End-tidal CO2 Research Articles

Comparison of the Time-Course and Magnitude of Cardiorespiratory Responses to Superimposed Surgical Masks or N95 Respirators during 20-min Treadmill Walking

Wearing medical barriers has recently expanded from healthcare to public settings, and could increase dead space and facilitate rebreathing of expired air resulting in heat accumulation, hypercapnia, and hypoxia, particularly during physical activity. We recently showed that participants wearing surgical masks (SM) and N95 respirators (N95) over 60-min during seated rest had mild and immediately reversible (a) increases face microclimate temperature, (b) increases in the pressure of end-tidal (PET)CO2, (c) decreases in PETO2, but (d) no differences in peripheral oxygen saturation (SpO2). Previous publications showed conflicting results of superimposed barrier wearing during physical activity, and there are limited studies that assessed face microclimate temperature and end-tidal gases, particularly comparing superimposed SM and N95. We hypothesized that participants wearing SM and N95 will experience mild face microclimate hyperthermia, hypoxia, and hypercapnia during 3mph treadmill walking. Participants (n=18; 8F) randomly wore (a) no barrier (NB), (b) SM or (c) N95 during a 10-min standing baseline, 20-min treadmill walking (3 mph), and a 10-min standing recovery. We continuously measured face microclimate temperature (thermistor), end tidal gases (PETCO2, PETO2; oro-nasal cannula), SpO2 (peripheral pulse oximeter). Average 20-min PETCO2 (higher; p<0.0001, P=0.0001) and PETO2 (lower; P=0.0003, P=0.0178) were significantly from baseline for both SM and N95, respectively. The delta between the 20-min average compared to the baseline data was not statistically significant for PETCO2 or PETO2 in all three conditions, except for ΔPETCO2 NB vs. N95 (higher; P=0.0344). Additionally, there was no difference in SpO2 across all barrier conditions during exercise. These mild physiological effects may account for qualitative reports of shortness of breath and increased perceived exertion while wearing barriers during physical activity. However, these effect-magnitudes are not physiologically-meaningful, and are immediately reversed upon cessation of exercise and/or barrier removal. NSERC. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Effect of Sex on Sympatho-inhibitors and Non-inhibitor Phenotypes during Acute Hyperoxia

Acute hyperoxia (i.e., breathing air consisting of 100% oxygen, O2) reduces muscle sympathetic nerve activity (MSNA), positioning hyperoxia as a potential anti-hypertensive therapeutic. However, the link between hyperoxia and MSNA has not been established in females. We tested the hypothesis that males would exhibit greater reductions in MSNA during hyperoxia than females. We tested healthy females (n=18, 27±5yr, body mass index [BMI] 23±3kg/m2) and males (n=13, 27±5yr, 25±3kg/m2) of similar age (P=0.99) and BMI (P=0.08). Integrated MSNA, blood pressure, and end-tidal O2 (ETO2) and CO2 (ETCO2) were measured during normal room air breathing (BSL; 3-min) and hyperoxic breathing (100% O2; 3-min). Integrated MSNA was quantified as burst frequency (BF; bursts/min), amplitude (BA; a.u.), and total MSNA (a.u.); blood pressure was quantified as mean arterial pressure (MAP). Baseline MSNA BF was not different between females and males (24±7 vs 23±8 bursts/min, respectively, P=0.68); MAP was lower in females than males (85±7 vs 93±7 mmHg; p<0.01). Hyperoxia increased ETO2 (effect of cond: p<0.01) and reduced ETCO2 (effect of cond: p<0.01) in a manner similar between sexes for ETO2 (sex*cond: P=0.56) whereas ETCO2 decreased more in females than males (sex*cond: P=0.01). Overall, hyperoxia evoked reductions in MSNA BF (effect of cond: P=0.02) but not BA (effect of cond: P=0.80) or total MSNA (effect of cond: P=0.26). Nadir MSNA responses during hyperoxia unveiled sex differences insofar as total MSNA was reduced consistently only in males (sex*cond: P=0.04); within the females we observed the presence of sympatho-inhibitors and non-inhibitors. Whereas female and male inhibitors reduced total MSNA via substantial reductions in BF and non-significant reductions in BA, female non-inhibitors demonstrated limited reductions in BF (P=0.11 vs inhibitors) coupled with increases in BA (p<0.01 vs inhibitors), resulting in no net change in total MSNA (p<0.01 vs inhibitors). Overall, these findings indicate sex differences exist in the sympathetic response to hyperoxia, in marked variability in the female sympathetic response to acute hyperoxia. The Women and Children's Health Research Institute. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Breathing 5% carbon dioxide for 1 minute increases cerebral blood flow during lower body negative pressure

