Bland-Altman Statistical Method Research Articles

The evaluation of agreement between the measurement methods used in the diagnosis of prostate cancer with the statistical methods

The aim of this study is to evaluate the compatibility of the "Computed Tomography (CT)" and "Magnetic Resonance (MR)" methods which are imaging techniques used to describe prostate cancer with the pathology accepted as the reference method. In this study, the concordance between CT and MR results and pathology results of 37 prostate cancer patients was evaluated using the Bland-Altman, Interclass Correlation Coefficient, Concordance Correlation Coefficient, Deming Regression and Passing-Bablok method comparison methods. Inter-class correlation coefficient and Concordance Correlation Coefficient values for CT-Pathology results were 0.62 and 0.62, respectively. Inter-class correlation coefficient and Concordance Correlation Coefficient values for MR-Pathology results were 0.74 and 0.75, respectively. The regression equation for the Deming regression method is y=-6.21+1.03x for CT-Pathology, whereas for the MR-Pathology y=-6.86+1.11x. When the CT-Pathology measurement values are evaluated by the Bland-Altman statistical method, the mean values of the measurement differences are -2.42 and the standard deviation is 33.50. When the agreement between MR-Pathology measurement values is examined by the Bland-Altman method, the mean values for the difference between the measurement values are 4.14 and the standard deviation is 26.78. Among the applied methods, the Bland-Altman method is the most suitable method for data structure. According to the results of the Bland-Altman method, the tumor size obtained by the pathology method can be found to be 2.4 smaller than the mean values obtained from the CT results and an average of 4.1 cc from the measurement values obtained by the MR imaging technique.

Continuous Critical Respiratory Parameter Measurements Using a Single Low-Cost Relative Humidity Sensor: Evaluation Study.

Accurate and portable respiratory parameter measurements are critical for properly managing chronic obstructive pulmonary diseases (COPDs) such as asthma or sleep apnea, as well as controlling ventilation for patients in intensive care units, during surgical procedures, or when using a positive airway pressure device for sleep apnea. The purpose of this research is to develop a new nonprescription portable measurement device that utilizes relative humidity sensors (RHS) to accurately measure key respiratory parameters at a cost that is approximately 10 times less than the industry standard. We present the development, implementation, and assessment of a wearable respiratory measurement device using the commercial Bosch BME280 RHS. In the initial stage, the RHS was connected to the pneumotach (PNT) gold standard device via its external connector to gather breathing metrics. Data collection was facilitated using the Arduino platform with a Bluetooth Low Energy connection, and all measurements were taken in real time without any additional data processing. The device's efficacy was tested with 7 participants (5 men and 2 women), all in good health. In the subsequent phase, we specifically focused on comparing breathing cycle and respiratory rate measurements and determining the tidal volume by calculating the region between inhalation and exhalation peaks. Each participant's data were recorded over a span of 15 minutes. After the experiment, detailed statistical analysis was conducted using ANOVA and Bland-Altman to examine the accuracy and efficiency of our wearable device compared with the traditional methods. The perfused air measured with the respiratory monitor enables clinicians to evaluate the absolute value of the tidal volume during ventilation of a patient. In contrast, directly connecting our RHS device to the surgical mask facilitates continuous lung volume monitoring. The results of the 1-way ANOVA showed high P values of .68 for respiratory volume and .89 for respiratory rate, which indicate that the group averages with the PNT standard are equivalent to those with our RHS platform, within the error margins of a typical instrument. Furthermore, analysis utilizing the Bland-Altman statistical method revealed a small bias of 0.03 with limits of agreement (LoAs) of -0.25 and 0.33. The RR bias was 0.018, and the LoAs were -1.89 and 1.89. Based on the encouraging results, we conclude that our proposed design can be a viable, low-cost wearable medical device for pulmonary parametric measurement to prevent and predict the progression of pulmonary diseases. We believe that this will encourage the research community to investigate the application of RHS for monitoring the pulmonary health of individuals.

Evaluation of a planar diode matrix for SRS patient-specific QA in comparison with GAFchromic films.

