Abstract
Introduction
Identifying acutely unwell patients at risk of deterioration and adverse outcomes is a clinical priority.
The National Early Warning Score (NEWS) is an aggregate weighted track and trigger tool to support
healthcare professionals in this endeavour. High-risk patients are readily identified by NEWS, but are
in the minority, while patients with a low NEWS, who account for the majority of acute hospital admissions may still be at risk.
Aim
The aim of this thesis is to see if acutely unwell adult medical patients with either a low-risk (<5) or
medium-risk NEWS (5-6) can be identified and stratified for their risk of in-hospital mortality. The thesis
also aims to understand how consultant acute physicians use NEWS when making decisions.
Methods
The study employed a segregated mixed methods design. A retrospective observational study of
routinely collected electronic patient data from a tertiary teaching hospital sought to identify presenting
complaints and primary discharge diagnoses with the greatest risk of in-hospital mortality in acutely
unwell medical patients, and to then identify which conditions have the greatest mortality risk when
the admission NEWS is low or medium risk. All acute medicine admissions from 01/04/2014 to
30/06/2022 with complete data were included. An interview based phenomenological study drew on
the experiences of consultant acute physicians to consider how they make clinical decisions and how
they use NEWS.
Results
There were 104,301 acute medicine admissions with a primary discharge diagnosis and complete NEWS
data, and 62,676 acute admissions with a documented presenting complaint and complete NEWS data.
Of the 104,301 total admissions, within 24 hours of admission to hospital, 357 (0.3%) died. Of the
patients who died, 102 (0.1%) had an admission NEWS <5, 53 (0.8%) a NEWS of 5-6 and 202 (4.1%) a
NEWS of ≥7. While the relative mortality rate was lower in admissions with a low NEWS <5, 1 in 908,
compared to those with a high NEWS ≥7, 1 in 24, in absolute terms patients with an admission NEWS <5
accounted for 28.6% of all deaths within 24 hours of hospital admission.
Using the International Classification of Diseases 10th revision (ICD-10), in the 104,301 admissions, four
ICD-10 diagnostic chapters were found to have an increased risk of 24-hour mortality when compared
to all other chapters combined: infections (odds ratio (OR) 3.1, 95% confidence interval (95% CI) 2.4
4.0), respiratory (OR 2.2, 95% CI 1.8-2.8), neoplasms (OR 2.1, 95% CI 1.3-3.2) and cardiovascular (OR 1.4,
95% CI 1.1-1.8). Within diagnostic chapters, 24-hour mortality was lower when the admission NEWS was
lower, although in relative terms there was variation in mortality between chapters, for example
infections were more strongly associated with mortality when NEWS is elevated (OR 32.2, 95% CI 19.8
52.5, for NEWS ≥5) compared to respiratory conditions, where mortality is relatively more likely with a
lower NEWS (OR 9.6, 95% CI 6.2-14.9, for NEWS ≥5).
Using Summary Hospital-level Mortality (SHMI) diagnosis groups, 19 groups had an increased risk of 24
hour mortality when compared to all other groups combined. Of these groups, nine included ≥400
admissions and represented important acute medicine conditions: pneumonia, septicaemia, congestive
heart failure, acute myocardial infarction, gastrointestinal haemorrhage, alcohol-related liver disease,
stroke, bronchial cancer and respiratory failure. While a higher admission NEWS conferred an absolute
increased mortality risk, in relative terms, respiratory failure (OR 1.3, 95% CI 0.3-6.4, for NEWS ≥5),
congestive heart failure (OR 7.4, 95% CI 2.9-18.8, for NEWS ≥5) and pneumonia (OR 9.7, 95% CI 6.0-15.9,
for NEWS ≥5) were more likely to die with a lower admission NEWS compared to all other SHMI groups
combined (OR 20.4, 95% CI 16.2-25.7, for NEWS ≥5).
There were 48 different presenting complaints. Shortness of breath (OR 3.8, 95% CI 2.9-5.1) and collapse
(OR 2.4, 95% CI 1.5-3.9) were associated with a statistically significant increase in 24-hour mortality
compared to all other complaints combined, while chest pain (OR 0.4, 95% CI 0.2-0.7) and falls (OR 0.3,
95% CI 0.1-0.8) were associated with a statistically significant decrease in 24-hour mortality. While a
higher admission NEWS conferred an absolute increased mortality risk, there was variation in the risk
of 24-hour mortality according to presenting complaint and admission NEWS. Although not statistically
significant, those presenting with shortness of breath were relatively more likely to die with a lower
admission NEWS compared to all other presenting complaints (OR 15.6, 95% CI 8.6-28.5, versus OR 20.0,
95% 14.5-27.6, for NEWS ≥5).
Eight semi-structured interviews were completed with eight consultant acute physicians. Three themes
were identified to understand how they make clinical decisions: the rituals of patient assessment,
decision-making support and making the decision. Information gathering was vital, while reaching a
decision was influenced by individual patient, environmental and personal factors. Cognitively, the
consultants adopted a qualitative Bayesian approach, where each piece of new information gathered
helped refine their prior clinical hypothesis. The consultants readily accepted an elevated NEWS as
identifying patients at high risk of an adverse outcome; however, when the NEWS was low they sought
further information to categorise each patient’s risk.
Conclusion
This mixed methods study has contributed to the understanding of the assessment and clinical decision
making processes undertaken by consultant acute physicians. The quantitative study shows that a patient’s risk of
in-hospital mortality is associated with their presenting complaint and final discharge
diagnosis. Furthermore, seemingly physiologically stable patients still die following admission to
hospital, and the mortality risk in low-risk patients varies according to their presenting complaint and
primary discharge diagnosis. Therefore, acute medicine clinicians need to be aware of the risk associated
with the conditions they see and the different levels of risk associated with these conditions in seemingly
stable patients. However, the quantitative data shows there are no absolute cut-offs to provide
information on which to make definitive decisions about a patient’s mortality risk. The qualitative study
was therefore complementary, showing that consultants use NEWS alongside other sources of
information when making decisions, either as qualitative Bayesian cognitive thinking, or as a binary
judgement that a high NEWS always equates to increased risk, while a seemingly low-risk NEWS requires
further information and evaluation.