Mechanical ventilation

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Mechanical ventilation
Servo I Ventilator.jpg
Servo-u Ventilator
ICD-9 93.90 96.7
MeSH D012121
OPS-301 code 8-71

Mechanical ventilation or assisted ventilation 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.

Contents

Mechanical ventilation is termed invasive if it involves an instrument to create an airway that is placed inside the trachea. This is done through an endotracheal tube or nasotracheal tube. [1] For non-invasive ventilation in people who are conscious, face or nasal masks are used. 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.

History

Hospital staff examine a patient in an Iron lung tank respirator during the polio epidemic. The machine creates a negative pressure around the thoracic cavity, thereby causing air to rush into the lungs to equalize intrapulmonary pressure. Poumon artificiel.jpg
Hospital staff examine a patient in an Iron lung tank respirator during the polio epidemic. The machine creates a negative pressure around the thoracic cavity, thereby causing air to rush into the lungs to equalize intrapulmonary pressure.

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. [2] 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. [3] 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.

Early ventilators were control style with no support breaths integrated into them and were limited to an inspiration to expiration ration of 1:1. In the 1970s, intermittent mandatory ventilation was introduced as well as synchronized intermittent mandatory ventilation. These styles of ventilation had control breaths that patients could breathe between. [4]

Uses

Respiratory therapist (RT) examining a mechanically ventilated patient in an intensive care unit. RTs participate in the optimization of ventilation management, adjustment, and weaning. Respiratory therapist.jpg
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 be indicated in anticipation of imminent respiratory failure, acute respiratory failure, acute hypoxemia, or prophylactically. 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 liberate them from the ventilator.

Common specific medical indications for mechanical ventilation include: [5] [6]

Mechanical ventilation is typically used as a short-term measure. It may, however, be used at home or in a nursing or rehabilitation institution for patients that have chronic illnesses that require long-term ventilatory assistance.

Risks and complications

Mechanical ventilation is often a life-saving intervention, but carries potential complications. A common complication of positive pressure ventilation stemming directly from the ventilator settings include volutrauma and barotrauma. [11] [12] Others include pneumothorax, subcutaneous emphysema, pneumomediastinum, and pneumoperitoneum. [12] [13] Another well-documented complication is ventilator-associated lung injury which presents as acute respiratory distress syndrome. [14] [15] [16] Other complications include diaphragm atrophy, [17] [18] [19] decreased cardiac output, [20] and oxygen toxicity. One of the primary complications that presents in patients mechanically ventilated is acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). ALI/ARDS are recognized as significant contributors to patient morbidity and mortality. [21] [22]

In many healthcare systems, prolonged ventilation as part of intensive care is a limited resource. For this reason, decisions to commence and remove ventilation may raise ethical debate and often involve legal orders such as do-not-resuscitate orders. [23]

Mechanical ventilation is often associated with many painful procedures and the ventilation itself can be uncomfortable. For infants who require opioids for pain, the potential side effects of opioids include problems with feeding, gastric and intestinal mobility problems, the potential for opioid dependence, and opioid tolerance. [24]

Withdrawal from mechanical ventilation

Timing of withdrawal from mechanical ventilation—also known as weaning—is an important consideration. People who require mechanical ventilation should have their ventilation considered for withdrawal if they are able to support their own ventilation and oxygenation, and this should be assessed continuously. [25] [5] There are several objective parameters to look for when considering withdrawal, but there are no specific criteria that generalizes to all patients.

The Rapid Shallow Breathing Index (RSBI, the ratio of respiratory frequency to tidal volume (f/VT), previously referred to as the "Yang Tobin Index" or "Tobin Index" after Dr. Karl Yang and Prof. Martin J. Tobin of Loyola University Medical Center) is one of the best studied and most commonly used weaning predictors, with no other predictor having been shown to be superior. It was described in a prospective cohort study of mechanically ventilated patients which found that a RSBI > 105 breaths/min/L was associated with weaning failure, while a RSBI < 105 breaths/min/L. [26]

Spontaneous breathing trials are conducted to assess the likelihood of a patient being able to maintain stability and breath on their own without the ventilator. This is done by changing the mode to one where they have to trigger breaths and ventilatory support is only given to compensate for the added resistance of the endotracheal tube. [27]

A cuff leak test is done to detect if there is airway edema to show the chances of post-extubation stridor. This is done by deflating to the cuff to check if air begins leaking around the endotracheal tube. [27]

Physiology

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. [6] [28] 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. [29] 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. [30] Alveolar volume is the volume of air entering and leaving the alveoli per minute. [31] 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.