Objective: Lower body negative pressure (LBNP) is an established surrogate of hypergravity to investigate responses to central hypovolemia, including the reduction in cerebral blood flow. Increased inspired carbon dioxide (CO2) causes cerebrovascular dilation and increases cerebral blood flow. We aimed to determine whether breathing 5% CO2 for 1 minute increased cerebral blood flow during LBNP. We hypothesized 5% inspired CO2 would increase cerebral blood flow during LBNP. Methods: We collected data from 15 (9 M/6 F, 31±8 yr, 25.6±3.2 kg/m2) healthy individuals. Subjects breathed room air or a mix of 5% CO2, 21% oxygen, balance nitrogen gas for 1 minute prior to initiation of 2 minutes of -60 mmHg LBNP and throughout the duration of LBNP. We allowed a 2-minute wash-out between trials. We measured middle cerebral artery velocity (MCAv) with transcranial Doppler ultrasound and continuous, non-invasive blood pressure (MAP) with a finger plethysmograph. We corrected MCAv for MAP and present it as cerebrovascular conductance index (CVCi). We also measure ventilation and gas exchange with a pneumotachometer and gas analyzer. Results: All measured variables were similar prior to the initiation of room air and 5% CO2 prebreathe ( p > 0.05). Inspired (1±1 vs. 36±1 mmHg) and end-tidal (38±4 vs. 47±3 mmHg) CO2 were greater during the 5% inspired CO2 trial ( p < 0.05, main effect of gas). LBNP caused an increase in heart rate, decrease in stroke volume, decrease in cardiac output, and an increase in total peripheral resistance ( p < 0.05, main effect of LBNP). These variables were similar regardless of inspiratory gas. MCAv (40±16 vs. 53±19 cm/s), MAP (94±10 vs. 99±11 mmHg), and CVCi (0.46±0.22 vs 0.56±0.24 cm/s/mmHg) were all greater during the 5% inspired CO2 trials ( p < 0.05, main effect of gas). Discussion: Breathing a mixture of 5% CO2 for 1 minute increased cerebral blood flow and blood pressure during a mimic of hypergravity stress. Despite technical challenges of integration into high-performance aircraft, increasing inspired CO2 could contribute to better tolerance to hypergravity stress. Funding was provided by the Air Force Offce of Scientific Research and King’s College London. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Can end-tidal CO2 measurement replace arterial partial CO2 in emergency department respiratory distress management?

ObjectiveTo assess the feasibility of using end-tidal carbon dioxide (EtCO2) as a non-invasive substitute for partial pressure of arterial carbon dioxide (PaCO2) in emergency department (ED) triage and follow-up, and to explore the potential of partial pressure of venous carbon dioxide (PvCO2) as an alternative to PaCO2. DesignProspective cross-sectional study. SettingTertiary university hospital. Patients or participants97 patients presenting with acute respiratory distress to the ED. InterventionsEtCO2, arterial blood gases, and venous blood gases measured at admission (0 min), 60 min, and 120 min. Main variables of interestCO2 levels. ResultsAmong 97 patients (mean age: 70.93 ± 9.6 years; 60.8% male), EtCO2 > 45 mmHg at admission showed strong positive correlations with PaCO2 and PvCO2 (r = 0.844, r = 0.803; p < 0.001, respectively). Significant positive correlation was observed between 60-min EtCO2 and PaCO2 (r = 0.729; p < 0.001). Strong correlation between PaCO2 and PvCO2 at 120 min when EtCO2 > 45 mmHg (r = 0.870; p < 0.001). EtCO2 was higher in hospitalized patients compared to discharged ones. ConclusionsEtCO2 appears promising as a substitute for PaCO2 in ED patients with acute respiratory distress within the initial two hours of treatment. Venous blood gas sampling offers a less invasive alternative to arterial sampling, facilitating simultaneous blood tests.

Does acute melatonin supplementation affect cerebrovascular reactivity in healthy young adults?

