Simon J Mitchell's research while affiliated with University of Auckland and other places

Publications (64)

Article
Inner ear decompression sickness (IEDCS) may occur after upward or downward excursions in saturation diving. Previous studies in non-saturation diving strongly suggest IEDCS is caused by arterialization of small venous bubbles across intracardiac or intrapulmonary right-to-left shunts, and bubble growth through inward diffusion of supersaturated ga...
Article
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Divers breathe higher partial pressures of oxygen at depth than at the surface. The literature and diving community are divided on whether or not oxygen is narcotic. Conversely, hyperbaric oxygen may induce dose‐dependent cerebral hyperexcitability. This study evaluated whether hyperbaric oxygen causes similar narcotic effects to nitrogen, and inve...
Article
Objective Cerebrovascular autoregulation impairment has been associated with stroke risk in cardiac surgery. We hypothesized that greater arterial emboli exposure in open-chamber surgery might promote dysautoreguation. Methods Forty patients underwent closed or open-chamber surgery. Transcranial Doppler detected emboli and measured bilateral middl...
Article
Decompression sickness, in which bubbles formed from dis-olved gas (usually nitrogen) cause tissue and vascular injury after a reducion in environmental pressure, may occur in diving, aviation, and spaceflight. Arterial gas embolism, in which bubbles introduced into the arterial circulation cause multifocal ischemia, may occur after diving-related,...
Article
Full-text available
Divers commonly breathe air, containing nitrogen. Nitrogen under hyperbaric conditions is a narcotic gas. In dives beyond a notional threshold of 30 m depth (405 kPa) this can cause cognitive impairment, culminating in accidents due to poor decision making. Helium is known to have no narcotic effect. This study explored potential approaches to deve...
Article
Background: The consequences of even mild inadvertent perioperative hypothermia (IPH) are significant. There is a perception laparoscopic abdominal surgery is less prone to cause hypothermia than open surgery. However, during laparoscopic surgery, the peritoneal cavity is insufflated with carbon dioxide, which has a greater evaporative capacity th...
Article
Objective Exposure to cerebral emboli is ubiquitous and may be harmful in cardiac surgery utilizing cardiopulmonary bypass. This was a prospective observational study aiming to compare emboli exposure in closed-chamber with open-chamber cardiac surgery, distinguish particulate from gaseous emboli and examine cerebral laterality in distribution. Me...
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Arterial blood gas (ABG) measurements at both maximum depth and at re-surfacing prior to breathing have not previously been measured during freedives conducted to extreme depth in cold open-water conditions. An elite freediver was instrumented with a left radial arterial cannula connected to two sampling syringes through a low-volume splitting devi...
Chapter
Cerebral perfusion pressure (CPP) lower limits of reactivity can be determined almost continuously after severe traumatic brain injury (TBI), and deviation below the lower limit carries important prognostic information. In this study, we used a recently derived coloured contour method for visualizing intracranial pressure (ICP) insults to describe...
Article
Hyperbaric oxygen for decompression sickness: 2021 update Decompression sickness (DCS, “bends”) is caused by the formation of bubbles in tissues and/or blood when the sum of dissolved gas pressures exceeds ambient pressure (supersaturation). This may occur when ambient pressure is reduced during: ascent from a dive; rapid ascent to altitude in an u...
Article
(Dapena JC, Lansdorp CA, Mitchell SJ. Persistent extravascular bubbles on radiologic imaging after recompression treatment for decompression sickness: A case report. Diving and Hyperbaric Medicine. 2020 December 20;50(4):424–430. doi: 10.28920/dhm50.4.424-430. PMID: 33325027.) Decompression sickness (DCS) is a condition arising when dissolved inert...
Article
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Introduction: Critical flicker fusion frequency (CFFF) has been used in various studies to measure the cognitive effects of gas mixtures at depth, sometimes with conflicting or apparently paradoxical results. This study aimed to evaluate a novel automatic CFFF method and investigate whether CFFF can be used to monitor gas-induced narcosis in diver...
Article
Background Nitrous oxide produces non–γ-aminobutyric acid sedation and psychometric impairment and can be used as scientific model for understanding mechanisms of progressive cognitive disturbances. Temporal complexity of the electroencephalogram may be a sensitive indicator of these effects. This study measured psychometric performance and the te...
