Shock is a medical emergency and it occurs when the body's tissues and organs are deprived of adequate oxygenated blood. Burn shock is a term used to describe certain signs such as: decreased cardiac output, increased vascular resistance, hypovolaemia and hypoperfusion that occur after severe burn injuries have been sustained. This incident leads to the release of inflammatory substances such as histamines and prostaglandins into the circulation resulting in large movements of fluid from the capillary space. Burn shock mostly occurs within the first 24hrs after sustaining burn injuries with its peak levels at 6 to 8 hours after the injury. It may extend up to 2 to 3 days and last longer in the elderly population.
Pathophysiology of Burn Shock
The interaction between hypovolaemia, direct tissue and anti-inflammatory substances in the body cause burn shock. Soon after burn injuries occur, Starling forces which determine the directionality of net water movement between different compartments begin to allow fluid to move from blood to both tissues that have and have not been damaged by burn injuries. The formation of oedema (increased interstitial fluid) that soon follows burn injuries is mainly due to the creation of a strong negative interstitial fluid pressure and increased capillary permeability (otherwise known as capillary leakage syndrome). Oedema reaches maximal levels in burn areas after 24hrs of burn occurence. Fluid loss from the blood is also accompanied by the extravasaton of proteins and electrolytes resulting in severe hypoproteinaemia and elctrolyte imbalance. A reduction in cardiac output which is a notable feature of burn shock occurs from an interaction between hypovolaemia, an increase in ventricular afterload and a decreased contractility of the myocardium
Clinical Features of Burn Shock
- Increased blood viscosity due to increased ratio of red blood cells to plasma
- Reduced cardiac output
- Increased heart rate
Management of Burn Shock
Burn shock is better prevented or minimized than treated. The administration of fluid resuscitation promptly, within the first 24hrs of the occurence of burn injuries is crucial, especially when burns are extensive and above 20% of the total burn surface area in both adults and children. Fluid resuscitation is primarily aimed at the maintenance of vital organ function while also avoiding the complications that may stem from over and under resuscitation. The Parkland formula is mostly used to determine the amount of fluid to infuse. It is given as:
Four mL lactated ringers solution × percentage total body surface area (%TBSA) burned × patient's weight in kilograms = total amount of fluid given in the first 24 hours.
It is advised that one-half of the quantity of the fluid obtained from the formula be administered over the first 8hrs post thermal injury while the second half should be given over the next 16hrs. The formula only serves to determine the initial fluid rate which is thereafter adjusted to achieve an hourly urine output between 30 and 50 mL in a 70-kg adult with urine output being an important factor that guides fluid management . It is important to achieve optimal fluid resuscitation as an under-resuscitation can lead to acute kidney injury, reduced perfusion and death, while an over-resuscitation may result in: massive oedema formation, compartment syndrome, acute respiratory distress syndrome and multiple organ dysfunction.
Contraindications to Fluid Resuscitation
Haemodynamically stable patients may not benefit from fluid resuscitation as this may lead to oedema.
Complications of Burn Shock
- Acute renal failure
- Decreased perfusion
- Pulmonary oedema
- Liver failure
- Cardiac failure
- Occlusion of arteries
- Permanent brain damage
Role of the Physiotherapist
Physiotherapists may not be directly involved in the management of burn shock but, it is pertinent to still have a knowledge about it since we will be involved in the rehabilitation of patients with burn injuries from their inception into the burn care unit.
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