Dysbarism

Hyperbaric oxygen therapy (HBOT) is commonly used for a wide range of clinical conditions. The tympanic membranes are at risk of barotrauma during this treatment. A fast, safe and effective technique of placing temporary tympanostomy tubes is employed at the Prince of Wales Hospital using intravenous cannulae. This technique is described, and the indications for and implications to HBOT are discussed.

Key words: tympanostomy, tympanic membrane, hyperbaric oxygen therapy.

Introduction

Hyperbaric Oxygen Therapy (HBOT) is a treatment modality which is frequently used in many larger medical centres for a variety of conditions. The most common adverse effect of HBOT is middle ear barotrauma. This is due to inefficient equalisation of middle ear pressure due to obtunded conscious state, abnormal airway or eustachian tube function, and can be readily prevented by the placement of temporary tympanostomy tubes. At the Prince of Wales Hospital a simple and effective method of temporary tympanostomy is used employing an intravenous catheter sheath.

Surgical technique

The insertion of tympanostomy tubes should be performed prior to compression in the hyperbaric unit by an advanced trainee or otolaryngologist. Equipment required is a headlight, aural speculum, wax curette, 2 x 18 gauge intravenous cannulae and a scalpel blade. With the headlight and speculum the external auditory canal is inspected and cleared of any obstructing wax or debris. The plastic sheath of the IN. cannula is "circumcised" 1.Scm from the tip using the scalpel (Figure 1). It is important to ensure that the cannula tip is now fully separated. Visualisation of the tympanic membrane is easier during the procedure if the cannula is bent approximately 20deg in the midshaft. The tip of cannula is now inserted through the anteroinferior tympanic membrane (Figure 2). The sheath is advanced forward while the rest of the cannula is withdrawn in a similar fashion to venous cannulation. The tip of the cannula now lies in situ (Figure 3). The procedure is repeated on the other side.

No local anaesthetic is necessary in the unconscious patient. In the awake patient the procedure is easily performed using local anaesthetic. We have used regional 'ring' blocklade of the external auditory canal with 1% lignocaine and 1 : 100,000 adrenalin, and topical anaesthesia of the tympanic membrane with 10% lignocaine solution, both with good patient tolerance. The temporary tubes are easily removed without any discomfort in the outpatient setting, and healing of the tympanic membranes occurs rapidly. Water precautions should be observed until the tympanic membranes are confirmed to be completely healed.

Discussion

HBOT was first reported in clinical surgical use in the mid 1950's by Boerema, a Dutch cardiovascular surgeon who described successful cardiac surgical procedures in an operating theatre pressurized to 3 atmospheres absolute pressure (ATA).1 Today applications include adjunctive treatment of tissue hypoxic conditions including nectrotizing fasciitis, osteo-radionecrosis, chronic osteomyelitis, non-healing wounds in micro and macrovasculopathies and clostridial myonecrosis. 2,3,4,5 It has also been used extensively in the treatment of carbon monoxide poisoning, although the evidence appears contraditory. 6,12

HBOT serves to increase the available oxygen to the tissues by increasing the arterial pO2. Oxygen diffuses down the greatly enhanced pressure gradient, significantly increasing tissue pO2. Increased oxygen availability may last some time after the exposure and during this time many immune and separative pathways are significantly enhanced. Neovascularization, on the other hand, is maximal during the period of declining pO2, making an intermittent application of HBOT most appropriate. Specific benefits include increased capillary growth, augmentation of fibroblast collagen cross linking, and increased fibroblast proliferation.7,8 Erythrocyte flexibility is improved and leukocyte (particularly macrophage) activity is increased.2

The increased partial pressure of oxygen is achieved by an increase in the ambient pressure in the HBOT chamber. Pressures of I to 2 atmospheres above sea level (equivalent to 10-20 metres sea water depth) are frequently used. Otological adverse reactions are the most common reported and range from otalgia without demonstrable pathology, to tympanic membrane haemorrhage, perforation, serous effusion, ossicular chain disruption and even oval or round window rupture with subsequent vestibulopathy and sensorineural hearing loss.9,10

