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Syncope refers to a transient loss of consciousness (TLOC) due to global cerebral hypoperfusion with a rapid onset, brief duration, and spontaneous complete recovery. The evaluation of syncope involves (1) an initial evaluation of stability and any needed resuscitation, (2) an evaluation for any trauma from the syncope, (3) a focused evaluation for cause of the syncope, and lastly (4) risk stratification and appropriate disposition. Unfortunately, there are conditions that resemble syncope causing TLOC which must be included in the initial differential work-up of a patient.


An initial evaluation of airway patency, adequate ventilation, and appropriate perfusion (blood pressure/pulse) is the first step in syncope evaluation. Patients with cardiac arrest can sometimes exhibit seizure-like activity with loss of consciousness, and their care should begin with advanced cardiopulmonary life support. Patients presenting with coma or altered mental status need a glucose check, evaluation for hypoxemia, and assessment for need of naloxone or thiamine. Patients presenting with seizures may initially mimic syncope. Most patients with true syncope require no resuscitation having normal vital signs and are back to normal neurologically. Place the patient on cardiac monitoring and establish intravenous access. After initial resuscitation, evaluate for any trauma that occurred due to the syncope. The syncope work-up can be done during the resuscitation as well as any treatment of traumatic injuries which takes precedence if significant trauma has occurred (Figure 18–1).


A focused evaluation is done to assess for causes of syncope. The mnemonic “head heart and vessels” can guide one in the work-up as it covers true causes of syncope, as well as syncope mimics. A detailed history from the patient as well as any witnesses, a focused thorough physical examination, electrocardiography (ECG) and orthostatic vital signs comprise the initial diagnostic approach. Further testing is guided by these initial investigations. The primary focus of the initial investigations are to assess for syncope mimics, look for overt causes, and search for lethal cardiac causes.

Cerebral malfunction causes of TLOC include (H) hypoglycemia, hypoxemia (carbon monoxide, ventilation/perfusion shunts, and hypercapnic respiratory failure), (E) epilepsy, (A) anxiety, and (D) dysfunction of the brain stem due to basal vertebral transient ischemic attack (TIA) or stroke. Cardiac causes of transient loss of consciousness include (H) heart attack (acute coronary syndrome [ACS]), (E) embolism (PE), (A) aortic obstruction due to hypertrophic obstructive cardiomyopathy, aortic stenosis or myxoma, (R) rhythm disturbances that are slow bradycardia and (T) tachydysrhythmias. Vascular causes include (V) vasovagal (the common faint), (E) ectopic pregnancy (a reminder of blood loss and/or volume loss), (S) subclavian steal, (S) situational (micturition, defecation, cough), (E) ENT (glossopharyngeal or trigeminal neuralgia), (L) low systemic vascular resistance (medications, diabetic neuropathy, Addison disease), and (S) sensitive carotid sinus.

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