Tidal volume

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TLCTotal lung capacity: the volume in the lungs at maximal inflation, the sum of VC and RV.
TVTidal volume: that volume of air moved into or out of the lungs during quiet breathing (TV indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation, the symbol TV or VT is used.)
RVResidual volume: the volume of air remaining in the lungs after a maximal exhalation
ERVExpiratory reserve volume: the maximal volume of air that can be exhaled from the end-expiratory position
IRVInspiratory reserve volume: the maximal volume that can be inhaled from the end-inspiratory level
ICInspiratory capacity: the sum of IRV and TV
IVCInspiratory vital capacity: the maximum volume of air inhaled from the point of maximum expiration
VCVital capacity: the volume of air breathed out after the deepest inhalation.
VTTidal volume: that volume of air moved into or out of the lungs during quiet breathing (VT indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation, the symbol TV or VT is used.)
FRCFunctional residual capacity: the volume in the lungs at the end-expiratory position
RV/TLC%Residual volume expressed as percent of TLC
VAAlveolar gas volume
VLActual volume of the lung including the volume of the conducting airway.
FVCForced vital capacity: the determination of the vital capacity from a maximally forced expiratory effort
FEVtForced expiratory volume (time): a generic term indicating the volume of air exhaled under forced conditions in the first t seconds
FEV1Volume that has been exhaled at the end of the first second of forced expiration
FEFxForced expiratory flow related to some portion of the FVC curve; modifiers refer to amount of FVC already exhaled
FEFmaxThe maximum instantaneous flow achieved during a FVC maneuver
FIFForced inspiratory flow: (Specific measurement of the forced inspiratory curve is denoted by nomenclature analogous to that for the forced expiratory curve. For example, maximum inspiratory flow is denoted FIFmax. Unless otherwise specified, volume qualifiers indicate the volume inspired from RV at the point of measurement.)
PEFPeak expiratory flow: The highest forced expiratory flow measured with a peak flow meter
MVVMaximal voluntary ventilation: volume of air expired in a specified period during repetitive maximal effort

Tidal volume (symbol VT or TV) is the volume of air moved into or out of the lungs in one breath. [1] In a healthy, young human adult, tidal volume is approximately 500 ml per inspiration at rest or 7 ml/kg of body mass. [2]


Mechanical ventilation

Tidal volume plays a significant role during mechanical ventilation to ensure adequate ventilation without causing trauma to the lungs. Tidal volume is measured in milliliters and ventilation volumes are estimated based on a patient's ideal body mass. Measurement of tidal volume can be affected (usually overestimated) by leaks in the breathing circuit or the introduction of additional gas, for example during the introduction of nebulized drugs.

Ventilator-induced lung injury such as Acute lung injury (ALI) /Acute Respiratory Distress Syndrome (ARDS) can be caused by ventilation with very large tidal volumes in normal lungs, as well as ventilation with moderate or small volumes in previously injured lungs, and research shows that the incidence of ALI increases with higher tidal volume settings in nonneurologically impaired patients. . [3] Similarly A 2018 systematic review by The Cochrane Collaboration provided evidence that low tidal volume ventilation reduced post operative pneumonia and reduced the requirement for both invasive and non invasive ventilation after surgery [4]

Initial settings of mechanical ventilation:

Patients without pre-existing lung disease

Protective lung ventilation strategies should be applied with VT 6ml/kg to 8ml/kg with RR = 12 to 20 and an average starting target minute ventilation of 7 L/min.[ citation needed ][ clarification needed ]

Patients with chronic obstructive lung disease

Protective lung volumes apply 6ml/kg to 8ml/kg with a rate high enough for proper alveolar ventilation but does not create or aggravate intrinsic Positive End-Expiry Pressure (PEEP).[ citation needed ][ clarification needed ]

Acute respiratory distress syndrome

Protective lung ventilation strategies apply. VT 6 to 8 ml/kg or as low as 5 ml/kg in severe cases. Permissive hypercapnia can be employed in an attempt to minimize aggressive ventilation leading to lung injury. Higher peeps are often required however not all ARDS patients require the same peep levels.[ clarification needed ] Patient should be started on 6 ml/kg and peep increased until plateau pressure is 30 cm H20 in most severe cases.[ citation needed ][ clarification needed ]

Related Research Articles

<span class="mw-page-title-main">Mechanical ventilation</span> Method to mechanically assist or replace spontaneous breathing

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.

<span class="mw-page-title-main">Extracorporeal membrane oxygenation</span> Technique of providing both cardiac and respiratory support

Extracorporeal membrane oxygenation (ECMO), also known as extracorporeal life support (ECLS), is an extracorporeal technique of providing prolonged cardiac and respiratory support to persons whose heart and lungs are unable to provide an adequate amount of oxygen, gas exchange or blood supply (perfusion) to sustain life. The technology for ECMO is largely derived from cardiopulmonary bypass, which provides shorter-term support with arrested native circulation. The device used is a membrane oxygenator, also known as an artificial lung.

<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.

