This study is the first comparative evaluation of two international guidelines regarding the possible discharge of mTBI patients with ICIs directly from the emergency department in a Scandinavian population. This is a large validation cohort of over 500 patients with 188 events, which matches previous sample size recommendations when validating prognostic models [17, 18]. The population in this study is demographically diverse, and the area from which it derived consists of urban and rural areas. This should make the cohort comparable to other similar cohorts in Sweden.
Neither guideline would have discharged a patient who would have deteriorated within 30 days. Application of either guideline would have led to a small but safe reduction of hospital admissions in this population. No significant difference in sensitivity, specificity, or proportion of patients eligible for discharge could be identified between the two guidelines.
Managing mTBI patients without a neurosurgical consultation is a subject that has been studied for some time and proven safe in selected cases. Huynh et al. found that patients with a GCS of 15 and either a solitary contusion less than 5 mm or a subdural hematoma less than 4 mm could safely be managed without a neurosurgical consultation . In their comparative study of patients with mTBI, who were managed either with or without a neurosurgical consultation, Joseph et al. showed that the patients managed with a consultation had higher rates of repeat CT scans and admission to the ICU but not a higher rate of neurosurgical intervention, in-hospital mortality, or readmissions within 30 days . Lewis et al. concluded that routine neurosurgical consultation seemed unnecessary and rarely changed the management plan, even in patients with pre-injury antiplatelet/anticoagulation or intoxication .
The specificity and proportion of patients eligible for discharge for both guidelines were lower when compared with their respective original studies. This might, in part, be due to the high levels of missing data in radiological measurements of intracranial hemorrhages. The researchers tried to circumvent this problem by subjectively determining if the hemorrhage was under 5 mm based on how the hemorrhage was described in the radiology report. Despite this effort, only 22.2% of the incomplete records could be completed. Interpretation of the radiology reports was made very conservatively. If there was any doubt whether the hemorrhage was over 4 mm, it was interpreted as such. It is, therefore, possible that a subset of these patients had hemorrhages under 5 mm and would, therefore, have been eligible for discharge based on both guidelines.
The radiologist is an invaluable resource for the emergency care provider, with his/her superior image interpretation. However, the lack of consensus on reporting terminology might lead to the loss of clinically relevant information [22, 23]. Detailed radiology reports in a tabulated format seem to be preferred over prose when non-radiologists are asked. Reports that follow a structured format are perceived as more comprehensible and with better content [24,25,26].
Suppose all patients who had neither their largest hemorrhage measurement provided nor a hemorrhage that could be interpreted as less than 5 mm had hemorrhages under 5 mm. In that case, an additional 15 patients could have been discharged by the BIG and 20 by the mTBI RS. Using these theoretical numbers, the discharge rates (BIG: 3.9% and mTBI RS: 5%) and specificities (BIG: 6.3% and mTBI RS: 8.3%) for both guidelines were more similar to those received by Marincowitz et al. in their study. However, it is unlikely that all these patients actually had hemorrhages under 5 mm. The lack of precise measurements is thus likely not the only cause for the observed difference in sensitivity and specificity between the original studies and the present study.
The cohorts were different in many aspects between all three studies. The patients in this study were significantly older than either original study. Almost half were treated with anticoagulants or antiplatelets, almost twice the proportion in the mTBI RS study and almost triple the proportion in the BIG study.
The patients in this study were seemingly less severely injured than those in the mTBI RS study when looking at GCS scores and ISS scores. On the other hand, the patients had more skull fractures, more neurological deficits on the initial exam, a higher proportion of midline shift present and deteriorated to a greater extent. These factors, including the use of anticoagulants/antiplatelets, are all reasons for being admitted by either guideline, subsequently reducing the proportion of patients eligible for discharge.
The above-mentioned factors that potentially drive the higher admittance rate can also contribute to the lower specificities through a greater admission rate of patients that do not deteriorate. The more advanced age of the patients in this study is potentially an important factor. Older patients are more likely to have baseline neurological deficits that can be hard to distinguish from new ones on initial examination. The higher rate of cerebral atrophy amongst older patients can also make them more resilient to the mass effect of an intracranial hemorrhage, and thus less prone to develop injuries requiring surgical evacuation. Older patients are more likely to be treated with anticoagulants or antiplatelets and this has shown only a moderately elevated odds ratio for deterioration . This could lead to many patients being admitted, but relatively few that will deteriorate.
The significant differences between the current and previous study populations, along with missing information in radiology reports, can possibly explain the inferior specificities and proportions of patients eligible for discharge by both guidelines in this cohort. However, the exact individual contribution of either of these factors cannot be investigated in the current study.
To have a guideline that helps managing these seemingly well patients with potentially deadly injuries would have been much appreciated by many physicians in the emergency department. At the current moment, neither BIG nor mTBI RS seem to provide much value to the clinical management in the current or similar settings. If their usability and true potential to affect care are to be studied further, precise measurements of ICIs need to be routinely provided.