User:Pulmonological/Mechanical ventilation

Mechanical ventilation
Nasotracheal intubation
ICD-9	93.90 96.7
MeSH	D012121
OPS-301 code	8-71

In medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing. This may involve a machine called a ventilator or the breathing may be assisted by a Clinician compressing a bag or set of bellows.

Medical uses

It can be used as a short term measure, for example during an operation or critical illness (often in the setting of an intensive care unit). It may be used at home or in a nursing or rehabilitation institution if patients have chronic illnesses that require long-term ventilatory assistance. Owing to the anatomy of the human pharynx, larynx, and esophagus and the circumstances for which ventilation is required then additional measures are often required to secure the airway during positive pressure ventilation to allow unimpeded passage of air into the trachea and avoid air passing into the esophagus and stomach. Commonly this is by insertion of a tube into the trachea 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 maneuvres, an oropharyngeal airway or laryngeal mask airway may be employed. If the patient is able to protect their own airway and non-invasive ventilation or negative-pressure ventilation is used then a airway adjunct may not be needed.

Artificial airways

Main article: Artificial airway

There are various procedures and mechanical devices that provide protection against airway collapse, air leakage, and aspiration:

Bag and mask

• Face mask — In resuscitation and for minor procedures under anaesthesia, a face mask is often sufficient to achieve a seal against air leakage. Airway patency of the unconscious patient is maintained either by manipulation of the jaw or by the use of nasopharyngeal or oropharyngeal airway. These are designed to provide a passage of air to the pharynx through the nose or mouth, respectively. Poorly fitted masks often cause nasal bridge ulcers, a problem for some patients. Face masks are also used for non-invasive ventilation in conscious patients. A full face mask does not, however, provide protection against aspiration.

Laryngeal mask airway

• Laryngeal mask airway — The laryngeal mask airway (LMA) causes less pain and coughing than a tracheal tube. However, unlike tracheal tubes it does not seal against aspiration, making careful individualised evaluation and patient selection mandatory.

Tracheal intubation

• Tracheal intubation is often performed for mechanical ventilation of hours to weeks duration. A tube is inserted through the nose (nasotracheal intubation) or mouth (orotracheal intubation) and advanced into the trachea. In most cases tubes with inflatable cuffs are used for protection against leakage and aspiration. Intubation with a cuffed tube is thought to provide the best protection against aspiration. Tracheal tubes inevitably cause pain and coughing. Therefore, unless a patient is unconscious or anaesthetized for other reasons, sedative drugs are usually given to provide tolerance of the tube. Other disadvantages of tracheal intubation include damage to the mucosal lining of the nasopharynx or oropharynx and subglottic stenosis.

Cricothyrotomy

Patients who require emergency airway management, in whom tracheal intubation has been unsuccessful, may require an airway inserted through a surgical opening in the cricothyroid membrane. This is similar to a tracheostomy but a cricothyrotomy is reserved for emergency access.

• Tracheostomy — When patients require mechanical ventilation for several weeks, a tracheostomy may provide the most suitable access to the trachea. A tracheostomy is a surgically created passage into the trachea. Tracheostomy tubes are well tolerated and often do not necessitate any use of sedative drugs. Tracheostomy tubes may be inserted early during treatment in patients with pre-existing severe respiratory disease, or in any patient who is expected to be difficult to wean from mechanical ventilation, i.e., patients who have little muscular reserve.
• Mouthpiece — Less common interface, does not provide protection against aspiration. There are lipseal mouthpieces with flanges to help hold them in place if patient is unable.

Indications

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.

