Automatic CPAP For OSAS

BY

AHMAD YOUNESPROFESSOR OF THORACIC MEDICINE

Mansoura Faculty Of Medicine

Attended polysomnographic • Treatment pressure is established by direct

inspection of sleep and breathing parameters during attended polysomnographic recording while adjusting pressures to find a setting that essentially eliminates apneas and hypopneas in all sleep stages and body positions.

• In addition to allowing direct observation by trained technologists to guide pressure selection, titration under attended polysomnography allows for interventions to adjust mask fit, eliminate leak, and help the patient adapt to the initial CPAP experience.

Potential limitations of attended polysomnography • The cost and inconvenience of repeat PSG due to incomplete

titrations, the potential bias of in-laboratory versus in-home environment, and the potential to prescribe pressures that are not suitable due to the inherent limited sampling introduced when titration takes place over only one, or in the case of split-night studies, one-half night of recording.

• Pressure requirements may change over time due to variability in weight, change in underlying medical conditions, or resolution of upper airway edema caused by repetitive apneas.

• One night of titration to eliminate respiratory events that occur during REM sleep or in supine positions may yield a therapeutic pressure estimate that is higher than that needed on average for effective therapy.

• Auto-positive airway pressure (APAP) devices provide a useful alternative for providing positive airway pressure (PAP) treatment for patients with obstructive sleep apnea (OSA) .

• One can separate the uses of these devices into two large categories These include:

(1) auto-titration PAP to determine an effective fixed level of continuous positive airway pressure (CPAP)

(2) auto-adjusting PAP for chronic treatment.

Auto-positive airway pressure (APAP) devices• When used in the auto-titration mode, the devices are used

by the patient for a period of time (one night to several weeks). Information stored in the device is transferred to a computer and can be used to select an optimal fixed level of CPAP for chronic treatment.

• When APAP devices are used for chronic treatment they have the potential advantage of delivering the lowest effective pressure in any circumstance (body position, sleep stage). The mean pressure for the night may be lower than a single pressure that would be effective in all circumstances (the prescription pressure). For example, higher CPAP is usually needed in the supine posture and during rapid eye movement (REM) sleep.

Auto-titrating mode

• Attended auto-titration in CPAP naïve patient (technologist extender)

• Unattended auto-titration in CPAP naïve patient• Check prescription pressure after weight gain/loss• Salvage a failed manual CPAP titration

Auto-adjusting mode• Initial chronic treatment of OSA (no titration needed)• Chronic treatment in patients not tolerating CPAP• Chronic treatment in patients with difficult

mask/mouth leak

DEVICE CHARACTERISTICS• The devices differ in the respiratory variables that are

monitored and in the algorithms used to adjust the delivered pressure.

• The devices typically monitor one or more of the following: airflow (or motor speed), airflow profile (flattening), snoring (airway vibration), or airway impedance (forced oscillation technique).

• The algorithms used to adjust pressure are proprietary but determine if the delivered pressure should be increased or decreased.

• Depending on the type of respiratory event that is detected the delivered pressure is increased by a certain amount.

DEVICE CHARACTERISTICS

• The S9 Series detects both obstructive and central sleep apneas (CSA). CSA detection uses the Forced Oscillation Technique (FOT) to determine the state of the patient’s airway during an apnea.

• When an apnea has been detected, small oscillations in pressure (1 cm H2O peak-to-peak at 4 Hz) are added to the current device pressure. The CSA algorithm uses the resulting flow and pressure (determined at the mask) to measure the airway patency.

DEVICE CHARACTERISTICS• Typically, pressure changes occur slowly over several

minutes to prevent pressure-induced arousals.• If no respiratory events are detected within a certain time

window the delivered pressure is slowly decreased. Thus, the lowest effective pressure is delivered.

• In some of the devices machine adjustment is available for various mask types and for the type of humidifier that is being used.

• Studies comparing different APAP devices provide evidence that devices from different manufacturers will not deliver the same pressure for a given clinical circumstance .

DEVICE CHARACTERISTICS• The responses of several devices differs markedly

in response to apnea. • Some of the devices increased the delivered

pressure in response to apnea while others did not .• Comparing the 95th percentile pressure of one

APAP device based on airflow to another based on the forced oscillation technique found poor agreement between the optimal pressure identified by the two devices.

• The adherence and clinical outcomes were similar although the median applied pressure was slightly higher with the device that responded to airflow limitation .Thus, differences in the devices do not always translate into differences in outcomes.

