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Reply to: Trajectories of vital signs in patients with Covid-19

      To the Editor,
      We thank Machiwenyika et al., for their interest in our paper. We are encouraged that their study of post-operative patients also demonstrates how incorporating inspired FiO2 can aid the identification deteriorating patients.
      • Zhu Y.
      • Chiu Y.-D.
      • Villar S.S.
      • et al.
      Dynamic individual vital sign trajectory early warning score (DyniEWS) versus snapshot national early warning score (NEWS) for predicting postoperative deterioration.
      In our study, we chose to combine vital signs into a novelty score as the COVID-19 cohort was insufficiently large to develop and validate a new scoring system on the primary outcome (continuous positive airway pressure/non-invasive positive pressure ventilation, ICU admission or death in hospital). The novelty score allowed us to explore the rate at which patients with COVID-19 deteriorate. The rapid deterioration observed in patients with COVID-19 is seen more clearly when using a novelty score that incorporates FiO2 (Figure 3) than one that does not (Figure S3).
      One advantage of unsupervised learning methods, such as those used in our novelty score, is that they are developed independently from how “deterioration events” are defined. Indeed, we have previously argued that optimising early warnings scores to identify patients at risk of specific adverse outcomes (e.g. death and unplanned intensive care admissions) risks missing early, yet clinically significant, deterioration.
      • Tarassenko L.
      • Clifton D.A.
      • Pinsky M.R.
      • Hravnak M.T.
      • Woods J.R.
      • Watkinson P.J.
      Centile-based early warning scores derived from statistical distributions of vital signs.
      Moreover, although we exploit similar methods to centile-based early warning scores, the novelty score is multivariate, and we do not suggest cut-offs for clinical intervention.
      As Machiwenyika et al. highlight, the novelty score equally weighs positive and negative deviations from “normal” vital sign measurements (e.g. bradypnoea and tachypnoea). While this could misrepresent the relationship between respiratory rate and the risk of specific outcomes, it is worth noting that bradypnoea is relatively uncommon. Only 6 of 374 COVID-19 patients in our study had a respiratory rate <12. These cases may well merit review.
      We agree that the absence of non-respiratory vital sign abnormalities observed in our study raise the question of whether NEWS2 is optimal for patients with COVID-19. In contrast, the recent editorial by Subbe and Thorpe discusses the simplicity of using a universal early warning score in clinical practice.
      • Subbe C.
      • Thorpe C.
      Finally good NEWS: something simple is working in COVID-19!.
      We would argue that NEWS2 should be extensively validated in much larger cohorts of patients with COVID-19 before being reassured that these patients are not disadvantaged. Our study supports the suggestion from Machiwenyika et al., that “one standard scoring system” could be sub-optimal in some patient groups. However, different scoring systems could increase “cognitive load” for clinical staff.
      • Subbe C.
      • Thorpe C.
      Finally good NEWS: something simple is working in COVID-19!.
      We agree that our novelty score and estimation of FiO2 could be challenging to implement in hospitals without an appropriate electronic vital signs system. Our FiO2 estimate was used a previously published formula, which could potentially be improved or simplified.
      • Malycha J.
      • Farajidavar N.
      • Pimentel M.A.F.
      • et al.
      The effect of fractional inspired oxygen concentration on early warning score performance: a database analysis.
      We hope a future NEWS3 steering committee will consider the emerging evidence that incorporating FiO2 could help identify patient deterioration. In a previous study, we have demonstrated how this might be achieved.
      • Malycha J.
      • Farajidavar N.
      • Pimentel M.A.F.
      • et al.
      The effect of fractional inspired oxygen concentration on early warning score performance: a database analysis.
      Moreover, we emphasise again the need to validate any changes introduced in NEWS3 robustly, prior to implementation in the NHS.
      • Gerry S.
      • Bonnici T.
      • Birks J.
      • et al.
      Early warning scores for detecting deterioration in adult hospital patients: systematic review and critical appraisal of methodology.

      Funding

      This publication presents independent research commissioned by the Health Innovation Challenge Fund (HICF-R9-524; WT-103703/Z/14/Z), a funding partnership between the Department of Health & Social Care and Wellcome Trust. The views expressed in this publication are those of the authors and not necessarily those of the Department of Health or Wellcome Trust. PW and LT are also supported by the National Institute for Health Research, Biomedical Research Centre, Oxford. RH is supported by an NIHR Doctoral Research Fellowship. This research has been conducted using the Oxford University Hospitals NHS Foundation Trust Clinical Data Warehouse, which is supported by the NIHR Oxford Biomedical Research Centre and Oxford University Hospitals NHS Foundation Trust.

      Conflicts of interest

      PW and LT report significant grants from the National Institute of Health Research (NIHR) and the NIHR Biomedical Research Centre, Oxford, during the conduct of the study. PW and LT report grants and personal fees from Sensyne Health, outside the submitted work. PW is a consultant to Sensyne Health and holds shares in the company. LT works part-time for Sensyne Health and holds share options in the company.

      References

        • Zhu Y.
        • Chiu Y.-D.
        • Villar S.S.
        • et al.
        Dynamic individual vital sign trajectory early warning score (DyniEWS) versus snapshot national early warning score (NEWS) for predicting postoperative deterioration.
        Resuscitation. 2020; 157: 176-184https://doi.org/10.1016/j.resuscitation.2020.10.037
        • Tarassenko L.
        • Clifton D.A.
        • Pinsky M.R.
        • Hravnak M.T.
        • Woods J.R.
        • Watkinson P.J.
        Centile-based early warning scores derived from statistical distributions of vital signs.
        Resuscitation. 2011; 82: 1013-1018https://doi.org/10.1016/j.resuscitation.2011.03.006
        • Subbe C.
        • Thorpe C.
        Finally good NEWS: something simple is working in COVID-19!.
        Resuscitation. 2020; (2020–1)https://doi.org/10.1016/j.resuscitation.2020.12.008
        • Malycha J.
        • Farajidavar N.
        • Pimentel M.A.F.
        • et al.
        The effect of fractional inspired oxygen concentration on early warning score performance: a database analysis.
        Resuscitation. 2019; 139: 192-199https://doi.org/10.1016/j.resuscitation.2019.04.002
        • Gerry S.
        • Bonnici T.
        • Birks J.
        • et al.
        Early warning scores for detecting deterioration in adult hospital patients: systematic review and critical appraisal of methodology.
        BMJ. 2020; : m1501https://doi.org/10.1136/bmj.m1501

      Linked Article

      • Trajectories of vital signs in patients with Covid-19
        ResuscitationVol. 162
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          We read with interest the recent article from Oxford exploring using trajectories of vital signs and inspired FiO2 in hospitalised Covid-19 patients.1 Given the paucity of published research in vital sign trends to predict clinical deterioration, this is an opportune addition to the literature.2,3 Our recent multicentre paper also highlights the potential added value of inclusion of dynamic trajectory and inspired FiO2 in a postoperative population.3
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