Shock is a life-threatening condition of circulatory failure most commonly presenting with hypotension. Initially reversible, the effects can rapidly become irreversible, resulting in multi-organ failure.
Hypovolemic shock is a condition in which severe blood or fluid loss makes the heart unable to pump enough blood to the body. (This is a "pre-load" problem for the heart: it can only pump what is delivered to it.)
There are two ways the preload can be insufficient in hypovolemic shock:
- Absolute Hypovolemia is a decreased preload due to loss of volume of circulating blood.
- Relative Hypovolemia is a decreased preload due to an increase in the capacity of blood vessels to sequester blood volume away from the heart, such as with shock from vasodilation. In essence, it results in the same thing absolute hypovolemia causes--less blood getting to the heart for circulation and perfusion of organs.
Either way, hypovolemic shock can cause many organs to stop working as the shock reaches a "point of no return,” meaning the shock state becomes irreversible and the patient's death is inevitable due to insufficient or improper pumping of blood.
Absolute hypovolemia is usually caused by hemorrhage (internal or external), resulting in reduced blood volume; or by extreme fluid losses seen in severe burns.
Although in the field most cases of hypovolemic shock are acute--due to trauma and hemorrhage, or burns, other causes of fluid loss are:
- GI losses from excessive vomiting or diarrhea,
- renal losses in kidney disease,
- ascites in liver disease, or
- skin losses from excessive exercise in dry climates.
External vs Internal Hemorrhage: external hemorrhage is obvious, but internal hemorrhage in trauma may take longer to identify, especially if there is compensatory vasoconstriction yielding a normal blood pressure initially.
Loss of blood into an adjacent space that won't be re-absorbed until days later, such as large hematomas or bleeding into tissues around a fracture (seen as large areas of discoloration to fractured long bones), can present with this initial compensatory vasoconstriction. Therefore, you may have to rely on other considerations to identify hypovolemic shock, such as tachypnea, cold, clammy extremities, etc. (see "Signs and Symptoms," next).
Signs and Symptoms
Although sever trauma, hemorrhage, and/or burns (the most likely things you'll encounter in the field) can present with all of the signs and symptoms of hypovolemic shock together, more subtle presentations can present in stages of progressive symptomatology, as with dehydration, GI causes, kidney disease, etc.
Symptoms due to volume depletion with decreased tissue perfusion and/or electrolyte and acid-base consequences (sodium and potassium) are:
- muscle cramps
- hypotension, first seen as orthostatic (from sitting to standing)
- rapid, shallow breathing (tachypnea due to metabolic acidosis)
- abdominal pain from mesenteric ischemia
- chest pain from coronary ischemia
- lethargy and confusion--from cerebral vascular ischemia
- hypotension in all positions (not just orthostatic)
Classes of Hemorrhage
In hypovolemic shock caused by hemorrhage, blood volume loss is categorized into 4 classes:
Class I hemorrhage:
- blood volume loss up to 15%, with
- minimal tachycardia,
- no change in blood pressure or respiratory rate. (This indicates a threshold of compensatory reserve.)
Class II hemorrhage:
- 15-20% blood volume loss with
- tachycardia (100-120),
- tachypnea (respirations 20-24),
- decreased pulse-pressure (Systolic - Diastolic, e.g., 100 - 70 = pulse-pressure of 30),
- cool + clammy skin, and
- delayed capillary refill.
Class III hemorrhage:
- 30-40% blood volume loss, with
- significant drop in BP and mental status,
- tachycardia (>120, thready),
Class IV hemorrhage:
- 40% of blood volume loss with
- pulse-pressure <25 mmHg,
- marked tachycardia.
In external bleeding, bleeding must be controlled as rapidly as possible, with direct pressure the primary way. Tourniquets for extremity wounds or clips for scalp lacerations may also be necessary.
Children and Hypovolemic Shock
In children, heart rate is an important physiologic indicator of circulatory status, although tachycardia can also occur with fever and anxiety.
Since children are not just "little adults," fluid bolus replacement is based on a formula of
20cc/Kg over 5-10 minutes, and repeated up to 4 times if there is no improvement (and no signs of fluid overload).
In children, targeted blood pressure goals are systolic blood pressures of
- 60 mmHG < 1 month age
- 70 + (2 x age in years) mmHG for children 1 month to 10 years of age
- 90 mmHg in children 10 years of age or older.
Malnutrition: in children, malnutrition (sunken eyes, lethargy) can occur which may mislead an EMS responder to assume hypovolemia. (Malnutrition is to be considered abuse which should be reported unless there is an underlying metabolic condition, such as celiac disease.)
- Normal blood pressure does not rule out hypovolemic shock.
Although it is assumed hypotension is a cardinal feature of hypovolemic shock, it may be absent during a time of compensatory vasoconstriction that can temporarily maintain a normal blood pressure. In this case, tachycardia, cold, clammy extremities, cyanosis, and agitation can be indicative of hypovolemic shock in a normotensive presentation. A history can also be helpful in pointing to a cause that establishes the diagnosis.
- Examples of non-hemorrhagic causes of hypovolemic shock are patients over-treated for edema or for congestive heart failure from improperly supervised diuretics; and patients with advanced cirrhosis, ascites, or renal disease with a mixed presentation of symptoms that makes actual hypovolemia difficult to identify.
- Fluid replacement should be for hypotensive patients only.
The latest literature indicates it could do more harm than good in Class I hemorrhage, and the goal of replacement should be based on the presence or absence of hypotension (90 mmHg systolic). This is changing information, and any "ideal" strategy of replacement may be dated once newer information becomes available. (Stay tuned and pay attention!)
- Stop external bleeding.
- Stabilize fractured long bones, noting discoloration from tissue blood accumulation.
- Aggressive fluid replacement, if hypotensive, initially with repeated 500 cc bolus of (isotonic) normal saline (NS) or Ringer's Lactate (RL) until a systolic BP of 90 mmHg is achieved.
(Caveat: excessive NS or RL can cause metabolic acidosis or metabolic alkalosis, respectively.)
- Warm and position the patient.
- Rapidly transport to a trauma center, where blood products can be used.
The sooner blood products can be used for replacement instead of NS or RL, the better chance of avoiding end-organ failure.
Medications such as dopamine, dobutamine, epinephrine, and norepinephrine may be needed to maintain blood pressure and tissue perfusion and improve cardiac output.
Whether the hypovolemic shock is caused by trauma and hemorrhage or the more insidious causes (non-hemorrhagic), definitive treatment is replacing any lost blood or fluids, electrolyte balancing, and ending the cause of the problem (i.e., resolution of the blood loss or the problem resulting in fluid loss).