Problems of APAP algorithms• The problems of mask/mouth leak and central apnea have

provided a challenge for the designers of APAP algorithms. • Mask/mouth leaks tend to raise the baseline flow delivered

by blower units and diminish the variations in flow during inspiration and expiration. The resulting airflow signal may be interpreted as an apnea or hypopnea and prompt an increase in pressure that may further increase leak.

• To handle the leak problem many APAP units have algorithms that limit pressure increases when leak exceeds certain values or when increases in blower speed no longer result in increases in mask pressure. Other units have leak alarms that can prompt the patient to adjust the mask.

Problems of APAP algorithms

• Mouth leaks can be approached by using a chin strap or full-face mask.

• Algorithms often include limits on upward titration of pressure for apnea to avoid the delivery of high pressure for central apneas. For example, pressure is not increased above 10 cm H2O unless apnea is associated with snoring or airflow profile flattening.

Expiratory pressure relief

• Expiratory pressure relief (C-Flex, Respironics, Inc., Murrysville,Pennsylvania, U.S.) is now available for one brand of APAP devices.

• This mode allows a reduction in pressure during early expiration with a return to the current set pressure at end expiration.

• This feature could improve patient tolerance to pressure.

Automatic adjustment of bilevel PAP• APAP machines providing automatic adjustment of bilevel PAP

(BPAP) are available. • These devices vary inspiratory positive airway pressure (IPAP)

and expiratory positive airway pressure (EPAP) according to a proprietary algorithm.

• The physician sets the minimum EPAP, maximum IPAP, and maximum IPAP–EPAP difference.

• The option of using inspiratory and expiratory pressure relief (Bi-Flex R, Respironics) is currently available for one device brand.

• Inspiratory pressure relief allows a drop in pressure at end inhalation (IPAP) while expiratory pressure relief allows a pressure drop at the start of exhalation (EPAP).

A single night profile showing changes in inspiratory positive airway pressure and expiratory positive airway pressure over

the night with auto-bilevel positive airway pressure.

• Manual PAP titration is labor intensive and usually a single technologist can titrate only two patients at a time.

• Patients in some geographical areas may have limited or delayed access to a sleep laboratory offering polysomnography.

• In addition, the gold standard PAP titration method may result in suboptimal titrations due to a number of problems including poor sleep, lack of supine REM sleep, high mask leak, or uncorrected mouth leak. Patient characteristics such as weight gain may also render previously selected pressures inadequate.

• Auto-titrating PAP devices can be used to address some of these problems.

AUTO-TITRATION • One important use of APAP devices is selection of a

fixed CPAP pressure as an alternative to traditional manual (attended) PAP titration .

• Information stored in the device memory can be analyzed and a pressure can be chosen for fixed CPAP treatment.

• A common method is to choose the 90th or 95th percentile pressure (pressure exceeded only 10% or 5% of the time, respectively) as the prescription pressure. This assumes periods of high leak have been eliminated from the analysis.

Efficacy of Auto-Titration

• Unattended APAP was successful at identifying an effective CPAP level.

• Treatment with fixed CPAP using a pressure identified by unattended APAP titration reduced the AHI to < 10/hour in 38/40 subjects.

• In 15 of 20 patients the difference between the APAP pressure (taken as P95) and the CPAP chosen by manual titration was equal to or less than 1 cm H2O.

Technique of Auto-Titration• As with manual attended PAP titrations with

polysomnography, patient education, and mask fitting are essential for successful auto-titration. Patients must feel comfortable applying the mask interface and operating the APAP device if an unattended titration is planned. A short 20-minute trial of APAP can be very useful in identifying patient problems including claustrophobia, mask leak or an inability to operate the device

• The physician ordering the APAP titration designates the lower and upper pressure limits (for example, 4 and 20 cm H2O). The APAP device then titrates between these limits.

Technique of Auto-Titration• Depending on the type of APAP device utilized,

information on applied pressure, leak, snoring, flattening, and a moving time average of the AHI is stored in the device memory.

• After transfer to a computer the information is available for review.

• It is possible to determine statistics for all or a portion of the data.

• Most devices allow the ability to look at one or more single nights of data in detail (pressure, leak, residual events vs. time) .

The leak and residual AHI are low. The 95th percentile pressure was 9.4 cm H2O. The patient was treated with a prescription pressure of 10 cm H2O

Technique of Auto-Titration

• High leak can result in many devices promptly increasing pressure until the upper pressure limit is reached.