Melatonin receptors have been found in the cerebrovasculature in animal models, and melatonin has been shown to improve systemic vascular control. While there is a correlation between low melatonin production and cardiovascular disease, the effect of acute melatonin supplementation on the cerebrovasculature, and more specifically, cerebrovascular reactivity (CVR), is unknown. PURPOSE: To determine if acute melatonin supplementation alters CVR via CO2 rebreathing in healthy, young adults. Methods: 14 healthy young adults (Age 23.7±4.39, 7 females tested during the first 5 days of their menstrual cycle) participated in a familiarization visit followed by 2 experimental visits separated by ≥48hrs. Participants received a sublingual dose of either a placebo (PLA, mixture of mint extract and filtered water, to mimic taste of melatonin) or 5mg of melatonin (MEL, mint flavor) in a single-blind, randomized, crossover design. After ingestion, participants rested for 30 minutes prior to the experiment to allow for melatonin levels to reach peak concentration in the blood (Bartoli et al., 2013). After which, mean arterial pressure (MAP, mmHg, finger photoplethysmography), middle cerebral artery velocity (MCAv, cm/s, Transcranial Doppler), and end-tidal CO2 concentration (PetCO2, mmHg, Gas Analyzer) were measured continuously for 5 minutes of supine rest while breathing atmospheric air followed by a CO2 rebreathing challenge (CO2=3%, O2=40%, balanced N2) until the participant displayed a PetCO2 increase of ≥10mmHg. Cerebrovascular conductance index was calculated as CVCi = MCAv/MAP (cm/s/mmHg). CVR was calculated in absolute ΔMCAv/ΔPetCO2, ΔCVCi/ΔPetCO2, and percent change from resting values. Results: Data presented as change (Δ) from rest to CO2 rebreathing, as mean ± SD. All values were not different between treatments during rest. No value was significantly different between treatments when comparing Δ from rest to CO2 rebreathing (MCAv PLA Δ13.35±5.1 vs. MEL Δ11.62±6.03, p = 0.31, d = 0.28, MAP PLA Δ1.75±3.91 vs. MEL Δ-0.55±4.49, p = 0.20, d = 0.34, CVCi PLA Δ0.11±0.04 vs. MEL Δ0.11±0.05, p = 0.55, r = 0.16, CVRMCAv PLA Δ2.75±1.30 vs. MEL Δ3.54±2.57, p = 0.92, r = 0.03, %CVRMCAv PLA Δ18.41±7.07 vs. MEL Δ16.12±10.00, p = 0.36, r = 0.24, CVRCVCi PLA Δ0.02±0.03 vs. MEL Δ0.02±0.02, d = 0.28, p = 0.31, %CVRCVCi PLA Δ2.32±2.58 vs. MEL Δ1.52±1.83, d = 0.28, p = 0.31). CONCLUSION: Our results indicate that melatonin does not affect MCAv, CVCi, MAP, or CVR during rest or CO2 rebreathing. Reactivity was variable individually and did not trend in any direction when comparing PLA treatment to MEL treatment. Thus, melatonin supplementation does not improve cerebrovascular function indicating melatonin supplementation may have differential responses between the cerebral and peripheral vasculature in humans. This work was supported by a Robberson Research Grant provided by the University of Oklahoma graduate college. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Effects of Medetomidine-Butorphanol and Medetomidine-Buprenorphine on Oxidative Stress and Vital Parameters in Dogs Undergoing Ovariohysterectomy.

Oxidative stress (OS) is caused by an imbalance between the production of oxygen-containing free radicals and their elimination. General anesthesia increases the production of reactive oxygen species (ROS) and therefore causes oxidative stress. Our objective was to determine the effects of medetomidine-butorphanol (MEDBUT) and medetomidine-buprenorphine (MEDBUP) on oxidative stress and cardiorespiratory parameters in dogs undergoing ovariohysterectomy (OHE). Ten healthy female dogs were randomly assigned to two groups: the MEDBUT group (n = 5) received medetomidine and butorphanol, while the MEDBUP group (n = 5) received medetomidine and buprenorphine. OS was evaluated by measuring total antioxidant status (TAS), total oxidant status (TOS), and oxidative stress index (OSI) during five different time points (from the administration of anesthetic drugs to 2 h after surgery). The observed vital cardiorespiratory parameters included heart rate (HR), respiratory rate (fR), noninvasive systolic (SAP) and diastolic (DAP) arterial blood pressures, oxygen saturation (SpO2), end-tidal CO2 (EtCO2), and body temperature (BT). Cardiorespiratory parameters were altered at a significantly greater degree in animals sedated with MEDBUT (p < 0.05). The administration of medetomidine-butorphanol was more likely to increase OS parameters, while medetomidine-buprenorphine showed decreased levels of oxidative stress throughout the study.

Dynamic cerebral autoregulation is preserved during orthostasis and intrathoracic pressure regulation in healthy subjects: A pilot study.

Resistance breathing may restore cardiac output (CO) and cerebral blood flow (CBF) during hypovolemia. We assessed CBF and cerebral autoregulation (CA) during tilt, resistance breathing, and paced breathing in 10 healthy subjects. Blood velocities in the internal carotid artery (ICA), middle cerebral arteries (MCA, four subjects), and aorta were measured by Doppler ultrasound in 30° and 60° semi-recumbent positions. ICA blood flow and CO were calculated. Arterial blood pressure (ABP, Finometer), and end-tidal CO2 (ETCO2) were recorded. ICA blood flow response was assessed by mixed-models regression analysis. The synchronization index (SI) for the variable pairs ABP-ICA blood velocity, ABP-MCA velocities in 0.005-0.08 Hz frequency interval was calculated as a measure of CA. Passive tilting from 30° to 60° resulted in 12% decrease in CO (p = 0.001); ICA blood flow tended to fall (p = 0.04); Resistance breathing restored CO and ICA blood flow despite a 10% ETCO2 drop. ETCO2 and CO contributed to ICA blood flow variance (adjusted R2: 0.9, p < 0.0001). The median SI was low (<0.2) indicating intact CA, confirmed by surrogate date testing. The peak SI was transiently elevated during resistance breathing in the 60° position. Resistance breathing may transiently reduce CA efficiency. Paced breathing did not restore CO or ICA blood flow.

Expanding safety boundaries in pediatric robotic-assisted laparoscopic surgery: are we protecting our children?