Image of endotracheal tube placement required to connect a patient's physiologic airway to the ventilator. Endotracheal Tube.png
Image of endotracheal tube placement required to connect a patient's physiologic airway to the ventilator.

Due to the anatomy of the human pharynx, larynx, and esophagus and the circumstances for which ventilation is needed, additional measures are 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 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 non-invasive ventilation or negative-pressure ventilation is used, then an airway adjunct is not 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 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. [32] The estimated shunt fraction refers to the amount of oxygen not being absorbed into the circulation. [32] 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. [32] When using 100% oxygen, the degree of shunting is estimated as 700 mmHg - measured PaO
2. For each difference of 100 mmHg, the shunt is 5%. [32] 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. [32] Other such causes of a shunt include:

Technique

Modes

Mechanical ventilation utilizes several separate systems for ventilation referred to as the mode. Modes come in many different delivery concepts but all conventional positive pressure ventilators modes fall into one of two categories; volume-cycled or pressure-cycled. [33] [25] A relatively new ventilation mode is flow-controlled ventilation (FCV). [34] FCV is a fully dynamic mode without significant periods of 'no flow'. It is based on creating a stable gas flow into or out of the patient's lungs to generate an inspiration or expiration, respectively. This results in linear increases and decreases in intratracheal pressure. In contrast to conventional modes of ventilation, there are no abrupt drop intrathoracic pressure drops, because of the controlled expiration. [35] Further, this mode allows to use thin endotracheal tubes (~2 – 10 mm inner diameter) to ventilate a patient as expiration is actively supported. [36] In general, the selection of which mode of mechanical ventilation to use for a given patient is based on the familiarity of clinicians with modes and the equipment availability at a particular institution. [37]

Types of Ventilation

Carl Gunnar Engstrom invented in 1950 one of the first intermittent positive pressure ventilator, which delivers air straight into the lungs using an endotracheal tube placed into the windpipe. Engstrom respirator Model 150 - Sweden - 1955-1970.jpg
Carl Gunnar Engström invented in 1950 one of the first intermittent positive pressure ventilator, which delivers air straight into the lungs using an endotracheal tube placed into the windpipe.

Positive pressure

The design of the modern positive-pressure ventilators were based mainly on technical developments by the military during World War II to supply oxygen to fighter pilots in high altitude. Such ventilators replaced the iron lungs as safe endotracheal tubes with high-volume/low-pressure cuffs were developed. The popularity of positive-pressure ventilators rose during the polio epidemic in the 1950s in Scandinavia [38] [39] and the United States and was the beginning of modern ventilation therapy. Positive pressure through manual supply of 50% oxygen through a tracheostomy tube led to a reduced mortality rate among patients with polio and respiratory paralysis. However, because of the sheer amount of man-power required for such manual intervention, mechanical positive-pressure ventilators became increasingly popular. [2]

Positive-pressure ventilators work by increasing the patient's airway pressure through an endotracheal or tracheostomy tube. The positive pressure allows air to flow into the airway until the ventilator breath is terminated. Then, the airway pressure drops to zero, and the elastic recoil of the chest wall and lungs push the tidal volume — the breath-out through passive exhalation.

Negative pressure

Negative pressure mechanical ventilators are produced in small, field-type and larger formats. [40] The prominent design of the smaller devices is known as the cuirass, a shell-like unit used to create negative pressure only to the chest using a combination of a fitting shell and a soft bladder. In recent years this device has been manufactured using various-sized polycarbonate shells with multiple seals, and a high-pressure oscillation pump in order to carry out biphasic cuirass ventilation. [41] Its main use has been in patients with neuromuscular disorders that have some residual muscular function. [42] The latter, larger formats are in use, notably with the polio wing hospitals in England such as St Thomas' Hospital in London and the John Radcliffe in Oxford. [2]

