Unintentional injury is typically a leading cause of death in the United States for patients of all ages. However, in 2011 it was the leading cause of death for patients between the ages of 1 and 44 years (Hoyert & Xu, 2012). A significant percentage of those deaths occur as the result of exsanguination (Sauaia et al.,1995), with many occurring before the patient even reaches the hospital.
Hemorrhagic shock is a subset of hypovolemic shock that results from a decrease in circulating blood volume. This decrease can occur because the patient actually loses blood or alternatively, loses only the fluid component of the blood.
While EMS personnel normally associate hypovolemic shock with trauma and bleeding, there are other potential causes of hypovolemic shock. Severe diarrhea, prolonged vomiting, and endocrine disorders can cause significant losses of circulating volume. Hypovolemic shock may also result from internal fluid shifts caused by burns and massive abdominal infections. Always assume hypovolemia as the underlying cause for shock until you can prove otherwise.
The presence of a mechanism of injury should raise the suspicion of bleeding in the traumatized patient (Rossaint et al., 2010). Often, external blood loss in patients with penetrating trauma is the earliest diagnostic clue for developing hemorrhagic shock. However, this sign is absent in patients who suffer blunt trauma which requires EMS personnel to focus on other predictors.
In many shock patients, the rate and depth of ventilation increases in an attempt to compensate for developing tissue acidosis. Radial pulse character (weak or absent), combined with the motor and verbal components of the Glasgow Coma Scale are predictive of the need for lifesaving interventions in non-head-injured trauma patients (Holcomb et al., 2005).
Determining pulse rate alone is a poor predictor of the need for surgery or blood transfusion following a traumatic event (Brasel, Guse, Gentilello, & Nirula, 2007; Demetriades et al., 1998).
In fact, almost half of all patients in one study who presented to the emergency department after suffering penetrating abdominal injuries or severe but isolated extremity trauma had a relative bradycardia, including about 35% of the patients with an initial systolic blood pressure less than 100 mm Hg (Thompson, Adams, & Barrett, 1990).
Historically, clinicians used systolic blood pressure measurement as a significant indicator of hypotension and shock, typically establishing the shock threshold at 90 mm Hg (Kerby & Cusick, 2012).
However, 15 percent of trauma patients in one study who ultimately required emergency thoracoabdominal surgery and more than five units of pack red blood cells presented to EMS personnel with a systolic blood pressure greater than 100 mm Hg (Luna, Eddy, & Copass, 1989).
Researchers now question whether true tissue hypoperfusion begins at the 90 mm Hg point or whether it is actually much higher (Bruns, Gentilello, Elliott, & Shafi, 2008; Eastridge et al., 2007; Eastridge, Salinas, Wade, & Blackbourne, 2011; Edelman, White, Tyburski, & Wilson, 2007) while others suggest that blood pressure readings are too unreliable for use in the diagnosis of tissue hypoperfusion (Hick, Rodgerson, Heegaard, & Sterner, 2001; McGee, Abernethy, & Simel, 1999).
There is universal agreement that the first step in the management of the hemorrhaging patient is to control blood loss. There is also universal agreement that medics must support the circulatory status of patients exhibiting signs and symptoms of hemorrhagic shock.
Crystalloids, such as lactated Ringer’s solution and saline are the most widely used solutions in the prehospital treatment of traumatic injury. Lactated Ringer’s solution has a theoretic advantage because it can buffer metabolic acidosis and prevent the acidosis resulting from excess chloride ion infusion associated with saline administration (Kobayashi, Costantini, & Coimbra, 2012).
However, outcome advantages is likely only when massive transfusions become necessary (Healey, Davis, Liu, Loomis, & Hoyt, 1998). Research involving mild to moderate hemorrhage demonstrate no outcome advantage provided by one of these solutions compared to the other (Moore et al., 2006; Schreiber, 2011).
The time-honored strategy for pre-hospital fluid resuscitation has followed the American College of Surgeons 3:1 rule – for every unit of blood lost, infuse 3 liters of crystalloid (American College of Surgeons Committee on Trauma, 2008).
However, fluids given before surgical control of hemorrhage may result in clot disruption, thereby allowing continued blood loss (McSwain & Barbeau, 2010). Fluid administration may also dilute coagulation factors (Bickell, Bruttig, Millnamow, O’Benar, & Wade, 1991; Hewson et al., 1985.; Maegele et al., 2007), which slows clot formation.
To prevent these complications, some advocate for a more restrictive fluid replacement strategy in the prehospital period before definitive bleeding control occurs. A permissive hypotension approach minimizes or restricts fluid administration as long as the patient can maintain adequate cerebral perfusion and systolic blood pressures remain above a certain threshold (Kobayashi, Costantini, & Coimbra, 2012).
Delayed fluid resuscitation improved survival in penetrating torso injuries (Bickell et al., 1994), traumatic amputation (Owens, Watson, Prough, Uchida, & Kramer, 1995), while restricting fluid volumes to maintain low mean arterial pressure resulted in lowered postoperative mortality (Morrison et al., 2011).
Animal data suggests that early use of vasoactive agents, particularly before surgical control of blood loss, may result in acceptable blood pressure maintenance without the need for large volume fluid resuscitation and its associated complications (Schwartz & Reid, 1981; Stadlbauer et al., 2003; Voelckel et al., 2003). To date, researchers have completed only one randomized-controlled trial using vasopressin in the acute resuscitation phase (Cohn et al., 2011).
Their results show no significant mortality improvements conferred to fluid + vasopressin administration when compared to standard fluid resuscitation alone. In patients presenting to EMS with blunt traumatic arrest and displaying pulseless electrical activity, researchers prospectively compared a small treatment cohort receiving vasopressin and hydroxyethyl starch solution to a historical control group who received standard resuscitation measures.
The treatment group had significant improvements in return of spontaneous circulation and 24-hour survival (Grmec, Strnad, Cander, & Mally, 2008). On the other hand, three large retrospective studies found that vasopressin administration in severely injured and hypotensive trauma patients increased the risk of death (Collier et al., 2010; Plurad et al., 2011; Sperry et al., 2008). The utility of vasopressin administration in the management of hemorrhagic shock remains unanswered.
Future of shock assessment
Researchers are now testing point-of-care devices that may be a useful tool in helping EMS personnel recognize occult bleeding or as an early indicator of tissue hypoperfusion secondary to blood loss.
For example, one hand held monitor uses a small sample of the patient’s blood to measure the quantity of serum lactate, similar to way glucometers measure blood glucose levels. In one study involving more than 2000 patients who suffered trauma and presented with an initial systolic blood pressure between 90 and 110 mm Hg, serum lactate monitors used in the emergency department were more accurate predictors of both the need for blood transfusion than the patient’s blood pressure and for mortality (Vandromme, Griffin, Weinberg, Rue, & Kerby, 2010).
Serum lactate levels obtained by paramedics in the field during transport of 1000 trauma patients, when added to initial vitals and GCS scores are predictive of the need for urgent surgical care, multiple organ failure syndrome, and mortality (Guyette et al., 2011). A multicenter prehospital trial on the utility of lactate biomarkers in the management of trauma patients is currently underway (Resuscitation Outcomes Consortium, n.d.).
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