Little is known about the effects of CO2 insufflation (CDI) on cerebral oxygen saturation (CrSO2) during laparoscopy in the pediatric population. In children undergoing robotic-assisted laparoscopic pyeloplasty (RALP), we prospectively assessed the effects of CDI using standard monitoring and cerebral near-infrared spectroscopy (NIRS). We also explored whether a correlation existed between CrSO2 and parameters known to affect cerebral blood flow. Between January 2021 and September 2023, a cohort of consecutive children older than 2years underwent RALP at Necker-Enfants Malades Hospital in Paris. A ventilation protocol aimed to prevent hypercarbia was implemented. Data collected included standard monitoring parameters and CrSO2 by NIRS. Thirty patients (16 females), mean age 5.5 ± 3.9 (2.0-9.5) years, were included. Twenty-three patients underwent a retroperitoneal approach. The mean baseline CrSO2 value was 83.0 ± 9.8. Mean CrSO2 decreased during progressive CDI, never below baseline values, while standard-monitoring parameters did not significantly change. No significant correlation was detected between CrSO2 and end tidal CO2, or between CrSO2 and mean arterial pressure, at any operative time. During RALP, a gradual CDI doesn't cause pathological derangements of CrSO2. The lack of correlation between CrSO2 and standard parameters affecting cerebral blood flow suggests the likely presence of cerebral autoregulation in our population.

Phenylephrine alters phase synchronization between cerebral blood velocity and blood pressure in ME/CFS with orthostatic intolerance.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) with orthostatic intolerance (OI) is characterized by neurocognitive deficits perhaps related to upright hypocapnia and loss of cerebral autoregulation (CA). We performed N-back neurocognition testing and calculated the phase synchronization index (PhSI) between arterial pressure (AP) and cerebral blood velocity (CBV) as a time-dependent measurement of cerebral autoregulation in 11 control (mean age = 24.1 yr) and 15 patients with ME/CFS (mean age = 21.8 yr). All patients with ME/CFS had postural tachycardia syndrome (POTS). A 10-min 60° head-up tilt (HUT) significantly increased heart rate (109.4 ± 3.9 vs. 77.2 ± 1.6 beats/min, P < 0.05) and respiratory rate (20.9 ± 1.7 vs. 14.2 ± 1.2 breaths/min, P < 0.05) and decreased end-tidal CO2 (ETCO2; 33.9 ± 1.1 vs. 42.8 ± 1.2 Torr, P < 0.05) in ME/CFS versus control. In ME/CFS, HUT significantly decreased CBV compared with control (-22.5% vs. -8.7%, P < 0.005). To mitigate the orthostatic CBV reduction, we administered supplemental CO2, phenylephrine, and acetazolamide and performed N-back testing supine and during HUT. Only phenylephrine corrected the orthostatic decrease in neurocognition by reverting % correct n = 4 N-back during HUT in ME/CFS similar to control (ME/CFS = 38.5 ± 5.5 vs. ME/CFS + PE= 65.6 ± 5.7 vs. Control 56.9 ± 7.5). HUT in ME/CFS resulted in increased PhSI values indicating decreased CA. Although CO2 and acetazolamide had no effect on PhSI in ME/CFS, phenylephrine caused a significant reduction in PhSI (ME/CFS = 0.80 ± 0.03 vs. ME/CFS + PE= 0.69 ± 0.04, P < 0.05) and improved cerebral autoregulation. Thus, PE improved neurocognitive function in patients with ME/CFS, perhaps related to improved neurovascular coupling, cerebral autoregulation, and maintenance of CBV.NEW & NOTEWORTHY We evaluated cognitive function before and after CO2, acetazolamide, and phenylephrine, which mitigate orthostatic reductions in cerebral blood velocity. Neither CO2 nor acetazolamide affected N-back testing (% correct answers) during an orthostatic challenge. Only phenylephrine improved upright N-back performance in ME/CFS, as it both blocked hyperventilation and increased CO2 significantly compared with those untreated. And only phenylephrine resulted in improved PSI values in both ME/CFS and control while upright, suggesting improved cerebral autoregulation.

Diagnostic utility of capnography in emergency department triage for screening acidemia: a pilot study

