Revista Americana de Medicina Respiratoria - Volumen 17, Número 3 - Septiembre 2017

Artículos Originales

Auto-adjusting CPAP Titrations at Home and Correlation between an Automatic Algorithm and the Hoffstein Formula

Autor : Borsini Eduardo1, 2, Ernst Glenda1, 2, Blanco Magalí1, 2, Di Tullio Fernando1, DecimaTamara1, Robaina Gabriela1, Campos Jerónimo1, Bosio Martín1, Meraldi Ana1, Blasco Miguel1, Salvado Alejandro1

1 Center for Respiratory Medicine. Hospital Británico de Buenos Aires 2Sleep and Ventilation Unit. Hospital Británico de Buenos Aires

Correspondencia : Eduardo Borsini


Introduction: Continuous positive airway pressure (CPAP) has proven to be effective in the treatment of obstructive sleep apnea/hypopnea syndrome (OSAHS). Effective pressure is traditionally acquired with a polysomnography (PSG). The performance of unconventional strategies, such as auto-adjusting positive airway pressure (APAP) and titration formulas (Tf) varies according to the population where they are applied.
Objective: To describe the APAP titration and correlate the mean airway pressure (Meanp), the Effp and the Hoffstein and Mateika Tf pressure (Hofff).
Results: We included 192 patients, 52 female (27%) and 140 male; age, 60.2 years old ± 11.7 and BMI (body mass index) of 33.8 ± 6.7 kg/m2. The apnea-hypopnea index (AHI) was: 33.1 ± 16.6 in females and 36.5 ± 16 in males (p > 0.24); and 190 cases (98.9%) had an AHI > 15 ev/hour. Mean compliance with APAP was: 380 minutes ± 101 in females and 370 ± 91.2 in males (p > 0.54). Less than 10% of the population presented unacceptability criteria.
We found a correlation between the Meanp and the Effp; rho: 0.73 (95% CI [confidence interval] 0.57-0.84) p < 0.001. However, between the Effp and the Hofff β: 0.519 and r2: 0.269 (p < 0.001) there was an underestimation by Hofff: - 1.98 cm H2O (95% CI, 1.48-2.49) and intraclass correlation index: 0.60 (95% CI: 0.47-0.80) p < 0.0001.
Conclusions: A high proportion of patients titrate at home with APAP without supervision and with acceptability criteria. We did not find a suitable correlation between the Hofff and the Effp in our population.

Key words: Titration; CPAP; Hoffstein and Mateika



The obstructive sleep apnea/hypopnea syndrome (OSAHS) is a clinical condition characterized by recurrent episodes of upper airway obstruction during sleep. The evidence gathered up to now demonstrates that the OSAHS without a suitable treatment is associated with arterial hypertension, stroke, deterioration in quality of life, traffic accidents and a higher risk of dying due to cardiovascular events1-5. Continuous positive airway pressure (CPAP) has proven to be the most effective treatment modality, since it corrects obstructive events during sleep and intermittent hypoxemia, and improves the sleep structure and quality of life of the affected individuals6-8.
Once the OSAHS diagnosis has been established by means of polysomnography (PSG) or respiratory polygraphy (RP), if the patient complies with the criteria to use the CPAP, some method shall be used to define the pressure values to be set in the equipment that will be used by the patient at home (titration procedure).
The effective pressure is traditionally acquired with a second nocturnal PSG7-11 or during the same night in which the diagnosis is established with the known split-night PSG12-14.
The proposal to use auto-adjusting or automatic CPAP equipment (APAP) as an unconventional titration method comes from centers with a great demand of sleep studies and long waiting lists. Though the auto-adjusting equipment was not originally designed to this end, the method has spread thanks to its capacity to register in its memory working pressure variations throughout the night in response to airway obstruction phenomena, making it possible to analyze the behavior of that variable according to the requirements of the patient during sleep.
APAP titration can be used at the patient´s home for several nights, thus increasing the range of registered data, making it possible to observe variations night after night, and reducing the waiting list and operational costs of the conventional titration procedure15-19.
The last update of the American Academy of Sleep Medicine (AASM) recommendations considers the APAP titration as a valid option for patients with no significant comorbidities, but it recommends manual data analysis by experienced personnel20. The practical guidelines of the Argentinian Association of Respiratory Medicine (AAMR, by its acronym in Spanish) acknowledge the usefulness of this procedure to titrate the pressure level at the sleep lab or“during one or several nights at the patient´s home with no supervision or additional monitoring”21.
There are remarkable differences among the different algorithms validated and proposed by the manufacturers of different equipment brands, so it is necessary to use the algorithms that have been compared with conventional titration PSG20-21.
On the other hand, experience with predictive titration formulas (Tf) based on anthropometric or clinical parameters varies according to the population where it is applied22. Since there are no validations of a Tf in our country, we recommended the correlation of pressures suggested by the algorithm of an APAP model in relation to predictive formulas and to the final recommendation of effective pressure (Effp).