We validate the routine use of a two-dimensional (2D) diode matrix for patient specific pre-treatment verification for Cyberknife (CK) stereotactic radiosurgery and to compare it with film dosimetry. A total of 46 patients were selected according to the most frequent diseases treated at our institution with the CK system, that is, brain metastases, meningiomas, spine metastases, and prostate tumors. All cases were evaluated with GAFChromic EBT-3 films and SRS MapCHECK for Fixed cone, IRIS, and MLC collimators of the CK. The highest mean passing rate was observed for the SRS MapCHECK system compared to films. In order to assess if the two techniques provide statistically different results, a Wilcoxon Signed-Rank non-parametric test was performed (p<0.05) and we found gamma values significantly lower for EBT-3 films with respect to the SRS MapCHECK. We noticed a moderately significant association between the two techniques using Spearman's rank correlation coefficient (rs>0.4). We also performed the Bland-Altman statistical method: less than 5% of the differences resulted outside the range (mean±1.96×SD), so the two methods can be considered interchangeable within the combined inaccuracy. The use of SRS MapCHECK for CK patient specific quality assurance (QA) is feasible for a variety of clinical districts and could be reliably used as a replacement for radiochromic films.

Evaluation of ocular biometric parameters in keratoconic eyes relative to healthy myopic eyes.

To assess the biometric features of keratoconic eyes using the Lenstar LS900 and Pentacam systems relative to healthy myopic eyes. Seventy-three eyes of keratoconic subjects and 83 eyes of control subjects were enrolled. To evaluate the reproducibility of the Lenstar and Pentacam devices' measurements, keratometric readings [in flattest meridian (Kf), in steepest meridian (Ks), and mean (Km)], central corneal thickness (CCT), and anterior chamber depth (ACD) were obtained using both systems. Axial length and lens thickness (LT) were measured by the Lenstar. The compatibility between the two devices was investigated using the Bland-Altman statistical method. Axial length was longer in the myopic group than in eyes with keratoconus (24.94 ± 0.7 and 23.88 ± 0.96 mm, respectively, p < 0.001). LT and vitreous depth were also higher in the myopic group, although ACD values were similar. Compared to the Lenstar, the Pentacam measured the ACD and CCT values higher in the myopia group [with a difference of 0.07 ± 0.12 mm (p <0.001) and 4.47 ± 11.33 µm (p = 0.001), respectively] and measured the CCT values higher in the keratoconus group. Pentacam found all keratometry values significantly lower than Lenstar in the keratoconus group. Axial length was longer in the myopic eyes due to the differences starting from the lens and extending to the posterior segment. Lenstar and Pentacam can be used interchangeably for Km, Kf, and ACD in the myopic group and only for ACD in the keratoconus group.

Comparing the corneal curvatures obtained from three different keratometers-IOL Master, Bausch &amp; Lomb Manual keratometer and TOPCON KR 8800 autokeratometer

AIM: To compare the corneal curvature and to investigate the agreement between three different keratometers. METHODS: In this prospective study, keratometry was performed using an IOL Master, a Bausch &amp; Lomb manual keratometer and TOPCON KR-8800 autokeratometer on 252 eyes of patients recruited from camps for cataract surgery. The average keratometry values were recorded and compared. The agreements between the instruments were analyzed using the Bland Altman statistical method. The main outcome measure was average keratometry values.RESULTS: The mean corneal power was 44.62±1.52 D with the IOL Master, 44.60±1.52 D with the manual keratometer, and 44.46±1.53 D with the autokeratometer. The paired t test demonstrated a statistically significant difference in the mean corneal power between the IOL Master and manual keratometer (P=0.001), IOL Master and autokeratometer (P&lt;0.0001), autokeratometer and manual keratometer (P&lt;0.0001). The 95% limits of agreement (LoA) of the IOL Master and manual keratometer were -0.22 to 0.26; IOL Master and autokeratometer were -0.24 to 0.55; autokeratometer and manual keratometer were -0.30 to 0.57 as shown in the Bland-Altman plot. CONCLUSION: Keratometry data obtained with different instruments may not be interchangeable, a fact that has important implications for cataract surgeons with respect to both surgical planning and outcomes auditing.

