Introduction: Rebreather diving carries an increased risk of hypercapnia. Hypercapnia can cause impaired cognition, breathlessness, and increase the risk of oxygen toxicity. We investigated whether a prior unblinded hypercapnia experience, compared to reading about hypercapnia symptoms, would improve divers’ ability to recognise hypercapnia and initiate self-rescue. Methods: Forty divers were recruited and randomised to receive either an unblinded hypercapnia experience (partial pressure of end-tidal carbon dioxide [PETCO2] of 8.5 kPa) or an information leaflet explaining hypercapnia symptoms. At least one month later, participants in each group were further randomised to undergo blinded exposure to hypercapnia or normocapnia, allocated at 3:1. The primary outcome was the proportion of participants who self-initiated bailout prior to reaching PETCO2 8.5 kPa. Continuous cardiorespiratory data (PETCO2 and PETO2, tidal volume, respiratory rate, minute ventilation, heart rate, and blood pressure) were also recorded. Subjective symptoms associated with hypercapnia were assessed with a visual analogue scale. Results: Thirteen of 15 participants (87%) who received the unblinded hypercapnia-experience self-initiated bailout compared to 10/15 information leaflet participants (67%) (P = 0.149). There was no difference in cardiorespiratory physiology parameters at bailout between the groups. Shortness of breath, light-headedness, and disorientation were the most intensely reported symptoms. Approximately half (47%) of participants who received a hypercapnia training experience had a correlated symptom response during their subsequent hypercapnia testing session. Conclusions: Although no significant training benefit was shown, becoming familiar with the sensations associated with hypercapnia under appropriate supervision could be useful to rebreather divers both recreationally and within occupational settings.

Studies involving breath-hold dives as deep as 60 m have identified a spike in arterial Po2 ([Formula: see text]) and Pco2 ([Formula: see text]) apparently associated with lung compression by water pressure as depth increases. Competitive breath-hold dives may exceed 100 m, raising the possibility that a spike in [Formula: see text] might contribute to narcosis-like symptoms sometimes experienced. To predict the magnitude of this spike, three elite breath-hold divers were instrumented with radial artery catheters and had arterial blood specimens taken at the bottom on separate dives to 20, 40, 60, and 80 m with another specimen either after beginning apnea but before leaving the surface (one participant) or on arrival back at the surface while still apneic (two participants). Contrary to previous expectations, the greatest spike in [Formula: see text] was at 40 m (mean: 29.3 kPa, 220 mmHg) and the trajectory of rise in [Formula: see text] also plateaued at 40 m [mean: 5.61 kPa, 42.1 mmHg (from a mean baseline of 2.53 kPa after predive hyperventilation) and 5.54 kPa, 41.6 mmHg at 60 m] before rising again after 60 m (80 m mean: 6.9 kPa, 51.5 mmHg). This suggests that a spike in arterial gases associated with lung compression was detectable until the greatest proportional changes in lung volume with increasing pressure had occurred. Thereafter, [Formula: see text] decreased through metabolism, and [Formula: see text] increased through simple metabolic accumulation. The compression effect seemed maximal at 40 m (five atmospheres absolute pressure) which may relate to the simple Boyle's law prediction that the lung may be compressed to close to residual volume (20%-30% of total lung capacity) at this pressure.NEW & NOTEWORTHY In descending deep breath-hold divers, spikes in [Formula: see text] and [Formula: see text] associated with compression of the lungs by increasing water pressure have been reported. This study, which reports the deepest arterial blood gas specimens taken to date, raises the possibility that these spikes are detectable until the greatest proportional changes in lung volume with increasing pressure have occurred, after which [Formula: see text] will decrease through metabolism and [Formula: see text] will increase through simple metabolic accumulation.

