Autor : Baldini MatÃas1 * MarÃa N. Chiapella1 Alejandra Fernández1 Sergio Guardia1
1 Lung Function and Sleep Laboratory, Hospital Nacional Profesor Dr. Alejandro Posadas, El Palomar, Buenos Aires, Argentina
Correspondencia :Dr. MatÃas Baldini, Maison 769, 1712 Castelar, Buenos Aires, Argentina - E-mail: mbaldini@intramed.net
Abstract
Introduction: The treatment of choice for the obstructive sleep apnea-hypopnea
syndrome (OSAHS) is continuous positive air pressure in the airway (CPAP),
titrating the effective pressure that eliminates obstructive events through
validated methods. From the beginning of the COVID 19 pandemic, it has been
recommended that conventional titration should be postponed, replacing it with
self-adjusting equipment. In our population, access to these devices is
difficult.
Objective: To show whether there is a difference between the CPAP pressure level
calculated through a prediction formula and the pressure determined by
titration under polysomnography.
Materials and Methods: We included patients with OSAHS who underwent effective CPAP titration
and compared it with the calÂculated CPAP by the Miljeteig
and Hoffstein formula.
Results: We included medical records of 583 patients, (56%) men, 51 years
(41-61), apnea-hypopnea index (AHI) of 51.3 (29.2 -84.4), calculated CPAP, 9.3
cm H2O vs. effective CPAP, 8 cm H2O
(p < 0.0001). Comparing according to the degree of severity of the OSAHS,
the average difference between calculated CPAP and effective CPAP was 0.24,
0.21, and 0.41 (non-significant differences) for mild, moderate and severe, up
to an AHI < 40; in patients with an AHI ≥ 40 this difference was 1.10
(p < 0.01). We found an acÂceptable correlation between the calculated CPAP
and the effective CPAP, with an intraclass
correlation coefficient of 0.621, p < 0.01.
Conclusion: We could use CPAP pressure prediction calculations to start treatment in
patients with OSAHS who don’t have access to self-adjusting therapies within
the context of the pandemic, until standard calibration measures can be taken.
Key words: Continuous positive pressure in the airway, Prediction, Titration, Sleep
apneas
Received: 06/08/2020 :
Accepted: 10/02/2020
Introduction
The apnea-hypopnea syndrome
(OSAHS) is a clinical entity characterized by the presence of recurrent
episodes of apneas and hypopneas secondary to the collapse of the pharynx during
sleep, and is associÂated with arterial hypertension, stroke, deterioration in quality of life, car accidents and higher
risk of death by cardiovascular events1.
A 2015 review of epidemiological studies showed a mean prevalence of 22% in men
and 17% in women2.
The use of continuous positive air pressure in the airway (CPAP) during sleep
is the treatment of choice for OSAHS3-6.
For the purpose of starting treatment with CPAP in a patient with OSAHS, the
effective pressure that removes obstructive events should be previously
titrated. The method of manual titration under polysomnography
(PSG) is considered the gold standard in the measurement of the CPAP effective
pressure level, but comparable results can be obtained using different
validated methods such as self-adjusting devices and split-night PSG7-11.
The literature includes various
prediction equations that try to calculate the CPAP effective presÂsures12
through the use of different variables. The equations were
subsequently used to estimate the initial pressures or during the assessment
studies of the positive airway pressure (PAP) at the laboraÂtory as reference
pressure, without replacing the validated methods. Thus, this obtained value
may be applied provisionally, though it should not be considered the definite
value. Miljeteig, H. and Hoffstein,
V. proposed the CPAP prediction using a formula that includes the
apnea-hypopnea index (AHI) and two anthropometric parameters such as the body
mass index (BMI) and the neck circumference (NC), validating their use in
subsequent studies13-15.
At the end of 2019, a new
coronavirus was identified as the cause of a group of pneumonia cases in Wuhan,
a city in the province of Hubei, China. This virus spread quickly, resulting in
an epidemic throughout China, followed by an increasing number of cases in
other countries of the world, and fiÂnally declared a pandemic by the World
Health Organization (WHO) in March, 2020. The entity was named COVID-19, which
means coronavirus disease 2019, and the virus producing it is the severe acute
respiratory syndrome coronavirus 2 (SARS-CoV-2)16.
PAP therapies are considered aerosol-generating procedures, one of the main
SARS-CoV-2 routes of transmission. As a consequence, within the context of the
pandemic and given the high degree of transmission and virulence of this virus,
the Center for Disease Control and Prevention (CDC) of the United States and
the main World Associations of Sleep Medicine recommended to postpone and
reschedule, the PAP titration studies, due to the risk of aeroÂsolization17-19.
The purpose of our study was to
show whether there is concordance between the level of CPAP calculated with the
Miljeteig and Hoffstein
formula and the pressure determined by means of manual titration under polysomnography. If there weren´t any significant
differences it would be possible to start CPAP treatment and wait until
titration of a definite pressure can be done by means of currently validated
methods.