A method for the assessment of facial hedonic reactions in newborns

ObjectiveThis study describes a quantitative and qualitative methodology to assess hedonic responses to sweet stimulus in healthy newborns. MethodsA descriptive, cross‐sectional, observational study, with healthy newborns (up to 24h of life), between 37 and 42 gestational weeks, vaginally born and breastfed previously to all tests. The evaluation of the newborns reactions was performed by hedonic facial expression analysis, characterized by facial expressions with rhythmic serial tongue protrusion after neutral or sweet solution intake. Initially, 1mL of water solution was provided to the newborn, followed by a 1‐minute recording. Afterwards, the same amount of 25% sucrose solution was provided, performing a second recording. The concordance between researchers was analyzed by the Bland–Altman statistical method. ResultsA total of 100 newborns (n=49 males, n=51 females; mean lifetime=15h 12min±6h 29min) were recorded for neutral and sucrose solution intake, totaling 197 videos (n=3 missing in the water treatment). These videos were double‐blind analyzed and the test revealed a 90% concordance between the two trained researchers, in relation to both solutions. The intraclass correlation coefficient was 0.99 for both solutions, with a significant increase in frequency of hedonic expressions evoked by sucrose solution intake. ConclusionsThese results confirm that the proposed method has an efficient power to detect significant differences between neutral and sucrose stimuli. In conclusion, this evaluation method of hedonic facial reactions in newborns reflects the response to a specific taste.

A method for the assessment of facial hedonic reactions in newborns

ObjectiveThis study describes a quantitative and qualitative methodology to assess hedonic responses to sweet stimulus in healthy newborns. MethodsA descriptive, cross-sectional, observational study, with healthy newborns (up to 24h of life), between 37 and 42 gestational weeks, vaginally born and breastfed previously to all tests. The evaluation of the newborns reactions was performed by hedonic facial expression analysis, characterized by facial expressions with rhythmic serial tongue protrusion after neutral or sweet solution intake. Initially, 1mL of water solution was provided to the newborn, followed by a 1-minute recording. Afterwards, the same amount of 25% sucrose solution was provided, performing a second recording. The concordance between researchers was analyzed by the Bland–Altman statistical method. ResultsA total of 100 newborns (n=49 males, n=51 females; mean lifetime=15h 12min±6h 29min) were recorded for neutral and sucrose solution intake, totaling 197 videos (n=3 missing in the water treatment). These videos were double-blind analyzed and the test revealed a 90% concordance between the two trained researchers, in relation to both solutions. The intraclass correlation coefficient was 0.99 for both solutions, with a significant increase in frequency of hedonic expressions evoked by sucrose solution intake. ConclusionsThese results confirm that the proposed method has an efficient power to detect significant differences between neutral and sucrose stimuli. In conclusion, this evaluation method of hedonic facial reactions in newborns reflects the response to a specific taste.

Análisis microbiológico del pulpo rojo en puertos pesqueros de Campeche, México

In this work we studied the microbiological quality of the red octopus given its important economic and social impact on the region South-Southeast of Mexico. Samples were taken in different areas of capture of the species and analyzed with biochemical tests described in the Mexican official standards, identifying strains belonging to the genus Vibrio, Salmonella and faecal coliforms, and E. coli O157: H7. We used the BAx System for the identification of microorganisms through their bacterial DNA. The results obtained in biochemical and molecular methods were confirmed. Bland-Altman statistical method pointed out that both techniques can be used interchangeably. McNemar test showed that both methods have the same efficacy for the identification of pathogens (value X2=0.5 ρ=0.4795). The microbiological quality of the octopus in the South-Southeast region of Mexico is deficient due to the presence of pathogenic intestinal flora that might represent an epidemiological risk. The indexes established by the regulations suggest the need to apply effective and rapid identification technologies, such as the BAx System.This alternative method of analysis can contribute to the implementation of effective strategies that allow compliance with the minimal sanitary specifications during the processing of fishing products, thus strengthening the control systems to decrease the risks of epidemiological outbreaks in the region.

