The influence of blood alcohol on the human body has been described many times [10,11,12]. In addition to the negative effects on, among others, liver function or the central nervous system caused by ethanol, there are studies that describe a protective effect on some aspects, such as the cardiovascular system [13]. Road accidents often occur under the influence of alcohol and drugs. The risk of a road accident increases with increasing inability to drive, caused by alcohol and drugs [14, 15]. However, it is not fully understood what effect a positive BAL has on the physiological parameters and outcome of a seriously injured patient. For example, some authors describe that they measured a lower GCS and lower blood pressure parameters in patients with positive BAL compared to BAL negative patients, and finally observed an increased mortality rate for BAL positive patients [9]. A positive BAL can also affect the occurrence of a traumatic brain injury (TBI). In animal models, alcohol has shown both adverse and neuroprotective effects, while clinical studies analyzing acute and long-term neurological and behavioral effects of intoxication show no consistent results [4, 16, 17]. Our study results confirm some of the hypotheses described. The majority of our study collective consists of young, male patients. This coincides with the characterization of the risk profile of injured, alcoholized patients that can also be found in other studies [18, 19].
First, we found no significant differences in the 24 h mortality. The overall mortality rate showed no significant difference between the groups. Furthermore, the RISC II analysis confirmed our findings (predicted mortality). Looking at all patients in our study collective, no differences in mortality were seen. At most, the length of stay in the hospital was lower in patients with a positive BAL.
We then performed a subgroup analysis to focus on the group of patients with a severe traumatic brain injury (AIS head ≥3) to look for further effects that might show different results. However, we showed that the mortality rate in BAL positive patients with TBI was significantly lower than the mortality rate in BAL negative patients with TBI. Additionally, in our subgroup analysis, we observed more patients with an isolated TBI. But the ISS was lower in the BAL positive group. The ISS might have an effect on the higher mortality rate in the BAL negative subgroup.
Age might be influencing the outcome of mortality in this subgroup, too. But we have the same significant age difference when testing for 24 h mortality and overall mortality in the whole collective. Thus, we do not think that age might be one of the main influencing factors.
Some research groups also found a positive, protective effect of ethanol in patients with moderate and severe TBIs. They showed a significantly lower mortality rate for this group [20].
Tien et al. showed that low to moderate BAL can be beneficial in patients with severe TBI but a high BAL appears to cause an increased risk of mortality during a hospital stay in these patients, which may be related to the adverse hemodynamic and physiological effects in BAL positive patients [21]. Sperry et al. investigated the influence of alcohol on GCS in TBI patients. They showed that positive BAL in patients with blunt TBI does not lead to clinically significant changes in GCS value [22]. On the other hand, Pandit et al. reported that patients with severe TBI and positive BAL more frequently develop complications during a hospital stay compared to BAL negative patients with TBI. They were therefore unable to detect any neuroprotective effect related to ethanol [23].
In conclusion, a neuro-protective effect of alcohol and the significant survival benefit for alcohol intoxicated patients with a traumatic brain injury [20, 24] cannot be clearly explained and remains of further interest.
In the BAL positive group, a change in physiological parameters such as blood pressure and BE was observed. Alcohol has complex effects on the circulatory system. The relationship between alcohol and high blood pressure is well known, but little is known about the effect of alcohol on the circulation in seriously injured patients. Our results show a small drop in blood pressure in patients in the alcohol group. These results are in line with those of other authors [5, 25]. In clinical trials, patients with an additional traumatic brain injury had lower amounts of catecholamines in the bloodstream, which in turn resulted in lower systolic blood pressure when admitted to the hospital [26,27,28].
Patients with a positive BAL have a lower base excess than those in the BAL negative group.
Since alcohol consumption itself leads to lower values of BE (or higher values of lactate), it is questionable whether these markers could be used as a screening tool for injured intoxicated patients. Normally, the BE is an indicator for tissue hypoperfusion. However, according to a study by Dunne et al., the positive significance of the base excess as a predictive value in relation to mortality remains regarding BAL positive patients [29].
Other studies show a comparable influence on various physiological parameters, in particular on base excess and lactate value, without measuring a difference in mortality [29].
The influence of alcohol on the coagulation system is controversial. In connection with traumatic brain injuries, many studies suggest that with the simultaneous presence of traumatic brain injury and a blood-increased alcohol level, the clotting system is affected. For example, Howard et al. showed that patients with brain injury and positive BAL had a significantly lower incidence of coagulopathies [30]. Since we did not focus on coagulopathies, we cannot make any further reliable statements based on our data but the effect remains of certain interest especially in trauma care.
In our analysis, patients in the alcohol group show an increased risk of falling from a low altitude (< 3 m) compared to patients in the control group. However, we have not been able to prove that patients from the alcohol group are more likely to be involved in accidents with e.g. cars, motorcycles or bicycles. This is likely due to the fact that the majority of BAL positive people no longer drive their own cars, motorbikes or bicycles, but rely on taxis or public transport. The increased number of low falls with an increased rate of severe traumatic brain injuries may be attributed to the fact that the sense of balance under alcohol consumption decreased. Moreover, it can be due to the increased risk of falling with limited protective reflexes.
Limitations
The analysis presented here as well as the data published in the current literature cannot clarify sufficiently the existing relationship of the effect of ethanol in the context of an existing trauma with and without additional TBI. The discrepancy may be due to the numerous dose-dependent effects of alcohol, the time of exposure in relation to the injury and the nature of the injury and its outcome. In addition, it is very difficult to find comparable collectives in which an effect on hemodynamics and other physiological blood parameters can be investigated. Also, in the present evaluation only correlations, no causal relationships can be described. Additional studies are needed to further investigate the mechanism and possible therapeutic implications of this association.
