medical electronics III

Medical ventilator

In medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing when patients cannot do so on their own, and must be done so after invasive intubation with an endotracheal or tracheostomy tube through which air is directly delivered (in contrast to noninvasive ventilation).

In its simplest form, a ventilator consists of a compressible air reservoir, air and oxygen supplies, a set of valves and tubes, and a disposable or reusable "patient circuit". The air reservoir is pneumatically compressed several times a minute to deliver room-air, or in most cases, an air/oxygen mixture to the patient. When overpressure is released, the patient will exhale passively due to the lungs' elasticity, the exhaled air being released usually through a one-way valve within the patient circuit. The oxygen content of the inspired gas can be set from 21 percent (ambient air) to 100 percent (pure oxygen). Pressure and flow characteristics can be set mechanically or electronically.

Ventilators may also be equipped with monitoring and alarm systems for patient-related parameters (e.g. pressure, volume, and flow) and ventilator function (e.g. air leakage, power failure, mechanical failure), backup batteries, oxygen tanks, and remote control. The pneumatic system is nowadays often replaced by a computer-controlled turbopump.

Modern ventilators are electronically controlled by a small embedded system to allow exact adaptation of pressure and flow characteristics to an individual patient's needs. Fine-tuned ventilator settings also serve to make ventilation more tolerable, and comfortable for the patient. In Germany, Canada, and the United States, respiratory therapists are responsible for tuning these settings.

The patient circuit usually consists of a set of three durable, yet lightweight plastic tubes, separated by function (e.g. inhaled air, patient pressure, exhaled air). In cases where long-term ventilator dependence may be required, the patient-end of the circuit will normally be connected to a tracheotomy canula, which is much more comfortable and practical for long-term care than is larynx or nasal intubation.