A retrospective review of divers treated for inner ear decompression sickness at Fiona Stanley Hospital hyperbaric medicine unit 2014-2020.

Introduction: Inner ear decompression sickness (IEDCS) is increasingly recognised in recreational diving, with the inner ear particularly vulnerable to decompression sickness in divers with a right-to-left shunt, such as is possible through a persistent (patent) foramen ovale (PFO). A review of patients treated for IEDCS at Fiona Stanley Hospital Hyperbaric Medicine Unit (FSH HMU) in Western Australia was performed to examine the epidemiology, risk factors for developing this condition, the treatment administered and the outcomes of this patient population. Methods: A retrospective review of all divers treated for IEDCS from the opening of the FSH HMU on 17 November 2014 to 31 December 2020 was performed. Patients were included if presenting with vestibular or cochlear dysfunction within 24 hours of surfacing from a dive, and excluded if demonstrating features of inner ear barotrauma. Results: There were a total of 23 IEDCS patients and 24 cases of IEDCS included for analysis, with 88% experiencing vestibular manifestations and 38% cochlear. Median dive time was 40 minutes and median maximum depth was 24.5 metres. The median time from surfacing to hyperbaric oxygen treatment (HBOT) was 22 hours. Vestibulocochlear symptoms fully resolved in 67% and complete symptom recovery was achieved in 58%. A PFO was found in 6 of 10 patients who subsequently underwent investigation with bubble contrast echocardiography upon follow-up. Conclusions: IEDCS occurred predominantly after non-technical repetitive air dives and ongoing symptoms and signs were often observed after HBOT. Appropriate follow-up is required given the high prevalence of PFO in these patients.

A prospective single-blind randomised clinical trial comparing two treatment tables for the initial management of mild decompression sickness.

INTRODUCTION: Limited evidence suggests that shorter recompression schedules may be as efficacious as the US Navy Treatment Table 6 (USN TT6) for treatment of milder presentations of decompression sickness (DCS). This study aimed to determine if divers with mild DCS could be effectively treated with a shorter chamber treatment table. METHODS: All patients presenting to the Fremantle Hospital Hyperbaric Medicine Unit with suspected DCS were assessed for inclusion. Participants with mild DCS were randomly allocated to receive recompression in a monoplace chamber via either a modified USN TT6 (TT6m) or a shorter, custom treatment table (FH01). The primary outcome was the number of treatments required until resolution or no further improvement (plateau). RESULTS: Forty-one DCS cases were included, 21 TT6m and 20 FH01. Two patients allocated to FH01 were moved to TT6m mid-treatment due to failure to significantly improve (as per protocol), and two TT6m required extensions. The median total number of treatments till symptom resolution was 1 (IQR 1-1) for FH01 and 2 (IQR 1-2) for TT6m (P = 0.01). More patients in the FH01 arm (17/20, 85%) showed complete symptom resolution after the initial treatment, versus 8/21 (38%) for TT6m (P = 0.003). Both FH01 and TT6m had similar overall outcomes, with 19/20 and 20/21 respectively asymptomatic at the completion of their final treatment (P = 0.97). In all cases where two-week follow-up contact was made, (n = 14 FH01 and n = 12 TT6m), patients reported maintaining full symptom resolution. CONCLUSIONS: The median total number of treatments till symptom resolution was meaningfully fewer with FH01 and the shorter treatment more frequently resulted in complete symptom resolution after the initial treatment. There were similar patient outcomes at treatment completion, and at follow-up. We conclude that FH01 appears superior to TT6m for the treatment of mild decompression sickness.

Oxygen toxicity seizure mimics.

INTRODUCTION: Oxygen toxicity seizures (OTS) are a well-recognised complication of hyperbaric oxygen treatment (HBOT). As such, seizure-like activity during HBOT is usually presumed to be a result of central nervous system oxygen toxicity (CNS-OT). Four cases are reported here where causes other than CNS-OT were determined as being the likely cause of the seizure; causes we have labelled 'OTS mimics'. Through review of the current literature, and our hyperbaric medicine unit's experience to date, we aimed to highlight the relevance of these OTS mimics, as the potential for significant morbidity and mortality exists with incorrect diagnoses. METHODS: A retrospective review of the medical records of all patients treated at the Fiona Stanley Hospital and Fremantle Hospital hyperbaric medicine units who had a seizure during HBOT between November 1989 and June 2020. These events were reviewed to determine whether causes for seizures other than oxygen toxicity were evident. RESULTS: Four OTS mimics were identified: posterior reversible encephalopathy syndrome, pethidine toxicity, previous subarachnoid haemorrhage with resultant epilepsy, and severe hypoglycaemia. CONCLUSIONS: This case series highlights the need for caution when diagnosing an apparent OTS. Multiple conditions may mimic the signs and symptoms of oxygen toxicity. This creates scope for misdiagnosis, with potential for consequent morbidity and mortality. A pragmatic approach is necessary to any patient exhibiting seizure-like activity during HBOT, with suspicion for other underlying pathologies.

Oxygen toxicity seizures during United States Navy Treatment Table 6: An acceptable risk in monoplace chambers?

