Decompressing rescue personnel during Australian submarine rescue operations.

INTRODUCTION: Personnel rescuing survivors from a pressurized, distressed Royal Australian Navy (RAN) submarine may themselves accumulate a decompression obligation, which may exceed the bottom time limits of the Defense and Civil Institute of Environmental Medicine (DCIEM) Air and In-Water Oxygen Decompression tables (DCIEM Table 1 and 2) presently used by the RAN. This study compared DCIEM Table 2 with alternative decompression tables with longer bottom times: United States Navy XVALSS_DISSUB 7, VVAL-18M and Royal Navy 14 Modified tables. METHODS: Estimated probability of decompression sickness (PDCS), the units pulmonary oxygen toxicity dose (UPTD), the volume of oxygen required and the total decompression time were calculated for hypothetical single and repetitive exposures to 253 kPa air pressure for various bottom times and prescribed decompression schedules. RESULTS: Compared to DCIEM Table 2, XVALSS_DISSUB 7 single and repetitive schedules had lower estimated PDCS, which came at the cost of longer oxygen decompressions. For single exposures, DCIEM schedules had PDCS estimates ranging from 1.8% to 6.4% with 0 to 101 UPTD and XVALSS_DISSUB 7 schedules had PDCS of less than 3.1%, with 36 to 350 UPTD. CONCLUSIONS: The XVALSS_DISSUB 7 table was specifically designed for submarine rescue and, unlike DCIEM Table 2, has schedules for the estimated maximum required bottom times at 253 kPa. Adopting these tables may negate the requirement for saturation decompression of rescue personnel exceeding DCIEM limits.

Decompressing recompression chamber attendants during Australian submarine rescue operations.

INTRODUCTION: Inside chamber attendants rescuing survivors from a pressurised, distressed submarine may themselves accumulate a decompression obligation which may exceed the limits of Defense and Civil Institute of Environmental Medicine tables presently used by the Royal Australian Navy. This study assessed the probability of decompression sickness (PDCS) for medical attendants supervising survivors undergoing oxygen-accelerated saturation decompression according to the National Oceanic and Atmospheric Administration (NOAA) 17.11 table. METHODS: Estimated probability of decompression sickness (PDCS), the units pulmonary oxygen toxicity dose (UPTD) and the volume of oxygen required were calculated for attendants breathing air during the NOAA table compared with the introduction of various periods of oxygen breathing. RESULTS: The PDCS in medical attendants breathing air whilst supervising survivors receiving NOAA decompression is up to 4.5%. For the longest predicted profile (830 minutes at 253 kPa) oxygen breathing at 30, 60 and 90 minutes at 132 kPa partial pressure of oxygen reduced the air-breathing-associated PDCS to less than 3.1 %, 2.1% and 1.4% respectively. CONCLUSIONS: The probability of at least one incident of DCS among attendants, with consequent strain on resources, is high if attendants breathe air throughout their exposure. The introduction of 90 minutes of oxygen breathing greatly reduces the probability of this interruption to rescue operations.

A pleural vacuum relief device for pleural drain unit use in the hyperbaric environment.

INTRODUCTION: When a standard water-seal pleural drain unit (PDU) is used under hyperbaric conditions there are scenarios where excessive negative intrapleural pressure (IPP) and/or fluid reflux can be induced, risking significant morbidity. We developed and tested a pleural vacuum relief (PVR) device which automatically manages these risks, whilst allowing more rapid hyperbaric pressure change rates. METHODS: The custom-made PVR device consists of a one-way pressure relief valve connected in line with a sterile micro filter selected for its specific flow capacity. The PVR device is designed for connection to the patient side sampling port of a PDU system, allowing inflow of ambient air whenever negative pressure is present, creating a small, controlled air leak which prevents excessive negative pressure. The hyperbaric performance of a Pleur-Evac A-6000 intercostal drain was assessed with and without this added device by measuring simulated IPP with an electronic pressure monitor connected at the patient end of the PDU. IPP readings were taken at 10, 15, 20 and 30 cmH2O of suction (set on the drain unit) at compression rates of 10, 30, 60, 80, 90 and 180 kPa·min⁻¹ to a pressure of 280 kPa. RESULTS: At any compression rate of > 10 kPa·min⁻¹, the negative IPP generated by the Pleur-Evac A-6000 alone was excessive and resulted in back flow through the PDU water seal. By adding the PVR device, the generated negative IPP remains within a clinically acceptable range, allowing compression rates of at least 30 kPa·min⁻¹ with suction settings up to -20 cmH2O during all phases of hyperbaric treatment. CONCLUSIONS: The PDU PVR device we have developed works well, minimising attendant workload and automatically avoiding the excessive negative IPPs that can otherwise occur. This device should only be used with suction.

