APRV and HFOV in the Management of Refractory Hypoxemia

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Table of Contents

Introduction
Claimed Disadvantages of APRV and HFOV
Clinical Evidence in Favor of HFOV
Clinical Evidence in Favor ofAPRV
Comparative Advantages of Both Methods
Conclusion
References

Introduction

In order to mitigate the complications of oxygen therapy and mechanical ventilation in refractory hypoxemia over the past decades, methods of lung ventilation have been used and are actively developing, with a comparable level of effectiveness. Until today, it has not been possible to prove that controlled ventilation has advantages over assisted ventilation, which provides adequate alveolar ventilation and a decrease in respiratory function. The advantages of APRV and HFOV include avoiding complications, improving patient comfort, and preserving the protective mechanisms of the respiratory tract, speech, and swallowing (Owens, 2017). This determines high potential of their application in clinical practice. However, based on clinical evidence, it could be claimed that APRV has more advantages as a first-line intervention in the adult patients. APRV can be considered as an alternative or advanced mechanical ventilation mode rather than a rescue strategy. On the other hand, HFOV would be an appropriate intervention in neonates.

Claimed Disadvantages of APRV and HFOV

A significant number of clinical studies have been conducted evaluating the efficacy and safety of various respiratory therapy methods in patients with ARDS related to refractory hypoxemia, which were conditionally divided into first and second choice methods, namely, APRV and HFOV, representing core ‘array’ for choosing (Cheriana et al., 2018; Meyers, Rodrigues, & Ari, 2019). Nevertheless, few ventilation method users have of a negative effect of HF mechanical ventilation on myocardial contractility (Jiang et al., 2018) and cellular immune responses (De Luca &Dell’Orto, 2016). Moreover, there have been reports of complications specific to HF mechanical ventilation associated with inadequate conditioning of the gas mixture, impaired patency of the catheter through which ventilation is carried out, a real risk of pulmonary barotrauma in case of obstruction of exhalation, and some psychological reasons (Jiang et al., 2018). There is an opinion about the insufficient ventilation efficiency by high-frequency vibrations. In particular, HFOV did not reduce the risk of death in a hospital in eight studies involving 1779 patients with refractory hypoxemia (Meyers et al., 2019). The ability of the lungs to oxygenate the blood (saturate the blood with oxygen), measured after 24 and 72 hours from the start of ventilation after randomization, was 18%-26% better in participants who received HFOV. It did not affect the time during which mechanical ventilation was necessary (Meyers et al., 2019). However, the risk of unwanted side effects, such as low blood pressure or further lung damage due to high airway pressure, has not been increased.

As for ventilation with variable pressure in the airways, this is the traditional way of artificial ventilation of the lungs. Significant disadvantages of pressure control (PC) are noted; one being that changing the patient’s respiratory mechanics affects the quality of the ventilation and requires changing ventilation parameters. Moreover, since the main task of the ventilator apparatus with PC is to create pressure in the respiratory circuit, the respiratory volume and LVV are controlled by the physician conducting the ventilation (Yehya et al., 2014). At the same time, dual control is in principle impossible.

However, the advantages of both the HFOV and APRV are much more significant. With high-frequency ventilation, transpulmonary pressure and airway pressure are lower than with traditional methods, and as with APRV, negative pressure in the pleural cavities is maintained. Unlike traditional mechanical ventilation, with high-frequency ventilation, hemodynamic depression and the activation of antidiuretic hormone are not observed, which is considered as a consequence of a decrease in stress reactions. With high-frequency ventilation, intrapulmonary gas distribution better than traditional ventilation methods and less blood shunting are noted. With inversion of inhalation/exhalation, it is about APRV. Preservation of spontaneous respiration in patients with ARDS allows for better blood oxygenation and hemodynamic stability compared to volume-controlled ventilation (Jain et al., 2016). In particular, a fundamentally new approach has been developed for the treatment of patients with acute lung injury and pneumothorax using pulmonary ventilation with two phases of positive airway pressure (BIPAP), followed by the earliest possible use of “mobilization of the alveoli” to improve treatment outcomes for the studied category of patients. The method allows, while maintaining independent patient breathing, to improve significantly gas exchange in the lungs, including in previously unventilated, damaged areas due to the discovery of previously collapsed alveoli (Bein&Wrigge, 2018).Thus, the advantages of both the HFOV and APRV provide not only admissible but rather effective risk/benefitratio.

Clinical Evidence in Favor of HFOV

The set pressure limit eliminates pressure peaks that are harmful to the lungs. In turn, ventilation with high-frequency oscillations (HFOV) differs from ordinary ventilation in that with HFOV, very short breaths are delivered very quickly (from 180 to 900 breaths per minute). HFOV helps to open collapsed lung, providing constant positive pressure in the airways. However, even considering the need to use therapeutic methods of respiratory support in critically ill patients, their use can pose certain risks for patients, and their implementation requires the determination of clear indications to avoid negative effects on the patient’s body.