Article
The South Pacific Underwater Medicine Society (SPUMS) diving medical for recreational scuba divers was last reviewed in 2011. From 2011 to 2019, considerable advancements have occurred in cardiovascular risk assessment relevant to divers. The SPUMS 48th (2019) Annual Scientific Meeting theme was cardiovascular risk assessment in diving. The meeting...
Article
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Introduction: Gas narcosis impairs divers when diving deeper. Pupillometry is sensitive to alcohol intoxication and it has been used in anaesthesia to assess nitrous oxide narcosis. It is a potential novel method to quantify narcosis in diving. The aim of this study was to evaluate pupillometry for objective measurement of narcosis during exposure...
Article
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Introduction: In 2018 12 children and one adult were anaesthetised before being extricated through over a kilometre of flooded cave in Thailand. Full face dive masks (FFMs) putatively capable of maintaining constant positive airway pressure (CPAP) were employed. Here we describe the anaesthetic intervention and investigate the CPAP capability of t...
Article
Introduction: The cutaneous form of decompression sickness (DCS) known as cutis marmorata is a frequent clinical presentation. Beyond a general acceptance that bubbles formed from dissolved inert gas are the primary vector of injury, there has been debate about pathophysiology. Hypotheses include: 1) local formation of bubbles in the skin or its b...
Article
INTRODUCTION: Divers with suspected decompression illness require high concentration oxygen (O₂). There are many different O₂ delivery devices, with few data comparing their performance. This study evaluated O₂ delivery, using tissue O₂ partial pressure (PtcO₂), in healthy divers breathing O₂ via three different delivery devices. METHODS: Twel...
Article
Full-text available
Introduction: Divers with suspected decompression illness require high concentration oxygen (O₂). There are many different O₂ delivery devices, with few data comparing their performance. This study evaluated O₂ delivery, using tissue O₂ partial pressure (PtcO₂), in healthy divers breathing O₂ via three different delivery devices. Methods: Twelve...
Article
Introduction: Professional divers, like many other specialised occupational groups, are subject to regulatory constraints that include mandatory initial medical certification and routine recertification. The New Zealand system of diver certification and health surveillance has undergone modifications in recent years, but its acceptance among end-u...
Article
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Introduction: Scrubbers in closed-circuit rebreather systems remove carbon dioxide (CO2) from the exhaled gas. In an attempt to be more user-friendly and efficient, the ExtendAir® non-granular, pre-formed scrubber cartridge has been developed. The cartridge manufacturer claims twice the absorptive capacity of granular CO2 absorbent, with less vari...
Article
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Background As the worldwide population has aged, the number of surgical procedures performed on older patients has increased. It is not known whether this increase has been proportional to growth in the elderly population. The aim of this study was to assess the population-adjusted incidence of acute and elective general and orthopaedic surgery in...
Article
There are few issues that generate as much confusion in diving medicine as the nomenclature of bubble-induced dysbaric disease. Prior to the late 1980s, the diagnosis 'decompression sickness' (DCS) was invoked for symptoms presumed to arise as a consequence of bubble formation from dissolved inert gas during or after decompression. These bubbles we...
Article
Decompression sickness (DCS, "bends") is caused by formation of bubbles in tissues and/or blood when the sum of dissolved gas pressures exceeds ambient pressure (supersaturation). This may occur when ambient pressure is reduced during any of the following: ascent from a dive; depressurization of a hyperbaric chamber; rapid ascent to altitude in an...
Article
Purpose of review: To identify and discuss emerging trends in the therapeutic use of hyperbaric oxygen. Recent findings: There has been a maturing of the clinical evidence to support the treatment of sudden hearing loss, a wide range of problematic chronic wound states and the prevention and treatment of end-organ damage associated with diabetes...
Article
Background: Aircrew training often includes an hypoxic experience aimed at improving symptom recognition and self-rescue in a subsequent hypoxic event. Similar training has been advocated for rebreather divers. We investigated the effect of a prior hypoxic experience on actual and perceived cognitive function during subsequent hypoxia and measured...
