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Effect of Heated Humidification on Compliance and Quality of Life in Patients With Sleep Apnea Using Nasal Continuous Positive Airway Pressure^*

^* From the Division of Pulmonary, Critical Care and Sleep Medicine (Drs. Mador, Krauza, and Pervez), State University of New York at Buffalo, and Veterans Affairs Western New York Healthcare System (Ms. Pierce and Mr. Braun), Buffalo, NY.

Correspondence to: M. Jeffery Mador, MD, Associate Professor of Medicine, Division of Pulmonary, Critical Care & Sleep Medicine, Section 111S, State University of New York at Buffalo, Veterans Administration Medical Center, 3495 Bailey Ave, Buffalo, NY 14215; e-mail: mador{at}acsu.buffalo.edu

	Abstract

TOP Abstract Introduction Materials and Methods Results Discussion References

 
Study objective: To determine whether the addition of heated humidification at treatment initiation with nasal continuous positive airway pressure (CPAP) would lead to better CPAP compliance and improve quality of life and subjective sleepiness in patients with sleep apnea.

Design: Randomized controlled trial.

Setting: An academic sleep center located at a Veterans Affairs hospital.

Patients: Ninety-eight patients with obstructive sleep apnea who had not received nasal CPAP previously.

Measurements and results: Patients received heated humidification at CPAP initiation in the treatment group. In the control group, patients could receive heated humidification only if they had upper airway symptoms that could not be treated successfully with simpler measures. Patients were followed up at 1 month, 3 months, and 12 months. Outcome measures were compliance with nasal CPAP (mean hours per night at effective pressure), quality of life as measured by the Calgary sleep apnea quality of life index, subjective sleepiness measured with the Epworth sleepiness scale, and CPAP side effects. There was no difference in CPAP compliance between groups. Quality of life and subjective sleepiness improved in both groups with nasal CPAP therapy, but there was no difference in the extent of improvement between groups. The overall CPAP side effect score was similar in both groups, but individual symptoms of dry nose and dry mouth and throat were significantly lower in the heated humidification group.

Conclusions: The addition of heated humidification when nasal CPAP was instituted did not lead to better compliance, greater improvement in sleepiness, or improved quality of life, but was associated with fewer symptoms attributable to the upper airway.

Key Words: compliance • continuous positive airway pressure • heated humidification • obstructive sleep apnea • quality of life

	Introduction

TOP Abstract Introduction Materials and Methods Results Discussion References

 
Obstructive sleep apnea (OSA) is extremely common¹ and if left untreated has considerable deleterious effects, including excessive daytime sleepiness, neurocognitive deficits, increased incidence of motor vehicle accidents, as well as possible associations with hypertension, myocardial infarction, and stroke. Nasal continuous positive airway pressure (CPAP) is the treatment of choice for this condition.²³⁴ Despite the effectiveness of nasal CPAP, patients have difficulty adhering with this treatment regimen.⁵ Indeed, when compliance with nasal CPAP was defined very liberally as using the machine for at least 4 h for 5 nights a week, only 46% of patients met these criteria.⁶ The pattern of nasal CPAP usage tends to be determined early, with usage at 1 month predicting usage at 3 months.⁶ In one study,⁷ patients with persistent suboptimal usage could be identified by their pattern of usage during the first 4 nights of therapy. Thus, interventions designed to improve compliance might be most beneficial if introduced when treatment is initiated. Improved compliance with nasal CPAP might also lead to greater improvements in quality of life with therapy.

