End-tidal Partial Pressure Research Articles

Factors Influencing Regional Cerebral Oxygen Saturation during One-lung Ventilation in Thoracic Surgery.

Objective To identify factors influencing regional cerebral oxygen saturation (rScO2) during one-lung ventilation (OLV) in thoracic surgery. Methods Totally 33 patients with an ASA physical status of 1-3 scheduled for elective thoracic surgery with one-lung ventilation under general anesthesia were recruited. After anesthesia was induced with propofol,fentanyl/sufentanil,and rocuronium. All patients received balanced anesthesia using sevoflurane. During OLV,volume-controlled ventilation was used with a tidal volume of 6-7 ml/kg and an inspiration:expiration ratio of 1:1.5. The ventilator frequency was adjusted with a target end-tidal carbon dioxide partial pressure (PetCO2) between 35 mmHg and 45 mmHg. During the anesthesia,patients were maintained at a pulse oxygen saturation (SpO2) of>90%,systolic blood pressure (SBP) of>90 mmHg (or reducing no more than 30% of the basic values),heart rate (HR) of>50 beat/min,and hemoglobin concentration of>90 g/L. Changes of rScO2 were monitored with FORESIGHT probes by specialized researchers. Patients were classified into low rScO2 (L-rScO2) group (n=10) or high rScO2 (H-rScO2)group(n=23) according to whether the lowest intraoperative rScO2 was under 65% or 15% lower than the baseline values. We compared gender,age,body mass index (BMI),intraoperative hemoglobin level,and the values of peak airway pressure (Ppeak),SBP,PetCO2,and SpO2 when rScO2 dropped to the lowest level between these two groups. Results Statistically higher Ppeak and lower SBP were noted in the L-rScO2 group compared with H-rScO2 group (P=0.028,P=0.046). SpO2 was lower in the L-rScO2 group compared with H-rScO2 group,but the difference was not statistically significant (P=0.421). There was also no significant difference between the two groups according to age,BMI,SpO2,PetCO2,or hemoglobin level. Ppeak appeared to be a risk factor for rScO2 reduction during OLV,as shown by unconditioned Logistic regression analysis. Conclusion During OLV in thoracic surgery,Ppeak is a risk factor for rScO2 reduction.

Effect of High-Flow Nasal Cannula on Expiratory Pressure and Ventilation in Infant, Pediatric, and Adult Models.

Heated and humidified high-flow nasal cannula (HFNC) is a widely used form of respiratory support; however, data regarding optimal flows for a given patient size or disease state are lacking. A comprehensive study of the physiologic effects of HFNC is needed to better understand the mechanisms of action. The objective of the current study was to quantify the effect of HFNC settings in age-specific, anatomically correct nasal airways and spontaneously breathing lung models. We hypothesized that there is an effect of flow on pressure and ventilation. Three-dimensionally printed upper airway models of a preterm neonate, term neonate, toddler, small child, and adult were affixed to the ASL 5000 test lung to simulate spontaneous breathing with age-appropriate normal ventilation parameters. CO2 was introduced to simulate profound hypercapneic respiratory failure with an end-tidal partial pressure of carbon dioxide (PETCO2 ) of 90 ± 1 mm Hg. Two commercially available HFNC systems were applied to the airway models, and PEEP, inspired CO2, and exhaled CO2 (PETCO2 ) were recorded for 6 min across a range of flow. Increasing HFNC flow provided a non-linear increase in PEEP in closed-mouth models, with maximum tested flows generating 6 cm H2O in the preterm neonate to 20 cm H2O in the small child. Importantly, PEEP decreased by approximately 50% in open-mouth models. Increasing HFNC flow improved expiratory CO2 elimination to a certain point, above which continued increases in flow had minimal additional effect. This change point ranged from 4 L/min in the preterm neonate to 10 L/min in the small child. These findings may help clinicians understand the effects of HFNC at different settings and may inform management guidelines for patients with respiratory failure.

Hypoxic, Hypercapnic, and Hyperoxic Responses of the Optic Nerve Head and Subfoveal Choroid Blood Flow in Healthy Humans