To describe our experience with APAP titration in patients with OSAHS who have no experience in the use of CPAP, and to establish the relationship between the airway mean pressure (Meanp) calculated by the APAP, the Effp defined by experts, and pressures calculated by the Hoffstein and Mateika titration formula22 (Hofff).

Study Design

Prospective, correlational study at a single center.

Materials and Methods

Prospective study based on home APAP titrations of systematic collection made between August, 2015 and August, 2016 (one year) in patients with OSAHS referred to the Sleep Unit for interface demonstration and unsupervised home titration. We only considered the records of patients with no previous experience in the use of the device. The authors did not participate in the indication of the CPAP, which was made by the respective attending pulmonologists.
Patients diagnosed with obesity hypoventilation syndrome, periodic breathing or central apneas on the baseline study and those who required other treatment modalities (ventilation with two pressure levels, servo-controlled ventilation, concomitant oxygen use) were not included in the study.
The baseline apnea-hypopnea index (AHI) was obtained from the PSG or RP records and anthropometric parameters; the body mass index (BMI) and neck circumference (Ncirc) were calculated before delivery of the CPAP device.

Auto-adjusting CPAP titration
The mask type, size and model were selected after an interface demonstration carried out by physiotherapists with experience in sleep medicine. The final selection of the mask depended on the patient´s preferences and the leakage test with the APAP equipment after a ≈ 30 minutes test. Every patient received basic instructions regarding the operation of the CPAP device together with their partner or roommate. The patients were also invited to participate in the educational program called “CPAP school”.
System One (Philips-Respironics) auto-adjusting devices were used. Unlike the conventional CPAP, which operates with a positive pressure fixed value, this algorithm automatically modifies pressures with a built-in flow sensor and adjusts working pressure according to the presence of apneas, limitation to inspiratory flow and snoring until a normal breathing pattern is allowed23. The minimum pressure was set to 4 cm of H2O and the maximum pressure to 15 cm of H2O. No ramp features, expiratory pressure relief or thermohumidifiers were used.
The titration period coincided with the current processes of the Sleep Unit (3 to 7 days), depending on the appointment and device availability.
Titration data were obtained after downloading the information from the CPAP memory (SD card) with the Encore pro II Philips-Respironics software.
The effective pressure data were obtained after the subjective visual analysis of the pressure/time curve night after night made by physicians and physiotherapists with experience in sleep medicine, excluding leakage periods of more than 25 liters/minute (compensation limit of the equipment). The resulting final effective pressure was selected taking into account the nights with greater use and less leakages.
> 6500 hours of APAP use recording were analysed. Compliance, mean leakage and residual apnea-hypopnea index (rAHI) data were gathered. Minimum compliance (Minc) was defined as the use of at least 4 hours per night, taking into account the total number of nights with effective use of CPAP, and optimum titration (OPTt) was defined as that with rAHI < 5 events per hour (ev/hour) and minimum compliance. When the rAHI was between 5 and 10 ev/hour, the titration was considered as acceptable. Finally, the titration was considered inadequate (Inadt) when there was a rAHI of more than 10 ev/hour, with a compliance of< 4/hours per night, or when there were leakages above the compensation limit > 50% of the nights.
The data of the EFFp reading made by experts in relation to the automatic data of the APAP (Meanp of the first day, Meanp of every day) were compared with the pressure previously stated by the Hofff(22), namely: (0.16 x BMI + 0.13 x Ncirc in centimeters + 0.04 x baseline AHI – 5.12 = effective pressure).