Contraindications

Are there contra indications to mechanical ventilation

Adverse effects

Problems associated with mechanical ventilation

Techniques

Prone ventilation

Prone ventilation refers to mechanical ventilation with the patient lying in the prone position. It improves oxygenation in most patients with acute respiratory distress syndrome (ARDS), although the mechanism and clinical benefit of this effect are uncertain. The improvement of oxygenation during prone ventilation is multifactorial. The most important factors are probably the optimization of ventilation and perfusion, although changes in the distribution of extravascular lung water and secretions may also play a role. Prone positioning improves ventilation by way of its effect on pleural pressure and lung compression. Increased functional residual capacity (FRC) has also been proposed, but changes in FRC have not been a dominant finding in most studies of prone ventilation

Positive pressure

The use of modern mechanical ventilators

Modes

Positive pressure ventilation

Spontaneous ventilation

Discuss CPAP and BIPAP

High frequency ventilation

High frequency ventilation refers to ventilation that occurs at rates significantly above that found in natural breathing. High frequency ventilation is further defined as any ventilation with a respiratory rate (V_f) greater than 150 respirations per minute. Within the category of high-frequency ventilation, the two principal types are high-frequency ventilation (passive) (i.e. high-frequency jet ventilation) and high-frequency ventilation (active) (i.e. high-frequency oscillatory ventilation).

Strategies

Positive end-expiratory pressure

Main article: Positive end-expiratory pressure

Positive end-expiratory pressure (PEEP) is the pressure in the lungs (alveolar pressure) above atmospheric pressure (the pressure outside of the body) that exists at the end of expiration. The two types of PEEP are extrinsic PEEP (PEEP applied by a ventilator) and intrinsic PEEP (PEEP caused by a non-complete exhalation). Pressure that is applied or increased during an inspiration is termed pressure support. A small amount of applied PEEP (3 to 5 cmH₂O) is used in most mechanically ventilated patients to mitigate end-expiratory alveolar collapse. A higher level of applied PEEP (>5 cmH₂O) is sometimes used to improve hypoxemia or reduce ventilator-associated lung injury in patients with acute lung injury, acute respiratory distress syndrome, or other types of hypoxemic respiratory failure.

Risks and complications

Ventilator associated lung injury

Main article: Ventilator-associated lung injury

Ventilator-associated lung injury (VALI) refers to acute lung injury that occurs during mechanical ventilation. It is clinically indistinguishable from acute lung injury or acute respiratory distress syndrome (ALI/ARDS).

Pulmonary barotrauma

Main article: Pulmonary barotrauma

Pulmonary barotrauma is a well-known complication of positive pressure mechanical ventilation. This includes pneumothorax, subcutaneous emphysema, pneumomediastinum, and pneumoperitoneum.

Diaphragm atrophy

Controlled mechanical ventilation may lead to a rapid type of disuse atrophy involving the diaphragmatic muscle fibers, which can develop within the first day of mechanical ventilation. This cause of atrophy in the diaphragm is also a cause of atrophy in all respiratory related muscles during controlled mechanical ventilation.

Motility of mucocilia in the airways

Positive pressure ventilation appears to impair mucociliary motility in the airways. Bronchial mucus transport was frequently impaired and associated with retention of secretions and pneumonia.

Society and culture

Perceptions of mechanical ventilation

Special populations

Pediatrics

Mechanical ventilation in pediatrics

Neonates

Mechanical ventilation in neonates

Recovery and rehabilitation

Weaning and general issues after mechanical ventilation

Withdrawal from mechanical ventilation—also known as weaning—should not be delayed unnecessarily, nor should it be done prematurely. Patients should have their ventilation considered for withdrawal if they are able to support their own ventilation and oxygenation, and this should be assessed continuously. There are several objective parameters to look for when considering withdrawal, but there is no specific criteria that generalizes to all patients.

Trials of spontaneous breathing have been shown to accurately predict the success of spontaneous breathing.

Economics

Cost of mechanical ventilation

Research

Research related to mechanical ventilation

History

The Roman 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." Vesalius too describes ventilation by inserting a reed or cane into the trachea of animals. In 1908 George Poe demonstrated his mechanical respirator by asphyxiating dogs and seemingly bringing them back to life.

Veterinary use

Mechanical ventilation in other animals.