Shock is a state in which there is failure of the circulatory system to maintain adequate cellular perfusion resulting in widespread reduction in delivery of oxygen and other nutrients to tissues. In shock, the mean arterial pressure is less than 60 mmHg or the systolic blood pressure is less than 90 mmHg. Regardless of the underlying pathology, shock constitutes systemic hypoperfusion due to reduction either in cardiac output or in the effective circulating blood volume. The end results are hypotension followed by impaired tissue perfusion and cellular hypoxia.
Adequate organ perfusion depends on arterial blood pressure (BP) which, in turn, depends on:
1. Cardiac output (CO)
2. Peripheral vascular resistance (PVR)
• CO = stroke volume X heart rate
In turn, stroke volume depends on:
a) Preload i.e. blood volume, b) Afterload i.e. arterial resistance c) Myocardial contractility. Therefore, shock (i.e. widespread decreased perfusion of tissues) occurs when the preload (i.e. the blood volume) is decreased, or when the afterload (the peripheral vascular resistance) is decreased, or when the myocardium fails to contract. These basic mechanisms of shock are used to classify it.
Shock can be divided into:
(A.) Hypovolemic shock (B.) Cardiogenic shock (C.) Distributive shock
This is shock caused by reduced blood volume. Reduction in circulating blood volume results in the reduction of the preload which leads to inadequate left ventricular filling, reflected as decreased left and right ventricular end diastolic volume and pressure. The reduced preload culminates in decreased cardiac output which leads to widespread tissue perfusion (shock).
This is shock that results from severe depression of cardiac performance. It primarily results from pump failure [myocardial failure]. Cardiogenic shock is hemodynamically defined as: DBP 18mm Hg, cardiac index< 1.8 l/min/m2, usually pulmonary oedema coexists.
Distributive shock refers to a group of shock subtypes caused by profound peripheral vasodilatation despite normal or high cardiac output.
Other categories of shock
Septic shock: Caused by an overwhelming infection, leading to vasodilatation.
Neurogenic shock: Caused by trauma to the spinal cord, resulting in sudden decrease in peripheral vascular resistance and hypotension.
Anaphylactic shock: Caused by severe allergic reaction to an allergen, or drug.
Low blood pressure (systolic BP below 80 mmHg) is the key sign of shock Weak and rapid pulse
Rapid and shallow breathe
Restlessness and altered mental state
Low urine output
Signs and symptoms of shock in children must be recognized while still in the compensated state to avoid irreversible deterioration. Therefore, the following are primarily assessed in children:
Prolonged capillary filling (more than 3 seconds)
Decreased pulse volume (weak thread pulse)
Increased heart rate (160/minute in infants and 120 in children)
Decreased level of consciousness (poor eye contact)
Decreased blood pressure and decreased urine output are late signs and while they can be monitored the above signs are more sensitive in detecting shock before irreversible.
Treatment depends on the type of shock. Intravenous fluid therapy is important in the treatment of all types of shock except for cardiogenic shock. Prompt diagnosis of underlying cause is essential to ensure optimal treatment.
Maintain open airway
Administer oxygen with face mask and if needed after intubation with assisted ventilation. Check for and manage hypoglycemia
Fluid replacement (Not for Cardiogenic shock) Adults:
A: 0.9% Sodium chloride given as the 1L bolus infusion. Repeat bolus until blood pressure is improved. Transfuse blood and plasma expanders (-) in hemorrhagic shock.
A: 0.9% Sodium chloride 20 mol/kg as a slow infusion. Do not administer IV fluids in case of cardiogenic shock but maintain IV access. If patient develops respiratory distress, discontinue fluids
Septicemia in children: All children with shock which is not obviously due to trauma or simple watery diarrhea should receive antibiotic cover for probable septicemia.
B: Ampicillin 20mg/kg/dose 6 hourly for 7-10 days OR
C: Ceftriaxone, IM, 50–80 mg/kg/dose immediately as a single dose. Do not administer fluids containing calcium, e.g. Ringer-lactate, within 48 hours of administering ceftriaxone. Contra-indicated in neonatal jaundice.