Patients most likely to suffer barotrauma are those who cannot 'equalise' middle ear pressure with Toynbee or Valsalva manouvres whether this is due to obtunded conscious state, abnormal airway (e.g. endotracheal tube or tracheostomy) or eustachian tube dysfunction. In the past three patients underwent formal tympanostomy with classic ventilation or grommet tubes. This technique itself is associated with a high level of complication. Clements found 38% of those treated with classic ventilation tubes had frequent complications, most more than one. This is significantly higher than the complication rate for patients having tympanostomy tubes placed. 29% of patients in their study had otorrhoea and 16% had persistent perforations.11 Other problems following classic tympanostomy tube insertion include conductive hearing loss and increased propensity to middle ear infections.

Thus far this technique has been without significant complication in over 250 patients treated in the last 10 years. It is simpler, faster and associated with a lower complication rate than the previous technique of tube placement. It is subsequently less likely to delay HBOT.

References

1 BOEREMA I. Operating at increased atmospheric pressure. Surgery. 1964; 49: 291.

2. KINDWALL E.P. Uses of Hyperbaric Oxygen Therapy in the 1990s. Cleveland Clinical Journal Medicine. 1992; 59(5): 51728.

3 NYLANDER G. ET AL. Effects of Hyperbaric Oxygen Therapy on oedema formatoin after scald burns. Bums. 1984; 10: 193.

4 MORREY B.F., DUNN J.M., HEIMBACH R.D., DAVIS J Hyperbaric Oxygen and Chronic Osteomyelitis. Clin Orthop 1979: 144:121-7.

5 FARMER J.C. Jnr et al. Treatment of radiation induced tissue injury by Hyperbaric Oxygen Therapy. Annals of Otolaryngology. 1972; 87: 707.

6 SCHEINKESTEL C.D., BAILEY M., MYLES P.S., JONES K., MILLER I.LL., TUXEN D.V. Hyperbaric or normbaric oxygen for acute carbon monoxide poisoning : a randomised controlled clinical trial. MJA 1999; 170: 203-10.

7 HAMMARLUND C., SUNDBERG T. Hyperbaric Oxygen reduced size of chronic leg ulcers: A randomised double-blind study. Plastic and Reconstructive Surgery. 1994 93; 829-33.

8 HOHN B.C. ET AL. The effects of oxygen tension on the microbial function of leucocytes in wounds and in vivo. Surgical Forum. 1976; 27: 18.

9 CARLSON S., JONES J., BROWN M., HESS C. Prevention of hyperbaric-associated middle ear barotrauma. Annals of Emergency Medicine. 1992; 21:1468-71.

10 JAMES B.P. Dysbarism: the medical problems from high and low atmospheric pressure. Journal of the Royal College of Physicians, London. 1993; 27:367-74.

11 CLEMENTS K., VRABEC J.T., MADER J.T. Complications of tympanostomy tubes inserted for facilitation of Hyperbaric Oxygen Therapy. Archives of Otolaryngology Head and Neck Surgery. 1998: 124: 278-81.

12 MOORE R.E., DELANY E. Hyperbaric oxygen for carbon monoxide poisoning. MJA 1999; 170: 197-99.

WILLIAM MOONEY and PETER CARTER Prince of Wales Hospital

Randwick, New South Wales Australia

William Mooney M.B., B.S., F.R.A.C.S. Peter Carter M.B., B.S., F.R.A.C.S.

Department of Otolaryngology, Head and Neck Surgery,

Prince of Wales Hospital, Randwick, New South Wales, Australia

Correspondence: William Mooney 119 Blair Street, Bondi 2026 New South Wales, Australia 0413 99 30 30 wwwmoon@ozemail.com.au

Copyright Australian Society of Otolaryngology Head & Neck Surgery Ltd. Oct 2001
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