- Pathophysiology of Hemorrhagic Shock
- Stages of Hypovolemic Shock
- Clinical Presentation of Hemorrhagic Shock
- Lab Studies
- Management of Hemorrhagic Shock
- Complications of Hemorrhagic Shock
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Hemorrhagic Shock is defined as an abnormality of the circulatory system that results in inadequate organ perfusion and tissue oxygenation due to loss of blood. In simple terms, it means that tissues are not getting adequate blood perfusion and oxygen following a loss of blood.
Perfusion means the quantity of blood being served to the area and oxygenation implies the amount of oxygen being supplied by the blood.
Hemorrhagic shock is a type of hypovolemic shock [ the cause is a reduction of circulatory blood volume].
Persistent shock leads to cellular metabolic dysfunction and organ failure. In trauma patient, the cause of shock is a loss of blood following injury.
The loss could be external which is obvious and visible, or internal which is concealed and could be overlooked easily if one is not alert enough.
It is essential to treat shock early and aggressively with emphasis on controlling hemorrhage, increasing oxygen carrying capacity, and improving perfusion pressure to vital organs.
Hemorrhagic shock is a leading cause of death among trauma patients.
Pathophysiology of Hemorrhagic Shock
With bleeding associated with trauma, external or internal, blood loss may occur.
Other conditions which cause bleeding such as childbirth or gastrointestinal bleed, surgery, aortic rupture etc can also cause the hemorrhagic shock.
Whenever there is blood loss, the body attempts to compensate by mechanisms which are
- Increasing heart rate to pump more blood
- Increased oxygen delivery
- Increased ventilation to grasp more oxygen
- Cutting down the blood supply to other tissues so as to continue supply to vital organs.
- increased oxygen consumption by tissues.
But still, the body may not provide adequate tissue perfusion and oxygenation.
Generally, the clinical hemorrhagic shock is an acute event with a clear precipitating factor.
Age and comorbid factors all may affect a patient’s response to hemorrhagic shock.
Failure of compensatory mechanisms in hemorrhagic shock can lead to death.
Stages of Hypovolemic Shock
Four stages of hemorrhagic shock are defined. Some systems may have up to 6 stages
- Up to 15% blood volume loss (750 mL)
- Compensated by constriction of vascular bed
- Blood pressure maintained
- Normal respiratory rate (12-20 breaths per minute)
- Pallor of the skin
- Normal mental status to slight anxiety
- Normal capillary refill (less than 2 seconds)
- Normal urine output
- 15–30% blood volume loss (750–1500 mL)
- Blood pressure cannot be maintained by arterial constriction
- Tachycardia >100 beats per minute
- Increased respiratory rate (more than 20 respirations per minute)
- Systolic blood pressure maintained
- Increased diastolic blood pressure
- Narrow pulse pressure (gap between the systolic and diastolic pressure)
- Pale, cold, and clammy skin as blood flow is directed away to major organs such as the heart, lungs, and brain
- Mild anxiety/Restless
- Delayed capillary refill
- Urine output of 20-30 milliliters/hour
- 30–40% blood volume loss (1500–2000 mL)
- Systolic BP falls to 100mmHg or less
- Marked tachycardia (increased heart rate) >120 bpm
- Marked tachypnea (increased rate of respiration) >30 respirations per minute
- Alteration in mental status (confusion, anxiety, agitation)
- Sweating with cool, pale skin
- Delayed capillary refill
- Urine output of approximately 20 milliliters/hour
- Loss greater than 40% (>2000 mL)
- Extreme tachycardia (>140) with weak pulse
- Pronounced tachypnea [increased respiratory rate]
- Significantly decreased systolic blood pressure of 70 mm Hg or less
- Decreased level of consciousness, lethargy, coma
- Skin is sweaty, cool, and extremely pale (moribund)
- Absent capillary refill
- Negligible urine output
- Survival is extremely unlikely
Clinical Presentation of Hemorrhagic Shock
Hemorrhagic shock after trauma is generally encountered in the field in prehospital care and casualty of the hospital.
It is an emergency, so the history, examination, and interventions often go side by side.
History is important to assess mode and severity of trauma, any bleeding disorders that patient might have and any previous intervention done before the patient is received.
Often the history may not available.
As usual, airway and breathing should be assessed first and then circulation to address the measures to correct shock which is usually by wide bore cannula and fluid replacement.
In the field, a quick examination must be done to assess the injury and for purpose of triage. Any injury needing immediate measures [like chest injury] should be attended to.