The larger units have their origin in the iron lung, also known as the Drinker and Shaw tank, which was developed in 1928 by J.H Emerson Company and was one of the first negative-pressure machines used for long-term ventilation. [4] [41] It was refined and used in the 20th century largely as a result of the polio epidemic that struck the world in the 1940s. The machine is, in effect, a large elongated tank, which encases the patient up to the neck. [3] The neck is sealed with a rubber gasket so that the patient's face (and airway) are exposed to the room air. While the exchange of oxygen and carbon dioxide between the bloodstream and the pulmonary airspace works by diffusion and requires no external work, air must be moved into and out of the lungs to make it available to the gas exchange process. In spontaneous breathing, a negative pressure is created in the pleural cavity by the muscles of respiration, and the resulting gradient between the atmospheric pressure and the pressure inside the thorax generates a flow of air. In the iron lung by means of a pump, the air is withdrawn mechanically to produce a vacuum inside the tank, thus creating negative pressure. [41] This negative pressure leads to expansion of the chest, which causes a decrease in intrapulmonary pressure, and increases flow of ambient air into the lungs. As the vacuum is released, the pressure inside the tank equalizes to that of the ambient pressure, and the elastic recoil of the chest and lungs leads to passive exhalation. However, when the vacuum is created, the abdomen also expands along with the lung, cutting off venous flow back to the heart, leading to pooling of venous blood in the lower extremities. The patients can talk and eat normally, and can see the world through a well-placed series of mirrors. Some could remain in these iron lungs for years at a time quite successfully. [3]

Some of the problems with the full body design were such as being unable to control the inspiratory to expiratory ratio and the flow rate. This design also caused blood pooling in the legs. [4]

Intermittent abdominal pressure ventilator

Another type is the intermittent abdominal pressure ventilator that applies pressure externally via an inflated bladder, forcing exhalation, sometimes termed exsufflation. The first such apparatus was the Bragg-Paul Pulsator. [43] [44] The name of one such device, the Pneumobelt made by Puritan Bennett has to a degree become a generic name for the type. [44] [45]

Oscillator

3100A Oscillator Oscillator 3100A.jpg
3100A Oscillator

The most commonly used high frequency ventilator and only one approved in the United States is the 3100A from Vyaire Medical. It works by using very small tidal volumes by setting amplitude and a high rate set in hertz. This type of ventilation is primarily used in neonates and pediatric patients who are failing conventional ventilation. [46]

High Frequency Jet Ventilation

The first type of high frequency ventilator made for neonates and the only jet type is made by Bunnell Incorporated. It works in conjunction with a separate CMV ventilator to add pulses of air to the control breaths and PEEP. [46]

Neonatal Jet ventilator VIP Bird2.jpg
Neonatal Jet ventilator

Monitoring

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 assess trends.

In ventilated patients, pulse oximetry is commonly used when titrating FIO2. A reliable target of Spo2 is greater than 95%. [47]

The total PEEP in the patient can be determined by doing an expiratory hold on the ventilator. If this is higher than the set PEEP, this indicates air trapping.

The plateau pressure can be found by doing an inspiratory hold. This shows the actual pressure the patient's lungs are experiencing.

Loops can be used to see what is occurring in the patient's lungs. These include flow-volume and pressure-volume loops. They can show changes in compliance and resistance.

Functional Residual Capacity can be determined when using the GE Carestation.

Modern ventilators have advanced monitoring tools. There are also monitors that work independently of the ventilator which allow for measuring patients after the ventilator has been removed, such as a Tracheal tube test.

Types of ventilators

SMART BAG MO Bag-Valve-Mask Resuscitator Ballon ventilation 1.jpg
SMART BAG MO Bag-Valve-Mask Resuscitator

Ventilators come in many different styles and method of giving a breath to sustain life. [6] There are manual ventilators such as bag valve masks and anesthesia bags that require the users to hold the ventilator to the face or to an artificial airway and maintain breaths with their hands. Mechanical ventilators are ventilators not requiring operator effort and are typically computer-controlled or pneumatic-controlled. [25] Mechanical ventilators typically require power by a battery or a wall outlet (DC or AC) though some ventilators work on a pneumatic system not requiring power. There are a variety of technologies available for ventilation, falling into two main (and then lesser categories), the two being the older technology of negative-pressure mechanisms, and the more common positive-pressure types.