Concordance between central venous and arterial blood gases in post-surgical myocardial revascularization patients in stable condition

The concordance between the parameters of arterial and central venous blood gases has not been defined yet. We studied the concordance between both parameters in post-surgical myocardial revascularization patients in stable condition. Consecutive subjects were studied in a cross-sectional design. The position of the central venous catheter was performed and simultaneously we obtained arterial and central venous blood samples prior to discharge from the intensive care unit. Data are expressed according to Bland-Altman statistical method and the intraclass correlation coefficient. Statistical result was accepted at P<.05. Two hundred and six samples were studied of 103 post-surgical patients, pH and lactate had a mean difference (limits of agreement) 0.029±0.048 (-0018, 0.077) and -0.12±0.22 (-0.57, 0.33) respectively. The magnitude of the intraclass correlation coefficient was 0.904 and 0.943 respectively. The values related to oxygen pressure were 27.86±6.08 (15.9, 39.8) and oxygen saturation 33.02±6.13 (21, 45), with magnitude of 0.258 and 0.418 respectively. The best matching parameters between arterial and central venous blood samples were pH and lactate.

Comparison of the corneal curvatures obtained from three different keratometers

Keratometry forms an important component of the biometry for a calculation of the intraocular lens power and selecting a contact lens' parameters. To investigate the agreement between three different keratometers commonly used in an ophthalmology clinic. In this prospective study, keratometry was performed using an IOL Master (IM), a manual keratometer (Man) and a autokeratometer (Top) in twenty five eyes of thirteen volunteer subjects. The average keratometry values and corneal astigmatism (J180 and J45 components) were computed and compared. The agreements between the instruments were analysed using the Bland Altman statistical method. The main outcome measures are average keratometry values and corneal astigmatism. The mean of average keratometry values obtained from the IOL Master, manual keratometry and autokeratometry were 44.388 ± 1.430, 44.297 ± 1.425 and 44.220 ± 1.497 D, respectively. The mean difference in the average keratometry between the instruments were 0.31 ± 0.09 for IM and Man (p = 0.012), 0.14 ± 0.17 for IM and Top (p = less than 0.001) and 0.29 ± 0.77 for Man and Top (p = 0.26). The mean differences in the J180 component of astigmatism were: 0.02 ± 0.11 for IM and Man, 0.02 ± 0.09 for IM and Top, and - 0.01 ± 0.11 for Man and Top. Similarly, for the J45 component, the mean differences were 0.02 ± 0.12 for IM and Man, 0.01 ± 0.13 for IM and Top and - 0.02 ± 0.10 for Man and Top. Average keratometry values obtained from different instruments vary significantly. The IOL Master consistently over-estimated the corneal power compared to the manual and the autokeratometer. All three instruments provided similar estimation of the corneal astigmatism.

Assessment of inter-examiner agreement and variability in the manual classification of auditory brainstem response

BackgroundThe analysis of the Auditory Brainstem Response (ABR) is of fundamental importance to the investigation of the auditory system behaviour, though its interpretation has a subjective nature because of the manual process employed in its study and the clinical experience required for its analysis. When analysing the ABR, clinicians are often interested in the identification of ABR signal components referred to as Jewett waves. In particular, the detection and study of the time when these waves occur (i.e., the wave latency) is a practical tool for the diagnosis of disorders affecting the auditory system. Significant differences in inter-examiner results may lead to completely distinct clinical interpretations of the state of the auditory system. In this context, the aim of this research was to evaluate the inter-examiner agreement and variability in the manual classification of ABR.MethodsA total of 160 ABR data samples were collected, for four different stimulus intensity (80dBHL, 60dBHL, 40dBHL and 20dBHL), from 10 normal-hearing subjects (5 men and 5 women, from 20 to 52 years). Four examiners with expertise in the manual classification of ABR components participated in the study. The Bland-Altman statistical method was employed for the assessment of inter-examiner agreement and variability. The mean, standard deviation and error for the bias, which is the difference between examiners’ annotations, were estimated for each pair of examiners. Scatter plots and histograms were employed for data visualization and analysis.ResultsIn most comparisons the differences between examiner’s annotations were below 0.1 ms, which is clinically acceptable. In four cases, it was found a large error and standard deviation (>0.1 ms) that indicate the presence of outliers and thus, discrepancies between examiners.ConclusionsOur results quantify the inter-examiner agreement and variability of the manual analysis of ABR data, and they also allows for the determination of different patterns of manual ABR analysis.

