single-compartment glucose distribution assumption embedded in the model has been indicated as a possible source of error. In this study, to directly examine the single-compartment assumption, we measured plasma and interstitial glucose concentrations after intravenous glucose injection. Additionally, we compared the accuracy of the estimates of glucose effectiveness from the Cold-MM and the single-compartment tracer minimal model (Hot-MM). Paired labeled intravenous glucose tolerance tests (IVGTTs) were performed in each of six C-peptide-negative type 1 diabetic subjects. Two different insulin infusion protocols were used: an infusion at constant basal rates and an infusion at variable rates to mimic a normal insulin response. During the labeled IVGTT with basal insulin infusion, the microperfusion technique was employed to sample adipose tissue interstitial fluid. Marked differences between the plasma and interstitial dynamics of (cold) glucose were observed during the first 22 min after glucose injection. These results suggest that the requirements for a single-compartment representation of glucose kinetics are not satisfied during at least the first 22 min of an IVGTT. Data from the labeled IVGTT with normal insulin response were used to identify the minimal-model parameters. The measure of S(G) derived using the Cold-MM was 3.44-fold higher than the direct measure obtained from the labeled IVGTT with basal insulin infusion (0.0179+/-0.0027 vs. 0.0052+/-0.0010 min(-1), P<0.01). The measure of glucose effectiveness (S(G)*) derived by the Hot-MM was 1.36-fold higher than the direct measure available from the labeled IVGTT with basal insulin infusion (0.0079+/-0.0013 vs. 0.0058+/-0.0004 min(-1), P>0.26). These results suggest that the Hot-MM is more appropriate for the evaluation of glucose effectiveness than the Cold-MM.

Adult↗