Undergraduate medical textbooks do not provide adequate information on intravenous fluid therapy: a systematic survey and suggestions for improvement.

BACKGROUND: Inappropriate prescribing of intravenous (IV) fluid, particularly 0.9% sodium chloride, causes post-operative complications. Fluid prescription is often left to junior medical staff and is frequently poorly managed. One reason for poor intravenous fluid prescribing practices could be inadequate coverage of this topic in the textbooks that are used. METHODS: We formulated a comprehensive set of topics, related to important common clinical situations involving IV fluid therapy, (routine fluid replacement, fluid loss, fluids overload) to assess the adequacy of textbooks in common use. We assessed 29 medical textbooks widely available to students in the UK, scoring the presence of information provided by each book on each of the topics. The scores indicated how fully the topics were considered: not at all, partly, and adequately. No attempt was made to judge the quality of the information, because there is no consensus on these topics. RESULTS: The maximum score that a book could achieve was 52. Three of the topics we chose were not considered by any of the books. Discounting these topics as "too esoteric", the maximum possible score became 46. One textbook gained a score of 45, but the general score was poor (median 11, quartiles 4, 21). In particular, coverage of routine postoperative management was inadequate. CONCLUSIONS: Textbooks for undergraduates cover the topic of intravenous therapy badly, which may partly explain the poor knowledge and performance of junior doctors in this important field. Systematic revision of current textbooks might improve knowledge and practice by junior doctors. Careful definition of the remit and content of textbooks should be applied more widely to ensure quality and "fitness for purpose", and avoid omission of vital knowledge.

Kinetics of anesthetic onset measured with a direct index of neural activity.

BACKGROUND: Previous modeling of the kinetics of uptake and elimination of anesthetic drugs from the site of action has used measures derived from the electroencephalogram. Such measures lag the current brain activity because of the time needed to acquire a signal sample and derive the measure. With a direct measure of anesthetic activity, we could model brain uptake more exactly. METHODS: In volunteers, using a double-blind single-session design, we made repeated measurements using a well-known psychomotor test, the 2 target tapping test, during the washin and washout of 30% nitrous oxide. We also assessed maximal drug effect with a test of cognitive function, the digit symbol substitution test. Concentration at the site of action was modeled from end-tidal measurements, using a simple exponential washin and washout function, with half-times between 0.5 and 3 minutes. Comparisons were made within subjects, using 0 and 5% nitrous oxide. RESULTS: We studied 20 subjects. Nitrous oxide, at 30%, consistently reduced performance of the digit symbol substitution test. Tapping frequency was also reduced, but the effect was less consistent, and only 9 of 20 subjects showed a significant individual reduction in tapping frequency. In these subjects, the relationship between the modeled brain concentration and drug effect was better with a half-time set at 2 minutes, compared with 1.5 or 3 minutes. CONCLUSIONS: Given in subanesthetic concentrations, nitrous oxide has rapid onset and offset, consistent with a half-time of 2 minutes. This value is less than the values expected from studies during anesthesia using processed electroencephalogram, but consistent with measures of blood flow to active cerebral tissue in conscious subjects. Studies of performance in conscious subjects may aid further studies of anesthetic kinetics.

Show the data, don't conceal them.

Current standards of data presentation and analysis in biological journals often fall short of ideal. This is the first of a planned series of short articles, to be published in a number of journals, aiming to highlight the principles of clear data presentation and appropriate statistical analysis. This article considers the methods used to show data, in particular the value of the dot plot, and methods to summarise the distribution of values. The uses of measures such as standard deviation, standard error of the mean, and confidence intervals are contrasted.

Recovery from sedation with remifentanil and propofol, compared with morphine and midazolam, for reduction in anterior shoulder dislocation.

