Intermittent mandatory ventilation

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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.


Synchronized intermittent mechanical ventilation (SIMV)

Synchronized Intermittent Mechanical Ventilation is a variation of IMV, in which the ventilator breaths are synchronized with patient inspiratory effort. [1] [2] SIMV, with and without pressure support has not been shown to have any advantages over continuous mandatory ventilation (CMV) in terms of mortality [3] or weaning success, [4] and has been shown to result in longer weaning times when compared to t-piece trials or gradual reductions in pressure support. [5] [6] [7] Some studies have shown an increase in patient work of breathing when switched from CMV to SIMV, [8] [9] and others [10] have demonstrated potential detrimental effects of SIMV on respiratory muscles and respiratory drive.

Mandatory minute ventilation (MMV)

Mandatory minute ventilation is a mode which requires the operator to determine what the appropriate minute ventilation for the patient should be, and the ventilator then monitors the patient's ability to generate this volume every 7.5 seconds. If the calculation suggests the volume target will not be met, SIMV breaths are delivered at the targeted volume to achieve the desired minute ventilation. [11] Allows spontaneous breathing with automatic adjustments of mandatory ventilation to the meet the patient’s preset minimum minute volume requirement. If the patient maintains the minute volume settings for VT x f, no mandatory breaths are delivered. If the patient's minute volume is insufficient, mandatory delivery of the preset tidal volume will occur until the minute volume is achieved. The method for monitoring whether or not the patient is meeting the required minute ventilation (VE) is different per ventilator brand and model, but generally there is a window of time being monitored and a smaller window being checked against that larger window (i.e., in the Dräger Evita® line of mechanical ventilators there is a moving 20-second window and every 7 seconds the current tidal volume and rate are measured against to make a decision for if a mechanical breath is needed to maintain the minute ventilation). MMV is the most optimal mode for weaning in neonatal and pediatric populations and has been shown to reduce long term complications related to mechanical ventilation. [11]

Proportional assist ventilation (PAV)

Proportional assist ventilation is a mode in which the ventilator guarantees the percentage of work regardless of changes in pulmonary compliance and resistance. [12] The ventilator varies the tidal volume and pressure based on the patients work of breathing, the amount it delivers is proportional to the percentage of assistance it is set to give.

Adaptive support ventilation (ASV)

Adaptive Support Ventilation is a positive pressure mode of mechanical ventilation that is closed-loop controlled. In this mode, the clinician enters patient ideal body weight and desired level of ventilation in percent of predicted alveolar ventilation and the ventilator then applies inspiratory pressures at a rate which leads to minimal work of breathing. The equation used to calculate this minimal work was derived from the work of Otis [13] and published and discussed in Grodins and Yamashiro as early as 1977. [14] In the ASV mode, every breath is synchronized with patient effort if such an effort exists, and otherwise, full mechanical ventilation is provided to the patient. Since the first implementation, ASV has undergone a number of refinements and is available on different ventilator brands under different names.

The invention of ASV is claimed by two competing groups, [15] published as scientific article by one group [16] and disclosed as one of the embodiments of US Patent No. 4986268. [17] In this invention, the control algorithm computes the optimal rate of respiration to minimize the work rate of breathing. The rationale is to make the patient's breathing pattern comfortable and natural within safe limits, and thereby stimulate spontaneous breathing and reduce the weaning time.

See also

Related Research Articles

Mechanical ventilation, assisted ventilation or intermittent mandatory ventilation (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 other first responder, or in some parts of the United States, by a respiratory therapist (RT), by compressing a bag valve mask device.

Respiratory arrest

Respiratory arrest is caused by apnea or respiratory dysfunction severe enough 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 damage vital organs especially the brain, possibly permanently. 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.

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.

Dual-control modes of ventilation

Dual-control modes of ventilation are auto-regulated pressure-controlled modes of mechanical ventilation with a user-selected tidal volume target. The ventilator adjusts the pressure limit of the next breath as necessary according to the previous breath's measured exhaled tidal volume. Peak airway pressure varies from breath to breath according to changes in the patient's airway resistance and lung compliance.

