/ Using a CPAP machine on Toubkal trek

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Jamie Wakeham - on 05 Mar 2019

Hi all

My wife has sleep apnea, and uses a CPAP machine to control it.  She's planning to go on a commercially run trek to Toubkal in a couple of months and I'm trying to work out how best to manage her apnea while she's away.  She can go a night without the CPAP, but it's not good for her (she'll basically Cheyne-Stokes all night long) and no-one within 50m of her will get any sleep...

At home the CPAP runs on the mains.  We've got a 12V battery (26Ah AGM) and a DC-DC converter which I know is good for at least two nights camping.  The CPAP draws about 60W, which works out to around 5AH for an 8 hour night.  After two nights of use the terminal voltage on the battery is down to 11.8V and I've never experimented with taking it any lower - it's always been easy to find somewhere to recharge it.  However we've keen for her not to have to carry the battery, either on the flights or up Toubkal!

Apparently this trip has three nights on the hill - two in refuges and one in tents.  So, first question - does anyone know if there's reliable mains power in the refuge(s) on Toubkal?

Secondly - the trip organiser has said they'll arrange a battery in country and get it portered up to the tent.  I very much imagine that it'll turn out to be a bog standard 12V lead-acid car battery.  I don't know enough about battery tech (I know just enough to realise that there's lots I don't know!) but a fully charged car battery will be able to put out the 60W she needs for a night, won't it?  I'm aware that car batteries are optimised for short durations of massive current, but they ought to be able to put out low power like this for eight hours without their terminal PD dropping too far, right?

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Lakeslina on 05 Mar 2019
In reply to Jamie Wakeham:

We camped rather than staying in the huts, but I believe both refuges have electricity.... just not necessarily all the time (sounds like the generator is only on at Les Mouflons approx. 6-9:30pm).

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ben b - on 05 Mar 2019
In reply to Jamie Wakeham:

There's a couple of other options I guess.

The first would be a mandibular advancement device. Weighs very little, no power required, very effective for OSA. Needs a bit of time to be made and adjusted, but would be a good investment for trips where CPAP can't readily be taken. Your local sleep lab should have a way of referring you for one. Can be expensive - here in NZ we advise about a GBP1k charge.

The other would be for the couple of nights in the hut (only) using something like ProVent valves. Weigh even less, but not anywhere near as effective for OSA as either CPAP or MADs. Cheap and probably worth a try though. They are self-adhesive flaps that fit over the nostrils. they allow air in but not out, so provide - in effect - resistance to breathe out against much like CPAP, although only at lower levels. These lower levels are however often enough to control about half the OSA (unlike CPAP which generally is set to control about 90% of the OSA events - aiming for 100% control is often impractical). The CPAP can be used for the rest of the trip as normal. Would need to try them out and see if they are tolerable first.

Have a great trip!

b

PS most modern CPAP machines can adjust for altitude (there's a lot of OSA in Denver!) but it's not a huge issue if hers doesn't.

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THE.WALRUS - on 05 Mar 2019
In reply to Jamie Wakeham:

There is reliable mains electricity at both the CAF and Nelter Refuge which will power the machine without any problem. I suspect it's solar / battery storage.

Do you know where she will be camping? Some of the villages nearby also have electricity and lodgings which may work better than a night in a tent.

If she were to use the Imlil valley to approach Toubkal, there wouldn't be any need to camp; she could spend the first night in Armed; there are plenty of places to stay and the village has mains electricity and the next couple of nights at the refuge...

Post edited at 22:50
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Jamie Wakeham - on 06 Mar 2019
In reply to Jamie Wakeham:

Thanks, all.  I will find out exactly what the itinerary is and where she'll be staying, and go from there.

Ben, thanks for suggestions of alternatives.  I'd prefer to make certain she can use her CPAP rather than having to go with them but it's good to know they exist; I might suggest she gets some ProVent valves as a backup in case the CPAP plans fail. 

You mention adjusting the CPAP for altitude - is that simply a case of changing the pressure?  I believe that's the only user-adjustable parameter I have access to.  She's currently on 7cm H20 (what a ridiculous unit!) - would altitude mean that needs to go up or down?

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ben b - on 06 Mar 2019
In reply to Jamie Wakeham:

Aye cmH2O is absurd (and so are mmHg!). 

Theoretically with lower air pressure the fan might need to spin faster to achieve the same pressure. But in reality as atmospheric pressure is low as well, the net gradient from inside the mouth to outside the neck probably stays the same. To make sure you could always switch to autoset mode from say 6-8cm and allow the software to sort it out for you. How easy that is depends on machine and/or your relationship with the provider!

7cm is pretty low, so possibly more upper airway resistance syndrome than OSA. In that setting provent might be just as good. 

HTH

b

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wintertree - on 06 Mar 2019
In reply to Jamie Wakeham:

Car battery Ah ratings are typically their C20 rating - that is the capacity they have when discharged over 20 hours.  60 W is 5 A @ 12 V.  So you’re looking for a rating of  (8 hours) x (5 A) = 40 Ah minimum.

