L12: shock and haemorrhage Flashcards
What is shock?
Shock = collapse and progressive failure of the cardiovascular system
- decreased effective circulating volume
- loss of volume or poor circulation
- inadequate perfusion of organs
- decreased or no urine production
4 types of shock
- hypovolaemic shock
- cardiogenic shock
- anaphylactic shock
- septic shock
Consequences of shock
- poor tissue perfusion - no O2 delivery, CO2 build up
- pale, cold, clammy, greyish/blue skin, thirst, dry mouth, low BP, dizziness, tachycardia, breathing, metabolic acidosis, altered mental state …
- hypoxia, mitochondrial dysfunction, widespread impairment of cellular metabolism
- organ failure
- death
Why do these symptoms arise? (Links to CVRS)
- E.g., haemorrhage will constrict vessels and keep heart and brain perfused, making you pale
- alerting sympathetic response, innervation to sweat glands will cause clamminess
- thirsty because less blood circulating and less plasma volume
- less saliva so dry mouth
- less oxygen to brain causes confusion
- oxygen deprivation to mitochondria cause dysfunction
What is hypovolemic shock?
Loss of fluid in the ECF compartment - hence inadequate volume (not poor circulation)
Examples causing hypovolemic shock?
- haemorrhage - blood loss
- burns - plasma loss
- diarrhoea/vomiting - fluid loss
- sweating/dehydration - fluid loss
- diabetes insipidus - fluid loss
Hypovolemic shock relation to cardiovascular system
Central venous pressure fall. Effective circulating volume and BP falls - so little volume that it cannot fill the circulatory system despite the vessels constricting.
Venous pressure decreases (CVP); so venous return to the heart also decreases; RVEDV decreases; right SV decreases so contractility decreases; decreases blood to the lungs; decreases blood to left ventricle; decreases LVEDV; decreases left stroke volume so decreases contractility; so decreased cardiac output.
Cardiogenic shock
- heart/‘pump’ failure such as during myocardial infarction - hence inadequate circulation not inadequate volume
- effective circulating volume and BP fall even though the volume of blood is not changed - this is because there is poor blood circulation around the body
Causes of cardiogenic shock
- systolic dysfunction
- diastolic dysfunction
- arrhythmias
- structural problems
Clinical symptoms of cardiogenic shock
Tachycardia, anxiety and delirium, increased preload, pulmonary congestion, decreased cardiac output, dusky skin colour, decreased BP, narrow pulse pressure, oliguria, dyspnea
Cardiovascular response to shock
- drop in ECV and BP is detected by baroreceptors in the carotid sinuses and aortic arch
- decreased baseline vagal tone, sympathetic stimulation and release of noradrenaline causes:
• widespread vasoconstriction - redistributes blood to the brain, heart and kidneys, away from skin, muscle and GI tract
• heart rate to increase - tachycardia
• heart contractility to increase - increases SV
Summary at 26:44
Renal response to shock
A drop in BP in response to shock will mean a fall in renal perfusion pressure, activating RAAS
Why is it important that glomerular filtration rate tightly regulated during shock and haemorrhage?
Sympathetic and hormonal mechanisms
Autoregulation myogenic control (renal blood flow lecture etc)
Anaphylactic shock and the dentist
Rapid allergic reaction following exposure to an:
- allergen - latex (nitrile gloves now used)
- drugs - penicillin, chlorhexidine (anti-bacterial mouthwash)
- local anaesthetic - lidocaine but very rare
What does anaphylactic shock cause?
Widespread vasodilation (heat, redness) to carry lots of inflammatory cells so WBCs can remove the reaction/bug; increased vessel permeability and subsequent oedema (massive swelling), to distribute the antibodies etc - loss of effective circulating volume and thus hypovolemia
