Chamber Recompression Therapy
“No-one who has seen the victim of compressed air illness, gravely ill or unconscious, put back into a chamber and brought back to life by the application of air pressure, will forget the extraordinary efficiency of recompression, or will be backward in applying it to a subsequent case of illness.”
(Robert Davis, 1935)
Diving accidents requiring recompressing divers in a Recompression Chamber, namely Decompression Sickness (DCS) and Gas Embolism (GE) are put together under the term Decompression Illness (DCI).
The goal of recompression therapy is to prevent both further and permanent injuries caused by DCI.
Fundamentals of Therapy for a DCI case are:
1- Raised atmospheric pressure to shrink the gas-phase (bubble) volume.
2- Raised inspired PO2 to washout the inert gas, promote tissue oxygenation and reduce edema.
3- Adequate treatment time.
4- Adequate fluid management.
5- Appropriate drug therapy.
Proper application of recompression therapy can abort the mechanisms by which this illness can cause permanent tissue deformation and in many cases complete resolution of symptoms can be achieved.
Frequently, it is very difficult to diagnose accurately the exact nature or seriousness of a diving accident, so if any manifestations of DCS or GE are observed, it is of much greater importance to evacuate the victim to initiate treatment immediately than to delay treatment for a more accurate diagnosis, and when differentiation between a serious case of DCS and GE can not be made, the treatment of AGE should be conducted.
An initial evaluation, which helps to identify the urgency of a DCI case, is determined by the following:
1- Onset of symptoms. (The longer the surface interval prior to symptoms, the less likely they are to worsen)
2- Severity of symptoms. (Describing the extent and intensity of DCI symptoms as: pain, inability to move or coordinate, walking difficulty, balance or urination problems, dyspnoea or level of consciousness deterioration) notice the terms; mild, moderate, massive and severe.
3- The organ systems affected. (Musculoskeletal - CNS- inner ear- circulatory- respiratory systems)
4- The change of symptoms with time. (Evolution)
Based on onset & severity of symptom, organ systems involved & time course, three degrees (categories) of urgency are defined:
-Category A (Emergent) in which all available resources should be mobilized to ensure that recompression treatment will be obtained as fast as possible (do not waste time for examination or proper diagnosis).
-Category B (Urgent) in which the patient will need treatment (recompression) as soon as it can be arranged (not an extreme emergency).
-Category C (Timely) in which symptoms are not obvious without detailed examination & the hyperbaric physician can make the decision to delay or abort the treatment of a patient in this category.
*In water recompression should never be attempted (even if the victim is fully conscious and equipped with an Oxygen rebreather having a full face mask) because of the following reasons:
1. The signs and symptoms of DCI are unpredictable as usually bubbles take time to develop and other serious manifestations can happen under water that can lead to serious complications.
2. Lack of proper medical attendance under water.
3. Recompression tables require a huge stock of different breathing gases and take long periods of time which can never be satisfactorily and safely achieved under water.
The approach to a diving casualty that needs chamber recompression has 3 views:
1. Recompress to a pressure (depth) similar to the depth of the original dive and decompress according to the time of exposure of that dive (old French technique).
2. Recompress to a depth that produces a clinically acceptable response (Australian technique of the depth of relief) or recompress to the depth of relief + 1 atmosphere and then decompress according to special tables.
The above 2 methods are not satisfactory because the choice of treatment tables will depend upon a lot of variables, which makes it confusing even for a skilful supervisor since a different table for each individual case should be worked out.
*These tables though, might be very effective for some cases when prompt recompression takes place.
3. Recompress to a predetermined fixed depth, i.e. according to standard recompression treatment tables.
These tables are scientifically developed taking in consideration bubble physics as well as the effect of gases under pressure, and are now most accepted by different organizations world wide.
A lot of gases were utilized in the development of such tables including Air, Oxygen, Heliox (Helium + Oxygen), Nitrox (Air + Oxygen) and Trimix (Helium + Nitrogen + Oxygen) or (Helium + Hydrogen + Oxygen)
The privileges of using these tables are:
1. They have a relatively high cure rate (up to 90% when the elapsed time before recompression is relatively short).
2. They enable the average operator to easily decide which tables to use according to the severity of symptoms, prognosis and recurrence during the different stages of treatment.(by following given Flow Charts)
3. They require a chamber of a maximum working pressure of 6 ATA, which is relatively low, compared to other chambers needed to carry out other suggested treatment tables. (except for US Navy treatment table8)
Which tables to choose?
This will depend entirely on:
*The diagnosis. (Is it TypeI DCS, TypeII DCS, TypeIII DCS or AGE?)