• summary statistics can be displayed for a single night or multiple nights. Typically available information includes: 90th or 95th percentile pressure, median pressure, maximum pressure, maximum leak, median leak, and residual AHI.

Technique of Auto-Titration

• Usually either the 90th or 95th percentile pressure is chosen for the prescription pressure. However, simply noting one number can be very misleading.

• The clinician must first determine if the titration duration (amount of sleep on the device ) was adequate and if the residual AHI is reasonably low (AHI < 5–10/hour).

• Patients with suboptimal or inconclusive APAP titrations should have a repeat APAP titration or be referred for an attended lab PAP titration.

Technique of Auto-Titration• High-residual AHI could be secondary to frequent central

apneas, high leak, or too low maximum pressure limit. • High leak could be secondary to inadequate mask seal or

mouth leak if a nasal mask is being utilized.• Patients with a high AHI and leak may undergo a repeat

APAP titration after mask adjustment or change to a full-face mask (or addition of a chin strap) as indicated.

• A persistently high-residual AHI despite repeated attempts at APAP titration would be an indication of the need for a traditional manual PAP titration.

The leak is higher than ideal (> 0.4 L/s) at times. However, the residual AHI remained low. The 95th percentile pressure was 7.8 cm H2O. The prescription pressure was chosen to be 8 cm H2O.

The leak is very high. The pressure increased to the upper limit (16 cm H2O) and remained there for most of the night. The AHI was also elevated. This titration would need to be repeated with a better mask seal.

Technique of Auto-Titration• A number of portable monitoring units can interface with

selected APAP devices. For example, airflow, respiratory effort, oxygen saturation, body position, and delivered pressure can be recorded for clinician analysis . This is especially helpful if one night of APAP titration is utilized. For example, absence of supine sleep could result in a lower than typically needed prescription pressure. This is also a reason that it is often helpful to have the patient use the APAP device for several nights.

• Average statistics over a week may more accurately represent a typical night’s pressure requirements. Information from pulse oximetry during the APAP titration can identify the need for the addition of supplemental oxygen.

In summary• There is convincing evidence that auto-titrating PAP devices can be

useful for identifying an appropriate fixed CPAP level in appropriate patients.

• Unattended as well as attended titration can be effective. However, it is likely that unattended APAP titration will not be effective in a significant proportion of OSA patients.

• In general, patients with a significant proportion of central apneas, those with low baseline SaO2 values or who have difficulty applying the mask and/or operating an APAP device are probably best studied using attended manual titration with polysomnography.

• A brief practice trial with APAP may be useful to identify mask leak or nasal congestion problems requiring intervention before the patient takes the APAP device home.

• If APAP titration is performed, close review of the data is needed to ensure that the titration was adequate.

• Those patients not having an adequate APAP titration should be referred for a traditional CPAP titration.

AUTO-ADJUSTING POSITIVE AIRWAY PRESSURE

• When originally developed one anticipated advantage of APAP devices was that delivery of the lowest effective pressure in any circumstance (sleep stage, body position) would improve acceptance and adherence to positive pressure treatment.

• This was based on the premise that a lower mean nightly pressure would improve patient tolerance to PAP treatment. Alternatively, chronic treatment with an auto-adjusting device would obviate the need for an attended or unattended PAP titration.

Auto-Positive Airway Pressure Vs. Continuous Positive Airway Pressure Treatment• A number of studies have examined the hypothesis that

chronic treatment with auto-adjusting PAP would increase the adherence.

• Some studies did find higher adherence with APAP compared to fixed CPAP treatment.

• Several other studies did not confirm this result. • In evaluating studies of adherence several issues must be

considered. First, pressure intolerance is not the major issue for many patients . Second, the difference in the mean pressure on APAP and an adequate fixed pressure is often only 1 to 2 cm H2O . One would not expect such a small pressure difference to change adherence

Auto-Positive Airway Pressure Vs. Continuous Positive Airway Pressure Treatment

• One might expect a potential advantage for APAP devices in patients with pressure intolerance, high prescription pressures, or a large variation in the required pressure during the night (postural or REM-related OSA) . Thus, if a patient is having difficulty with CPAP, a trial of APAP is a reasonable intervention.

• If APAP is preferred, improved adherence is likely with this mode of treatment compared to fixed CPAP. Furthermore, information stored in the machine such as leak or residual events may help diagnose problems with treatment .

