patients reach abnormal vital sign triggers. Early recognition and aggressive treatment of shock may prevent progression to the later stages of shock that can result in the death of potentially salvageable patients [10].
Prehospital hypotension may predict in‐hospital morbidity and mortality in both trauma and medical patients [11–13]. Medical patients may have a 30% higher mortality if there has been prehospital hypotension [11]. Trauma patients with prehospital hypotension have similar outcomes, even with subsequent normotension in the emergency department. This emphasizes the importance and value of accurate in‐field assessments, so that the next echelon of patient care can be informed and aware of the potential for critical illness or injury.
Despite their questionable value, orthostatic vital signs are often evaluated in the emergency department, and occasionally in the field. A positive orthostatic vital sign test for pulse rate would result in a pulse increase of 30 beats/min after 1 minute of standing [14]. Symptoms of lightheadedness or dizziness are considered a positive test. Occasionally, orthostatic vital signs are performed serendipitously by the patient who refuses treatment while lying down, then stands up to leave the scene, and suffers a syncopal or near‐syncopal episode. This demonstration of orthostatic hypotension is often helpful in convincing the patient to consent to treatment and transport. However, EMS clinicians should not routinely obtain orthostatic vital signs, and they should not equate absence of orthostatic response with euvolemia.
Capillary refill, an easy test to perform in the field setting, is not a useful test for mild‐to‐moderate hypovolemia [15]. Moreover, environmental considerations, such as cold temperatures and adverse lighting conditions, also affect the accuracy of this technique for shock assessment.
On‐scene estimates of blood loss by EMS clinicians may influence therapeutic interventions, including fluid administration. However, studies suggest that field clinicians are not accurate at estimating spilled blood volumes [16].
Hypoxia is a common manifestation of shock states. Patients in various stages of exsanguination may not have sufficient blood volume to perfuse adequately the body with oxygen. Unfortunately, pulse oximetry alone cannot detect the adequacy of oxygen delivery. Pulse oximetry may fail to detect a pulse (and give inaccurate oxygen saturation readings) when blood flow is reduced [15, 17]. Like pulse oximetry, capnography may also serve as an important tool in the evaluation and treatment of shock in the prehospital setting [18–21]. Exhaled end‐tidal carbon dioxide (EtCO2) levels vary inversely with minute ventilation, providing feedback regarding the effect of changes in ventilatory parameters [22, 23]. Additionally, changes in EtCO2 are virtually immediate when the airway is obstructed or the endotracheal tube becomes dislodged [24]. EtCO2 concentration may be influenced by factors other than ventilation. For example, levels are reduced when pulmonary perfusion decreases in shock, cardiac arrest, and pulmonary embolism [25–27]. EtCO2 is most useful as an indicator of perfusion when minute ventilation is held constant (e.g., when mechanical ventilation is applied) [19, 25]. Under these conditions, changes in EtCO2 levels reliably indicate changes in pulmonary perfusion. In any patient suffering from a potential shock state, diminished EtCO2 should be a warning of the critical nature of the patient’s problem.
Additional Modalities to Assess Shock
Use of portable ultrasound in the field can facilitate the recognition of immediately life‐threatening causes of shock including intra‐abdominal bleeding and cardiac tamponade. Many EMS agencies, primarily air medical services, have deployed point‐of‐care ultrasound for field evaluations, including the focused assessment by sonography in trauma (FAST) examination, the EFAST incorporating a lung assessment for pneumothorax, and various shock protocols to assess volume status, a limited cardiac exam, or reversible causes of shock [28]. Ultimately, the EMS medical director must determine if the cost and effort required to acquire the equipment, training, and performance of these skills translates into improved patient outcomes. The use of field ultrasound has the potential to worsen patient outcome if the procedure delays the time to definitive care, does not influence patient destination or care, or interferes with maintenance of critical parameters such as airway, ventilation, and hemorrhage control.
There is growing interest in the use of biomarkers that can be employed to identify, monitor, and predict the outcome in shock [29]. Point‐of‐care testing devices make measurement of biomarkers in the field an attractive option. Elevation of serum lactate may reflect anaerobic tissue metabolism in acute sepsis and shock [29, 30]. In the setting of infection, elevated lactic acid may indicate septic shock and the need for early goal‐directed therapy. Elevated venous lactate is associated with increased mortality risk and the need for resuscitative care in trauma patients. Prehospital trauma research indicates that an elevated lactate level in the setting of trauma predicts the need for aggressive resuscitation [31]. Serial lactate measurements may indicate the effectiveness of ongoing resuscitation [32].
Prehospital telemedicine holds the promise of providing access to the highest levels of care to patients and field clinicians by using EMS as a “telemedicine facilitator” (see Chapter 73). In the event that the patient is in profound shock or extremis, EMS clinicians can engage a wide range of expertise to help manage the patient [33].
Artificial intelligence technology (“assisted intelligence”) is also uniquely suited to prehospital medicine. Diagnostic algorithms can interpret trends in data and identify patients who are in compensated shock prior to clinical deterioration [34]. Further recognition of those patterns may lead to individualized care in the form of direct decision support informing EMS clinicians in how to best care for their patients.
Treatment
All treatment approaches to shock must include the following basic principles:
1 Perform the initial assessment.
2 Deal with issues identified during the initial assessment such as airway, breathing, and circulation issues, including active external bleeding.
3 Determine the need for early definitive care:hemorrhage control and volume resuscitationneedle thoracostomyelectrical therapy for dysrhythmiainvasive airway management.
4 Maintain adequate oxygen saturation (SaO2 greater than 94%).
5 Ensure adequate ventilation without hyperventilating.
6 Monitor vital signs, ECG, oxygen saturation, capnography, and lactate (if available).
7 Prevent additional injury or exacerbation of existing medical conditions.
8 Protect the patient from the environment.
9 Determine the etiology of the shock state and treat accordingly.
10 Notify and transport to an appropriate facility.
Often the etiology of the patient’s shock state and the initial management options are clear from the history. For example, the out‐of‐hospital treatment of a young, previously healthy college student with hypotension secondary to severe vomiting and diarrhea includes intravenous (IV) fluids. The treatment of cardiogenic shock in an unresponsive elderly patient with ventricular tachycardia requires prompt cardioversion. Occasionally, the primary problem may be strongly suspected but not readily diagnosable or treatable in the field (e.g., pulmonary embolism). Less frequent, but most difficult to manage, is the patient in shock without an obvious cause. With the understanding of the limited treatment options in the prehospital setting (primarily fluids, inotropic agents, and vasopressors), field treatment may be individualized for the four categories of shock: hypovolemic, distributive, obstructive, and cardiogenic.
Hypovolemic Shock
Hypovolemic shock is the result of significant loss of intravascular volume resulting in hypotension. The many etiologies of hypovolemic shock include external fluid loss and shifting of fluids from the vascular system to a nonvascular body compartment. The treatment of hypotension and shock caused by hypovolemia is relatively straightforward. External bleeding