Shock is the generalized inadequate perfusion of the tissues of the body.

The cause of shock may be low cardiac output (cardiogenic shock), low blood volume (hypovolemic shock), or other other etiologies (septic shock, toxic shock).

The greater the blood loss, the worse the clinical problem and the more dramatic the clinical findings. This has led to a number of systems to categorize hemorrhage according to its severity. One such system is shown here:

	Class I	Class II	Class III	Class IV
Severity	Compensated	Mild	Moderate	Severe
% Loss	Up to 15%	15-30%	30-40%	>40%
Volume Loss	Up to 500 ml	750-1500 ml	1500-2000	>2000
Pulse	<100	>100	>120	>140
BP	Normal	Orthostatic change	Mod. Decrease	Frank Hypotension
Respiratory Rate	Normal	Mild increase	Tachypnea	Marked tachypnea, Respiratory failure
Urine (ml/hour)	>30	20-30	5-20	None
Symptoms	Normal	Agitated, anxious	Confused, disoriented	Lethargic, unresponsive, Skin cold and clammy

In real patients, there is often some overlap between classes, and not all individuals within a class will show all of these signs and symptoms.

Pregnancy itself can be a complicating factor. Following a normal vaginal or cesarean delivery, maternal blood loss may average as much as 1,000 ml, or about 20% of the maternal blood volume. In a non-pregnant adult, such a loss would likely provoke signs and symptoms of shock. But in pregnant women, this loss is tolerated, often without any significant symptoms, primarily because the mother’s blood volume needs immediately after delivery are significantly less than just before delivery.

After delivery, the uterus is firmly contracted, reducing blood flow through it and the eliminating the shunting effect of the intervillous space. The maternal peripheral blood flow, previously widely dilated, vasoconstricts, reducing the distensibility of her cardiovascular system.

Her pre-preganancy blood volume has increased by about 50% over the course of pregnancy(30% increase in red cell mass) and so the loss of 20% of her blood volume during delivery is generally tolerated very well. Blood loss in excess of the normal loss, however, can be problematic, as can any significant blood loss while she remains pregnant.

Unfortunately, the bleeding associated with placenta previa and placental abruption both occur while she continues to have strong metabolic needs of the fetus and placenta, significant cardiac output directed to the uterus, and significant shunting through the intervillous space.

Management of hemorrhagic shock involves two processes, recognition and treatment.

Recognition

Recognition requires being alert to the significance of any observed bleeding and its context.

• Rapid loss of 500 cc of bright red blood during a normal vaginal delivery would not attract clinical attention, so long as it stopped as soon as the uterus firmly contracted.
• The same 500 cc loss from a woman not in labor would constitute hemorrhage.
• The sudden appearance of 500 cc of bright red blood and clots in a woman in active labor at 6 cm suggests both hemorrhage and a placental abruption.
• The sudden appearance of 500 cc of bright red blood and clots immediately after delivery suggests some combination of uterine atony and traumatic injury.

Recognition is complicated by some of the routine procedures used during labor. Many patients receive IV fluids during labor that may partially compensate for active bleeding. It is not unusual for a woman who is steadily bleeding, but who is receiving IV fluids, to have reasonably normal vital signs up until she experiences cardiovascular collapse.

Recognition involves watching maternal vital signs for the classical signs of tachycardia, tachypnea, hypotension and oliguria, as well as the symptoms of agitation, anxiety, confusion, disorientation and lethargy. The second part of recognition is observing significant blood loss, either at an unusual time, or in excess of the expected. Either may trigger treatment for hemorrhage.

Treatment

IV crystalloid. Up to two liters can effectively treat mild degrees of hemorrhage. In more severe hemorrhage, it can stabilize the patient long enough to get blood transfusions going. Some physicians prefer a colloid solution (and there are arguments both for and against this). Either should be effective in helping expand the intravascular volume.

Remember that crystalloid remains within the vascular space for only a limited amount of time. It leaks steadily into the extravascular spaces. So whatever improvement in vascular volume the patient experiences from crystalloid will be transient and brief.

Oxygen. This won’t help a lot because the hemoglobin is already nearly 100% saturated with oxygen, but it helps enough that it is worth doing.

Blood. The problem with shock is that not enough oxygen is getting to the tissues. Expanding the blood volume with crystalloid won’t create any more red blood cells to carry oxygen to the tissues. In cases of moderate to severe shock, blood transfusions are needed.

Blood products, including coagulation factors and platelets are valuable at replacing those lost during the hemorrhage.

Trendelenberg position. If blood is not immediately available, placing the patient in a head-down position (ie, legs up in the air, or Trendellenberg position) will make available 250 to 500 cc of blood that had been pooled in the lower extremeties.

Stop the bleeding. Do whatever needs to be done to stop the bleeding. There is an old medical expression: “All bleeding eventually stops.” That’s true.