A medical ventilator can be defined as any machine designed to mechanically move breatheable air into and out of the lungs, to provide the mechanism of breathing for a patient who is physically unable to breathe, or breathing insufficiently.

While modern ventilators are generally thought of as computerized machines, patients can be ventilated indefinitely with a bag valve mask

Bag valve mask

A bag valve mask is a hand-held device used to provide positive pressure ventilation to a patient who is not breathing or who is breathing inadequately. The device is a normal part of a resuscitation kit for trained professionals, such as ambulance crew...

, a simple hand-operated machine. After Hurricane Katrina

Hurricane Katrina

Hurricane Katrina of the 2005 Atlantic hurricane season was a powerful Atlantic hurricane. It is the costliest natural disaster, as well as one of the five deadliest hurricanes, in the history of the United States. Among recorded Atlantic hurricanes, it was the sixth strongest overall...

, dedicated staff "bagged" patients in New Orleans hospitals for days with simple bag valve masks.

Ventilators are chiefly used in intensive care medicine

Intensive care medicine

Intensive-care medicine or critical-care medicine is a branch of medicine concerned with the diagnosis and management of life threatening conditions requiring sophisticated organ support and invasive monitoring.- Overview :...

, home care

Home care

Home Care, , is health care or supportive care provided in the patient's home by healthcare professionals Home Care, (also referred to as domiciliary care or social care), is health care or supportive care provided in the patient's home by healthcare professionals Home Care, (also referred to as...

, and emergency medicine

Emergency medicine

Emergency medicine is a medical specialty in which physicians care for patients with acute illnesses or injuries which require immediate medical attention. While not usually providing long-term or continuing care, emergency medicine physicians diagnose a variety of illnesses and undertake acute...

 (as standalone units) and in anesthesia

Anesthesia

Anesthesia, or anaesthesia , traditionally meant the condition of having sensation blocked or temporarily taken away...

 (as a component of an anesthesia machine).

Function

In its simplest form, a modern positive pressure ventilator consists of a compressible air reservoir or turbine, air and oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 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. If a turbine is used, the turbine pushes air through the ventilator, with a flow valve adjusting pressure to meet patient-specific parameters. When overpressure is released, the patient will exhale passively due to the lung

Lung

The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

s' elasticity, the exhaled air being released usually through a one-way valve within the patient circuit called the patient manifold. 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

Turbopump

A turbopump is a gas turbine that comprises basically two main components: a rotodynamic pump and a driving turbine, usually both mounted on the same shaft, or sometimes geared together...

.

Modern ventilators are electronically controlled by a small embedded system

Embedded system

An embedded system is a computer system designed for specific control functions within a larger system. often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal...

 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 while biomedical technologists are responsible for the maintenance.

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). Determined by the type of ventilation needed, the patient-end of the circuit may be either noninvasive or invasive.

Noninvasive methods, which are adequate for patients who require a ventilator only while sleeping and resting, mainly employ a nasal mask. Invasive methods require intubation

Intubation

Tracheal intubation, usually simply referred to as intubation, is the placement of a flexible plastic or rubber tube into the trachea to maintain an open airway or to serve as a conduit through which to administer certain drugs...

, which for long-term ventilator dependence will normally be a tracheotomy

Tracheotomy

Among the oldest described surgical procedures, tracheotomy consists of making an incision on the anterior aspect of the neck and opening a direct airway through an incision in the trachea...

 cannula, as this is much more comfortable and practical for long-term care than is larynx or nasal intubation.

Life-critical system

Because the failure of a mechanical ventilation system may result in death, it is classed as a life-critical system

Life-critical system

A life-critical system or safety-critical system is a system whose failure ormalfunction may result in:* death or serious injury to people, or* loss or severe damage to equipment or* environmental harm....

, 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 fail.

Ventilation

The early history of mechanical ventilation begins with various versions of what was eventually called the iron lung

Iron lung

A negative pressure ventilator is a form of medical ventilator that enables a person to breathe when normal muscle control has been lost or the work of breathing exceeds the person's ability....

, a form of noninvasive negative pressure ventilator widely used during the polio

Poliomyelitis

Poliomyelitis, often called polio or infantile paralysis, is an acute viral infectious disease spread from person to person, primarily via the fecal-oral route...

 epidemics of the 20th century after the introduction of the "Drinker respirator" in 1928, and the subsequent improvements introduced by John Haven Emerson

John Haven Emerson

John Haven "Jack" Emerson was an American inventor of biomedical devices, specializing in respiratory equipment. He is perhaps best remembered for his work in improving the iron lung.-Early life:...

 in 1931. Other forms of noninvasive ventilators, also used widely for polio patients, include Biphasic Cuirass Ventilation

Biphasic Cuirass Ventilation

Biphasic cuirass ventilation is a method of ventilation which requires the patient to wear an upper body shell or cuirass, so named after the body armor worn by medieval soldiers. The ventilation is biphasic because the cuirass is attached to a pump which actively controls both the inspiratory and...

, the rocking bed, and rather primitive positive pressure machines.

In 1949, John Haven Emerson developed a mechanical assister for anesthesia with the cooperation of the anesthesia department at Harvard University

Harvard University

Harvard University is a private Ivy League university located in Cambridge, Massachusetts, United States, established in 1636 by the Massachusetts legislature. Harvard is the oldest institution of higher learning in the United States and the first corporation chartered in the country...