Forty-six to 73% of patients receiving nasal CPAP report significant local side effects such as nasal congestion, dry nose or throat, and discomfort associated with cold air.⁸⁹¹⁰¹¹ Heated humidity has been successfully used to treat these symptoms.¹²¹³¹⁴ In patients complaining of upper airway symptoms when receiving nasal CPAP, the addition of heated humidification significantly improved CPAP compliance.¹² In a crossover short-term study,¹³ patients starting nasal CPAP therapy received cold humidification, heated humidification, or no humidification in a randomized fashion. Nasal CPAP compliance was significantly higher when patients were receiving heated humidification.¹³ In another crossover study,¹⁴ heated humidification also modestly improved compliance with nasal CPAP when compared to no humidification. These crossover studies suggest that nasal CPAP compliance might be improved if all patients received heated humidification during the initiation of nasal CPAP therapy. However, it may be that only patients with significant upper airway symptoms benefit from heated humidification. Furthermore, heated humidification adds significant cost and complexity to nasal CPAP therapy.¹³¹⁴¹⁵ The purpose of this study was to determine if the addition of heated humidification when nasal CPAP therapy is initiated would lead to better compliance with nasal CPAP therapy and improve quality of life and reduce subjective sleepiness in patients with sleep apnea. Patients were randomized to receive either heated humidification with initiation of nasal CPAP or standard care. In the standard care group, patients prescribed nasal CPAP followed a treatment algorithm for treatment of nasal CPAP side effects in which persistent symptoms of nasal or throat dryness unresponsive to simpler measures were prescribed heated humidification. Thus, the study addresses whether the addition of heated humidification at treatment initiation would provide superior outcomes compared to providing heated humidification only when patients complain of relevant upper airway symptoms that are unresponsive to simple measures.

	Materials and Methods

TOP Abstract Introduction Materials and Methods Results Discussion References

 
Subjects
Patients were enrolled in the study from the pulmonary sleep clinic at the Veterans Affairs Western New York Healthcare System from March 2002 to November 2003. To be eligible for the study, patients had to have a diagnosis of OSA (defined in our laboratory as an apnea-hypopnea index [AHI] 10/h with the majority of events being obstructive in nature and a subjective complaint of sleepiness), to have never received CPAP treatment previously, to be willing to try nasal CPAP therapy, to have had a successful nasal CPAP titration study, and to be able to breath through the nose sufficiently to tolerate nasal CPAP. Patients who were initially prescribed a full oronasal mask based on the laboratory CPAP titration were excluded. Comorbid medical conditions were not an exclusion criteria unless they were believed to interfere potentially with nasal CPAP therapy. The study was approved by the appropriate institutional review boards, and written informed consent was obtained from all participants.

Polysomnography
Standard overnight polysomnography included recordings of EEG, electro-oculogram, submental and bilateral leg electromyograms, and ECG. Airflow was measured by a nasal pressure transducer (Pro-flo plus; Pro-Tech; Mukiteo, WA) and respiratory effort by thoracoabdominal piezoelectric belts. Measurement of arterial oxyhemoglobin saturation was performed with a finger pulse oximeter (Nonin 8600M; Nonin Medical; Plymouth, MA). All signals were collected and digitized on a computerized polysomnography system (Sandman; Nellcor Puritan Bennett; Ottawa, ON, Canada).

Sleep stages were scored in 30-s epochs using the Recht-schaffen and Kales sleep scoring criteria.¹⁶ Each epoch was analyzed for the number of apneas and hypopneas. An apnea was defined as the absence of airflow for > 10 s. An obstructive apnea was defined as the absence of airflow in the presence of rib cage and/or abdominal excursions, while a central apnea was defined as the absence of airflow and rib cage and abdominal excursions. Events were considered hypopneas when a visible reduction in airflow lasting at least 10 s was associated with either a 4% decrease in arterial oxyhemoglobin saturation or an EEG arousal occurred. An arousal was defined according to the criteria proposed by the Atlas Task Force.¹⁷ The AHI was defined as the number of apneas and hypopneas per hour of sleep. A sleep study finding for OSA was considered positive when the AHI was 10/h.

All patients underwent a nasal CPAP titration study in the sleep laboratory either as part of the initial diagnostic study (split-night study) or during a separate night. Patients were initially started at a CPAP pressure of 4 cm H₂O, and the pressure was increased in 2-cm increments. The final CPAP pressure chosen was the one that minimized respiratory events and snoring in all postures and sleep stages.