In HFOV, an extremely small intermittent volume is supplied, the frequency of respiratory cycles can be from 3 to 28 Hz. MAP (mean airway pressure), inspiratory/expiratory ratio and, importantly, amplitudes can be set separately from each other. Its greatest advantage is an active expiratory phase, which ensures the absence of PEEP accumulation, meaning it virtually eliminates the risk of barotrauma. Oscillations are generated by an electromagnetic coil, which drives either a piston or a membrane (by the principle of sound dynamics). Modern systems have servo control MAP, which gives a special guarantee of patient safety. Moreover, any change in any parameter by the medical staff invariably leads to automatic alignment of the initially installed MAP, thus the risk of barotrauma for the patient is minimized (Meyers et al., 2019). With high-frequency ventilation, transpulmonary pressure and airway pressure are lower than with traditional methods, and, as with spontaneous ventilation, negative pressure in the pleural cavities is preserved (Guo et al., 2016). In addition, intrapulmonary gas distribution and less blood shunting are noted.

Clinical Evidence in Favor ofAPRV

APRV for adults is the most commonly used ventilation regimen to wean adult patients from the device. It has many appealing features applicable to current understanding of ALI/ ARDS treatment, in particular, minimization of ventilator-induced lung injury under the use of lung protective strategies. Numerous studies have been conducted to evaluate PSV in adult intensive care. As a result, the following benefits were recognized as most important (Mehta, 2016; Mehta, 2016):

Better synchronization between patient and apparatus,
More patient comfort,
Less need for sedation,
Decreased breathing,
Reduced oxygen consumption during breathing,
Reduced weaning time (observed in only a few studies),
Respiratory muscle endurance training,
Deepening inadequate (superficial) spontaneous breathing.

With this method, a constant positive airway pressure arises at a level of 2.5-6.0 cm water column, which contributes to better oxygen diffusion through the alveolar-capillary membrane (Meyers et al., 2019). Its advantage is the ability to ventilate with a controlled gas mixture and easily regulate the minute volume of breathing. Its disadvantage is the limitation of the ventilation frequency to 100-110 cycles per minute (with increasing frequency, the final expiratory pressure increases even more), which increases the risk of lung barotrauma (Papazian et al., 2019). Unlike convective ventilation, this method has a number of positive effects (Gupta, Patail, &Patadia, 2019). The mechanisms of influence on hemodynamics and clinical physiology of jet HF mechanical ventilation continue to cause controversy. Therefore, researchers’ efforts are aimed at further development of high-frequency ventilation methods to optimize the relief of hypoxic conditions, intracranial hypertension, and fewer undesirable effects.

Comparative Advantages of Both Methods

The very first experiments with HFOV in refractory hypoxiemia revealed its positive effect on hemodynamics. All researchers unanimously associate the reasons for this with low peak and medium airway pressures, where low transpulmonary pressure is invariably recorded (Stawicki, Goyal, &Sarani, 2009). The main difference between the effect on the hemodynamics of HF mechanical ventilation and convective one is to reduce the fluctuations in blood pressure due to changes in intrapulmonary pressure during the respiratory cycle.

The feature of High Frequency Positive Pressure Ventilation is the use of the so-called pneumatic collapse (Meyers et al., 2019), which creates a wide front of the gas flow and, due to its pressure, prevents the suction of atmospheric air (injection). With this method of ventilation, there is a constant positive pressure in the airways at the level of 2.5-6.0 cm water column, which contributes to better diffusion of oxygen through the alveolar-capillary membrane. The advantage of this method is the ability to ventilate with a controlled gas mixture and easily regulate the minute volume of breathing. Its disadvantage is the limitation of the ventilation frequency to 100-110 cycles per minute (with increasing frequency, the final expiratory pressure increases even more), which increases the risk of lung barotrauma (Meyers et al., 2019). Thus, both methods have specific and unique advantages and drawbacks. However, HFOV manifested better efficiency and safety in neonats (Mekik et al., 2018). This contributes to the choice of the method for different categories of patient – adults and neonats.

One of the modern developments in respiratory therapy of newborns is precisely high-frequency oscillatory ventilation of the lungs. This method is now of interest in neonatal practice, including in children with surgical pathology, as in this ventilation mode respiratory volumes equal to or less than the anatomically dead space are used and, consequently, the damaging effect on the lung parenchyma is reduced.

