User:Aparnasankar/Mechanical ventilation

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Mechanical ventilation, assisted ventilation or intermittent mandatory ventilation (IMV), is the medical term for using a machine called a ventilator to fully or partially provide artificial ventilation. Mechanical ventilation helps move air into and out of the lungs, with the main goal of helping the delivery of oxygen and removal of carbon dioxide. Mechanical ventilation is used for many reasons, including to protect the airway due to mechanical or neurologic cause, to ensure adequate oxygenation, or to remove excess carbon dioxide from the lungs. Various healthcare providers are involved with the use of mechanical ventilation and people who require ventilators are typically monitored in an intensive care unit.

Mechanical ventilation is termed invasive if it involves an instrument to create an airway that is placed inside the trachea. This can be achieved with many instruments, most commonly through an endotracheal tube. Face or nasal masks are used for non-invasive ventilation in appropriately selected people who are conscious.

The two main types of mechanical ventilation include positive pressure ventilation where air is pushed into the lungs through the airways, and negative pressure ventilation where air is pulled into the lungs. There are many specific modes of mechanical ventilation, and their nomenclature has been revised over the decades as the technology has continually developed.

Article body
History The Greek physician Galen may have been the first to describe mechanical ventilation: "If you take a dead animal and blow air through its larynx [through a reed], you will fill its bronchi and watch its lungs attain the greatest distention." In the 1600s, Robert Hooke conducted experiments on dogs to demonstrate this concept. Vesalius too describes ventilation by inserting a reed or cane into the trachea of animals. These experiments predate the discovery of oxygen and its role in respiration. In 1908, George Poe demonstrated his mechanical respirator by asphyxiating dogs and seemingly bringing them back to life. These experiments all demonstrate positive pressure ventilation.

To achieve negative pressure ventilation, there must be a sub-atmospheric pressure to draw air into the lungs. This was first achieved in the late 19th century when John Dalziel and Alfred Jones independently developed tank ventilators, in which ventilation was achieved by placing a patient inside a box that enclosed the body in a box with sub-atmospheric pressures. This machine came to be known colloquially as the Iron lung, which went through many iterations of development. The use of the iron lung became widespread during the polio epidemic of the 1900s.

Uses[edit]
Respiratory therapist (RT) examining a mechanically ventilated patient in an intensive care unit. RTs participate in the optimization of ventilation management, adjustment, and weaning. Mechanical ventilation is indicated when a patient's spontaneous breathing is inadequate to maintain life. It may also be indicated in anticipation of imminent collapse of other physiologic functions, or ineffective gas exchange in the lungs. Because mechanical ventilation serves only to provide assistance for breathing and does not cure a disease, the patient's underlying condition should be identified and treated in order to resolve over time. One of the main reasons why a patient is admitted to an ICU is for delivery of mechanical ventilation. Monitoring a patient in mechanical ventilation has many clinical applications: Enhance understanding of pathophysiology, aid with diagnosis, guide patient management, avoid complications and assessment of trends. In general, mechanical ventilation is initiated to protect the airway or reduce the work of breathing.

Common specific medical indications for use include:


 * Surgical procedures
 * Acute lung injury, including acute respiratory distress syndrome (ARDS), trauma, COVID-19
 * Apnea with respiratory arrest, including cases from intoxication
 * Hypoxemia
 * Prevention of atelectasis
 * Acute severe asthma requiring intubation
 * Acid/base derangements such as respiratory acidosis
 * Neurological diseases such as muscular dystrophy, amyotrophic lateral sclerosis (ALS), Guillain–Barré syndrome, myasthenia gravis, etx.
 * Newborn infants with breathing problems may require mechanical ventilation

Mechanical ventilation is typically used as a short-term measure. It may be used at home or in a nursing or rehabilitation institution if patients have chronic illnesses that require long-term ventilatory assistance.[citation needed]

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In theory, the transairway pressure is simply the difference between the pressure at airway opening and the pressure in the alveoli. That is,



where PTA is the transairway pressure, PAO is the pressure at the airway opening, and PALV is the pressure in the alveoli.[citation needed]

The following are further parameters related to ventilation.


 * Alveolar ventilation:


 * The amount of gas per unit of time that reaches the alveoli and becomes involved in gas exchange
 * where  is the Alveolar ventilation,  is the tidal volume,  is the dead space volume, and  is the respiratory rate
 * where  is the Alveolar ventilation,  is the tidal volume,  is the dead space volume, and  is the respiratory rate


 * Arterial PaCO2:


 * PaCO2 is the partial pressure of carbon dioxide of arterial blood, which determines how well carbon dioxide is able to move out of the body
 * where  is the partial pressure of carbon dioxide,  is the carbon dioxide production[clarification needed],  is the alveolar ventilation
 * where  is the partial pressure of carbon dioxide,  is the carbon dioxide production[clarification needed],  is the alveolar ventilation


 * Alveolar volume:


 * Alveolar volume is defined as the volume of air entering and leaving the alveoli per minute
 * where  is the Alveolar Volume,  is the tidal volume,  is the anatomic dead space
 * where  is the Alveolar Volume,  is the tidal volume,  is the anatomic dead space


 * Estimated physiologic shunt equation:[clarification needed][citation needed]



When 100% oxygen (1.00 FiO

2) is used initially for an adult, it is easy to calculate the next FiO

2 to be used, and easy to estimate the shunt fraction. The estimated shunt fraction refers to the amount of oxygen not being absorbed into the circulation. In normal physiology, gas exchange (oxygen/carbon dioxide) occurs at the level of the alveoli in the lungs. The existence of a shunt refers to any process that hinders this gas exchange, leading to wasted oxygen inspired and the flow of un-oxygenated blood back to the "left heart" (which ultimately supplies the rest of the body with unoxygenated blood). When using 100% oxygen, the degree of shunting is estimated as:


 * 700 mmHg - measured PaO 2 (from an arterial blood gas)

For each difference of 100 mmHg, the shunt is 5%. A shunt of more than 25% should prompt a search for the cause of this hypoxemia, such as mainstem intubation or pneumothorax, and should be treated accordingly. If such complications are not present, other causes must be sought after, and positive end-expiratory pressure (PEEP) should be used to treat this intrapulmonary shunt. Other such causes of a shunt include:


 * alveolar collapse from major atelectasis; and
 * alveolar collection of material other than gas, such as pus from pneumonia, water and protein from acute respiratory distress syndrome, water from congestive heart failure, or blood from haemorrhage.

Mechanical dead space is a further important parameter in ventilator design and function.[according to whom?] It is defined as the volume of gas breathed again as the result of use in a mechanical device.[citation needed] The following is an example calculation for mechanical dead space:


 * (Bohr–Enghoff equation)

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Mechanism
The function of the lungs is to provide gas exchange via oxygenation and ventilation. This phenomenon of respiration involves the physiologic concepts of air flow, tidal volume, compliance, resistance, and dead space. . Other relevant concepts include alveolar ventilation, arterial PaCO2, alveolar volume, and FiO2. Alveolar ventilation is the amount of gas per unit of time that reaches the alveoli and becomes involved in gas exchange. PaCO2 is the partial pressure of carbon dioxide of arterial blood, which determines how well carbon dioxide is able to move out of the body. Alveolar volume is the volume of air entering and leaving the alveoli per minute. Mechanical dead space is another important parameter in ventilator design and function, and is defined as the volume of gas breathed again as the result of use in a mechanical device.

Due to the anatomy of the human pharynx, larynx, and esophagus and the circumstances for which ventilation is needed, additional measures are often required to secure the airway during positive-pressure ventilation in order to allow unimpeded passage of air into the trachea and avoid air passing into the esophagus and stomach. The common method is by insertion of a tube into the trachea: intubation, which provides a clear route for the air. This can be either an endotracheal tube, inserted through the natural openings of mouth or nose, or a tracheostomy inserted through an artificial opening in the neck. In other circumstances simple airway maneuvers, an oropharyngeal airway or laryngeal mask airway may be employed. If the patient is able to protect his/her own airway and non-invasive ventilation or negative-pressure ventilation is used, then an airway adjunct may not be needed.

Pain medicine such as opioids are sometimes used in adults and infants who require mechanical ventilation. For preterm or full term infants who require mechanical ventilation, there is no strong evidence to prescribe opioids or sedation routinely for these procedures, however, some select infants requiring mechanical ventilation may require pain medicine such as opioids. It is not clear if clonidine is safe or effective to be used as a sedative for preterm and full term infants who require mechanical ventilation.

When 100% oxygen (1.00 Fi) is used initially for an adult, it is easy to calculate the next Fi to be used, and easy to estimate the shunt fraction. The estimated shunt fraction refers to the amount of oxygen not being absorbed into the circulation. In normal physiology, gas exchange of oxygen and carbon dioxide occurs at the level of the alveoli in the lungs. The existence of a shunt refers to any process that hinders this gas exchange, leading to wasted oxygen inspired and the flow of un-oxygenated blood back to the left heart, which ultimately supplies the rest of the body with de-oxygenated blood. When using 100% oxygen, the degree of shunting is estimated as 700 mmHg - measured Pa. For each difference of 100 mmHg, the shunt is 5%. A shunt of more than 25% should prompt a search for the cause of this hypoxemia, such as mainstem intubation or pneumothorax, and should be treated accordingly. If such complications are not present, other causes must be sought after, and positive end-expiratory pressure (PEEP) should be used to treat this intrapulmonary shunt. Other such causes of a shunt include:


 * alveolar collapse from major atelectasis
 * alveolar collection of material other than gas, such as pus from pneumonia, water and protein from acute respiratory distress syndrome, water from congestive heart failure, or blood from hemorrhage