Omitted Decompression and In-water Recompression (IWR)… some thoughts


Occasionally, in fact with an almost predictably cyclic regularity, two questions that surface on the internet dive forums ask about missed decompression and/or in-water recompression (IWR).

My standard answer on a public forum is to suggest that when the diver shows signs or complains of DCS symptoms, notifying EMS, keep the diver on the surface, warm and hydrated, monitor for changes in their condition (a correctly conducted five-minute neurological exam is a decent protocol for this), have them breathe pure oxygen (preferably from a demand face mask), take notes that will be useful for EMS/Hyperbaric staff, and prepare for fast evac.

The suggested strategy for a diver who has omitted a “deco stop” or safety stop but is SHOWING NO SIGNS or who is NOT COMPLAINING OF ANY SYMPTOMS, is the same as above but without the call to EMS and rather than preparing for evac., collecting their kit for them and keeping them out of the water for at least 24 hours.

However, neither is a very good answer to the actual questions posed, and occasionally, I throw my hat in the ring… something like this.

The first step for anyone brave enough to attempt an answer is to define the differences between the two topics; and in particular, the circumstances that might necessitate the call for a diver to conduct an omitted decompression protocol, as opposed to those that indicate IWR as an option.

Let’s start with the easiest: Omitted Decompression.


The protocols for Omitted Deco are discussed and outlined in several technical diving student manuals – including a couple of TDI manuals – and the procedure is taught as part of TDI’s decompression and trimix courses. It is based on the protocol published in the US Navy Diving Manual and may only be attempted when the diver shows NO SIGNS and has no SYMPTOMS of DCS; and the omitted stop was no deeper than six metres.

There are a couple of other prerequisites relating to water conditions, weather conditions, thermal protection, available gases in sufficient volume, having a tender diver available to monitor the subject diver during the whole procedure, and the diver being in a position to return to the water within five minutes of surfacing.

All that as taken and confirmed: First, return to 12 metres and conduct the stop required at that depth by the original ascent schedule PLUS one quarter of the omitted three-metre stop time. If no stop was originally required, remain there for one quarter of the omitted three-metre stop time. Ascend to nine metres at a speed no greater than three metres per minute (the ascent speed for the whole procedure) and remain there for one third of the three-metre stop time. Ascend to six metres and wait there for half of the three-metre stop time. And finally ascend to three metres for one-and-a-half times the scheduled three-metre time.

Here’s the way that looks for an omitted or partially omitted deco stop at three-metres.

Depth (metres/feet) Original Stop (mins)/Gas Omitted Stop Procedure
12 metres/40 feet None/ bottom gas 3-minute stop
9 metres/30 feet 3 / bottom gas 4-minute stop
6 metres/20 feet 5 / oxygen 6-minute stop on oxygen if CNS allows
3 metres/10 feet 12 /oxygen (omitted) 18-minute stop on oxygen if CNS allows

For the record, I have tendered for divers who have missed all or part of a decompression schedule and for whom the missed deco protocol worked.

Now let’s attempt to clarify the issue of IWR. This is suggested when a diver surfaces and complains of symptoms (type one) and IWR is the ONLY option available… i.e. there is no hope of stabilizing them and getting them to a hyperbaric facility.

Important to establish first off that this is a highly risky endeavor. The risks of IWR include several minor issues relating to thermal stress and volume of gases needed, but the strong emphasis in the entire risk assessment analysis center on the subject diver getting worse far worse once in the water and becoming, for example, paralyzed and/or losing consciousness. Oh, and then dying.

Various protocols and tables for IWR have been developed over the years. The recognized tables include the Australian, the Hawaiian, the US Navy, and the Pyle tables… I believe Pyle’s modification to the Hawaiian table are the most “up-to-date.” I am reasonably sure that NONE carries sanction from the major sport agencies. The technical agency I teach for, that I do consultant work for, and on whose training advisory panel I served for several years, does not sanction IWR either. Essentially, within the context of recreational diving (tech or sport), IWR is simply NOT an option.

Just in case we wonder why, here’s a checklist of the minimum kit and personnel requirements for attempting IWR in a remote location.

  • A heavily weighted shot line secured in a sheltered spot where surface waves will not influence comfort of subject diver and/or the tender (who will be in the water) and treatment supervisor (who will be on the surface).
  • Some way to hold the subject diver in place… a climbing harness works as does a sidemount harness with some modifications
  • Stages in the shot line to hold the subject diver at a set position in the water column… prussik loops and a locking carabiner work if tied and anchored correctly.
  • Full-face masks with coms to the surface and each other
  • Surface supplied gas (oxygen et al) supplied to the subject diver via umbilical
  • An experienced tender and supervisor who have at very least certification and some background in hyperbaric treatment
  • Adequate and possibly additional thermal protection for both subject diver and tender
  • A valid IWR treatment “table”


As someone who is occasionally involved in expedition diving (the only situation I can imagine where the whole team would discuss IWR as part of the SOPs during pre-trip planning sessions), IWR is considered highly risky even when ALL the above, and a few more details, are available. It is also understood that IWR (just as recompression in a chamber on the deck of a boat or in a medical facility) may not resolve the issue. In other words, the subject diver may die.

The preferred option if a portable chamber is NOT AVAILABLE – and something many expedition leaders seem to have less hesitation using – is saline IV (intravenous) therapy, oxygen and the use of pain medication all administered by a practicing medical practitioner of some sort… NP, Paramedic, MD et al. It is therefore considered best practice to have at least one of these as part of the team on ALL expeditions to remote locations.

(For the record, I have been lucky enough to lead several expeditions to various spots where there may have been a temptation to use IWR, and I have certainly tried to make sure that at least one team member is an experienced diving MD. To date, one of my team has had to supervise an autopsy on one of our fellow team members, but we have not had to deal with IWR. Therefore, my first-hand experience in this issue has been ZERO.

You can read more at Gene Hobbs excellent online resource:
http://archive.rubicon-foundation.org/xmlui/handle/123456789/5629

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