--- module: 010-01 language: en chapter: 10 title: "Shock, Perfusion Failure, Fluids, and Vasoactive Therapy" module_title: "Foundations" source_sha256: 8c4b6ae8ec2b79fdfddc7832f2f7746365085dba762d52a6a2968ddb720a6dbb --- # Shock, perfusion failure, fluids and vasoactive therapy ## What shock is ### Acute circulatory failure of tissue perfusion ### Pressure may be low, normal or maintained ### Self-reinforcing injury #### Inflammation and endothelial injury #### Coagulation and myocardial dysfunction #### Microvascular shunting and organ failure ## Oxygen delivery and extraction ### Delivery equals output times arterial content ### Output equals rate times stroke volume ### Normal saturation can hide poor delivery ### Consumption equals delivery times extraction ### Beyond a critical point, supply-dependent ### Lactate is a trend marker, not a meter #### Adrenergic drive, clearance, mitochondria, drugs ### Mean pressure is not effective perfusion ## Shock categories ### Hypovolaemic: reduced venous return ### Cardiogenic: pump failure, high filling pressures ### Distributive: vasodilation and maldistribution #### Sepsis: dilation, leak, depression, microvascular failure #### Anaphylaxis: leakage, bronchospasm, airway oedema #### Neurogenic: bradycardia with warm skin ### Obstructive: filling or outflow blocked #### Embolism, tamponade, tension pneumothorax, hyperinflation ### Mixed shock is expected ## Obstructed filling and tamponade ### Shared septum in one pericardial enclosure ### Filling one ventricle competes with the other ### Inspiratory septal shift cuts left filling ### Pulsus paradoxus follows the stroke-volume fall ### External restriction, not contractile failure ### Rate and compliance, not effusion volume ### Pulsus paradoxus also in airway obstruction ## Recognition and monitoring ### Mental state, mottled skin, delayed refill ### Rising lactate, acidosis, narrow pulse pressure ### Warm shock can have bounding pulses early ### One normal pressure excludes nothing ### Bedside ultrasound needs skill and context ### Repeated reassessment beats invasive numbers ## Fluids ### Fluid is a drug with a stop criterion ### A bolus tests stressed volume against output ### Crystalloid spreads through extracellular fluid ### Balanced solutions limit chloride load ### Albumin is selective, starches cause harm ### Excess fluid: oedema, congestion, delayed healing ### Dynamic tests over static filling pressure ### Haemorrhage needs blood and bleeding control ## Vasoactive and inotropic therapy ### Norepinephrine first in septic vasodilatory shock ### Vasopressin supplements catecholamines ### Epinephrine for anaphylaxis and cardiac arrest ### Excess vasoconstriction costs regional flow ### Inotropes when output stays low despite filling ### Dobutamine risks tachyarrhythmia and hypotension ### Choose from the haemodynamic problem ### Reliable access and extravasation surveillance ## Mechanism-specific treatment ### Sepsis: antimicrobials, cultures, source control ### Anaphylaxis: intramuscular epinephrine first ### Cardiogenic: revascularisation, rhythm, mechanical support ### Tamponade drained, pneumothorax decompressed ### Resuscitation is a repeating cycle ### Pressure without perfusion is incomplete success ### De-resuscitation once shock resolves ## Cellular and organ consequences ### Flow diverted from skin, gut and kidney ### Mucosal injury and acute kidney injury ### Endothelial activation and leukocyte adhesion ### Thrombosis and bleeding at the same time ### Permeability oedema and respiratory distress syndrome ### Myocardial depression from ischaemia and catecholamines ## Special contexts and safety traps ### Pregnancy hides haemorrhage before hypotension ### Supine caval compression, left lateral displacement ### Older adults: less tachycardia, less fluid tolerance ### Burn formulae are starting estimates only ### Adrenal insufficiency resists vasopressors ### Sedation and positive pressure cut venous return ### Imaging must not delay time-critical treatment