*The initial evaluation. (Severity & urgency)
*How much time already elapsed before getting into the chamber?
*Any change of clinical picture on normobaric Oxygen breathing.
*Response of the patient to chamber treatment stages. (Recompression,O2 breathing & decompression) symptoms can improve, remain stable, progress or even deteriorate during the course of the treatment.
Once the treatment table has been chosen, treatment is conducted by carrying out recompression and decompression procedures specified in this chosen table including times and rates of ascent and descend.
A flow chart is given to provide a systematic method for selection, activation and extension of each individual table, and procedures to take in case of complications or relapses during or after the treatment.
The inside tender(s) who wish to leave the chamber whilst carrying out the treatment tables for the victim should be decompressed on Air or Oxygen in the outer (transfer) lock of the chamber all the way back to the surface using Standard Air Decompression tables or Surface Decompression tables using Oxygen putting into consideration calculating their residual nitrogen from previous in-water or in-chamber exposures (dives).
Follow-up HBO treatment
Some cases of serious DCI will require further treatment in the chamber in the form of Hyperbaric Oxygen (HBO) sessions until full recovery achievement or reaching a plateau in the response to HBO treatment.
CNS O2 toxicity in HBO treatment is rare because all treatments are carried out at pressure below 2.8 ATA and the duration of a single treatment seldom exceeds 3 hours, and the factors that increase the incidence of CNS O2 toxicity as exercise and CO2 retention are normally not encountered inside the chamber.
Pulmonary O2 toxicity (more often seen as a result of prolonged normobaric O2 exposure) should as well be put in consideration despite that most clinical findings reported no remarkable impairment of lung functions after prolonged HBO treatment.
Diving fitness after a decompression accident:
Following DCS, unless conservative changes are made to the exposure profiles, the past is likely to be repeated – but with greater severity.
It has been shown by researchers that changes in blood composition following a decompression incident takes at least 10 days before returning to normal picture even when the patient shows full recovery after treatment so, it thus seems wise to prohibit diving during this period.
In cases of severer DCS forms, the victim is asked to refrain from diving for at least 6 weeks.
If any neurological residue persists after 3 months, some authors will permit diving for short periods to a maximum of 9 meters provided that the diver’s psychological and physical fitness are not impaired.
I personally think that, that diver should be advised to stop diving altogether due to increased susceptibility to future damage by the already hampered nervous system.
Finally I would like to say that diving is still one of the safest sports ever practiced provided that divers shall receive proper training, stick to good planning, maintain fitness and take all possible health precautions. You do this and I promise you that you will never have to visit a chamber.
Wishing you all safe and enjoyable diving practice.
Why am I more susceptible to Decompression Sickness DCS?
A question that is more frequently asked nowadays with the increasing incidence of DCS amongst professional and recreational scuba divers?
It would take more than one article to answer.
Generally, any physiological or environmental factor that increases the uptake of the inert gas IG (mainly nitrogen) of the breathing mixture during compression or hinders its elimination during decompression is a risk factor.
1.Exertion muscle exercise performed while at depth; increase the rate of IG absorption at that site, increasing consequently the decompression requirements up to three fold as suggested by some authors. Severe exercise at shallow stops or following decompression dives results in enhancing bubble formation.
2. Temperature low temperature increases IG solubility, in some studies; doubling of decompression time is required for these long cold dives though the rate of muscles blood perfusion is proved to be halved.
3. female divers during premenstrual and menstruating periods have less efficient blood circulation due to fluid retention and subsequent edema in many tissues, as well as the increased viscosity of blood , the two factors hinders IG elimination, so safer profiles should be followed without adding other risk factors.
4. Obesity Nitrogen is 4 times more soluble in fat than in water, thus increasing IG intake, professional divers weight should not exceed 20 % more than the average ideal weight for age, sex, height and build. Sport obese divers should reduce their bottom time by 25-50% depending on the degree of obesity. 5. Increased carbon dioxide pressures, either from pressure (depth), exercise, or breathing resistances with equipment, may lead to increased perfusion with more IG loading.
6. Dehydration reduces perfusion of tissues with hindering of IG elimination, breathing is the most dehydrating factor in diving, if we add this to long, cold (more urine output) dives we can easily conclude that diving in winter time is as dehydrating as during summer time.
7. Alcohol dehydration, vasodilatation and heat loss affecting the diver for many hours after alcohol consumption will contribute to DCS risk.
We continue next issue with dive profiles, multiple ascents, age, repetitive dives, adaptation, breathing different gas mixtures and traveling to altitudes.
Till then, I wish you safe diving.
Dr. Hanaa M. Nessim