Background

Artificial ventilation has served many patients who were admitted to the Intensive Care Unit (ICU). Normally, artificial ventilation is achieved through positive pressure ventilation, which results in gas delivery and expansion of the alveoli and gas exchange. However, artificial ventilation was non-physiological and presented several challenges. Moreover, it was not effective for patients with lung diseases since they could not receive enough oxygen or eliminate carbon dioxide. It could also cause lung or alveolar damage from high air pressure.

High-Frequency Oscillatory Ventilation (HFOV) emanated as an option for artificial ventilation. This paper explores HFOV and shows areas of applications of HFOV and some specific aspects nurses consider when handling patients under HFOV.

HFOV involves a fast delivery of little fluctuating volumes of gas and the use of the high mean airway pressures (Chan, Stewart and Mehta, 2007). This is a form of mechanical ventilation, which relies on a steady increasing pressure accompanied by pressure changes oscillating within the airway at extremely rapid rates. The rapid pressure and associated changes result in small tidal volumes. The tidal volumes are a minute that dead space.

HFOV uses alternative systems of gas exchanges, such as “molecular diffusion, Taylor dispersion, turbulence, asymmetric velocity profiles, Pendelluft, cardiogenic mixing, and collateral ventilation” (Pillow, 2005, p. s135).

Methods applied in HFOV

HFOV has three techniques that are applicable in a clinical setting. They include high-frequency percussive ventilation, high-frequency jet ventilation (HFJV), and HFVO. However, the paper focuses on HFOV.

The use of HFOV involves oscillation of a piston pump with the range of 180 to 600 breaths every minute. HFOV has unique capabilities relative to other techniques. The return stroke of the piston enhances the movement of the gas. This creates an active expiration, which reduces cases of gas trapping. At the same time, HFOV results in humidification when the gas passes through the humidifier.

HFOV also controls and separates ventilation and oxygenation (inspired oxygen).

Gas flow during HFOV

In the HFOV process, gas delivery takes place through “bulk means because of the convection within the airways to the alveolar areas” (Chan et al., 2007). Some quantities of the transported gas remain at the center of the airways to create the dead space volume. Therefore, the volume of the delivered gas must be “more than the dead space so that gas exchange may take place” (Chan et al., 2007).

It is believed that gas delivery takes place through several convective and diffusive methods (Chan et al., 2007). The process involves the movement of the gas into the alveolar areas near the airways. Taylor dispersion and asymmetric velocity elements lead to increased mixing of the gas in the airways due to the high concentration of energies in the HFOV process.

Asynchronous filling of the nearby alveolar areas also takes place, which results from empty spaces, cardiogenic mixing, and connections in alveoli.

Applications of HFOV

Studies have documented the application of HFOV in pediatric patients and newborn children (van Velzen, De Jaegere, van der Lee and van Kaam, 2009). However, the use of HFOV among adults has not gained popularity as further research with adult patients continues.

HFOV offers several advantages, which include small fluctuating volumes of gas, constant supply with low variations, and enhanced airway pressure. The method is suitable for patients with lung conditions and atelectasis. These conditions may escalate and result in lung injuries due to pressure and effect of the ventilator for the gas exchange during administration. In some cases, atelectasis may be reversed when HFOV is used because HFOV can reduce enlargement of the airways and alveolar areas.

HFOV is effective in reducing lung injuries and other ventilator-related conditions. The small, fluctuating gas volumes, pressure changes, and minimized over enlargement explain why HFOV is effective for managing patients with lung conditions.

The high rate of gas flow also increases gas mixing. However, it is imperative to note that tidal gas volumes are normally smaller than usual. Thus, one should understand the movement of oxygen and carbon dioxide under non-physiologic conditions.

  • Bulk transportation of the gas offers conventional gas transfer to alveoli with areas occupied by dead space volumes
  • HFOV gas flow results from coaxial flow in which gases flow both inwards and outwards based on the position.
  • Taylor dispersion may create gas mixing within the tube
  • Pendelluft may also cause gas mixing in the lung areas
  • Improved molecular movement may take place at the secondary alveolar and enhance kinetic energy from the oscillations

Although these are possible explanations for the gas flow during HFOV, their importance is still under review and debates. However, some scholars have pointed out that these processes may operate simultaneously in HFOV.

These non-physiological factors, rapid gas transfer, and steady airway pressure are some of the advantages of using HFOV over the traditional ventilation approaches. Moreover, the ability of the HFOV to reduce enlargement of tissues has touted it as the best option rather than the conventional positive pressure ventilation.

Complications when using HFOV

Some studies have noted that HFOV has some complications (Chan et al., 2007). Although HFOV and other oscillatory ventilators are in use, their effects are still understudies and review. Also, some issues have emerged with user training and technical expertise because generalization of HFOV systems may not be effective.

