As ultrasound is integrated into the bedside evaluation of many emergent symptoms and disease states, multiple protocols have emerged for the rapid assessment of critically ill patients in shock and cardiac arrest states. By combining many of the exams described previously in this chapter, one can quickly assess for the cause of a patient’s hypotension or cardiac arrest, helping to sort through what is often an extensive differential diagnosis. A common approach is termed the “RUSH” protocol—Rapid Ultrasound for Shock and Hypotension. Though there are distinct protocols proposed by different authors, they combine a sonographic assessment of a patient’s gross cardiac function, intravascular volume status, and identification of pathologic conditions (such as AAA or pneumothorax) that threaten a patient’s hemodynamic stability. One group of authors promotes the use of the heuristic “Pump, Tank, and Pipes” as the mental framework for this evaluation, while another uses the mnemonic “HI-MAP” (heart, IVC, Morison [and other FAST views], aorta, and pulmonary/pneumothorax) to outline the protocol. Regardless of which specific protocol one uses for evaluation of the hypotensive patient, when combined with a history and physical exam, bedside ultrasound can be used to guide resuscitative efforts and tailor them to the type of shock encountered.
In addition, when confronted with a patient in cardiac arrest, bedside ultrasound can be used during CPR to help guide therapies and decision making. The protocols described previously can be used to search for the cause of a patient’s arrest. Additionally, the subxiphoid and apical four-chamber windows can even be used during compressions or rapidly during pulse checks to determine the native function of the heart and distinguish between true PEA or “electromechanical dissociation” (where there is an electrical rhythm conducted but no cardiac activity) and “pseudo-PEA” where the heart’s contractions are so poor that they do not produce palpable pulsations. One can sometimes even distinguish between asystole and fine ventricular fibrillation on the monitor by looking closely at the mitral valve for motion during a pulse check. Alternatively, some emergency physicians are utilizing transesophageal ultrasound probes for use in cardiac arrest—obviating the need to interrupt compressions and allowing for assessment of cardiac compressions during CPR.
Once the patient has been evaluated, findings on ultrasound may be correlated with one of the types of shock identified below. The table below lists representative findings within each shock state. Note that each finding listed below is neither sufficient nor required for the diagnosis of different types of shock, and is merely suggestive. Of course, the clinical context of each patient’s presentation must be taken into account in any resuscitation.