Liquid ventilator

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Example of a liquid ventilator (Inolivent-5 research group Inolivent, Universite de Sherbrooke) Inolivent-5.jpg
Example of a liquid ventilator (Inolivent-5 research group Inolivent, Université de Sherbrooke)

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 (a perfluorocarbon). [1] [2] Liquid ventilators are prototypes that may have been used for animal experimentations but experts recommend continued development of a liquid ventilator toward clinical applications. [3]

Contents

Function and technology

Driving liquid

In total liquid ventilation (TLV), the lungs are completely filled with a perfluorocarbon (PFC) liquid while the liquid ventilator renews the tidal volume of PFC. The liquid ventilator operates in mandatory mode: it must force the PFC in and out of the lungs with a pumping system.

The pumping system is either a peristaltic pump (in the simplest liquid ventilators) or two piston pumps (in the most advanced liquid ventilators).

Because of the PFC viscosity, the head loss in the airways requires a low negative driving pressure during the expiration phase that can collapse the airways. This is the choked flow phenomenon in TLV [4] [5] which compromises the minute ventilation and consequently the gas exchanges. [6] To address this limitation, liquid ventilator integrates a control of the pumping system.[ citation needed ]

Controlling liquid ventilator

The introduction of computers in liquid ventilators to control the pumping system provides different control modes, monitoring and valuable data for decision making. [7] [8]

The liquid ventilator is always volume-controlled because the specified tidal volume of PFC must be accurately delivered and retrieved. It is also pressure-limited because it must stop the expiratory or inspiratory phase when a too low, or a too large, driving pressure is detected. [9]

However, during the expiratory phase, the expiratory flow can be commanded by an open-loop controller or a closed-loop controller:

Also, during the inspiratory phase, the volume-controlled mode is realized by open-loop or closed loop control of the PFC flow.

Oxygenating and heating liquid

The liquid ventilator removes Carbon dioxide (CO2) from the PFC by saturating it with oxygen (O2) and medical air. This procedure can be performed with either a membrane oxygenator (a technology used in extracorporeal oxygenators) or a bubble oxygenator. [13]

The liquid ventilator heats the PFC to body temperature. This is performed with a heat exchanger connected to the oxygenator or with dedicated heaters integrated in the oxygenator. [13]

The oxygenator and the heater produce PFC vapor which is recuperated with a condenser in order to limit the evaporation loss (the PFC is a greenhouse gas).

Example

Example of the pumping cycle in a liquid ventilator (Inolivent-4, research group Inolivent, Universite de Sherbrooke) AnimInolivent.gif
Example of the pumping cycle in a liquid ventilator (Inolivent-4, research group Inolivent, Université de Sherbrooke)

An example of a liquid ventilator is the Inolivent-4. It is composed of two independent piston pumps and integrated unit allowing for oxygenation of PFC, temperature control, and recovery of evaporated PFC. [13] This liquid ventilator also includes volume and pressure control strategies to optimize the ventilatory cycle: it performs a pressure-regulated volume-controlled ventilation mode. [12] It is designed for experimental research on animal models weighing between 0.5 kg to 9 kg.

A typical cycle is composed of four steps :

  1. Inspiratory pump inserts a volume of PFC in the lungs (valve 1 open, valve 2 closed), and the expiratory pump pushes PFC in the oxygenator via the filter (valve 3 closed, valve 4 open).
  2. During the inspiratory pause (all valves are closed), the lung volume is at its maximal value. The measured pressure is the Positive End-Inspiratory Pressure (PEIP).
  3. Expiratory pump retrieves a volume of PFC in the lungs (valve 3 open, valve 4 closed), and the inspiratory pump draws PFC from the reservoir (valve 1 closed, valve 2 open).
  4. During the expiratory pause (all valves are closed), the lung volume is at its minimal value. The measured pressure is the Positive End-expiratory Pressure (PEEP).

Potential applications

Studies have shown both the efficacy and safety of liquid ventilation in normal, mature and immature newborn lungs. Overall, liquid ventilation improves gas exchange and lung compliance and prevents the lungs against ventilation-induced lung injury. [1]

Respiratory support

Studies suggest clear benefits of liquid ventilation in acute respiratory distress syndrome (ARDS). [14] For example, total liquid ventilation could be used for newborns with severe neonatal respiratory distress syndrome [15] in which conventional treatment has failed. Typical cases are late preterm newborns who have an increased risk of intracranial hemorrhage and for whom their small vessel size poses technical limitations for Extracorporeal membrane oxygenation (ECMO).