Comparison of Four Refractometers for the Investigation of the Passive Transfer in Beef Calves

Failure of passive transfer (FPT) in beef calves can be detected by refractometry. Nevertheless, different models of refractometers are available, and few studies compare them for the detection of FPT. To compare the accuracy of 4 different refractometers for measuring serum total protein concentrations in comparison with results obtained by the biuret method and, based on the serum IgG threshold of 1,600 mg/mL, to determine, for each refractometer, the optimal serum protein concentration's lowest threshold for successful passive transfer. One hundred and eight healthy beef calves, 3-8 days of age. Observational study. The concentrations of serum total proteins were determined with 4 different models of refractometers and compared with the biuret method by a Bland-Altman statistical method. The optimal serum protein concentration's lowest threshold for successful passive transfer was determined for each refractometer by receiver operating characteristic (ROC) analysis. In addition, the serum immunoglobulin G (IgG) concentration was compared with the serum gamma-glutamyl transferase (γ-GT) activity and with the total immunoglobulin concentration. The refractometric measurements were highly correlated with those obtained by the biuret method. Serum total protein concentration threshold values of 56, 58, 54, and 56 g/L were found respectively for the Atago, Atago ATC, Wolf ATC, and digital ATC refractometers. Immunoglobulins were highly correlated with IgG, whereas γ-GT only reflected colostrum uptake by the calf. All refractometers could be used for the assessment of passive transfer using their individual serum protein concentration threshold.

A comparative study of the accuracy and reliability of multidetector CT and cone beam CT in the assessment of dental implant site dimensions: Author response

A comparative study of the accuracy and reliability of multidetector CT and cone beam CT in the assessment of dental implant site dimensions: Author response

ICSH review of the measurement of the erythocyte sedimentation rate

In recognition of the need for a standardization of the measurement of the erythrocyte sedimentation rate (ESR), the International Council for Standardization in Haematology makes the following recommendations: (i) The reference method for measurement of the ESR should be based on the Westergren method, which is a specific test for the ESR, with modifications, (ii) The reference method for measurement of the ESR should use either whole blood anticoagulated with EDTA and later diluted with sodium citrate or saline (4 : 1) or whole blood anticoagulated with sodium citrate (4 : 1) in Westergren pipettes, (iii) The ESR pipettes can be of glass or plastic (with specific characteristics). It must be colourless; a minimum sedimentation scale of 200 mm, a minimum bore of 2.55 mm, which should be constant within 5%. A protocol for the evaluation of alternative methodologies against the reference method is outlined: The new technologies must be tested over a range of ESR values of 2-120 mm. In this comparison, 95% of the differences should be 5 mm or less, with larger differences associated with higher ESR values. A minimum of 40 samples should be tested in 3 different groups of values: 1-20, 21-60 and more than 60 mm. The statistical methods recommended for ESR evaluations are the coefficient of correlation, the Passing-Bablock regression and the Bland-Altman statistical method. This reference method replaces all earlier standardized and reference methods.

Reliability and reproducibility of clinic and home blood pressure measurements in hypertensive women according to age and ethnicity

The purposes of this study were to establish the reproducibility and reliability of clinic and home blood pressure readings and to determine whether correlations differed according to age and ethnicity. Blood pressure readings taken in a clinical setting and at home from 161 hypertensive women who were either younger or older (including 91 White American and 61 African-American) were compared with 24-h ambulatory blood pressure monitoring (ABPM) readings (considered the gold standard of blood pressure measurement). Bland-Altman statistical method showed good levels of agreement between clinic blood pressures measured 30 days apart, and blood pressures measured at home in the morning over a 30-day program, when compared with mean 24-h ABPM readings. On examining individual Bland-Altman plots for younger and older women, White American and African-American women's blood pressures were well correlated for home measures and 24-h ABPM readings. The correlation between daytime systolic home blood pressure readings and systolic 24-h ABPM readings was much stronger for White American women (r=0.75) than for African-American women (r=0.57). There were also correlation differences in mean systolic blood pressure between home blood pressure readings and 24-h ABPM readings according to age (r=0.66 for younger and r=0.72 for older). These results support current research findings that home blood pressure measurements are reliable when compared with 24-h ABPM readings both in African-American and White women.

