Mechanical ventilation, assisted ventilation or
intermittent mandatory ventilation Intermittent Mandatory Ventilation (IMV) refers to any mode of mechanical ventilation where a regular series of breaths are scheduled but the ventilator senses patient effort and reschedules mandatory breaths based on the calculated need of the pati ...
(IMV), is the
medical
Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care practic ...
term for using a machine called a
ventilator
A ventilator is a piece of medical technology that provides mechanical ventilation by moving breathable air into and out of the lungs, to deliver breaths to a patient who is physically unable to breathe, or breathing insufficiently. Ventilators ...
to fully or partially provide
artificial ventilation
Artificial ventilation (also called artificial respiration) is a means of assisting or stimulating respiration, a metabolic process referring to the overall exchange of gases in the body by pulmonary ventilation, external respiration, and interna ...
. 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
220px, Intensive care unit
An intensive care unit (ICU), also known as an intensive therapy unit or intensive treatment unit (ITU) or critical care unit (CCU), is a special department of a hospital or health care facility that provides intensiv ...
.
Mechanical ventilation is termed invasive if it involves an instrument to create an airway that is placed inside the
trachea
The trachea, also known as the windpipe, is a Cartilage, cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends ...
. This is done through an
endotracheal tube
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.
Many different types of tracheal tubes are a ...
or nasotracheal tube.
For
non-invasive ventilation
Non-invasive ventilation (NIV) is the use of breathing support administered through a face mask, nasal mask, or a helmet. Air, usually with added oxygen, is given through the mask under positive pressure; generally the amount of pressure is alter ...
in people who are conscious, face or nasal masks are used.
The two main types of mechanical ventilation include
positive pressure ventilation
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 pref ...
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
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 pref ...
, and their nomenclature has been revised over the decades as the technology has continually developed.
History
![Poumon artificiel](https://upload.wikimedia.org/wikipedia/commons/5/56/Poumon_artificiel.jpg)
The Greek physician
Galen
Aelius Galenus or Claudius Galenus ( el, Κλαύδιος Γαληνός; September 129 – c. AD 216), often Anglicized as Galen () or Galen of Pergamon, was a Greek physician, surgeon and philosopher in the Roman Empire. Considered to be one of ...
may have been the first to describe mechanical ventilation: "If you take a dead animal and blow air through its larynx
hrough a reed you will fill its bronchi and watch its lungs attain the greatest distention." In the 1600s,
Robert Hooke
Robert Hooke FRS (; 18 July 16353 March 1703) was an English polymath active as a scientist, natural philosopher and architect, who is credited to be one of two scientists to discover microorganisms in 1665 using a compound microscope that ...
conducted experiments on dogs to demonstrate this concept.
Vesalius
Andreas Vesalius (Latinized from Andries van Wezel) () was a 16th-century anatomist, physician, and author of one of the most influential books on human anatomy, ''De Humani Corporis Fabrica Libri Septem'' (''On the fabric of the human body'' '' ...
too describes ventilation by inserting a reed or cane into the
trachea
The trachea, also known as the windpipe, is a Cartilage, cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends ...
of animals.
These experiments predate the discovery of oxygen and its role in respiration. In 1908,
George Poe
George Poe, Jr. (May 8, 1846 – February 3, 1914) was a pioneer of mechanical ventilation of asphyxiation victims. He was the first person to manufacture nitrous oxide for commercial use in his Trenton, New Jersey company.
Birth
He was t ...
demonstrated his mechanical respirator by
asphyxiating
Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can i ...
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
An iron lung is a type of negative pressure ventilator (NPV), a mechanical respirator which encloses most of a person's body, and varies the air pressure in the enclosed space, to stimulate breathing.Shneerson, Dr. John M., Newmarket General ...
, 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 Intermittent Mandatory Ventilation (IMV) refers to any mode of mechanical ventilation where a regular series of breaths are scheduled but the ventilator senses patient effort and reschedules mandatory breaths based on the calculated need of the pati ...
was introduced as well as synchronized intermittent mandatory ventilation. These styles of ventilation had control breaths that patients could breath between.
Uses
![Respiratory therapist](https://upload.wikimedia.org/wikipedia/commons/a/a7/Respiratory_therapist.jpg)
Mechanical ventilation is indicated when a patient's spontaneous
breath
Breathing (or ventilation) is the process of moving air into and from the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxygen.
