Bi-level Positive Airway Pressure

BYAHMAD YOUNES

PROFESSOR OF THORACIC MEDICINE

Mansoura faculty of medicine

Non-invasive ventilation• Non-invasive ventilation refers to the application of

ventilatory assistance without the use of an invasive airway.

• In the vast majority of cases therapy will be delivered with positive pressure devices , although a few individuals still use negative pressure devices.

• Negative pressure devices present a number of difficulties with regard to home ventilation including bulkiness, fit ,comfort, they can induce significant upper airway obstruction , rendering therapy ineffective.

Non-invasive ventilation• Positive pressure therapy may be delivered with

either volume or pressure preset ventilators .

1-Volume preset ventilation delivers a stable tidal volume irrespective of the patient’s pulmonary system mechanics (compliance, resistance and active inspiration) .

2- Pressure preset ventilation delivers a set pressure during inspiration and expiration, and changes in the patient’s pulmonary mechanics directly influence the flow and the delivered tidal volume .

What is a mode• A mode of mechanical ventilation has three essential

components :

1- The control variable (the mechanical breath goal e.g. a set pressure or a set volume )

2- The breath sequence

3- The target scheme• Inspiration is an active process ,driven either by the patients

effort ,the ventilator or both .• The machine can control only the volume (and flow) or the

pressure given.• The breath can be described on the basis of what triggers the

breath what limits it (the maximum value of a control variable)and what ends (cycles ) it.

Modes of ventilation • Volume controlled breath is triggered by the patients or

by the machine , limited by flow and cycled by volume.• Pressure controlled breath is triggered by the patients

or by the machine , limited by pressure and cycled by flow or time.

The breath sequence

1- Control mode (timed) : all breaths are controlled by the machine (but can be triggered by the patient)

2- Assisted mode (spontaneous) :all breaths are spontaneous .

3- Assisted /control (spontaneous/ timed): patient can take spontaneous breaths between mandatory breaths .

The target scheme

• The ventilator settings and programming that dictate its response to the patients lung compliance ,lung resistance ,and respiratory effort.

• The regulation can be

1-simple as controlling pressure in pressure controlled mode or

2- can be based on a complicated algorithm as in dual mode of ventilation ( AVAPS).

Non-invasive ventilation• Most studies evaluating these two modes in patients with

chronic respiratory failure have shown equivalent effects with respect to maintaining nocturnal gas exchange and improving daytime blood gases.

• Due to lower cost and greater patient comfort , most patients in the majority of centres are now prescribed pressure preset devices, mostly commonly , bi-level machines.

• Volume ventilators are recommended for patients with the most severe respiratory failure including those with tracheostomy and when continuous or near continuous ventilatory support is needed.

• A switch from pressure to volume preset ventilation may also be required in patients who are adherent to pressure preset ventilation but who fail to respond to treatment .

Non-invasive ventilation• Volume preset ventilators are usually set in an

assist/control or control mode of support.• No difference in blood gas improvement, lung

function or compliance with therapy was seen between the two modes.

• Pressure preset ventilators may be set in an assist (“spontaneous”) mode where each breath is patient triggered; an assist/control (“spontaneous / timed”) mode where breaths may be patient or machine triggered; and a control (“timed”) mode where all breaths are machine triggered only .

Non-invasive ventilation• The spontaneous mode has been used in patients able to

trigger the ventilator consistently, whereas the spontaneous/timed mode is used when the ability of the patient to trigger the device reliably is reduced due to poor or absent inspiratory flows being generated (e.g. respiratory muscle weakness, drive to breathe is reduced or absent, or specific characteristics of the patient’s pulmonary mechanics), where the goal of therapy is to control the respiratory pattern .

• The pressure settings used in bilevel devices include the inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP), with the difference between the two determining the level of pressure support

Bi-level Positive Airway Pressure

• Bi-level PAP (BiPAP) was developed in mid 1990's by Respironics Corporation, trademarked 'BiPAP'.

• Since BiPAP is a trademark, other companies use different terms, such as 'bilevel', VPAP (variable positive airway pressure), and "duo."

• One internet ad shows 4 different bilevel machines from 4 different manufacturers; only Respironics' machine is "BiPAP."

