Clinical paperUsing administrative data to develop a nomogram for individualising risk of unplanned admission to intensive care☆
Introduction
Patients who are transferred from the general wards to the intensive care unit (ICU) for critical care management, commonly referred to as unanticipated or unplanned ICU admissions,1, 2, 3 have higher mortality rates and poorer prognoses than those who are admitted directly from the emergency department (ED) or the operating rooms.4, 5, 6 Unplanned ICU admission has been used as a surrogate marker of adverse events,2 and is used by the Australian Council of Healthcare Accreditation as a reportable quality indicator.7
Although a number of observational studies have suggested that the Medical Emergency Team (MET) reduced unplanned ICU admissions,3, 8, 9, 10 this was not borne out in a multi-site cluster-randomised controlled trial.11 Whilst not negating the benefits of the MET, findings from this randomised controlled trial gave impetus to explore other strategies of identifying patients who are at risk of unplanned ICU admissions.
One way of objectively identifying at risk patients is the use of vital signs routinely measured as physiological variables, to derive a ‘Patient-At-Risk’ score, as suggested by Goldhill and McNarry.12 However, the authors cautioned that critical thresholds of these scores were likely to be change with different patient cohorts; in addition this algorithm also lacks the ability to individualise risk, thus limiting its usefulness. Added to this, it is also recognised that monitoring and documentation of changes in vital signs are not always adequate in the general wards.11 Taking these into consideration, we sought an alternate method of developing a predictive model, using readily available administrative data to develop a nomogram, which may assist with evidence-based medical decision-making of identifying patients at risk of unplanned ICU admissions.
Nomograms are statistical models designed to provide prognostic information using a combination of variables for an individualised prediction of outcome.13 Nomograms have been shown to be superior to traditional risk grouping systems in identifying at risk patients, with the use of more complex predictive models that maximise individualised prediction.14 The graphical representation of a nomogram enables the magnitude and the direction of each contributing variable to be easily visualised. The use of nomograms has been attributed a change in treatment decision-making process of prostate cancer, which has resulted in improved health outcomes.15 Nomograms are also widely use in osteoporosis research and management, to improve the decision-making of both physicians and patients, in determining the most effective treatment option by taking into account the patient's particular physiological status or disease state.16
Section snippets
Design
A retrospective study design was used to examine the characteristics of unplanned admissions to an intensive care unit over a 7-year period.
Setting
Data for this study were collected at a 370-bed non-teaching hospital in the South Western region of Sydney, Australia that has approximately 22,000 paediatric and adult patients being admitted to the hospital each year. This region is culturally and linguistically diverse, with more than one-third of residents born overseas in a non-English speaking
Results
Six hundred and seventy-two unplanned ICU admissions were identified over the 7-year study period. During this time, the hospital had 94,482 admissions of 54,458 individuals. The admission characteristics overall and in relation to unplanned ICU status are presented in Table 1. The incidence of unplanned ICU admission was greater in men (P < 0.001), and increased with age (P for trend <0.001). Admissions to hospital via the emergency department accounted for 73% of the unplanned ICU admissions.
Discussion
The identification of patients with clinical markers at risk of adverse events such as unplanned ICU admission during a hospital stay has become an important area of research in patient safety.21, 22 For this reason the ability of clinicians to identify patients at increased risk may be valuable to prevent such events from occurring. This study has been able to identify risk factors related to unplanned admission to ICU, and to develop a nomogram for assigning individual risk to patients.
The
Conclusion
This study used readily available administrative data to develop a nomogram, a graphically display of a prediction model that uses numeric scales based on well-established multivariable logistic regression analysis, as a tool for individual risk assessment of unplanned ICU admission. Although independent validation is required, this nomogram has the potential of being a useful tool in assisting clinicians in management-related decisions, as to which patients may require monitoring and follow-up
Conflict of interest
None.
Acknowledgments
Tracy Heath who coordinated the hospital MET system and Jennevie Tan in Clinical Information Department who assisted in retrieving the hospital administrative database.
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A Spanish translated version of the summary of this article appears as Appendix in the online version at doi:10.1016/j.resuscitation.2008.06.023.