All aerobic creatures need oxygen for cellular ...
ing 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:
* Surgical procedures
* Acute lung injury, including
acute respiratory distress syndrome
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 colo ...
(ARDS), trauma, or
COVID-19
Coronavirus disease 2019 (COVID-19) is a contagious disease caused by a virus, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The first known case was COVID-19 pandemic in Hubei, identified in Wuhan, China, in December ...
*
Pneumonia
Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity ...
* Pulmonary hemorrhage
*
Apnea
Apnea, BrE: apnoea, is the temporal cessation of breathing. During apnea, there is no movement of the muscles of inhalation, and the volume of the lungs initially remains unchanged. Depending on how blocked the airways are ( patency), there ...
with respiratory arrest
*
Hypoxemia
Hypoxemia is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood. Hypoxemia has many causes, and often causes hypoxia as the blood is not supplying enough oxygen to the tissues of the body ...
*
Acute severe asthma
Acute severe asthma, also known as status asthmaticus, is an acute exacerbation of asthma that does not respond to standard treatments of bronchodilators (inhalers) and corticosteroids. Asthma is caused by multiple genes, some having protective ef ...
requiring intubation
* Obstruction, such as a
tumor
A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
* Acid/base derangements such as
respiratory acidosis
Respiratory acidosis is a state in which decreased ventilation (hypoventilation) increases the concentration of carbon dioxide in the blood and decreases the blood's pH (a condition generally called acidosis).
Carbon dioxide is produced continuou ...
* Neurological diseases such as
muscular dystrophy
Muscular dystrophies (MD) are a genetically and clinically heterogeneous group of rare neuromuscular diseases that cause progressive weakness and breakdown of skeletal muscles over time. The disorders differ as to which muscles are primarily affe ...
,
amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most comm ...
(ALS),
Guillain–Barré syndrome
Guillain–Barré syndrome (GBS) is a rapid-onset muscle weakness caused by the immune system damaging the peripheral nervous system. Typically, both sides of the body are involved, and the initial symptoms are changes in sensation or pain often ...
,
myasthenia gravis
Myasthenia gravis (MG) is a long-term neuromuscular junction disease that leads to varying degrees of skeletal muscle weakness. The most commonly affected muscles are those of the eyes, face, and swallowing. It can result in double vision, dro ...
, etc.
* Newborn premature infants with
neonatal respiratory distress syndrome
Infantile respiratory distress syndrome (IRDS), also called respiratory distress syndrome of newborn, or increasingly surfactant deficiency disorder (SDD), and previously called hyaline membrane disease (HMD), is a syndrome in premature infants c ...
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
Barotrauma is physical damage to body tissues caused by a difference in pressure between a gas space inside, or contact with, the body and the surrounding gas or liquid. The initial damage is usually due to over-stretching the tissues in tensio ...
.
Others include
pneumothorax
A pneumothorax is an abnormal collection of air in the pleural space between the lung and the chest wall. Symptoms typically include sudden onset of sharp, one-sided chest pain and shortness of breath. In a minority of cases, a one-way valve ...
,
subcutaneous emphysema
Subcutaneous emphysema (SCE, SE) occurs when gas or air accumulates and seeps under the skin, where normally no gas should be present. ''Subcutaneous'' refers to the subcutaneous tissue, and ''emphysema'' refers to trapped air pockets resembling t ...
,
pneumomediastinum
Pneumomediastinum (from Greek ''pneuma'' – "air", also known as mediastinal emphysema) is pneumatosis (abnormal presence of air or other gas) in the mediastinum, the central part of the chest cavity. First described in 1819 by René Laennec, th ...
, and
pneumoperitoneum
Pneumoperitoneum is pneumatosis (abnormal presence of air or other gas) in the peritoneal cavity, a potential space within the abdominal cavity. The most common cause is a perforated abdominal organ, generally from a perforated peptic ulcer, althou ...
.
Another well-documented complication is
ventilator-associated lung injury
Ventilator-associated lung injury (VALI) is an acute lung injury that develops during mechanical ventilation and is termed ventilator-induced lung injury (VILI) if it can be proven that the mechanical ventilation caused the acute lung injury. In c ...
which presents as acute respiratory distress syndrome.
Other complications include diaphragm atrophy,
decreased cardiac output, 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.
In many healthcare systems, prolonged ventilation as part of
intensive care
Intensive care medicine, also called critical care medicine, is a medical specialty that deals with seriously or critically ill patients who have, are at risk of, or are recovering from conditions that may be life-threatening. It includes pro ...
