Hypovolemic shock refers to a medical or surgical condition in which rapid fluid loss results in multiple organ failure due to inadequate circulating volume and subsequent inadequate perfusion. Most often, hypovolemic shock is secondary to rapid blood loss (hemorrhagic shock).
Acute external blood loss secondary to penetrating trauma and severe GI bleeding disorders are 2 common causes of hemorrhagic shock. Hemorrhagic shock can also result from significant acute internal blood loss into the thoracic and abdominal cavities.
Two common causes of rapid internal blood loss are solid organ injury and rupture of an abdominal aortic aneurysm. Hypovolemic shock can result from significant fluid (other than blood) loss. Two examples of hypovolemic shock secondary to fluid loss include refractory gastroenteritis and extensive burns. The remainder of this article concentrates mainly on hypovolemic shock secondary to blood loss and the controversies surrounding the treatment of this condition. The reader is referred to other articles for discussions of the pathophysiology and treatment for hypovolemic shock resulting from losses of fluid other than blood.
The many life-threatening injuries experienced during the wars of the 1900s have significantly affected the development of the principles of hemorrhagic shock resuscitation. During World War I, W.B. Cannon recommended delaying fluid resuscitation until the cause of the hemorrhagic shock was repaired surgically. Crystalloids and blood were used extensively during World War II for the treatment of patients in unstable conditions. Experience from the Korean and Vietnam wars revealed that volume resuscitation and early surgical intervention were paramount for surviving traumatic injuries resulting in hemorrhagic shock. These and other principles helped in the development of present guidelines for the treatment of traumatic hemorrhagic shock. However, recent investigators have questioned these guidelines, and today, controversies exist concerning the optimal treatment of hemorrhagic shock.
History:
In a patient with possible shock secondary to hypovolemia, the history is vital in determining the possible causes and in directing the workup. Hypovolemic shock secondary to external blood loss typically is obvious and easily diagnosed. Internal bleeding may not be as obvious as patients may complain only of weakness, lethargy, or a change in mental status.
Symptoms of shock, such as weakness, lightheadedness, and confusion, should be assessed in all patients.
In the patient with trauma, determine the mechanism of injury and any information that may heighten suspicion of certain injuries (eg, steering wheel damage or extensive passenger compartment intrusion in a motor vehicle accident).
If conscious, the patient may be able to indicate the location of pain.
Vital signs, prior to arrival in the ED, should also be noted.
Chest, abdominal, or back pain may indicate a vascular disorder.
The classic sign of a thoracic aneurysm is a tearing pain radiating to the back. Abdominal aortic aneurysms usually result in abdominal, back pain, or flank pain.
In patients with GI bleeding, inquiry about hematemesis, melena, alcohol drinking history, excessive nonsteroidal anti-inflammatory drug use, and coagulopathies (iatrogenic or otherwise) is very important.
The chronology of vomiting and hematemesis should be determined.
The patient who presents with hematemesis after multiple episodes of forceful vomiting is more likely to have Boerhaave syndrome or a Mallory-Weiss tear, whereas a patient with a history of hematemesis from the start is more likely to have peptic ulcer disease or esophageal varices.
If a gynecologic cause is being considered, gather information about the following: last menstrual period, risk factors for ectopic pregnancy, vaginal bleeding (including amount and duration), vaginal passage of products of conception, and pain. All women of childbearing age should undergo a pregnancy test, regardless of whether they believe that they are pregnant. A negative pregnancy test typically excludes ectopic pregnancy as a diagnosis.
Physical: The physical examination should always begin with an assessment of the airway, breathing, and circulation. Once these have been evaluated and stabilized, the circulatory system should be evaluated for signs and symptoms of shock.
Do not rely on systolic BP as the main indicator of shock; this practice results in delayed diagnosis. Compensatory mechanisms prevent a significant decrease in systolic BP until the patient has lost 30% of the blood volume. More attention should be paid to the pulse, respiratory rate, and skin perfusion. Also, patients taking beta-blockers may not present with tachycardia, regardless of the degree of shock.
Classes of hemorrhage have been defined, based on the percentage of blood volume loss. However, the distinction between these classes in the hypovolemic patient often is less apparent. Treatment should be aggressive and directed more by response to therapy than by initial classification.
Class I hemorrhage (loss of 0-15%)
In the absence of complications, only minimal tachycardia is seen.
Usually, no changes in BP, pulse pressure, or respiratory rate occur.
A delay in capillary refill of longer than 3 seconds corresponds to a volume loss of approximately 10%.
Class II hemorrhage (loss of 15-30%)
Clinical symptoms include tachycardia (rate >100 beats per minute), tachypnea, decrease in pulse pressure, cool clammy skin, delayed capillary refill, and slight anxiety.
The decrease in pulse pressure is a result of increased catecholamine levels, which causes an increase in peripheral vascular resistance and a subsequent increase in the diastolic BP.
Class III hemorrhage (loss of 30-40%)
By this point, patients usually have marked tachypnea and tachycardia, decreased systolic BP, oliguria, and significant changes in mental status, such as confusion or agitation.
In patients without other injuries or fluid losses, 30-40% is the smallest amount of blood loss that consistently causes a decrease in systolic BP.
Most of these patients require blood transfusions, but the decision to administer blood should be based on the initial response to fluids.
Class IV hemorrhage (loss of >40%)
Symptoms include the following: marked tachycardia, decreased systolic BP, narrowed pulse pressure (or immeasurable diastolic pressure), markedly decreased (or no) urinary output, depressed mental status (or loss of consciousness), and cold and pale skin.