Some studies have focused on any possible gas trapping that may result in the lung over enlargement (Leipälä, Sharma, Lee, Milner and Greenough, 2005). Inadvertent Positive End Expiratory Pressure (PEEP) associated with distending pressure is difficult to gauge directly. Consequently, it remains a controversial issue about HFOV complications. One possible complication of HFOV is the progressive atelectasis. Although many viewed HFOV as an effective solution to this challenge, small fluctuating gas volumes at a steady pressure could increase the condition. However, it also remains a controversial issue.

Also, other studies have shown that HFOV could be responsible for tracheal inflammation and other conditions in the bronchial. These conditions indicate the need to improve gas humidification.

Overall, HFOV offers some benefits, which include the following:

  • Stable increase of the lung
  • The use of alveolar space
  • Lowers potential risks of volutrauma
  • Eliminates challenges related to high airway pressure
  • Lowers risks associated with airway expansion
  • Enhances gas mixing and ventilation and perfusion matching

Caring for patients under HFOV

It is imperative for care providers to understand some certain nursing aspects for patients under HFOV.

The sight of patients undergoing oscillation might disturb families, friends, and relatives. Therefore, it is imperative to prepare the family about the treatment. The pressure increases once the patient is under the oscillator. Therefore, it is advisable to monitor the patient for changes in the chest vibrations. The process is referred to as chest wiggle factor, which denotes equal and variations in the chest shapes. It is advisable to monitor chest wiggle throughout the process after initiation. Any movement or obstruction of the ET tube could result in a diminished chest wiggle. When the chest wiggle occurs on a single side, then the patient may have a pneumothorax. Therefore, it is necessary to evaluate chest wiggle after repositioning of the patient.

It is nearly impossible to examine a patient with a stethoscope during an oscillation process. Nurses must also use different tools and clinical signs to evaluate the movement of air in the chest during HFOV (Leipälä et al., 2005). Air movement in the chest differs during treatment. Nurses may listen to the piston through the chest and be able to note the intensity and sound produced by it. However, the nature of the sound that care providers should hear remains controversial and unclear. As a result, many studies have concluded that it may not be useful to conduct chest auscultation when a patient is under HFOV.

HFOV requires a closed system suction unit because it is not advisable to disengage the patient because of the de-recruitment of the lung volume. However, within the first 24 hours, suction may not be required. Nurses should draw the suction catheter from the ET tube once the procedure is complete. However, it is advisable to conduction suction before engaging a patient on the HFOV.

Care providers should note the appropriate time to engrave and lock the gas tube. The measure is important because it will act as a point of reference for future procedures.

Nurses should observe the ET tube and its position regularly. Nurses must not disengage the ET tube immediate after the procedure because disconnection may result in de-recruitment of the alveolar.

It is also advisable to assess blood gases and condition of the patients’ cardiovascular. However, all procedures must be within acceptable and safe limits.

Nurses must be able to notice complications, particularly when obstruction occurs in the tube. This may involve changes in the amplitude and increase in carbon dioxide production. Pneumothorax may involve observing any abnormalities in the size of the chest walls and declines in blood pressure. Such observations may also include noting any changes in the gas pressure and increment in the central venous pressure. In case of any challenges, nurses must inform physicians immediately. During positioning of the patient, two nurses may protect the ET tube and prevent it from disconnection.

Lastly, before the administration of the HFOV, it is necessary to ensure that the gas is sufficiently humidified to prevent any possible Necrotizing Tracheobronchitis (Chan et al., 2007).

Conclusion

HFOV is a major improvement on the conventional artificial ventilation for many patients admitted into the ICU. Some of the improvements include gas mixing, a steady supply of gas, and enhanced ventilation. HFOV reduces risky pressure swings and eliminates cases of airway pressure peaks while atelectasis is lessened.

Although HFOV has several complications, many studies show that it is an improvement and safe for patients who require advanced oscillation (Li, Wang, Li, and Yan, 2013). Moreover, nurses must observe and meet specific requirements for patients under HFOV.

References

Chan, K., Stewart, T., and Mehta, S. (2007). High-Frequency Oscillatory Ventilation for Adult Patients With ARDS. Chest Journal, 131(6), 1907-1916. Web.

Leipälä, A., Sharma, A., Lee, S., Milner, D., and Greenough, A. (2005). An in vitro assessment of gas trapping during high frequency oscillation. Physiological Measurement, 26(3), 329-36.

Li, S., Wang, X., Li, S., and Yan, J. (2013). High-frequency oscillatory ventilation for cardiac surgery children with severe acute respiratory distress syndrome. Pediatric Cardiology, 34(6), 1382-8. Web.

Pillow, J. (2005). High frequency oscillatory ventilation: Mechanisms of gas exchange and lung mechanics. Critical Care Medicine, 33(3 suppl.), S135-S141.

van Velzen, A., De Jaegere, A., van der Lee, J., and van Kaam, A. (2009). Feasibility of weaning and direct extubation from open lung high-frequency ventilation in preterm infants. Pediatric Critical Care Medicine, 10(1), 71-5. Web.

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