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.
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
Opioid use disorder (OUD) is a substance use disorder characterized by cravings for opioids, continued use despite physical and/or psychological deterioration, increased tolerance with use, and withdrawal symptoms after discontinuing opioids. Op ...
, and opioid tolerance.
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.
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
Martin John Tobin (born 23 April 1951) is an Irish-American critical care physician, pulmonologist, and academic who is a recognised expert in acute respiratory failure, mechanical ventilation, and neuromuscular control of breathing.
Accordin ...
of
Loyola University Medical Center
Loyola Medicine, also known as Loyola University Health System, is a quaternary-care system with a main medical center campus in the western suburbs of Chicago, in the U.S. state of Illinois. The medical center campus is located in Maywood, w ...
) 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.
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.
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.
Physiology
The function of the lungs is to provide gas exchange via oxygenation and ventilation. This phenomenon of
respiration
Respiration may refer to:
Biology
* Cellular respiration, the process in which nutrients are converted into useful energy in a cell
** Anaerobic respiration, cellular respiration without oxygen
** Maintenance respiration, the amount of cellul ...
involves the physiologic concepts of air flow, tidal volume, compliance, resistance, and
dead space
''Dead Space'' is a science fiction/horror fiction, horror media franchise created by Glen Schofield and Michael Condrey, developed by Visceral Games, and published and owned by Electronic Arts. The franchise's chronology is not presented in a lin ...
.
Other relevant concepts include alveolar ventilation, arterial PaCO2, alveolar volume, and
FiO2
Fraction of inspired oxygen (''FI''O2), corrected denoted with a capital "I", is the molar or volumetric fraction of oxygen in the inhaled gas. Medical patients experiencing difficulty breathing are provided with oxygen-enriched air, which means a ...
. 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.
![Endotracheal Tube](https://upload.wikimedia.org/wikipedia/commons/4/4f/Endotracheal_Tube.png)
Due to the anatomy of the human
pharynx
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struc ...
,
larynx
The larynx (), commonly called the voice box, is an organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal inlet is about ...
, and
esophagus
The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...
and the circumstances for which ventilation is needed, additional measures are required to secure the
airway
The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa.
Air is breathed in through the nose to th ...
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
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.
Many different types of tracheal tubes are a ...
, inserted through the natural openings of mouth or nose, or a
tracheostomy
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 Vertebrate trachea, trache ...
inserted through an artificial opening in the neck. In other circumstances simple
airway maneuvers, an
oropharyngeal airway
An oropharyngeal airway (also known as an oral airway, OPA or Guedel pattern airway) is a medical device called an ''airway adjunct'' used in airway management to maintain or open a patient's airway. It does this by preventing the tongue from cover ...
or
laryngeal mask airway
A laryngeal mask airway (LMA), also known as laryngeal mask, is a medical device that keeps a patient's airway open during anaesthesia or while they are unconscious. It is a type of supraglottic airway device. They are most commonly used by anae ...
may be employed. If
non-invasive ventilation
Non-invasive ventilation (NIV) is the use of breathing support administered through a face mask, nasal mask, or a helmet. Air, usually with added oxygen, is given through the mask under positive pressure; generally the amount of pressure is alter ...
or
negative-pressure ventilation is used, then an
airway adjunct is not needed.
Pain medicine such as
opioid
Opioids are substances that act on opioid receptors to produce morphine-like effects. Medically they are primarily used for pain relief, including anesthesia. Other medical uses include suppression of diarrhea, replacement therapy for opioid us ...
s 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
Clonidine, sold under the brand name Catapres among others, is an α2-adrenergic agonist medication used to treat high blood pressure, ADHD, drug withdrawal ( alcohol, opioids, or nicotine), menopausal flushing, diarrhea, spasticity, and c ...
is safe or effective to be used as a
sedative
A sedative or tranquilliser is a substance that induces sedation by reducing irritability or excitement. They are CNS depressants and interact with brain activity causing its deceleration. Various kinds of sedatives can be distinguished, but t ...
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 Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit.
Uses in anatomy and zoology
* Pulmonary alveolus, an air sac in the lungs
** Alveolar cell or pneumocyte
** Alveolar duct
** Alveolar macrophage
* ...
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
A pneumothorax is an abnormal collection of air in the pleural space between the lung and the chest wall. Symptoms typically include sudden onset of sharp, one-sided chest pain and shortness of breath. In a minority of cases, a one-way valve ...
