Table of modes of mechanical ventilation

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Modes of mechanical ventilation refers to the methods a Ventilator offers to assist or replace spontaneous breathing [1] . Modern Ventilators provide a number of such methods called Modes (derived from Modus operandi) to enable the most suitable respiratory support for the individual patient. [2] Each Mode has its particular set of Controls to adapt the breath delivery to the patient. CAVEAT: Although manufacturers may offer identical breath delivery methods, the names of the Modes may be different [3] .

Contents

Composition of breathing gas mixture

Most ventilators can deliver higher oxygen concentration than available in room air and can provide increased levels of pressure at the end of exhalation. Thus, the following functions and controls are available to the clinician:

While technological differences exist among devices to implement these two functions , their use is clear and the terminology is widely accepted. In contrast, the terminology of breath delivery methods can be quite confusing [3] .

Basic breath delivery modes

In the basic breath delivery modes, the ventilator acts as a high-fidelity delivery device. The clinician's settgins are direct commands to the inspiratory and expiratory valve controls. The ventilator uses fast sensors for intra-breath control to match the clinicians settings exactly. Breath delivery follows the phases of breathing, [4] i.e., inhalation and exhalation. Each Mode defines how breath delivery and timing are controlled by the clinician [1] .

Inhalation trigger

The start of inhalation is initiated by the machine or the patient and that point in time is called InspiratoryTrigger. The ventilator needs to know when to start delivering gas to the patient. If the patient does not breathe at all, a timer starts inhalation. If the patient has some breathing activity, the ventilator can sense this effort by measuring pressure or flow and start inhalation if pressure or flow drop below a certain threshold. That threshold is called Trigger Sensitivity. Thus, the controls available to the clinician are respiratory rate and trigger sensitivity.

NOTE: Trigger sensitivity plays a double role. Evidently, it determines the start of inhalation and, by the same toke, it ends expiration. For example, if trigger sensitiviy is set too sensive, it may influence respiratory rate and create tachypnea [5] .

Breath delivery

Once the ventilators is triggered to deliver respiratory gas, two methods to deliver the gas mixture are technically possible: flow controlled or pressure controlled [6] gas gelivery. Both methods have their advantages and disadvantages. If flow controlled gas delivery is chosen, it is often combined with a Volume limit which stops gas delivery when a set volume is reached. Thus, the term Volume Controlled Ventilation is often used. The controls available to the clinician are inspiratory pressure, inspiratory flow and/or inspiratory volume.

Cycling to exhalation

Inhalation must eventually stop and cycle to exhalation to enable the lungs to exhale. If the patient does not breathe, the ventilator must switch to exhalation after a pre-set time (time cycled) has elapsed, a certain pressure is exceeded (pressure cycled) or a pre-set volume (volume cycled) has been delivered [1] . If the patient has some breathing activity, the ventilator can sense this by measuring flow and start exhalation, for example, if flow drops below a certain threshold. That threshold may be termed "Expiratory Trigger Sensitivity". The controls available to the clinician are inspiratory time, inspiratory volume, inspiratory flow, maximum pressure and/or expiratory trigger sensitivity.

NOTE: Inspiratory flow can be expressed as V'I = Vt/Ti and respiratory rate f = 60/(Ti+Te). Both formulas have three variables and two degrees of freedom. This means that only two variables can be controlled independently, the third variable follows.

Exhalation

Emtpying the lungs requires time which starts with the onset of exhalation and ends with the start of the subsequent inhalation. If the patient is passive, the exhalation is terminated by a timer. If the patient has some breathing activity, exhalation may be terminated by the subsequent inhalation effort of the patient. Controls include a selection of expiratory time, respiratory rate and/or trigger sensitivity.

NOTE: The pressure maintained throughout exhalation is termed Positive End-Expiratory Pressure PEEP. CPAP differs from PEEP because the patient can inhale and exhale in CPAP.

Table of basic modes and their acronyms

The table below lists the working principles of some of the common modes of ventilation.