Article
Introduction: Approximately 77% of professional divers leave the industry within five years of entry, for reasons that are uncertain. One possibility is that attrition is due to ill-health. The health of New Zealand occupational divers is surveyed by a comprehensive medical examination every five years and by a health questionnaire in the interven...
Article
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Background: Postoperative infection is a serious problem in New Zealand and internationally with considerable human and financial costs. Also, in New Zealand, certain factors that contribute to postoperative infection are more common in Māori and Pacific populations. To date, most efforts to reduce postoperative infection have focussed on surgical...
Preprint
Background Postoperative infection is a serious problem in New Zealand, and internationally with considerable human and financial costs. Also, in New Zealand, certain factors that contribute to postoperative infection are more common in Māori and Pacific populations. To date, most efforts to reduce postoperative infection have focused on surgical a...
Article
Introduction: Surveillance of professional divers' hearing is routinely undertaken on an annual basis despite lack of evidence of benefit to the diver. The aim of this study was to determine the magnitude and significance of changes in auditory function over a 10-25 year period of occupational diving with the intention of informing future health s...
Article
Introduction: Diving rebreathers use canisters containing soda lime to remove carbon dioxide (CO2) from expired gas. Soda lime has a finite ability to absorb CO₂. Temperature sticks monitor the exothermic reaction between CO₂ and soda lime to predict remaining absorptive capacity. The accuracy of these predictions was investigated in two rebreathe...
Preprint
Background Postoperative infection is a serious problem in New Zealand, and internationally with considerable human and financial costs. Also, in New Zealand, certain factors that contribute to postoperative infection are more common in Māori and Pacific populations. To date, most efforts to reduce postoperative infection have focused on surgical a...
Preprint
Background Postoperative infection is a serious problem in New Zealand, and internationally with considerable human and financial costs. Also, in New Zealand, certain factors that contribute to postoperative infection are more common in Māori and Pacific populations. To date, most efforts to reduce postoperative infection have focused on surgical a...
Article
Full-text available
Objectives To extend reliability of WHO Behaviourally Anchored Rating Scale (WHOBARS) to measure the quality of WHO Surgical Safety Checklist administration using generalisability theory. In this context, extending reliability refers to establishing generalisability of the tool scores across populations of teams and raters by accounting for the rel...
Article
Introduction: Health and safety within the recreational diving industry are poorly described. We aimed to obtain the true prevalence of decompression illness (DCI) and other diving and non-diving injuries, including occupational injuries, in a large recreational diving charter operation. Methods: A New Zealand recreational diving operator keeps...
Article
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Introduction: Vibration from a helicopter during aeromedical retrieval of divers may increase venous gas emboli (VGE) production, evolution or distribution, potentially worsening the patient's condition. Aim: To review the literature surrounding the helicopter transport of injured divers and establish if vibration contributes to increased VGE....
Article
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INTRODUCTION: High concentration normobaric oxygen (O₂) is a priority in treating divers with suspected decompression illness. The effect of different O₂ mask configurations on tissue oxygenation when breathing with a demand valve was evaluated. METHODS: Sixteen divers had tissue oxygen partial pressure (PtcO₂) measured at six limb sites. Part...
Preprint
Background: Postoperative infection is a serious problem in New Zealand, and internationally with considerable human and financial costs. Also, in New Zealand, certain factors that contribute to postoperative infection are more common in Māori and Pacific populations. To date, most efforts to reduce postoperative infection have focused on surgical...
Article
Full-text available
While the WHO Surgical Safety Checklist (the Checklist) can improve patient outcomes, variable administration can erode benefits. We sought to understand and improve how operating room (OR) staff use the Checklist. Our specific aims were to: determine if OR staff can discriminate between good and poor quality of Checklist administration using a val...
Article
Divers suspected of suffering decompression illness (DCI) in locations remote from a recompression chamber are sometimes treated with in-water recompression (IWR). There are no data that establish the benefits of IWR compared to conventional first aid with surface oxygen and transport to the nearest chamber. However, the theoretical benefit of IWR...