Materials and Methods
Concordance of methods study. We analyzed the information obtained from the patients’ database used in the Pulmonary Function/ Sleep Laboratory of the Hospital Posadas for statistical purposes between January, 2016 and December, 2019. We included all the patients with complete medical records with an OSAHS diagnosis who had undergone effective CPAP titration.
We evaluated the AHI recorded in
the basal PSG and the anthropometric parameters such as BMI and NC obtained
from the medical records. In all the cases we carried out CPAP titration during
a second PSG night or else during the same night the diagnosis was established
(split-night study). In all the cases the titration was done manually under PSG
supervision. Leak control was performed according to the criteria established
by the clinical guidelines of the American Academy of Sleep MediÂcine for
full-night and split-night titration. The effective pressure titration was the
one that fulfilled the established criteria as optimum, good and acceptable,
where respiratory events are eliminated or partially corrected (AHI of less
than 10/hour)1, 19.
We used the Miljeteig
and Hoffstein formula (effective pressure = 0.16 ×
BMI + 0.13 × NC in cenÂtimeters + 0.04 × basal AHI – 5.12) for calculating the
prediction value of the CPAP pressure.
We compared the data of the
effective pressure (effective CPAP) in the global group and according to the
AHI severity degrees with the pressure predicted by the Miljeteig
and Hoffstein formula (calc. CPAP).
Statistical Analysis
The results are expressed as
percentages in the categorical variables or as median and interquartile range
in the continuous variables, according to the distribution of the population.
For the comparison of differences of continuous data, we used Wilcoxon. We
compared both methods by means of the inÂtraclass
correlation coefficient. We also used plot representation with Bland Altman for
the graphical analysis of the relationship between measurement types. A
two-tailed value of p < 0.05 was considered to be significant.
Results
We included the medical records
of 583 patients, median age 51 years (41-61), 329 (56%) men. Table 1 shows the
anthropometric and polysomnographic variables and the
CPAPs obtained by both methods. Patient distribution according to the OSAHS
degree of severity defined by the AHI: mild OSAHS 32 (5.5%), moderate OSAHS 121
(20.7%), severe OSAHS 430 (73.8%). The median of calc. CPAP for all the
patients was 9.3 cm H2O
vs. effect. CPAP 8 cm H2O
p < 0.01. Whereas the difference is statistically significant, the difference
in absolute values was 1.3 cm H2O
with an average value of 0.79 cm H2O.
We found that with the Miljeteig and Hoffstein formula we were getting closer to a successful presÂsure (calculated CPAP pressure within ± 3 cm H2O in comparison with the effective CPAP pressure obtained during titration) in 430 patients (74%), observing an acceptable correlation between both methods, with an intraclass correlation coefficient of 0.621 (95% CI 0.555-0.679) p < 0.01, Figure 1.
In the comparison of CPAP
pressures obtained through every method according to the degree of severity of
the OSAHS, we observed that there isn’t any significant difference between the calculated
CPAP and the effective CPAP in patients with mild and moderate OSAHS. The
difference between both pressures in patients with severe OSAHS is
statistically significant, but in absolute values that difference was only 1 cm
H2O (Table 2).
For the purpose of maximizing the performance of the formula for most severe patients (severe OSAHS), they were divided in 2 groups. In the first group, patients with AHI ≥ 30 and < 40, and in the second group, patients with AHI ≥ 40. Thus, we can observe that there isn’t a significant difference beÂtween the calc. CPAP and the effect. CPAP in the group of severe patients with an AHI < 40 (Table 3).
Discussion
In this study, we found that the
level of CPAP obtained by means of standard calibration in patients with sleep
apneas does not differ significantly from that obtained by means of the
prediction formula of Miljeteig and Hoffstein, up to values of AHI< 40.
The treatment of choice for OSAHS
is the use of PAP. The effective pressure that corrects the respiÂratory events
must be determined individually in each patient regardless of the method that
is used. Manual titration during a second night under PSG is the gold standard
method for measuring the level of effective CPAP pressure; however, comparable
results can be obtained during the same night of the basal study (split night)
or using an auto-adjusting CPAP device (APAP) under supervision or at the
patient’s home for several nights7-11, 20.
Since the beginning of the
pandemic, in Wuhan, China, produced by the SARS CoV-2 virus, we were forced to
establish strategies, from the different areas and specialties of medicine, for
the prevention of infection, diagnosis and treatment not only in COVID-19
patients, the general population, and healthcare staff, but also regarding the
way we approach the diseases seen daily in the practice of our profession. For
that reason, renowned professionals of different disciplines have created
guidelines and recommendations to be followed in each case. COVID-19 is highly
contagious; it is transmitted through respiratory drops from carriers which are
spread until they reach the mouth, nose or eyes of people who are less than 2
meters apart16.
The CDC of the United States and
the main world and national associations of sleep medicine recÂommended to postpone and reschedule the administration of PAP therapy
in sleep laboratories due to the risk of aerosolization,
one of the main SARS-CoV-2 routes of transmission. It is recommended that
outpatient studies should be prioritized with APAP in selected patients that
need to be treated due to the severe clinical impact of OSAHS and with high
probabilities that they won’t start treatment17, 18, 20.