Nitrogen narcosis causes acute cognitive impairment in divers breathing compressed air at depth, increasing injury and fatality risk. Susceptibility varies widely between individuals, making real-time cortical monitoring a potential safety tool. We recorded 32-channel electroencephalography (EEG) from 45 divers (both sexes; aged 20-55 years) at rest across four randomized crossover hyperbaric studies. We manipulated pressure (101-811 kPa) and breathing gas (air or heliox) to create two classes of recordings: narcotic (high-pressure air) or non-narcotic (low-pressure air; heliox at any pressure); our outcome was therefore gas composition, not direct cognitive impairment. We extracted 2,720 features (17 feature types × 32 channels × 5 frequency subbands) from preprocessed EEG epochs, trained six machine-learning classifiers using leave-one-participant-out cross-validation on a training set (24 participants), and evaluated the best-performing model on a test set (9 participants) and hold-out set (12 participants). Linear discriminant analysis (LDA) achieved a Matthews correlation coefficient (MCC) of 0.50 (chance ≈ 0; p = 0.001) and accuracy of 82% (baseline 76%; p = 0.001) on the test set, and MCC of 0.25 (chance ≈ 0; p = 0.001) and accuracy of 69% (baseline 69%; p = 0.77) on the hold-out set collected years later. Feature elimination retained 157 features; feature importance analysis identified zero-crossing rate, Hjorth mobility, and Katz fractal dimension at delta-band frequencies (< 4 Hz) over the anterior and posterior midline as the most important features. Easily computed EEG features with an LDA classifier can detect neurophysiological signatures of nitrogen narcosis, potentially enabling real-time passive monitoring of divers.

Introduction: First aid for injured divers includes oxygen delivery prior to definitive care. Delay to specialist assessment and/or hyperbaric oxygen treatment (HBOT) may be due to dive site remoteness and limited access to facilities. Townsville has the only hyperbaric facility along the Great Barrier Reef. Analysis of oxygen therapy and retrieval pathways of divers treated in Townsville may assist with establishing future education strategies and resource allocation. Methods: Data were retrospectively collected on divers assessed at the Townsville hyperbaric medicine unit from November 2003 through December 2018. Demographics, dive incident location, oxygen treatment, retrieval platform and pathway, and initial disease grade were reviewed. Data are presented as frequencies and percentages. Results: A total of 306 cases were included (184 males). Divers typically received oxygen therapy (87%, 267/305 known) prior to specialist review. The non-rebreather mask was the most frequently used (44%, 28/63) followed by in-water recompression (24%, 15/63). While 34% of the divers were retrieved from the scene (n = 104), only 11 (11%, 11/104) were retrieved directly to Townsville. Most divers initially classified as severe were retrieved from the scene (82%, 27/33), only two directly to Townsville. Fifteen cases had three retrieval legs (5%, 15/306). Conclusions: Most injured divers received oxygen first aid and were transported to Townsville for definitive care with a variable number of retrieval stages. Continuing education of retrieval physicians should address knowledge of diving related injuries and highlight cases that may benefit from expedited transfer.

Introduction: Malfunctions and human errors in diving rebreathers can cause hypoxia, hyperoxia, and/or hypercapnia. We evaluated whether a prior unblinded hypoxia experience enhances a diver’s ability to recognise hypoxia and initiate self-rescue. Methods: Forty participants were randomised to receive either an information leaflet describing hypoxia symptoms or an unblinded hypoxia experience, prior to a blinded hypoxia testing exposure during a virtual reality dive over one month later. The primary outcome was the comparison of the proportion of participants in these two groups who initiated self-rescue before reaching a peripheral oxygen saturation of 70% in the blinded exposure. An individual’s ‘symptom profile’ was assessed by comparing symptoms during the unblinded hypoxia experience and blinded testing exposures. Results: During the blinded hypoxia testing exposure, 18/20 (90%) participants in the hypoxia experience group performed a self-initiated rescue compared to 6/18 (33%) in the information leaflet group (P < 0.001). Participants in the information leaflet group had lower mean SpO2 (73.4% vs 81.4%, mean difference 8% [95% CI = 2.5–13.5%, P = 0.005]) and lower inhaled oxygen fraction (7.6% vs 9.4%, mean difference 1.8% [95% CI = 0.6−3.1%, P = 0.005]) at self-rescue. The most frequent and severe symptoms were light-headedness and shortness of breath. Of the 20 participants completing both hypoxia exposures, 14 (70%) had a consistent hypoxia symptom profile, which was not related to the ability to recognise hypoxia. Conclusions: Self-rescue was approximately three times more likely for participants who had previously experienced hypoxia compared to simply receiving information on relevant symptoms. Most participants exhibited a consistent pattern of individual symptoms, which did not result in earlier or improved detection of hypoxia.