All the external bleeding must receive compression dressing.
In the hospital, after the patient has been stabilized, a detailed evaluation of the injuries should be carried.
Following measures may be needed in the emergency
- Tube thoracostomy
- Central venous pressure monitoring
It must be noted that injury to any part, from head to lower limb, including chest and abdomen can result in shock due to bleeding.
Usually, the source of bleeding is apparent. Special attention should be paid to chest, abdomen and pelvic injuries which may not be visible externally but internal injuries could lead to great losses.
Shock is recognized by increased heart rate [tachycardia], decrease in blood pressure [hypotension], pallor on the skin [due to vasoconstriction] and decreased capillary refill [not that reliable]
The patient may feel dizzy and develops a thirst. But these signs are for most of the shocks, therefore, history and examination of injury is of immense importance for establishing a diagnosis of traumatic hypovolemic shock.
Children need a special mention. They can develop high blood pressure despite the loss of volume, because of compensatory mechanisms.
Children for a longer period than adults, but deteriorate rapidly and severely once they do begin to decompensate. Thus they need an approach which is more aggressive
Lab studies should not be awaited to establish diagnoses and work for treatment. Samples are sent but resuscitation must continue without waiting for results.
Lab studies are most important to assess the changes in response to therapy.
Only lab study that is required early is typing and crossmatching to arrange for packed red blood cells should. Fresh frozen plasma and platelets also may be required to correct or prevent coagulopathies that develop in severe hemorrhagic shock.
But even if that cannot be waited for due to the severity of shock, O-negative blood may be given.
Diagnostic peritoneal lavage is used to detect intra-abdominal blood, fluid, and intestinal contents. It is sensitive but not specific for an abdominal injury.
Serial measurement of the following can help guide ongoing therapy.
- Prothrombin time and/or activated partial thromboplastin time
- Urine output rate can help guide adequacy of perfusion.
- Arterial blood gas analysis
- Lactate and base deficit
These studies are not required for early management of shock. In fact, these do not have any direct role in the emergency management of shock.
However, these are required for evaluation of injuries and planning the definitive management.
Cervical spine, chest, and pelvis radiographs are the standard screening images for severe trauma. Other radiographs may be indicated depending on the spectrum of injuries.
CT scanning is often the method of choice for intra-abdominal and/or retroperitoneal hemorrhage.
Ultrasound aids in rapid intra-abdominal fluid hemothorax or pericardial tamponade.
ECG can be useful for the detection of cardiac arrhythmias and other cardiac problems.
Management of Hemorrhagic Shock
Fluid replacement is beneficial in hypovolemia of stage 2 and is necessary for stage 3 and 4.
Management of hemorrhagic shock should be directed toward optimizing perfusion of and oxygen delivery to vital organs.
As previously noted, diagnosis and treatment of the underlying cause of bleeding must be performed rapidly and concurrently with the management of shock.
Management of shock aims at maintaining the perfusion and oxygen carrying capacity to vital organs, while hemorrhage is being treated.
Following measures are taken for management of hemorrhagic shock
- Oxygen administration
- Establishment of intravenous access
- Vital monitoring
- Central venous pressure monitoring
- Fluid replacement
- Blood and blood products transfusion
The initial management of hemorrhagic shock involves controlling active bleeding with the application of external pressure compression dressings and the splinting of fractures.
At the same time, fluid resuscitation to restore adequate intravascular volume and tissue oxygen delivery is undertaken.
The response to the initial fluid resuscitation serves as a guide to further therapy
- A rapid response to initial fluid therapy occur in minimal blood loss
- Temporary improvement followed by deterioration after fluid therapy indicates ongoing blood loss or inadequate resuscitation. These patients require additional fluid resuscitation, blood transfusion, and possibly surgical intervention to control hemorrhage.
- Minimal or no response means ongoing, severe hemorrhage with the need for continuous, aggressive fluid and blood transfusion and emergent surgical intervention.
Monitoring of Resuscitation
The primary goal of resuscitation is, by definition, restoration of adequate organ perfusion and tissue oxygenation. Another factor is the correction of acidosis if present
Clinical parameters that indicate adequate resuscitation
- Stable mean arterial pressure and heart rate
- Adequate urine output [indicates good renal perfusion in the absence of renal failure]
- Improved cardiac filling pressures
- Warm limbs with good peripheral perfusion
- Good distal capillary filling.
