Intermittent mandatory ventilation
Encyclopedia
Intermittent Mandatory Ventilation (IMV) refers to any mode of mechanical ventilation with preset tidal volume
(VT) and inspiratory flow. Spontaneous breaths (i.e., inspiration is patient triggered and patient cycled) can exist between mandatory breaths. For intermittent mandatory ventilation utilizing pressure regulation, the term pressure controlled intermittent mandatory ventilation is used.
Pressure Controlled Intermittent Mandatory Ventilation (PC-IMV) is any mode of mechanical ventilation with preset inspiratory pressure (Pressure Control) and inspiratory time (Ti). Spontaneous breaths (i.e., inspiration is patient triggered and patient cycled) can exist between mandatory breaths (denoted by the term "intermittent"). In other words, PC-IMV means a mode of ventilation where the pressure is controlled and has an allowance for patient triggered breaths without providing an assisted breath as seen in pressure controlled continuous mandatory ventilation
, but instead it allows the additional breaths to co-exist with ventilator breaths.
is a pressure controlled mode (even though "volume control" is used in the name) with a VT set as a goal amount. Pressure varies with a peak pressure limit included to reduce lung trauma and use only the minimum pressure required to deliver the goal tidal volume (VT). Pressure regulated volume control is a mode of mechanical ventilation where the breaths are delivered mandatorily to assure preset volumes, with a constant inspiratory pressure continuously adapting to the patient
's condition. The flow pattern is decelerating. This mode is a form of intermittent mandatory ventilation, the breaths can either be ventilator initiated or patient initiated. This mode combines the advantages of volume controlled and pressure control
led ventilation.
The first breath delivered to the patient is a volume controlled breath. The measured plateau pressure is used as the pressure level for the next breath. The pressure is constant during the set inspiratory time and the flow is decelerating. The set tidal volume
is achieved by automatic, breath-by-breath pressure regulation. The ventilator will adjust the inspiratory pressure control level, according to the mechanical properties of the airway
s/lung
/thorax, to the lowest possible level to guarantee the preset tidal volume. If the measured tidal volume increases above the preset, the pressure level decreases in steps of maximum 3 cmH2O (300 Pa
) between consecutive breaths until the preset tidal volume is delivered. Maximum available pressure level is 5 cmH2O (500 Pa) below a preset upper pressure limit.
and resistance. 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) — ASV is a positive pressure mode of mechanical ventilation that is closed-loop controlled. In this mode, the frequency and tidal volume of breaths of a patient on the ventilator are automatically adjusted based on the patient’s requirements. The lung mechanics data are used to adjust the depth and rate of breaths to minimize the work rate of breathing. 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.
ASV is a patented technology originally described as one of the embodiments of US Patent No. 4986268. 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.
in the mid-1990s. APRV differs fundamentally from that of conventional positive-pressure ventilation. Whereas conventional modes of mechanical ventilation
begin the breathing cycle at a baseline pressure and elevate airway pressure (PIP) to accomplish tidal ventilation (VT), APRV begins at a pressure higher than the baseline pressure and follows with a deflation to accomplish tidal ventilation. Fundamentally APRV is a time-cycled alternant between two levels of positive airway pressure, with the main time on the high level and a brief expiratory release to facilitate ventilation.
This is a type of inverse ratio ventilation
. The exhalation time (Tlow) is shortened to usually less than one second to maintain alveoli inflation. Fundamentally this is a continuous pressure with a brief release. APRV currently the most efficient conventional mode for lung protective ventilation.
, a very similar mode, biphasic positive airway pressure (BIPAP), was introduced in Europe. The term APRV has also been used in American journals where, from the ventilation characteristics, BIPAP would have been the appropriate terminology. To further confusion, BiPAP© is a registered trade-mark for a noninvasive ventilation mode in a specific ventilator (Respironics Inc.). Other names (BILEVEL, DUOPAP, BIVENT) have been created for legal reasons. Although similar in modality, these terms describe how a mode is intended to inflate the lung, rather than defining the characteristics of synchronization or the way spontaneous breathing efforts are supported.
but may be referred to clinically by the brand name.
Some of these names include:
Tidal volume
Tidal volume is the lung volume representing the normal volume of air displaced between normal inspiration and expiration when extra effort is not applied.Typical values are around 500ml or 7ml/kg bodyweight.-Mechanical Ventilation:...
(VT) and inspiratory flow. Spontaneous breaths (i.e., inspiration is patient triggered and patient cycled) can exist between mandatory breaths. For intermittent mandatory ventilation utilizing pressure regulation, the term pressure controlled intermittent mandatory ventilation is used.
