Elsevier

Australian Critical Care

Volume 20, Issue 4, November 2007, Pages 126-131
Australian Critical Care

High flow nasal oxygen generates positive airway pressure in adult volunteers

https://doi.org/10.1016/j.aucc.2007.08.001Get rights and content

Summary

Introduction

The use of non-invasive ventilation (NIV) as an alternative to intubation in respiratory failure is associated with better outcomes in certain conditions. NIV is often poorly tolerated by patients hence precipitating the need for invasive ventilation. High flow nasal (HFN) oxygen delivery is a potential alternative to NIV as it delivers air and oxygen via a humidified circuit at flows greater than those traditionally used with a nasal interface.

Body

Studies of paediatric patient using high flow nasal oxygen therapy have been shown to have similar efficacy as nasal continuous positive airway pressure (CPAP). Although the degree of positive pressure and the effect of different flow rates on positive pressure generation have not been well defined or studied in the adult intensive care population.

St. Vincent's Health Human Research and Ethics Committee granted approval to this study and also awarded a $3000 grant. Volunteers were fitted with the Fisher & Paykel high flow nasal interface (RT034) and pharyngeal pressures were recorded with flows from 0 to 60 L/min.

Expiratory pressures with the mouth closed were higher than those with the mouth open and this was statistically significant (<0.001). Expiratory pressures were higher with the mouth closed and were statistically different (p < 0.001). EPPs were higher amongst female subjects compared to male subjects and were statistically different between genders for both open (p < 0.05) and closed (p < 0.001) measurements.

Conclusion

This study has demonstrated that high flow nasal therapy is associated with the generation of significant positive airway pressure in volunteers. In conclusion there is a degree of CPAP generated with the HFN therapy, which is flow dependent and also dependent on whether the person is breathing with mouth open or closed.

Introduction

The use of non-invasive ventilation (NIV) as an alternative to intubation in respiratory failure is often associated with better outcomes. However, NIV requires a tight fitting mask that is often poorly tolerated by patients with a resultant need for invasive ventilation.1 If adequate oxygen could be delivered by a non-occlusive delivery system that is both more comfortable for patients and better tolerated, invasive ventilation due to intolerance might be avoided.

High flow nasal (HFN) oxygen delivery is a potential alternative to NIV in respiratory failure. HFN refers to delivery of air and oxygen via a humidified circuit at flows greater than those traditionally used with a nasal interface. In adults it has been demonstrated that flows of up to 40 L/min are well tolerated. Importantly even at these high flows inspired gas remains adequately warmed and humidified.2, 3, 4 In the paediatric population studies of high flow nasal oxygen therapy has been shown to have similar efficacy as nasal continuous positive airway pressure (CPAP).5, 6

One mechanism by which HFN may be of benefit is through the development of positive airway pressure that may improve ventilation perfusion matching and balance intrinsic positive end expiratory pressure (PEEP). Studies in both paediatric and adult patients have demonstrated the presence of positive airway pressure with HFN. It has been demonstrated in infants that nasal cannulae could result in “inadvertant’ positive pressure the level of which was influenced by flow rates and the diameter of nasal cannulae.7 In preterm infants it has been found that HFN generated similar intrathoracic pressures to CPAP. Work of breathing was similar between CPAP and HFN leading them to conclude that HFN is a comparable treatment to CPAP.6 Low flow and HFN were compared during exercise in subjects with chronic obstructive pulmonary disease (COPD). They concluded that high flows of humidified oxygen improved exercise performance in patients with COPD and severe oxygen dependency.8 The effect of HFN on adult volunteers at both rest and exercise was investigated using the Fisher & Paykel system. Both delivered oxygen concentration and pharyngeal pressures were evaluated at a range of different oxygen flow rates. It was found that there was flow dependent CPAP during nasal breathing.9

However the degree of positive pressure and the effect of different flow rates on positive pressure generation have not been well defined. The aim of this study is to document airway pressures during the use of HFN with different gas flows and breathing conditions and to determine factors that influence the amount of positive expiratory pressure generated. Vapotherm® and Fisher & Paykel, both manufacture high flow nasal humidification systems that are alternatives to face masks for oxygen delivery. We chose to use the Fisher & Paykel MR 850 as the Food and Drug Administration (FDA) had temporarily recalled the Vapotherm® machine from use.

Section snippets

Method

Human Research and Ethics Committee approval was granted for this study and also a grant-in-aid of $3000 was awarded. Informed consent was required and obtained from the volunteer participants. Five male volunteers and five female volunteers were recruited from the intensive care unit (ICU) staff. Two other volunteers were excluded from taking part because of difficulties in passing the catheter via the nose. We used height and weight data as reported by the participants. We did not ask for a

Results

Ten adult subjects were studied of whom five were male. Demographic data are displayed in Table 1. In comparison the male and female participants were of approximately the same age 33 years with a range of 29–41 years, although the body mass index (BMI) of the female participants was slightly higher then the males.

Expiratory pharyngeal pressures (EPP) for both mouth open and mouth closed measurements are presented by gender in Table 2. As flow rates increased so did EPP with both the mouth open

Discussion

It has been suggested that if high flow nasal humidification devices prove to be effective further research is required to determine how the therapy would be incorporated into clinical practice guidelines.2

Although many studies have been published regarding the devices use in the paediatric intensive care population. No comprehensive study has been undertaken into the use of high flow nasal humidification for the Australian intensive care adult patient group. Although a number of studies have

Acknowledgements

We would like to thank the staff at St. Vincent's Hospital Melbourne Intensive Care Unit who volunteered to be involved in the study. We would like to acknowledge the financial contribution in the form of a grant-in-aid from the HREC at St. Vincent's Health.

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