• Whereas CPAP sets a single pressure above the ambient pressure, BiPAP sets two pressures above the ambient, a higher (IPAP) and a lower (EPAP), e.g., 10/5 cm H2O . Note that both pressures are always above ambient.

Pressure curve when BiPAP = 10/5 cm H2O; now the pressure is higher on inspiration than on expiration, but both pressures are above ambient. NOTE: BiPAP is equivalent to PSV (pressure support ventilation) + PEEP (positive end-expiratory pressure) in the intubated patient; in that situation PEEP is the same as EPAP.

Bi-level Positive Airway Pressure• Bi-level Positive Airway Pressure therapy with a variable

pressure setting would conceivably decrease the amount of pressure against which the patient exhales, thereby decreasing abdominal muscle recruitment and consequent respiratory discomfort during the expiratory cycle

• During the inspiratory cycle, the greater level of pressure assist would combat the inspiratory flow limitation suffered by the upper airway . An additional benefit with bi-level PAP is the greater tidal volume ( VT) and unloading of the respiratory muscles, when compared to CPAP.

• The difference between the IPAP and EPAP could be considered as pressure support level that could augment the inspired VT. This feature can be exploited to combat “non-obstructive” hypoventilation that may occur due to a host of conditions.

Bi-level Positive Airway Pressure

• In adults, the maximum IPAP setting for bi-level PAP is not to exceed 30 cm H2O, and the minimum difference between IPAP and EPAP level should not be < 4 cm H2O. •A transition from CPAP to bilevel PAP is encouraged when the CPAP level approaches 15 cm H2O. This is because exhalation against CPAP levels approaching 15 cm H2O can be uncomfortable for most patients. •Bi-level PAP therapy was not superior to conventional CPAP therapy from an adherence standpoint.•The cycling of the device from IPAP to the EPAP and vice-versa may be triggered by the spontaneously breathing patient (spontaneous mode) or by a set respiratory rate programmed into the device (timed mode). •The sensitivities or the triggering threshold for causing the device to cycle in the spontaneous mode may be based on pressure, flow-contour, hardwired timing, or a proprietary combination of such measures.

Rise time , trigerring and cycling

Bi-Flex comfort feature

Ramp comfort feature

Bi-level Positive Airway Pressure• Dys-synchronous cycling between the patient and the device can be

uncomfortable and could lead to hyperinflation and further dys-synchrony.

• In some older devices the triggering sensitivities could be adjusted by the physician, but in most modern bi-level PAP devices for home use the technology has veered in favor of automation and higher levels of sensitivity.

• The rate of pressurization from EPAP to IPAP level (the “rise time”) can be adjusted to climb more briskly or more slowly. Such a feature may need to be adjusted for individual patient comfort .

• Some reports suggest that a brisk response (or shorter rise time) may have some inherent oscillatory behavior that may set the stage for “emergent” central ,However, the effect of rise time on emergent central apneas has not been demonstrated in clinical studies outside of mathematical or bench models.

Autotitrating bilevel devices• A recent innovation is that of autotitrating bilevel devices.

The algorithms of these machines are designed to automatically titrate pressure support levels, and in some devices EPAP, based on minute ventilation or flow targets.

• There is mounting evidence for the use of these devices in managing sleep disordered breathing in patients with central sleep apnea / Cheyne–Stokes respiration .

• There is currently a paucity of data and clinical experience with the algorithms and technology to automatically titrate ventilatory support in patients with chronic respiratory failure . Consequently, it is not possible to make recommendations about the role and effectiveness of autotitrating bilevel devices for chronic respiratory failure at the present time

The administration of a backup rate (timed mode) during bi-level PAP therapy may be considered under 2 circumstances.

1- The backup rate could be considered in patients with alveolar hypoventilation, with or without chronic respiratory insufficiency (elevated arterial PCO2 ) of various etiologies, which is primarily aimed at increasing minute ventilation (VE) and resolving the hypoventilation.

2- Another circumstance would be to treat central sleep apnea or prevent the appearance of emergent central apneas in patients undergoing PAP therapy for OSA.

