Version May 2024
| Broad categories of MV | |
| Conventional mechanical ventilation (CMV) | CMV generally refers to MV that provides breaths with Tvs and frequencies that approximate physiologic breathing. CMV is a broad category comprised of many different modes, with different types of breath triggering (eg, ACV, SIMV, PSV), and different types of breath limitation (eg, VTV and PLV). |
| High-frequency ventilation (HFV) | HFV refers to ventilation that delivers very small Tvs at very high frequencies on a sustained MAP. There are two types of HFV commonly used in neonates:
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| Types of breath triggering in CMV | |
| Assist-control ventilation (ACV) | ACV provides mandatory breaths at a set rate (control breaths) and also supports spontaneous breaths above the set rate (assist breaths). The support is the same regardless of whether it is an assist or control breath. ACV can be used to deliver volume-targeted or pressure-limited breaths. |
| Pressure-support ventilation (PSV) | In PSV, all breaths are triggered by the patient's spontaneous effort (ie, there is no set rate). All breaths are pressure-limited. |
| Synchronized intermittent mandatory ventilation (SIMV) | In SIMV, all breaths are "mandatory" (ie, determined by a set rate), but the ventilator attempts to synchronize each breath with the patient's spontaneous effort, if present. SIMV can be used with either volume-targeted or pressure-limited breaths. |
| Synchronized intermittent mandatory ventilation + pressure support (SIMV + PS) | SIMV + PS is a combination of SIMV and PSV. Like ACV, it provides both mandatory and spontaneous breaths. Unlike ACV, the mandatory and spontaneous breaths are not the same. For example, if the SIMV component uses VTV, the mandatory breaths will be volume-targeted, while the spontaneous (PS) breaths will be pressure-limited. |
| Types of breath control or limitation in CMV | |
| Volume-targeted ventilation (VTV) | In VTV, the desired Tv is set, and the inspiratory pressure delivered to achieve it varies. There are different subtypes and terms for VTV, including VC, VG, and PRVC. The specific properties of each may differ among ventilator manufacturers. |
| Pressure-limited ventilation (PLV) | In PLV, the inspiratory pressure is set, and the size of the Tv depends on the compliance of the lungs and respiratory circuit. PC is the main mode in this category. In PC, the ventilator controls both the PIP and the Ti. PSV is another pressure-limited mode in which the ventilator controls the inspiratory pressure, but there is no Ti setting and breaths terminate based on declining flow. |
| Ventilator settings | |
| Inspiratory time (Ti) | Ti is the duration of the inspiratory phase for each breath. The Ti and the respiratory rate together determine the inspiratory to expiratory (i:e) ratio. |
| Mean airway pressure (MAP) | MAP is the average pressure applied over the entire respiratory cycle (including inspiration and expiration). In CMV, MAP is measured by the ventilator and is largely determined by the PEEP setting. In HFOV, MAP is a ventilator setting. |
| Minute ventilation (Ve) | The volume of gas exchanged per minute. It is determined by Tv and RR. |
| Peak inspiratory pressure (PIP) | PIP is the peak pressure during inspiration. In PLV, PIP is controlled by the ventilator (ie, it is a setting). In VTV, PIP will vary depending on the patient's lung compliance. However, some ventilators allow the clinician to set upper and lower PIP limits in VTV modes to provide some control over PIP. |
| Positive end-expiratory pressure (PEEP) | PEEP is the amount of pressure applied during expiration. PEEP acts to prevent atelectasis (derecruitment) and is a key setting for ensuring adequate oxygenation. |
| Respiratory rate (RR) | As a ventilator setting, RR refers to the number of mandatory breaths per minute. |
| Tidal volume (Tv) | Tv is the volume of each breath in mL. In VTV, Tv is controlled by the ventilator (ie, it is a setting). In PLV, Tv is not controlled by the ventilator and will vary depending on other settings (ie, inspiratory pressure and Ti) and the patient's lung compliance. |
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