Mechanical Ventilators

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Mechanical ventilators provide controlled ventilation during general anaesthesia or in critical care settings. Classification: Pneumatic (gas-driven, no electricity required, simple), electronic (microprocessor-controlled, multiple modes), transport (portable, pneumatic or battery). Power source: Pneumatic (driving gas 400 kPa), electric (mains or battery backup), or combined. Control variables: Volume control (set tidal volume, variable pressure), pressure control (set inspiratory pressure, variable volume), dual control (switches between volume and pressure targets). Modes: Controlled Mandatory Ventilation (CMV), Assist-Control (A/C), Synchronized Intermittent Mandatory Ventilation (SIMV), Pressure Support Ventilation (PSV), Continuous Positive Airway Pressure (CPAP), Bilevel Positive Airway Pressure (BiPAP). Anaesthesia ventilator specifics: Time-cycled (inspiratory time determines breath), pressure-limited (safety), piston or bellows design, minute volume divider or fresh gas decoupled (modern machines). Lung protective ventilation: Tidal volume 6-8 mL/kg IBW, plateau pressure <30 cm H₂O, PEEP 5-10 cm H₂O, FiO₂ minimum to maintain SpO₂ >92%. Alarms: High/low pressure, high/low tidal volume, high/low respiratory rate, apnea, disconnect, power failure. Weaning criteria: Adequate oxygenation (PaO₂/FiO₂ >200), hemodynamic stability, adequate cough, minimal secretions, no respiratory acidosis. Complications: Barotrauma (pneumothorax from high pressures), volutrauma (alveolar overdistension), atelectrauma (repeated opening/closing), biotrauma (inflammatory mediators). Monitoring: Airway pressures (peak, plateau, PEEP), exhaled tidal volume, respiratory rate, compliance, resistance, capnography. Patient-ventilator asynchrony: Trigger asynchrony (sensitivity settings), flow asynchrony (inspiratory flow patterns), cycle asynchrony (inspiratory time), expiratory asynchrony (insufficient expiratory time). [1-10]