Article
Full-text available
Introduction: Diving rebreathers use "scrubber" canisters containing soda lime to remove carbon dioxide (CO2) from the expired gas. Soda lime has a finite ability to absorb CO2. We undertook an experiment to determine whether the manner of storage of a partly used scrubber affected subsequent CO2 absorption. Methods: An Evolution Plus™ rebreathe...
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(Mitchell SJ, Bennett MH, Bryson P, Butler FK, Doolette DJ, Holm JR, Kot J, Lafère P. Pre-hospital management of decompression illness: expert review of key principles and controversies. Diving and Hyperbaric Medicine. 2018 March;48(1):45е.doi.10.28920/dhm48.1.45-55.) Guidelines for the pre-hospital management of decompression illness (DCI) had not...
Article
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Introduction: This is the second report based on a survey of Divers Alert Network Asia-Pacific (DAN AP) members who dive with cardiovascular and respiratory conditions and diabetes. It examines the medical management of the divers' conditions, any diving modifications used to mitigate the risk and outcomes. Methodology: An online cross-sectional...
Article
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Introduction: This report examines Diver Alert Network Asia-Pacific (DAN AP) members with and without cardiac or respiratory conditions, diabetes or hypertension and compares their demographics, health and diving activities. Methodology: Two online cross-sectional surveys of DAN AP members were conducted. The first sought information from 833 di...
Article
Aims: A new approach to administering the surgical safety checklist (SSC) at our institution using wall-mounted charts for each SSC domain coupled with migrated leadership among operating room (OR) sub-teams, led to improved compliance with the Sign Out domain. Since surgical specimens are reviewed at Sign Out, we aimed to quantify any related cha...
Article
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Harvey D, Pollock NW, Gant N, Hart J, Mesley P, Mitchell SJ. The duration of two carbon dioxide absorbents in a closed-circuit rebreather diving system. Diving and Hyperbaric Medicine. 2016 June;46(2):92-97.) Introduction: Diving rebreathers use canisters containing sodalime preparations to remove carbon dioxide (CO 2) from the expired gas. These p...
Article
Full-text available
Introduction: Diving rebreathers use canisters containing sodalime preparations to remove carbon dioxide (CO2) from the expired gas. These preparations have a limited absorptive capacity and therefore may limit dive duration. The InspirationTM rebreather is designed for use with Sofnolime 797TM but some divers use SpherasorbTM as an alternative. Th...
Article
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Objective: To compare the emboli filtration efficiency of five integrated or non-integrated oxygenator-filter combinations in cardiopulmonary bypass circuits. Methods: Fifty-one adult patients underwent surgery using a circuit with an integrated filtration oxygenator or non-integrated oxygenator with a separate 20 µm arterial line filter (Sorin...
Article
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This consensus statement is the result of a workshop at the SPUMS Annual Scientific Meeting 2014 with representatives of the UK Sports Diving Medical Committee (UKSDMC) present, and subsequent discussions including the entire UKSDMC. Right-to-left shunt across a persistent or patent foramen ovale (PFO) is a risk factor for some types of decompressio...
Article
Full-text available
Introduction: Closed-circuit underwater breathing apparatus (‘CCRs’) recycle expired gas through a carbon dioxide (CO2) ‘scrubber’. Prior to diving, users perform a 5-minute ‘prebreathe’ during which they self-check for symptoms of hypercapnia that might indicate a failure in the scrubber. There is doubt that this strategy is valid. Methods: Thirty...
Article
Introduction: Deep dives using rebreather devices result in oxygen exposures that carry a risk of cerebral oxygen toxicity. Elevation of arterial CO2 levels increases this risk. CO2 retention may occur during the deep working phases of dives, but it has not been investigated in 'real world' dives at the end of resting decompression when oxygen exp...
Article
Unestablished indications are conditions in which systematic clinical use of hyperbaric oxygen treatment (HBOT) is not supported by adequate proof of benefit. HBOT is vulnerable to use in many such conditions for various reasons, perhaps the most important being that a placebo or participation effect may create an impression of efficacy. The system...
Article
Intraoperative anaphylaxis is a rare but serious occurrence, often triggered by neuromuscular-blocking drugs (NMBDs). Previous reports suggest that the rates of anaphylaxis may be greater for rocuronium than for other NMBDs, but imprecise surrogate metrics for new patient exposures to NMBDs complicate interpretation. This was a retrospective, obser...