Common positive-pressure mechanical ventilators include:

  1. Transport ventilators—These ventilators are small and more rugged, and can be powered pneumatically or via AC or DC power sources.
  2. Intensive-care ventilators—These ventilators are larger and usually run on AC power (though virtually all contain a battery to facilitate intra-facility 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.
  3. Neonatal ventilators (bubble CPAP, HFJV, HFOV[ clarification needed ])—Designed with the preterm neonate in mind, these are a specialized subset of ICU ventilators that are designed to deliver smaller volumes and pressures to these patients. These may be conventional or high frequency types. [46]
  4. Positive airway pressure ventilators (PAP) — These ventilators are specifically designed for non-invasive ventilation. This includes ventilators for use at home for treatment of chronic conditions such as sleep apnea or COPD and in the ICU setting.

Breath delivery mechanisms

Trigger

The trigger, either flow or pressure, is what causes a breath to be delivered by a mechanical ventilator. Breaths may be triggered by a patient taking their own breath, a ventilator operator pressing a manual breath button, or based on the set respiratory rate.

Cycle

The cycle is what causes the breath to transition from the inspiratory phase to the exhalation phase. Breaths may be cycled by a mechanical ventilator when a set time has been reached, or when a preset flow or percentage of the maximum flow delivered during a breath is reached depending on the breath type and the settings. Breaths can also be cycled when an alarm condition such as a high pressure limit has been reached.

Limit

Limit is how the breath is controlled. Breaths may be limited to a set maximum pressure or volume.

Breath exhalation

Exhalation in mechanical ventilation is almost always completely passive. The ventilator's expiratory valve is opened, and expiratory flow is allowed until the baseline pressure (PEEP) is reached. Expiratory flow is determined by patient factors such as compliance and resistance.

Artificial airways as a connection to the ventilator

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

See also

Related Research Articles

<span class="mw-page-title-main">Tracheal intubation</span> Placement of a tube into the trachea

Tracheal intubation, usually simply referred to as intubation, is the placement of a flexible plastic tube into the trachea (windpipe) to maintain an open airway or to serve as a conduit through which to administer certain drugs. It is frequently performed in critically injured, ill, or anesthetized patients to facilitate ventilation of the lungs, including mechanical ventilation, and to prevent the possibility of asphyxiation or airway obstruction.

<span class="mw-page-title-main">Respiratory failure</span> Inadequate gas exchange by the respiratory system

Respiratory failure results from inadequate gas exchange by the respiratory system, meaning that the arterial oxygen, carbon dioxide, or both cannot be kept at normal levels. A drop in the oxygen carried in the blood is known as hypoxemia; a rise in arterial carbon dioxide levels is called hypercapnia. Respiratory failure is classified as either Type 1 or Type 2, based on whether there is a high carbon dioxide level, and can be acute or chronic. In clinical trials, the definition of respiratory failure usually includes increased respiratory rate, abnormal blood gases, and evidence of increased work of breathing. Respiratory failure causes an altered state of consciousness due to ischemia in the brain.

<span class="mw-page-title-main">Tracheotomy</span> Temporary surgical incision to create an airway into the trachea

Tracheotomy, or tracheostomy, is a surgical airway management procedure which consists of making an incision (cut) on the anterior aspect (front) of the neck and opening a direct airway through an incision in the trachea (windpipe). The resulting stoma (hole) can serve independently as an airway or as a site for a tracheal tube or tracheostomy tube to be inserted; this tube allows a person to breathe without the use of the nose or mouth.

<span class="mw-page-title-main">Acute respiratory distress syndrome</span> Human disease

Acute respiratory distress syndrome (ARDS) is a type of respiratory failure characterized by rapid onset of widespread inflammation in the lungs. Symptoms include shortness of breath (dyspnea), rapid breathing (tachypnea), and bluish skin coloration (cyanosis). For those who survive, a decreased quality of life is common.

A tracheal tube is a catheter that is inserted into the trachea for the primary purpose of establishing and maintaining a patent airway and to ensure the adequate exchange of oxygen and carbon dioxide.

<span class="mw-page-title-main">Airway management</span> Medical procedure ensuring an unobstructed airway

Airway management includes a set of maneuvers and medical procedures performed to prevent and relieve airway obstruction. This ensures an open pathway for gas exchange between a patient's lungs and the atmosphere. This is accomplished by either clearing a previously obstructed airway; or by preventing airway obstruction in cases such as anaphylaxis, the obtunded patient, or medical sedation. Airway obstruction can be caused by the tongue, foreign objects, the tissues of the airway itself, and bodily fluids such as blood and gastric contents (aspiration).

