Similar to findings in studies involving alcohol and brain injury, substance abuse was associated with poorer neuropsychological and functional outcomes . Literature reviews also support this finding, with findings indicating that almost 40% of TBI patients had a positive toxicology screen, or had reported using drugs, with marijuana use accounting for more than half of the drug use . Similar to the large percentage of missing data for alcohol screen, the variable presence of other drugs also had a large percentage of missing data . This is important to consider, as a large percentage of missing data may cause bias. Yet, in this study, even with the large percentage of missing data, the presence of other drugs was found to have a negative influence on TBI severity as indicated by lower GCS scores compared to those who did not have other drugs present on admission. It is important to consider that both alcohol and drug use at the time of injury can confound GCS assessment in trauma patients. Although findings from this study corroborate findings from TBI literature examining substance use, it may be judicious to acquire GCS scores after any intoxicating substances have worn off, perhaps hours or even up to a few days post injury. The GCS score is often assessed numerous times in a trauma patient’s hospital stay, however, the NTDB data set does not include other GCS scores, only the first one on arrival at the hospital. Finally, the large percentage of missing data for both alcohol screen result and presence of other drugs should be considered and addressed. Because blood alcohol and drug measurements in emergency departments are likely biased towards intoxicated and incoherent patients. This can help explain the large percentage of missing data when it comes to these two variables. As mentioned previously, clinicians often will forget to draw a blood sample for alcohol and or drugs, and even if they do, these results may not be entered into the medical record or the registry in a timely and accurate manner. These variations in practice create a large proportion of missing data as it relates to alcohol and toxicology screens performed and documented. For purposes of this study,vertical grow rack alcohol screen results were imputed, but as helpful as imputation can be to an analysis, it can also misrepresent the actual number of participants with a positive alcohol result thereby biasing the results.

Participants with a known history of substance abuse were found to have slightly higher GCS scores when compared to patients who did not. For every participant who had a history and a diagnosis of substance abuse, GCS scores increased by .075 units. Higher GCS scores indicated better neurological function and a less severe TBI. The study by Nguyen et al. and Leskovan et al. explore the relationship between marijuana use, and alcohol, on mortality. The effect of marijuana on TBI severity is far less studied than alcohol, though preclinical studies have shown that the presence of marijuana is associated with some neuroprotective effects, including attenuated cell apoptosis, alleviation of cerebral edema, and improved cerebral blood flow . Further studies are needed to investigate the effects of marijuana on TBI severity alone, not when combined with alcohol or other substances. These findings cannot be discussed without addressing the issue of missing data. Variables that influence GCS scores and TBI severity, such as alcohol screen result, sex, presence of drugs, history of cancer, history of mental and personality disorder, and history of alcohol abuse all had some element of missing data. All the aforementioned variables had less than 6% of the data missing, with some of them having less than 1% missing data . Similarly, history of comorbid conditions all had less than 3% missing data. The two variables that had a large percentage of data missing were the presence of THC and the presence of other drugs . Despite the missing data, both those variables were found to have a statistically significant influence on GCS scores, hence, TBI severity. Though statistically significant, the validity of those findings should be cautiously interpreted within the context of such large percentage of missing values for these hypothesized explanatory variables. One of the leading causes of injuries resulting in TBI incidence are collision related, such as motor vehicle or motorcycle crashes. Furthermore, almost half of the US states have legalized marijuana for medical use with some states allowing recreational use of marijuana. Therefore, collision type mechanism of injuries was examined to see if there was any mediating influence on TBI severity in the presence of THC.

It was determined that motor vehicle collisions did not influence, or mediate, the relationship between THC and TBI severity. However, motorcycle collisions suggested a partial influence on TBI severity. This was an expected result as studies have shown that head injuries are the leading cause of death in fatal motorcycle crashes . It is therefore not surprising to see that GCS scores were reduced when motorcycle collisions were examined for mediating influences on TBI severity in the presence of THC. In one study by Steinemann et al. , THC positivity among road traffic collisions in one US state tripled, with the number of THC positive patients presenting to the highest-level trauma center doubling. However, this data should be interpreted cautiously within the context of such large percentages of missing values for hypothesized explanatory variables. Finally, it is important to note the surprising finding that only 22 participants were found to have been involved in a motor vehicle collision, and only 16 were involved in a motor cycle crash. In the original data set, only 16,324 of 997,970 were involved in a motor vehicle collision, and 12,826 of 997,970 were involved in a motor cycle collision. In 2015, the CDC reported that more than 2.3 million people presented to the emergency department with motor vehicle-related injuries. Because not every single motor vehicle collision warrants a trauma activation or for the patient to be seen by a trauma surgeon, the number represented in the trauma registries would be much less. Hence, this may somewhat explain the lower numbers presented in the 2017 NTDB data set . Several limitations of this study should be noted. Primarily, this study was a retrospective cohort study, therefore it may be missing potentially relevant data. Retrospective cohort studies,though time efficient and cost effective, can be limited due to the nature of data collected. Missing data on several important predictor variables represents another drawback. The patient population in this study was heavily skewed towards moderate and severe TBI patients from one year of available data. A more evenly distributed sample over a longer time period with a larger number of moderate and severe TBI patients would provide more sensitive analyses. The retrospective nature of this study limits the conclusions that can be determined as the methodology was not able to ascertain any measure of acute versus chronic marijuana use. Urine toxicology screens, such as those used in the ED, detectable levels of THC can be present for up to 4.6 days after the last noted use for individuals who do not use marijuana frequently, or up to 15.4 days after last use for those who are frequent users .

