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Intermittent Manditory Ventilation

- Discussion: 
- Delivers a preset tidal volume at preset rate 
- Remainder of patient's minute ventilation is self generated and is independent of the ventilator;
- IMV rate is initally set at the same respiratory rate as the assist control mode and is slowly reduced if the arterial blood gas levels (particularly the PaCO2 and pH) remain satisfactory until it is minimal (2 per minute); 
- when the IMV rate is minimal, the spontaneous respiratory rate is not markedly elevated, and the arterial blood gases are satisfactory discontinuation of the mechanical ventilation may be considered); 
- if PaO2 & pH are within normal limits and PaO2 is about 100 mm but only w/ high FiO2 or on therapeutic levels of PEEP, the patient should be left to breath spontaneously with therapeutic PEEP
- this is termed CPAP: continuous positive airway pressure; 
- as arterial oxygenation improves, PEEP can be reduced in small steps, sequentially following the arterial oxygenation tension; 
- when the PEEP level reaches 5 cm H2O, the possibility of extubation may be entertained; 
- theoretical problem: mechanical volume delivered at the peak of spontaneous inhalation or exhalation; 
- IMV is preferred to ACMV because it allows a longer mean intra-thoracic pressure and the patient is allowed to breath spontaneously, thus preventing dissuse and fascilitating weaning