Hypovolemic Shock

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Diagnosis | Management

Definition

Hypovolemic shock occurs when there is a significant loss of blood or other fluids, leading to inadequate circulation and oxygen delivery to the tissues. This type of shock can cause multiple organ failures and, if not treated promptly, can be fatal.

Aetiology

Hypovolemic shock is primarily caused by a loss of at least 20% of the body’s blood volume. The most common causes include:

• External Bleeding: From trauma or surgical wounds.
• Internal Bleeding: Due to conditions such as gastrointestinal haemorrhage, ruptured aneurysm, or fractures.
• Severe Dehydration: From prolonged diarrhoea, vomiting, or inadequate fluid intake.
• Severe Burns: Fluid loss through damaged skin can lead to hypovolemic shock.
• Other Causes: Including excessive sweating, diuretic use, and third-spacing in conditions like pancreatitis or peritonitis.

Pathophysiology

Hypovolemic shock progresses through several stages:

• Pre-shock State (Compensatory Stage): The body attempts to compensate for fluid loss by increasing heart rate, enhancing cardiac contraction, and inducing vasoconstriction. This helps to maintain diastolic blood pressure, resulting in a slight increase in overall blood pressure.
• Shock State: As fluid loss continues, compensation fails, leading to a drop in systolic blood pressure, tachycardia, and oliguria (reduced urine output). Blood flow is redirected to vital organs like the heart and brain, but decreased perfusion to other tissues leads to lactic acid accumulation, tissue ischaemia, and metabolic acidosis.
• End-Organ Failure: Prolonged hypoperfusion results in the failure of multiple organs, including the kidneys, liver, and heart, ultimately leading to death if untreated.

Risk Factors

Several factors can increase the risk of developing hypovolemic shock, including:

• Recent Trauma or Surgery: Which may result in significant blood loss.
• Chronic Medical Conditions: Such as gastrointestinal diseases or clotting disorders that predispose to bleeding.
• Severe Dehydration: Due to excessive vomiting, diarrhoea, or inadequate fluid intake.
• Advanced Age: Older adults may have less physiological reserve to compensate for fluid loss.

Signs and Symptoms

The clinical presentation of hypovolemic shock includes:

• Increased Thirst: A compensatory response to fluid loss.
• Abdominal or Chest Pain: May be indicative of internal bleeding or stress on the heart.
• Confusion or Altered Mental State: Due to reduced cerebral perfusion.
• Cold, Clammy Skin: A result of vasoconstriction and reduced peripheral perfusion.
• Pallor: Caused by reduced blood flow and oxygenation to the skin.
• Oliguria: Decreased urine output as the body attempts to conserve fluid.
• Tachypnoea: Rapid breathing as the body tries to compensate for metabolic acidosis.
• Unconsciousness: May occur in severe cases due to inadequate cerebral blood flow.
• Haematochezia or Melaena: Blood in stool may indicate gastrointestinal bleeding.

Investigations

Several investigations are crucial in diagnosing and managing hypovolemic shock:

• Full Blood Count (FBC): To assess haemoglobin levels, haematocrit, and white blood cell count.
• Urea & Electrolytes (U&E): To evaluate kidney function and electrolyte imbalances.
• Liver Function Tests (LFTs): To assess liver function, which may be impaired in shock.
• Coagulation Screen: To evaluate clotting function, which may be impaired in cases of significant blood loss.
• Blood Gases (Arterial or Venous): To assess acid-base balance and detect metabolic acidosis.
• Urine Output Monitoring: Often via catheterisation, to assess kidney perfusion and function.
• Imaging: CT scans, x-rays, or ultrasound as appropriate to identify sources of bleeding or other causes of shock.
• Echocardiogram: To assess cardiac function and exclude cardiac causes of shock.
• Electrocardiogram (ECG): To monitor heart rhythm and detect any myocardial ischaemia.

Diagnosis

The diagnosis of hypovolemic shock is primarily clinical, supported by investigations:

• Physical Examination: Key findings include hypotension, tachycardia, tachypnoea, and signs of poor perfusion such as cold, clammy skin.
• Vital Signs: Hypotension and tachycardia are indicative of shock. Hypothermia may also be present in severe cases.
• Clinical Assessment: Focus on identifying the underlying cause, such as trauma, bleeding, or dehydration, to guide treatment.

Management

Immediate management of hypovolemic shock is crucial and includes the following steps:

1. Initial Stabilisation

• Keep the Patient Warm: Use blankets or a warming device to prevent hypothermia, which can exacerbate shock.
• Position the Patient: Lay the patient flat with legs elevated (if not contraindicated) to promote venous return.
• Avoid Oral Fluids: As the patient may require surgical intervention or has a compromised airway, oral fluids should be avoided.

2. Advanced Life Support

• Cardiopulmonary Resuscitation (CPR): If the patient is unconscious and unresponsive, initiate CPR and follow advanced life support protocols.
• Intravenous Fluid Resuscitation: Begin with crystalloid solutions (e.g., normal saline or Ringer's lactate) to restore circulating volume.
• Blood Products: In cases of significant blood loss, transfusion of packed red blood cells, platelets, and plasma may be required.
• Oxygen Therapy: Administer high-flow oxygen to ensure adequate tissue oxygenation.
• Vasopressors: If hypotension persists despite fluid resuscitation, consider using vasopressors (e.g., noradrenaline) to support blood pressure.

3. Definitive Management

• Identify and Treat the Underlying Cause: Surgical intervention may be necessary for conditions like internal bleeding or a ruptured aneurysm.
• Monitoring: Continuous monitoring of vital signs, urine output, and laboratory parameters is essential to guide ongoing management.
• Transfer to Higher Level of Care: Consider transferring the patient to an intensive care unit (ICU) for further management and monitoring.

References

1. National Institute for Health and Care Excellence (NICE) (2024) Guidelines for the Management of Hypovolemic Shock. Available at: https://www.nice.org.uk/guidance/ng216 (Accessed: 26 August 2024).
2. British Heart Foundation (2024) Emergency Management of Shock. Available at: https://www.bhf.org.uk (Accessed: 26 August 2024).
3. British National Formulary (BNF) (2024) Fluid and Electrolyte Management. Available at: https://bnf.nice.org.uk/ (Accessed: 26 August 2024).

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