Statistical Analysis
Results were presented as percentages for the categorical variables or as mean and standard deviation (±) for the numerical variables. For the comparison of differences, we used the Mann-Whitney or Fisher tests or χ2. For the comparison of titration pressures we carried out Bland and Altman plot representation, linear regression analysis and calculation of the intraclass correlation coefficient (ICC). For the statistical analysis, STATA 12 and Graph Pad Prism-5™ software were used.


During 12 moths, we included 192 patients; 52 females (27%) and 140 males; mean age, 60.2 years old ± 11.7 and mean BMI of 33.8 ± 6.7 kg/m2. Table 1. 57.7% of females and 70% of males were obese (BMI > 30 kg/m2); and 58.8% of females and 45% of males had a subjective Epworth sleepiness scale (ESS) value of > 11 points (p > 0.96). Table 2.



Table 1. Demographic variables of the population


Table 2. Clinical variables and auto-adjustable CPAP titration data according to gender

141 cases (73.5%) were diagnosed through RP, and 25.5% through PSG. The mean AHI was 33.1 ± 16.6 in females and 36.5 ± 16 in males (p > 0.24); and 190 cases (98.9%) presented an AHI > 15 ev/hour.
The use of the APAP was 3.4 nights ± 1.2 (range between 2 and 8). 83.8% (163) used the device for 3 nights. Mean compliance with APAP treatment of the whole population was 373 minutes (6.05 hours ± 1.55), with no gender differences; 380 minutes ± 101 in females and 370 ± 91.2 in males (p > 0.54). Seventeen patients used full face masks (8.8%) and minimal contact nasal pillows (3%), whereas most patients used 14 different models of nasal masks (88.2%).
Mean pressure values at 90th percentile (P90), Effp, day 1 Meanp and every day Meanp are detailed in table 2. Both for males and females, there were differences regarding the rAHI but not in airway pressures. Less than 10% of the population presented unacceptability criteria, and the Optt proportion was lower in males (78.9% versus 65.7%) p < 0.001. Table 2.
There was a good correlation between the Meanp and the titration pressure (Effp) that was finally indicated; r Spearman (rho): 0.73 (95% CI, 0.57-0.84) p < 0.001, y-axis (intercept); 0.1 to -0.1 (Figure 1 and 2). In a similar way, the Meanp of the first night correlated with the Effp; rho: 0.73 (95% CI, 0.56-0.85) p < 0.001, intercept; 0.2 to -0.3 (Figure 3). The Bland and Altman representation between the Effp and the Hofff showed: intercept: 3.96, β: 0.519 and r2: 0.269 (p < 0.001) (Figure 4). 26% of titrations showed absolute concordance between both methods, and pressure underestimation by Hofff was frequent, with a negative mean difference: - 1.98 cm of H2O (95% CI, 1.48-2.49). The ICC was 0.60 (95% CI: 0.47-0.80) p < 0.0001, showing a low degree of correlation.

Figure 1. Correlation between the Meanp of all the titration nights and the effective pressure (Effp).


Figure 2. Distribution of the Meanp of all the titration nights in relation to the effective pressure.

Figure 3. Correlation between the Meanp of the first night and the effective pressure.