Our laboratory is located in the
west area of the outskirts of Buenos Aires, and it is included in the category
of Self-Management Public Hospitals. It has an influence area of approximately
6,000,000 inhabitants and referrals from all the country, since it is a
National Reference Center for the treatment of diseases that require complex
treatment.
In our area, patients can obtain
the equipment they need for their treatment (CPAP) through 3 difÂferent types
of health coverage: prepaid medical care, health insurance obtained through
trade unions and the state public system. Most patients don’t have prepaid
medical care or health insurance, and the PAP equipment is provided to them
through state social support, with a delay of 60-120 days. Patients who require
a second study night for the titration also have to wait between 60-90 days.
Both situaÂtions definitely generate a late therapeutic response in patients
with OSAHS and, consequently, a risk in their morbidity and mortality, mainly
in the case of patients with severe OSAHS.
The demographic and resource
characteristics in our area make it difficult to use self-adjusting home
therapies as methods of calibration or treatment. The need for a different
alternative to be able to start the treatment led us to propose the possibility
of using CPAP pressure prediction calculations within the context of this
pandemic until a standard calibration can be performed.
Throughout the years, different
prediction equations have been described, trying to calculate the effective
CPAP12 pressures by means of the use of different variables. Miljeteig and Hoffstein, who were
pioneers in this field, proposed and validated their equation13-15.
According to these authors, the use of the formula would be to determine an
approximate initial pressure in the calibration through convenÂtional methods.
The equations have been subsequently used to calculate initial pressures or
during the PAP assessment studies at the laboratory as referential pressure,
minimizing the time necessary to reach the optimum pressure and achieve a
larger amount of sleep in such pressure and thus increase the probability of
reaching the REM sleep. It would also be useful in patients with high pretest
that could benefit from split-night studies, reducing diagnostic time and cost.
Masa et al compared CPAP levels obtained through titration with
self-adjusting home equipment, with CPAP values calculated through the Miljeteig and Hoffstein formula
and with CPAP titration supervised under PSG. No significant difference was
found between the CPAP level obtained by the standard method and the one
adjusted with the mentioned formula, but the latter was different from
titration with self-adjusting CPAP: 8.4 ± 1 cm H2O vs. 9.1 ± 1.9 cm
H2O (p < 0.05). However, there were no significant differences in
the somnolence scale, the AHI or adherence in the three groups. In our group of
patients, the calc. CPAP was statistically different from the effect. CPAP, 9.3
cm H2O vs. 8 cm H2O p < 0.0001; but this absolute
difference of 1.3 cm H2O doesn’t seem to be clinically signifiÂcant,
just like the values observed in the Masa group with
a similar difference. Also, we found that if we classify patients according to
the AHI degree of severity, we can reduce this difference of pressure between
both methods to 0.55 cm H2O for the mild degree and 0.77 cm H2O
for the moderate; whereas in the severe group this difference was stronger:
1.45 cm H2O. Thus, we look for a cut-off point for the AHI that
allows us to predict the CPAP pressure more precisely within the group of
severe patients, who benefit the most from the treatment and should access to
it as soon as possible, given the higher risk of morbidity and mortality. We
found that for an AHI cut-off point of 40, this difference between the calc.
CPAP and the effect. CPAP was only 0.13 cm H2O, not statistically
significant.
In their original work, Miljeteig and Hoffstein obtained
an optimum subgroup of variables with the maximum regression R2
coefficient13 using a statistical procedure of lineal regression.
This group of predictor variables (AHI, NC and BMI) resulted in R2 =
0.671, that is to say, the model represented 64% of variation in the
calculation of the CPAP pressure, evidencing the presence of other variables
for determining the pressure that were not considered in this model. In our work, the more severe the OSAHS, the stronger the difference
between the calc. CPAP and the effect. CPAP.
This loss of acÂcuracy could be caused by the influence of these other
variables in the determination of the pressure, not expressed in it.
Conclusion
In this study we have shown that,
in our population, CPAP pressure prediction calculations could be used to start
treatment early in patients with OSAHS who don’t have access to self-adjusting
therapies within the context of the COVID 19 pandemic, until standard
calibration measures can be taken. Also, this could be done quite accurately in
patients with an AHI of up to 40. In patients with a higher AHI, a closer
clinical follow-up should be carried out so as to determine the need to adjust
the indicated pressure.
Every center should analyze the
characteristics and resources of its population with the aim of evaluating the
possibility to start CPAP treatment through this pressure prediction method
until the endemic and biosafety conditions of the environment in which they
work allow for the performance of conventional techniques.
Conflict of interest: The authors of this work declare there is no conflict of interest
related to this publication.
Acknowledgement:
To our technicians, Mirtha
González, Patricia Tapia and Ronaldo Hurley, who perform all the polysomnography studies and CPAP titrations.
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