Comparative study of four fluorescent probes for evaluation of natural killer cell cytotoxicity assays

Cytotoxicity is one of the major defence mechanisms against both virus-infected and tumor cells. Radioactive 51chromium ( 51Cr) release assay is a “gold standard” for assessment of natural killer (NK) cytolytic activity in vitro. Several disadvantages of this assay led us to design alternative tools based on flow cytometry analysis. Four different fluorescent dyes, calcein acetoxymethyl ester (CAM), carboxyfluorescein succinimidyl ester (CFSE), Vybrant DiO (DiO) and MitoTracker Green (MTG) were tested for labeling of NK target K-562 cells. Target staining stability, spontaneous release of fluorochromes and subsequent accumulation in bystander unstained cells were measured using fluorimetry and flow cytometry. Healthy donor peripheral blood mononuclear cells and affinity column purified NK cells were used as effectors coincubated with target K-562 cells at different E:T ratios for 3 h and 90 min, respectively. Fluorescent probe 7-amino-actinomycin D was used for live and dead cell discrimination. Bland–Altman statistical method was applied to measure true agreement for all CAM– 51Cr, CFSE– 51Cr, DiO– 51Cr and MTG– 51Cr pairs analyzed. Based on the data, none of the four proposed methods can be stated equivalent to the standard 51Cr release assay. Considering linear relationships between data obtained with four fluorochromes and 51Cr release assay as well as linear regression analysis with R 2=0.9393 value for CAM– 51Cr pair, we found the CAM assay to be the most closely related to the 51Cr assay.

Validity and Repeatability of a New Test for Aniseikonia

The Aniseikonia Inspector 1.1 (AI) is a new software product to measure aniseikonia using red-green anaglyphs. The purpose of this study was to test whether the AI is a valid and reliable test. There were two groups of sample subjects: one at risk of aniseikonia, with anisometropia greater than or equal to 1.00 D (n= 29), and a control group (n= 45). The validity was studied by comparing the measured aniseikonia with the aniseikonia simulated with size lenses. The reliability was estimated by the Bland-Altman statistical method. The results showed that the AI underestimated aniseikonia and that the underestimation was greater in the horizontal than in the vertical direction. The reliability was low, with biases that were clinically insignificant, but the 95% limits of agreement were around +/-2%. The behavior of the test was similar in both groups of subjects. The reliability of the AI is only moderate, and professionals are therefore warned to use the results of this test with caution.

Quantitative real-time RT-PCR monitoring of BCR-ABL in chronic myelogenous leukemia shows lack of agreement in blood and bone marrow samples

Molecular monitoring of the BCR-ABL transcript in chronic myelogenous leukemia (CML) using quantitative RT-PCR provides clinicians with important diagnostic and prognostic information. To determine whether molecular detection and monitoring of CML is comparable using peripheral blood (PB) and bone marrow (BM) aspirate samples, we performed a prospective study using quantitative real-time RT-PCR (QRT-PCR) of paired PB and BM samples from 41 patients with CML entered onto a single Cancer and Leukemia Group B (CALGB) treatment study. QRT-PCR analysis of PB and BM samples was performed prior to initiation of, and during, treatment with homoharringtonine and cytarabine on a CALGB study for previously untreated CML. Statistical analyses demonstrated good agreement of PB and BM pre-treatment samples. However, using the Bland-Altman statistical method that measures true agreement between PB and BM values, we found that there was only modest agreement of BCR-ABL measurements in PB and BM for samples obtained during treatment. PB values obtained during treatment tended to be lower than the corresponding BM values [average difference = -0.37 (p<0.001) in 36 paired samples] and the 95% limits of agreement ranged from -1.23 to 0.48. Nevertheless, our study demonstrates that BM and PB QRT-PCR values followed a similar trend during treatment (Spearman correlation coefficient, 0.83; 95% CI, 0.70, 0.96). Our data suggest that, quantitatively, PB and BM measurements of BCR-ABL are frequently disparate. Since BM values tended to be higher than PB values, BM sampling provides the most accurate assessment of minimal residual disease (MRD). Based on these results, we caution against interchanging BM with PB sampling for MRD monitoring during treatment of CML since this may lead to misinterpretation of treatment results.