To investigate the impact of different gas mixtures (hyperoxia, hypoxia, and hypercapnia) on the optic nerve head (ONH) and choroidal (Ch) hemodynamics. Twenty-three healthy subjects (28 ± 6 years) took part in the study. Variations in inspired oxygen and carbon dioxide fraction were produced by a gas mixing device. Arterial oxygen saturation (SpO2) was measured continuously using a transcutaneous sensor and end-tidal carbon dioxide partial pressure by capnography. The experiment comprised three successive periods: 3-minute baseline (room air breathing), 15-minute gas mixture inhalation (normocapnic hypoxia, hypercapnia, or hyperoxia), and 15-minute recovery (room air breathing). Laser Doppler flowmeter parameters-velocity (VEL), volume (VOL), and flow (BF) of red blood cells-were measured. Two-way ANOVAs were performed for statistical analysis. In response to hyperoxia, ONHBF significantly decreased by -18% ± 6% (P = 0.04) from baseline, due to significant changes in VEL (-12% ± 3% P = 0.0002). During hypoxia at 85% SpO2, ONH VEL increased by +12% ± 3% (P = 0.0009), whereas VOL and BF did not change significantly. ChBF significantly increased by +7% ± 2% (P = 0.004) in response to hypoxia, due to significant changes in VEL +5% ± 2% (P = 0.03). Both Ch and ONHBFs did not vary significantly in response to hypercapnia. The magnitude of the blood flow response is the most significant during hyperoxia for ONH and hypoxia for ChBF. For ONHBF, a 37% difference between hyperoxia and hypoxia can be useful when vasoreactivity to O2 will be tested in patients.

The Effects of Hyperoxia on Sea-Level Exercise Performance, Training, and Recovery: A Meta-Analysis.

Acute exercise performance can be limited by arterial hypoxemia, such that hyperoxia may be an ergogenic aid by increasing tissue oxygen availability. Hyperoxia during a single bout of exercise performance has been examined using many test modalities, including time trials (TTs), time to exhaustion (TTE), graded exercise tests (GXTs), and dynamic muscle function tests. Hyperoxia has also been used as a long-term training stimulus or a recovery intervention between bouts of exercise. However, due to the methodological differences in fraction of inspired oxygen (FiO2), exercise type, training regime, or recovery protocols, a firm consensus on the effectiveness of hyperoxia as an ergogenic aid for exercise training or recovery remains unclear. The aims of this study were to (1) determine the efficacy of hyperoxia as an ergogenic aid for exercise performance, training stimulus, and recovery before subsequent exercise; and (2) determine if a dose-response exists between FiO2 and exercise performance improvements. The PubMed, Web of Science, and SPORTDiscus databases were searched for original published articles up to and including 8 September 2017, using appropriate first- and second-order search terms. English-language, peer-reviewed, full-text manuscripts using human participants were reviewed using the process identified in the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement. Data for the following variables were obtained by at least two of the authors: FiO2, wash-in time for gas, exercise performance modality, heart rate, cardiac output, stroke volume, oxygen saturation, arterial and/or capillary lactate, hemoglobin concentration, hematocrit, arterial pH, arterial oxygen content, arterial partial pressure of oxygen and carbon dioxide, consumption of oxygen and carbon dioxide, minute ventilation, tidal volume, respiratory frequency, ratings of perceived exertion of breathing and exercise, and end-tidal oxygen and carbon dioxide partial pressures. Data were grouped into type of intervention (acute exercise, recovery, and training), and performance data were grouped into type of exercise (TTs, TTE, GXTs, dynamic muscle function), recovery, and training in hyperoxia. Hedges' g effect sizes and 95% confidence intervals were calculated. Separate Pearson's correlations were performed comparing the effect size of performance versus FiO2, along with the effect size of arterial content of oxygen, arterial partial pressure of oxygen, and oxygen saturation. Fifty-one manuscripts were reviewed. The most common FiO2 for acute exercise was 1.00, with GXTs the most investigated exercise modality. Hyperoxia had a large effect improving TTE (g=0.89), and small-to-moderate effects increasing TTs (g=0.56), GXTs (g=0.40), and dynamic muscle function performance (g=0.28). An FiO2≥0.30 was sufficient to increase general exercise performance to a small effect or higher; a moderate positive correlation (r=0.47-0.63) existed between performance improvement of TTs, TTE, and dynamic muscle function tests and FiO2, but not GXTs (r=0.06). Exercise training and recovery supplemented with hyperoxia trended towards a large and small ergogenic effect, respectively, but the large variability and limited amount of research on these topics prevented a definitive conclusion. Acute exercise performance is increased with hyperoxia. An FiO2≥0.30 appears to be beneficial for performance, with a higher FiO2 being correlated to greater performance improvement in TTs, TTE, and dynamic muscle function tests. Exercise training and recovery supplemented with hyperoxic gas appears to have a beneficial effect on subsequent exercise performance, but small sample size and wide disparity in experimental protocols preclude definitive conclusions.

Application of the Novel Ventilation Mode FLow-Controlled EXpiration (FLEX): A Crossover Proof-of-Principle Study in Lung-Healthy Patients.

