Out-of-Hospital AAM and Outcomes in TBI, Hemorrhagic Shock
Out-of-Hospital AAM and Outcomes in TBI, Hemorrhagic Shock
This study offers new insights to clarify the connections between AAM and injury outcomes. Numerous prior studies evaluating the association of out-of-hospital AAM with TBI outcomes have suggested potential harm compared with ED AAM or similarly injured patients not receiving AAM. For example, in an analysis of over 4000 TBI patients in Pennsylvania, we observed increased adjusted odds of death and poor neurological outcome among patients receiving endotracheal intubation in the out-of-hospital setting versus those receiving intubation the ED. These studies combined TBI and shock cases in the same analysis, controlling for the confounding effect of hypotension through multivariable adjustment and assuming similar associations with mortality in both groups.
Our contrasting study examined TBI and shock subgroups separately. We observed that the increased mortality associated with out-of-hospital AAM was limited primarily to patients in shock. If the relationship between AAM and outcomes were due primarily to selection bias, one would expect similar associations when stratified by TBI and shock. Our results are further bolstered by the use of multicentre trial data with subjects prospectively identified using all available out-of-hospital vital signs and Glasgow Coma Scale measurements. This approach better approximated the perspective of the treating paramedic and minimised potential for post hoc misclassification.
If validated, the findings of this study would have important implications for out-of-hospital AAM research and practice. Reasons postulated for the connection between out-of-hospital AAM and poor outcomes in injured patients include suboptimal paramedic training or skill, poor intubation technique, prolonged laryngoscopy, iatrogenic hypotension and bradycardia, or the low rate of out-of-hospital neuromuscular blockade use, among others. More importantly, some experts believe that the worsened AAM outcomes are primarily due to inadvertent hyperventilation. In TBI, hyperventilation is associated with decreased brain oxygen delivery and perfusion. In victims of shock, hyperventilation may decrease venous return, mean arterial pressure and cardiac output. We observed that the physiologic interactions with AAM in the shock state are more closely correlated with mortality than the interactions with TBI. Therefore, clinicians and scientists must strive to better characterise the interaction between airway, ventilation and the shock state. Serum lactate is often used as a marker of cellular perfusion, and differences in serum lactate might indicate airway-related perfusion differences. However, we did not observe associations between out-of-hospital AAM and initial ED lactate in either TBI or shock groups.
Observational studies have inherent limitations, including selection bias and incomplete risk adjustment, among others. However, this approach remains one of the best and only available approaches for evaluating the effectiveness of out-of-hospital AAM strategies in injured patients. We note that the association between AAM and mortality was relatively large, supporting the validity of the relationship. While a prospective controlled trial is the optimal approach for evaluating the effectiveness of AAM, clinical trials of out-of-hospital AAM are exceedingly difficult to perform, since many patients possess intact airway reflexes, and most EMS providers in North America do not have access to neuromuscular blocking agents. To date, Bernard et al have conducted the only prospective clinical trial evaluating the comparative effectiveness of out-of-hospital intubation, identifying a small benefit in select TBI patients. However, this Australian trial utilised paramedics specially trained in neuromuscular blockade use, and thus, it is unclear if the results can be extrapolated elsewhere.
Based upon prior studies of TBI patients, some experts have condemned field intubation of injured patients by paramedics. We urge a more restrained interpretation. The techniques of out-of-hospital intubation and advanced airway insertion are likely similar for both TBI and shock patients. Our study highlights differing connections with mortality between TBI and shock patients, pointing to the likely presence of other factors influencing outcomes such as postintubation ventilatory and hemodynamic management. Additional study is urgently needed to better characterise the physiology of the haemorrhagic shock state, the interactions with airway and ventilatory techniques, and the optimal methods for clinical management.
Discussion
This study offers new insights to clarify the connections between AAM and injury outcomes. Numerous prior studies evaluating the association of out-of-hospital AAM with TBI outcomes have suggested potential harm compared with ED AAM or similarly injured patients not receiving AAM. For example, in an analysis of over 4000 TBI patients in Pennsylvania, we observed increased adjusted odds of death and poor neurological outcome among patients receiving endotracheal intubation in the out-of-hospital setting versus those receiving intubation the ED. These studies combined TBI and shock cases in the same analysis, controlling for the confounding effect of hypotension through multivariable adjustment and assuming similar associations with mortality in both groups.
Our contrasting study examined TBI and shock subgroups separately. We observed that the increased mortality associated with out-of-hospital AAM was limited primarily to patients in shock. If the relationship between AAM and outcomes were due primarily to selection bias, one would expect similar associations when stratified by TBI and shock. Our results are further bolstered by the use of multicentre trial data with subjects prospectively identified using all available out-of-hospital vital signs and Glasgow Coma Scale measurements. This approach better approximated the perspective of the treating paramedic and minimised potential for post hoc misclassification.
If validated, the findings of this study would have important implications for out-of-hospital AAM research and practice. Reasons postulated for the connection between out-of-hospital AAM and poor outcomes in injured patients include suboptimal paramedic training or skill, poor intubation technique, prolonged laryngoscopy, iatrogenic hypotension and bradycardia, or the low rate of out-of-hospital neuromuscular blockade use, among others. More importantly, some experts believe that the worsened AAM outcomes are primarily due to inadvertent hyperventilation. In TBI, hyperventilation is associated with decreased brain oxygen delivery and perfusion. In victims of shock, hyperventilation may decrease venous return, mean arterial pressure and cardiac output. We observed that the physiologic interactions with AAM in the shock state are more closely correlated with mortality than the interactions with TBI. Therefore, clinicians and scientists must strive to better characterise the interaction between airway, ventilation and the shock state. Serum lactate is often used as a marker of cellular perfusion, and differences in serum lactate might indicate airway-related perfusion differences. However, we did not observe associations between out-of-hospital AAM and initial ED lactate in either TBI or shock groups.
Observational studies have inherent limitations, including selection bias and incomplete risk adjustment, among others. However, this approach remains one of the best and only available approaches for evaluating the effectiveness of out-of-hospital AAM strategies in injured patients. We note that the association between AAM and mortality was relatively large, supporting the validity of the relationship. While a prospective controlled trial is the optimal approach for evaluating the effectiveness of AAM, clinical trials of out-of-hospital AAM are exceedingly difficult to perform, since many patients possess intact airway reflexes, and most EMS providers in North America do not have access to neuromuscular blocking agents. To date, Bernard et al have conducted the only prospective clinical trial evaluating the comparative effectiveness of out-of-hospital intubation, identifying a small benefit in select TBI patients. However, this Australian trial utilised paramedics specially trained in neuromuscular blockade use, and thus, it is unclear if the results can be extrapolated elsewhere.
Based upon prior studies of TBI patients, some experts have condemned field intubation of injured patients by paramedics. We urge a more restrained interpretation. The techniques of out-of-hospital intubation and advanced airway insertion are likely similar for both TBI and shock patients. Our study highlights differing connections with mortality between TBI and shock patients, pointing to the likely presence of other factors influencing outcomes such as postintubation ventilatory and hemodynamic management. Additional study is urgently needed to better characterise the physiology of the haemorrhagic shock state, the interactions with airway and ventilatory techniques, and the optimal methods for clinical management.
Source...