This amount of hemorrhage is immediately life threatening.
In the patient with trauma, hemorrhage usually is the presumed cause of shock. However, it must be distinguished from other causes of shock. These include cardiac tamponade (muffled heart tones, distended neck veins), tension pneumothorax (deviated trachea, unilaterally decreased breath sounds), and spinal cord injury (warm skin, lack of expected tachycardia, neurological deficits).
The 4 areas in which life-threatening hemorrhage can occur are as follows: chest, abdomen, thighs, and outside the body.
The chest should be auscultated for decreased breath sounds, because life-threatening hemorrhage can occur from myocardial, vessel, or lung laceration.
The abdomen should be examined for tenderness or distension, which may indicate intraabdominal injury.
The thighs should be checked for deformities or enlargement (signs of femoral fracture and bleeding into the thigh).
The patient's entire body should then be checked for other external bleeding.
In the patient without trauma, the majority of the hemorrhage is in the abdomen. The abdomen should be examined for tenderness, distension, or bruits. Look for evidence of an aortic aneurysm, peptic ulcer disease, or liver congestion. Also check for other signs of bruising or bleeding.
In the pregnant patient, perform a sterile speculum examination. However, with third-trimester bleeding, the examination should be performed as a "double set-up" in the operating room. Check for abdominal, uterine, or adnexal tenderness.
Causes: The causes of hemorrhagic shock are traumatic, vascular, GI, or pregnancy related.
Lab Studies:
After the history is taken and the physical examination is performed, further workup depends on the probable cause of the hypovolemia, as well as on the stability of the patient's condition.
Initial laboratory studies should include analysis of the CBC, electrolyte levels (eg, Na, K, Cl, HCO3, BUN, creatinine, glucose levels), prothrombin time, activated partial thromboplastin time, ABGs, urinalysis (in patients with trauma), and a urine pregnancy test. Blood should be typed and cross-matched.
Imaging Studies:
Patients with marked hypotension and/or unstable conditions must first be resuscitated adequately. This treatment takes precedence over imaging studies and may include immediate interventions and immediately taking the patient to the operating room.
The workup for the patient with trauma and signs and symptoms of hypovolemia is directed toward finding the source of blood loss.
The atraumatic patient with hypovolemic shock requires ultrasonographic examination in the ED if an abdominal aortic aneurysm is suspected. If GI bleeding is suspected, a nasogastric tube should be placed, and gastric lavage should be performed. An upright chest radiograph should be obtained if a perforated ulcer or Boerhaave syndrome is a possibility. Endoscopy can be performed (usually after the patient has been admitted) to further delineate the source of bleeding.
A pregnancy test should be performed in all female patients of childbearing age. If the patient is pregnant and in shock, surgical consultation and the consideration of bedside pelvic ultrasonography should be immediately performed in the ED. Hypovolemic shock secondary to an ectopic pregnancy is common. Hypovolemic shock secondary to an ectopic pregnancy in a patient with a negative pregnancy test, although rare, has been reported.
If thoracic dissection is suspected because of the mechanism and initial chest radiographic findings, the workup may include transesophageal echocardiography, aortography, or CT scanning of the chest.
If a traumatic abdominal injury is suspected, a FAST (Focused Abdominal Sonography for Trauma) ultrasound exam may be performed in the stable or unstable patient. Computed Tomography (CT) scanning typically is performed in the stable patient.
If long-bone fractures are suspected, radiographs should be obtained.
Prehospital Care: The treatment of patients with hypovolemic shock often begins at an accident scene or at home. The prehospital care team should work to prevent further injury, transport the patient to the hospital as rapidly as possible, and initiate appropriate treatment in the field. Direct pressure should be applied to external bleeding vessels to prevent further blood loss.
Prevention of further injury applies mostly to the patient with trauma. The cervical spine must be immobilized, and the patient must be extricated, if applicable, and moved to a stretcher. Splinting of fractures can minimize further neurovascular injury and blood loss.
Although in selected cases stabilization may be beneficial, rapid transport of sick patients to the hospital remains the most important aspect of prehospital care. Definitive care of the hypovolemic patient usually requires hospital, and sometimes surgical, intervention. Any delay in definitive care, eg, such as delayed transport, is potentially harmful.
Most prehospital interventions involve immobilizing the patient (if trauma is involved), securing an adequate airway, ensuring ventilation, and maximizing circulation.
In the setting of hypovolemic shock, positive-pressure ventilation may diminish venous return, diminish cardiac outcome, and worsen the shock state. While oxygenation and ventilation are necessary, excessive positive-pressure ventilation can be detrimental for a patient suffering hypovolemic shock.
Appropriate treatment usually can be initiated without delaying transport. Some procedures, such as starting intravenous (IV) lines or splinting of extremities, can be performed while a patient is being extricated. However, procedures in the field that prolong transportation should be delayed. Benefits to giving IV fluids prior to departure from the scene are not clear; however, IV lines and fluid resuscitation should be started and continued once the patient is en route to definitive care.
In recent years, there has been considerable debate regarding the use of military antishock trousers (MAST). MAST were introduced in the 1960s and, based mostly on anecdotal reports of success, their use became standard therapy in the prehospital treatment of hypovolemic shock in the late 1970s. By the 1980s, the American College of Surgeons Committee on Trauma included their use in the standard of care for all patients with trauma and signs or symptoms of shock. Since that time, studies have failed to show improved outcome with the use of MAST. The American College of Surgeons Committee on Trauma no longer recommends the use of MAST.