<span class="mw-page-title-main">Respiratory arrest</span> Medical condition

Respiratory arrest is a serious medical condition caused by apnea or respiratory dysfunction severe enough that it will not sustain the body. Prolonged apnea refers to a patient who has stopped breathing for a long period of time. If the heart muscle contraction is intact, the condition is known as respiratory arrest. An abrupt stop of pulmonary gas exchange lasting for more than five minutes may permanently damage vital organs, especially the brain. Lack of oxygen to the brain causes loss of consciousness. Brain injury is likely if respiratory arrest goes untreated for more than three minutes, and death is almost certain if more than five minutes.

<span class="mw-page-title-main">Artificial ventilation</span> Assisted breathing to support life

Artificial ventilation or respiration is when a machine assists in a metabolic process to exchange gases in the body by pulmonary ventilation, external respiration, and internal respiration. A machine called ventilator provides the person air manually by moving air in and out of the lungs when an individual is unable to breathe on their own. The ventilator prevents the accumulation of carbon dioxide so that the lungs don't collapse due to the low pressure. The use of artificial ventilation can be traced back to the seventeenth century. There are three ways of exchanging gases in the body: manual methods, mechanical ventilation, and neurostimulation.

<span class="mw-page-title-main">Capnography</span> Monitoring of the concentration of carbon dioxide in respiratory gases

Capnography is the monitoring of the concentration or partial pressure of carbon dioxide (CO
2) in the respiratory gases. Its main development has been as a monitoring tool for use during anesthesia and intensive care. It is usually presented as a graph of CO
2 (measured in kilopascals, "kPa" or millimeters of mercury, "mmHg") plotted against time, or, less commonly, but more usefully, expired volume (known as volumetric capnography). The plot may also show the inspired CO
2, which is of interest when rebreathing systems are being used. When the measurement is taken at the end of a breath (exhaling), it is called "end tidal" CO
2 (PETCO2).

Stridor is a high-pitched extra-thoracic breath sound resulting from turbulent air flow in the larynx or lower in the bronchial tree. It is different from a stertor which is a noise originating in the pharynx.

<span class="mw-page-title-main">Bag valve mask</span> Hand-held device to provide positive pressure ventilation

A bag valve mask (BVM), sometimes known by the proprietary name Ambu bag or generically as a manual resuscitator or "self-inflating bag", is a hand-held device commonly used to provide positive pressure ventilation to patients who are not breathing or not breathing adequately. The device is a required part of resuscitation kits for trained professionals in out-of-hospital settings (such as ambulance crews) and is also frequently used in hospitals as part of standard equipment found on a crash cart, in emergency rooms or other critical care settings. Underscoring the frequency and prominence of BVM use in the United States, the American Heart Association (AHA) Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiac Care recommend that "all healthcare providers should be familiar with the use of the bag-mask device." Manual resuscitators are also used within the hospital for temporary ventilation of patients dependent on mechanical ventilators when the mechanical ventilator needs to be examined for possible malfunction or when ventilator-dependent patients are transported within the hospital. Two principal types of manual resuscitators exist; one version is self-filling with air, although additional oxygen (O2) can be added but is not necessary for the device to function. The other principal type of manual resuscitator (flow-inflation) is heavily used in non-emergency applications in the operating room to ventilate patients during anesthesia induction and recovery.

Ventilator-associated pneumonia (VAP) is a type of lung infection that occurs in people who are on mechanical ventilation breathing machines in hospitals. As such, VAP typically affects critically ill persons that are in an intensive care unit (ICU) and have been on a mechanical ventilator for at least 48 hours. VAP is a major source of increased illness and death. Persons with VAP have increased lengths of ICU hospitalization and have up to a 20–30% death rate. The diagnosis of VAP varies among hospitals and providers but usually requires a new infiltrate on chest x-ray plus two or more other factors. These factors include temperatures of >38 °C or <36 °C, a white blood cell count of >12 × 109/ml, purulent secretions from the airways in the lung, and/or reduction in gas exchange.

High-frequency ventilation is a type of mechanical ventilation which utilizes a respiratory rate greater than four times the normal value and very small tidal volumes. High frequency ventilation is thought to reduce ventilator-associated lung injury (VALI), especially in the context of ARDS and acute lung injury. This is commonly referred to as lung protective ventilation. There are different types of high-frequency ventilation. Each type has its own unique advantages and disadvantages. The types of HFV are characterized by the delivery system and the type of exhalation phase.

