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Ventilation How to Initiate Mechanical Ventilation
The ventilation strategy is determined by whether the patient has failure to ventilate or failure to oxygenate. The first problem is managed by increasing the patients minute ventilation, the second by recruiting collapsed lung units and controlling mean airway pressure. I do not know of two doctors who agree on an initial ventilatory strategy. Every patient who is intubated is in need of a rest, and I always start my patients on controlled modes. If failure to ventilate or protect the airway was the problem, I use volume ventilation, to correct the respiratory acidosis, being careful not to damage the lung. If failure to oxygenate is the problem, I use pressure modes of ventilation, and carefully titrate the CPAP and the pressure control levels to set targets. While the choice of control mode is probably irrelevant (assist control (AC) or intermittent mandatory ventilation (IMV)), it is important that the patient’s spontaneous breaths are supported, which means adding pressure support to (S)IMV. It is important to be aware that patients often wake up from the short neuromuscular blockers/hypnotic agents and start thrashing around and bucking the ventilator. You must sedate your patient until (at least) you are in full control of the cardiorespiratory situation. A bolus of fentanyl or morphine along with lorazepam, midazolam or propofol is usually required. For profoundly hypoxemic patients, the addition of a neuromuscular blocking agent (ensuring that the patient is deeply sedated) is often required. The figure above describes an initial ventilatory strategy, designed around the cause of respiratory failure. Every intensivist must develop their own ideas about ventilation strategy, and this is one such. For patients with ventilatory failure, controlled minute ventilation is required, with reversal of the precipitating cause and rapid weaning to extubation. For hypoxemic respiratory failure, a more malignant course is to be expected, and I would advocate a pressure controlled strategy. Pressure controlled ventilation has several advantages over volume control, principally unlimited flow in assisted breaths, better distribution of gas, avoidance of overdistension of more compliant lung units, and the ability to tightly control mean airway pressure (by varying the inspiratory time). How do I set PEEP for my patient?
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