Monday, October 24, 2005

Dry Diving



If you didn't have decompression sickness and entered a recompression chamber for treatment or demonstration purposes, would there be any medical problems due to hyperbaric treatment when it was not needed?



Treating decompression illness (decompression sickness and arterial gas embolism) is just one of the uses for recompression chambers. They are now being used to treat quite a few other illnesses. In the United States, chamber treatment is approved by Medicare for some 13 conditions.

Being compressed in a chamber is in essence a "dry dive" without the dangers of being in a watery, alien environment. You would, however, be subjected to the same risks of barotrauma to air-containing body spaces and the possibility of ear, lung and sinus problems. If 100 percent oxygen were being used, you would also be at risk of oxygen toxicity if the oxygen intervals and pressure were not properly controlled. "Older divers remember the 'oxygen toxicity' test dives - in days bygone there was the periodic oxygen tolerance test. It was finally decided that the test results were good for the day you took the test without much predictive value. (Glen Egstrom, PhD). Dry dives can be fun if you are in a group with a good sense of humor".

The London Diving Chamber has a website that appears to be promoting a taste of Nitrogen Narcosis in the dry without risk of drowning or DCI. "It is not a bad idea to demonstrate a chamber to a trainee diver; this may both reassure but at the same time endorse the need to avoid an unscheduled visit - at a later date!" (Dr. Nick McIver).

"Dry dives mimic some of the effects of diving, such as N2 narcosis and the increase in gas density. Indeed, much of what we know about diving physiology comes from experiments in dry chambers. However, neither equipment not humans behave exactly the same in the water as in the dry". (Richard Moon, MD).

Captain Dick Carson, USN (Ret) (PADI Instr) recounts the following about 'dry dives'. "Being a frequent diver at Stoney Cove near Birmingham in England, I was often amazed as the dive store there used their mini-chamber to assemble semi-dry suits. The near 1-inch thick neoprene suit was compressed while taking the store clerk "down" to the point the "Whites Valve" could be installed on the suit at the location specified by the buyer. I did not time the "dive" but it seemed a bounce dive at the time. Another use for a chamber, and risks discounted." The USN practiced similar events for wannabe pilots up to the mid 90's as I recall to determine if the student was "susceptible to the bends."

Dr. Ed Kay relates that, "We still do (more conservative) dry chamber runs for scuba clubs and others interested in commercial diving at the Divers Institute (DIT)."

Dr. Allen Dekelboum describes his experience doing a dry dive with his course at NOAA. " We dove 200 feet on air and then on helium. For the air dive, we were all extremely narced, but we were told we had a great time. No one got bent, but I did have a very slight case of niggles on the helium dive, all disappearing very quickly on 100% O2 ."

Other comments include: "It circumnavigates the actual causes of diving deaths, and so it probably does little harm". (Carl Edmonds, MD). "A clever way to support running a chamber. Trying to experience narcosis in a relatively safe environment isn't totally a bad idea." (Ed Golembe, MD)

Some side effects of hyperbaric oxygenation treatment include seizures and lung damage from oxygen toxicity, finger numbness, inflamed middle ear and refractive changes in the lens of the eye.
In a 10-year study of 1,505 patients who received 52,758 2-hour HBO treatments at 2.4 ata once or twice daily (The maximum treatment protocol used for problem wounds around the world), the following side effects were noted:
Inability to equalize middle ear pressure 0.37%
Paranasal sinus blocks 0.09%
Confinement anxiety 0.05%
Oxygen convulsions 0.009% (all ceased after removing hood/masks)
Pulmonary oxygen toxicity 0.00%
Permanent ocular refractive changes 0.00%

Some of the contraindications for hyperbaric oxygenation are listed here. These could also apply to dry diving - but in each instance the person would probably not be certified as 'fit to dive' anyway.
1. Asthma - Small airway hyper-reactivity may result in air trapping and pulmonary barotrauma on ascent. A decision to treat such patients should not be undertaken lightly, particularly in light of evidence that the administration of some bronchodilators may increase the incidence of cerebral arterial gas embolism through pulmonary shunts from vasodilation. .
2. Congenital spherocytosis - Such patients have fragile red cells and treatment may result in massive hemolysis
3. Cisplatinum - There is some evidence that this drug retards wound healing when combined with HBO.
4. Disulphiram (Antabuse) - There is evidence to suggest that this drug blocks the production of suproxide dismutase and this may severely effect the body's defenses against oxygen free radicals. Experimental evidence suggest that a single exposure to HBO is safe but that subsequent treatments may be unwise. Whether or not this would apply to air diving is unknown.
5. Doxorubicin - (Adriamycin). This chemotherapeutic agent becomes increasingly toxic under pressure and animal studies suggest at least a one week break between last dose and first treatment in the chamber.
6. Emphysema with CO2 retention - Caution should be exercised in giving high pressures + concentrations of oxygen to patients who may be existing on the hypoxic drive to ventilation. Such patients may become apneic in the chamber and require IPPV (intermittent positive pressure ventilation). In addition, gas trapping and subsequent lung rupture are associated with bullous disease.
7. High Fevers - High fevers (>38.5degC) tend to lower the seizure threshold due to O2 toxicity and may result in delaying of relatively routine therapy. If patients are to be treated then attempt should be made to lower their core temperature with antipyretics and physical measures. Whether or not this would apply to air diving is unknown.
8. History of middle ear surgery or disorders - These patients may be unable to clear their ears, or risk further injury with vigorous attempts to do so. An ENT consult for possible placement of tubes is usually wise. The risk for a dry dive would not be worth the benefit.
9. History of seizures - HBO therapy may lower the seizure threshold and some workers advocate increasing the baseline medication for such patients. Whether or not this would apply to air diving is unknown.
10. Optic Neuritis - There have been reports in patients with a history of optic neuritis of failing sight and even blindness after HBO therapy. This complaint would seem to be extremely rare but of tragic consequence. Whether or not this would apply to air diving is unknown.
11. Pneumothorax - A pocket of trapped gas in the pleura will decrease in volume on compression and re-expand on surfacing during a cycle of HBO therapy. During oxygen breathing at depth nitrogen will be absorbed from the space and replaced with oxygen. These fluxes of gases and absolute changes in volume may result in further lung damage and or arterial gas embolization. If there is a communication between lung and pneumothorax with a tension component, then a potentially dangerous situation exists as the patient is brought to the surface. As Boyle's Law predicts, a 1.8 litre pneumothorax at 20 msw is potentially a 6 litre pneumothorax at sea level - certainly a life threatening situation. For this reason it is mandatory to place a chest tube to relieve a pneumothorax before contemplating HBO therapy. Particular care must be taken with patients who give a history of chest trauma or thoracic surgery. Whether or not this would apply to air diving is unknown.
12. Pregnancy - The fears that either retrolental fibroplasia or closure of the ductuc arteriosus may result in the fetus whose mother undergoes HBO appear to be groundless from considerable Russian experience. However, HHI continues to exercise caution in limiting treatment of pregnant women to emergency situations.
13. Upper Respiratory Tract Infections - These are relative contra-indications due to the difficulty such patients may have in clearing their ears and sinuses. Elective treatment may be best postponed for a few days in such cases.
14. Viral Infections - Many workers in the past have expressed concern that viral infections may be considerably worsened after HBO. There have been no studies to give convincing evidence of this and no reported activation of herpetic lesions associated with HBO.
For more information, go to: www.scuba-doc.com/hbocont.htm.

Ern Campbell, MD
Scubadoc's Diving Medicine
http://scuba-doc.com/