As to APRV, it has been found that the use of BIPAP mode compared to traditional lung ventilation results in better adaptation of the patient to the respirator, limiting the use of muscle relaxants and sedatives, and reduces the negative effect of mechanical ventilation on hemodynamics (Mallory &Cheifetz, 2019). Obviously, control of airway pressure and the possibility of spontaneous breathing reduce the negative impact of mechanical ventilation on hemodynamics and the risk of barotrauma when using the BIPAP mode and allows making respiratory support more objective, controlled, and safe.

Conclusion

Mechanical ventilation is undoubtedly only a method of replacing the functions of the diaphragm and respiratory muscles. Due to various specialists’ efforts and the most advanced engineering solutions, a large number of ventilation equipment has been created, allowing selection and use of a fairly diverse number of modes for respiratory support of patients in critical conditions of various origins. Constant innovation process is taking place in this field of medical science.

By replacing one of the very important functions in the body, mechanical ventilation creates great opportunities for the correction of other processes of the body’s life support. However, the evidence confirms that HFOV mechanical ventilation has a significant advantage over controlled volume mechanical ventilation in improving outcomes in people with acute lung injury (refractory hypoxemia) under mechanical ventilation, especially in newborns, while APRV is preferable for adults. Further studies involving more participants could provide reliable evidence to reach some definite conclusions.

References

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Cheriana, C. V., Kumarb, A., Akasapu, K., Ashtond, R. W., Aparnathe, M., & Malhotra, A. (2018). Salvage therapies for refractory hypoxemia in ARDS. Respiratory Medicine, 141, 150-158.

Claar, D. D.,&Hyzy, R. C. (2017). Refractory Hypoxemia and Acute Respiratory Distress Syndrome Adjunctive Therapies: An Open Question? Annals of the American Thoracic Society, 14(12), 1768-1769.

De Luca, D. &Dell’Orto, V. (2016). Non-invasive high-frequency oscillatory ventilation in neonates: review of physiology, biology and clinical data. Arch Dis Child Fetal Neonatal Ed., 101, F565-F570.

Guo, Y., Wang, Z., Li, Y., Pan, L., Yang, L., Hu, Y., Sun, Y., …Chen, Z. (2016). High-frequency oscillatory ventilation is an effective treatment for severe pediatric acute respiratory distress syndrome with refractory hypoxemia. Therapeutics and Clinical Risk Management, 12, 1563-1571.

Gupta, R., Patail, H., &Patadia, D. (2019). Airway pressure release ventilation (APRV) ventilator mode in ICU. EC Pulmonology and Respiratory Medicine, 8(11), 101-112.

Jain, S. V., Kollisch-Singule, M., Sadowitz, B., Dombert, L., Satalin, J., Andrews, P., …, Habashi, M. (2016). The 30-year evolution of airway pressurerelease ventilation (APRV). Intensive Care Medicine Experimental, 4(11), 1-18.

Jiang, H., Zhang, B., Zhao, J., Hu, A., Qiu, Y., Ding, A.,…, Song, Y. (2018). Efficacy of high-frequency ventilation in adult patients with acute respiratory distress syndrome: a meta-analysis with trial sequential analysis of randomized clinical trials. International Journal of Clinical and Experimental Medicine, 11(12), 12828-12841.

Mallory, P., &Cheifetz, I. (2019). A comprehensive review of the use and understanding of airway pressure release ventilation. Expert Review of Respiratory Medicine, 14(3), 307-315.

Mehta, C., & Mehta, Y. (2016). Management of refractory hypoxemia. Annals of Cardiac Anaesthesia, 19(1), 89-96.

Mekik, E., Erdeve O., Okulu, E., &Atasay, M. (2018). Rescue High-Frequency Oscillatory Ventilation in Neonatal Respiratory Failure Unresponsive to Conventional Mechanical Ventilation. Iranian Journal of Pediatrics, 22, 1-12.

Meyers, M., Rodrigues, N., & Ari, A. (2019). High-frequency oscillatory ventilation: A narrative review. Canadian Journal of Respiratory Therapy, 55, 40-46.

Owens, W. (2017). The advanced ventilator book. Berlin, Germany: First Draught Press.

Papazian, L., Aubron, C., Brochard, L., Chiche, J.-D., Combes, A., Dreyfuss, D., …. Faure, H. (2019). Formal guidelines: Management of acute respiratory distress syndrome. Annals of Intensive Care, 9(69), 1-18.

Stawicki, S. P., Goyal, M., &Sarani, B. (2009). Analytic reviews: High-frequency oscillatory ventilation (HFOV) and airway pressure release ventilation (APRV): A practical guide. Journal of Intensive Care Medicine, 24(4), 215-229.

Yehya, N., Topjian, A. A., Lin, R., Berg, R. A., Thomas, N., &Friess, S. H. (2014). High frequency oscillation and airway pressure release ventilation in pediatric respiratory failure. Pediatric Pulmonology, 49(7), 707-715.

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