Shock is a state of tissue hypoperfusion that leads to impaired cellular metabolism and—if uncorrected—progresses to multiple organ failure and death.
Shock is classified according to the 4 primary pathophysiologic mechanisms involved:
oligemic, or hypovolemic (eg, hemorrhage, diabetic ketoacidosis, burns, or sequestration)
cardiogenic (eg, myocardial infarction or arrhythmia)
obstructive (eg, pericardial tamponade, pulmonary embolus, or tension pneumothorax)
distributive, characterized by maldistribution of the vascular volume secondary to altered vasomotor tone (eg, sepsis, anaphylaxis, spinal cord insult, beriberi, or arteriovenous fistula)
The type of shock can often be determined by the history, physical examination, and appropriate diagnostic tests. Regardless of the event that precipitated the state of shock, microcirculatory failure is the common factor that eventually leads to death in individuals in advanced shock. Ventilatory failure appears to be the most significant factor in the morbidity and mortality of shock, with subsequent hypoxemia and metabolic acidosis leading to many complications.
If vasovagal syncope is ruled out (due to its short duration and because of familiarity with the situations that produce this condition), the basic life-support measures for the initial emergency care of the unconscious patient are similar to the measures used when treating patients with shock. The most important aspects of treatment are the CABs, the same principles used in CPR (see the section Cardiopulmonary Arrest earlier in this chapter).
Failure of respiratory gas exchange is the most frequent single cause of death in patients with shock; thus, respiratory obstruction must be ruled out first. Oxygen is then given by mask; if respiratory movements are shallow, mechanical ventilation is necessary. Respiratory obstruction can be assumed if there is stridor with respiratory movements or if cyanosis persists even when adequate ventilatory techniques have been applied. A conscious patient in distress who cannot speak and who is developing cyanosis may be choking on food or a foreign body.
Excerpted from BCSC 2020-2021 series: Section 1 - Update on General Medicine. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.