Non-Invasive Shock: Differentiating Shock in the Emergency Department

Shock is a common final pathway for many disease states, occurring when oxygen and nutrient delivery are not sufficient to maintain normal cellular function. The incidence of shock in the emergency department (ED) is approximated to be 1-3% of ED patients(1), and it carries a high mortality, ranging from 20-50% depending on the underlying cause of shock(2). Early recognition and treatment of shock significantly improves outcomes in critically ill patients(2, 3), and so the majority of efforts to this point have focused on identifying patients with shock.

The many etiologies of shock may be grouped into several broader categories: cardiogenic, distributive, hemorrhagic, hypovolemic, anaphylactic, and neurogenic. These categories cause shock through different mechanisms, but they have a significant amount of clinical overlap (4-7), making differentiating the cause of shock challenging for the emergency provider. While some overlap also exists between the treatments for these categories, several have vastly different therapeutic approaches. Since the early treatment of shock influences outcomes(2, 3, 8, 9), identifying the correct etiology to treat should logically impact outcomes as well, although this has not been studied in shock patients. However, Moore, et al., did show that physicians were only able to correctly identify the cause of hypotension in 25% of hypotensive patients in the ED, speaking to both the difficulty in diagnosing shock etiologies and the high percentage of patients with undifferentiated shock(10).

Recently, a number of different devices and biomarkers have been suggested to have clinical utility in differentiating shock and guiding resuscitation(11-13). These devices have potential to aid in the differentiation of shock.

We will conduct a prospective, observational study of patients found to have shock and "near-shock" physiology in the emergency department. We will identify patients meeting our inclusion criteria which will identify shock and "near shock" patients. Inclusion criteria will include: HR > 120, SBP \< 90, or a shock index (HR/SBP) > 1 for at least five minutes. Patients that do meet vital sign requirements, but have a lactate > 4 mmol/L, will also be included.

Enrolled patients will undergo physiologic assessments using echocardiography, Microscan, Non-invasive cardiac output monitor (NICOM), and extremity temperature device, as well as a blood draw for biomarker assessment.