A 75-year-old man is brought to the emergency department after his family found him to be lethargic and confused. The patient has a history of hypertension, coronary artery disease, and heart failure. Temperature is 35 C (95 F), blood pressure is 78/46 mm Hg, and pulse is 110/min. The patient is admitted to the intensive care unit and a pulmonary artery catheter is placed, which demonstrates the following readings:
| Cardiac output | high |
| Central venous pressure | low |
| Pulmonary capillary wedge pressure | low |
| Mixed venous O2 saturation | high |
| Systemic vascular resistance | low |
Which of the following is the most likely cause of this patient's hypotension?
Hemodynamic measurements in shock | ||||
Parameter | Hypovolemic | Cardiogenic | Obstructive | Distributive shock |
CVP | ↓ | ↑ | ↑ | ↓ |
PCWP | ↓ | ↑ | ↓* | ↓ |
Cardiac index | ↓ | ↓ | ↓ | ↑** |
SVR | ↑ | ↑ | ↑ | ↓ |
SvO2 | ↓ | ↓ | ↓ | ↑** |
*In tamponade, left-sided preload is decreased, but measured PCWP is paradoxically increased due to external compression by pericardial fluid. **Cardiac index & SvO2 are usually decreased in neurogenic shock due to impaired sympathetic reflexes. CVP = central venous pressure; LV = left ventricular; PCWP = pulmonary capillary wedge pressure; SvO2 = mixed venous oxygen saturation; SVR = systemic vascular resistance. | ||||
This patient with severe hypotension and evidence of end-organ dysfunction (eg, confusion) is in shock, which is a state of inadequate oxygen delivery to the organs and tissues of the body. Left untreated, shock can rapidly lead to multiorgan failure and death; therefore, prompt diagnosis and treatment are essential. Pulmonary arterial catheterization can help determine the type of shock to help guide treatment.
The low systemic vascular resistance (SVR) in this patient is consistent with the peripheral vasodilation that occurs in distributive shock; septic shock (usually due to bacterial infection) is the most common type of distributive shock. Central venous pressure (CVP), or right-sided preload, is decreased in septic shock due to widespread vasodilation in response to systemic release of proinflammatory mediators. Pulmonary capillary wedge pressure (PCWP), which is an estimate of left atrial pressure (left-sided preload), is decreased as well due to reduced venous return. A compensatory increase in sympathetic drive increases cardiac contractility and heart rate resulting in increased cardiac output (CO). The high rate of blood flow through the systemic capillaries prevents complete extraction of oxygen by the tissues, resulting in high mixed venous oxygen saturation.
(Choice B) Gastrointestinal bleeding can lead to hemorrhagic (hypovolemic) shock characterized by low CVP, PCWP, and CO, with a compensatory increase in SVR.
(Choices C and E) Myocardial infarction can lead to heart failure and cardiogenic shock, characterized by high PCWP and CVP. CO decreases, with a compensatory increase in SVR.
(Choice D) Moderate to severe hypothermia (ie, <32 C) can produce hypotension due to bradycardia, but mild hypothermia does not typically lead to shock. Septic shock can present with either hyper- or hypothermia; hypothermic presentation may be due to cytokine-induced dysregulation of temperature control in the hypothalamus and is associated with poorer outcomes.
(Choice F) Acute pulmonary embolism is a potential cause of obstructive shock. Blood flow through the pulmonary circulation is impeded, resulting in reduced left-sided preload (low PCWP) and consequently reduced CO with a compensatory increase in SVR. Blood backs up in the capacitance veins leading to high CVP.
Educational objective:
Septic shock can present with either hyper- or hypothermia. The initial disturbance is peripheral vasodilation leading to decreased systemic vascular resistance, decreased central venous pressure, and decreased pulmonary capillary wedge pressure. A compensatory increase in sympathetic drive causes an increase in cardiac output; the resulting high flow rates lead to incomplete oxygen extraction in the tissues, resulting in high mixed venous oxygen saturation.