Cardiovascular System
Usually two distinct phases, though the first is not seen in all patients
- Hyperdynamic phase (sympathetic overactivity)
- Transient catecholamine 'storm' (particularly adrenaline and noradrenaline) leads to:
- Intense arterial constriction and hypertension with tachycardia and increase in cardiac output
- Cushing's reflex due to massive increase in afterload with secondary baroreceptor activity causing bradycardia (occurs in about one-third of patients
- Imbalance between myocardial oxygen supply and demand, manifesting as:
- Acute myocardial injury and ST segment change
- Arrhythmias and heart blocks
- Apical ballooning and generalised LV dysfunction
- Transient catecholamine 'storm' (particularly adrenaline and noradrenaline) leads to:
- Cardiovascular collapse phase (sympathetic underactivity)
- Hypotension results from:
- Loss of sympathetic tone and profound vasodilatation
- Myocardial depression and arrhythmias:
- Depletion of high energy phosphate
- Mitochondrial inhibition
- Reduction in T3 production
- Electrolyte disturbance
- Hypovolaemia:
- Diabetes insipidus
- Osmotic diuresis (mannitol, hyperglycaemia)
- Therapeutic fluid restriction
- Asystolic cardiac arrest generally occurring within 72 hours
- Hypotension results from:
Respiratory System
- Neurogenic pulmonary oedema common due to catecholamine surge:
- Elevated pulmonary capillary hydrostatic pressure caused by acute LV dysfunction
- Capillary endothelial damage and increased permeability triggered by endogenous noradrenaline
- Pneumonia, aspiration of gastric contents, atelectasis can exacerbate respiratory failure
Endocrine & Metabolic System
- Failure of hypothalamic-pituitary axis due to ischaemia with:
- Impairment of temperature regulation
- ADH depletion:
- Diabetes insipidus (DI) which occurs in up to 65% of organ donors
- Characterised by diuresis, hypovolaemia, plasma hyperosmolality and hypernatremia
- ACTH depletion:
- Reductions in cortisol production are unrelated to the degree of hypotension but may impair the stress response
- TSH depletion:
- Reductions in the circulating levels of tri-iodothyronine (T3) and thyroxine (T4)
- Insulin depletion:
- Contributes to the development of hyperglycemia
- Aggravated by
- Administration of large volumes of glucose containing fluids, if used to treat hypernatremia
- Increased levels of catecholamines
- Inflammatory mediators released from damaged brain
- Generalized ischaemia– reperfusion (IR) injury
- Metabolic changes at the time of the catecholamine storm
Coagulation
- Hemostatic disorders due to:
- Release of tissue thromboplastin by ischaemic or necrotic brain
- Catecholamine induced platelet dysfunction can occur
- Disseminated intravascular coagulation (common)