INTRODUCTION: Hyperbaric oxygen treatment (HBOT) may be complicated by oxygen toxicity seizures, which typically occur with hyperbaric partial pressures of oxygen exceeding 203 kPa (2 atmospheres absolute). All other hyperbaric units in Australia exclusively use a multiplace chamber when treating with United States Navy Treatment Table 6 (USN TT6) due to this perceived risk. The purpose of this study was to determine the safety of a monoplace chamber when treating decompression illness (DCI) with USN TT6. METHODS: A retrospective review of the medical records of all patients treated at Fiona Stanley Hospital Hyperbaric Medicine Unit with USN TT6 between November 2014 and June 2020 was undertaken. These data were combined with previous results from studies performed at our hyperbaric unit at Fremantle Hospital from 1989 to 2014, creating a data set covering a 30-year period. RESULTS: One thousand treatments with USN TT6 were performed between 1989 and 2020; 331 in a monoplace chamber and 669 in a multiplace chamber. Four seizures occurred: a rate of 0.59% (1/167) in a multiplace chamber; and none in a monoplace chamber, indicating no statistically significant difference between seizures in a monoplace versus multiplace chamber (P = 0.31). CONCLUSIONS: The rate of oxygen toxicity seizures in a monoplace chamber is not significantly higher than for treatment in the multiplace chamber. We conclude that using the monoplace chamber for USN TT6 in selected patients poses an acceptably low seizure risk.

Effect of antiplatelet and/or anticoagulation medication on the risk of tympanic barotrauma in hyperbaric oxygen treatment patients, and development of a predictive model.

INTRODUCTION: Middle ear barotrauma (MEBt) is a common side effect of hyperbaric oxygen treatment (HBOT) and can result in pain, hearing loss, tinnitus and otorrhagia. The use of antiplatelet/anticoagulant drugs is thought to increase the risk and severity of MEBt during HBOT. METHODS: Single centre, retrospective observational cohort study of all patients treated with HBOT over a 4-year period (between 01 January 2015 to 31 December 2018) looking at the incidence of MEBt and the concurrent use of antiplatelet and/or anticoagulant drugs. MEBt was assessed by direct otoscopy of the tympanic membrane post-HBOT and scored using the modified Teed classification. Multivariate modelling assessed the relationship between antiplatelet and/or anticoagulation drug use, age, sex, and MEBt during HBOT. RESULTS: There was no evidence that antiplatelet and/or anticoagulation drugs increase the risk of tympanic barotrauma in HBOT patients. The prevalence of MEBt was higher in female patients than in males (χ2 P = 0.004), and increased with age (χ2 P = 0.048). No MEBt was recorded in patients undergoing recompression therapy for decompression sickness or cerebral arterial gas embolism. CONCLUSIONS: In this retrospective single-centre study, antiplatelet and/or anticoagulation drugs did not affect the risk of MEBt, but both age and sex did, with greater prevalence of MEBt among older patients and females compared with younger patients and males. A predictive model, requiring further validation, may be helpful in assessing the likelihood of MEBt in patients undergoing HBOT.

Emergency Medicine Advanced Ultrasound Service: A new paradigm.

OBJECTIVE: Point-of-care ultrasound (POCUS) is now ubiquitous in emergency medicine. Increased accessibility does not, however, ensure expertise in its use. We present a unique model of an Emergency Medicine Advanced Ultrasound Service (EMAUS). In our model specialist emergency physicians with advanced ultrasound (US) qualifications (emergency sonologists), provide images and reports for the entire department. The service is considered an extension of the traditional radiology model. It is consultative, diagnostic and procedural, and includes full US examinations as well as POCUS examinations. METHODS: A 4-month prospective descriptive observational study was conducted at a tertiary hospital during which data was recorded about emergency medicine US use and its outcomes. RESULTS: A total of 1336 US scans were recorded. Emergency sonologists conducted the majority of examinations, 69.8%. Half the consultative USs demonstrated positive findings. Follow-up computed tomography (CT) was recommended in 8.8% of consultative US studies and 12.4% of POCUS studies. Concerning incidental findings requiring further investigation (usually CT/magnetic resonance imaging) were infrequent at 1.6%. CONCLUSION: Globally POCUS has proliferated with varying expertise and data to support its use. The EMAUS provides a trusted and accountable service with the advantages of simultaneously integrating consultative US into the clinical context by an emergency physician. A diverse range of indications, scan types and pathology was recorded over the period demonstrating the utility of combining the roles of senior clinician, sonographer and radiologist and the benefits of advanced training and credentialing.

Cerebral arterial gas embolism after pre-flight ingestion of hydrogen peroxide.

Cerebral arterial gas embolism (CAGE) is a feared complication of ambient depressurisation and can also be a complication of hydrogen peroxide ingestion. We present an unusual case of CAGE in a 57-year-old woman exposed to both of these risk factors. We describe her subsequent successful treatment with hyperbaric oxygen, despite a 72-hour delay in initial presentation and diagnosis, and discuss the safety of aero-medical transfer following hydrogen peroxide ingestions.

