What are the different types of shock and the basics of treatment for each type? What would you do for this patient?
Many classifications of shock have been described. Schematically, shock can be divided into cardiogenic, obstructive, hypovolemic, and distributive.
· Cardiogenic shock is due to a primary pump failure with a decrease in cardiac output. It can be further classified as nonventricular (e.g., acute mitral regurgitation due to rupture of chordae) or ventricular (e.g., dilated or hyper-trophic cardiomyopathy, myocardial ischemia). The treat-ment is to correct a nonventricular cause surgically, if amenable, after temporizing with medical treatment. In ventricular causes, treatment is aimed at correcting the decreased contractility, such as treating the ischemia or administering inotropes. Occasionally, an intra-aortic balloon pump (to improve myocardial perfusion and decrease afterload) or a ventricular assist device (usually as a bridge to transplantation) may be indicated.
· Obstructive shock results from impediment to blood return (tension pneumothorax, pericardial tamponade). In addition to fluid resuscitation, the cause needs to be treated, such as chest tube insertion or drainage of a pericardial effusion.
· Hypovolemic shock is due to absolute hypovolemia sec-ondary to dehydration, third-spacing or hemorrhage. The treatment is fluid or blood administration, respectively.
· Distributive shock is due to relative hypovolemia sec-ondary to loss of vascular tone. It can be secondary to sepsis or nonseptic systemic inflammatory response syndrome (SIRS), anaphylaxis, or neurogenic shock. Anaphylactic and neurogenic shock benefit from fluid resuscitation, but the primary treatment is restoration of vascular tone with vasopressors. Septic shock has a com-plex pathophysiology. The main characteristics are a hyperdynamic state with increased cardiac output (CO) (in spite of depressed myocardial contractility) and decreased SVR. Besides the treatment of the septic focus with antibiotics and surgery if needed, therapy is mainly supportive. This would include adequate fluid resuscita-tion and pressors to maintain MAP within acceptable limits. Recent studies have shown the administration of human recombinant activated protein C (brand name XIGRIS), an inhibitor of coagulation, improves outcome from sepsis. A full discussion of sepsis is beyond the scope of this chapter.
For this patient, the first step should be an oriented phys-ical examination, to gather elements suggesting one of the above diagnoses. The most likely causes of hypotension in this case are hypovolemia due to bleeding or third-spacing, sepsis, or myocardial ischemia. In the absence of a presen-tation suggesting cardiogenic shock, fluid and/or blood administration is appropriate. At the same time, more diag-nostic data should be obtained from a 12-lead electrocar-diogram (ECG), invasive hemodynamic monitoring, and possibly an echocardiogram. Vasopressors can be used with caution pending restoration of intravascular volume.
In spite of the result of meta-analyses suggesting that colloid administration might lead to poor outcomes, no broad consensus has emerged as to the best type of fluid to use for fluid resuscitation.