Anesthesiology and hyperbaric medicine.

in this issue1 underlines the necessity of instituting hyperbaric oxygen treatment for suspected iatrogenic arterial gas embolism even if a delay of days has occurred. The commonest reasons for delay are a failure to consider the diagnosis and treatment; concern related to the critical status of the patient; and a mistaken belief that the patient is not fit for transportation or treatment in a hyperbaric chamber. Hospital-based chambers are capable of invasive monitoring and treatment, including drug infusions and mechanical ventilation. Transportation to a hyperbaric treatment centre by road, or by air at low altitude (less than 1,000 feet), or preferably in an aircraft pressurized to sea level,2 is virtually always possible within a matter of hours. The associated costs of transportation and operation of hyperbaric treatment facilities are small in comparison to the costs of major neurological damage. Numerous (in fact hundreds of) cases of cerebral arterial gas embolism have been witnessed, especially during military training for submarine escape3 but also during a variety of medical procedures. Hyperbaric chambers are located at the top of navy submarine escape training towers for this reason. The often-speedy effectiveness of hyperbaric oxygen treatment has been witnessed so many times it is beyond dispute. Hyperbaric oxygen is the definitive treatment. One recent unpublished case in St. John’s, Newfoundland, was due to disconnection of a central venous pressure line and again was effectively treated with hyperbaric oxygen. A skeptic could argue that an increased sedation requirement does not constitute conclusive evidence of the efficacy of hyperbaric oxygen in the case described by Dr. Wherrett. However, a combative patient inside the confines of a hyperbaric chamber is a frightening experience indeed, particularly once the decompression obligation of staff prohibits depressurization. This has led to a trend towards greater use of iv anesthesia and sedation particularly for patients requiring positive pressure ventilation inside hyperbaric chambers. The case described highlights the close link between anesthesia and hyperbaric medicine. No doubt this link contributed to the implementation, albeit delayed, of the only treatment known to be specific and effective in arterial gas embolism and the consequent favourable outcome. Apart from administration of anesthesia during hyperbaric treatment, expertise in monitoring, ventilation, breathing systems, and critical care link the two areas of practice together. Anesthesiology and hyperbaric medicine also share an interest in physics, the gas laws, compressed gases, pharmacology, and physiology. Like anesthesia, remuneration in hyperbaric medicine is generally based upon time periods. Hyperbaric medicine is a small area of clinical practice in Canada that is without a separate Canadian journal, society, or certification mechanism. Many hyperbaric centres are closely associated with departments of anesthesia. Facilities in St. John’s, Toronto, Ottawa, Hamilton, and Edmonton were established by or with assistance from anesthesiologists. Hospitalbased hyperbaric facilities also exist in Halifax, Montreal and Vancouver. A similar situation is found in countries such as the USA, UK, Australia, and Russia. Strong links have also developed between these facilities and intensive care units. While anesthesiologists are perhaps the largest single specialist group involved in hyperbaric medicine, others include ex-navy physicians, family physicians, respirologists, neurologists, intensivists, and surgeons. A number of anesthesiologists have undertaken hyperbaric medicine fellowships, and recently an anesthesia resident undertook an elective rotation in hyperbaric medicine in St. John’s. Future certification may necessitate the small field of hyperbaric medicine becoming 1