Therapeutic lung lavage

Liquid ventilator can perform therapeutic lung lavage, the washout of endogenous and exogenous debris from the lungs, without suspension of ventilation support (without apnea). For example, literature data suggest a radical change in the treatment of meconium aspiration syndrome (MAS) by considering the use of a liquid ventilator. The demonstration of its efficacy was performed in the neonatal lamb.. [16] [17]

Therapeutic hypothermia with rapid cooling

The liquid ventilator with advanced control temperature of PFC allows the rapid cooling of the body. Consequently, therapeutic hypothermia is an expected clinical application. For example, studies present that rapid cooling instituted by TLV can improve cardiac and mitochondrial function [18] or can induce favorable neurological and cardiac outcomes after cardiac arrest in rabbits. [19]

See also

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), is a form of extracorporeal life support, 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">Respiratory arrest</span> Medical condition

Respiratory arrest is a serious medical condition caused by apnea or respiratory dysfunction severe enough that 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 permanently damage vital organs, especially the brain. 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.

<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">Capnography</span> Monitoring of the concentration of carbon dioxide in respiratory gases

Capnography is the monitoring of the concentration or partial pressure of carbon dioxide (CO
2) in the respiratory gases. Its main development has been as a monitoring tool for use during anesthesia and intensive care. It is usually presented as a graph of CO
2 (measured in kilopascals, "kPa" or millimeters of mercury, "mmHg") plotted against time, or, less commonly, but more usefully, expired volume (known as volumetric capnography). The plot may also show the inspired CO
2, which is of interest when rebreathing systems are being used. When the measurement is taken at the end of a breath (exhaling), it is called "end tidal" CO
2 (PETCO2).

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.

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 their own respiratory rate and tidal volume.

<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.

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.

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 for mechanical ventilation. CMV today can assist or control itself dynamically, depending on the 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 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.

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.

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.

<span class="mw-page-title-main">SensorMedics high-frequency oscillatory ventilator</span>

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.

Mean airway pressure typically refers to the mean pressure applied during positive-pressure mechanical ventilation. Mean airway pressure correlates with alveolar ventilation, arterial oxygenation, hemodynamic performance, and barotrauma. It can also match the alveolar pressure if there is no difference between inspiratory and expiratory resistance.

<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.