. Mechanical ventilators began to be used increasingly in anesthesia and intensive care during the 1950s. Their development was stimulated both by the need to treat polio patients and the increasing use of muscle relaxant

Muscle relaxant

A muscle relaxant is a drug which affects skeletal muscle function and decreases the muscle tone. It may be used to alleviate symptoms such as muscle spasms, pain, and hyperreflexia. The term "muscle relaxant" is used to refer to two major therapeutic groups: neuromuscular blockers and spasmolytics...

s during anesthesia. Relaxant drugs paralyze the patient and improve operating conditions for the surgeon, but also paralyze the respiratory muscles
In the United Kingdom, the East Radcliffe and Beaver models were early examples, the later using an automotive wiper motor to drive the bellows used to inflate the lungs. Electric motors were, however, a problem in the operating theatres of that time, as their use caused an explosion hazard in the presence of flammable anesthetics such as ether

Diethyl ether

Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...

 and cyclopropane

Cyclopropane

Cyclopropane is a cycloalkane molecule with the molecular formula C3H6, consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms...

. In 1952, Roger Manley of the Westminster Hospital

Westminster Hospital

Westminster Hospital was a hospital in London, England, founded in 1719. In 1834 a medical school attached to the hospital was formally founded....

, London, developed a ventilator which was entirely gas driven, and became the most popular model used in Europe. It was an elegant design, and became a great favourite with European anesthetists for four decades, prior to the introduction of models controlled by electronics. It was independent of electrical power, and caused no explosion hazard. The original Mark I unit was developed to become the Manley Mark II in collaboration with the Blease company, who manufactured many thousands of these units. Its principle of operation was very simple, an incoming gas flow was used to lift a weighted bellows unit, which fell intermittently under gravity, forcing breathing gases into the patient's lungs. The inflation pressure could be varied by sliding the movable weight on top of the bellows. The volume of gas delivered was adjustable using a curved slider, which restricted bellows excursion. Residual pressure after the completion of expiration was also configurable, using a small weighted arm visible to the lower right of the front panel. This was a robust unit and its availability encouraged the introduction of positive pressure ventilation techniques into mainstream European anesthetic practice.

The 1955 release of Forrest Bird

Forrest Bird

Forrest M. Bird is an American aviator, inventor and biomedical engineer. He is best known for creating some of the first reliable mass-produced mechanical ventilators for acute and chronic cardiopulmonary care.-Biography:...

's "Bird Universal Medical Respirator" in the United States, changed the way mechanical ventilation was performed with the small green box becoming a familiar piece of medical equipment. The unit was sold as the Bird Mark 7 Respirator and informally called the "Bird". It was a pneumatic

Pneumatics

Pneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...

 device and therefore required no electrical power source to operate.

Intensive care environments around the world revolutionalized in 1971 by the introduction of the first SERVO 900 ventilator (Elema-Schönander). It was a small, silent and effective electronic ventilator, with the famous SERVO feedback system controlling what had been set and regulating delivery. For the first time, the machine could deliver the set volume in volume control ventilation.

Ventilators used under increased pressure (hyperbaric) require special precautions and few ventilators can operate under these conditions. In 1979, Sechrist Industries introduced their Model 500A ventilator which was specifically designed for use with hyperbaric chambers.

In 1991 the SERVO 300 ventilator series was introduced. The platform of the SERVO 300 series enabled treatment of all patient categories, from adult to neonate, with one single ventilator. The SERVO 300 series provided a completely new and unique gas delivery system, with rapid flow-triggering response.

A modular concept, meaning that the hospital has one ventilator model throughout the ICU department instead of a fleet with different models and brands for the different user needs, was introduced with SERVO-i in 2001. With this modular concept the ICU departments could choose the modes and options, software and hardware needed for a particular patient category.

Biphasic Cuirass Ventilation

Biphasic Cuirass Ventilation

Biphasic Cuirass Ventilation

Biphasic cuirass ventilation is a method of ventilation which requires the patient to wear an upper body shell or cuirass, so named after the body armor worn by medieval soldiers. The ventilation is biphasic because the cuirass is attached to a pump which actively controls both the inspiratory and...

(BCV) is a method of ventilation

Ventilation (physiology)

In respiratory physiology, ventilation is the rate at which gas enters or leaves the lung. It is categorized under the following definitions:-Sample values:...

 which requires the patient to wear an upper body shell or cuirass

Cuirass

A cuirass is a piece of armour, formed of a single or multiple pieces of metal or other rigid material, which covers the front of the torso...

, so named after the body armor worn by medieval soldiers. The ventilation is biphasic because the cuirass is attached to a pump which actively controls both the inspiratory

Inhalation

Inhalation is the movement of air from the external environment, through the air ways, and into the alveoli....

 and expiratory

Exhalation

Exhalation is the movement of air out of the bronchial tubes, through the airways, to the external environment during breathing....

 phases of the respiratory cycle. This method has also been described as 'Negative Pressure Ventilation' (NPV), 'External Chest Wall Oscillation' (ECWO), 'External Chest Wall Compression' (ECWC) and 'External High Frequency Oscillation' (EHFO). BCV may be considered a refinement of the iron lung

Iron lung

A negative pressure ventilator is a form of medical ventilator that enables a person to breathe when normal muscle control has been lost or the work of breathing exceeds the person's ability....

 ventilator. Biphasic Cuirass Ventilation was developed by the late Dr Zamir Hayek, a pioneer in the field of assisted ventilation. Some of Dr Hayek's previous inventions include the Hayek Oscillator, an early form of the technology.

External links

• Simulation of an anesthesia machine with a piston ventilator
• International Ventilator Users Network (IVUN), a subsidiary of Post-Polio Health International
  Post-Polio Health International
  Post-Polio Health International , is a relatively new name for a non-profit organization that officially began its work in 1960. For many years it was known in medical, rehabilitation, and disability circles variously as GINI, or the International Polio Network, or the Rehabilitation Gazette...
  
  . Information about home mechanical ventilation.
• Information about SERVO ventilation
• United Hayek Industries - Only manufacturer of Biphasic Cuirass Ventilation