An observation of venous gas emboli in divers and susceptibility to decompression sickness.

INTRODUCTION: Decompression sickness (DCS) results from the formation of bubbles within the tissues and blood in response to a reduction in environmental pressure. Venous gas emboli (VGE) are common after diving and are usually only present in small numbers. Greater VGE numbers are an indication of decompression stress, and can be reliably detected using ultrasound imaging. AIM: To examine the relationship between production of VGE following a routine dive and the risk of DCS. METHODS: A matched population of divers with and without a history of DCS were monitored for the production of VGE at 15-minute intervals using ultrasound, following a 405 kPa air dive in a hyperbaric chamber using the DCIEM air decompression table. VGE production was graded using a validated grading system and the data analysed to compare maximum VGE grade and duration of VGE formation. RESULTS: Eleven divers with a history of DCS were compared with 13 divers with no history of DCS. Divers with a history of DCS demonstrated both a higher maximum grade (P=0.04) and longer duration (P=0.002) of VGE production compared to divers without a history of DCS. CONCLUSION: Higher maximum VGE grades and longer durations of VGE following decompression were associated with a history of DCS and, in particular, musculoskeletal DCS. Although the exact mechanism of DCS remains poorly understood, our data suggest some individuals are inherently more prone to develop VGE, increasing the probability of DCS. Modification of diving practices in those with high VGE grades could potentially decrease DCS risk in these individuals.

The cardiac effects of hyperbaric oxygen at 243 kPa using inchamber echocardiography.

INTRODUCTION: The adverse effects of hyperbaric oxygen (HBO) on cardiac physiology are considered a potential hazard during the treatment of some patients. The haemodynamic effects of HBO are poorly understood and the incompatibility of electrical equipment inside the chamber has made assessment difficult. At Fremantle Hyperbaric Unit, we have modified an ultrasound machine (Logiq™ e) for safe use within the hyperbaric environment. The aim of this study was to evaluate the cardiac changes that occur during HBO using in-chamber transthoracic echocardiography (TTE) in subjects without evidence of active cardiac disease. METHODS: Eleven patients and nine members of staff underwent comprehensive TTE examinations before and during HBO administered at a pressure of 243 kPa. The TTE examinations were reported by two independent cardiologists and statistically evaluated using paired Student's t-tests. RESULTS: There was a significant decrease in heart rate during HBO (65 vs. 70 bpm on air at atmospheric pressure, P = 0.002) resulting in a decrease in cardiac output (5.3 vs. 5.9 L·min⁻¹, P = 0.003). Left ventricular outflow tract (LVOT) dimension was larger during HBO than baseline imaging (2.30 vs. 2.23 cm, P = 0.0003). LVOT velocity time integrals (VTI) decreased (19.9 vs. 21.5 cm, P = 0.009) and therefore a similar stroke volume was maintained (61 vs. 65 ml, P = 0.5). Ventricular and atrial volumes, intracardiac flows and minor valvular abnormalities were not significantly affected by HBO. No adverse cardiac effects were observed. CONCLUSIONS: TTE can be safely performed within a hyperbaric chamber. Cardiac physiology is not adversely affected by HBO in individuals without active cardiac disease.

Acute paraspinal compartment syndrome as an unusual cause of severe low back pain.

This report describes a case of acute paraspinal compartment syndrome in a 25-year-old man. The diagnosis was significantly delayed, perhaps to some extent because of the rarity of the condition. The patient was managed with forced diuresis, analgesia and hyperbaric oxygen therapy. The discussion addresses an unusual site for compartment syndrome and a diagnosis not commonly considered in the differential of low back pain. Treatment options are discussed and we review previous published case reports.

Ultrasound in diving and hyperbaric medicine.

Ultrasound is a safe and effective imaging modality, the use of which is increasing exponentially in many areas of clinical medicine. In this article, we present what is, to our knowledge, the first in-chamber use of an ultrasound machine. We discuss the challenges this presented, how they were addressed and explore the possible clinical applications that in-chamber ultrasound may deliver in hyperbaric medicine.

Creating thoracic phantoms for diagnostic and procedural ultrasound training.

The use of pleural and lung ultrasound is being performed increasingly by respiratory and critical care clinicians around the world. This article describes how to create cheap and reliable lung and pleural phantoms for teaching. The phantoms described replicate the appearance of normal ventilating lung, pneumothorax (including the contact or lung point), pulmonary oedema, pleural effusion and empyema. The pleural effusion phantom can be used to teach procedural ultrasound (pleurocentesis).

Splenic artery aneurysm rupture: case report of this uncommon presentation.

Rupture of a splenic artery aneurysm remains an uncommon cause of hypovolaemic shock in the emergency department. This case report highlights that rapid resuscitation, diagnostic imaging, surgical consultation and subsequent laparotomy remain the priorities in patient management.

A mysterious case of chest pain.

Atrial myxomas can present a diagnostic dilemma attributed to their broad spectrum of clinical presentations. We report the case of a 46-year-old woman in whom the diagnosis of atrial myxoma initially eluded cardiologists despite the large size of her tumour.