References

  1. 1 2 M. R. Wolfson; T. H. Shaffer (2005). "Pulmonary applications of perfluorochemical liquids: ventilation and beyond". Paediatr Respir Rev. 6 (2): 117–27. doi:10.1016/j.prrv.2005.03.010. PMID   15911457.
  2. ↑ Kaisers, K., Kelly, K.P., Busch, T. (2003). "Liquid ventilation". British Journal of Anaesthesia. 91 (1): 143–151. doi: 10.1093/bja/aeg147 . PMID   12821573.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  3. ↑ Maria Laura Costantino; Philippe Micheau; Thomas H. Shaffer; Stefano Tredici; Maria R. Wolfson (2009). "Clinical Design Functions: Round table discussions on bioengineering of liquid ventilators". ASAIO J. 55 (3): 206–8. doi: 10.1097/MAT.0b013e318199c167 . PMID   19282746.
  4. ↑ Baba; Brant, D; Brah, SS; Grotberg, J; Bartlett, RH; Hirschl, RB; et al. (2004). "Assessment of the development of choked flow during liquid ventilation". Crit. Care Med. 32 (1): 201–208. doi:10.1097/01.CCM.0000104918.48411.91. PMID   14707580. S2CID   36430068.
  5. ↑ Bull; Foley, DS; Bagnoli, P; Tredici, S; Brant, DO; Hirschl, RB; et al. (2005). "Location of Flow Limitation in Liquid Filled Rabbit Lungs". ASAIO J. 51 (6): 781–788. doi: 10.1097/01.mat.0000179252.02471.9e . PMID   16340368.
  6. ↑ D. Corno; G.B. Fiore; M.L. Costantino (2004). "A mathematical model of neonatal tidal liquid ventilation integrating airway mechanics and gas transfer phenomena". IEEE Trans. Biomed. Eng. 51 (4): 604–611. doi:10.1109/TBME.2004.824144. PMID   15072214. S2CID   2509380.
  7. ↑ Sekins; Nugent, L; Mazzoni, M; Flanagan, C; Neer, L; Rozenberg, A; Hoffman, J; et al. (1999). "Recent innovation in total liquid ventilation system and component design". Biomed. Eng. & Tech. 33 (3): 277–284. PMID   10360218.
  8. ↑ JL. Heckman; J Hoffman; TH Shaffer; MR Wolfson (1999). "Software for real-time control of a tidal liquid ventilator". Biomedical Instrumentation & Technology. 33 (3): 268–276.
  9. ↑ Larrabe; et al. (October 2001). "Development of a time-cycled volume-controlled pressure-limited respirator and lung mechanics system for total liquid ventilation". IEEE Trans Biomed Eng. 48 (10): 1134–44. doi:10.1109/10.951516. PMID   11585037.
  10. ↑ R. Robert; P. Micheau; O. Avoine; B. Beaudry; H. Walti (2009). "A Regulator for Pressure Controlled Liquid Ventilation". IEEE Trans. Biomed. Eng. 57 (9): 2267–76. doi:10.1109/TBME.2009.2031096. PMID   19744909. S2CID   10157073.
  11. ↑ Tredici; Komori, E; Funakubo, A; Brant, DO; Bull, JL; Bartlett, RH; Hirschl, RB (2004). "A prototype of a liquid ventilator using a novel hollow-fiber oxygenator in a rabbit model". Crit. Care Med. 32 (10): 2104–2109. doi:10.1097/01.CCM.0000142701.41679.1B. PMID   15483421. S2CID   20271333.
  12. 1 2 R. Robert; P. Micheau; H. Walti (2009). "Optimal expiratory volume profile in tidal liquid ventilation under steady state conditions, based on a symmetrical lung model". ASAIO J. 55 (1): 63–72. doi: 10.1097/MAT.0b013e3181911821 . PMID   19092655. S2CID   1857204.
  13. 1 2 3 R. Robert; P. Micheau; S. Cyr; O. Lesur; J.P. Praud; H. Wallti (2005). "A prototype of volume-controlled tidal liquid ventilator using independent piston pumps". ASAIO J. 52 (6): 638–645. doi: 10.1097/01.mat.0000249016.31910.11 . PMID   17117053.
  14. ↑ Wolfson, M. R., R. B. Hirschl; et al. (2008). "Multicenter comparative study of conventional mechanical gas ventilation to tidal liquid ventilation in oleic acid injured sheep". ASAIO J. 54 (3): 256–269. doi: 10.1097/MAT.0b013e318168fef0 . PMID   18496275. S2CID   2647244.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  15. ↑ Hirschl; Pranikoff, T; Gauger, P; Schreiner, RJ; Dechert, R; Bartlett, RH; et al. (1995). "Liquid ventilatory in adults, children, and full-term neonates". Lancet. 346 (8984): 1201–1202. doi:10.1016/S0140-6736(95)92903-7. PMID   7475663. S2CID   42437233.
  16. ↑ R. Foust; N. Tran; et al. (1996). "Liquid assisted ventilation: an alternative ventilatory strategy for acute meconium aspiration injury". Pediatr. Pulmonol. 21 (5): 316–22. doi:10.1002/(SICI)1099-0496(199605)21:5<316::AID-PPUL7>3.0.CO;2-K. PMID   8726157. S2CID   13598492. Archived from the original on 2012-10-19.
  17. ↑ Avoine; et al. (2011). "Total Liquid Ventilation efficacy in an Ovine Model of severe meconium aspiration syndrome". Critical Care Medicine. 39 (5): 1097–103. doi:10.1097/ccm.0b013e31820ead1a. PMID   21317652. S2CID   22319306.
  18. ↑ R. Tissier; N. Couvreur; B. Ghaleh (2009). "Rapid cooling preserves the ischaemic myocardium against mitochondrial damage and left ventricular dysfunction". Cardiovasc. Res. 83 (2): 345–53. doi:10.1093/cvr/cvp046. PMC   2701717 . PMID   19196828.
  19. ↑ Chenoune; et al. (2011). "Ultrafast and whole-body cooling with total liquid ventilation induces favorable neurological and cardiac outcomes after cardiac arrest in rabbits". Circulation. 124 (8): 9011–11. doi:10.1161/circulationaha.111.039388. PMC   3375236 . PMID   21810660.
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