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 lung volume representing the normal volume of air displaced between[ clarification needed ] normal inhalation and exhalation when extra effort is not applied. In a healthy, young human adult, tidal volume is approximately 500 mL per inspiration or 7 mL/kg of body mass. [1]


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 ALI/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. [2] . 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 [3]

Initial settings of mechanical ventilation:

For patient without preexisting 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.

For 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 peep

Acute respiratory distress syndrome

Protective Lung Ventilation Strategies apply. VT 6 to 8 ml/kg or as low as 5ml/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 same peep levels. Patient should be started on 6 ml/kg and peep increased till plateau pressure is 30 cmH20 in most severe cases.

Related Research Articles

Respiratory failure 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 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 either acute or chronic. The definition of respiratory failure in clinical trials usually includes increased respiratory rate, abnormal blood gases, and evidence of increased work of breathing. Respiratory failure causes an altered mental status due to ischemia in the brain.

Mechanical ventilation, or assisted ventilation, sometimes abbreviated as IMV, is the medical term for artificial ventilation where mechanical means are used to assist or replace spontaneous breathing. This may involve a machine called a ventilator, or the breathing may be assisted manually by a suitably qualified professional, such as an anesthesiologist, Registered Nurse (RN), paramedic, or in some parts of the United States, by a respiratory therapist (RT), by compressing a bag valve mask device.

Fluid replacement medical practice of replenishing bodily fluid lost

Fluid replacement or fluid resuscitation is the medical practice of replenishing bodily fluid lost through sweating, bleeding, fluid shifts or other pathologic processes. Fluids can be replaced with oral rehydration therapy (drinking), intravenous therapy, rectally such as with a Murphy drip, or by hypodermoclysis, the direct injection of fluid into the subcutaneous tissue. Fluids administered by the oral and hypodermic routes are absorbed more slowly than those given intravenously.

Barotrauma Injury caused by pressure

Barotrauma is physical damage to body tissues caused by a difference in pressure between a gas space inside, or in contact with, the body, and the surrounding gas or fluid. The initial damage is usually due to over-stretching the tissues in tension or shear, either directly by expansion of the gas in the closed space or by pressure difference hydrostatically transmitted through the tissue. Tissue rupture may be complicated by the introduction of gas into the local tissue or circulation through the initial trauma site, which can cause blockage of circulation at distant sites or interfere with normal function of an organ by its presence.

Acute respiratory distress syndrome 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, rapid breathing, and bluish skin coloration. For those who survive, a decreased quality of life is common.

Liquid breathing is a form of respiration in which a normally air-breathing organism breathes an oxygen-rich liquid, rather than breathing air.

Bag valve mask 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.

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.

The Surviving Sepsis Campaign (SSC) is a global initiative to bring together professional organizations in reducing mortality from sepsis. The purpose of the SSC is to create an international collaborative effort to improve the treatment of sepsis and reduce the high mortality rate associated with the condition. The Surviving Sepsis Campaign and the Institute for Healthcare Improvement have teamed up to achieve a 25 percent reduction in sepsis mortality by 2009. The guidelines were last updated in 2016.

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.

Airway pressure release ventilation 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.

Liquid ventilator

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.

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.

Inverse ratio ventilation (IRV) is not necessarily a mode of mechanical ventilation though it may be referred to as such. IRV is a strategy of ventilating the lungs in such a way that the amount of time the lungs are in inhalation is greater than the amount of time they are in exhalation, allowing for a constant inflation of the lungs, ensuring they remain "recruited". The primary goal for IRV is improved oxygenation by forcing inspiratory time to be greater than expiratory time increasing the mean airway pressure and potentially improving oxygenation. Normal I:E ratio is 5:6, so forcing the I:E to be 2:1, 3:1, 4:1, is the source of the term for the strategy.

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.

Pathophysiology of acute respiratory distress syndrome

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.

Proning Nursing technique

Proning or prone positioning is the placement of patients into a prone position so that they are lying on their stomach. 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.


  1. Beardsell, I et al: MCEM Part A:MCQs, page 33, Royal Society of Medicine Press, 2009
  2. 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.
  3. 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: CD011151. doi:10.1002/14651858.cd011151.pub3. ISSN   1465-1858. PMC   6513630 . PMID   29985541.