Figure 4. Correlation of the Effp in relation to the Hofff


Our work summarizes a one year experience of unsupervised unconventional titrations with autoadjusting CPAP in patients not previously adapted to the therapy.
This strategy seems to be useful for acquiring working pressures; it facilitates interface selection and the initial training of the patient, and makes it possible to gather data from multiple nights at the place where the patient usually sleeps with a low Inadt.
The use of auto-adjustable equipment as a titration method has been validated in the literature and represents an interesting option18-21, for it simplifies the procedure and it is not necessary to make sleep laboratory appointment dates, giving priority to patients with initial home titration failure.
We use the visual reading of the pressure/time and leakage/time chart to define the final Effp value. The values showed by the statistical analysis derived from the automatic algorithm (P90) used in this study tend to be higher in bench studies, since the software can´t exclude in the calculation the moments in which the mask is not adequately adjusted24. In this case, visual reading can discriminate and exclude pressure values shown under that circumstance. Also, the Effp is determined after several nights, excluding periods of no use or with leakages that imply a not yet corrected rAHI. We found that 5 to 10 % of APAP titrations have residual AHIs between 5 and 10 ev/hour with a greater proportion in males (Table 2). Some definitions consider an acceptable reduction of the AHI with an APAP of < 10 ev/hour for patients with OSAHS, though these definitions have not been evaluated in patients with upper airway resistance syndrome (UARS) or individuals who remain sleepy with the use of CPAP25.
Additionally, in our experience, the total Meanp and the Meanp of the first night have a good correlation between themselves and with the Effp (Figures 1 and 3), serving as a guide when there is great variability of pressures during the night/s. The rAHI of this kind of devices is reliable information when it is < 10 ev/hour in comparison with the manual titration by PSG23. However, our results can´t be extrapolated to other algorithms since there may be an evident variation in the performance of each device24.
The influence of the kind of mask on the Meanp and Effp has been previously described. The values are higher with full face masks, which represented the minority in our series26. The analysis of our data shows that careful interface selection and initial supervision allows ≈ 90% of patients with no previous experience to use the CPAP > 4 hours per night with AHI correction.
The compliance figures vary and fluctuate between 50% and 70%, if a criterion of at least 4 hours/night27-28 is used, although we know that adherence to the treatment is gradually lost with time. In the same way, a good initial experience in the implementation of the treatment is very important, in such a way that the first CPAP week is determinant of long-term compliance29-30.
A higher socio-economic level and the increase in patient age determine a better compliance and could partly explain the results, since it is an adult population (≈ 60 years) of a private place21, 32-34 referred to home titration (possible selection bias). On the other hand, clinical management carried out by trained personnel and the influence of the use of cognitive-behavioral strategies can´t be ignored as a possible incentive to improve shortterm compliance(35-36).
Remarkably, some studies showed that APAP titration improves mean compliance in approximately one hour, compared to PSG titration at the sleep laboratory, when compliance was evaluated three months later37, 38.
On the other hand, the existence of waiting lists or the delays in the titration have generated predictive formulas based on coefficients according to anthropometric and functional parameters as the desaturation index39 or the AHI22, 40. An interesting study that compared acquired pressures by means of unsupervised titrations with a different APAP model (P95 of the Autoset II algorithm) and three titration formulas, did not find a good correlation (r2 between 0.66-0.71) and concluded that such equations must be used carefully41, 42. One strength of our analysis is that we use the Effp of the manual edition of several nights (finally recommended pressure) without finding an adequate correlation.
The indices we used (AHI) differ from those of the PSG (AHI or RDI [respiratory disturbance index]), since in the RP they result from the quotient between the events and the total recorded time(21, 43, 44), an underestimation factor43, 44 that shall be taken into account when interpreting the performance of coefficients in the titration formulas.


A high proportion of patients without experience in the use of CPAP titrate at home with APAP without surveillance and with acceptability criteria.
We did not find an adequate correlation between the prediction by Hoffstein and Mateika formula and the effective pressure in our population.

Conflicts of interest: The authors of this work declare there is no conflict of interest related to this publication.


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