Injury Severity Bias in Missing Prehospital Vital Signs: Identifying and Addressing Trauma Registry Missingness

Injury severity bias in missing prehospital vital signs: identifying and addressing trauma registry missingness.

Authors: Melissa O’Neill1,2, Sheldon Cheskes2-4, Ian Drennan2-6, Charles Keown-Stoneman2,6, Steve Lin1-3,5,6, Brodie Nolan1-3 
Author Affiliations: 1Institute of Medical Science University of Toronto, 2Li Ka Shing Knowledge Institute St. Michael’s Hospital, 3Division of Emergency Medicine University of Toronto, 4Sunnybrook Research Institute Sunnybrook Health Sciences Centre, 5Institute of Health Policy Management and Evaluation University of Toronto, 6Dalla Lana School of Public Health University of Toronto 

Abstract:
Background: Vital signs are important factors in assessing injury severity and guiding trauma resuscitation, especially among severely injured patients. Despite this, physiological data are frequently missing from trauma registries. 
Objective: This study aimed to evaluate the extent of missing data in a hospital-based trauma registry and to assess the associations between prehospital vital sign completeness and indicators of injury severity.
Methods: We conducted a retrospective review on all adult trauma patients brought directly to a level 1 trauma centre in Toronto, Ontario by paramedics from January 1, 2015, to December 31, 2019. We evaluated the proportion of missing data for each variable and assessed for patterns of missingness. To investigate the associations between prehospital data completeness and injury severity factors, we performed descriptive and unadjusted logistic regression analyses. 

Results: A total of 3,528 patients were included. We considered prehospital data missing if any of heart rate, systolic blood pressure, respiratory rate or oxygen saturation were incomplete. Each individual variable was missing from the registry in approximately 20% of patients, with oxygen saturation missing most frequently (n=831; 23.6%). Over 25% (n=909) of patients were missing at least one prehospital vital sign, of which 69.1% (n=628) were missing all four of these variables. Patients with incomplete data were more severely injured, had higher mortality, and more frequently received lifesaving interventions such as blood transfusion and intubation. Patients were most likely to have missing prehospital physiological data if they died in the trauma bay (unadjusted OR: 9.79; 95% CI: 6.35-15.10), did not survive to discharge (unadjusted OR: 3.55; 95% CI: 2.76-4.55), or had a prehospital GCS less than 9 (OR: 3.24; 95% CI: 2.59-4.06). 

Conclusions: In this single centre trauma registry, over 25% of patients were missing key prehospital variables. Missing prehospital vital signs were more frequent among more severely injured patients. Death in the trauma bay and in-hospital mortality were most strongly associated with missing physiological data. This injury severity bias suggests that these data are not missing completely at random, and therefore need to be addressed appropriately to ensure their validity.