Automatic Positive Airway Pressure For Sleep Related

Breathing Disorders

BYAHMAD YOUNES

PROFESSOR OF THORACIC MEDICINEMansoura Faculty Of Medicine

Several conditions can cause sleep related breathing disorders, including:• Obstructive sleep apnea (OSA) syndrome in which inadequate

ventilation occurs despite continued efforts to breath due to upper airway obstruction.

• Central sleep apnea (CSA) syndrome in which inadequate ventilation resulting from absent or diminished respiratory effort.

• Complex sleep apnea syndrome These patients have predominantly obstructive or mixed apneas during the diagnostic portion of the study but with use of CPAP or BPAP without a backup rate, they show a pattern of apneas and hypopneas that meets the definition of CSA.

• Sleep hypoventilation syndromes,

1-There is an increase in the arterial PaCO2 (or surrogate) to a value > 55 mm Hg for ≥ 10 minutes.

2. There is ≥ 10 mm Hg increase in PaCO2 (or surrogate) during sleep (in comparison to an awake supine value) to a value exceeding 50 mm Hg for ≥ 10 minutes.

Representative tracings of flow, tidal volume, and airway pressure (Paw) during administration of continuous positive airway pressure (CPAP) and bi-level PAP

Attended polysomnographic titration of PAP

• 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 , hypopneas ,snoring and hypoventilation 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 PAP experience.

Attended polysomnographic titration of PAP

Potential limitations of attended polysomnographic titration of PAP• 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.

Automatic Positive Airway Pressure

• Intelligent devices with in-built microprocessors for detection and treatment of events of SRBD have gone by different names ranging from self-adjusting, to automatic , auto-adjusting, smart CPAP, and auto-titrating PAP (APAP).

• The purpose of APAP devices included the replacement of in-laboratory manual titration, reducing mean pressures to achieve better adherence, and adapting CPAP levels to changes in severity of OSA in response to changes in weight, sleep state,, and body position .

Advanced methods of titration

• More recently, devices have developed to differentiate central from obstructive apneas (using forced oscillation technique), identify Cheyne-Stokes respiration (by breath-by-breath changes in peak flow), identify hypoventilation (by measuring tidal volume or minute ventilation using calibrated flow sensors), compensate for air-leaks (using sophisticated flow-based algorithms), and measure both upper and lower airway resistance (using forced oscillation techniques).

• Such signals are computed and analyzed instantaneously by a built-in microprocessor with preset hierarchical set of algorithms that will determine the rate and magnitude of pressure response.

 

Technology• The functioning of APAP devices can be broken

down into three components:• sensing of events of SRBD (sensors), • automated computing and analysis of the

sensed signals (analysis), and• hierarchal set of algorithms that will determine

the action taken by the APAP device in response to the conditions exposed (effectors).

Automatic Positive Airway Pressure

• In the older generation of APAP devices, the sensors were simplistic and measured only the pressure inflections (vibrations) of a certain frequency and amplitude that were caused by snoring.

• The next generation of APAP devices became more sophisticated and were able to sense flow-based changes such as apnea, hypopnea, or inspiratory flow limitation based upon the inspiratory flow contour (i.e., flattening of the inspiratory flow waveform).

Advanced methods of titration

• Newer generation devices can can increase the IPAP alone in order to ameliorate obstructive events (Auto Bi-level PAP),correct hypoventilation (averaged volume assured pressure support [AVAPS], Intelligent Volume Assured Pressure Support (iVAPS ) or combat central apneas in patients with complex sleep apnea (Servo-Ventilation).

• Devices may also introduce a back-up rate to prevent central apneas and although in general they are not referred to as APAP devices, they function using similar principles and can be judged as the latest generation of APAP devices .

BiPAP AVAPS and VPAP™ ST with iVAPS

BiPAP A40 Ventilator• BiPAP A40 comes with well-known and clinically

proven Philips Respironics technology such as Auto-Trak, AVAPS and a Dry Box humidifier design.

• The device is capable of non invasive and invasive pressure ventilation, up to 40 cmH2O, providing treatment for your chronic respiratory insufficiency patients.

• The device features AVAPS-AE, the first fully automatic ventilation mode, designed to help clinicians during titration process, while maintaining comfort and therapy optimization at the lowest pressures.

SomnoVent CR Respironics autoSV ResMed VPAP Adapt SV

Advanced methods of titration• Servo-ventilation made by different manufacturers

can successfully detect and treat central apneas . • During servo-ventilation, the expiratory positive

airway pressure is set at a level to treat obstructive apneas and obstructive hypopneas.

• Combining APAP and servo-ventilation, with APAP determining the EPAP level automatically, whereas the servo-ventilation controlling periodic breathing and central apneas has been recently reported to be effective in ameliorating SRBD .

Package Contents

Auto CPAP

Auto-adjusting (auto-titrating) CPAP, devices Auto-CPAP devices provide a useful alternative for providing positive airway pressure (PAP) treatment for patients with 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 CPAP)

2- Auto-adjusting CPAP for chronic treatment with the advantage of delivering the lowest effective pressure in any circumstance.

Chronic treatment with APAP would also eliminate the requirement for a CPAP titration

Auto-CPAP 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 CPAP 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.

Open unrestricted airway

Silent partial airway obstruction

Noisy partial airway obstruction

Complete airway obstruction

Open unrestricted airway

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.

80-90% reduction in flow for 6 seconds results in a short pulse of pressure. Here, “obstructive apnea” really means “closed airway apnea” because inspiratory effort is not monitored.

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 .

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 EPR for Res med and C-Flex , for Respironics are now available .

• These mode allow 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.

AUTO-TITRATION

• 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• Auto-titrating CPAP 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.

• 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 CPAP device are best studied using attended manual titration with polysomnography.

In summary• 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.

CHRONIC TREATMENT WITH Auto-CPAP

AUTO-ADJUSTING CPAP

• 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- CPAP Vs. CPAP 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-CPAP Vs. CPAP 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-CPAP Vs. CPAP Treatment

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

• 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 < 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.

• 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-CPAP Treatment• The physician 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.

Technique of Chronic Auto-CPAP Treatment

• 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).

• 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).

Technique of Chronic Auto-CPAP Treatment

• 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 CHF, significant lung disease such

as COPD, 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 co-morbidities (CHF, COPD, central sleep apnea syndromes, or hypoventilation syndromes). (Option)

Recommendations• 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 re-evaluation 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 auto-

titrating 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.