Mechanical ventilation choosing amongst ventilator modes

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Syed Hassan A. Kazmi BSc, MD [2]

Overview[edit | edit source]

Choice of ventilator mode depends upon the clinical condition of the patient. Choice of ventilator mode can be tailored to achieve specific goals of management and set to achieve spontaneous breathing, volume-targeted ventilation, pressure-targeted ventilation, or some combination. In some conditions, for example in case of spontaneously breathing patient, the patient sets the respiratory rate and generates the desired flow rate. Different modes of ventilation include pressure support ventilation (PSV), continued mandatory ventilation (CMV) or assist control mode (AC), synchronous intermittent mandatory ventilation (SIMV), proportional assist ventilation (PAV), dual control mode, high frequency ventilation, pressure and volume targeted modes.

Choosing Amongst Ventilator Modes[edit | edit source]

Choice of ventilator mode depends upon the clinical condition of the patient. Choice of ventilator mode can be tailored to achieve specific goals of management and set to achieve spontaneous breathing, volume-targeted ventilation, pressure-targeted ventilation, or some combination. In some conditions, for example in case of spontaneously breathing patient, the patient sets the respiratory rate and generates the desired flow rate.^[1][2][3] The following are the various ventilator modes and their features:^{[4][5][6][7][8][9]}

Pressure support ventilation (PSV)[edit | edit source]

• This mode supports patient initiated breaths with a set inspiratory pressure and positive end expiratory pressure (PEEP)
• Mode of partial ventilatory support because there is no set rate
• The clinician sets the FiO2 and PEEP. The patient sets the respiratory rate and generates their desired flow rate. 
• After the optimal flow is achieved, the applied pressure can be turned off.
• The volume given depends upon the patient's effort and lung/chest wall compliance
• There is no minimal rate

Continued mandatory ventilation (CMV) or assist control (AC)[edit | edit source]

• Ventilator delivers a minimum number of supported breaths
• Mode of fully assisted ventilatory support
• Additional patient initiated breaths trigger fully assisted vent breaths. Therefore, vent-triggered breaths are identical to patient triggered breaths
• May be pressure targeted or volume targeted
• If patient develops tachypnea, may lead to respiratory alkalosis, breath stacking and auto PEEP

Synchronous intermittent mandatory ventilation (SIMV)[edit | edit source]

• Ventilator develops a minimum number of supported breaths
• Tidal volume of additional breaths is determined by the patients effort
• This strategy also supplies inspiratory pressure during spontaneous breaths (similar to pressure support ventilation)
• May be used to wean off patient after extubation (maybe combined with pressure support ventilation- PSV)

Proportional assist ventilation (PAV)[edit | edit source]

• Delivers variable pressure to achieve targeted percentage of work of breathing

Dual control modes[edit | edit source]

• Combination of volume and pressure targeted ventilation
• Use a closed loop ventilator logic
• Automatically alter control variables, either breath-to-breath or within a breath, to ensure a minimum tidal volume or minute-ventilation

High frequency ventilation[edit | edit source]

• Helps to achieve optimum gas exchange when using high respiratory rates (RR) with tidal volumes (Vt) lesser than the anatomical dead space
• Used in neonatal respiratory failure
• May be used in cases of acute lung injury (ALI) or acute respiratory distress syndrome (ARDS)

Volume targeted modes[edit | edit source]

• Both assist control (AC) and syncronous intermittent support ventilation (SIMV) can be volume controlled
• Ventilator delivers a set tidal volume (Vt)
• Pressures depend on lung compliance

Advantages

• Safe in cases of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS)
• Ideal initial ventilator setting
• Easy to measure mechanics (PIP, Pplat, airway resistance, compliance)

Pressure targeted modes[edit | edit source]

• Ventilator delivers a fixed inspiratory pressure regardless of Vt
• Vt depends on lung/chest wall compliance

Advantages

• May increase patient comfort (PSV) requiring less sedation

Proportional assist ventilation plus and proportional pressure support[edit | edit source]

References[edit | edit source]

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