The impacts of degradation and deforestation on tropical forests are poorly understood, particularly at landscape scales. We present an extensive ecosystem analysis of the impacts of logging and conversion of tropical forest to oil palm from a large-scale study in Borneo, synthesizing responses from 82 variables categorized into four ecological levels spanning a broad suite of ecosystem properties: (i) structure and environment, (ii) species traits, (iii) biodiversity, and (iv) ecosystem functions. Responses were highly heterogeneous and often complex and nonlinear. Variables that were directly impacted by the physical process of timber extraction, such as soil structure, were sensitive to even moderate amounts of logging, whereas measures of biodiversity and ecosystem functioning were generally resilient to logging but more affected by conversion to oil palm plantation.

Technical and scientific divers breathing gases delivering hyperbaric pressures of inspired oxygen may be at risk of developing cerebral oxygen toxicity which can manifest as a seizure with little or no warning. The principle preventative strategy is adherence to time limits based on inspired PO2 levels promulgated in 1991. These limits had their origins in US Navy studies of exposures to higher inspired PO2s than are typically utilised by modern divers. Indeed, the duration limits for inspired PO2s in the range typically utilised by technical divers (≤ 1.3–1.4 atm) have relatively little experimental provenance. Contemporary technical dives often involve decompression durations that result in breaches of these limits, and anecdotally, this common occurrence seems associated with a low risk of cerebral oxygen toxicity. A committee of experts recently sought experimental evidence that might support an adjustment to the recommended duration limits for typical technical dives. Such evidence exists only for an inspired PO2 of 1.3 atm, which is a common default in use of constant PO2 rebreather devices. The (1991) limit for a single exposure to an inspire PO2 of 1.3 atm is 180 min with a 24-hour maximum of 210 min. Recent studies provide reassurance that dives with an inspired PO2 of 1.3 atm consisting of up to 240 min of working dive activity followed by up to 240 min of resting decompression are associated with an acceptably low risk of cerebral oxygen toxicity. This recommendation was promulgated and endorsed at a recent workshop convened by the National Oceanographic and Atmospheric Administration (NOAA) involving technical and scientific divers.

This consensus statement is the product of a workshop at the South Pacific Underwater Medicine Society Annual Scientific Meeting 2024 with representation of the United Kingdom Diving Medical Committee (UKDMC) present, and subsequent discussions included the entire UKDMC. A large right-to-left shunt across a persistent (patent) foramen ovale (PFO), an atrial septal defect (ASD) or a pulmonary shunt is a risk factor for some types of decompression sickness (DCS). It is agreed that routine screening for a right-to-left shunt is not currently justifiable, but certain high risk sub-groups can be identified. Individuals with a history of cerebral, spinal, vestibulocochlear, cardiovascular or cutaneous DCS, migraine with aura or cryptogenic stroke; a family history of PFO or ASD and individuals with other forms of congenital heart disease have a higher prevalence, and for those individuals screening should be considered. If screening is undertaken, it should be by bubble contrast transthoracic echocardiography with provocative manoeuvres (including Valsalva release and sniffing). Appropriate quality control is important. If a shunt is present, advice should be provided by an experienced diving physician taking into account the clinical context and the size of shunt. If shunt-mediated DCS is diagnosed, the safest option is to stop diving. Another is to perform dives with restrictions to reduce the inert gas load, which is facilitated by limiting depth and duration of dives, breathing a gas with a lower percentage of nitrogen and reducing repetitive diving. Divers may consider transcatheter device closure of the PFO or ASD in order to return to normal diving. If transcatheter PFO or ASD closure is undertaken, repeat bubble contrast echocardiography must be performed to confirm adequate reduction or abolition of the right-to-left shunt, and the diver should have stopped taking potent anti-platelet therapy (low dose aspirin is acceptable) before resuming diving.

Introduction: Hyperbaric oxygen treatment (HBOT) is considered definitive treatment for decompression illness. Delay to HBOT may be due to dive site remoteness and limited facility availability. Review of cases may help identify factors contributing to clinical outcomes. Methods: Injured divers treated in Townsville from November 2003 through December 2018 were identified. Information on demographics, initial disease severity, time to symptom onset post-dive, time to pre-HBOT oxygen therapy (in-water recompression or normobaric), time to HBOT, and clinical outcome was reviewed. Data were reported as median (interquartile range [IQR]) with Kruskal-Wallis and chi-square tests used to evaluate group differences. Significance was accepted at P < 0.05. Results: A total of 306 divers (184 males, 122 females) were included with a median age of 29 (IQR 24, 35) years. Most divers had mild initial disease severity (n = 216, 70%). Time to symptom onset was 60 (10, 360) min, time to pre-HBOT oxygen therapy was 4:00 (00:30, 24:27) h:min, and time to start of HBOT was 38:51 (22:11, 69:15) h:min. Most divers (93%) had a good (no residual or minor residual symptoms) outcome and no treated diver died. Higher initial disease severity was significantly associated with shorter times to symptom onset, oxygen therapy, and HBOT, and with worse outcomes. The paucity of cases receiving HBOT with minimal delay precluded meaningful evaluation of the effect of delay to HBOT. Conclusions: Most divers had mild initial disease severity and a good outcome. Higher initial disease severity accelerated the speed of care obtained and was the only factor associated with poorer outcome.

