essay 23 - acute circulatory insufficiency - syncope, shock - definition, types, etiology, pathogenesis

what is acute circulatory insufficiency

• a sudden failure of a circulatory system to maintain adequate perfusion of tissues and organs. It manifests as syncope or shock

decsribe syncope

• syncope is brief, transient loss of consciousness due to decreased cerebral blood

• etiology:
  - vasovagal = excessive vagal stimulation (emotional stress) leading to bradycardia and vasodilation
  - orthostatic hypotension = failure of compensatory vasoconstriction when standing; pooling of blood in legs
  - situational= rapid evacuation of ascites fluid, prolonged cough attack

• Pathogenesis:

1. temporary reduction in cerebral blood flow

2. transient cerebral hypoxia

3. syncope

describe shock

• syndrome of circulatory failure leading to inadequate tissue perfusion, cellular hypoxia, metabolic acidosis and possible organ failure

• the types of shock are hypovolemic, extracardia obstructive, cardiogenic, distributive shock HECD

describe hypovolemic shock

• due to loss of intravascular fluid volume. most common form. used as a standard to compare other forms of shock in differential diagnosis

• haemorrhagic = blood loss e.g internal/external haemorrhage, traumatic haemorrhage

• dehydration = fluid loss e.g burns, diabetic ketoacidosis, excessive sweating

• third space loss = bowel obstruction, peritonitis, pancreatitis, ascites

describe extracardiac obstructive shock

• blood flow is physically blocked, leading to reduced cardiac output, despite a normal heart function. the obstruction is outside the heart (extracardiac) and prevents adequate filling or ejection of blood

• pulmonary embolism = blocked pulmonary circulation

• tension pneumothorax = increased intrathoracic pressure

• cardiac tamponade = pressure on myocardium → decreased preload

describe cardiogenic shock

• caused by the heart's inability to pump enough blood to meet the body's demands. When around 40% of the Myocardium is damaged due to acute myocardial infarction

• severe left ventricular failure

• chronic progressive heart disease

• rupture of papillary heart muscles or intraventricular septum

describe distributive shock

• characterised by widespread vasodilation and abnormal distribution of blood flow, leading to inadequate tissue perfusion, despite normal or increased cardiac output

• neurogenic = spinal cord injury, or drug overdose affects nervous systems ability to maintain vascular tone, leading to vasodilation

• anaphylactic = due to severe allergic reaction. vasodilation and fluid shifting from capillary to cell. leads to micro clotting and smooth muscle contraction

• septic = vasodilation and fluid shifting due to overwhelming infection

stages of shock

1. initial stage

• decreased circulating blood volume and/or decreased cardio output

• decreased tissue perfusion → decreased oxygen delivery

2. compensatory stage

• baroreceptors activate SNS → tachycardia, vasoconstriction

• RAAS and ADH activated → fluid retention to maintain BP

• blood is shunted to vital organs (heart, brain)

3. progressive stage

• prolonged hypoperfusion → anaerobic metabolism → lactic acidosis

• capillary permeability increases → fluid shift into interstitium → worsening hypovolemia

4. irreversible stage

• severe cellular injury (ATP depletion, lysosomal enzyme release)

• multi-organ failure (kidneys, liver, lungs, heart)

• death without intervention