Hypovolemic shock occurs when there is loss of blood or plasma, as in burns, hemorrhage and trauma. Septic shock occurs as a result of systemic microbial infection. Other types of shock have also been defined: distributive and obstructive (Schwarz, eMedicine). Distributive shock occurs when the normal peripheral vascular tone becomes inappropriately relaxed leading to relative hypovolemia. It is caused by anaphylaxis, neurologic injury, sepsis, and drug-related causes. Obstructive shock is seen in newborns with obstructive congenital heart disease like coarctation of aorta, interrupted aortic arch, and severe valvular stenosis (Schwarz, eMedicine). In older children and adults, rheumatic fever, subacute bacterial endocarditis, and hypertrophic cardiomyopathy can lead to direct obstruction of cardiac output (Schwarz, eMedicine).
1. Non-progressive stage: This is an initial stage where in the reflex mechanisms of the body are activated, thus maintaining normal perfusion of the vital organs. The various neuro-humoral mechanisms maintain the cardiac output and blood pressure. The hypothalamus situated in the brain secretes adrenocorticotrophic releasing hormone which in turn stimulates the adrenal or the suprarenal glands to secrete the catecholamines, aldosterone and the cortisol. Blood is diverted from the less vital to more vital organs like brain, heart and kidneys, heart rate increases to supply more blood quickly, blood pressure increases to supply blood efficiently, respiratory rate increases to get more oxygen from the atmosphere, glycogen stores in the liver and muscle are broken down to get more glucose (glycogenolysis) and beyond a certain level, glucose is formed from non-carbohydrate sources like fats and proteins (gluconeogenesis) (Ron de Kloet, p.187). In the heart, adrenaline causes increase in the heart rate and also the force of contraction leading to increased