, and should be treated accordingly. If such complications are not present, other causes must be sought after, and
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 ...
(PEEP) should be used to treat this intrapulmonary shunt.
Other such causes of a shunt include:
* alveolar collapse from major
atelectasis
Atelectasis is the collapse or closure of a lung resulting in reduced or absent gas exchange. It is usually unilateral, affecting part or all of one lung. It is a condition where the alveoli are deflated down to little or no volume, as distinct ...
* alveolar collection of material other than gas, such as pus from
pneumonia
Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity ...
, water and protein from
acute respiratory distress syndrome
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 colo ...
, water from
congestive heart failure
Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...
, or blood from hemorrhage
Technique
Modes
Mechanical ventilation utilizes several separate systems for ventilation referred to as the mode. Modes come in many different delivery concepts but all positive pressure ventilators modes fall into one of two categories; volume-cycled or pressure-cycled.
In general, the selection of which mode of mechanical ventilation to use for a given patient is based on the familiarity of
clinician
A clinician is a health care professional typically employed at a skilled nursing facility or clinic. Clinicians work directly with patients rather than in a laboratory or as a researcher. A clinician may diagnose, treat, and otherwise care for pa ...
s with modes and the equipment availability at a particular institution.
Types of Ventilation
![Engström_respirator_Model_150_-_Sweden_-_1955-1970](https://upload.wikimedia.org/wikipedia/commons/d/d7/Engstr%C3%B6m_respirator_Model_150_-_Sweden_-_1955-1970.jpg)
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 and the United States and was the beginning of modern ventilation therapy. Positive pressure through manual supply of 50% oxygen through a
tracheostomy
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 Vertebrate trachea, trache ...
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.
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
Tidal volume (symbol VT or TV) is the volume of air moved into or out of the lungs during a normal breath. In a healthy, young human adult, tidal volume is approximately 500 ml per inspiration or 7 ml/kg of body mass.
Mechanical vent ...
— the breath-out through passive exhalation.
Negative pressure
Negative pressure mechanical ventilators are produced in small, field-type and larger formats. The prominent design of the smaller devices is known as the
cuirass
A cuirass (; french: cuirasse, la, coriaceus) is a piece of armour that covers the torso, formed of one or more pieces of metal or other rigid material. The word probably originates from the original material, leather, from the French '' cuira ...
, 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
Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. They are easily work ...
shells with multiple seals, and a high-pressure oscillation pump in order to carry out
biphasic cuirass ventilation
An iron lung is a type of negative pressure ventilator (NPV), a mechanical respirator which encloses most of a person's body, and varies the air pressure in the enclosed space, to stimulate breathing.Shneerson, Dr. John M., Newmarket Genera ...
.
Its main use has been in patients with neuromuscular disorders that have some residual muscular function. The latter, larger formats are in use, notably with the polio wing hospitals in
England
England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...
such as
St Thomas' Hospital
St Thomas' Hospital is a large NHS teaching hospital in Central London, England. It is one of the institutions that compose the King's Health Partners, an academic health science centre. Administratively part of the Guy's and St Thomas' NHS Foun ...
in London and the
John Radcliffe in
Oxford
Oxford () is a city in England. It is the county town and only city of Oxfordshire. In 2020, its population was estimated at 151,584. It is north-west of London, south-east of Birmingham and north-east of Bristol. The city is home to the ...
.
The larger units have their origin in the
iron lung
An iron lung is a type of negative pressure ventilator (NPV), a mechanical respirator which encloses most of a person's body, and varies the air pressure in the enclosed space, to stimulate breathing.Shneerson, Dr. John M., Newmarket General ...
, 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.
It was refined and used in the 20th century largely as a result of the
polio
Poliomyelitis, commonly shortened to polio, is an infectious disease caused by the poliovirus. Approximately 70% of cases are asymptomatic; mild symptoms which can occur include sore throat and fever; in a proportion of cases more severe s ...
epidemic
An epidemic (from Ancient Greek, Greek ἐπί ''epi'' "upon or above" and δῆμος ''demos'' "people") is the rapid spread of disease to a large number of patients among a given population within an area in a short period of time.
Epidemics ...
that struck the world in the 1940s. The machine is, in effect, a large elongated
tank
A tank is an armoured fighting vehicle intended as a primary offensive weapon in front-line ground combat. Tank designs are a balance of heavy firepower, strong armour, and good battlefield mobility provided by tracks and a powerful engin ...
