hemorrhagic shock, produce flat neck veins, tachycardia, and pallor
An important problem in the prehospital diagnosis of shock is the frequent inaccuracy of field assessment. For example, in one analysis, emergency medical technicians (EMTs) made vital sign errors more than 20% of the time [6]. Subsequently, when critical medical decisions are based on the data gathered in the field, multiple assessments should be performed.
EMS clinicians should look for the signs and symptoms of system‐wide reduction in tissue perfusion, such as tachycardia, tachypnea, mental status changes, and cool, clammy skin (Box 7.1). When available, adjunctive technologies can provide improved recognition and assessment of shock by revealing reductions in expired CO2, hypovolemia, obstruction or poor cardiac contractility, and elevated serum lactate levels.
Vital signs that fall outside of expected ranges must be correlated with the overall clinical presentation. Vital signs have a broad range of normal values. They must be interpreted in the context of the individual patient. A petite 45‐kg, 16‐year‐old girl with lower abdominal pain with a reported blood pressure of 88 mmHg systolic by palpation may have a ruptured ectopic pregnancy, or may just be at her baseline blood pressure. An elderly patient with significant epistaxis may be hypertensive due to catecholamine release and vasoconstriction despite being relatively volume depleted. Consideration should be given to patient age, comorbid conditions, and medications that may affect the interpretation of vital signs.
Box 7.1 Signs and symptoms of shock
Cardiovascular
Tachycardia, arrhythmias, hypotension
Jugular venous distension in obstructive and cardiogenic shock states
Tracheal deviation away from the affected side in tension pneumothorax
Central nervous system
Agitation, confusion
Alterations in level of consciousness
Coma
Respiratory
Tachypnea, dyspnea
Skin
Pallor, diaphoresis
Cyanosis (in obstructive and cardiogenic shock cases), mottling
In the noisy field environment, EMS clinicians often measure blood pressure by palpation rather than auscultation. Blood pressure by palpation provides only an estimate of sBP [7]. Without an auscultated diastolic pressure, the pulse pressure (the difference between systolic and diastolic pressure) cannot be calculated. A pulse pressure less than 30 mmHg or 25% of the sBP may provide an early clue to the presence of hypovolemic or obstructive shock [3]. Conversely, a wide pulse pressure may be indicative of distributive shock. Dividing the pulse rate by the sBP typically produces a ratio of approximately 0.5 to 0.8, which is called the “shock index.” When that ratio exceeds 0.9, then a shock state may be present [8].
Previously healthy patients with acute hypovolemic shock may maintain relatively normal vital signs with up to 25% blood volume loss [3]. Sympathetic nervous system stimulation with vasoconstriction and increased cardiac contractility may result in normal blood pressure in the face of decreasing intravascular volume, especially in the pediatric population. In some patients with intra‐abdominal bleeding (e.g., ruptured abdominal aneurysm, ectopic pregnancy), the pulse may be relatively bradycardic despite significant blood loss [9].
EMS personnel may equate “normal” vital signs with normal cardiovascular status [5]. The field team may be lulled into a false sense of security initially if the early signs of shock are overlooked, and then they are caught off guard when the patient’s condition dramatically worsens during transport. Following trends in the vital signs may also help identify shock before 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