BackgroundCapnography is a quantitative and reliable method of determining the ventilatory status of patients. We describe the test characteristics of capnography obtained during Emergency Department triage for screening acidemia.ResultsWe performed an observational, pilot study of adult patients presenting to Emergency Department (ED) triage. The primary outcome was acidemia, as determined by the basic metabolic panel and/or blood gas during the ED visit. Secondary outcomes include comparison of estimated and measured respiratory rates (RR), relationships between end-tidal CO2 (EtCO2) and venous partial pressure of CO2, admission disposition, in-hospital mortality during admission, and capnogram waveform analysis. A total of 100 adult ED encounters were included in the study and acidemia (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\left[HC{O}_{3}^{-}\\right]\\le 22 \ ext{mEq/L}$$\\end{document} or \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ pH< 7.35$$\\end{document}) was identified in 28 patients. The measured respiratory rate (20.3 ± 6.4 breaths/min) was significantly different from the estimated rate (18.4 ± 1.6 breaths/min), and its area under the receiver operating curve (c-statistic) to predict acidemia was only 0.60 (95% CI 0.51–0.75, p = 0.03). A low end-tidal CO2 (EtCO2 < 32 mmHg) had positive (LR+) and negative (LR−) likelihood ratios of 4.68 (95% CI 2.59–8.45) and 0.34 (95% CI 0.19–0.61) for acidemia, respectively—corresponding to sensitivity 71.4% (95% CI 51.3–86.8) and specificity 84.7% (95% CI 74.3–92.1). The c-statistic for EtCO2 was 0.849 (95% CI 0.76–0.94, p = 0.00). Waveform analysis further revealed characteristically abnormal capnograms that were associated with underlying pathophysiology.ConclusionsCapnography is a quantitative method of screening acidemia in patients and can be implemented feasibly in Emergency Department triage as an adjunct to vital signs. While it was shown to have only modest ability to predict acidemia, triage capnography has wide generalizability to screen other life-threatening disease processes such as sepsis or can serve as an early indicator of clinical deterioration.

Age-specific sex-differences in cerebral blood flow velocity in relation to haemoglobin levels.

Cerebral blood flow (CBF) declines with age and abnormalities in CBF are associated with age-related cerebrovascular disease and neurodegeneration. Women have higher CBF than men, although this sex-difference diminishes to some extent with age in healthy subjects. The physiological drivers of these age/sex differences are uncertain, but might be secondary to age and sex-differences in haemoglobin (Hb) level. Hb levels are inversely correlated with CBF, are lower in women, and decline with age in men, but the interrelations between these factors have not been explored systematically either in healthy subjects or across the full age-range in patients with vascular risk factors. We aimed to determine the age-specific interrelations between sex, Hb, and CBF velocity in a large cohort of patients with cerebrovascular disease. In patients with a recent transient ischaemic attack or minor stroke (Oxford Vascular Study) and no ipsilateral or contralateral stenosis of the carotid or intracranial arteries, we related peak-systolic velocity (PSV) and other parameters on transcranial Doppler ultrasound (TCD) of the middle cerebral artery to sex, age, Hb and vascular risk factors. Of 958 eligible subjects (mean age/SD = 68.04/14.26, 53.2% male), younger women (age < 55 years) had higher CBF velocities than men (mean sex difference in PSV at age < 55 years = 16.31 cm/s; p < 0.001), but this difference declined with age (interaction p < 0.001), such that it was no longer significant at age 75-84 (∆PSV = 3.26 cm/s; p = 0.12) and was reversed at age ⩾ 85 (∆PSV = -7.42 cm/s; p = 0.05). These changes mirrored trends in levels of Hb, which were higher in men at age < 55 (∆Hb = 1.92 g/dL; p < 0.001), but steadily decreased with age in men but not in women (interaction p < 0.001), with no residual sex-difference at age ⩾ 85 (∆Hb = 0.12 g/dL; p = 0.70). There was an inverse correlation between Hb and PSV in both women and men (both p ⩽ 0.01), and the sex-difference in PSV at age < 55 was substantially diminished after adjustment for Hb (∆PSV = 6.92; p = 0.036; ∆PSV = 5.92, p = 0.13 with further adjustment for end-tidal CO2). In contrast, the sex difference in PSV was unaffected by adjustment for systolic and diastolic blood pressure, heart rate, and vascular risk factors (history of hypertension, diabetes, hyperlipidaemia and smoking). CBF velocity is strongly correlated with Hb level at all ages, and sex-differences in CBF velocity appear to be explained in major part by age-related sex-differences in Hb.

Oxygenation and ventilation during prolonged experimental cardiopulmonary resuscitation with either continuous or 30:2 compression-to-ventilation ratios together with 10 cmH20 positive end-expiratory pressure

BackgroundIn refractory out-of-hospital cardiac arrest, the patient is commonly transported to hospital with mechanical continuous chest compressions (CCC). Limited data are available on the optimal ventilation strategy. Accordingly, we compared arterial oxygenation and haemodynamics during manual asynchronous continuous ventilation and compressions with a 30:2 compression-to-ventilation ratio together with the use of 10 cmH2O positive end-expiratory pressure (PEEP).MethodsIntubated and anaesthetized landrace pigs with electrically induced ventricular fibrillation were left untreated for 5 min (n = 31, weight ca. 55 kg), after which they were randomized to either the CCC group or the 30:2 group with the the LUCAS® 2 piston device and bag-valve ventilation with 100% oxygen targeting a tidal volume of 8 ml/kg with a PEEP of 10 cmH2O for 35 min. Arterial blood samples were analysed every 5 min, vital signs, near-infrared spectroscopy and electrical impedance tomography (EIT) were measured continuously, and post-mortem CT scans of the lungs were obtained.ResultsThe arterial blood values (median + interquartile range) at the 30-min time point were as follows: PaO2: 180 (86–302) mmHg for the 30:2 group; 70 (49–358) mmHg for the CCC group; PaCO2: 41 (29–53) mmHg for the 30:2 group; 44 (21–67) mmHg for the CCC group; and lactate: 12.8 (10.4–15.5) mmol/l for the 30:2 group; 14.7 (11.8–16.1) mmol/l for the CCC group. The differences were not statistically significant. In linear mixed models, there were no significant differences between the groups. The mean arterial pressures from the femoral artery, end-tidal CO2, distributions of ventilation from EIT and mean aeration of lung tissue in post-mortem CTs were similar between the groups. Eight pneumothoraces occurred in the CCC group and 2 in the 30:2 group, a statistically significant difference (p = 0.04).ConclusionsThe 30:2 and CCC protocols with a PEEP of 10 cmH2O resulted in similar gas exchange and vital sign outcomes in an experimental model of prolonged cardiac arrest with mechanical compressions, but the CCC protocol resulted in more post-mortem pneumothoraces.

