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Dr. Brown is Medical Director, New Mexico Center for Sleep Medicine, and Associate Medical Director (Medical Specialties), Lovelace Health Systems, Inc., Albuquerque, NM; and Clinical Professor of Medicine, Division of Pulmonary, Critical Care, and Allergy, University of New Mexico School of Medicine, Albuquerque, NM.
Correspondence to: Lee K. Brown, MD, FCCP, Clinical Professor of Medicine, University of New Mexico School of Medicine, Medical Director, New Mexico Center for Sleep Medicine, Associate Medical Director (Medical Specialties), Lovelace Health Systems Inc., 4700 Jefferson Blvd NE, Suite 800, Albuquerque, NM 87109; e-mail: lkbrown{at}alum.mit.edu
The question of humidification during nasal continuous positive airway pressure (CPAP) therapy is an important issue because of the high prevalence of nasal symptoms associated with CPAP treatment and the effect these symptoms have on patient compliance. To enhance compliance, it would seem to make sense that the drying effect of the CPAP flow should be countered by humidifying the inspired gas as much as possible. Unfortunately, regional payers have resisted underwriting the cost of heated humidifiers (retail, ca. $580.00), which are significantly more expensive than simple passover humidifiers (ca. $115.00). Increasingly, payers are looking for data in the medical literature that would justify the use of humidifiers, and these data are sorely lacking. Outcomes data (eg, comparing CPAP compliance and side effects with and without various humidifiers) would constitute the best kind of evidence, but have appeared only recently, and partly in abstract form.1 2 Given our current state of knowledge, can we make a reasonable case for the use of humidification during CPAP therapy, and what does the article in the January issue of CHEST by Martins de Araújo and colleagues3 contribute to this case?
The use of humidified CPAP air would best be justified by a train of evidence that demonstrates the following: (1) CPAP compliance is adversely affected by local nasal and oral symptoms; (2) CPAP can alter nasal physiology in such a way as to produce these symptoms; (3) a humidifier significantly raises the relative humidity (rH) of CPAP air; and (4) humidification improves compliance with therapy or positively impacts one or more measures of CPAP efficacy.
Effect of Local Nasal and Oral Symptoms on CPAP Compliance
The high incidence of nasal/oral side effects in patients treated with nasal CPAP has been widely reported. In a series of studies published over the last decade, one or more of the symptoms of nasal/oral dryness, nasal congestion, rhinorrhea, sneezing, or epistaxis were experienced by at least 65% of patients.4 5 6 7 However, studies that correlate nasal/oral side effects from CPAP therapy with objectively measured CPAP use have generally not shown a strong relationship. Of the several small-scale studies that examined this issue, Engleman and colleagues8 were able to demonstrate reduced compliance in patients with more frequent (mainly nasal/oral) side effects, while Pepin and coworkers6 found no correlation with side effects, and Kribbs et al5 found a relationship with "claustrophobia" but not with nasal/oral complaints. The most definitive study of CPAP compliance to date was recently published by McArdle and coworkers,9 who quantified objective CPAP use in 1,211 consecutive patients. They found correlations with the degree of pretreatment sleepiness and with the apnea/hypopnea index, but unfortunately do not report whether they analyzed their data with respect to frequency of side effects.
Upper Airway Pathology Induced by Dry Nasal CPAP Air
Although extensive research is available concerning the effects of dry air on the tracheobronchial tree,10 relatively less attention has been paid to the upper airway. In patients with allergic rhinitis, warm humidified air is known to attenuate the response to inhaled antigen,11 while cold dry air increases the osmolality of nasal secretions, thereby triggering the release of inflammatory mediators that induce symptoms.12 In addition, two studies are available directly assessing changes in nasal physiology produced by high flows of unhumidified CPAP air associated with mouth leaks. Hayes and colleagues13 applied nasal CPAP to eight subjects (we are not told of any history of allergic rhinitis) who were instructed to produce a mouth leak for a time sufficient to exhale 500 L of air. Blood flux in the nasal mucosa was measured using a laser Doppler flowmeter, and nasal volume and cross-sectional area were determined by acoustic rhinometry. Measurements were made on 2 separate days, before and after application of unhumidified CPAP air as well as CPAP air passed through a heated humidifier. Significant increases in nasal blood flux (averaging 65%) were associated with dry air but not with heated, humidified air. However, nasal geometry was not affected by either dry or humidified air. Interestingly, the experiment with dry air was repeated in four subjects who were instructed to prevent mouth leaks, and no change in nasal blood flux occurred. Richards and coworkers14 studied six subjects (one with seasonal allergic rhinitis) subjected to nasal CPAP air at a variety of temperatures and humidities, and with and without mouth leakage. Nasal resistance as measured by posterior rhinomanometry increased by > 300% when dry air was applied in the presence of a mouth leak. This effect was not attenuated by a cold, passover humidifier, but was largely prevented by use of a heated humidifier or by eliminating the mouth leak.