Study Design
Patients were all assigned nasal CPAP machines (HC221; Fisher & Paykel; Auckland, New Zealand), had their masks fitted, and were instructed in CPAP usage by a respiratory therapist highly experienced with nasal CPAP therapy. Patients were randomly assigned using a random-number generator to receive heated humidification at CPAP initiation or standard care. The nasal CPAP machine employed has a built-in heated humidifier. For those patients who were not assigned to heated humidification, the heater on the humidifier was turned off. Patients were not instructed in its usage and were told specifically not to use humidification. Those patients assigned to heated humidity were provided detailed instructions on its usage. The dial of the humidifier was set initially at 2 as per the recommendations of the manufacturer. The heated humidifier employed is equipped with ambient tracking and according to the manufacturer is supposed to automatically adjust the heater plate temperature as room temperature changes, minimizing condensation while maintaining satisfactory humidification. Nevertheless, if droplets formed in the mask, the patients were told to reduce the setting by 0.5 U until the condensation disappeared, while the patients were allowed to increase the setting in 0.5-U increments if symptoms of dryness persisted.

Patients were called within 7 days of CPAP initiation to attempt to address any problems arising from CPAP usage. Patients were seen in regular study visits at 1 month, 3 months, and 12 months but could call the therapist or their provider if problems developed at any time during the study period.

Outcome Measures
Nasal CPAP compliance was directly measured using compliance software provided by the CPAP manufacturer. The compliance monitor provided data on how many hours per night the machine was on and how many hours it was at the prescribed pressure. These data were provided on a nightly basis, and mean usage was calculated. We used the average number of hours at the prescribed pressure as our compliance measure.

Quality of life was assessed with the disease-specific Calgary sleep apnea quality of life index,¹⁸¹⁹ which has been shown to be a highly responsive tool for measuring quality of life in patients with sleep apnea.¹⁹ It assesses four domains: daily functioning, social interactions, emotional functioning, and symptoms. For each domain, patients answer a series of questions (for daily functioning, n = 11 questions; social interactions, n = 13; emotional functioning, n = 11; and symptoms, the patient chooses the five most troublesome symptoms from a list of potential symptoms). Each question has seven response options. Mean scores for each domain are calculated by summing the total score and dividing by the number of questions. For the total score, the sums of the four mean domain scores are divided by four. After treatment, treatment-related side effects or symptoms are also assessed (the patient chooses the five most troublesome from a long list of potential side effects). Treatment-related side effects or symptoms scores are then summed (after recoding) and divided by five. Treatment-related side effects are then weighted by calculating global impact scores (positive and negative). To obtain the total score after treatment, the four domain scores are summed and then the weighted side effect score is subtracted, and then the total is divided by four.¹⁹ Subjective sleepiness was assessed with the Epworth sleepiness scale.²⁰ The Epworth sleepiness scale is a self-administered questionnaire in which patients are asked to score the likelihood of falling asleep during eight different sedentary situations with different levels of stimulation. Patients estimate their likelihood of falling asleep on a 4-point scale, from 0 = never falling asleep during this situation, to 3 = high probability of falling asleep. Scores are summed to yield an overall total, which can range from 0 to 24. A score of 0 to 10 is within the normal range, while a score > 12 suggests excessive subjective sleepiness.²¹ At study entry, patients were asked whether they experienced 12 nasal symptoms on a regular basis.¹³ Patients answered yes or no for each symptom. CPAP side effects were assessed using a self-administered questionnaire¹³ and by sections E and F of the Calgary sleep apnea quality of life index. With the CPAP side effect questionnaire, patients were asked to rate the following potential adverse side effects: pressure from mask or straps, air leak from mask, air leak from mouth, machine noise, cold face or nose, claustrophobia, dry mouth or throat, running nose, congested nose, dry nose, nose bleeds, headache, difficulty breathing, chest discomfort, mask coming off face, skin irritation, and air pressure being too much. Patients rated each effect as follows: 0 = not a problem; 1 = slight problem but did not interfere with using CPAP; 2 = moderate problem, sometimes CPAP could not be used; and 3 = major problem, CPAP could often not be used. Measurements were obtained at baseline (except for CPAP compliance and side effects) and at 1 month, 3 months, and 12 months.