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.

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.

Pressure support ventilation (PSV), also known as pressure support, is a spontaneous mode of ventilation. The patient initiates every breath and the ventilator delivers support with the preset pressure value. With support from the ventilator, the patient also regulates his own respiratory rate and tidal volume.

Pressure control (PC) is a mode of mechanical ventilation alone and a variable within other modes of mechanical ventilation. Pressure control is used to regulate pressures applied during mechanical ventilation. Air delivered into the patients lungs (breaths) are currently regulated by Volume Control or Pressure Control. In pressure controlled breaths a tidal volume achieved is based on how much volume can be delivered before the pressure control limit is reached.

Airway pressure release 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.

The rapid shallow breathing index (RSBI) 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.

Continuous mandatory ventilation (CMV) is a mode of mechanical ventilation in which breaths are delivered based on set variables. Still used in the operating room, in previous nomenclature CMV referred to "controlled mechanical ventilation", a mode of ventilation characterized by a ventilator that makes no effort to sense patient breathing effort. In continuous mandatory ventilation, the ventilator can be triggered either by the patient or mechanically by the ventilator. The ventilator is set to deliver a breath according to parameters selected by the operator. "Controlled mechanical ventilation" is an outdated expansion for "CMV"; "continuous mandatory ventilation" is now accepted standard nomenclature of mechanical ventilation. CMV today can assist or control dynamically, depending on transient presence or absence of spontaneous breathing effort. Thus, today's CMV would have been called ACV in older nomenclature, and the original form of CMV is a thing of the past. But despite continual technological improvement over the past half century, CMV sometimes may still be uncomfortable for the patient.

Many terms are used in mechanical ventilation, some are specific to brand, model, trademark and mode of mechanical ventilation. There is a standardized nomenclature of mechanical ventilation that is specific about nomenclature related to modes, but not settings and variables.

Mandatory minute ventilation (MMV) is a mode of mechanical ventilation which requires the operator to determine what the appropriate minute ventilation for the patient should be and the ventilator then monitors the patient's ability to generate this volume. If the calculation suggests the volume target will not be met, supplemental breaths are delivered at the targeted volume to achieve the desired minute ventilation.

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.

SensorMedics high-frequency oscillatory ventilator

The SensorMedics High-Frequency Oscillatory Ventilator is a patented high-frequency mechanical ventilator designed and manufactured by SensorMedics Corp. of Yorba Linda, California. After a series of acquisitions, Vyaire Medical, Inc. marketed the product as 3100A/B HFOV Ventilators. Model 3100 received premarket approval from the United States Food and Drug Administration (FDA) in 1991 for treatment of all forms of respiratory failure in neonatal patients. In 1995, it received pre-market approved for Pediatric Application with no upper weight limit for treating selected patients failing on conventional ventilation.

There are many modes of mechanical ventilation. In medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing.

Dynamic hyperinflation is a phenomenon that occurs when a new breath begins before the lung has reached the static equilibrium volume.

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.


