Volume controlled continuous mandatory ventilation

Volume controlled continuous mandatory ventilation — (VC-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.

Volume controlled continuous mandatory ventilation

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 (V_T), respiratory rate (f), flow rate and trigger sensitivity (for sensing patient effort). Additional variables like peak-end expiratory pressure (P_EEP) and pressure support (P_S) may be added for additional support.

Expected outcomes and considerations

Assist Control is associated with profound diaphragm muscle dysfunction and atrophy.^[1] AC is no longer the preferred mode of mechanical ventilation.^[2]

Trigger, limit, cycle

Trigger — Breath initiation is based on time or patient initiation. Time is set by respiratory rate (V_f 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 T_i (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.

Terms no longer accepted

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^[3] there are many different names that historically were used to reference CMV but now reference Assist Control^[3]. Names such as: volume control ventilation, and volume cycled ventilation in modern usage refer to the Assist Control mode.

• Assist/control
• A/C
• CMV
• Volume assist/control
• Volume control
• Volume limited ventilation
• Volume controlled ventilation
• Controlled ventilation
• Volume targeted ventilation

See also

• Modes of mechanical ventilation
• Volume controlled intermittent mandatory ventilation
• Pressure controlled continuous mandatory ventilation
• Pressure controlled intermittent mandatory ventilation
• Continuous spontaneous ventilation

Reference

1. ^ Sassoon CS, Zhu E, Caiozzo VJ (2004). "Assist-control mechanical ventilation attenuates ventilator-induced diaphragmatic dysfunction.". Am J Respir Crit Care Med 170 (6): 626–32. doi:10.1164/rccm.200401-042OC. PMID 15201132. http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15201132. 
2. ^ Macintyre N (2011). "Counterpoint: Is Pressure Assist-Control Preferred Over Volume Assist-Control Mode for Lung Protective Ventilation in Patients With ARDS? No.". Chest 140 (2): 290–2. doi:10.1378/chest.11-1052. PMID 21813526. http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21813526. 
3. ^ ^{a b} Chatburn RL. Classification of ventilator modes: update and proposal for implementation. Respir Care 2007; 52:301–323.