properties. Methylprednisolone is far more widely available in the prehospital environment and may have some limited utility in refractory shock. Patients exposed to potent cellular toxins such as cyanide or hydrogen sulfide may present with refractory shock, requiring therapy with agent‐specific antidotes. Consider transport to a facility capable of mechanical support for patients with refractory shock.
Pediatric Shock
Recognition and management of shock in the pediatric population follow the same general principles as in adults, with a few notable exceptions [46]. Children in shock more commonly present with a low cardiac output and a relatively high systemic vascular resistance (SVR). This has been described as “cold shock,” as opposed to the low‐SVR state or “warm shock” frequently seen in adults. Children presenting in distributive shock usually require more aggressive fluid resuscitation with volumes of 60 cc/kg or more [47]. If children fail to respond to the initial fluid resuscitation, epinephrine is preferred as the first‐line vasopressor to counter the relatively low cardiac output seen in pediatric shock. Additional support for patients with low SVR and wide pulse pressure may be provided with norepinephrine or vasopressin. Dobutamine may provide inotropic and chronotropic support in patients with very low cardiac output and improve delivery of oxygen to tissues.
Following initial treatment with fluids and vasoactive agents, pediatric patients may also benefit from adjunctive therapies for shock [46]. Early airway management should be considered, as children may use up to 40% of their cardiac output to support the work of breathing. Ketamine is the preferred induction agent, as it preserves cardiac output and will not result in the hypotension or adrenal suppression potentially seen with other induction agents. Hydrocortisone should be administered to children with adrenal insufficiency. Transport to an appropriate facility with pediatric critical care should be an important consideration.
Shock Interventions
Fluids
The treatment of shock must be customized to the individual EMS agency and geographic location. In the urban setting with short transport times, the victim of a penetrating cardiac wound would probably benefit most from airway maintenance and rapid transport to the hospital. IV or intraosseous (IO) access could be attempted en route, if it will not delay delivery to definitive care [48]. On the other hand, with longer transport times in the rural setting, a similar patient might benefit from a carefully titrated crystalloid volume infusion during transport. Fluid delivery could be initiated while the patient is en route to the hospital, thereby prolonging neither scene time nor time until definitive care [49]. In the patient who presents a difficult IV access problem, IO infusions may be attempted. Placing the IO needle in the humeral head may result in faster infusion rates than the proximal tibia.
The ideal fluid for use in the field would be small in volume, portable, non‐allergenic, inexpensive, and would not interfere with clotting factors [35]. Unfortunately, this ideal fluid has yet to be discovered. Isotonic crystalloids are currently the fluid of choice for out‐of‐hospital resuscitation in the United States [1, 36, 49, 50]. Among critically ill patients requiring large volume resuscitation, there is a benefit of balanced crystalloid solutions over normal saline but there is insufficient evidence to recommend them for initial resuscitation. Moreover, as they are relatively hypotonic, they may be detrimental in traumatic brain injury [51]. Crystalloid fluids are inexpensive and widely available but may contribute to dilutional coagulopathy, hyperchloremic acidosis, and hypothermia when given in large volumes.
Whole blood would arguably provide the greatest benefit as a resuscitative fluid in the setting of hemorrhagic shock but lacks availability due to issues of cost, storage, and limited supply. Use of blood products in the prehospital environment is generally limited to a few air medical services and EMS systems that carry blood for administration to victims of hemorrhagic shock. Prehospital administration of plasma reduces mortality in trauma victims but suffers the same limitations as blood administration [52]. Freeze‐dried plasma that has a long shelf life and can be made readily available is being used outside the United States. It may become important in prehospital resuscitation [53–55].
The optimal volume of fluids to administer in the field is not known, especially in the trauma victim with uncontrolled hemorrhage [36, 48, 49,56–61]. Current trauma algorithms call for the administration of IV fluid for all major trauma victims. Insufficient fluid volume may allow exposure to increasing “doses” of hypotension, leading to worsening mortality from hypoperfusion [62]. Evidence suggests, however, that attempts at normalization of blood pressure with a large volume of fluids in a patient with uncontrolled hemorrhagic shock may be deleterious to patient outcome. Complications may include acidosis, dislodgement of blood clots, and dilution of clotting factors [56]. In such a patient, it appears that the best course is to give sufficient crystalloid to maintain perfusion (such as a peripheral pulse and mentation) pending the delivery of the patient to the appropriate facility [57–59].
Extremity veins are the typical sites for venous access. External jugular veins are also useful in many patients. Few EMS systems use central venous access. IO access has become so important as a method of vascular access that it is supported by a position statement from the National Association of EMS Physicians [63]. In patients in extremis or cases in which peripheral access is not immediately available, IO access may be preferred.
Ventilation
The patient in shock may require assisted ventilation. Venous return requires a relative negative pressure in the right atrium to ensure return of blood to the heart. Assisted ventilation using any of the typical techniques, such as bag‐valve‐mask ventilation, endotracheal intubation, or supraglottic devices, results in an increase in airway pressure, raising intrathoracic pressure. Patients in shock from any cause are extremely sensitive to increases in intrathoracic pressure. Studies in a swine hemorrhagic shock model showed that even modest increases in the rate of positive‐pressure ventilation significantly reduce brain blood flow and oxygenation [64]. EMS personnel must carefully control the rate of assisted positive‐pressure ventilation in the shock patient, as overventilation is common. Generally, a one‐handed squeeze on the ventilation bag at a rate of approximately once every 8 seconds is reasonable for an adult, producing a minute ventilation of about 5 L/min. Minute ventilation should be adjusted to ensure an EtCO2 between 35 cmH2O and 45 cmH2O.
Vasopressors
Administration of vasoactive medications in combination with volume resuscitation may be required to reverse systemic hypoperfusion from shock. These agents increase vasoconstriction and may support inotropy and chronotropy [65]. Although a wide variety of vasoactive agents are available in the hospital, the drugs carried by prehospital services are limited by local, regional, or statewide protocols or regulations. Historically, most services carried epinephrine and dopamine. Norepinephrine is increasingly used in place of dopamine, following randomized controlled trials demonstrating improved survival with norepinephrine over dopamine in cardiogenic and distributive shock [40, 66]. Vasopressin, a potent vasoconstrictor that is effective at low pH, is available in some systems. It may be beneficial in patients with shock refractory to norepinephrine [67]. Among patients with hemorrhagic shock, vasopressin decreases blood product requirements, but additional studies are necessary to demonstrate improved patient‐centered outcomes [68].
The choice of vasopressor depends on the suspected underlying pathological process and the patient’s response to therapy. Unfortunately, in the field, the etiology of the shock state is often unclear, and close monitoring of vital signs is difficult. The administration of vasoactive agents in the field has multiple challenges including the need to calculate weight‐based dosages, mix and dilute drugs, and administer precise volumes. EMS clinicians should use calculators or templates or seek direct medical oversight. When available, portable IV infusion pumps should be used to ensure accurate and precise medication administration.
An alternative to vasopressor infusions are boluses of vasopressors used to temporize patients in profound shock or peri‐arrest until the patient can be stabilized with volume or vasopressor infusions.