Physiology in the Winch

Dr Alan Garner has a blog post in the context of a report just published. A catastrophe during a winching operation highlights the physiological challenges we sometimes add in the work we do. 

The death of a patient during a winching incident in Victoria in 2013 was distressing for everyone concerned.  I was asked by the Victorian Coroner’s Office to provide an expert opinion on the death based on some previous research I had conducted with one of our registrars, Dave Murphy, looking at the effects on respiratory function of various methods of helicopter rescue.  I’m pretty sure at the time we were the only group in Australia who had published in this area so I guess we were the obvious choice.

As part of trying to avoid a similar incident the coroner’s office agreed to us publishing the case in an appropriate scientific journal so that operators worldwide would benefit from the lessons learned rather than just the industry in Australia.  That report has just been published in Aerospace Medicine and Human Performance and can be found here.

The details of the case are now on the public record in both the coronial inquest and the ATSB investigation.  Our case report focuses more on the physiology of hoisting than either of these forums needed.

For those not aware of the case the brief version is that a man of approximately 60 years of age and BMI of 45 with borderline cardiac failure injured his ankle whilst on a hunting trip in Victoria about a kilometre from the nearest road.  Carrying him was considered risky for the rescuers (the terrain was steep) and a hoist extrication by helicopter was organised.  An accompanied single sling technique was utilised.

Unfortunately as they approached the aircraft skid the patient became combative and then unconscious.  He slipped from the strop despite the best efforts of the paramedic and crewman and fell to his death.  I can only imagine the distress of the crew when this occurred.

The actions of the crew on the day were consistent with their company/Ambulance Victoria procedures and were within the specifications of the equipment utilised. They were just doing their best to provide their best care as they’d been trained. Neither was any of the equipment found to be faulty.  The obvious question then is why did the fall happen?

What happens when you put someone in that hoist?

You need to go looking in the climbing literature to find the physiological effects of suspension with chest compression which is what happens when you are in a single strop.  As you would expect, there is a constrictive effect upon respiration but there is also a considerable decrease in cardiac output resulting from the decreased venous return with raised intrathoracic pressure.  The decrease in cardiac output has been demonstrated to be as much as a third in fit young climbers.  The decrease in respiratory function parameters is similar (in both the Murphy paper and the one referenced in the link in the previous sentence).

HMS Montrose conducts Rapid Roping and Winch Training
When you think through what’s involved, the physiology makes sense.

Given that the chest compression associated with hoist rescue is of short duration it is generally adequately tolerated long enough to complete the rescue in fit young people.  Having said that one of the best studies of the physiological effects of suspension in a chest harness was precipitated by the death of a 25 year old soldier who was left suspended in a single strop for just 6 minutes.  Cardiovascular collapse can occur surprisingly rapidly.  The man in the Victorian incident with his significant comorbidities was however not able to tolerate even a short period of thoracic compression and rapidly became unconscious.

The effects of single strop rescue in people who have been immersed even where they are otherwise fit and young is perhaps better known and the second sling under the knees (or hypostrop as it is often called) is in widespread use in this situation.  For winches of non-immersed persons it seems that the physiological consequences of various rescue techniques are not well known in the industry however.

Subsequent actions by Ambulance Victoria, the helicopter operator, the Victorian Coroner, CASA and the Australian Transportation Safety Bureau (ATSB) all rightly concentrated on determining how a repeat of the incident could be avoided by better educating both clinical and operational crews about the physiological implications of hoisting techniques.

What are the options?

We have previously published on the use of the Coast Guard Rescue Basket due to its benign effect on physiology compared with other techniques (Murphy).  It remains a surprise to us that this device is not in more widespread use.  Ambulance Victoria has now introduced a sit type harness which is definitely to be preferred in hoists over land.  The Rescue Basket can be used in winches out of water as well and we think is the more flexible option.

jim-howard
You can see that this sort of option would be easier on the physiology.

Should the single strop technique be banned entirely?  We don’t believe so. Every rescue is a balance of risks and sometimes the risk to either the patient, aircraft or both means that an immediate single sling extrication may be the safest option overall.  We certainly have not banned its use within CareFlight.  Knowing about the physiological downsides we have discouraged its use for many years and encouraged use of the rescue basket.  We have not removed it from the armamentarium however.  If a crew elect to use it they have to provide a report in writing to the chief pilot about why they chose that technique.  Knowing that there is that little bit of extra documentation required is enough to make teams make sure they’ve covered their options and risks carefully before they go ahead, but the option remains on the table.

Hoisting is risky for lots of reasons. We train for a range of safety considerations. And equally we have to make sure we’re aware of the physiological changes we might inflict on our all important patients.

Conflict of Interest Statement:

Neither I, nor either of my employers have any interest, financial or otherwise, in the manufacturer or distribution of the Coast Guard Rescue Basket.

Notes:

The first image here is from the Royal Navy Media Archive while the second was posted by Jim Howard, both to the Creative Commons area of flickr. Both are unchanged.

And now those references.

First is the paper derived from this case:

Biles J, Garner AA. Loss of Consciousness During Single Sling Helicopter Hoist Rescue Resulting in a Fatal Fall. Aerospace Medicine and Human Performance. 2016;87:821-4.

Next is the paper written with Dave Murphy:

Murphy D, Garner A, Bishop R. Respiratory function in Hoist Rescue: Comparing Slings, Stretcher and Rescue Basket. Aviat Space Environ Med 2011; 82(2):123-27

And the first of the climbing things:

Roeggla M, Brunner M, Michalek A, Gamper G, Marschall I, Hirschl MM, et al. Cardiorespiratory response to free suspension simulating the situation between fall and rescue in a rock climbing accident. Wild Environ Med 1996;7(2):109-14

And the next one:

Madsen P, Svendsen L B, Jørgensen L G, Matzen S, Jansen E, Secher N H. Tolerance to head-up tilt and suspension with elevated legs. Aviat Space Environ Med 1998; 69(8):781-4

And you can find the ATSB report here.

5 thoughts on “Physiology in the Winch”

  1. Thanks for the interesting blog. Such a shame your report in Aerospace Medicine and Human Performance isn’t FOAMed so we can all learn further.
    MattCW

    Like

  2. Thank you very much for the interesting blog. I´ve been working as a Rescue Swimmer within the Finnish Border Guard for over two decades now. Im currently studying Emergency Care Nursing / Paramedic (Bachelor of Healthcare) aside my work and started to work with my thesis about this very subject. There is no national research to be found about this important topic and Im struggling to find good researches and full text articles about the matter. I realize there isnt too much to be found, but would be happy for any help I might receive.

    Kind Regards, Sami Ollila
    email: sami.ollila@metropolia.fi

    Like

  3. Thanks Sami for your interest. I have heard only good things about the rescue services in Finnland. You guys have a very challenging environment! Pleased to help out in any way I can. I will email you with all the material I have.

    Alan

    Like

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