--- module: 010-02 language: en chapter: 10 title: "Shock, Perfusion Failure, Fluids, and Vasoactive Therapy" module_title: "Haemodynamic phenotyping, oxygen debt, and staged resuscitation" source_sha256: 6cda2c6cc7dce26be5510625183e16ae16f44dd65378b2caec908f04371fc714 --- # Haemodynamic phenotyping and staged resuscitation ## Shock is a mismatch, not a pressure ### Hypotension neither necessary nor sufficient ### A young patient holds pressure while bleeding ### Chronic low pressure can be tolerated ### Dominant phenotype #### Preload failure reduces venous return #### Pump failure despite adequate filling #### Vasoplegia reduces tone and stressed volume #### Obstruction creates a mechanical barrier #### Microcirculatory failure wastes delivered blood ### Compensation hides severity ### Extraction reserve is finite ## Oxygen content and extraction ### Haemoglobin-bound oxygen dominates content ### Saturation useless without haemoglobin and flow ### Carbon monoxide misleads pulse oximetry ### Low venous saturation: flow, anaemia, hypoxaemia, demand ### High venous saturation does not prove perfusion #### Shunting, impaired extraction, mitochondrial failure ### Oxygen debt accumulates when supply lags demand ### Reperfusion washes metabolites into the circulation ### Temperature, glucose, calcium, acidity, coagulation ### One restored number is not recovery ## Lactate and acid-base context ### Rises when production exceeds clearance ### Catecholamine glycolysis raises it despite oxygen ### Liver failure, seizure, muscle, drugs, regional ischaemia ### Mechanism guides treatment, not the number alone ### Blind fluid loading can be the wrong answer ### Acidosis impairs contractility and vascular response ### Anion gap depends on albumin and method ### Hyperchloraemic acidosis from chloride-rich fluid ## Fluid responsiveness is not fluid need ### Stroke volume likely to rise after preload ### Responsive but already oedematous ### Non-responsive but still bleeding ### Static filling pressures predict poorly ### Passive leg raising is a reversible preload change ### Respiratory variation fails in common conditions ### Specify type, amount, rate, target, stop condition ### Convincing: stroke volume or perfusion improves ### Against repeating: crackles, hypoxaemia, venous pressure ### Composition follows the deficit being treated ## Vascular tone and vasoactive selection ### Pressure approximates output times resistance ### More resistance can mean less flow ### Vasopressor aids coronary flow but adds work ### Titrate to organ perfusion, not a universal target ### Norepinephrine raises arterial and venous tone ### Venoconstriction recruits unstressed volume ### Vasopressin acts outside the catecholamine pathway ### Epinephrine raises lactate and provokes arrhythmia ### Inotrope after filling and pressure are addressed ### Inodilators can deepen hypotension and persist ### Escalating dose means search for the cause ## Congestion and the right ventricle ### Sensitive to acute afterload rise ### Embolism, hypoxia, ventilatory pressure, lung disease ### Dilation raises wall stress and oxygen demand ### Tricuspid regurgitation and leftward septal shift ### Large boluses worsen the cycle ### Cautious preload, correct hypoxia and acidosis ### Systemic pressure for right-coronary perfusion ### Venous congestion injures organs #### Renal venous pressure narrows the gradient #### Hepatic and gut congestion impair drug handling ## Phases of resuscitation ### Rescue: mechanism-directed action on threats ### Optimisation: preload, pressure, output, carriage ### Stabilisation: prevent recurrence, reduce support ### De-resuscitation removes accumulated fluid ### Phases overlap and patients regress ### Capillary leak can make removal premature ### Balance, weight, ultrasound, kidney function ## Mechanical support and causal testing ### Devices differ in preload, afterload and flow ### Selection by cause, reversibility, ventricle, timing ### Support needs recovery, bridge or destination ### State the mechanism, choose a measurable test ### Revise when the response contradicts the model ### Pressure, flow, congestion, extraction improve together ### Endpoint is durable organ recovery with least harm