  1. Sassoon CS, Del Rosario N, Fei R, et al. Influence of pressure- and flow-triggered synchronous intermittent mandatory ventilation on inspiratory muscle work. Crit Care Med 1994; 22:1933.
  2. Christopher KL, Neff TA, Bowman JL, et al. Demand and continuous flow intermittent mandatory ventilation systems" Chest 1985; 87:625.
  3. Ortiz, G; Frutos-Vivar, F; Ferguson, ND; Esteban, A; Raymondos, K; Apezteguía, C; Hurtado, J; González, M; Tomicic, V; Elizalde, J; Abroug, F; Arabi, Y; Pelosi, P; Anzueto, A; Ventila Group (Jun 2010). "Outcomes of patients ventilated with synchronized intermittent mandatory ventilation with pressure support: a comparative propensity score study". Chest. 137 (6): 1265–77. doi:10.1378/chest.09-2131. PMID   20022967. Archived from the original on 2013-04-14.
  4. Jounieaux, V; Duran, A; Levi-Valensi, P (Apr 1994). "Synchronized intermittent mandatory ventilation with and without pressure support ventilation in weaning patients with COPD from mechanical ventilation". Chest. 105 (4): 1204–10. doi:10.1378/chest.105.4.1204. PMID   8162750. Archived from the original on 2013-04-14.
  5. Boles, JM; Bion, J; Connors, A; Herridge, M; Marsh, B; Melot, C; Pearl, R; Silverman, H; Stanchina, M; Vieillard-Baron, A; Welte, T (May 2007). "Weaning from mechanical ventilation". The European Respiratory Journal. 29 (5): 1033–56. doi: 10.1183/09031936.00010206 . PMID   17470624.
  6. Brochard, L; L Brochard; A Rauss; S Benito; G Conti; J Mancebo; N Rekik; A Gasparetto; F Lemaire (1 October 1994). "Comparison of three methods of gradual withdrawal from ventilatory support during weaning from mechanical ventilation". Am J Respir Crit Care Med. 150 (4): 896–903. doi:10.1164/ajrccm.150.4.7921460. PMID   7921460.
  7. Esteban, A; Frutos, F; Tobin, MJ; Alía, I; Solsona, JF; Valverdú, I; Fernández, R; de la Cal, MA; Benito, S; Tomás, R (Feb 9, 1995). "A comparison of four methods of weaning patients from mechanical ventilation. Spanish Lung Failure Collaborative Group". The New England Journal of Medicine. 332 (6): 345–50. doi:10.1056/NEJM199502093320601. PMID   7823995.
  8. Marini, JJ; Smith, TC; Lamb, VJ (Nov 1988). "External work output and force generation during synchronized intermittent mechanical ventilation. Effect of machine assistance on breathing effort". The American Review of Respiratory Disease. 138 (5): 1169–79. doi:10.1164/ajrccm/138.5.1169. PMID   3202477.
  9. Imsand, C; Feihl, F; Perret, C; Fitting, JW (Jan 1994). "Regulation of inspiratory neuromuscular output during synchronized intermittent mechanical ventilation". Anesthesiology. 80 (1): 13–22. doi:10.1097/00000542-199401000-00006. PMID   8291702. S2CID   19312777.
  10. Leung, P; Jubran, A; Tobin, MJ (Jun 1997). "Comparison of assisted ventilator modes on triggering, patient effort, and dyspnea". American Journal of Respiratory and Critical Care Medicine. 155 (6): 1940–8. doi:10.1164/ajrccm.155.6.9196100. PMID   9196100.
  11. 1 2 Scott O. Guthrie; Chris Lynn; Bonnie J. Lafleur; Steven M. Donn; William F. Walsh (October 2005). "A crossover analysis of mandatory minute ventilation compared to synchronized intermittent mandatory ventilation in neonates". Journal of Perinatology. 25 (10): 643–646. doi: 10.1038/ . PMID   16079905.
  12. Younes M. Proportional assist ventilation, a new approach to ventilatory support. Theory. Am Rev Respir Dis 1992; 145(1):114-120.
  13. Otis, AB; Fenn, OW; Rahn, H (1950). "Mechanics of breathing in man". J Appl Physiol. 2 (11): 592–607. doi:10.1152/jappl.1950.2.11.592. PMID   15436363.
  14. Grodins, FS; Yamashiro, SM (1977). West, John B (ed.). Control of Ventilation. New York: Marcel Dekker Inc. pp. 546ff. ISBN   0-8247-6378-5.
  15. Brunner, JX; Iotti, GA (2008). "Computerized system for mechanical ventilation". J Clin Monit Comput. 22 (5): 385–386. doi:10.1007/s10877-008-9138-8. PMID   18766445.
  16. Laubscher, TP; Heinrichs, W; Weiler, N; Hartmann, G; Brunner, JX (1994). "An adaptive lung ventilation controller". IEEE Trans Biomed Eng. 41 (1): 51–59. doi:10.1109/10.277271. PMID   8200668. S2CID   10907949.
  17. Tehrani, Fleur T., "Method and Apparatus for Controlling an Artificial Respirator" US Patent No. 4986268, issued Jan. 22, 1991.