OBJECTIVE: To compare recovery from sedation using remifentanil and propofol with our standard regimen of morphine and midazolam for closed reduction in shoulder dislocation in an ED. METHODS: We randomised 40 patients for closed shoulder reduction to receive either remifentanil and propofol (R&P) (20 patients) or morphine and midazolam (M&M) (20 patients). A suitably trained ED doctor gave the sedation. R&P patients received oxygen from a tight-fitting facemask and Mapleson C circuit to prevent hypocapnia and thus reduce the risk of apnoea. Shoulder reduction was performed by another doctor with an ED nurse also present. We noted recovery times, pain and sedation scores, operative conditions, additional medication and adverse events. RESULTS: All patients given remifentanil and propofol had recovered within 30 min in contrast to the morphine and midazolam group where 17 of 20 patients had recovered after 60 min, the remainder requiring a total of 90 min. Median recovery times were 15 min (95% CI 15 to 20) for the remifentanil and propofol group, and 45 min (95% CI 29 to 48) for the morphine and midazolam group. Reduction conditions and scores for pain/distress did not differ between the groups. Seven patients required additional sedation (four R&P, three M&M) to enable shoulder reduction. Five patients (three R&P, two M&M) had received analgesia prior to the procedure from the ambulance service (one R&P, one M&M) and ED (two R&P). Two patients given morphine and midazolam required flumazenil to counter oversedation. CONCLUSIONS: Remifentanil and propofol reduces patient recovery time and provides equivalent operating conditions compared with morphine and midazolam for the reduction of anterior glenohumeral dislocation.

Classifying signals from a wearable accelerometer device to measure respiratory rate.

BACKGROUND: Automatic measurement of respiratory rate in general hospital patients is difficult. Patient movement degrades the signal and variation of the breathing cycle means that accurate observation for ≥60 s is needed for adequate precision. METHODS: We studied acutely ill patients recently admitted to a teaching hospital. Breath duration was measured from a triaxial accelerometer attached to the chest wall and compared with a signal from a nasal cannula. We randomly divided the patient records into a training (n=54) and a test set (n=7). We used machine learning to train a neural network to select reliable signals, automatically identifying signal features associated with accurate measurement of respiratory rate. We used the test records to assess the accuracy of the device, indicated by the median absolute difference between respiratory rates, provided by the accelerometer and by the nasal cannula. RESULTS: In the test set of patients, machine classification of the respiratory signal reduced the median absolute difference (interquartile range) from 1.25 (0.56-2.18) to 0.48 (0.30-0.78) breaths per min. 50% of the recording periods were rejected as unreliable and in one patient, only 10% of the signal time was classified as reliable. However, even only 10% of observation time would allow accurate measurement for 6 min in an hour of recording, giving greater reliability than nurse charting, which is based on much less observation time. CONCLUSION: Signals from a body-mounted accelerometer yield accurate measures of respiratory rate, which could improve automatic illness scoring in adult hospital patients.

Current clinical methods of measurement of respiratory rate give imprecise values.

BACKGROUND: Respiratory rate is a basic clinical measurement used for illness assessment. Errors in measuring respiratory rate are attributed to observer and equipment problems. Previous studies commonly report rate differences ranging from 2 to 6 breaths·min-1 between observers. METHODS: To study why repeated observations should vary so much, we conducted a virtual experiment, using continuous recordings of breathing from acutely ill patients. These records allowed each breathing cycle to be precisely timed. We made repeated random measures of respiratory rate using different sample durations of 30, 60 and 120 s. We express the variation in these repeated rate measurements for the different sample durations as the interquartile range of the values obtained for each subject. We predicted what values would be found if a single measure, taken from any patient, were repeated and inspected boundary values of 12, 20 or 25 breaths·min-1, used by the UK National Early Warning Score, for possible mis-scoring. RESULTS: When the sample duration was nominally 30 s, the mean interquartile range of repeated estimates was 3.4 breaths·min-1. For the 60 s samples, the mean interquartile range was 3 breaths·min-1, and for the 120 s samples it was 2.5 breaths·min-1. Thus, repeat clinical counts of respiratory rate often differ by >3 breaths·min-1. For 30 s samples, up to 40% of National Early Warning Scores could be misclassified. CONCLUSIONS: Early warning scores will be unreliable when short sample durations are used to measure respiratory rate. Precision improves with longer sample duration, but this may be impractical unless better measurement methods are used.

