Intermittent Mandatory Ventilation (IMV) refers to any mode of mechanical ventilation with preset tidal volume (VT) and inspiratory flow. Spontaneous breaths (i.e., inspiration is patient triggered and patient cycled) can exist between mandatory breaths. For intermittent mandatory ventilation utilizing pressure regulation, the term pressure controlled intermittent mandatory ventilation is used.
IMV — IMV is similar to AC in two ways: the minute ventilation is determined (by setting the respiratory rate and tidal volume); and the patient is able to increase the minute ventilation. However, IMV differs from AC in the way that the minute ventilation is increased. Specifically, patients increase the minute ventilation by spontaneous breathing, rather than patient-initiated ventilator breaths.
SIMV — SIMV is a variation of IMV, in which the ventilator breaths are synchronized with patient inspiratory effort.[1][2] SIMV with pressure support is the most efficient and effective mode of mechanical ventilation.[3]
MMV — Mandatory minute ventilation is a mode which requires the operator to determine what the appropriate minute ventilation for the patient should be, and the ventilator then monitors the patient's ability to generate this volume every 7.5 seconds. If the calculation suggests the volume target will not be met, SIMV breaths are delivered at the targeted volume to achieve the desired minute ventilation.[4] Allows spontaneous breathing with automatic adjustments of mandatory ventilation to the meet the patient’s preset minimum minute volume requirement. If the patient maintains the minute volume settings for VT x f, no mandatory breaths are delivered. If the patient's minute volume is insufficient, mandatory delivery of the preset tidal volume will occur until the minute volume is achieved. The method for monitoring whether or not the patient is meeting the required minute ventilation (VE) is different per ventilator brand and model, but generally there is a window of time being monitored and a smaller window being checked against that larger window (i.e., in the Dräger Evita® line of mechanical ventilators there is a moving 20-second window and every 7 seconds the current tidal volume and rate are measured against to make a decision for if a mechanical breath is needed to maintain the minute ventilation). MMV is the most optimal mode for weaning in neonatal and pediatric populations and has been shown to reduce long term complications related to mechanical ventilation.[5]
Pressure Controlled Intermittent Mandatory Ventilation (PC-IMV) is any mode of mechanical ventilation with preset inspiratory pressure (Pressure Control) and inspiratory time (Ti). Spontaneous breaths (i.e., inspiration is patient triggered and patient cycled) can exist between mandatory breaths (denoted by the term "intermittent"). In other words, PC-IMV means a mode of ventilation where the pressure is controlled and has an allowance for patient triggered breaths without providing an assisted breath as seen in pressure controlled continuous mandatory ventilation, but instead it allows the additional breaths to co-exist with ventilator breaths.
PRVC — Pressure regulated volume control is a pressure controlled mode (even though "volume control" is used in the name) with a VT set as a goal amount. Pressure varies with a peak pressure limit included to reduce lung trauma and use only the minimum pressure required to deliver the goal tidal volume (VT). Pressure regulated volume control is a mode of mechanical ventilation where the breaths are delivered mandatorily to assure preset volumes, with a constant inspiratory pressure continuously adapting to the patient's condition. The flow pattern is decelerating. This mode is a form of intermittent mandatory ventilation, the breaths can either be ventilator initiated or patient initiated. This mode combines the advantages of volume controlled and pressure controlled ventilation.
The first breath delivered to the patient is a volume controlled breath. The measured plateau pressure is used as the pressure level for the next breath. The pressure is constant during the set inspiratory time and the flow is decelerating. The set tidal volume is achieved by automatic, breath-by-breath pressure regulation. The ventilator will adjust the inspiratory pressure control level, according to the mechanical properties of the airways/lung/thorax, to the lowest possible level to guarantee the preset tidal volume. If the measured tidal volume increases above the preset, the pressure level decreases in steps of maximum 3 cmH2O (300 Pa) between consecutive breaths until the preset tidal volume is delivered. Maximum available pressure level is 5 cmH2O (500 Pa) below a preset upper pressure limit.
PAV — Proportional assist ventilation is a mode in which the ventilator guarantees the percentage of work regardless of changes in pulmonary compliance and resistance.[6] The ventilator varies the tidal volume and pressure based on the patients work of breathing, the amount it delivers is proportional to the percentage of assistance it is set to give.
Adaptive Support Ventilation (ASV) — ASV is a positive pressure mode of mechanical ventilation that is closed-loop controlled. In this mode, the frequency and tidal volume of breaths of a patient on the ventilator are automatically adjusted based on the patient’s requirements. The lung mechanics data are used to adjust the depth and rate of breaths to minimize the work rate of breathing. In the ASV mode, every breath is synchronized with patient effort if such an effort exists, and otherwise, full mechanical ventilation is provided to the patient.
ASV is a patented technology originally described as one of the embodiments of US Patent No. 4986268.[7] In this invention, the control algorithm computes the optimal rate of respiration to minimize the work rate of breathing. The rationale is to make the patient's breathing pattern comfortable and natural within safe limits, and thereby stimulate spontaneous breathing and reduce the weaning time.
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