(Harris RJ, Challen CJ, Mitchell SJ. The first deep rebreather dive using hydrogen: case report. Diving and Hyperbaric Medicine. 2024 31 March;54(1):69-72. doi: 10.28920/dhm54.1.69-72. PMID: 38507913.) Bounce diving with rapid descents to very deep depths may provoke the high-pressure neurological syndrome (HPNS). The strategy of including small fractions of nitrogen in the respired gas to produce an anti-HPNS narcotic effect increases the gas density which may exceed recommended guidelines. In 2020 the 'Wetmules' dive team explored the Pearse Resurgence cave (New Zealand) to 245 m breathing trimix (approximately 4% oxygen, 91% helium and 5% nitrogen). Despite the presence of nitrogen, one diver experienced HPNS tremors beyond 200 m. The use of hydrogen (a light yet slightly narcotic gas) has been suggested as a solution to this problem but there are concerns, including the potential for ignition and explosion of hydrogen -containing gases, and accelerated heat loss. In February 2023 a single dive to 230 m was conducted in the Pearse Resurgence to experience hydrogen as a breathing gas in a deep bounce dive. Using an electronic closedcircuit rebreather, helihydrox (approximately 3% oxygen, 59% helium and 38% hydrogen) was breathed between 200 and 230 m. This was associated with amelioration of HPNS symptoms in the vulnerable diver and no obvious adverse effects. The use of hydrogen is a potential means of progressing deeper with effective HPNS amelioration while maintaining respired gas density within advised guidelines.

The functional stability of ecosystems depends greatly on interspecific differences in responses to environmental perturbation. However, responses to perturbation are not necessarily invariant among populations of the same species, so intraspecific variation in responses might also contribute. Such inter-population response diversity has recently been shown to occur spatially across species ranges, but we lack estimates of the extent to which individual populations across an entire community might have perturbation responses that vary through time. We assess this using 524 taxa that have been repeatedly surveyed for the effects of tropical forest logging at a focal landscape in Sabah, Malaysia. Just 39 % of taxa – all with non-significant responses to forest degradation – had invariant responses. All other taxa (61 %) showed significantly different responses to the same forest degradation gradient across surveys, with 6 % of taxa responding to forest degradation in opposite directions across multiple surveys. Individual surveys had low power (< 80 %) to determine the correct direction of response to forest degradation for one-fifth of all taxa. Recurrent rounds of logging disturbance increased the prevalence of intra-population response diversity, while uncontrollable environmental variation and/or turnover of intraspecific phenotypes generated variable responses in at least 44 % of taxa. Our results show that the responses of individual species to local environmental perturbations are remarkably flexible, likely providing an unrealised boost to the stability of disturbed habitats such as logged tropical forests.### Competing Interest StatementThe authors have declared no competing interest.

This joint position statement (JPS) on immersion pulmonary oedema (IPO) and diving is the product of a workshop held at the 52nd Annual Scientific Meeting of the South Pacific Underwater Medicine Society (SPUMS) from 12-17 May 2024, and consultation with the United Kingdom Diving Medical Committee (UKDMC), three members of which attended the meeting. The JPS is a consensus of experts with relevant evidence cited where available. The statement reviews the nomenclature, pathophysiology, risk factors, clinical features, prehospital treatment, investigation of and the fitness for future compressed gas diving following an episode of IPO. Immersion pulmonary oedema is a life-threatening illness that requires emergency management as described in this statement. A diver with previous suspected or confirmed IPO should consult a medical practitioner experienced in diving medicine. The SPUMS and the UKDMC strongly advise against further compressed gas diving if an individual has experienced an episode of IPO.