Citations

... Hyperbaric oxygen did not increase functional connectivity at 284 kPa suggesting oxygen cannot be narcotic in a similar way as nitrogen. 6 This finding resolves a perennial debate among divers, some of whom believe oxygen may be more narcotic than nitrogen based solely on comparison of lipid solubility. Normobaric and hyperbaric oxygen at 101, 142 and 284 kPa caused a non-dose-dependent significant decrease in temporal complexity of 14%, 16% and 16% compared with normobaric air breathing (p=0.010, ...
... Thank you very much for your interest and comments [1] on the review by Mankowska et al. [2], aiming at providing an overview of the use of critical flicker fusion frequency (CFFF) to investigate cognitive functions. ...
... Des bulles de diazote peuvent atteindre la circulation artérielle par différents mécanismes [17] : ...
... Air breathing at 284 (no noticeable narcotic effect) and 608 kPa (experienced as mild nitrogen narcosis) caused significant increases of 19% and 35% (respectively) in functional connectivity, compared with breathing air at the surface (p=0.050 and p=0.001). 5 Thus, signals exhibited greater similarity while breathing air at increased pressure. Heliox did not cause a significant increase in functional connectivity. ...
... L'augmentation de la P I O 2 permet théoriquement d'accélérer la résorption des bulles d'azote en augmentant gradient de d'azote entre l'air alvéolaire et la circulation [42]. L'augmentation du gradient de pressions en oxygène au niveau alvéolaire se fait sans diminution de la pression atmopshérique, et l'administration d'une oxygénothérapie normobare à 1 atmosphère n'augmente que peu la P v O 2 , ne modifiant pas sensiblement la pression partielle du mélange des gaz sanguins dont l'azote [43] ; • un traitement de recompression en caisson hyperbare [44,45]. Il est recommandé d'utiliser des tables thérapeutiques de recompression (Table US Navy 6 ou Heliox Comex C × 30) [45]. ...
... The output of this real-time analysis is a CPP at which PRx is at a minimum (CPPopt). The upper limit of reactivity (ULR) and lower limit of reactivity (LLR), are computed as the lower and upper limits of CPP values where PRx rises above + 0.25 [19,[22][23][24][25]. A management algorithm aiming to maintain CPP as close as possible to CPPopt has proven to be feasible and safe in a phase 2 RCT [21]. ...
... Insight into respiratory and cardiovascular physiology during diving has been largely achieved through modeling based on practical studies on a small sample of participants (Fitz-Clarke 2007a, b). Some research has been published about arterial blood gas (ABG) analysis at depths of up to 60 m (Scott et al. 2021); however, to our knowledge, no studies have been published which showcase a sample of blood for ABG analysis being taken at depths in which a person's TLC is lower than his RV on the surface. ...
... In order to establish a PBt/AGE post-mortem diagnosis, it is essential to know the deceased person's dive profile, to use specific autopsy techniques and/or image diagnoses, to obtain various toxicological and histopathological studies and to know their medical record [2,[22][23][24][28][29][30][31][32][33][34]. This diagnosis is met when the following four major criteria are met [17,18]: history of rapid ascent followed by loss of consciousness; air in the left side of the heart and circle of Willis; low probability of post-mortem decompression artefact (PMDA) or decomposition; and mediastinal or subcutaneous emphysema limited to the perithoracic area and/ or pneumothorax. ...
... Critical flicker fusion frequency (CFF or CFFF), as a frequency at which flickering light stops being visible and starts being perceived as a steady light, has been used in various fields of research and various groups or species. Research has focused on dementia [1][2][3], visual impairment [4], cognitive functioning [5][6][7][8] and divers [9][10][11][12][13][14], among other topics. ...
... In the nitrous oxide exposures, EEG temporal complexity correlated (r=0.50) with the psychometric test results in a mixed effects model (p<0.001). 3 Temporal complexity was decreased (signals were more repetitive) with higher nitrous oxide concentrations and lower cognitive performance. Exposure to hyperbaric air did not change the temporal complexity. ...