• In both cases, the choice of the backup rate seems arbitrary and is probably best guided by polysomnography resolution of central apneas or persistent hypoxemia due to alveolar hypoventilation (SpO2 < 88% in the absence of obstructive hypopneas or apneas as an indirect measure of hypoventilation).

• In general, a backup rate set at 2 breaths below the patient’s spontaneous rate during calm wakefulness breathing with titration upwards at 2-breath increments can be considered.

 

Auto-bilevel positive airway pressure with a minimum (EPAP) of 6 cm H2O and a maximum (IPAP) of 25 cm H2O.

Principal Indications

• Non-acute setting: 1) When CPAP doesn't work for sleep apnea. 2) For patients with chronic CO2 retention who also have sleep apnea ( OHS). 3) For patients with neuromuscular disease who need some assistance with nocturnal ventilation.

• Acute setting: Pulmonary edema or COPD exacerbation, when there is CO2 retention and a desire to avoid endotracheal intubation.

How is the pressure applied non-invasively?• Same as with CPAP, but machine used is designed to deliver BiPAP.

S9 VPAP S Bilevel VPAP 111 SOMNOvent auto-S/ST BiPAP S/T

What kind of mask is used?• Same as for CPAP

The nasal mask (left) and nasal pillows (middle) and full face mask (left)

Medicare Coverage GuidelinesSame criteria for CPAP

1. Face-to-face clinical evaluation by treating physician prior to sleep study

2. Medicare-covered sleep test that shows AHI 15 event/hr. or higher, or AHI 5-14 events/hr. with documentation of excessive daytime sleepiness, impaired cognition, mood disorders or insomnia or hypertension, ischemic heart disease, or history of stroke and CPAP has been tried and proven ineffective .

• Note that there are additional criteria for continued coverage, including a face-to-face evaluation between the 31st and 90th day of treatment.

VOLUME-TARGETED BiPAP• Volume-targeted bilevel positive airway pressure (VT-

BPAP) has been developed in which the IPAP-EPAP difference is automatically adjusted to deliver a target tidal volume.

• VT-BPAP has the potential advantage of automatically varying the PS to deliver a targeted tidal volume if the condition of the patient changes. For example, if respiratory muscle strength declined and the tidal volume decreased, the device would deliver higher PS to return the delivered tidal volume to the targeted level.

• VT-BPAP can be used in the S, ST, or T mode. • VT-BPAP device is available (Average Volume Assured

Pressure Support [AVAPS], Philips-Respironics).

BiPAP AVAPS "Average Volume Assured Pressure Support," is a variant of BPAP that automatically adjusts pressure support to meet changing patient needs while maintaining a target tidal volume.

Ideal body weight

• Estimated ideal body weight in (kg)Males: IBW = 50 kg + 2.3 kg for each inch over 5 feet.Females: IBW = 45.5 kg + 2.3 kg 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.

• 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.

VOLUME-TARGETED BPAP

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

VPAP™ ST with iVAPS

Why Alveolar Ventilation?• Gas exchange only occurs at alveolar level • We have a continuous demand for a supply of

O2 and removal of CO2 • Conducting airways do NOT participate in gas

exchange

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

Anatomical dead space in relation to height of the patient

Alveolar Ventilation • Vt (500ml) – Vd (120ml) = alveolar ventilation for one

breath• 500 - 120 = 380 ml participates in gas exchange for each

breath • Vta x RR (respiratory rate) = Va (minute alveolar

ventilation) = 0.380 x 15 = 5.7L/min

Benefits Of Alveolar Ventilation • Supply of O2 (PaO2) .Normal = 80 – 100 mm Hg • Removal of CO2 (PaCO2) . Normal = 35 – 45 mm Hg • Alveolar ventilation provides necessary gas exchange to

satisfy metabolic demand

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 .

Auto-TriLevel• IPAP: inspiratory pneumatic

splinting of the airways (ventilation)

• EPAP: easier exhalation at a low expiratory pressure level for a pleasant breathing sensation

• Additional end-expiratory pressure (EEPAP): required minimum pressure for adequate splinting of airways during phase when risk of collapse is highest

• PDIFF (Δ IPAP-EPAP): need-oriented ventilation support by means of changes between inspiratory (IPAP) and expiratory (EPAP) pressure levels

Auto-TriLevel• Reduced mean and maximum therapy pressure

under TriLevel: Results of a bench test comparison with BiLevel therapy.

