Correspondence
Hyperbaric-Oxygen Therapy
N Engl J Med 1996; 335:1684-1686November 28, 1996
- Article
To the Editor:
Tibbles and Edelsberg (June 20 issue)1 present a complete and cogent summary of the therapeutic usefulness of hyperbaric-oxygen therapy. However, their review contains a recommendation that is not supported by evidence. In the section on the treatment of carbon monoxide poisoning, the authors present a balanced discussion of studies demonstrating conflicting results. The available evidence does not guide us one way or the other as to the effectiveness of hyperbaric-oxygen therapy in this setting. Yet in a seeming non sequitur the authors state,
we think that patients with severe carbon monoxide poisoning should receive at least one treatment with hyperbaric oxygen at 2.5 to 3.0 atmospheres; additional treatments may produce greater improvement in neuropsychological deficits. For patients with lesser degrees of poisoning, we advise consultation with a toxicologist to determine whether the administration of 100 percent normobaric oxygen for four to six hours, or until symptoms abate, would be adequate therapy.
We find this recommendation incomplete at best, and misleading at worst. In a recent review, Tibbles and Perrotta stated that “no randomized, controlled, blinded clinical trial demonstrated a clear advantage of HBO [hyperbaric-oxygen therapy] over NBO [normobaric-oxygen therapy] in reducing morbidity and mortality in carbon monoxide poisoning.” 2 An accompanying article in the same journal concluded that “the standard of care for patients exposed to CO [carbon monoxide] is yet to be determined.”3 We believe readers need to be reminded of these facts.
3 ReferencesJoel M. Geiderman, M.D.
Mark J. Ault, M.D.
Cedars–Sinai Medical Center, Los Angeles, CA 90048-07501
Tibbles PM ,Edelsberg JS . Hyperbaric-oxygen therapy. N Engl J Med 1996;334:1642-1648
Full Text | Web of Science | Medline2
Tibbles PM ,Perrotta PL . Treatment of carbon monoxide poisoning: a critical review of human outcome studies comparing normobaric oxygen with hyperbaric oxygen. Ann Emerg Med 1994;24:269-276
CrossRef | Web of Science | Medline3
Seger D ,Welch L . Carbon monoxide controversies: neuropsychologic testing, mechanism of toxicity, and hyperbaric oxygen. Ann Emerg Med 1994;24:242-248
CrossRef | Web of Science | Medline
To the Editor:
As a complication of hyperbaric-oxygen therapy, reversible myopia is not, as Tibbles and Edelsberg claim, “a consequence of the direct toxic effect of oxygen on the lens.” It is considered to be mainly due to deformity of the lens as a result of repeated compressions and decompressions, with a possible contribution by reversible metabolic disturbances in the lens. Pain in the ear and sinuses is common, but it is rarely due to “rupture of the middle ear [or] the cranial sinuses” in conscious patients who are not subjected to excessive pressures. Seizures and pulmonary toxicity are extremely rare. The safety record of hyperbaric oxygen is better than that of several other modern medical and surgical therapies.
K.K. Jain, M.D.
Innere Margarethenstrasse 17, CH-4051 Basel, SwitzerlandTo the Editor:
In their excellent review of hyperbaric-oxygen treatment, Tibbles and Edelsberg mention arterial gas embolism, induced by orogenital sex during pregnancy, as an indication for such therapy. However, they refer to a report by Fyke et al.,1 which describes a case of venous air embolism treated conservatively. In fact, most of the reported cases of air embolism are venous embolism after orovaginal insufflation and have resulted in lethal pulmonary embolism and acute cardiac failure, with most patients never receiving hyperbaric-oxygen therapy. Similar conditions have been seen during pregnancy after vaginal douching, manual manipulation, and insufflation of powder or cocaine smoke. Lately, hyperbaric-oxygen therapy has been successfully used in some of these cases after air has entered the systemic arterial — especially cerebral — circulation.
Two pathophysiologic mechanisms through which arterial gas embolism may occur after orogenital sex have been suggested.2 If the patient has a patent foramen ovale or other septal defect, present in as many as 25 percent to 35 percent of adults, paradoxical embolism might occur right after insufflation. It is also possible for air emboli to pass through the vessels of the lungs, possibly due to the collection of surface active agent (surfactant) in capillary areas containing air bubbles and to a change in bubble geometry.
2 ReferencesBenjamin Schaefer
Free University of Berlin, 12200 Berlin, Germany1
Fyke FE III ,Kazmier FJ ,Harms RW . Venous air embolism: life-threatening complication of orogenital sex during pregnancy. Am J Med 1985;78:333-336
CrossRef | Web of Science | Medline2
Bernhardt TL ,Goldmann RW ,Thombs PA ,Kindwall EP . Hyperbaric oxygen treatment of cerebral air embolism from orogenital sex during pregnancy. Crit Care Med 1988;16:729-730
CrossRef | Web of Science | Medline
To the Editor:
Tibbles and Edelsberg perpetuate a common error about the formation of inert gas bubbles in blood vessels and tissues. They assert that Boyle's law, which states that the volume of gas in an enclosed space is inversely proportional to the pressure exerted on it, governs this process. Boyle's law does, in fact, govern the size and volume of existing gas bubbles in blood and tissue. However, it is Henry's law that governs the formation of gas bubbles. Henry's law states that the vapor pressure of a volatile dissolved substance is proportional to the mole fraction of the substance in solution.1 When the pressure on a solution is reduced, gas solubility is reduced and volatile solutes come out of solution.
