Current Monthly Briefing

Monthly Briefing Archive

July 2021

From time to time the NBDHMT receives requests for its position on various operational and safety issues. Our replies vary depending upon the specific nature of the question. In terms of a formal Position Statement, eleven appear on our web site which we trust you have read and remain compliant with those that relate to CHT Code of Conduct attestation. Beyond these statements, our replies will offer advice or guidance by such things as provision of a published paper, information from textbook chapters, a meeting presentation (with provision of its Abstract), an email if the answer is deemed straightforward enough, or perhaps referral to another authoritative source. Importantly, while these latter responses are intended to be helpful and consistent with our mission, they do not necessarily reflect the Board’s formal position.

We will feature example responses in these Briefings from time to time, and begin here with a common one, namely is there an appropriate/standard chamber compression rate for clinical treatments, in the context of middle ear barotrauma (MEB) risk. This is a valid enquiry. While HBO therapy is considered a mastered medical technology in the right hands, it is not complication free with MEB leading the way. Reported incidence ranges as high as 80%, although fortunately a great majority of cases are minor, don’t require treatment and will not interfere with the subsequent treatment course. Our answer is that there is no standardized rate, per se. Rather, it is very much based upon individual patient tolerance. The first compression should preferably be “slow” (in the order of 1.0 psi/2.0 fsw per minute), and may be incrementally increased with confirmation of tolerance, as directed by the hyperbaric provider.  Ideally, this will include routine ear assessment (pre/post-ascent) as injury can occur in the absence of a patient’s complaint. Auto-inflation technique(s) should be taught and demonstrated, patient compliance attempts observed, preferably including otoscopic exam, during initial hyperbaric consultation. Encouraging frequent auto-inflation during compression tends to pay dividends. Patients should be observed during all pressure changes and advised to promptly report ear discomfort.

Several studies have attempted to identify ways to reduce MEB. Examples include which of three different compression rates is least injurious, 1   are scheduled pauses (compression stops) vs traditional constant rate more protective 2 and routine pre-treatment with anti-inflammatory/vasoconstrictive agents. 3 None were associated with a lowered incidence, although having compared rates of 1.0, 1.5 and 2.0 psi/min. during monoplace operations, Heyboer et al. did recommend 2.0 psi/min. 1  There was no difference in MEB between rates, (nor with respect to differing chamber treatment pressures) but as their facility uniquely starts treatment time upon leaving surface pressure rather than the more traditional start point of arrival at prescribed chamber pressure, they wished to minimize travel time in order to optimize oxygen dosing. Getting to pressure without undue delay also has value for the traditional treatment start point. It lessens contribution of oxygen uptake resulting from drawn-out compressions, particularly involving one or more forced pauses, to uptake at pressure in the context of CNS oxygen toxicity risk. It will also reduce overall chamber exposure periods in patients with degrees of confinement anxiety and improve patient turnaround times.

Dick Clarke, President
National Board of Diving & Hyperbaric Medicine

1. Heyboer M, et al. Undersea Hyperbaric Med 2014;41(5)
2. Ng A, et al. Undersea Hyperbaric Med 2017;44(2)
3. Millian SB, et al. Undersea Hyperbaric Med 2021;48(2)