Continuous mandatory ventilation — (CMV) is a mode of mechanical ventilation where breaths are delivered based on set variables. The patient may initate breaths by attempting to breathe. Once a breath is initated, either by the patient or by the ventilator the set tidal volume is delivered.
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VC-CMV — Most commonly referred to as assist control (AC) though not preferred is a mode of ventilation where breaths are delivered based on set variables. The patient may initate breaths by attempting to breathe. Once a breath is initated, either by the patient or by the ventilator the set tidal volume is delivered. Assist Control is also called Volume Control or Assist Control Volume Control (AC/VC).
This mode was created out of the need for patient-initiation in breaths. Fundamentally, AC is controlled mechanical ventilation (CMV) with a sensitivity for patient breathing. The use of CMV in the original version required the patient be completely unconscious, either pharmacokinetically or otherwise in a coma. With the addition of breath sensitivity, that requirement is relaxed but if the patient is actively breathing synchronization may be required in a mode such as pressure controlled intermittent mandatory ventilation or volume controlled intermittent mandatory ventilation.
The variables required in VC-CMV are: tidal volume (VT), respiratory rate (f), flow rate and trigger sensitivity (for sensing patient effort). Additional variables like peak-end expiratory pressure (PEEP) and pressure support (PS) may be added for additional support.
Assist Control is associated with profound diaphragm muscle dysfunction and atrophy.[1] AC is no longer the preferred mode of mechanical ventilation.[2]
Trigger — Breath initiation is based on time or patient initiation. Time is set by respiratory rate (Vf or RR) and patient initiation is sensed by a flow, volume or pressure trigger and a full ventilator breath (the set tidal volume) is given.
Limit — Limits in VC-CMV may be set and pressure based. The ventilator will attempt to deliver the set tidal volume utilizing whatever pressure is required to reach its setting. A pressure limit may be added to limit damage to the lungs (barotrauma).
Cycle — Expiration cycling can be set by time or the pressure limit. Once the Ti (inspiratory time) is reached, or a pressure limit is reached the ventilator will cycle into expiratory mode and allow passive exhalation until another breath is triggered.
PC-CMV — Pressure Control Ventilation (PCV) also Pressure Control (PC) is a controlled mode of ventilation. The ventilator delivers a flow to maintain the preset pressure at a preset respiratory rate over a preset inspiratory time.[3]
The pressure is constant during the inspiratory time and the flow is decelerating. If for any reason pressure decreases during isnpiration, the flow from the ventilator will immediately increase to maintain the set inspiratory pressure.[4]
Pressure Controlled Continuous Mandatory Ventilation is any mode of mechanical ventilation with preset inspiratory pressure and inspiratory time. Every breath is mandatory (ie, patient or machine trigged and machine cycled).
Many terms have been developed to describe the same modes of mechanical ventilation. Nomenclature of mechanical ventilation has become more standardized and these terms are no longer preferred but still may be seen in older research[5] there are many different names that historically were used to reference CMV but now reference Assist Control[5]. Names such as: volume control ventilation, and volume cycled ventilation in modern usage refer to the Assist Control mode.
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