Treatment Algorithm
CPAP side effects were treated in a standard fashion. Nasal dryness was treated with nasal saline solution sprays and if ineffective with heated humidification. Nasal congestion was treated with topical steroids and if ineffective with heated humidification. Rhinorrhea as the only complaint was treated with intranasal ipratropium bromide. Nose bleeding was treated as a symptom of nasal dryness. Patients with severe nasal obstruction were identified during the laboratory CPAP titration study and were prescribed a full facemask and excluded from the study. Mouth leak was treated with a chinstrap and if ineffective with either heated humidification or full oronasal mask. Cold humidification was not offered to patients since it appeared from prior studies¹²¹³ that heated humidification was superior in treating nasal symptoms and improving CPAP compliance, and heated humidification was the standard next step after simpler measures failed at the Veterans Affairs Western New York Healthcare System at the time that this study was performed. Pressure from mask, skin irritation, or air leak from the mask was treated with mask adjustment or administering a different mask. Complaints of the pressure being too high were treated with the ramp function. Claustrophobia was treated by reassurance and if ineffective with a trial of nasal pillows. Complaints of machine noise were treated by putting the machine in a closet and using longer tubing.

Data Analysis
Data are expressed as mean ± SD. Baseline characteristics between the two treatment arms were compared by unpaired t test. Changes in outcome measures over time and between groups were compared by repeated-measures analysis of variance. Power analysis using estimates of variance from prior related studies¹³¹⁴²⁰ indicated that 93 subjects would be required to detect a 0.6 difference between therapies in any of the domains of the Calgary sleep apnea quality of life indexes with 80% power. Ninety-four patients would be required to detect a 0.7-h difference in CPAP compliance between therapies with 80% power.

	Results

TOP Abstract Introduction Materials and Methods Results Discussion References

 
Two hundred patients were screened. There were 161 patients who were eligible for enrollment, of which 100 patients agreed to participate. Two patients were excluded after enrollment because they did not meet our inclusion criteria (inadequate nasal CPAP titration in one patient and subsequently diagnosed coexisting narcolepsy in the other patient). Patient characteristics are shown in Table 1 . There were no significant differences in the patients who agreed to participate compared to those who did not (Table 1). Forty-nine patients were randomized to each group. There were 21 patients who did not complete the study: 11 patients in the control group and 10 patients in the humidity group. The reasons for dropout included the following: no wish to continue nasal CPAP (n = 9; four patients in the control group and five patients in the heated humidification group); moved out of area (n = 2); death (n = 1); transportation problems (n = 3), unavailable for follow-up (n = 1); and no wish to continue participating (n = 5). The mean time to dropout was 42.2 ± 54.3 days. Patient characteristics of those patients who dropped out were not significantly different from those who remained in the study. Nasal symptoms prior to initiation of nasal CPAP are shown in Table 2 . Chronic nasal symptoms were extremely common, and there were no significant differences in the prevalence of any symptom between groups.

In the control group, eight patients were treated with nasal steroids and one patient was started on an anticholinergic nasal spray. In the heated humidification group, seven patients were treated with nasal steroids. Six patients in each group were switched to nasal pillows from a nasal mask.

	Discussion

TOP Abstract Introduction Materials and Methods Results Discussion References

 
In this study, addition of heated humidification when nasal CPAP was instituted did not lead to better CPAP compliance, greater improvement in sleepiness, or improved quality of life compared to addition of heated humidification only when patients complained of relevant upper airway symptoms that were unresponsive to simpler measures.