Correction to: Predictive validity of a novel non-invasive estimation of effective shunt fraction in critically ill patients.

An amendment to this paper has been published and can be accessed via the original article.

Reporting ethical matters in the Journal of Physiology: standards and advice.

Reporting of ethical matters in The Journal is very important. To advise and assist authors, particularly those who may be less familiar with the legislation in the UK, this article sets out the basic principles and methods that should be used and provides many key web sources of information. It addresses the structure of regulations, and introduces the concept of research governance. The UK law is summarized. Advice is given on the format and description of experiments, and common problems addressed. Aspects of human studies are addressed. Ethical considerations of publication such as authorship and originality, and problems such as plagiarism and fabrication are described. Updates will be published regularly.

Low-frequency changes in finger volume in patients after surgery, related to respiration and venous pressure.

BACKGROUND AND OBJECTIVE: In patients after surgery, we observed large-amplitude low-frequency changes in digital plethysmograph measurements when DC coupling of the signal was used. We set out to assess factors that might contribute to these events and in particular to test the possibility that low-frequency signals could be used to assess respiratory disturbances. METHODS: We recorded values in 23 patients who had undergone gynaecological surgery. We measured nasal flow, abdominal pressure (by urinary catheter), venous pressure in the hand, and DC-coupled optical transmission plethysmography. Signals were replayed and analysed to assess the incidence of specific patterns of events. RESULTS: Most patients received morphine for postoperative analgesia. Respiratory irregularity and expiratory muscle action were very frequent. Increases in abdominal pressure during expiration caused increases in venous pressure and pulsation. In 12 out of 23 patients, a characteristic response consistent with vasoconstriction was noted after increases in breath size, and, in seven patients, very-low-frequency (0.2-0.7 Hz) oscillations of finger volume were present that appeared unrelated to respiratory events. Patients who did not receive morphine had very different plethysmograph patterns, with significantly smaller pulse amplitude. CONCLUSION: Low-frequency changes in finger volume can be simply obtained and provide considerable information about peripheral circulatory dynamics. Diverse patterns can be recognized, but the range of responses suggests that current techniques cannot be used alone to assess cardiorespiratory status. However, a combination of plethysmography with respiratory measurements shows characteristic events.

Predictive validity of a novel non-invasive estimation of effective shunt fraction in critically ill patients.

BACKGROUND: Accurate measurement of pulmonary oxygenation is important for classification of disease severity and quantification of outcomes in clinical studies. Currently, tension-based methods such as P/F ratio are in widespread use, but are known to be less accurate than content-based methods. However, content-based methods require invasive measurements or sophisticated equipment that are rarely used in clinical practice. We devised two new methods to infer shunt fraction from a single arterial blood gas sample: (1) a non-invasive effective shunt (ES) fraction calculated using a rearrangement of the indirect Fick equation, standard constants, and a procedural inversion of the relationship between content and tension and (2) inferred values from a database of outputs from an integrated mathematical model of gas exchange (DB). We compared the predictive validity-the accuracy of predictions of PaO2 following changes in FIO2-of each measure in a retrospective database of 78,159 arterial blood gas (ABG) results from critically ill patients. RESULTS: In a formal test set comprising 9,635 pairs of ABGs, the median absolute error (MAE) values for the four measures were as follows: alveolar-arterial difference, 7.30 kPa; PaO2/FIO2 ratio, 2.41 kPa; DB, 2.13 kPa; and ES, 1.88 kPa. ES performed significantly better than other measures (p < 10-10 in all comparisons). Further exploration of the DB method demonstrated that obtaining two blood gas measurements at different FIO2 provides a more precise description of pulmonary oxygenation. CONCLUSIONS: Effective shunt can be calculated using a computationally efficient procedure using routinely collected arterial blood gas data and has better predictive validity than other analytic methods. For practical assessment of oxygenation in clinical research, ES should be used in preference to other indices. ES can be calculated at http://baillielab.net/es .