The effects of acute normobaric hypoxia on standing balance while dual-tasking with and without visual input.

To investigate the influence of acute normobaric hypoxia on standing balance under single and dual-task conditions, both with and without visual input. 20 participants (7 female, 20-31years old) stood on a force plate for 16, 90-s trials across four balance conditions: single-task (quiet stance) or dual-task (auditory Stroop test), with eyes open or closed. Trials were divided into four oxygen conditions where the fraction of inspired oxygen (FIO2) was manipulated (normoxia: 0.21 and normobaric hypoxia: 0.16, 0.145 and 0.13 FIO2) to simulate altitudes of 1100, 3,400, 4300, and 5200m. Participants breathed each FIO2 for ~ 3min before testing, which lasted an additional 7-8min per oxygen condition. Cardiorespiratory measures included heart rate, peripheral blood oxygen saturation, and pressure of end tidal (PET) CO2 and O2. Center of pressure measures included total path length, 95% ellipse area, and anteroposterior and mediolateral velocity. Auditory Stroop test performance was measured as response accuracy and latency. Significant decreases in oxygen saturation and PETO2, and increased heart rate were observed between normoxia and normobaric hypoxia (P < 0.0001). Total path length was higher at 0.13 compared to 0.21 FIO2 for the eyes closed no Stoop test condition (P = 0.0197). No other significant differences were observed. These findings suggest that acute normobaric hypoxia has a minimal impact on standing balance and does not influence auditory Stroop test or dual-task performance. Further investigation with longer exposure is required to understand the impact and time course of normobaric hypoxia on standing balance.

1 Sex Differences in Middle Cerebral Artery Velocity in Patients with Persistent Post-Concussion Convergence Insufficiency (PPCS-CI)

OBJECTIVES/GOALS: The objective of this study is to investigate the neurophysiological mechanism of vision therapy in male and female adolescents with persistent post-concussion convergence insufficiency (PPCS-CI). This study may improve diagnostics and inform more effective personalized point of care treatment strategies to remediate symptoms. METHODS/STUDY POPULATION: Participants (ages 11-25) were diagnosed with PPCS by a physician, CI was diagnosed by an optometrist and OBVAT was performed by certified therapists. Patients with PPCS-CI were randomly assigned to a therapy type (immediate therapy or natural recovery). Hemodynamic measures were examined in patients with PPCS-CI at baseline (1-3 months post-concussion), and post OBVAT to evaluate recovery outcomes. Non-invasive techniques were used to measure middle cerebral artery velocity (MCAv), blood pressure, heart rate, and end-tidal CO2 at rest and during objective symmetrical convergence step eye movements. Functional magnetic resonance imaging (fMRI) was acquired during convergence step eye movement experiments contrasted to sustained fixation and resting state data collection. RESULTS/ANTICIPATED RESULTS: To investigate the neural mechanism of OBVAT, eye movements, fMRI and physiological measures were collected in 8 patients with PPCS-CI (4 men and 4 women). Results show an 10% decrease in the MCA during 4-degree symmetrical convergent eye movement responses in males post-OBVAT and a 19% increase in MCA during convergent eye movement responses in females. Furthermore, there was a group level activation of the frontal eye fields, which improves post-OBVAT. The beta weights in the left frontal eye fields show a trending decrease in male patients post-OBVAT and trending increase in females. Males had a decrease in MCAv post OBVAT (baseline 83.6 ± 7.5 cm/sec &amp; 75.7 ± 12.5 cm/sec post-OBVAT), while females show a significant increase post-OBVAT (baseline 53.77 ± 5.2 cm/sec &amp; post-OBVAT 65.13 cm/sec ± 12.5). DISCUSSION/SIGNIFICANCE: This initial pilot demonstrates there may be different underlying pathophysiological outcomes associated with a concussion dependent on sex. This work may have direct implications on treatment strategies for male and female adolescent patients with PPCS-CI.

Application of End-Tidal CO2 Monitoring to ICU Management.