Logged and disturbed forests are often viewed as degraded and depauperate environments compared with primary forest. However, they are dynamic ecosystems(1) that provide refugia for large amounts of biodiversity2,3, so we cannot afford to underestimate their conservation value4. Here we present empirically defined thresholds for categorizing the conservation value of logged forests, using one of the most comprehensive assessments of taxon responses to habitat degradation in any tropical forest environment. We analysed the impact of logging intensity on the individual occurrence patterns of 1,681 taxa belonging to 86 taxonomic orders and 126 functional groups in Sabah, Malaysia. Our results demonstrate the existence of two conservation-relevant thresholds. First, lightly logged forests (<29% biomass removal) retain high conservation value and a largely intact functional composition, and are therefore likely to recover their pre-logging values if allowed to undergo natural regeneration. Second, the most extreme impacts occur in heavily degraded forests with more than two-thirds (>68%) of their biomass removed, and these are likely to require more expensive measures to recover their biodiversity value. Overall, our data confirm that primary forests are irreplaceable5, but they also reinforce the message that logged forests retain considerable conservation value that should not be overlooked.

Decompression illness is a collective term for two maladies (decompression sickness [DCS] and arterial gas embolism [AGE]) that may arise during or after surfacing from compressed gas diving. Bubbles are the presumed primary vector of injury in both disorders, but the respective sources of bubbles are distinct. In DCS bubbles form primarily from inert gas that becomes dissolved in tissues over the course of a compressed gas dive. During and after ascent (‘decompression’), if the pressure of this dissolved gas exceeds ambient pressure small bubbles may form in the extravascular space or in tissue blood vessels, thereafter passing into the venous circulation. In AGE, if compressed gas is trapped in the lungs during ascent, pulmonary barotrauma may introduce bubbles directly into the pulmonary veins and thence to the systemic arterial circulation. In both settings, bubbles may provoke ischaemic, inflammatory, and mechanical injury to tissues and their associated microcirculation. While AGE typically presents with stroke-like manifestations referrable to cerebral involvement, DCS can affect many organs including the brain, spinal cord, inner ear, musculoskeletal tissue, cardiopulmonary system and skin, and potential symptoms are protean in both nature and severity. This comprehensive overview addresses the pathophysiology, manifestations, prevention and treatment of both disorders.

Breast cancer causes the highest cancer-related mortality for New Zealand women. Surgical treatment mandating general anaesthesia (GA) is common. However, research has raised concerns about the impact of anaesthetic agents on cancer pathogenesis. This study investigated associations between GA technique, ethnicity, and breast cancer recurrence and mortality, in a New Zealand cohort.This retrospective cohort study used 12 years of data from Te Rēhita Mate Ūtaetae (The Breast Cancer Foundation National Register) and intraoperative electronic records. Primary outcome was breast cancer recurrence (to 5 years) measured in patients grouped according to ethnicity and anaesthetic exposure (total intravenous anaesthesia [TIVA] versus low, medium and high volatile anaesthetic exposure [LVE, MVE, HVE respectively] in all surgeries since diagnosis), using Cox proportional hazard models. The cohort was weighted according to propensity scores to account for differences in demographic data, and models were re-assessed using the weighted cohort.2,989 patients with a total of 6,200 surgeries were included. Recurrence in these groups was as follows TIVA:19/411 (4.7%), LVE: 92/1,353 (6.4%), MVE:72/661 (11%) and HVE:81/564 (14%). There was no significant effect of total volatile exposure (HR of 1.00 [1.00-1.00]) in either whole cohort or propensity weighted groups for recurrence. There were significant differences with respect to ethnicity; with Asians having lower recurrence (HR 0.47 (0.28-0.78) compared to Europeans. No association between ethnicity, recurrence and type of anaesthetic was found.After propensity weighting, no difference in recurrence was found with increasing levels of exposure to volatile anaesthetic agent. There are ethnic variations in breast cancer recurrence.

