Mechanical ventilation modes are combinations of operating functions that affect how ventilators are run. A ventilator is triggered and cycled into inspiration and exhalation, the two operating modes that allow it to work. During inspiration, some ventilators allow spontaneous breaths, while others operate on regulated breaths only. Mechanical ventilation modes affect these types of characteristics of the ventilators.
Most ventilators are either positive or negative pressure ventilators. Negative pressure ventilators reduce the atmospheric pressure around the chest, which results in expansion of the chest. This mimics spontaneous breathing, during which the diaphragm descends close to the abdomen. Positive pressure ventilators are more common, and they work by forcing air into the lungs.
Control mode is one of the mechanical ventilation modes where the ventilator delivers the breaths at a set rate to the patient on life support. It is typically only used when the patient is sedated and experiencing severe respiratory failure or paralysis. Control mode is not recommended if the patient is physically able to breathe on his or her own because it takes away all effort on the patient’s part. In assist mode, artificial respiration kicks in when the ventilator senses that the patient is trying to take a breath on his or her own. With assist mechanical ventilation modes, patients essentially control the amount of breathing assistance they receive from the ventilators.
Continuous mechanical ventilation modes are a combination of control modes and assist modes, and they involve setting the control rate to a minimum number of breaths per minute, which the ventilator will deliver. If the patient takes more on his or her own, the machine adjusts to coincide with the patient’s breathing pattern. Intermittent mandatory ventilation is a combination of control mechanical ventilation modes and spontaneous breathing. With intermittent modes, a set number of breaths is delivered, but the patient may breathe spontaneously between mechanical breaths as he or she wishes. Humidified oxygen will be available in this case for the patient to breathe.
In pressure support mode, the ventilator monitors both the mechanical breaths and the spontaneous breaths, and inspiratory flow rates are delivered to the breathing circuit to maintain the airway pressure. When the patient's inspiration stops, the ventilator cuts off the breathing flow to the circuit, and the patient can exhale. Pressure control ventilation holds the airway pressure constant while tidal volume varies, depending on the behavior of the lungs. The rate, inspiratory time and pressure limit are all regulated by the doctor with this type of mechanical ventilation mode.
