eMedicine Specialties > Trauma > Blood Loss and Trauma Management

Shock, Hemorrhagic

Author: John Udeani, MD, FAAEM, Assistant Professor, Department of Emergency Medicine, Charles Drew University/UCLA School of Medicine
Contributor Information and Disclosures

Updated: Sep 22, 2008

Introduction

Background

Hemorrhagic shock is a condition of reduced tissue perfusion, resulting in the inadequate delivery of oxygen and nutrients that are necessary for cellular function. Whenever cellular oxygen demand outweighs supply, both the cell and the organism are in a state of shock.

On a multicellular level, the definition of shock becomes more difficult because not all tissues and organs will experience the same amount of oxygen imbalance for a given clinical disturbance. Clinicians struggle daily to adequately define and monitor oxygen utilization on the cellular level and to correlate this physiology to useful clinical parameters and diagnostic tests.

The 4 classes of shock, as proposed by Alfred Blalock, are as follows:¹

• Hypovolemic
• Vasogenic (septic)
• Cardiogenic
• Neurogenic

Hypovolemic shock, the most common type, results from a loss of circulating blood volume from clinical etiologies, such as penetrating and blunt trauma, gastrointestinal bleeding, and obstetrical bleeding. Humans are able to compensate for a significant hemorrhage through various neural and hormonal mechanisms. Modern advances in trauma care allow patients to survive when these adaptive compensatory mechanisms become overwhelmed.

Pathophysiology

Well-described responses to acute loss of circulating volume exist. Teleologically, these responses act to systematically divert circulating volume away from nonvital organ systems so that blood volume may be conserved for vital organ function. Acute hemorrhage causes a decreased cardiac output and decreased pulse pressure. These changes are sensed by baroreceptors in the aortic arch and atrium. With a decrease in the circulating volume, neural reflexes cause an increased sympathetic outflow to the heart and other organs. The response is an increase in heart rate, vasoconstriction, and redistribution of blood flow away from certain nonvital organs, such as the skin, gastrointestinal tract, and kidneys.

Concurrently, a multisystem hormonal response to acute hemorrhage occurs. Corticotropin-releasing hormone is stimulated directly. This eventually leads to glucocorticoid and beta-endorphin release. Vasopressin from the posterior pituitary is released, causing water retention at the distal tubules. Renin is released by the juxtamedullary complex in response to decreased mean arterial pressure, leading to increased aldosterone levels and eventually to sodium and water resorption. Hyperglycemia commonly is associated with acute hemorrhage. This is due to a glucagon and growth hormone–induced increase in gluconeogenesis and glycogenolysis. Circulating catecholamines relatively inhibit insulin release and activity, leading to increased plasma glucose.

In addition to these global changes, many organ-specific responses occur. The brain has remarkable autoregulation that keeps cerebral blood flow constant over a wide range of systemic mean arterial blood pressures. The kidneys can tolerate a 90% decrease in total blood flow for short periods of time. With significant decreases in circulatory volume, intestinal blood flow is dramatically reduced by splanchnic vasoconstriction. Early and appropriate resuscitation may avert damage to individual organs as adaptive mechanisms act to preserve the organism.

Age

Hemorrhagic shock is tolerated differently, depending on the preexisting physiologic state and, to some extent, the age of the patient. Very young and very old people are more prone to early decompensation after loss of circulating volume.

• Pediatric patients have smaller total blood volumes and, therefore, are at risk to lose a proportionately greater percentage of blood on an equivalent-volume basis during exsanguination compared to adults. The kidneys of children younger than 2 years are not mature; they have a blunted ability to concentrate solute. Younger children cannot conserve circulating volume as effectively as older children. Also, the body surface area is increased relative to the weight, allowing for rapid heat loss and early hypothermia, possibly leading to coagulopathy.
• Elderly people may have both altered physiology and preexisting medical conditions that may severely impair their ability to compensate for acute blood loss. Atherosclerosis and decreased elastin cause arterial vessels to be less compliant, leading to blunted vascular compensation, decreased cardiac arteriolar vasodilation, and angina or infarction when myocardial oxygen demand is increased. Older patients are less able to mount a tachycardia in response to decreased stoke volume because of decreased beta-adrenergic receptors in the heart and a decreased effective volume of pacing myocytes within the sinoatrial node. Also, these patients frequently are treated with a variety of cardiotropic medications that may blunt the normal physiological response to shock. These include beta-adrenergic blockers, nitroglycerin, calcium channel blockers, and antiarrhythmics.
• The kidneys also undergo age-related atrophy, and many older patients have significantly decreased creatinine clearance in the presence of near-normal serum creatinine. Concentrating ability may be impaired by a relative insensitivity to antidiuretic hormone. These changes in the heart, vessels, and kidneys can lead to early decompensation after blood loss. All of these factors in concert with comorbid conditions make management of elderly patients with hemorrhage quite challenging.