Mode examples, not exhaustive!TriggerBreath delivery

Mechanism

CycleRemark
Volume Controlled Ventilation, VC CMV, VCV, A/CVent or PatFlowVentClinicians sets tidal volume, flow waveform and timing. Ventilator adjusts the valves to deliver that exact volume irrespective of changing resitance and compliance of the patient [8] .
Pressure Controlled Ventilation PCVent or PatPressureVentClinician sets a pressure trajectory (inspiratory pressure level and inspiratory time). Ventilator uses a pressure transducer to servo-control the valve, creating the desired pressure wave (usually a square wave) at the airway opening [9] .
Synchronized Intermittent Mandatory Ventilation SIMV (volume cycled)Vent or PatFlow (mandatory breath) or Pressure (spontaneous breath)Vent or PatCombination of VC and PS. Basis is Volume Controlled Ventilation. Patient can take breaths in between.
Synchronized Intermittent Mandatory Ventilation SIMV (pressure limited)Vent or PatPressureVent or PatCombination of PC and PS. Basis is Volume Controlled Ventilation. Patient can take breaths in between.
Continuous Positive Airway Pressure CPAPPatPressurePatVentilator maintains a set pressure (PEEP) independent of patient effort.
Pressure Support PSPatPressurePatClinician sets a pressure level. The control loop is identical to PCV for maintaining pressure, but breath cycling is determined by patient flow decay [10] . The level of support is fixed until changed by the clinician.
Airway Pressure Release Ventilation, APRV, Bilevel Positive Airway Pressure, BiPAP, DuoPAPVent or PatPressureVent or PatClinician sets two levels of pressure and the time to switch between the two. Ventilator maintains each level independet of patient effort. Patient can breathe on both levels.
Proportional Assist Ventilation PAV [7] PatPressurePatAdvanced basic mode. Clinician sets a fixed degree of support (assist %) rather than a pressure level. Pressure level is calculated by ventilator as a proportion of delivered volume and flow [11] .
Neurally Adjusted Ventilation Assist NAVA [7] PatPressurePatThe diaphragm's electrical activity (EAdi) is the commanding waveform; the ventilator delivers pressure in proportion to the EAdi signal with a fixed gain set by the clinician [12] .

PAV and NAVA provide superior synchrony with the patient's breathing by using a physiological signal as the command source.

Dual control modes

Dual control modes introduce an outer control loop that wraps around a Basic Mode. The clinician sets a performance target (for example Vt and respiratory rate) and the ventilator then uses a Basic Mode (usually a pressure-controlled or pressure-support breath) as its actuator and automatically adjusts the pressure level from breath to breath to meet the performance target.

This represents a significant user-interface advantage. The clinician can manage the fundamental goals of ventilation—for example tidal volume or respiratory rate —while the machine handles the technical translation into the required pressure, adapting automatically to changes in the patient's respiratory system compliance and resistance and spontaneous activity [13] .

Table of dual control modes and their acronyms

The table below lists the working principles of some of the dual control modes. The clinician set a desired target, for example the tidal volume Vt and the ventilator adjusts one of the variables of provided by the basic mode it uses [14] .