A familiar demonstration of Henry's law occurs when the cap is removed from a bottle of carbonated beverage. When the pressure in the gas at the top of the bottle is suddenly released, the dissolved gas in the beverage comes out of solution in the form of bubbles. This same law accounts for the sudden formation of inert gas bubbles in plasma and tissue fluid in decompression sickness. In addition, after recompression, Boyle's law first takes effect and makes the intravascular bubbles smaller, but then Henry's law takes over and makes the two-phase bubble–solvent mixture form a single-phase solution as the inert gas dissolves completely.
1 ReferencesV. Moss Weinstock
S. Joseph Weinstock, M.D.
University of Toronto, Toronto, ON M5S 1A1, CanadaAuthor/Editor Response
The authors reply:
To the Editor: Drs. Geiderman and Ault imply that recommendations for any medical therapy should not be made unless randomized, controlled trials establish a therapy as beneficial. Since in only 10 to 50 percent of cases is the rationale for using medical interventions thought to be supported by solid scientific evidence,1,2 such as that obtained with randomized, controlled trials, this policy would leave a great void in medical therapeutics. The purpose of our review was to provide an overview of hyperbaric-oxygen therapy for the general clinician, with recommendations based on the weight of scientific evidence. Our review shows there is more clinical and laboratory evidence of the efficacy of hyperbaric-oxygen therapy in this potentially lethal illness than of the opposite, although we acknowledge that definitive evidence is lacking. We do not propose hyperbaric-oxygen therapy as the standard of care in the treatment of carbon monoxide poisoning.
Mr. Schaefer correctly notes that an air embolus from vaginal insufflation during pregnancy initially enters the venous system. In the case reported by Fyke et al.3 the absence of findings specific for venous air embolism and the presence of several central neurologic signs are highly suggestive of a concomitant cerebral arterial air embolism, occurring through the pathophysiologic mechanisms described by Schaefer. We included this report because it is a commonly cited example of a unique mechanism of air entry into the circulation.
Dr. Jain's claim that reversible myopia is “mainly due to deformity of the lens as a result of repeated compressions and decompressions . . . [and] reversible metabolic disturbances in the lens” is not supported by any data beyond inference from a few refractive measurements in humans.4 We agree with Clark5 that although myopia “appears to be lenticular in origin, the exact mechanism remains obscure.” The most common adverse effect of hyperbaric-oxygen therapy is ear and sinus pain. Occasionally, the pressure changes lead to edema and hemorrhage, but rupture of these closed cavities is rare, as Dr. Jain states.
We thank Weinstock and Weinstock for their explanation of Henry's law, one of several additional laws of physics at work in bubble diseases. We chose to confine our discussion of bubble physics to the post-nucleation phase (immediately after bubbles come out of solution and just before they dissolve), during which Boyle's law is dominant in governing the growth of bubbles to the size responsible for pathophysiologic effects and also explains the benefits of pressure during hyperbaric-oxygen therapy.
5 ReferencesPatrick M. Tibbles, M.D.
John S. Edelsberg, M.D., M.P.H.
University of Massachusetts Medical Center, Worcester, MA 016551
Williamson JW, Goldschmidt PG, Jillson IA. Medical Practice Information Demonstration Project: final report. Baltimore: Policy Research, 1979.
2
Ellis J ,Mulligan I ,Rowe J ,Sackett DL . Inpatient general medicine is evidence based. Lancet 1995;346:407-410
CrossRef | Web of Science | Medline3
Fyke FE III ,Kazmier FJ ,Harms RW . Venous air embolism: life-threatening complication of orogenital sex during pregnancy. Am J Med 1985;78:333-336
CrossRef | Web of Science | Medline4
Anderson B Jr ,Farmer JC Jr . Hyperoxic myopia. Trans Am Ophthalmol Soc 1978;76:116-124
Medline5
Clark JM. Oxygen toxicity. In: Kindwall EP, ed. Hyperbaric medicine practice. Flagstaff, Ariz.: Best, 1994:33-43.
- Citing Articles (3)
Citing Articles
1
Martin Tobin. (2008) Answer to E.
W. Ely: “Remembrance of weaning past”. Intensive Care Medicine 34:2, 385-385
CrossRef2
Wes Ely. (2007) Comment on “Remembrance of weaning past: the seminal papers,” by Dr. Martin Tobin. Intensive Care Medicine 33:4, 746-746
CrossRef3
Louise W. Kao, Kristine A. Nañagas. (2005) Carbon Monoxide Poisoning. Medical Clinics of North America 89:6, 1161-1194
CrossRef