Critique of Methods
We used the Fisher-Paykel CPAP machine in this study. This machine has a built-in heated humidifier. Thus, patients who were assigned to the control arm could have used the heated humidifier. Although they were not instructed in its usage, the heated humidifier is not complicated to use and the patients could have figured out how to use it. In the control group, the heater was turned off when given to the patient, and visual inspection of the machine did not indicate that it had been turned on by any of the patients in the control group. Similarly, visual inspection of the water chamber also did not provide any evidence that it had been used in this group. In the heated humidification group, only one patient turned off the heater initially, which was corrected on his first follow-up visit. However, we do not have objective evidence that the subjects actually filled the chamber with water every time they used their machines. This criticism would also apply to all previous studies addressing heated humidification, as an objective measure of compliance for humidification is not presently available. It is possible that compliance with heated humidification might not be as good when it is administered to prevent symptoms rather than when it is given to treat upper airway symptoms.

Although this trial was randomized, it was not blinded. It would be difficult to blind the patients who have to fill or not fill the water chambers of their humidifiers. The investigator evaluating the patient with the treatment algorithm also needed to be unblinded.

Effect of Heated Humidification on Nasal Symptoms
In our study, we found that patients who received heated humidification when nasal CPAP was initiated had significantly fewer complaints of dry nose or dry mouth and throat than patients who did not receive heated humidification at treatment initiation. Relative humidity of inspired air is decreased during nasal CPAP administration compared to spontaneous breathing.²² This decrease in humidity is exacerbated by the presence of a mouth leak, which causes high unidirectional inspiratory nasal airflow promoting drying of the nasal mucosa as the nasal mucosa cannot recover water delivered to inspired gases during expiration. When mouth leaks during nasal CPAP administration are simulated in normal subjects, there are pronounced increases in nasal resistance²³ and nasal mucosal blood flux.²⁴ Both these effects can be largely prevented by heated humidification. Heated humidification abolishes the decrease in humidity observed with nasal CPAP when the mouth is closed and attenuates the decrease in humidity observed with nasal CPAP when there is a mouth leak.¹⁶ Mouth leak may be quite common when patients complain of upper airway symptoms during nasal CPAP administration.²² Heated humidification reduced the amount of time spent with a mouth leak during nasal CPAP administration in patients complaining of upper airway symptoms.²² Given this background, it is not surprising that heated humidification provided at initiation of CPAP therapy was effective at reducing the symptoms of dry nose and dry mouth or throat. A complaint of mouth air leak was also more common in the control group than in the heated humidification group, but this difference did not reach statistical significance. A similar improvement in upper airway symptoms has been observed in prior studies.¹³¹⁴²⁵

Effect of Heated Humidification on CPAP Compliance, Subjective Sleepiness, and Quality of Life
The addition of heated humidification when nasal CPAP was instituted did not lead to better compliance with nasal CPAP, a greater reduction in subjective sleepiness, or improved quality of life in the treatment group compared to a control group who received heated humidification if they had relevant upper airway symptoms that were unresponsive to simpler measures. In two prior short-term (3 weeks) crossover studies,¹³¹⁴ heated humidification led to a modest improvement in nasal CPAP compliance compared to no humidification (0.4 h and 0.6 h, respectively). Interestingly, in one study¹⁴ there was a tendency for the difference in compliance to decrease over time being greatest at 1 week (0.5 h) and smallest at 3 weeks (0.2 h). Our study had sufficient power to detect a 0.7-h difference in compliance between therapies; thus, we could have missed such a modest difference in compliance. However, similar to our study, neither of the two crossover studies¹³¹⁴ noted a difference in subjective sleepiness (Epworth scores) between heated humidification and the control study arm. During both study arms, there were significant improvements in subjective sleepiness with nasal CPAP, but there was no difference in the extent of improvement. Our study is the first study to our knowledge to examine whether quality of life is different with heated humidification. We found absolutely no difference in the extent of improvement in quality of life with nasal CPAP when heated humidification was added at treatment initiation. Our study was adequately powered to detect small differences in quality of life between treatment groups. The minimum clinically important difference in any of the domains of the Calgary sleep apnea quality of life index has been conservatively estimated as 1.0.¹⁹ Our study had the power to detect a 0.6 difference between treatment groups and, thus, was clearly able to detect a clinically significant difference between groups if such a difference had occurred. Ultimately, the goal of treatment for sleep apnea is to reduce symptoms and improve quality of life. Since heated humidification at treatment initiation did not improve these outcomes, our study does not support the use of heated humidification as initial therapy when nasal CPAP is instituted.