Intermittent Mechanical Ventilation
IMV — IMV is similar to AC in two ways: the minute ventilation is determined (by setting the respiratory rate and tidal volume); and the patient is able to increase the minute ventilation. However, IMV differs from AC in the way that the minute ventilation is increased. Specifically, patients increase the minute ventilation by spontaneous breathing, rather than patient-initiated ventilator breaths.Syncronized Intermittent Mechanical Ventilation
SIMV — SIMV is a variation of IMV, in which the ventilator breaths are synchronized with patient inspiratory effort. SIMV with pressure support is the most efficient and effective mode of mechanical ventilation.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. 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.Pressure Controlled Intermittent Mandatory Ventilation (PC-IMV) is any mode of mechanical ventilation with preset inspiratory pressure (Pressure Control) and inspiratory time (Ti). Spontaneous breaths (i.e., inspiration is patient triggered and patient cycled) can exist between mandatory breaths (denoted by the term "intermittent"). In other words, PC-IMV means a mode of ventilation where the pressure is controlled and has an allowance for patient triggered breaths without providing an assisted breath as seen in pressure controlled continuous mandatory ventilation
Pressure controlled continuous mandatory ventilation
Pressure Controlled Continuous Mandatory Ventilation is any mode of mechanical ventilation with preset inspiratory pressure and inspiratory time. Every breath is mandatory .-Pressure control:...
, but instead it allows the additional breaths to co-exist with ventilator breaths.
Pressure regulated volume control
PRVC — Pressure regulated volume controlPressure Regulated Volume Control
Pressure regulated volume control is a mode of mechanical ventilation with a VT set as a goal amount. Pressure varies with a peak pressure limit included to reduce lung trauma and use only the minimum pressure required to deliver the goal tidal volume...
is a pressure controlled mode (even though "volume control" is used in the name) with a VT set as a goal amount. Pressure varies with a peak pressure limit included to reduce lung trauma and use only the minimum pressure required to deliver the goal tidal volume (VT). Pressure regulated volume control is a mode of mechanical ventilation where the breaths are delivered mandatorily to assure preset volumes, with a constant inspiratory pressure continuously adapting to the patient
Patient
A patient is any recipient of healthcare services. The patient is most often ill or injured and in need of treatment by a physician, advanced practice registered nurse, veterinarian, or other health care provider....
's condition. The flow pattern is decelerating. This mode is a form of intermittent mandatory ventilation, the breaths can either be ventilator initiated or patient initiated. This mode combines the advantages of volume controlled and pressure control
Pressure control
Pressure control 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 are currently regulated by Volume Control or...
led ventilation.
The first breath delivered to the patient is a volume controlled breath. The measured plateau pressure is used as the pressure level for the next breath. The pressure is constant during the set inspiratory time and the flow is decelerating. The set tidal volume
Tidal volume
Tidal volume is the lung volume representing the normal volume of air displaced between normal inspiration and expiration when extra effort is not applied.Typical values are around 500ml or 7ml/kg bodyweight.-Mechanical Ventilation:...
is achieved by automatic, breath-by-breath pressure regulation. The ventilator will adjust the inspiratory pressure control level, according to the mechanical properties of the airway
Airway
The pulmonary airway comprises those parts of the respiratory system through which air flows, conceptually beginning at the nose and mouth, and terminating in the alveoli...
s/lung
Human lung
The human lungs are the organs of respiration in humans. Humans have two lungs, with the left being divided into two lobes and the right into three lobes. Together, the lungs contain approximately of airways and 300 to 500 million alveoli, having a total surface area of about in...
/thorax, to the lowest possible level to guarantee the preset tidal volume. If the measured tidal volume increases above the preset, the pressure level decreases in steps of maximum 3 cmH2O (300 Pa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
) between consecutive breaths until the preset tidal volume is delivered. Maximum available pressure level is 5 cmH2O (500 Pa) below a preset upper pressure limit.
Advantages
- Maintains a minimum positive pressure(PIP)
- Guaranteed tidal volume (VT)
- Patient has very little work of breathing (WOB) requirement.
- Allows patient control of respiratory rate Decelerating flow waveform for improved gas distribution
- Breath by breath analysis
Disadvantages
- Varying mean airway pressure
- May cause or worsen autoPEEP
- When patient demand is increased, pressure level may diminish when support is needed
- May be tolerated poorly in awake non-sedated patients
- A sudden increase in respiratory rate and demand may result in a decrease in ventilator support
Proportional Assist Ventilation
PAV — Proportional assist ventilation is a mode in which the ventilator guarantees the percentage of work regardless of changes in pulmonary compliancePulmonary compliance
Pulmonary compliance can refer to either dynamic or static lung compliance. Static lung compliance is the change in volume for any given applied pressure...
and resistance. 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
Adaptive Support Ventilation (ASV) — ASV is a positive pressure mode of mechanical ventilation that is closed-loop controlled. In this mode, the frequency and tidal volume of breaths of a patient on the ventilator are automatically adjusted based on the patient’s requirements. The lung mechanics data are used to adjust the depth and rate of breaths to minimize the work rate of breathing. 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.