Comparison of gastric emptying scintigraphy based on the geometric mean of the gastric proportion of the abdominal radioactivity or on the geometric mean of the intragastric radioactivity

Using gastric emptying scintigraphy the gastric retention rate is commonly calculated within a gastric region of interest (intragastric method). This technique may have significant limitations when left oblique anterior views are acquired, due in part to attenuation resulting from intragastric redistribution. To minimize these drawbacks, it was proposed to express the intragastric content as a percentage of the abdominal radioactivity (abdominal method). Our goal was to compare these two methods when anterior-posterior scanning is used. Antero-posterior scintigraphic data of 272 consecutive patients were analysed by both methods. Retention rates were obtained by both observation and calculation by power exponential fit. Gastric emptying parameters (half-emptying time of solids (T(50,S)) and liquids (T(50,L)), lag phase (T(lag)) time and real emptying time (T(RE))), and quality of fit were also computed and compared. For solids, the intragastric method resulted in weakly higher experimental retention rates, whereas retention rates were quite similar for liquids. Differences between experimental and calculated retention rates were smaller for abdominal method, for both liquids and solids. As a result, values for the quality of fit were higher for the abdominal method. Significant differences were observed only for calculated T(50,S) (122+/-46 min vs. 124+/-48 min, mean difference 2+/-2 min, P<0.00001) and T(RE) (163+/-64 min vs. 168+/-68 min, mean difference 4.5+/-3.8 min, P<0.05), respectively, for the abdominal and the intragastric methods. However, the Bland-Altman statistical method revealed good agreements (<5% outliers). Intragastric and abdominal methods can be used indifferently to treat antero-posterior data of gastric scintigraphy.

A new method for rationalising blood transfusion in paediatric surgery

Introduction Two to three hundred transfusion complications are reported annually (1). Human variant CJD poses a relatively new and difficult concern with allogeneic blood transfusion. Cost (∼£100.00 per unit from donation to provision) is an additional consideration. With these and other considerations in mind the Association of Anaesthetists has published new guidelines for blood transfusion, which recommend a more cautious approach (2).A 5 year (July 1995–June 2000) retrospective review of transfusion requirements in children under 16 requiring debridement and split skin grafting was conducted in the North Trent regional burns unit, Northern General Hospital, Sheffield. In this 5 year period, 92 patients went to theatre a total of 107 times for debridement and grafting. 108 units of blood were cross‐matched for 61 cases, with a total of 66 units transfused over 44 operations. Thirty‐seven patients were over cross‐matched with 6 under cross‐matched.Analysis of the 5 year retrospective review reveals that with 10 g·dl−1 as an ideal target haemoglobin 8 patients were over transfused (to above normal range) and 19 were transfused more than necessary (to above 10 g·dl−1). Using 8 g·dl−1 as an ideal target haemoglobin the number of patients transfused more than necessary rises to 32. These results were analysed using a mathematical model based on 1st order kinetics with the equation dHb/Hb = dBL/EBV (where BL = blood loss and EBV = estimated blood volume) (3). This showed that without transfusion 17 of these patients would have had a Hb of above 8 g·dl−1 with 7 above 10 g·dl−1.Objectives Using the above mathematical model to devise a computer aided means for preoperative prediction of allowable blood loss before a threshold haemoglobin is reached peroperative realtime prediction of haemoglobin concentration peroperative realtime prediction of transfusion requirements testing the model in a clinical setting Materials and Methods Formulae developed were incorporated into a programme built using Microsoft Access 97. The programme facilitates the first 3 objectives outlined above. Ethical approval was obtained and a trial commenced in both a burns and spinal surgery setting to assess the how close computer predicted Hb results were to laboratory results.Key results Thus far, 16 measurements taken during 2 burns and 5 spinal fusion operations show close correlation between predicted and tested Hb results. This was validated using the Bland Altman statistical method (see Fig. 1).Bland Altman plot comparing predicted and measured Hb results following blood loss ranging from 5% to 23% of estimated circulating volume in 7 patients (16 measurements). The dotted lines indicate the mean difference &amp;plusmn;2 standard deviations.imageConclusion Computer aided prediction of Hb concentration concurrent with blood lost peroperatively could provide a useful cost effective tool in rationalising the use of allogeneic blood transfusion in paediatric surgical patients.