Medical Ventilators Information
Medical ventilators are mechanical apparatuses that forcibly respire a patient whose lung function is compromised. These machines are considered a "life-critical system" since patients rely on the device to complete the biological exchange of oxygen and carbon dioxide, which would otherwise result in organ tissue damage and death. Several fail-safes are built into medical ventilators so power or suspension outages do not affect ventilator performance.
Medical ventilators respire a patient's lungs via a breathing tube. This tube is supplied with ambient air or an air/oxygen mixture through a compressor or turbine. When the lungs reach capacity, the natural elasticity of the tissue forces the air out through an exhaust known as a patient manifold. A series of interfaces and displays allow parameters such as pressure, volume, flow, air leakage, operating efficiency, backup systems, and gas supply to be measured by healthcare professionals, such as respiratory therapists.
Ventilator types are broken up into two categories: noninvasive ventilators and invasive ventilators.
Noninvasive ventilators provide breathing support through an external interface, such as a mask or nasal prongs. These are positive airway pressure ventilators that use positive pressure to force gas or air into a patient’s lungs. Breathing can be triggered by either the patient or the machine. There are six types of positive pressure ventilators.
- Volume-cycled ventilators—deliver a preset volume of gas/air or a “tidal” volume and allow passive exhalation. This is ideal for patients with acute respiratory distress syndrome or bronchospasm.
- Pressure-cycled ventilators—deliver gases at a preset pressure and allow passive exhalation. They decrease the risk of lung damage from high inspiratory pressures. A disadvantage is that the tidal volume delivered can vary with changes in lung resistance and compliance if the patient has poor lung compliance and increased airway resistance. It is often used in short-term therapy.
- Flow-cycled ventilators—deliver oxygenation until a preset flow rate is achieved during inhalation.
- Time-cycled ventilators—deliver oxygenation over a preset time period. These are not used as frequently as the volume-cycled and pressure-cycled ventilators.
- Continuous positive airway pressure ventilators—increase the work of breathing by forcing the user to exhale against resistance. Because this ventilator provides a continuous flow of air at the same level of pressure during inhalation and exhalation to keep the airway open, it is ideal for treating obstructive sleep apnea. This type of ventilator is not considered a true ventilator because it doesn’t assist with breathing.
- Bi-level positive airway pressure ventilators—deliver air at two pressures for inhalation and for exhalation. They help treat neuromuscular disease with a spontaneous timed mode or backup rate that initiates breathing, particularly at night.
Invasive ventilators deliver air through an endotracheal tube inserted into the patient’s nose or mouth, or through a tracheostomy, a surgical incision in the neck to access the trachea. Air is delivered on a timed cycle through the tube and ensures that the patient takes a minimum number of breaths per minute. These ventilators can be adjusted to respond to the patient’s own efforts to breathe or to override these efforts.
- Concerns: A disadvantage of invasive breathing assistance is that it interferes with the body’s normal mechanisms for clearing the respiratory tract of mucus. If mucus collects, the lungs don’t get enough oxygen and lung infections can occur. Lack of humidification in the nose and mouth are another concern. Because the person cannot speak, special efforts must be made to monitor his or her condition.
Video credit: Richard Savel