<span class="mw-page-title-main">Liquid breathing</span> Respiration of oxygen-rich liquid by a normally air-breathing organism

Liquid breathing is a form of respiration in which a normally air-breathing organism breathes an oxygen-rich liquid (such as a perfluorocarbon), rather than breathing air, by selecting a liquid that can hold a large amount of oxygen and is capable of CO2 gas exchange.

<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.

Permissive hypercapnia is hypercapnia in respiratory insufficient patients in which oxygenation has become so difficult that the optimal mode of mechanical ventilation is not capable of exchanging enough carbon dioxide. Carbon dioxide is a gaseous product of the body's metabolism and is normally expelled through the lungs.

Positive end-expiratory pressure (PEEP) is the pressure in the lungs above atmospheric pressure that exists at the end of expiration. The two types of PEEP are extrinsic PEEP and intrinsic PEEP. Pressure that is applied or increased during an inspiration is termed pressure support.PEEP is a therapeutic parameter set in the ventilator, or a complication of mechanical ventilation with air trapping (auto-PEEP).

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.

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 contrast, ventilator-associated lung injury (VALI) exists if the cause cannot be proven. VALI is the appropriate term in most situations because it is virtually impossible to prove what actually caused the lung injury in the hospital.

Neurally adjusted ventilatory assist (NAVA) is a mode of mechanical ventilation. NAVA delivers assistance in proportion to and in synchrony with the patient's respiratory efforts, as reflected by an electrical signal. This signal represents the electrical activity of the diaphragm, the body's principal breathing muscle.

<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.

<span class="mw-page-title-main">Liquid ventilator</span> Medical device

A liquid ventilator is similar to a medical ventilator except that it should be able to ensure reliable total liquid ventilation with a breatheable liquid ·. Liquid ventilators are prototypes that may have been used for animal experimentations but experts recommend continued development of a liquid ventilator toward clinical applications.

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.

The rapid shallow breathing index (RSBI) or Yang Tobin index is a tool that is used in the weaning of mechanical ventilation on intensive care units. The RSBI is defined as the ratio of respiratory frequency to tidal volume (f/VT). People on a ventilator who cannot tolerate independent breathing tend to breathe rapidly and shallowly, and will therefore have a high RSBI. The index was introduced in 1991 by Karl Yang and Martin J. Tobin.

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 patient. Similar to continuous mandatory ventilation in parameters set for the patients pressures and volumes but distinct in its ability to support a patient by either supporting their own effort or providing support when patient effort is not sensed. IMV is frequently paired with additional strategies to improve weaning from ventilator support or to improve cardiovascular stability in patients who may need full life support.

Within the medical field of respiratory therapy, Open lung ventilation is a strategy that is utilized by several modes of mechanical ventilation to combine low tidal volume and applied PEEP to maximize recruitment of alveoli. The low tidal volume aims to minimize alveolar overdistention and the PEEP minimizes cyclic atelectasis. Working in tandem the effects from both decrease the risk of ventilator-associated lung injury.

Prone ventilation, sometimes called prone positioning or proning, refers to 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">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.

<span class="mw-page-title-main">Proning</span> Nursing technique

Proning or prone positioning is the placement of patients into a prone position so that they are lying on their front. This is used in the treatment of patients in intensive care with acute respiratory distress syndrome (ARDS). It has been especially tried and studied for patients on ventilators but, during the COVID-19 pandemic, it is being used for patients with oxygen masks and CPAP as an alternative to ventilation.

<span class="mw-page-title-main">Pendelluft</span>

Pendelluft refers to the movement of gas between two regions of the lung, usually between regions of differing compliance or airway resistance. Pendelluft is an important physiological concept to take into account during mechanical ventilation, particularly in patients with an open thorax, severe bronchospasm, or with heterogeneous lung compliance. It was first published as a physiological concept in 1956.


  1. Haddad, Moshe; Sharma, Sandeep (2021), "Physiology, Lung", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID   31424761 , retrieved 2021-03-17
  2. Beardsell, I et al: MCEM Part A:MCQs, page 33, Royal Society of Medicine Press, 2009
  3. Gajic, Ognjen; Saqib Dara; Jose Mendez; Abedola Adensanya; Emir Festic; Sean Caples; Rimki Rana; Jennifer StSauver; James Lymp; Bekele Afessa (2004). "Ventilator-associated lung injury in patients without acute lung injury at the onset of mechanical ventilation". Critical Care Medicine. 32 (9): 1817–1824. doi:10.1097/01.CCM.0000133019.52531.30. PMID   15343007. S2CID   6386675.
  4. Guay, Joanne; Ochroch, Edward A; Kopp, Sandra (2018-07-09). "Intraoperative use of low volume ventilation to decrease postoperative mortality, mechanical ventilation, lengths of stay and lung injury in adults without acute lung injury". Cochrane Database of Systematic Reviews. 7 (10): CD011151. doi:10.1002/14651858.cd011151.pub3. ISSN   1465-1858. PMC   6513630 . PMID   29985541.