Early warning scores and chronic respiratory disease

Editor – The article by O'Driscoll et al (Clin Med February 2012 pp79–81)¹ describes some of the challenges of providing an early warning score (EWS) based on vital signs observation for use in all adult patients in acute hospital settings, given the specific physiology of patients with chronic respiratory disease.

The VitalPAC Early Warning Score (ViEWS),² which has been used as the template for the National Early Warning Score (NEWS) by the Royal College of Physicians, allocates points both for SpO₂ values below 96% and for the use of supplementary oxygen therapy. However, O'Driscoll et al criticise ViEWS because it ‘would subject COPD patients to potential risk as an SpO₂ above the target range of 88–92% is associated with increased risk of death in COPD’.

The title of the ViEWS paper² and the text itself clearly indicates that ViEWS was the first point along a journey towards the development of a validated EWS. Additionally, the limitations of the study, including that all patients were unselected, acute medical admissions in a single hospital, and that there is no guarantee that similar results would be obtained in other locations, clinical settings or patient groups, were made clear in the paper. Indeed, subsequent, as yet unpublished, work demonstrates that the sensitivity and specificity values of ViEWS and NEWS for patients with respiratory disease are lower than those of the unselected medical group upon which ViEWS was first tested, although they are still higher than for any other published EWS. Therefore, we have no doubt that NEWS will require future modification and that changes are probably necessary in order to make it entirely suitable for use in patients with chronic respiratory disease.

However, any EWS that is going to be truly useful has to ensure that it does not disadvantage any patients, irrespective of whether they have chronic respiratory disease or not. Although the higher end of the target range for SpO₂ is currently 92% for patients at risk of hypercapnic respiratory failure, all patients are likely to be harmed if they become hypoxic (ie SpO₂ falls below their ‘normal’ target range). O'Driscoll et al describe the trialling of an EWS in which three points are allocated for SpO₂ values above or below the British Thoracic Society target ranges (88–92% for patients at risk of hypercapnic respiratory failure and 94–98% for all others).³ We think that this simple approach may prove to be too unrefined, as we have shown an increase in hospital mortality in patients admitted with initial SpO₂ values of <96%.⁴ Consequently, we suggest that an EWS that can be used for all patients with or without chronic respiratory disease might need to have separate SpO₂ weighting scales for patients with or without a risk of hypercapnic respiratory failure. However, further work is required to confirm this.

Declaration of potential conflict of interest

Professor Smith is a member of the Royal College of Physicians' National Early Warning Score Development and Implementation Group (NEWSDIG). VitalPAC is a collaborative development of The Learning Clinic Ltd (TLC) and Portsmouth Hospitals NHS Trust (PHT). PHT has a royalty agreement with TLC to pay for the use of PHT intellectual property within the VitalPAC product. Professor Prytherch and Drs Schmidt, Featherstone and Meredith are employed by PHT. Professor Smith was an employee of PHT until 31 March 2011. Dr Schmidt and the wives of Professors Smith and Prytherch are shareholders in TLC. Professors Smith and Prytherch, and Dr Schmidt are unpaid research advisors to TLC. Professors Smith and Prytherch have received reimbursement of travel expenses from TLC for attending symposia in the UK.