Bounce diving with rapid descents to very deep depths may provoke the high-pressure neurological syndrome (HPNS). The strategy of including small fractions of nitrogen in the respired gas to produce an anti-HPNS narcotic effect increases the gas density which may exceed recommended guidelines. In 2020 the 'Wetmules' dive team explored the Pearse Resurgence cave (New Zealand) to 245 m breathing trimix (approximately 4% oxygen, 91% helium and 5% nitrogen). Despite the presence of nitrogen, one diver experienced HPNS tremors beyond 200 m. The use of hydrogen (a light yet slightly narcotic gas) has been suggested as a solution to this problem but there are concerns, including the potential for ignition and explosion of hydrogen-containing gases, and accelerated heat loss. In February 2023 a single dive to 230 m was conducted in the Pearse Resurgence to experience hydrogen as a breathing gas in a deep bounce dive. Using an electronic closed-circuit rebreather, helihydrox (approximately 3% oxygen, 59% helium and 38% hydrogen) was breathed between 200 and 230 m. This was associated with amelioration of HPNS symptoms in the vulnerable diver and no obvious adverse effects. The use of hydrogen is a potential means of progressing deeper with effective HPNS amelioration while maintaining respired gas density within advised guidelines.

Introduction: Hypoxia can cause central nervous system dysfunction and injury. Hypoxia is a particular risk during rebreather diving. Given its subtle symptom profile and its catastrophic consequences there is a need for reliable hypoxia monitoring. Electroencephalography (EEG) is being investigated as a real time monitor for multiple diving problems related to inspired gas, including hypoxia. Methods: A systematic literature search identified articles investigating the relationship between EEG changes and acute cerebral hypoxia in healthy adults. Quality of clinical evidence was assessed using the Newcastle-Ottawa scale. Results: Eighty-one studies were included for analysis. Only one study investigated divers. Twelve studies described quantitative EEG spectral power differences. Moderate hypoxia tended to result in increased alpha activity. With severe hypoxia, alpha activity decreased whilst delta and theta activities increased. However, since studies that utilised cognitive testing during the hypoxic exposure more frequently reported opposite results it appears cognitive processing might mask hypoxic EEG changes. Other analysis techniques (evoked potentials and electrical equivalents of dipole signals), demonstrated sustained regulation of autonomic responses despite worsening hypoxia. Other studies utilised quantitative EEG analysis techniques, (Bispectral index [BISTM], approximate entropy and Lempel-Ziv complexity). No change was reported in BISTM value, whilst an increase in approximate entropy and Lempel-Ziv complexity occurred with worsening hypoxia. Conclusions: Electroencephalographic frequency patterns change in response to acute cerebral hypoxia. There is paucity of literature on the relationship between quantitative EEG analysis techniques and cerebral hypoxia. Because of the conflicting results in EEG power frequency analysis, future research needs to quantitatively define a hypoxia-EEG response curve, and how it is altered by concurrent cognitive task loading.

Agricultural expansion across the tropics is the primary driver of biodiversity declines and ecosystem service degradation. However, efforts to mitigate these negative impacts may reduce commodity production. We quantify trade-offs between oil palm cultivation and ecological outcomes (biodiversity, above-ground carbon storage and dung nutrient cycling) across different potential set-aside (uncultivated areas in agricultural landscapes) strategies. We show that all set-aside configurations yield substantial gains in ecological outcomes. The best strategy involves spatially targeted riparian reserves, such as those used in oil palm certification schemes, where species occurrence can be doubled without reducing overall cultivation area. Adopting this strategy throughout the 8 million hectares of plantations in Borneo would lead to extensive improvements in ecological outcomes without losses to production area, and consequently, enhancing agricultural sustainability.

Introduction:Capnography aids assessment of the adequacy of mechanical patient ventilation. Physical and physiological changes in hyperbaric environments create ventilation challenges which make end-tidal carbon dioxide (ETCO2) measurement particularly important. However, obtaining accurate capnography in hyperbaric environments is widely considered difficult. This study investigated the EMMA capnograph for hyperbaric use.Methods:We compared the EMMA capnograph to sidestream capnography and the gold standard arterial carbon dioxide blood gas analysis in a hyperbaric chamber. In 12 resting subjects breathing air at 284 kPa, we recorded ETCO2 readings simultaneously derived from the EMMA and sidestream capnographs during two series of five breaths (total 24 measurements). An arterial blood gas sample was also taken simultaneously in five participants.Results:Across all measurements there was a difference of about 0.1 kPa between the EMMA and sidestream capnographs indicating a very slight over-estimation of ETCO2 by the EMMA capnograph, but fundamentally good agreement between the two end-tidal measurement methods. Compared to arterial blood gas pressure the non-significant difference was about 0.3 and 0.4 kPa for the EMMA and sidestream capnographs respectively.Conclusions:In this study, the EMMA capnograph performed equally to the sidestream capnograph when compared directly, and both capnography measures gave clinically acceptable estimates of arterial PCO2.