Identification of an Effective Humidifier
This task was, in part, already tackled by Richards and colleagues14 in the study just mentioned, since the increase in nasal airway resistance produced by CPAP with a mouth leak was prevented by a heated humidifier but not by a cold, passover humidifier. This is also where the investigation by Martins de Araújo and coworkers3 contributes another link in the chain of evidence. Their study actually comprises two separate experiments performed on different groups of patients with moderate-to-severe obstructive sleep apnea syndrome (OSAS) on long-term treatment with nasal CPAP and complaining of nasal symptoms. In one experiment encompassing eight patients, rH and temperature of the CPAP air within the mask were measured during a full night of polysomnography at their usual CPAP pressure. They received unhumidified air during the first half of the night and heated humidified air during the second half, while an oral thermistor identified mouth leaks. Not surprisingly, when mouth leaks were not present, rH during treatment with dry air was significantly lower compared with treatment with warm humidified air. More importantly, when mouth leaks were present (totaling just under one third of the night on average), the heated humidifier was able to maintain rH levels comparable to those measured with dry air and no mouth leak. The heated humidifier also reduced the time spent with mouth leakage, suggesting that these patients experienced less nasal obstruction, and therefore less need for mouth breathing. The second study involved 17 patients who were studied during the day while using CPAP. Measurements were made for 30-min periods breathing through the nose and 5-min periods with mouth leakage, while utilizing a sequence of dry air, heated humidified air, and dry air administered with a full face mask rather than the usual nasal mask. The heated humidifier attenuated the decrease in rH caused by periods of mouth leak, while breathing through the full face mask completely prevented the drying effect of mouth leakage even without a humidifier of any sort. One can conclude that heated humidification of CPAP air is indeed effective in maintaining improved levels of rH even in the presence of mouth leaks, but that the most "bang for the buck" is obtained by using a full face mask. This option was, indeed, offered to some of the patients studied by Martins de Araújo and colleagues.3 Unfortunately, they reported that acceptance of the use of full face masks was extremely low: only 2 of 17 patients agreed to this change in their therapy. This finding is corroborated by the report of Mortimore et al15 of reduced compliance with CPAP use when full face masks were prescribed instead of nasal masks.
Outcome Studies
Unfortunately, this category of evidence has received the least amount of attention from investigators. However, two studies (one published as an abstract) hold out the promise that this situation will be remedied in the near future. Rakotonanahary and coworkers,2 from the same investigative group as the Martins de Araújo study, prospectively enrolled 87 consecutive patients with severe OSAS who were beginning treatment with nasal CPAP. If nasal symptoms developed, a cold passover humidifier was added; if they persisted, a heated humidifier was substituted. Use of CPAP was measured in terms of hours of use per night, although it is not specified in the abstract whether this was obtained by patient report or from CPAP elapsed-time monitors. Almost 30% of the study group required the heated humidifier for persistent nasal symptoms, and CPAP use increased from median values of 3 to 5.5 h in these patients. Advanced age, the presence of chronic nasal disease, or a history of uvulopalatopharyngoplasty predicted the need for heated humidification.
Most recently, Massie and coworkers1 reported a randomized, crossover study comparing heated, cold, and no humidification in 38 patients receiving CPAP therapy for OSAS. Three-week periods using each humidifier were separated by 2-week periods using no humidifier, and outcome measures included objective compliance (time of pressure recorded in the CPAP internal memory), a questionnaire, and a Likert scale quantifying satisfaction with CPAP therapy. Objective CPAP use increased by about 0.6 h/night on average with heated humidification compared to dry air, while cold humidification did not improve compliance at all. Heated humidification elicited fewer symptoms that could potentially interfere with CPAP use when compared to both dry air and cold humidification; cold humidification again did not differ in this respect from dry air. The symptoms of dry mouth/throat/nose demonstrated the most significance. Heated humidification was preferred by 76% of patients over cold humidification.
In summary, the available data support the following conclusions: (1) a large proportion of CPAP users complain of nasal and oral symptoms, but no conclusive proof is available that patients with poor compliance have more of these symptoms then those with better compliance; (2) credible mechanisms exist by which CPAP could induce nasal and oral symptoms; (3) heated humidification improves the rH of CPAP air more reliably then cold humidification, particularly in the presence of a mouth leak, while a full face mask also performs well but is poorly tolerated; and (4) outcome studies have been performed that support the use of heated humidification over dry or cold humidified air, but only one study has thus far been published in a peer-reviewed journal. For clinicians dealing with the issue of poor compliance with nasal CPAP on a daily basis, these data are sufficiently compelling to justify the prescribing of heated humidification for patients complaining of nasal/oral symptoms, particularly when nasal corticosteroids and a chin strap are not effective. Consideration should also be given to a full face mask for the minority of patients able to tolerate this type of interface. As our dermatology colleagues have been teaching us for years, "if it’s dry, wet it."
Acknowledgements
The author would like to thank Dr. John E. Heffner for his thoughtful review of this manuscript.
References
This article has been cited by other articles:
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  M. J. Mador, M. Krauza, A. Pervez, D. Pierce, and M. Braun Effect of Heated Humidification on Compliance and Quality of Life in Patients With Sleep Apnea Using Nasal Continuous Positive Airway Pressure Chest, October 1, 2005; 128(4): 2151 - 2158. [Abstract] [Full Text] [PDF]
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J. C. Winck, J. L. Delgado, J. Almeida, J. A. Marques, and B. Fleury Heat It or Wet It? Nasal Symptoms Secondary to the Use of Continuous Positive Airway Pressure in Sleep Apnea Chest, January 1, 2001; 119(1): 310 - 312. [Full Text] [PDF]
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