Clinical

History

• No single historical feature is diagnostic of shock. Some patients may report fatigue, generalized lethargy, or lower back pain (ruptured abdominal aortic aneurysm). Others may arrive by ambulance or in the custody of law enforcement for the evaluation of bizarre behavior.
• Obtaining a clear history of the type, amount, and duration of bleeding is very important. Many decisions in regard to diagnostic tests and treatments are based on knowing the amount of blood loss that has occurred over a specific time period.
• If the bleeding occurred at home or in the field, an estimate of how much blood was lost is helpful.
• For GI bleeding, knowing if the blood was per rectum or per os is important. Because it is hard to quantitate lower GI bleeding, all episodes of bright red blood per rectum should be considered major bleeding until proven otherwise.
• Bleeding because of trauma is not always identified easily. The pleural space, abdominal cavity, mediastinum, and retroperitoneum are all spaces that can hold enough blood to cause death from exsanguination.
• External bleeding from trauma can be significant and can be underestimated by emergency medical personnel.
• Scalp lacerations are notorious for causing large underestimated blood loss.
• Multiple open fractures can lead to the loss of several units of blood.

Physical

The physical examination in patients with hemorrhagic shock is a directed process. Often, the examination will be paramount in locating the source of bleeding and will provide a sense of the severity of blood loss. Differences exist between medical patients and trauma patients in these regards. Both types of patients usually will require concurrent diagnosis and treatment.

• The hallmark clinical indicators of shock have generally been the presence of abnormal vital signs, such as hypotension, tachycardia, decreased urine output, and altered mental status. These findings represent secondary effects of circulatory failure, not the primary etiologic event. Because of compensatory mechanisms, the effects of age, and use of certain medications, some patients in shock will present with a normal blood pressure and pulse. However, a complete physical examination must be performed with the patient undressed.
  • The general appearance of a patient in shock can be very dramatic. The skin may have a pale, ashen color, usually with diaphoresis. The patient may appear confused or agitated and may become obtunded.
  • The pulse first becomes rapid and then becomes dampened as the pulse pressure diminishes. Systolic blood pressure may be in the normal range during compensated shock.
  • The conjunctivae are inspected for paleness, a sign of chronic anemia. The nose and pharynx are inspected for blood.
  • The chest is auscultated and percussed to evaluate for hemothorax. This would lead to loss of breath sounds and dullness to percussion on the side of bleeding.
  • The abdominal examination searches for signs of intra-abdominal bleeding, such as distention, pain with palpation, and dullness to percussion. The flanks are inspected for ecchymosis, a sign of retroperitoneal bleeding. Ruptured aortic aneurysms are one of the most common conditions that cause patients to present in unheralded shock. Signs that can be associated with a rupture are a palpable pulsatile mass in the abdomen, scrotal enlargement from retroperitoneal blood tracking, lower extremity mottling, and diminished femoral pulses.
  • The rectum is inspected. If blood is noted, take care to identify internal or external hemorrhoids. On rare occasion, these are a source of significant bleeding, most notably in patients with portal hypertension.
  • Patients with a history of vaginal bleeding undergo a full pelvic examination. A pregnancy test is warranted to rule out ectopic pregnancy.
• Trauma patients are approached systematically, using the principles of the primary and secondary examination. Trauma patients may have multiple injuries that need attention concurrently, and hemorrhage may accompany other types of insults, such as neurogenic shock.
• The primary survey is a quick maneuver that attempts to identify life-threatening problems.
  • To assess the airway, ask the patient's name. If the answer is articulated clearly, the airway is patent.
  • The oral pharynx is inspected for blood or foreign materials.
  • The neck is inspected for hematomas or tracheal deviation.
  • The lungs are auscultated and percussed for signs of pneumothorax or hemothorax.
  • The radial and femoral pulses are palpated for strength and rate.
  • A quick inspection is made to rule out any external sources of bleeding.
  • A gross neurological examination is performed by asking the patient to squeeze each hand and dorsiflex both feet against pressure. Advanced trauma life support (ATLS) suggests that a "miniature" neurologic examination categorizes the patient's level of consciousness by whether the patient is alert, responds to voice, responds to pain, or is unresponsive (ie, AVPU).
  • The patient then is exposed completely, taking care to maintain thermoregulation with blankets and external warming devices.
• The secondary examination is a head-to-toe, careful examination that attempts to identify all injuries.
  • The scalp is inspected for bleeding. Any active bleeding from the scalp should be controlled before proceeding with the examination.
  • The mouth and pharynx are examined for blood.
  • The abdomen is inspected and palpated. Distention, pain on palpation, and external ecchymosis are indications of intra-abdominal bleeding.
  • The pelvis is palpated for stability. Crepitus or instability may be an indication of a pelvis fracture, which can cause life-threatening hemorrhage into the retroperitoneum.
  • Long bone fractures are noted by localized pain to palpation and boney crepitus at the site of fracture. All long bone fractures should be straightened and splinted to prevent ongoing bleeding at the sites. Femur fractures are especially prone to large blood losses and should be immobilized immediately in a traction splint.
  • Further diagnostic tests are warranted to diagnose intrathoracic, intra-abdominal, or retroperitoneal bleeding.

Causes

Hemorrhagic shock is caused by the loss of both circulating blood volume and oxygen-carrying capacity. The most common clinical etiologies are penetrating and blunt trauma, gastrointestinal bleeding, and obstetrical bleeding.

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