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Automatic Positive Airway Pressure For Sleep Related Breathing Disorders. BY AHMAD YOUNES PROFESSOR OF THORACIC MEDICINE Mansoura Faculty Of Medicine. Several conditions can cause sleep related breathing disorders, including:.
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Automatic Positive Airway Pressure For Sleep Related Breathing Disorders BYAHMAD YOUNESPROFESSOR OF THORACIC MEDICINE Mansoura 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.
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.
Potential limitations of attended polysomnographictitration 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) and compensate for air-leaks (using sophisticated flow-based algorithms). • 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).
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.
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.
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 Resmed 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.
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.
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)
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 .
Autobilevel positive airway pressure with a minimum EPAP of 6 cm H2O and a maximum IPAP of 25 cm H2O.
Ideal body weight • Estimated ideal body weight in (kg)Males: IBW = 50 + 2.3 for each inch over 5 feet.Females: IBW = 45.5 + 2.3 for each inch over 5 feet. • Estimated adjusted body weight (kg)If the actual body weight is greater than 30% of the calculated IBW, calculate the adjusted body weight (ABW): ABW = IBW + 0.4(actual weight - IBW) • The IBW and ABW are used to calculate medication dosages when the patient is obese. • This formula only applies to persons 60 inches (152 cm) or taller.
VOLUME-TARGETED BPAP • Comparing BPAP and AVAPS (both in the ST mode) in patients with OHS. AVAPS resulted in a slightly higher ventilation and lower PaCO2 without any better sleep quality or quality of life measures compared with BPAP-ST. On AVAPS, the minute ventilation was greater than on BPAP but sleep quality was comparable between the two NPPV modes. • When VT-BPAP is used, the purpose of a polysomnography PAP titration is to select a level of EPAP that eliminates obstructive events (obstructive apnea and hypopnea) and document that the device does deliver adequate tidal volumes.
Intelligent Volume Assured Pressure Support ( iVAPS ) • Intelligent. Automatic. Personalized. • Maintain a preset target alveolar minute ventilation • Monitors delivered ventilation • Adjusts pressure support • Provides an intelligent backup breath Two mechanisms independent of one another 1-Variable Pressure Support to guarantee Alveolar Ventilation 2- iBR: intelligent Back-up rate
Anatomical Dead space • Inspired/expired air remaining in conducting airways • Not involved in gas exchange • Correlation between patient’s height and dead space (Vd) • Height is used to calculate anatomical dead space (Vd) for each breath of air (Tidal Volume) • Example dead space volume (Vd) : 120 ml for height 175 cm or 70 inches
As alveolar ventilation drops , iVAPS rapidly increase pressure support until target Va is reached, and as alveolar ventilation increase , iVAPS rapidly decrease pressure support .
Intelligent back up rate (iBR) stays out of the way at 2/3 spontaneous rate whenever the patient spontaneously triggers above 2/3 of the target . once the patient rate reach minimum back up rate (2/3 of the target ) iBR increase towards patient spontaneous rate to maintain alveolar ventilation .Once spontaneous trigering returns, iBR drops back to 2/3 of the target / spontaneous rate.
Auto-TriLevel • The auto-TriLevel principle by Weinmann combines two proven types of therapy – auto-CPAP and BiLevel – into a synthesis that offers the most therapy effectiveness. Your benefits with these products: • Therapeutically effective maximum and mean pressures that are lower than BiLevel with the same tidal volume for fewer side effects such as leakage. • It‘s like a new titration every day – adjusts to patient‘s high variability . • Effortless titration and monitoring .