- Improved mental status
However, the presence of physiologic compensatory mechanisms decreases the utility of these measures alone to assess the complete resuscitation from shock.
The arterial base deficit, easily available from an arterial blood gas, and the serum lactate are better indicators of severity of hemorrhagic shock and the response to resuscitation. These variables are good markers of the adequacy of tissue perfusion.
Fluids are used to expand the decreased blood volume so that tissue perfusion is maintained. Fluids do not have any capacity to carry oxygen. Only blood has.
There are two types of fluids used for resuscitation- crystalloids and colloids.
Most advocate initiating resuscitation with crystalloid solutions, followed by colloid and blood products based on the severity of hemorrhage.
Most crystalloid solutions administered for resuscitation are isotonic with respect to the human plasma. Ringer’s lactate solution, normal saline, Isolyte are examples of crystalloids.
Crystalloid solutions are usually the first IV solutions administered to the trauma patient for the resuscitation of hypovolemic shock.
Larger volumes (up to three times the blood loss) are required to replace hemorrhage when only crystalloid solutions are used. They can pass to extravascular space as guided by pressure and too much use of these fluids causes complications like edema.
Crystalloid solutions lower the blood viscosity and may improve capillary blood flow.
Colloid solutions include human albumin, Hexastrarch, and dextran. Because they contain larger molecules that do not readily migrate into the interstitial space, colloid solutions tend to remain relatively intravascular. Colloid solutions expand the intravascular space by increasing the colloid osmotic pressure.
Resuscitation with colloid solution produces a rapid and effective correction of intravascular fluid deficits with less peripheral edema than with crystalloid solutions.
Colloid solutions are used in conjunction with crystalloid solutions to increase blood volume. Like crystalloids, they also lack oxygen carrying capacity.
Transfusion of blood and its components has an important role in the management of the trauma patient. As transfusion is not without risks, decisions must weigh the benefits of potential improvement in outcome versus the associated risks.
Blood and blood products have the ability to replace red blood cells and improve oxygen transport capacity and to correct coagulation defects.
Complications of blood product transfusion include the risk of febrile, allergic, or hemolytic transfusion reactions, infectious disease transmission, coagulation defects and bleeding, and immunosuppression.
Red Blood Cell Transfusion
Packed red blood cells are used to restore red cell mass and oxygen-carrying capacity. The decision to use red blood cell transfusion in the trauma patient should take into consideration the potential for continued hemorrhage and the complications of inadequate tissue oxygen delivery.
A blood needs to crossmatched before which might consume time and the delay may not be acceptable in case of severe blood loss. In such cases type O-negative red blood cells can be used for the unstable patient with severe, ongoing blood loss not responsive to nonblood therapy.
Type-specific/uncrossmatched or partially crossmatched blood requires approximately 5 to 10 minutes before availability and is safe for use in patients requiring the ongoing transfusion of fluids and blood to maintain stability
Autotransfusion involves the collection of shed blood from wounds, body cavities, or drains for reinfusion. Blood is collected from body cavities, such as the thorax, using a suction device with citrate anticoagulant and directly reinfused into the trauma patient through a macroaggregate filter.
Transfusion of platelets is indicated in the trauma patient with evidence of microvascular surgical bleeding and a severely decreased platelet count.
Fresh Frozen Plasma
Fresh frozen plasma provides both stable and labile plasma coagulation factors. Indications include the correction of microvascular bleeding with a documented coagulopathy, and for known coagulation factor deficiencies.
Cryoprecipitate is administered for evidence of microvascular bleeding in massively transfused patients with low fibrinogen levels.
It is an antifibrinolytic drug that prevents blood clots from breaking down. It reduces mortality in trauma patients.
Vasopressors increase coronary and cerebral blood flow during the low-flow state. Vasopressors commonly used are
- Dopamine – Stimulates both adrenergic and dopaminergic receptors.
- Norepinephrine – Stimulates adrenergic receptors, which, in turn, increase cardiac muscle contractility and heart rate. Also causes constriction of vessels which increases blood pressure and coronary blood flow.
- Vasopressin has a vasopressor and antidiuretic hormone activity. Increases water resorption.
- Epinephrine is an alpha-agonist that causes increased peripheral vascular resistance
Complications of Hemorrhagic Shock
- Sepsis and multiple organ system failure
- Death may occur
- Within minutes of hemorrhage due blood loss
- After 1 to several hours due to progressive decompensation
- Days to weeks later due to sepsis and organ failure.