Mode examples, not exhaustive!Underlying basic modeTarget VariableControlled VariableRemark
Pressure-Regulated Volume Control PRVC, VC+, AutoFlowPressure ControlledTidal volumeInspiratory pressureVentilator operates in a Pressure Control (Basic Mode) scheme. After each mandatory breath, it compares the delivered Vt to the clinician-set target Vt. It then adjusts the inspiratory pressure level for the next mandatory breath upward or downward [13] .
Volume Support VSPressure SupportedTidal volumePressure support levelThis is the Targeted Spontaneous Mode counterpart to PRVC. It uses Pressure Support (Basic Mode) as its actuator. After each spontaneous breath, ventilator adjusts the PS level for the subsequent breath to achieve the set Vt target [15] .
Mandatory Rate Ventilation MRVPressure SupportedRespiratory RatePressure support levelThis is the Respiratory Rate counterpart to VS. Uses Pressure Support (Basic Mode) as its actuator. After each spontaneous breath, ventilator adjusts the PS level for the subsequent breath to achieve the set Respiratory Rate target [16] .
Mandatory Minute Ventilation MMVPressure SupportedMinute VentilationNumber of Mandatory BreathsVentilator provides a spontaneous mode with or without inspiratory support set by the clinician. Clinician also sets desired Minute Ventilation MVtarget. The ventilator monitors Minute Ventilation taken by the patient (MVpat). If MVpat drops below MVtarget, ventilator provides a VC breath to the patient with volume and timing as preset by the clinican [17] .
Volume Assured Pressure Support Ventilation VAPSVPressure Control and Volume ControlTidal VolumePressure support level plus volume addThis mode represents intra-breath target enforcement. Ventilator primarily delivers Pressure Support (Basic Mode). Within the ongoing inspiratory phase, if the algorithm predicts that the decaying flow of the PS breath will not meet the set Vt target, ventilator automatically switches the control logic to a Volume Control (Basic Mode) waveform for the remainder of that breath to guarantee the volume. This is sophisticated targeting, but the goal remains achieving the clinician's predefined Vt [18] .
AutomodeSelectable Mode 1 and Mode 2Switching criteriumMode 1 or Mode 2This is a mode-manager that operates on top of dual control modes. It pairs two Dual Control Modes (e.g., PRVC and VS) and ventilator automatically switches between them based on the presence or absence of patient triggering, all while maintaining the clinician-set volume targets [19] .

