Mechanical Ventilator - Complete Detailed Notes
Introduction & Physiology
Mechanical ventilation is the use of a machine (ventilator) to assist or replace spontaneous
breathing when the patient is unable to maintain adequate ventilation or oxygenation on their own.
Goals of mechanical ventilation: - Maintain adequate gas exchange (oxygenation and CO■
removal) - Reduce the work of breathing - Provide lung protection (avoid ventilator-induced lung
injury) - Allow time for the underlying disease to resolve Basic principles: The ventilator delivers a
flow of gas into the pulmonary system, generating a pressure gradient that overcomes the elastic
and resistive loads of the respiratory system and inflates the alveoli. Terms & variables: - Tidal
Volume (VT): Volume of gas delivered in one breath - Respiratory Rate (RR): Number of breaths
per minute - Inspiratory:Expiratory Ratio (I:E ratio) - Positive End-Expiratory Pressure (PEEP):
Pressure maintained at end of expiration to prevent alveolar collapse - Fraction of Inspired Oxygen
(FiO■) - Peak Inspiratory Pressure (PIP) / Plateau Pressure - Compliance (C = ∆V / ∆P) -
Resistance (R = ∆P / flow) The ventilator parameters are adjusted in response to the patient’s
airway pressures, gas exchange (ABGs), ventilator waveforms, and clinical status.
Indications for Mechanical Ventilation
Mechanical ventilation is indicated when the patient’s spontaneous breathing is insufficient or when
support is needed to maintain oxygenation or ventilation. Key indications include: - Acute
respiratory failure, e.g.: - Type I (hypoxemic) respiratory failure: PaO■ low even with supplemental
oxygen - Type II (hypercapnic) respiratory failure: elevated PaCO■ with respiratory acidosis -
Severe hypoxemia / ARDS - Respiratory muscle fatigue / impending respiratory arrest - Inadequate
ventilation in neuromuscular disease or spinal cord injury - Airway protection / sedation (e.g. in
coma or severe head injury) - During anesthesia / surgery - To reduce the work of breathing in
severe cardiopulmonary disease Brunner & Suddarth discuss ventilatory support modalities under
the respiratory care / oxygenation chapters (e.g. “Respiratory Care Modalities”).
Types & Classifications of Ventilators
Ventilators can be classified by many criteria: **Invasive vs Noninvasive Ventilation** - Invasive:
using an endotracheal tube or tracheostomy (mechanical ventilator directly connected to airway) -
Noninvasive: via masks (e.g. CPAP, BiPAP) without intubation **Cycle / Trigger / Limit Variables** -
Volume-cycled ventilators: deliver a preset tidal volume; pressure is variable - Pressure-cycled
ventilators: deliver until a set pressure is reached - Time-cycled ventilators - Triggering:
patient-triggered vs ventilator-triggered breaths **Modes of Ventilation (combinations of support
and control)** Some common modes: - Control / Assist-Control (AC) Mode: Each breath delivers a
set VT. - Synchronized Intermittent Mandatory Ventilation (SIMV): Allows spontaneous breaths
between mandatory ones. - Pressure Support Ventilation (PSV): Patient initiates breath and is
given pressure boost. - Pressure-Control Ventilation (PCV): Preset pressure is delivered; volume
Introduction & Physiology
Mechanical ventilation is the use of a machine (ventilator) to assist or replace spontaneous
breathing when the patient is unable to maintain adequate ventilation or oxygenation on their own.
Goals of mechanical ventilation: - Maintain adequate gas exchange (oxygenation and CO■
removal) - Reduce the work of breathing - Provide lung protection (avoid ventilator-induced lung
injury) - Allow time for the underlying disease to resolve Basic principles: The ventilator delivers a
flow of gas into the pulmonary system, generating a pressure gradient that overcomes the elastic
and resistive loads of the respiratory system and inflates the alveoli. Terms & variables: - Tidal
Volume (VT): Volume of gas delivered in one breath - Respiratory Rate (RR): Number of breaths
per minute - Inspiratory:Expiratory Ratio (I:E ratio) - Positive End-Expiratory Pressure (PEEP):
Pressure maintained at end of expiration to prevent alveolar collapse - Fraction of Inspired Oxygen
(FiO■) - Peak Inspiratory Pressure (PIP) / Plateau Pressure - Compliance (C = ∆V / ∆P) -
Resistance (R = ∆P / flow) The ventilator parameters are adjusted in response to the patient’s
airway pressures, gas exchange (ABGs), ventilator waveforms, and clinical status.
Indications for Mechanical Ventilation
Mechanical ventilation is indicated when the patient’s spontaneous breathing is insufficient or when
support is needed to maintain oxygenation or ventilation. Key indications include: - Acute
respiratory failure, e.g.: - Type I (hypoxemic) respiratory failure: PaO■ low even with supplemental
oxygen - Type II (hypercapnic) respiratory failure: elevated PaCO■ with respiratory acidosis -
Severe hypoxemia / ARDS - Respiratory muscle fatigue / impending respiratory arrest - Inadequate
ventilation in neuromuscular disease or spinal cord injury - Airway protection / sedation (e.g. in
coma or severe head injury) - During anesthesia / surgery - To reduce the work of breathing in
severe cardiopulmonary disease Brunner & Suddarth discuss ventilatory support modalities under
the respiratory care / oxygenation chapters (e.g. “Respiratory Care Modalities”).
Types & Classifications of Ventilators
Ventilators can be classified by many criteria: **Invasive vs Noninvasive Ventilation** - Invasive:
using an endotracheal tube or tracheostomy (mechanical ventilator directly connected to airway) -
Noninvasive: via masks (e.g. CPAP, BiPAP) without intubation **Cycle / Trigger / Limit Variables** -
Volume-cycled ventilators: deliver a preset tidal volume; pressure is variable - Pressure-cycled
ventilators: deliver until a set pressure is reached - Time-cycled ventilators - Triggering:
patient-triggered vs ventilator-triggered breaths **Modes of Ventilation (combinations of support
and control)** Some common modes: - Control / Assist-Control (AC) Mode: Each breath delivers a
set VT. - Synchronized Intermittent Mandatory Ventilation (SIMV): Allows spontaneous breaths
between mandatory ones. - Pressure Support Ventilation (PSV): Patient initiates breath and is
given pressure boost. - Pressure-Control Ventilation (PCV): Preset pressure is delivered; volume