Therefore,vertical farming racks the presence of marijuana at the time of exposure may not correlate with recent use. Timing of exposure may be a factor and is an important limitation in this study. Additionally, study findings are based on patients with TBI that have had a urine THC test performed. Since not all patients with moderate or severe TBI were tested for the presence of THC, bias is thus introduced. There was a large percentage of study participants who were not tested or had missing test results for THC . Consequently, a more accurate analysis of THC prevalence and association was not possible as there was no way to determine which of those cases that were not tested or had no results documented were positive for THC. It is important to note that despite there being a small percentage of THC prevalence, this study reflects only one year worth of data, from 2017, and that establishing previous prevalence rates for comparison from the NTDB cannot be calculated. This is because the presence of THC was never abstracted nor documented in the data set prior to 2017. Future studies examining prevalence rates for a series of years is warranted. Observational research has been shown to provide mis-estimations of the outcome of interest. Data analyzed from the NTDB is extracted from various trauma registries across the United States and Canada. Each hospital employs its own registry abstractors who input the data collected from the electronic medical record into the registry which then feeds into the NTDB. This is an important limitation as the documentation and accuracy of data inputted may be inaccurate, incomplete, or inconsistent. This can result in information bias. Furthermore, systematic under reporting of data by participating hospitals can result in selection bias and create an inconsistent database. An example of this was the lack of consistency in the measurement and documentation of blood alcohol levels at time of hospital admission, and the missed opportunities for urine testing. This contributed to a large percentage of missing data which may have also introduced informational bias. Additionally, this variation in reporting results in incomplete data, as seen in this study, as well as conflicting data. There were two occasions where participants were documented as having not being tested for any substances yet were each found to have been positive for THC and/or cocaine. Outcomes of such practices and variations between trauma registries leads to a lack of confidence regarding data accuracy and resulting analyses. Traumatic brain injury is a significant public health concern and a leading cause of death and disability. Many TBI patients have substance use exposure at the time of injury. This study aimed at examining the relationship between marijuana exposure at the time of injury and TBI severity in moderate and severely injured TBI patients. The study findings are timely as the number of states legalizing marijuana for both medical and recreational use increases. This retrospective cross-sectional design study analyzed a large data set retrieved from the National Trauma Data Bank of patients with traumatic brain injury and the association between the presence of THC and brain injury severity, as defined by the GCS score. This is the first known study to examine the presence of THC at the time of injury and its effect on brain injury in a large demographic from a national dataset. The NTDB dataset captures 65% of all trauma hospitals capture; so, with some confidence the claim can be made that moderate and severe TBI, in this data set, are representative of the TBI population in North America. This study found a smaller prevalence rate of THC presence in a purposive sample of TBI patients, but further studies are needed to estimate more accurate prevalence rates now that future datasets from the NTDB will delineate the types of substances tested. This will also allow for larger datasets to be analyzed which may yield different results. As is, the current dataset is not sufficient to establish strong analyses due to the large percentage of missing data, inconsistencies within the data itself, and limited to one dataset as previous datasets did not have the necessary drug information needed for analysis. Despite the limitations inherent to retrospective studies and to databases such as the NTDB, findings from this study suggest an important link between the presence of a positive THC results and GCS score, hence TBI severity. Only one research study at the time of when the systematic literature review for this present study was done investigated the effects of THC presence in TBI patients and its influence on mortality. To date, there has been one identified study that investigated the influence of marijuana on TBI mortality . When examining the differences between participants who tested positive for THC and those who did not, it was found that GCS scores were lower for those who tested positive, indicating a more serious TBI. Additionally, participants who had a had a current diagnosis, or history of, cancer or substance abuse, were more likely to have tested positive for THC. This study found that the presence of THC was significantly associated with lower GCS scores and a potentially more severe TBI; this relationship was significant without controlling for other predicting variables.