--- module: 062-01 language: en chapter: 62 title: "Critical Care Physiology, Oxygen Support, Ventilation, and Organ Support" module_title: "Foundations" source_sha256: 640f9dc1ffe459cb3974f4e1eaf8a331c329d6b79869d5f09ab3437a0379b28f --- # Critical care foundations ## Orientation and recognition ### Support failing physiology, treat cause, prevent harm ### Organ failures interact #### Ventilation alters circulation #### Shock injures kidney and brain #### Immobility weakens respiratory muscles ### Targets, reassessment, minimal invasiveness, team ### Trends and concern outweigh a single score ### Airway-to-exposure assessment while calling help ### Monitoring should answer a question #### Lines and blood draws cause infection and anaemia ## Oxygen physiology and delivery ### Delivery is cardiac output times oxygen content #### Haemoglobin-bound oxygen dominates content #### Normal saturation cannot offset anaemia or low flow ### Falling delivery raises extraction #### Sustained imbalance: lactate, organ failure, cell death ### Lactate is not a direct oxygen meter ### Excess oxygen causes atelectasis and oxidative injury ### Cannulae low flow, Venturi controlled concentration ### High-flow oxygen reduces dead space and work ### Oximetry limits: perfusion, pigment, dyshaemoglobins ## Non-invasive respiratory support ### Continuous pressure recruits alveoli, lowers afterload ### Bilevel adds inspiratory assistance ### Best in cardiogenic oedema, hypercapnic obstruction ### Unsafe without airway protection or with vomiting ### Reassess within minutes to hours #### Worsening acidosis, rate, consciousness mean failure #### Prolonged failed trials delay definitive airway ## Intubation and ventilation ### Intubation is a physiological procedure #### Correct hypotension before positive pressure #### Positive pressure reduces venous return ### Rapid-sequence induction limits aspiration time ### Confirm with sustained exhaled carbon dioxide ### Tidal volume and rate remove carbon dioxide ### Inspired oxygen and end-expiratory pressure oxygenate ### Targets and synchrony matter more than mode ## Lung protection and distress syndrome ### Injury from stretch, pressure, cyclic opening ### Tidal volume from predicted body weight #### Lung size follows height and sex ### Limit plateau and driving pressures ### End-expiratory pressure prevents collapse ### Distress syndrome: bilateral opacities, not cardiac #### Low tidal volume, conservative fluid after shock #### Prone positioning for severe disease ### Permissive hypercapnia not for raised intracranial pressure ## Synchrony and liberation ### Agitation may reflect pain, delirium, secretions ### Treat cause before escalating sedation ### Analgesia-first light sedation ### Liberation needs improving cause and airway protection ### Breathing trial tests integrated reserve #### Upper-airway obstruction can still defeat extubation ### High-flow or non-invasive support if high risk ## Shock and circulation ### Low volume, pump failure, vasodilation, obstruction ### Central venous pressure predicts response poorly ### Fluid challenge has dose, response, stopping rule #### Excess fluid impairs gas exchange and recovery ### Norepinephrine first line for distributive shock ### Inotropes for persistent low output #### Arrhythmia and oxygen demand cost ### Source control treats the mechanism ## Kidney and metabolic support ### Diuretics do not restore injured nephrons ### Replacement therapy for complications, not creatinine ### Intermittent haemodialysis rapid, continuous if unstable ### Avoid hypoglycaemia; tight control harmful ### Early enteral feeding when gut works ### Steroids for adrenal insufficiency, refractory sepsis ## Neurological critical care ### Serial pupils, motor responses, sedation breaks ### Intracranial pressure worsened by hypoxia, hypotension ### Brief hyperventilation only bridges herniation ### Status epilepticus: benzodiazepine then longer agent ### Electroencephalography for non-convulsive seizure ### Brain death is a formal legal process ## Infection, delirium, and outcomes ### Cultures must not delay antibiotics ### Fever also from drugs, thrombosis, transfusion ### Daily device removal review ### Delirium: fluctuating inattention and cognition #### Minimise benzodiazepines and anticholinergics ### Time-limited trials with a review point ### Survivors: weakness, cognitive impairment, distress