• SOMNOvent auto-ST is the world‘s first automatic BiLevel device that permits goal-oriented therapy settings(SCOPES).

• With the combination of the autoTriLevel principle and the automatic trigger WMtrak, this device delivers the greatest effectiveness, reliability and breathing comfort – simply the fastest therapy results.

• Particularly for cases of complicated SDB, SOMNOvent auto-S, convinces with its intelligent combination of automatic BiLevel S therapy and auto-CPAP.

Auto-TriLevel

• Auto-bilevel spontaneous (SOMNOvent auto-S ).• Auto-bilevel spontaneous/timed (SOMNOvent

auto-ST ).• Anti-cyclic modulated ventilation (SOMNOvent

auto-CR ).

ASV is a variant of BPAP that was developed to treat Cheyne-Stokes central apnea. Both ASV and BPAP devices with a backup rate are approved for use with patients with central apnea and complex sleep apnea

ASV is BiPAP with a twist. The IPAP and EPAP can vary, depending on the patient's needs. In some ASV-type machines , the EPAP is fixed and only the IPAP changes; in others both can change.Basically, in ASV one or both pressures is continously adjusted, so that the ventilation delivered to the patient 'adapts' to the situation.

SomnoVent CR Respironics autoSV ResMed VPAP Adapt SV

The top graph is pressure and bottom is flow. Note that EPAP is set at 5 cm H2O. The IPAP is variable. When central apnea ensues , the machine senses less air flow and ratchets up the IPAP, eventually reaching the pre-set limit of 15 cm H2O. The prescription for this patient would read: "IPAP 5, PS 3-10."

A peak flow target is established around the 4-minute average and the machine changes the air delivery as needed, to deliver 95% of the target, as shown below.

Dynamic pressure support inversely proportionate to peak flow

Periodic breathing treated with BiPAP auto SV

Trilevel ASV uses three different pressure levels over the course of the breathing cycle. The IPAP pressure provides the inspiratory splint and ventilation. Expiratory pressure is varied between a lower level at the start of expiration (EPAP) and a higher level at the end of expiration (EEPAP).

Confusing Points Clarified• BiPAP is used for non-invasive ventilation. It is

designed to augment alveolar ventilation because it delivers two pressures, one higher IPAP and one lower EPAP; however, both IPAP and EPAP are above ambient presure.

• BiPAP is the same as PSV + PEEP in the intubated patient.

• BiPAP is actually a trademark of Philips Respironics, and so cannot be used in advertising by other manufacturers. ResMed Corporation, for example, uses the term "Bilevel" instead of BiPAP.

• Many machines are on the market that can deliver BiPAP as somnovent ST .

Confusing Points Clarified• Also confusing is that BiPAP comes in several 'modes'

-- all variations on the simple two pressure model: • S (Spontaneous) Mode. The device triggers IPAP when

flow sensors detect spontaneous inspiratory effort and then cycles back to EPAP.

• T (Timed) Mode. Here the IPAP/EPAP cycling is purely machine-triggered, at a set rate, typically expressed in breaths per minute.

• S/T (Spontaneous/Timed) Mode. Here the machine triggers to IPAP on patient's inspiratory effort, but there is also a 'backup" rate. This rate is set to ensure that patients still receive a minimum number of breaths per minute if they fail to breathe spontaneously. However, this is not a ventilator mode and will not provide life support for the continously apneic patient.

Confusing Points Clarified• While BiPAP is generally better than CPAP for patients

with CO2 retention, or who need augmentation in alveolar ventilation, there is no rule of thumb about which BiPAP mode is 'best'. That can only be determined with a careful titration of pressures in the hospital or sleep lab.

• BiPAP AVAPS machine designed specifically for patients with hypoventilation disorders (e.g., restrictive thoracic disorders, obesity hypoventilation syndrome, some cases of central apnea and COPD). Not to be confused with ASV, AVAPS is not for complex sleep apnea or sleep apnea unresponsive to CPAP and BiPAP (which are the indications for ASV).