ASV is a patented technology originally described as one of the embodiments of US Patent No. 4986268. 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.
Airway pressure release ventilation
Airway pressure release ventilation (APRV) — is a relatively new strategy of ventilation that became commercially available in the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
in the mid-1990s. APRV differs fundamentally from that of conventional positive-pressure ventilation. Whereas conventional modes of mechanical ventilation
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. Mode selection is generally based on clinician familiarity and institutional preferences since there is a paucity of evidence...
begin the breathing cycle at a baseline pressure and elevate airway pressure (PIP) to accomplish tidal ventilation (VT), APRV begins at a pressure higher than the baseline pressure and follows with a deflation to accomplish tidal ventilation. Fundamentally APRV is a time-cycled alternant between two levels of positive airway pressure, with the main time on the high level and a brief expiratory release to facilitate ventilation.
This is a type of inverse ratio ventilation
Inverse ratio ventilation
Inverse ratio ventilation 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 some inspired air is not allowed to be exhaled, creating intrinsic positive-end expiratory pressure and allowing for...
. The exhalation time (Tlow) is shortened to usually less than one second to maintain alveoli inflation. Fundamentally this is a continuous pressure with a brief release. APRV currently the most efficient conventional mode for lung protective ventilation.
Settings and measurements
Settings are sometimes brand specific and the term for the individual settings may differ, however generally the settings listed here are a fundamental explanation of the purpose of the settings within the APRV mode.- Phigh — This is the inspiratory pressure (just like in pressure control).
- Thigh — This value is the number of seconds during the inhalation phase.
- Tpeep — Also known as the Tlow, this is the time allotted for expiration.
- FiO2 — The fractional O2 percentage that is being added to the delivered air.
Perceptions and Receptions
Different perceptions of this mode may exist around the globe. While 'APRV' is common to users in North AmericaNorth America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, a very similar mode, biphasic positive airway pressure (BIPAP), was introduced in Europe. The term APRV has also been used in American journals where, from the ventilation characteristics, BIPAP would have been the appropriate terminology. To further confusion, BiPAP© is a registered trade-mark for a noninvasive ventilation mode in a specific ventilator (Respironics Inc.). Other names (BILEVEL, DUOPAP, BIVENT) have been created for legal reasons. Although similar in modality, these terms describe how a mode is intended to inflate the lung, rather than defining the characteristics of synchronization or the way spontaneous breathing efforts are supported.
Other terms
APRV is used by many brands and models of mechanical ventilators under different names. Most names are copyrighted as trademarks and do not represent nomenclature of mechanical ventilationNomenclature of mechanical ventilation
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.-Volume Controlled...
but may be referred to clinically by the brand name.
Some of these names include:
- BiVent - (Servo-i ventilator by Maquet)
- BiLevel
- DuoPAP
Further reading
- Kaplan LJ. Bailey H. Formosa V. “Airway pressure release ventilation increases cardiac performance in patients with acute lung injury/adult respiratory distress syndrome” Critical Care (London). 5(4):221-6, 2001 Aug.
- Wrigge H. Zinserling J. Hering R. Schwalfenberg N. Stuber F. von Spiegel T. Schroeder S. Hedenstierna G. Putensen C. “Cardiorespiratory effects of automatic tube compensation during airway pressure release ventilation in patients with acute lung injury.” Anesthesiology. 95(2):382-9, 2001 Aug
- Räsänen J, Cane RD, Downs JB, Hurst JM, Jousela IT, Kirby RR, Rogove HJ “Airway pressure release ventilation during acute lung injury: A prospective multicenter trial” Crit Care Med 1991; 19: 1234–41
- Putensen C. Mutz NJ. Putensen-Himmer G. Zinserling J. “Spontaneous breathing during ventilatory support improves ventilation-perfusion distributions in patients with acute respiratory distress syndrome.” American Journal of Respiratory & Critical Care Medicine. 159(4 Pt 1):1241-8, 1999 Apr.
- Sydow M. Burchardi H. Ephraim E. Zielmann S. Crozier TA. “Long-term effects of two different ventilatory modes on oxygenation in acute lung injury. Comparison of airway pressure release ventilation and volume-controlled inverse ratio ventilation.” American Journal of Respiratory & Critical Care Medicine. 149(6):1550-6, 1994 Ju