A 25-year-old woman, gravida 2 para 1, at 10 weeks gestation is brought to the emergency department by her boyfriend, who found her lying on the bed in a pool of blood. Her previous pregnancy was uncomplicated and resulted in a normal term vaginal delivery. She has no chronic medical problems. The patient takes a daily prenatal vitamin and does not smoke or drink alcohol. Temperature is 36.7 C (98 F), pulse is 120/min, and respirations are 20/min. Pelvic examinations shows blood clots throughout the vagina. The cervix is dilated, and there is a large amount of blood from the cervical os. On neurologic examination, she is somnolent but responsive to verbal stimuli and has 2+ deep tendon reflexes. Weak posterior tibial and dorsalis pedis pulses are palpable bilaterally. Which set of parameters is most likely to be seen in this patient?
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 incomplete abortion (eg, open cervical os, vaginal bleeding) and accompanying evidence of poor organ and tissue perfusion (eg, altered mental status, weak peripheral pulses) likely has hypovolemic shock due to massive hemorrhage. Loss of intravascular volume decreases right ventricular preload, leading to a downstream decrease in pulmonary capillary wedge pressure (PCWP), a representation of left atrial pressure (and left ventricular end-diastolic pressure). There is a consequent decrease in left ventricular preload, resulting in decreased cardiac output (CO) and decreased systemic blood pressure (BP). This in turn stimulates the sympathetic nervous system, leading to increased heart rate and peripheral vasoconstriction (increased systemic vascular resistance [SVR]) in an attempt to maintain BP.
(Choice A) Low CO and BP in combination with elevated PCWP and SVR are consistent with cardiogenic shock. Left ventricular dysfunction leads to decreased ejection fraction, hypotension, and elevated PCWP. Heart rate and SVR are increased in an effort to compensate for decreased CO.
(Choice B) Low SVR is suggestive of vasodilatory or distributive shock (eg, shock due to sepsis, anaphylaxis, systemic inflammatory response syndrome). In the hyperdynamic phase of distributive shock, low SVR leads to low BP and a compensatory rise in heart rate and CO. PCWP is usually low.
(Choice D) Elevated BP, CO, and SVR with normal PCWP may be seen in a hyperadrenergic state due to catecholamine surge, or may be seen in preeclampsia. Absence of hyperreflexia in this patient makes preeclampsia less likely.
(Choice E) Elevated SVR in combination with normal BP, CO, and PCWP is consistent with pre-shock or compensated shock, as may be seen in patients with mild hypovolemia. An initial small decrease in CO and BP causes an increase in SVR, which in combination with an increase in heart rate allows for maintenance of relatively normal CO, BP, and tissue perfusion. However, as the underlying condition worsens, the increase in heart rate cannot sustain adequate CO and shock ensues.
Educational objective:
Hypovolemic shock is characterized by low cardiac output and a compensatory elevation in systemic vascular resistance. Central venous pressure and pulmonary capillary wedge pressure are low due to decreased intravascular blood volume.