Ventilator
A medical ventilator is a device designed to provide mechanical ventilation to a patient. Ventilators are chiefly used in intensive care medicine, home care, and emergency medicine (as standalone units) and in anesthesia (as a component of an anesthesia machine).
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 set". The air reservoir is pneumatically compressed several times a minute to deliver an air/oxygen mixture to the patient; when overpressure is released, the patient will exhale passively due to the lungs' elasticity. 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 and flow) and ventilator function (e.g. air leakage, power failure), backup batteries, air and oxygen tanks, and remote control and alarms. 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 for the patient. In Germany, Canada, and the United States, respiratory therapists are responsible for tuning these settings.
Life-critical system
Because the failure of a mechanical ventilation system may result in death, it is classed as a life-critical system, and precautions must be taken to ensure that mechanical ventilation systems are highly reliable. This includes their power-supply provision.
Mechanical ventilators are therefore carefully designed so that no single point of failure can endanger the patient. They usually have manual backup mechanisms to enable hand-driven respiration in the absence of power. Some systems are also equipped with compressed-gas tanks and backup batteries to provide ventilation in case of power failure or defective gas supplies, and methods to operate or call for help if their mechanisms or software fails.
Mechanical ventilation
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 many cases, mechanical ventilation is used in acute settings such as in the ICU for a short period of time during a serious illness. For some patients who have certain chronic illnesses that require long-term ventilation assistance, they are also able to do so at home or other nursing/rehabilitation institution with the help of respiratory therapists and physicians. The main form of mechanical ventilation currently is positive pressure ventilation, which works by incresing the pressure in the patient's airway and thus forcing additional air into the lungs. This is in contrast to the more historically common negative pressure ventilators (for example, the "iron-lung") that create a negative pressure environment around the patient's chest, thus sucking air into the lungs. Although often a life-saving technique, mechanical ventilation carries many potential complications including pneumothorax, airway injury, alveolar damage, and ventilator-associated pneumonia, among others. Accordingly it is generally weaned off or to minimal settings as soon as possible.
Types of ventilators
Ventilation can be delivered via:
- Hand-controlled ventilation such as:
- Bag valve mask
- Continuous-flow or Anaesthesia (or T-piece) bag
- A mechanical ventilator. Types of mechanical ventilators include:
- Transport ventilators. These ventilators are small, more rugged, and can be gas powered or via AC or DC power sources.
- ICU ventilators. These ventilators are larger and usually run on AC power (though virtually all contain a battery to facilitate intrafacility transport and as a back-up in the event of a power failure). This style of ventilator often provides greater control of a wide variety of ventilation parameters (such as inspiratory rise time). Many ICU ventilators also incorporate graphics to provide visual feedback of each breath.
- NICU ventilators. Designed with the preterm neonate in mind, these are a specialized subset of ICU ventilators which are highly accurate at delivering the smaller volumes, pressures, and oxygen concentrations required to ventilate this patient subset.
- PAP ventilators. these ventilators are specifically designed for non-invasive ventilation. this includes ventilators for use at home, in order to treat sleep apnea.
Indications for use
Mechanical ventilation is indicated when the patient's spontaneous ventilation is inadequate to maintain life. It is also indicated as prophylaxis for imminent collapse of other physiologic functions, or ineffective gas exchange in the lungs. Because mechanical ventilation only serves to provide assistance for breathing and does not cure a disease, the patient's underlying condition should be correctable and should resolve over time. In addition, other factors must be taken into consideration because mechanical ventilation is not without its complications (see below)
Common medical indications for use include:
- Acute lung injury (including ARDS, trauma)
- Apnea with respiratory arrest, including cases from intoxication
- Chronic obstructive pulmonary disease (COPD)
- Acute respiratory acidosis with partial pressure of carbon dioxide (pCO2) > 50 mmHg and pH < 7.25, which may be due to paralysis of the diaphragm due to Guillain-Barré syndrome, Myasthenia Gravis, spinal cord injury, or the effect of anaesthetic and muscle relaxant drugs
- Increased work of breathing as evidenced by significant tachypnea, retractions, and other physical signs of respiratory distress
- Hypoxemia with arterial partial pressure of oxygen (PaO2) with supplemental fraction of inspired oxygen (FiO2) < 55 mm Hg
- Hypotension including sepsis, shock, congestive heart failure