860 e-Letters

  • This article incorrectly defines "power" and should not have been published.

    The following quote from the article is incorrect and misses the basic definition of power: "Strictly speaking 'power' refers to the number of patients required to avoid a type II error in a comparative study. Sample size estimation is a more encompassing term that looks at more than just the type II error and is applicable to all types of studies. In common parlance the terms are used interchangeably."

    "Power" is the probability that the test correctly rejects the null hypothesis H0 when a specific alternative hypothesis H1 is true. It's equal to 1 - type II error probability. "Power" and "sample size" are not the same thing and they are not used interchangeably. It's possible to derive power given sample size, or calculate sample size based on desired power.

    Please correct the article as it'll be highly misleading to beginners.

  • The need for explicit documentation of degree of skin pigmentation

    In an observational study where 200 participants were black, 269 asian, and 4330 white, the authors demonstrated an inverse association between blood pressure and pulse oximetry accuracy that was not influenced by ethnicity[1]. In that study no specific mention was made of the degree of pigmentation in individual members of the ethnic subgroups, presumable because self-reported ethnicity was accepted as a surrogate for skin colour. This acceptance is in sharp contrast with the methodology in the study where subjects of African-American descent were further characterised by a description of their degree of pigmentation, using terminology such as "very darkly pigmented".. This was one of the earliest prospective studies conclusively to show that some oximeters overestimate arterial oxygen saturation in hypoxic subjects who are "darkly pigmented" [2].
    In retrospective studies such as the ones subsequently undertaken to explore the theme of racial bias in oximetry it was easy to fall into the trap of using ethnicity as a surrogate for skin colour[3],[4], largely because skin colour is not consistently recorded as part of the medical record[3]. Explicit description of skin colour also gets omitted when race and ethnicity are defined using self-reported demographic data[4].
    Future studies, however, might seek to ascertain whether or not skin pigmentation compounds the overestimation of oxygen saturation attributable to hypotension....

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  • Clarifying the Canadian C-Spine Rule

    We thank Dr. Delaney and colleagues for their valuable research into the concept of midline cervical tenderness. Unlike the NEXUS critiera, the Canadian C-Spine Rule does not use midline tenderness as a positive indication for imaging. Our original study in JAMA 2001 found that assessment of this criterion amongst alert trauma patients at risk of c-spine tenderness had excellent interobserver agreement between ED physicians with a kappa of 0.78. We found that absence of midline tenderness was a good negative predictor of c-spine injury but that presence of of such tenderness was non-specific and not useful. Hence, absence of midline tenderness is considered a low-risk factor. Our NEJM 2003 validation study found that the CCR had both better sensitivity and specificity than NEXUS.
    Best regards
    1. Stiell IG, Wells GA, Vandemheen K, Clement C, Lesiuk H, De Maio VJ et al. The Canadian Cervical Spine Radiography Rule for alert and stable trauma patients. JAMA 2001; 286(15):1841-1848.
    2. Stiell IG, Clement C, McKnight RD, Brison R, Schull MJ, Rowe BH et al. The Canadian C-spine Rule versus the NEXUS low-risk criteria in patients with trauma. N Engl J Med 2003; 349:2510-2518.

  • Maybe codeine's pharmacokinetics are an issue too

    A well timed project with the contemporary interest in the subject of drug misuse in Scottish politics, and also with the recent airing of Dopesick on streaming services about the US experience.

    I wonder whether the known CYP2D6 polymorphism leading to poor metabolism of codeine has a role in the increase of opioid prescriptions? Mikus and Weiss (2005) state that 5-10% of Caucasian have severely impaired metabolism of codeine and that a further 10-15% show some impairment. This means up to 1 in 4 Caucasians don't get a full analgesic effect from codeine.

    Maybe we are seeing a lessening of patients putting up with their lot of suboptimal pain control? And in turn an increase in prescriptions to accommodate that demand.

    Dihydrocodeine by contrast doesn't have the same issues with metabolism and ineffective analgesia. While acknowledging the past issues when DF118s were misused, perhaps prescribing dihydrocodeine instead of codeine we'll see better analgesia in our patients and perhaps a reduction in demand for prescriptions?

