The haemodynamics of human septic shock*

In the time it has taken medicine to develop the techniques to describe the circulatory changes of severe infections, both pattern and process have been profoundly influenced by the use of intravenous fluids, vasopressors, antibiotics, steroids, mechanical ventilation and haemoflltration. Constant features of severe sepsis include a reduction in peripheral vascular tone on both the arterial and venous sides of the circulation, a defect in oxygen utilisation resulting in lactic acidosis, and varying degrees of myocardial dysfunction. These events have a temporal progression, the precise pattern observed depending on the tempo of the infection, the influence of therapeutic manoeuvres, the age and comorbidities of the patient, and the time the observations are made in the course of events. Early sepsis is accompanied by a decrease in systemic vascular resistance and a metabolic acidosis. The clinical picture includes fever, tachycardia, tachypnoea, respiratory alkalosis and an increased cardiac output with warm, dry peripheries and a bounding pulse. Advanced sepsis involves varying degrees of venous and myocardial contractile failure, and is characterised by progressive acidaemia, respiratory failure and marked sympathetic adrenergic activation. In the absence of vigorous fluid resuscitation, the cardiac output is decreased and the patients are cold, clammy peripherally shut down, and frequently confused, obtunded or comatose. In infections with a silent primary focus (predominantly involving Gram-negative organisms), this stage is frequently the first to attract the attention of attending staff. Late sepsis is characterised by profound acidaemia, vascular hypo-responsiveness, multiple organ failure and death.