<span class="mw-page-title-main">Tracheobronchial injury</span> Damage to the tracheobronchial tree

Tracheobronchial injury is damage to the tracheobronchial tree. It can result from blunt or penetrating trauma to the neck or chest, inhalation of harmful fumes or smoke, or aspiration of liquids or objects.

<span class="mw-page-title-main">Airway pressure release ventilation</span> Pressure control mode of mechanical ventilation

Airway pressure release ventilation (APRV) is a pressure control mode of mechanical ventilation that utilizes an inverse ratio ventilation strategy. APRV is an applied continuous positive airway pressure (CPAP) that at a set timed interval releases the applied pressure. Depending on the ventilator manufacturer, it may be referred to as BiVent. This is just as appropriate to use, since the only difference is that the term APRV is copyrighted.

Modes of mechanical ventilation are one of the most important aspects of the usage of mechanical ventilation. The mode refers to the method of inspiratory support. In general, mode selection is based on clinician familiarity and institutional preferences, since there is a paucity of evidence indicating that the mode affects clinical outcome. The most frequently used forms of volume-limited mechanical ventilation are intermittent mandatory ventilation (IMV) and continuous mandatory ventilation (CMV). There have been substantial changes in the nomenclature of mechanical ventilation over the years, but more recently it has become standardized by many respirology and pulmonology groups. Writing a mode is most proper in all capital letters with a dash between the control variable and the strategy.

Prone ventilation, sometimes called prone positioning or proning, is a method of mechanical ventilation with the patient lying face-down (prone). It improves oxygenation in most patients with acute respiratory distress syndrome (ARDS) and reduces mortality. The earliest trial investigating the benefits of prone ventilation occurred in 1976. Since that time, many meta-analyses and one randomized control trial, the PROSEVA trial, have shown an increase in patients' survival with the more severe versions of ARDS. There are many proposed mechanisms, but they are not fully delineated. The proposed utility of prone ventilation is that this position will improve lung mechanics, improve oxygenation, and increase survival. Although improved oxygenation has been shown in multiple studies, this position change's survival benefit is not as clear. Similar to the slow adoption of low tidal volume ventilation utilized in ARDS, many believe that the investigation into the benefits of prone ventilation will likely be ongoing in the future.

<span class="mw-page-title-main">Surgical airway management</span>

Surgical airway management is the medical procedure ensuring an open airway between a patient’s lungs and the outside world. Surgical methods for airway management rely on making a surgical incision below the glottis in order to achieve direct access to the lower respiratory tract, bypassing the upper respiratory tract. Surgical airway management is often performed as a last resort in cases where orotracheal and nasotracheal intubation are impossible or contraindicated. Surgical airway management is also used when a person will need a mechanical ventilator for a longer period. The surgical creation of a permanent opening in the larynx is referred to as laryngostomy. Surgical airway management is a primary consideration in anaesthesia, emergency medicine and intensive care medicine.

<span class="mw-page-title-main">Advanced airway management</span>

Advanced airway management is the subset of airway management that involves advanced training, skill, and invasiveness. It encompasses various techniques performed to create an open or patent airway – a clear path between a patient's lungs and the outside world.

<span class="mw-page-title-main">Pathophysiology of acute respiratory distress syndrome</span>

The pathophysiology of acute respiratory distress syndrome involves fluid accumulation in the lungs not explained by heart failure. It is typically provoked by an acute injury to the lungs that results in flooding of the lungs' microscopic air sacs responsible for the exchange of gases such as oxygen and carbon dioxide with capillaries in the lungs. Additional common findings in ARDS include partial collapse of the lungs (atelectasis) and low levels of oxygen in the blood (hypoxemia). The clinical syndrome is associated with pathological findings including pneumonia, eosinophilic pneumonia, cryptogenic organizing pneumonia, acute fibrinous organizing pneumonia, and diffuse alveolar damage (DAD). Of these, the pathology most commonly associated with ARDS is DAD, which is characterized by a diffuse inflammation of lung tissue. The triggering insult to the tissue usually results in an initial release of chemical signals and other inflammatory mediators secreted by local epithelial and endothelial cells.

References

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