    Mikus G and Weiss J. (2005) 'Influence of CYP2D6 Genetics on Opioid Kinetics, Metabolism and Response', Current Pharmacogenomics, 3, pp43-52

  • Response to ‘Delivering Community Emergency Medicine during the COVID-19 pandemic: the Physician Response Unit’

    We read with interest your experience of creating care pathways for patients in the out-of-hospital setting during the Covid-19 pandemic, in particular for those with palliative care needs. The benefits of the Physician Response Unit (PRU) being tasked to end of life care related 999 calls, their enhanced level of assessment and management and the resulting reduction in inappropriate hospital admission is to be applauded. There is additionally a need to recognise the wider use of such care pathways, available pan London, that support palliative and end of life care (EoLC) patients accessing emergency care.

    In collaboration with hospice and palliative care teams the London Ambulance Service NHS Trust (LAS) has to date, created 19 EoLC appropriate care pathways. These offer our clinicians access to specialist advice, support with complex decision making and provide an alternative to Emergency Department (ED) conveyance. In the last 2.5 years we have undertaken an extensive programme to improve EoLC within the LAS; providing tailored education to augment our clinicians’ knowledge and confidence, creating guidance which includes medications and symptom management at the end of life and increasing clinician use of advance care plans. As a result we have seen a 15% increase in staff confidence and an 18% median reduction in ED conveyance for this patient group; most importantly more patients are being cared for in their place of choice and in line with their wishes....

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  • Consequences of the emergency response to COVID-19

    Dear Sir,

    Within their conclusion, Charlton et al recommend further research to understand patient behaviour toward seeking help during the pandemic. In response to this, we would like to highlight the findings of our work which address this. We undertook a mortality review of all deaths in Salford during the peak 7 weeks of the initial pandemic surge (522 deaths), looking at themes which, if addressed could result in reduced mortality in future waves. We reviewed all 111, 999, general practice and hospital contacts for all patients from the 1st March 2020, to ensure all help seeking behaviour and the system response was understood. We have summarised these here.
    We noted 60 cases where patients delayed seeking help. We were also concerned that patients who were advised to call 111 by their GP, and were offered advice, would only call back when seriously ill. “COVID phobia” was evident in a small number of cases, at its extreme, including refusal to attend hospital and subsequent death at home.
    Fewer than half of NHS 111 calls were answered during the review period. Of those that were answered, 46% resulted in advice to contact their GP. Of these, 5 were subsequently admitted to hospital later the same day. Indeed, despite the national directive to telephone 111 as the first point of contact, only 13% actually did. 81% of patients contacted their GP in the period prior to their death.
    However, a lack of early face to face assessments was identi...

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  • Interrater-variability in frailty screening using the Safety Management System (VMS).


    To the editor,

    In their article “Agreement and predictive value of the Rockwood Clinical Frailty Scale (CFS) at emergency department triage”, Shrier et al (1) nicely illustrate that the level of agreement between different health care professionals in obtaining the CFS at different clinical settings is weak. The CFS was rated for 8,568 patients over 65 years by the triage nurse at the emergency department (ED) and by the attending physician on admission on the ward. Both scores were compared using the Cohen’s kappa coefficient, which was  0.21 and therefore is considered weak (2). 
    We found similar results in our AmsterGEM study. The AmsterGEM study is an observational prospective cohort study that investigates the prognostic accuracy of frequently used frailty screening instruments (3). Patients aged over 70 years old attending the ED were screened with four screening instruments, including the Safety Management System (VMS) (4). The VMS consists of four geriatric domains, which are associated with functional decline: delirium, malnutrition, falls and ADL limitations (5,6). All Dutch hospitals have implemented the VMS screening instrument for hospitalized older patients. In a sub-analysis of our study, the VMS was applied on 173 hospitalized patients over 70 years old, at the ED by a research student and at admission by the attending nurse on the ward. The average age was 81.2 years old, 81 (47%) were male and 111 s...

