TOPIC ResMed ASV Respironics AutoSV Comment

History For years there was just CPAP and BiPAP to treat sleep apnea patients. In 2001 a paper appeared about a novel treatment for one form of central sleep apnea: Teschler H, et al. Adaptive pressure support servo-ventilation: a novel treatment for Cheyne-Stokes respiration in heart failure. Am J Respir Crit Care Med 2001;164:614-9. The study used ResMed Corporation's new ASV machine to deliver variable pressures to patients with Cheyne-Stokes respiration -- the waxing and waning breathing often seen during sleep in heart failure patients. Soon the machine was used for treating all types of central sleep apnea as well as complex sleep apnea, a condition not recognized until after the machine was already in use. "ASV" as a label and a particular methodology to adjust pressures was patented by ResMed. A few years later, another large equipment manufacturer, Philips Respironics, came out with their own ASV-type machine; they call it "autoSV." Auto SV is also an adaptive servo ventilator device that uses a different algorithm to adjust bilevel pressures. A newer model is called Auto-SV Advanced (discussed below). ASV is but a way station on the road to newer and smarter machines. Expense (about $6000 per machine) limits their wider use, but no doubt these machines will become cheaper and at some point replace our basic CPAP/BiPAP units.

Methodology The basic difference between the two devices is the way the patient's breathing is tracked so that IPAP and/or EPAP can be adjusted. Per ResMed's fact sheet, the algorithm for ResMed's VPAP Adapt SV (as their machine is called): "uses three factors to achieve synchronization between pressure support and the patient's breathing.

1. The patient's own recent average respiratory rate, including the ratio of inspiration to expiration and the length of any expiratory pause.

2. The instantaneous direction, magnitude, and rate of change of the patient's airflow, which are measured at a series of set points during each breath.

3. A backup respiratory rate of 15 breaths per minute." In other words, the algorithm is proprietary and unique to ResMed. To highlight this point, below is a quote about the ResMed algorithm from Brown LK. Whither adaptive servo-ventilation? Current Opinion in Pulmonary Medicine 2010;16:527-29: "The [ResMed] VPAP Adapt SV relies on a complicated estimate of recent average ventilation using mask pressure and total airflow to obtain target minute ventilation and determines respiratory phase using an estimate of intantateous respiratory airflow (and may also utilize 'fuzzy' catergories of resipratory phase). Furthermore, a host of internal constants and parameters govern the microprocessor's decisions with respect to pressure changes and cycling times, none of which are user-adjustable or explicitly stated." The Philips Respironics FAQ states that the device tracks flow. "The flow signal is analyzed and a target flow is calculated. If the patient reaches the flow target, the device does not offer any additional pressure support. If the patient does not reach the flow target the device will dynamically change pressure support breath to breath." Omitted from this FAQ is that the device tracks peak flow over a 4-minute cycle, as shown below.

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.

If these graphs make the Respironics algorithm seem simpler than the ResMed model, Dr. Brown assures us it is not (Brown LK. Whither adaptive servo-ventilation? Current Opinion in Pulmonary Medicine 2010;16:527-29). He writes: "...this device's algorithm employs an even geater number of internal parameters [than ResMed's machine] that are not explicitly disclosed and not adjustable. ...The [Respironics] Advanced model adds automatic titration of expiratory positive airway pressure to the generator's capabilities, utilizing an algorithm borrowed from their auto-CPAP machines." Despite the fact that the proprietary algorithms are rather opaque, both machines seem to work well in their stated objectives of treating central sleep apnea and complex sleep apnea. As such, they compete in the market for treatment of these conditions. And while each company claims its methodology is superior to the other, there is no head-to-head study. From the standpoint of the sleep medicine specialist, neither machine is clearly superior or inferior. Since ResMed was first out with an ASV machine, most of the articles in the medical literature are based on ResMed's device, but there are now several publications for autoSV as well. More importantly, this is a rapidly evolving field, and new machines will likely appear soon, from these two companies as well as other competitors.

Principal Indications

There are two principal indications:

1) Central sleep apnea

2) Complex sleep apnea 1) Central sleep apnea can basically be divided into Cheyne-Stokes (C-S) and non-Cheyne Stokes breathing. C-S breathing pattern - waxing and waning respirations punctuated by periods of no respiratory effort and no air flow - is usually seen in patients with congestive heart failure or cerebrovascular disease. Non C-S central sleep apnea does not show the waxing and waning respirations, just abrupt cessation of all respiratory effort and air flow - is seen in patients taking chronic opiates, in patients with no obvious cause, and as the manifestation of Complex Sleep Apnea. 2) Complex Sleep Apnea is diagnosed when a patient with obstructive sleep apnea is treated with CPAP or BiPAP, and the treatment itself elicits central apneas.

1) Central sleep apnea

2) Complex sleep apnea See comment under ResMed If complex sleep apnea ("CompSA") is a result of CPAP, BiPAP may be tried, though it is not usually successful. When CompSA doesn't respond to BiPAP, or is a result of BiPAP in the first place, there are two choices:

a) Continue CPAP or BiPAP to treat the OSA, hoping that the central apneas will remit over time (they sometimes do);

b) Start the patient on ASV. There is no clear standard about when to start ASV on patients who manifest CompSA.

What kind of mask is used to deliver ASV? ResMed recommends their full face mask. Shown below is the ResMed Quattro Pro full face mask.

Respironics states any mask used for CPAP should work with their autoSV machine. Below is the Respironics Comfort Gel full face mask.

Mask type and size is best determined in the sleep lab, when a patient is being titrated on an ASV machine.

Prescription Examples ResMed VPAP Adapt SV: Backup rate: 12 breaths/minute

Rise time: (the time it takes the device to change from EPAP to IPAP. Settings range from 1 [fastest] to 6 [slowest]. The range of values corresponds to 1/10 seconds, so that a rise time of 4 = 0.4 seconds)

Inspiratory time: 2 seconds (range is 0.5 to 3.0 seconds)

EPAP [expiratory positive airway pressure] = 7.0 cm H2O

Minimum PS [pressure support] = 4.0 cm H2O

Maximum PS = 13.0 cm H2O

Maximum pressure for device (generally <=30 cm H2O)

Mask: ResMed Quattro Full Face Mask (recommended by company for their ASV machine), with heated humidity Below is the ResMed ASV machine.

Respironics currently has TWO devices on the market, the regular AutoSV and the AutoSV Advanced. Respironics recommends that physcians now prescribe ONLY the AutoSV Advanced , so it seems likely that the regular machine will be phased out soon. Below are prescription examples for both. Regular AutoSV

For the regular AutoSv you can use the same prescription example as listed under ResMed. A detailed approach to prescribing is provided in the Respironics pdf file.

Below is the Respironics auto SV machine. Prescribing AutoSV Advanced

The same settings as for the regular Respironics AutoSV and the ResMed ASV machine, with one important addition. Respironics autoSV Advanced allows the EPAP to vary, so you have to specify a minimum and maximum EPAP. For example, to the settings for Respironics regular autoSV you would add: ...

EPAP-min = 7 cm H2O

EPAP-max = 12 cm H2O

... For more information see autoSV Advanced. The technology is evolving and this section should change as new machines (and methods of delivering ASV) come on the market.