A 10-year estimate of the incidence of decompression illness in a discrete group of recreational cave divers in Australia.

INTRODUCTION: The vast majority of freshwater cave diving in Australia occurs within the limestone caves of the Gambier karst in the south-east of South Australia. The incidence of decompression illness (DCI) in cave divers is presumed to be higher than open-water recreational divers because of the greater depths involved, but has not previously been reported. Our aim was to determine the incidence of DCI in cave divers, the patterns of diving and the outcome of hyperbaric treatment. METHODS: This was a retrospective cohort study of cave divers with DCI presenting to the Royal Adelaide Hospital or The Alfred Hospital over a 10-year period between 2002 and 2012. We reviewed case notes of cave divers who were treated for DCI after diving in the Mt Gambier karst. As there are no records of the number of dives performed during the study period we generated a denominator for the incidence of DCI by extrapolating available data and making a number of assumptions about the number of dives per dive permit issued. RESULTS: Sixteen patients were treated for DCI during the study period. The precipitating dive was a single deep decompression dive in seven cases, multiday repetitive dive sequences in eight and a non-decompression dive in one. Three of the 16 cases of DCI involved dives in excess of 90 metres' fresh water (mfw) using trimix. As the total estimated number of dives in the study period was approximately 57,000 the incidence of DCI in Australian cave divers was estimated to be 2.8:10,000 (0.028%). It is possible that the overall incidence of DCI is as high as 0.05%, and even higher when dives to depths greater than 90 mfw are involved. CONCLUSIONS: The estimated incidence of DCS in this series is lower than expected but consistent with other series describing DCI in cold-water recreational diving.

Pediatric hyperbaric oxygen therapy in Victoria, 1998-2010.

OBJECTIVES: The aim of this review is to identify clinical conditions currently treated in a pediatric population referred to the Alfred hyperbaric unit, to describe outcomes, and detail any complications occurring during treatment or transfer between units. DESIGN: Retrospective, noncontrolled, clinical study. SETTING: Adult hyperbaric unit in a university hospital. PATIENTS: Children aged <16 yrs referred for hyperbaric oxygen therapy between January 1998 and December 2010. INTERVENTIONS: Hyperbaric oxygen therapy at pressures from 2.0 to 3.0 atmospheres absolute. MEASUREMENTS AND MAIN RESULTS: Fifty-four patients with a median age at presentation of 15 yrs (range, 0.25-16 yrs) received 668 treatment sessions (mean, 12.4; 95% confidence interval, 9.2-15.5). Fourteen patients were identified as having successfully completed treatment while managed in intensive care units. There were 44 events in 668 treatments (6.6%) in the pediatric group and 12 events in 126 treatments (9.6%) in the pediatric intensive care unit group. There were two oxygen toxicity convulsion (0.3%), two episodes of progressive hypoxemia (0.3%), and four episodes of brief hypotension (0.6%). CONCLUSIONS: Provision of hyperbaric oxygen to children with significant illness is feasible and associated with a low risk of complications. The most difficult aspect of managing pediatric hyperbaric oxygen therapy is in the coordination of the treatment with ongoing surgical and intensive care management. The lack of pediatric staff and facilities in major hyperbaric units necessitates multiple transfers for appropriate treatment.

Cerebral arterial gas embolism with delayed treatment and a fatal outcome in a 14-year-old diver.

In today's recreational diving climate, diving fitness examinations are not mandatory, and even divers who go for these examinations may not have routine chest X-rays (CXR) done in the absence of respiratory symptoms or a past history of respiratory problems. We present a case of an ultimately fatal cerebral arterial gas embolism in a 14-year-old boy with an undiagnosed lung cyst, the contribution of which to his death is uncertain. Various factors such as lack of oxygen first aid at the remote dive site; poor communication; lack of diving medicine expertise, poor oxygen administration and management in a local hospital and long delay to recompression therapy contributed to the poor outcome. It is imperative that dive operators and physicians working in close proximity to popular dive sites be educated on how to recognise and treat diving emergencies and be well-acquainted, as should divers, with the contact numbers of diving medical hotlines that offer timely and appropriate advice in case of emergency.