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  • Could assay choice and sample storage explain the poor D-dimer sensitivity found by the DiPEP study?

    Having recently updated our Emergency Department guidelines for suspected PE in pregnancy, we read the secondary analysis of the DiPEP study with great interest.1 However, we were quite surprised at the poor overall D-dimer sensitivity. Only 66% (8/12) of PEs would have been identified based on the recommended positivity threshold of 400ng/ml. This is considerably lower than the pooled estimate of 97% (95% CI 96-98%) found by a recent meta-analysis evaluating D-dimer for PE, and largely explains the poor performance of the YEARS and Geneva algorithms in the DiPEP cohort.2

    This result does not seem to fit with the known physiology of pregnancy. We know that D-dimer levels increase throughout pregnancy, which should improve sensitivity and worsen specificity.3 To our knowledge there are no other studies demonstrating impaired sensitivity of D-dimer in pregnant vs. non-pregnant populations.

    The DiPEP authors note that most of the study participants had received anticoagulation before blood samples were taken, which can decrease D-dimer levels by up to 25% in the first 24 hours.1 They also note however, that this would be insufficient to explain all their false negative D-dimer results. Aside from random error, we wondered if anything else could explain the poor sensitivity.

    One feature of the DiPEP study that stood out to us was the D-dimer assay used. As a microplate ELISA assay, the Zymutest D-dimer should be very sensitive but we could not find any st...

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  • Identification of technical factors associated with first-pass success of intubation with C-MAC video laryngoscope in children

    To the Editor
    We have read with great interest the recent article of Miller et al1 determining the technical factors associated with first-pass success (FPS) during endotracheal intubation with C-MAC video laryngoscope (VL) in children. They showed that placement of the blade tip into the epiglottic vallecula regardless of blade types, adequate glottic view and locating the glottic opening within second quintile of video displayer were significantly associated with FPS. Given that paediatric airway management is a great challenge to emergency physicians and the benefits of videolaryngoscopy are often significant in airway management of emergency paediatric patients,2 their findings have potentially clinical implications. Other than limitations described by authors in discussion, however, we noted several methodological issues in their article on which we invited authors to comment.
    First, primary outcome of this study was FPS, which was defined as passage of C-MAC VL into the mouth with the intention of intubation that terminated with successful intubation at first attempt. As described by authors in introduction, however, C-MAC VL is an intubating device with ability to perform both direct and video laryngoscopy using same device. That is, the larynx can be seen either under direct vision or on a monitor when using C-MAC VL.3 This advantage of C-MAC VL makes it exceptionally useful for emergency intubation. For example, in the event of a failed video laryngosc...

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  • The Prognostic Value of the Quick Walk Test during COVID-19 Outbreaks: the Experience of the Fenice Network

    We read with great interest the study by Goodacre et al. [1], where post-exertion oxygen saturation adds modest prognostic information to clinical assessment of suspected COVID-19 in the ED.

    This is partially in contrast with the findings of our study [2], performed within the Fenice Network (Italian group for clinical research in Emergency Medicine). In consecutive ED patients with SpO2 ≥ 95%, the most promising version of a standardised quick walk test (QWT) yielded a sensitivity of 83.3% (95% confidence interval [CI] = 35.9% to 99.6%), and specificity of 93.4% (95% CI = 91.5% to 95.0%). The positive and negative predictive values (PPVs and NPVs) were 8.6% (95% CI = 2.9% to 19.0%) and 99.9% (95% CI = 99.3% to 100.0%).

    This difference is probably due to 3 factors:

    1. The test standardisation. In our case series, the test was standardised for all centres and consists of a 30-40 metres walk at the maximun possible speed for each patient. Conversely, in the study by Goodacre et al., exertion SpO2 was either recorded after different, not standardised, intentional tests or could have made opportunistically after a spontaneous patient’s effort. The latter condition is particularly worrisome for the purpose of a thorough assessment of the prognostic value of the post-exertion oxygen saturation.

    2. The outcome definition. Goodacre et al. considered patients who died or required respiratory, cardiovascular or renal support within 30 days after initial p...

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