, which encases the patient up to the neck.
The neck is sealed with a rubber
gasket
Some seals and gaskets
A gasket is a mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression. It is a deformable material that is used to c ...
so that the patient's face (and airway) are exposed to the room air. While the exchange of
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
and
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
between the bloodstream and the pulmonary airspace works by
diffusion
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
and requires no external work, air must be moved into and out of the
lungs
The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of th ...
to make it available to the
gas exchange
Gas exchange is the physical process by which gases move passively by Diffusion#Diffusion vs. bulk flow, diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liqui ...
process. In spontaneous breathing, a negative pressure is created in the
pleural cavity
The pleural cavity, pleural space, or interpleural space is the potential space between the pleurae of the pleural sac that surrounds each lung. A small amount of serous pleural fluid is maintained in the pleural cavity to enable lubrication bet ...
by the muscles of respiration, and the resulting gradient between the
atmospheric pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, 7 ...
and the pressure inside the
thorax
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...
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.
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.
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.
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
Exsufflation is a strongly forced expiration of air.
In medicine, airway secretions can be cleared with manual and mechanical exsufflation. Mechanical insufflation-exsufflation devices (also known as In-Exsufflator, Cofflator, and cough machine) ...
. The first such apparatus was the
Bragg-Paul Pulsator
The Bragg-Paul Pulsator, also known as the Bragg-Paul respirator, was a non-invasive medical ventilator invented by William Henry Bragg and designed by Robert W. Paul in 1933 for patients unable to breathe for themselves due to illness.
It was the ...
.
The name of one such device, the Pneumobelt made by
Puritan Bennett
Puritan Bennett has been a provider of respiratory products since 1913 originally as a medical gas supplier. In addition to critical care ventilation, Puritan Bennett provided medical devices for patients outside of the acute care environment. I ...
has to a degree become a
generic name for the type.
Oscillator
![Oscillator 3100A](https://upload.wikimedia.org/wikipedia/commons/8/80/Oscillator_3100A.jpg)
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.
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.
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%.
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
Functional residual capacity (FRC) is the volume of air present in the lungs at the end of passive expiration. At FRC, the opposing elastic recoil forces of the lungs and chest wall are in equilibrium and there is no exertion by the diaphragm ...
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
Ventilators come in many different styles and method of giving a breath to sustain life.
There are manual ventilators such as
bag valve mask
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 breathin ...
s 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.
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:
#Transport ventilators—These ventilators are small and more rugged, and can be powered pneumatically or via AC or DC power sources.
#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.
#Neonatal ventilators (bubble CPAP, HFJV, HFOV)—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.
#
Positive airway pressure
Positive airway pressure (PAP) is a mode of respiratory ventilation used in the treatment of sleep apnea. PAP ventilation is also commonly used for those who are critically ill in hospital with respiratory failure, in newborn infants (neonates), ...
ventilators (PAP) — These ventilators are specifically designed for
non-invasive ventilation
Non-invasive ventilation (NIV) is the use of breathing support administered through a face mask, nasal mask, or a helmet. Air, usually with added oxygen, is given through the mask under positive pressure; generally the amount of pressure is alter ...
. This includes ventilators for use at home for treatment of chronic conditions such as
sleep apnea
Sleep apnea, also spelled sleep apnoea, is a sleep disorder in which pauses in breathing or periods of shallow breathing during sleep occur more often than normal. Each pause can last for a few seconds to a few minutes and they happen many times ...
or
COPD
Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce mu ...
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
Peep, Peeps, or PEEP may refer to:
People
*Peep (given name), Estonian masculine given name
*Lil Peep (1996–2017), American singer and rapper
*Helend Peep (1910–2007), Estonian actor
*Viljar Peep (born 1969), Estonian historian and civil serv ...
) 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:
*
Face mask
The face is the front of an animal's head that features the eyes, nose and mouth, and through which animals express many of their emotions. The face is crucial for human Personal identity, identity, and damage such as scarring or developmental d ...
— 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
An oropharyngeal airway (also known as an oral airway, OPA or Guedel pattern airway) is a medical device called an ''airway adjunct'' used in airway management to maintain or open a patient's airway. It does this by preventing the tongue from cover ...
''. These are designed to provide a passage of air to the
pharynx
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struc ...