Waveform capnography is a noninvasive measurement of ventilation and perfusion commonly employed in the prehospital setting. It is easy to apply, and modern cardiac monitors are equipped with the necessary ports and capability to display results. Despite its ease of use, end-tidal CO2 monitoring has not yet achieved widespread adoption within the hospital setting. It is routinely used in the emergency department and by anesthesiologists, but its application could support ICU management in critically ill patients. Its use is routinely supported by multiple professional societies, and it has been recommended as a requirement in all cardiac arrests. Careful analysis of the waveform and expired carbon dioxide can guide therapy for patients experiencing respiratory emergencies, hemodynamic compromise, metabolic acidosis, and shock due to trauma, hypovolemia, or sepsis. Use of capnography throughout the hospital could improve patient outcomes and prevent unidentified deterioration.

A new method of pulse control in cardiopulmonary resuscitation; Continuous femoral pulse check

ObjectivesThe reliability of manual pulse checks has been questioned but is still recommended in cardiopulmonary resuscitation (CPR) guidelines. The aim is to compare the 10-s carotid pulse check (CPC) between heart massage cycles with the continuous femoral pulse check (CoFe PuC) in CPR, and to propose a better location to shorten the interruption times for pulse check. MethodsA prospective study was conducted on 117 Non-traumatic CPR patients between January 2020 and January 2022. A total of 702 dependent pulse measurements were executed, where carotid and femoral pulses were simultaneously assessed. Cardiac ultrasound, end-tidal CO2, saturation, respiration, and blood pressure were employed for pulse validation. ResultsThe decision time for determining the presence of a pulse in the last cycle of CPR was 3.03 ± 1.26 s for CoFe PuC, significantly shorter than the 10.31 ± 5.24 s for CPC. CoFe PuC predicted the absence of pulse with 74% sensitivity and 88% specificity, while CPC predicted the absence of pulse with 91% sensitivity and 61% specificity. ConclusionCoFe PuC provides much earlier and more effective information about the pulse than CPC. This shortens the interruption times in CPR. CoFe PuC should be recommended as a new and useful method in CPR guidelines.

A multimodal stacked ensemble model for cardiac output prediction utilizing cardiorespiratory interactions during general anesthesia

This study examined the possibility of estimating cardiac output (CO) using a multimodal stacking model that utilizes cardiopulmonary interactions during general anesthesia and outlined a retrospective application of machine learning regression model to a pre-collected dataset. The data of 469 adult patients (obtained from VitalDB) with normal pulmonary function tests who underwent general anesthesia were analyzed. The hemodynamic data in this study included non-invasive blood pressure, plethysmographic heart rate, and SpO2. CO was recorded using Vigileo and EV1000 (pulse contour technique devices). Respiratory data included mechanical ventilation parameters and end-tidal CO2 levels. A generalized linear regression model was used as the metalearner for the multimodal stacking ensemble method. Random forest, generalized linear regression, gradient boosting machine, and XGBoost were used as base learners. A Bland–Altman plot revealed that the multimodal stacked ensemble model for CO prediction from 327 patients had a bias of − 0.001 L/min and − 0.271% when calculating the percentage of difference using the EV1000 device. Agreement of model CO prediction and measured Vigileo CO in 142 patients reported a bias of − 0.01 and − 0.333%. Overall, this model predicts CO compared to data obtained by the pulse contour technique CO monitors with good agreement.

Colorimetric CO2 Detector to Improve Effective Mask Ventilations in Very Preterm Infants: A Pilot Randomized Controlled Study

Introduction: End-tidal CO2 (ETCO2) detector is currently recommended for confirmation of endotracheal tube placement during neonatal resuscitation. Whether it is feasible to use ETCO2 detectors during mask ventilation to reduce risk of bradycardia and desaturations, which are associated with increased risk of death in preterm babies, is unknown. Methods: This is a pilot randomized controlled trial (NCT04287907) involving newborns 24 + 0/7 to 32 + 0/7 weeks gestation who required mask ventilation at birth. Infants were randomized into groups with or without colorimetric ETCO2 detectors. Combined duration of any bradycardia (<100 bpm) and time below prespecified target oxygen saturation (SpO2) as measured by pulse oximetry were compared. Results: Fifty participants were randomized, 47 with outcomes analysed (2 incomplete data, 1 postnatal diagnosis of trachea-oesophageal fistula). Mean gestational age and birthweight were 28.5 ± 1.9 versus 29.4 ± 1.6 weeks (p = 0.1) and 1,252.7 ± 409.7 g versus 1,334.6 ± 369.1 g (p = 0.5) in the intervention and control arm, respectively. Mean combined duration of bradycardia and desaturation was 276.7 ± 197.7 s (intervention) and 322.7 ± 277.7 s (control) (p = 0.6). Proportion of participants with any bradycardia or desaturation at 5 min were 38.1% (intervention) and 56.5% (control) (p = 0.2). No chest compressions, epinephrine administration, or death occurred in the delivery room. Conclusion: This pilot study demonstrates the feasibility of a trial to evaluate colorimetric ETCO2 detectors during mask ventilation of very preterm infants to reduce bradycardia and low SpO2. Further assessment with a larger population will be required to determine if ETCO2 detector usage at resuscitation reduces risk of adverse outcomes, including death and disability, in very preterm infants.