Auto-Positive Airway Pressure Vs. Continuous Positive Airway Pressure Treatment

• Patients with difficulty tolerating CPAP due to pressure intolerance (“cannot breathe out”) are often switched to BPAP.

• Although the fact that APAP treatment does not improve adherence over fixed CPAP selected by manual titration,patients diagnosed with OSA could be treated with chronic APAP without the need for either traditional laboratory titration or auto-titration. Any additional cost of APAP devices over CPAP would usually be less than the cost of an in-laboratory CPAP titration.

• Both a cost saving and a reduction in the time needed to adjust the PAP treatment occur to a satisfactory level.

• Indeed it is a common experience that the optimal level of CPAP determined by an attended in-laboratory titration often requires alteration for patient tolerance, side effects, or control of daytime sleepiness.

Technique of Chronic Auto-Positive Airway Pressure Treatment• The physician usually orders the lower and upper limits of positive pressure.

The APAP device then delivers the lowest effective pressure between these limits.

• The upper and lower pressure limits could be placed as wide as possible (4–18 cm H2O) or narrowed based on information from a previous CPAP titration or previous nights of APAP use.

• Some patients find starting at 4 cm H2O uncomfortable and it may take some APAP machines several minutes to reach a pressure level that they find comfortable. In this case the lower pressure could be increased to 6–10 cm H2O.

• Awakening with the feeling of insufficient pressure could be another situation in which the lower pressure limit should be increased.

• Bloating or evidence of excessive mouth leak might be an indication to lower the upper pressure limit .Alternatively, if the 90th percentile pressure essentially equals the upper pressure limit, then a higher upper pressure limit is likely needed (especially if the residual AHI is high).

Technique of Chronic Auto-Positive Airway Pressure Treatment• Information on delivered pressure is not the only data

stored in the APAP device that is potentially useful for tailoring treatment.

• High leak may indicate the need for another mask or a full-face mask (mouth leak).

• A high-residual AHI might indicate a need for an increase in either the lower or upper pressure.

• A high number of residual apneas might suggest that central apneas could be present.

• Financial constraints may limit the use of APAP devices for chronic treatment of OSA at least in some circumstances.

Recommendations

• APAP is not recommended to diagnose OSA. (Standard)• Patients with congestive heart failure, significant lung

disease such as chronic obstructive pulmonary disease, patients expected to have nocturnal arterial oxyhemoglobin desaturation due to conditions other than OSA (e.g., obesity hypoventilation syndrome), patients who do not snore (either naturally or as a result of palate surgery), and patients who have central sleep apnea syndromes are not currently candidates for APAP titration or treatment. (Standard)

Recommendations• APAP devices are not currently recommended for

split-night titration. (Standard)• Certain APAP devices may be used during

attended titration with polysomnography to identify a single pressure for use with standard CPAP for treatment of moderate to severe OSA. (Guideline)

• Certain APAP devices may be initiated and used in the self-adjusting mode for unattended treatment of patients with moderate to severe OSA without significant comorbidities (CHF, COPD, central sleep apnea syndromes, or hypoventilation syndromes). (Option)

Recommendations

• Certain APAP devices may be used in an unattended way to determine a fixed CPAP treatment pressure for patients with moderate to severe OSA without significant comorbidities (CHF, COPD, central sleep apnea syndromes, or hypoventilation syndromes). (Option)

• Patients being treated with fixed CPAP on the basis of APAP titration or being treated with APAP must have close clinical follow up to determine treatment effectiveness and safety. This is especially important during the first few weeks of PAP use. (Standard)

• A reevaluation and, if necessary, a standard attended CPAP titration should be performed if symptoms do not resolve or if the APAP treatment otherwise appears to lack efficacy .(Standard)

CONCLUSIONS

• APAP devices can be effective in the autotitrating and auto-adjusting modes. They provide a useful titration or chronic treatment alternative for patients with sleep apnea.

• Success depends on proper patient selection, education, and detailed physician review of the stored information.

• Treatment or titration results could vary between brands of APAP devices.

• The devices may not work well in patients with central apneas or those with large mouth or mask leak.

CONCLUSIONS• Careful physician evaluation of treatment

efficacy is essential. For example, it is possible that a given patient may have better alertness or sleep with a slightly higher or lower pressure than the 90th or 95th percentile pressure identified by APAP titration.

• Familiarity with type of information provided by a given brand of device is essential to benefit from the stored information.

• As with any type of PAP treatment, close follow-up of objective adherence and outcome measures such as subjective sleepiness is essential.