Car batteries range from ~60 Ah to ~115 Ah so should be up to the task.  Unless they’re knackered which - on average - a car battery no longer in a car is.  

28 V and 40 V interchangeable battery power tools have nice robust lithium battery packs and chargers.  Much less likely to cause grief than an AGM in your luggage - lighter, a whole product not a battery etc.  My lot are “Greenworks” 40V units with 80 Ah lithium batteries.  The power looks pretty accessible on them...  They actually do a battery to 110 V AC inverter availilbe from the US as well.

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Jamie Wakeham - on 06 Mar 2019
In reply to Jamie Wakeham:

Thanks again, both.

Wintertree, I fear that the 60W figure I gave earlier is not correct.  I quoted it from the bottom of the device without questioning it, but you're right - it's not compatible with an overall use of 5Ah for the night!

The ResMed website has a pdf about using batteries and they say that this device needs a 5Ah battery to get it through a night.  They also say it draws 0.4A at 12V... so a power of about 5W.  I wonder if 60W is a peak power that it might draw at start-up?

Anyway, 5Ah is consistent with what I've found (ie that my 26Ah battery happily does two nights) and that would suggest that even a slightly knackered 60Ah car battery should get her through?  I'm only really worrying about this because of a statement on the ResMed pdf that says :

Can I use a stand-alone car battery to power my device?
No. This guide provides information about powering ResMed devices using deep-cycle batteries rated at specific amp-hours (AH). Automotive batteries are designed to be continually charged and deep discharges (as would occur when using the battery by itself) significantly decrease the life of the battery. Further, automotive batteries are rated in cold cranking amps (CCA) which is not equivalent to the AH ratings of deep-cycle batteries.

Edit - looking on some dedicated apnea forums confirms what I thought - the pump itself barely uses 4 or 5Ah a night.  The 60W is for when the optional humidifier is turned on, and we won't be using that.  And there are references to managing with a regular car battery overnight in emergency, with the caveat that it'll damage the battery if done repeatedly (and you might not be able to start your car in the morning!)

Post edited at 12:09
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graeme jackson - on 06 Mar 2019
In reply to Jamie Wakeham:

I'm interested I this as my missus also needs a cpap so we've had to curtail weekend camping trips. As it happens I have a new unfitted car battery sitting in the garage. Can someone recommend an inverter that would suit?

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Jamie Wakeham - on 06 Mar 2019
In reply to graeme jackson:

This I can help on, as I went through the process you need a few years ago when we got our CPAP camping set-up!  Firstly, you almost certainly want a convertor (DC-DC) not an invertor (DC-AC).  If it's a ResMed CPAP, then you need their own brand 12v-24v convertor -they're £60.

Using a car battery long term will probably kill the battery very quickly.  Car batteries are intended to be used briefly at very high current, but only depleted a little (20-30%), and then recharged.   Instead you need a deep cycle battery, intended to be drained slowly but relatively deeply.  You can get this in lithium ion (if weight is more important to you than cost) but if this is for car camping then sealed lead acid is the way to go - cheap but heavy.  AGM seems to be the best design of lead acid to use because it's impervious to being tipped over.

Then you need to decide how big a battery to buy.  Look up how much capacity your CPAP will use - this varies between model and also with what pressure you need.  As above, my wife's uses about 5Ah in a night, but that's without the humidifier attachment - they use a LOT more energy so we make do without when camping.  Times that by the number of nights you need to go between charges, double it so you don't discharge the battery too deeply, and maybe add a bit for safety.  Our regular battery is 26Ah, and weighs about 7kg.  I'm happy with it for two nights and I'm sure it'd be fine for three at a push.  Think it was about £40.

Finally you'll need a charger that can recharge AGM - they want a different regime to wet lead acid so a regular car charger isn't perfect (I understand that it will do the job but will probably cost you battery life overall).

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graeme jackson - on 06 Mar 2019
In reply to Jamie Wakeham:

Brilliant!  Thanks for that Jamie.

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L RobLane001 - on 10 Mar 2019
In reply to Jamie Wakeham:

Hi Jamie

I climbed Toubkal over three days in October with my CPAP and a travel CPAP battery and slept at 3,200 meters for two nights, one in the refuge and one in a tent next to the refuge. My pressure is 11cmH2O

Here are the highlights:

Their electricity supply shouldn't be relied on and don't expect to find a plug by the bed.

Firstly not many get 8 hours sleep on Toubkal because of people coming and going all night so a battery designed for two full nights will work for 3.

Don't try adjusting the pressure of the CPAP yourself. I adjusted mine upwards and it was like wearing a hairdryer! The machine knows best!

When using the CPAP, I kept the battery in the sleeping bag to keep it warm and maintain charge. No idea if this is right or safe but it felt the right thing to do and I had charge left.

I've also got an inverter? and it works fine on a car battery for night fishing for a couple of nights but I know the history of my battery. I'd use theirs as a backup but take a purpose built travel CPAP battery to make sure. They can also be used on planes if you red eye which is a big plus

Good luck to her. Its an amazing experience.

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