Cardiorespiratory Effects of Yogic Versus Slow Breathing in Individuals with a Spinal Cord Injury: An Exploratory Cohort Study.

Background: An intricate physiological and pathophysiological connection exists between the heart and lungs, which is especially important in individuals with spinal cord injury (SCI). While an exercise intervention may seem the best approach to leverage this relationship, the prior work has shown that, despite numerous health benefits, regular exercise training does not improve cardiorespiratory control in individuals with SCI. Breath training presents an alternative intervention that is uniquely accessible, with yogic breathing directly engaging linked fluctuations in respiration and cardiovascular control. In addition, there is evidence across a range of populations that regular yogic breathing reduces cardiovascular disease risk. It is possible that the chronic decrease in breathing frequency associated with regular yogic breathing, rather than the specific yogic breathing techniques themselves, is the primary contributor to the observed risk reduction. Methods: Therefore, in 12 individuals with traumatic SCI from C4 to T8, the authors compared Unpaced and conventional 0.083 Hz (Slow) paced breathing with various yogic breathing techniques including: (1) inspiratory-expiratory breath holds (i.e., Kumbhaka or "Box Breathing"), (2) extended exhalation (1:2 duty cycle), and (3) expiratory resistance via throat constriction (i.e., Ujjayi). Beat-to-beat heart rate and blood pressure were measured as well as end-tidal CO2 and O2 saturation were measured. Statistical analysis was performed using a one-way repeated-measures analysis of variance with post hoc pairwise t tests corrected for multiple comparisons. Results: As expected, all slow breathing patterns markedly increased respiratory sinus arrhythmia (RSA) compared with Unpaced in all (n = 12) individuals. More importantly, Ujjayi breathing appeared to improve ventilatory efficiency over Unpaced breathing in individuals with SCI by increasing O2 saturation (97.6% vs. 96.1%; p = 0.042) and tended to decrease end-tidal CO2 (32 mmHg vs. 35 mmHg; p = 0.08). While other slow breathing patterns demonstrated similar effects, only Ujjayi improved RSA while increasing heart rate and improving ventilatory efficiency. Conclusions: Hence, slow breathing per se can result in important cardiorespiratory changes, but the yogic breathing practice of Ujjayi, with glottic throat resistance, may hold the greatest promise for improving cardiorespiratory control in individuals with SCI (CTR ID No. NCT05480618).

Effects of the prone position on gas exchange and ventilatory mechanics and their correlations with mechanical power in burn patients with ARDS

Background Prone position has many documented benefits on severe ARDS patients especially on mortality. The benefits in ARDS secondary to severe burns have not been fully documented. Aim To quantify the effects of prone positioning on gas exchange, ventilatory mechanics and their correlations with mechanical power in burn subjects with ARDS. Methods Cross-sectional observational analytical study that took place between January 2023 and October 2023 in Burns ICU in Brazil on subjects with moderate to severe ARDS ventilated with the volume controlled mode. Data were collected in the first prone positioning lasting 24 hours in the first 30 minutes after changing position and 30 minutes before returning to the supine position. The parameters of the components of mechanical ventilation and mechanical power calculated by the Gatinoni’s formula (respiratory rate, tidal volume, driving pressure, PEEP, peak and plateau pressures) were collected to evaluate ventilatory mechanics, and the values of the FiO2, PaO2, PaO2/FiO2 ratio, SpO2, EtCO2, PaCO2, PaCO2 - EtCO2 gradient to assess gas exchange. Mean, minimum and maximum values, 1st and 3rd quartiles, median and standard deviation are calculated. To compare the results obtained at the two evaluation moments, the student’s t-test for dependent samples and non-parametric Wilcoxon tests were considered. To evaluate the association between the variation between the two moments of each variable, and the variation in mechanical power, the Pearson correlation coefficient was calculated. The normality of the variables was assessed using the Jarque-Béra test. P values &lt;0.05 indicated statistical significance. Results Except for EtCO2 (P 0.939) and PaCO2 (P 0.391) all other variables presented statistical significance in relation to their variations with reduction in FiO2 (P &lt;0.001), reduction in PaCO2 - EtCO2 gradient (P 0.011), and increases in PaO2 (P 0.008), PaO2/FiO2 (P &lt;0.001), SpO2 (P 0.004). In the analysis of variables, reduction in respiratory rate (P 0.142), VT (P 0.385), peak pressure (P 0.085), plateau pressure (P 0.009), PEEP (P 0.032), driving pressure (P 0.083), elastance (P 0.180), mechanical power (P &lt; 0.001) with increase static compliance (P 0.414) and resistance pressure (P 0.443). Among the ventilatory mechanics variables, only the reductions in plateau pressure, PEEP, and mechanical power showed statistical significance. Conclusion The prone position in burns induced ARDS improved oxygenation and reduced arterial partial pressure to end tidal CO2 gradient, furthermore, reducing plateau pressures and PEEP, which in turn reduced mechanical power. Keywords: mechanical power, burns, ARDS, prone position