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
Non-invasive ventilation (NIV) is the use of breathing support administered through a face mask, nasal mask, or a helmet. Air, usually with added oxygen, is given through the mask under positive pressure; generally the amount of pressure is alter ...
in conscious patients. A full-face mask does not, however, provide protection against aspiration.
Non-invasive ventilation
Non-invasive ventilation (NIV) is the use of breathing support administered through a face mask, nasal mask, or a helmet. Air, usually with added oxygen, is given through the mask under positive pressure; generally the amount of pressure is alter ...
can be considered for epidemics of
COVID-19
Coronavirus disease 2019 (COVID-19) is a contagious disease caused by a virus, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The first known case was COVID-19 pandemic in Hubei, identified in Wuhan, China, in December ...
where sufficient invasive ventilation capacity is not available (or in some milder cases), but pressurized protection suits for caregivers are recommended due to the risks of poorly fitting masks emitting contaminating aerosols.
*
Tracheal intubation
Tracheal intubation, usually simply referred to as intubation, is the placement of a flexible plastic catheter, tube into the vertebrate trachea, trachea (windpipe) to maintain an open airway or to serve as a conduit through which to administer ce ...
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
The trachea, also known as the windpipe, is a Cartilage, cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends ...
. 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
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struct ...
or
oropharynx
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struct ...
and
subglottic stenosis.
*
Supraglottic 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 cl ...
— a supraglottic airway (SGA) is any airway device that is seated above and outside the trachea, as an alternative to endotracheal intubation. Most devices work via masks or cuffs that inflate to isolate the trachea for oxygen delivery. Newer devices feature esophageal ports for suctioning or ports for tube exchange to allow intubation. Supraglottic airways differ primarily from tracheal intubation in that they do not prevent aspiration. After the introduction of the
laryngeal mask airway
A laryngeal mask airway (LMA), also known as laryngeal mask, is a medical device that keeps a patient's airway open during anaesthesia or while they are unconscious. It is a type of supraglottic airway device. They are most commonly used by anae ...
(LMA) in 1998, supraglottic airway devices have become mainstream in both elective and emergency anesthesia. There are many types of SGAs available including the
esophageal-tracheal combitube (ETC),
laryngeal tube
The laryngeal tube (also known as the King LT)
, ''University of Toronto, Department of Anesthesia'' Website retrieved ...
(LT), and the obsolete esophageal obturator airway (EOA).
*
Cricothyrotomy
A cricothyrotomy (also called cricothyroidotomy) is an incision made through the skin and cricothyroid membrane to establish a patent airway during certain life-threatening situations, such as airway obstruction by a foreign body, angioedema, or ...
— Patients requiring emergency airway management, in whom tracheal intubation has been unsuccessful, may require an airway inserted through a surgical opening in the
cricothyroid membrane
The cricothyroid ligament (also known as the cricothyroid membrane or cricovocal membrane) is a ligament in the neck. It connects the cricoid cartilage to the thyroid cartilage. It prevents these cartilages from moving too far apart. It is cut dur ...
. This is similar to a
tracheostomy
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 Vertebrate trachea, trache ...
but a
cricothyrotomy
A cricothyrotomy (also called cricothyroidotomy) is an incision made through the skin and cricothyroid membrane to establish a patent airway during certain life-threatening situations, such as airway obstruction by a foreign body, angioedema, or ...
is reserved for emergency access.
*
Tracheostomy
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 Vertebrate trachea, trache ...
— 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
The trachea, also known as the windpipe, is a Cartilage, cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends ...
. 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 expected to be difficult to wean from mechanical ventilation, i.e., patients with 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.
See also
*
* , inventor of the pulmoventilateur
References
External links
*, article on mechanical ventilation along with technical information.
International Ventilator Users Network (IVUN) Resource of information for users of home mechanical ventilation.
''Mechanical Ventilation,''(detailed, illustrated slideshow presentation), by Amirali Nader, MD FCCP, Critical Care Medicine, Suburban Hospital,
Johns Hopkins Medicine
The Johns Hopkins University School of Medicine (JHUSOM) is the medical school of Johns Hopkins University, a private research university in Baltimore, Maryland. Founded in 1893, the School of Medicine shares a campus with the Johns Hopkins Hospi ...
.
{{DEFAULTSORT:Mechanical Ventilation
Emergency medicine
Intensive care medicine
Emergency medical services
Respiratory system procedures
Respiratory therapy