See also

References

  1. 1 2 3 Cairo, J.M. (2020). Pilbeam's Mechanical Ventilation. Physiological and clinical applications. St. Louis, Missouri: Elsevier. pp. 62ff. ISBN   978-0-323-87164-8.
  2. ↑ Esteban A, Alía I, Ibañez J, Benito S, Tobin MJ (1994). "Modes of mechanical ventilation and weaning. A national survey of Spanish hospitals. The Spanish Lung Failure Collaborative Group". Chest. 106 (4): 1188–93. doi:10.1378/chest.106.4.1188. PMID   7924494.
  3. 1 2 Adams, Alexander B. (2012). "Too many ventilator modes!". Respiratory Care. 57 (4): 653–654. doi:10.4187/respcare.01787. ISSN   0020-1324. PMID   22472503.
  4. ↑ Brunner, J.; Wolff, G.; Langenstein, H.; Cumming, G. (December 1985). "Reliable detection of inspiration and expiration by computer". International Journal of Clinical Monitoring and Computing. 1 (4): 221–226. doi:10.1007/BF01720186. ISSN   0167-9945. PMID   3836286.
  5. ↑ Gurevitch, Michael J.; Gelmont, David (1989). "Importance of trigger sensitivity to ventilator response delay in advanced chronic obstructive pulmonary disease with respiratory failure". Critical Care Medicine. 17 (4): 354–359. doi:10.1097/00003246-198904000-00011. ISSN   0090-3493. PMID   2639663.
  6. ↑ Garnero, A.J.; Abbona, H.; Gordo-Vidal, F.; Hermosa-Gelbard, C. (2013). "Modos controlados por presión versus volumen en la ventilación mecánica invasiva" . Medicina Intensiva (in Spanish). 37 (4): 292–298. doi:10.1016/j.medin.2012.10.007.
  7. 1 2 3 Navalesi P, Costa R (2003). "New modes of mechanical ventilation: proportional assist ventilation, neurally adjusted ventilatory assist, and fractal ventilation". Curr Opin Crit Care. 9 (1): 51–8. doi:10.1097/00075198-200302000-00010. PMID   12548030.
  8. ↑ Chatburn, Robert L (2007). "Classification of ventilator modes: update and proposal for implementation". Respiratory Care. 3 (3): 301–323.
  9. ↑ Muñoz, Javier; Guerrero, Jose Eugenio; Escalante, Jose Luis; Palomino, Ricardo; La Calle, Braulio De (1993). "Pressure-controlled ventilation versus controlled mechanical ventilation with decelerating inspiratory flow". Critical Care Medicine. 21 (8): 1143–1148. doi:10.1097/00003246-199308000-00012. ISSN   0090-3493. PMID   8339578.
  10. ↑ Brochard, Laurent (2013). Pressure support ventilation. In: Tobin MJ, ed. Principles and Practice of Mechanical Ventilation. McGraw-Hill. ISBN   9780071736268.
  11. ↑ Younes, Magdy (1992). "Proportional Assist Ventilation, a New Approach to Ventilatory Support: Theory". American Review of Respiratory Disease. 145 (1): 114–120. doi:10.1164/ajrccm/145.1.114. ISSN   0003-0805. PMID   1731573.
  12. ↑ Sinderby, Christer; Navalesi, Paolo; Beck, Jennifer; Skrobik, Yoanna; Comtois, Norman; Friberg, Sven; Gottfried, Stewart B.; Lindström, Lars (1999). "Neural control of mechanical ventilation in respiratory failure". Nature Medicine. 5 (12): 1433–1436. doi:10.1038/71012. ISSN   1078-8956. PMID   10581089.
  13. 1 2 Guldager, Henrik; Nielsen, Soeren L; Carl, Peder; Soerensen, Mogens B (1997). "A comparison of volume control and pressure-regulated volume control ventilation in acute respiratory failure". Critical Care. 1 (2) 75. doi: 10.1186/cc107 . ISSN   1364-8535.
  14. ↑ Troxell, David (2024-06-15). "Volume Targeted Algorithms. Are they a one-size-fits-all approach to noninvasive ventilation?". Journal of Mechanical Ventilation. 5 (2): 69–79. doi:10.53097/jmv.10101. ISSN   2694-0450.
  15. ↑ Larraza, S.; Dey, N.; Karbing, D.S.; Jensen, J.B.; Nygaard, M.; Winding, R.; Rees, S.E. (2015-04-01). "A mathematical model approach quantifying patients' response to changes in mechanical ventilation: Evaluation in volume support". Medical Engineering & Physics. 37 (4): 341–349. doi:10.1016/j.medengphy.2014.12.006. ISSN   1350-4533. PMID   25686673.
  16. ↑ Taniguchi, Corinne; Eid, Raquel C; Saghabi, Cilene; Souza, Rogério; Silva, Eliezer; Knobel, Elias; Paes, Ângela T; Barbas, Carmen S (2009-01-26). "Automatic versus manual pressure support reduction in the weaning of post-operative patients: a randomised controlled trial". Critical Care. 13 (1) R6. doi: 10.1186/cc7695 . ISSN   1364-8535. PMID   19171056.
  17. ↑ Hewlett, A. M.; Platt, A. S.; Terry, V. G. (1977). "Mandatory minute volume: A new concept In weaning from mechanical ventilation". Anaesthesia. 32 (2): 163–169. doi:10.1111/j.1365-2044.1977.tb11588.x. ISSN   0003-2409.
  18. ↑ Amato, Marcelo Britto Passos; Barbas, Carmen Silvia Valente; Bonassa, Jorge; Saldiva, Paulo Hilario Nascimento; Zin, Walter Araujo; de Carvalho, Carlos Roberto Ribeiro (1992). "Volume-Assured Pressure Support Ventilation (VAPSV)". Chest. 102 (4): 1225–1234. doi:10.1378/chest.102.4.1225. PMID   1395773.
  19. ↑ Holt, SJ; Sanders, RC; Thurman, TL; Heulitt, TL (2001). "An evaluation of Automode, a computer-controlled ventilator mode, with the Siemens Servo 300A ventilator, using a porcine model". Respiratory Care. 46 (1): 26–36.
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