In a prior study¹² in which heated humidification was administered for upper airway symptoms unresponsive to simpler measures, four factors were predictive of the requirement for heated humidification: age > 60 years, medicines that can potentially cause nasal mucosa drying (psychotropic drugs, antihypertensives, and drugs used to treat benign prostatic hypertrophy), chronic nasal mucosal disease, and prior uvulopalatopharyngoplasty. Our patients were older, mean age 58.3 ± 11.4 years, and had a very high incidence of receiving antihypertensive medications (70%), psychotropic drugs (38%), or drugs for prostatic hypertrophy (15%). Only 15 patients (7 control patients and 8 patients heated humidity) were not receiving at least one of these agents. None of our patients had undergone uvulopalatopharyngoplasty. We did not assess our patients formally for chronic mucosal disease, although they had a high incidence of nasal complaints prior to initiation of nasal CPAP therapy, suggesting that chronic mucosal disease was common. Thus, our patients should have been an ideal group to test for the effects of heated humidification, since they would appear to be at high risk for disabling upper airway symptoms.

Our study is also the first study to examine the effects of heated humidification over a long period of time (1 year). Prior studies¹³¹⁴ examining this issue were short-term crossover studies; these studies compared the short-term effects of heated humidification to no humidification or cold humidification. In contrast, our study allowed us to compare addition of heated humidification at treatment initiation to addition of heated humidification only in patients who complained of relevant upper airway symptoms unresponsive to simpler measures, which is the current standard of care. We found no advantage to up-front initiation of heated humidification, and there was no tendency for this to change over the year of follow-up.

In this study, we asked patients to rate side effects of nasal CPAP on a 4-point scale based on whether they believed the symptom was sufficiently bothersome to interfere with CPAP use. Although upper airway symptoms were common, only a minority of patients rated the symptoms sufficiently bothersome to interfere with CPAP usage. Furthermore, when we followed our treatment algorithm, we were able to improve these symptoms in the majority of patients. Thus, although nasal and oral dryness were more common in patients who did not receive heated humidification, these symptoms could be easily dealt with during follow-up visits, and our study showed that prevention of these symptoms by heated humidification did not lead to long-term improvements in nasal CPAP compliance, symptoms, or quality of life.

In a prior study, institution of heated humidification in symptomatic patients who were unresponsive to simpler measures led to a significant improvement in nasal CPAP compliance in these patients.¹² We had six patients in the control study arm who eventually received heated humidification. In these patients, compliance with nasal CPAP did not significantly improve after initiation of heated humidification (3.7 ± 2.1 h before vs 3.7 ± 2.3 h after), likely reflecting the small number of such patients and the fact that a few patients also had concurrent complaints of claustrophobia or a feeling that air pressure was too much, which would not be expected to improve with heated humidification; and in these patients compliance worsened over time. In conclusion, the addition of heated humidification when nasal CPAP was instituted reduced upper airway symptoms but did not lead to better compliance with nasal CPAP, greater improvement in sleepiness, or improved quality of life compared to addition of heated humidification only when patients complained of relevant upper airway symptoms that were unresponsive to simpler measures.

	Footnotes

 
Abbreviations: AHI = apnea-hypopnea index; CPAP = continuous positive airway pressure; OSA = obstructive sleep apnea

Received for publication January 13, 2005. Accepted for publication March 31, 2005.

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