Traditionally, mechanical ventilation is achieved via active lung inflation during inspiration and passive lung emptying during expiration. By contrast, the novel FLEX (FLow-controlled EXpiration) ventilator mode actively decreases the rate of lung emptying. We investigated whether FLEX can be used during intraoperative mechanical ventilation of lung-healthy patients. In 30 adult patients scheduled for neurosurgical procedures, we studied respiratory system mechanics, regional ventilation, oxygenation, and hemodynamics during ventilation with and without FLEX at positive end-expiratory pressure (PEEP) of 5 and 7 cm H2O. The FLEX system was integrated into the expiratory limb and modified the expiratory flow profile by continuously changing expiratory resistance according to a computer-controlled algorithm. Mean airway pressure increased with PEEP by 1.9 cm H2O and with FLEX by 1 cm H2O (all P < .001). The expiratory peak flow was 42% lower with FLEX than without FLEX (P < .001). FLEX caused significant shifts in aeration from ventral to the dorsal lung regions. Respiratory mechanics, end-tidal carbon dioxide partial pressure, oxygenation, and hemodynamics were independent from FLEX and PEEP. We observed no critical incidents or FLEX malfunctions in any measurement that would have required an intervention or termination of the FLEX mode. FLEX can be used in lung-healthy patients who are mechanically ventilated during general anesthesia. FLEX improves the homogeneous distribution of ventilation in the lungs.

Effect of hypocapnia on the sensitivity of hyperthermic hyperventilation and the cerebrovascular response in resting heated humans.

Elevating core temperature at rest causes increases in minute ventilation (V̇e), which lead to reductions in both arterial CO2 partial pressure (hypocapnia) and cerebral blood flow. We tested the hypothesis that in resting heated humans this hypocapnia diminishes the ventilatory sensitivity to rising core temperature but does not explain a large portion of the decrease in cerebral blood flow. Fourteen healthy men were passively heated using hot-water immersion (41°C) combined with a water-perfused suit, which caused esophageal temperature (Tes) to reach 39°C. During heating in two separate trials, end-tidal CO2 partial pressure decreased from the level before heating (39.4 ± 2.0 mmHg) to the end of heating (30.5 ± 6.3 mmHg) ( P = 0.005) in the Control trial. This decrease was prevented by breathing CO2-enriched air throughout the heating such that end-tidal CO2 partial pressure did not differ between the beginning (39.8 ± 1.5 mmHg) and end (40.9 ± 2.7 mmHg) of heating ( P = 1.00). The sensitivity to rising Tes (i.e., slope of the Tes - V̇E relation) did not differ between the Control and CO2-breathing trials (37.1 ± 43.1 vs. 16.5 ± 11.1 l·min-1·°C-1, P = 0.31). In both trials, middle cerebral artery blood velocity (MCAV) decreased early during heating (all P < 0.01), despite the absence of hyperventilation-induced hypocapnia. CO2 breathing increased MCAV relative to Control at the end of heating ( P = 0.005) and explained 36.6% of the heat-induced reduction in MCAV. These results indicate that during passive heating at rest ventilatory sensitivity to rising core temperature is not suppressed by hypocapnia and that most of the decrease in cerebral blood flow occurs independently of hypocapnia. NEW & NOTEWORTHY Hyperthermia causes hyperventilation and concomitant hypocapnia and cerebral hypoperfusion. The last may underlie central fatigue. We are the first to demonstrate that hyperthermia-induced hyperventilation is not suppressed by the resultant hypocapnia and that hypocapnia explains only 36% of cerebral hypoperfusion elicited by hyperthermia. These new findings advance our understanding of the mechanisms controlling ventilation and cerebral blood flow during heat stress, which may be useful for developing interventions aimed at preventing central fatigue during hyperthermia.

Acidosis, but Not Alkalosis, Affects Anaerobic Metabolism and Performance in a 4-km Time Trial.

This study aimed to determine the effect of preexercise metabolic acidosis and alkalosis on power output (PO) and aerobic and anaerobic energy expenditure during a 4-km cycling time trial (TT). Eleven recreationally trained cyclists (V˙O2peak 54.1 ± 9.3 mL·kg·min) performed a 4-km TT 100 min after ingesting in a double-blind matter 0.15 g·kg of body mass of ammonium chloride (NH4Cl, acidosis), 0.3 g·kg of sodium bicarbonate (NaHCO3, alkalosis), or 0.15 g·kg of CaCO3 (placebo). A preliminary study (n = 7) was conducted to establish the optimal doses to promote the desirable preexercise blood pH alterations without gastrointestinal distress. Data for PO, aerobic and anaerobic energy expenditure, and blood and respiratory parameters were averaged for each 1 km and compared between conditions using two-way repeated-measures ANOVA (condition and distance factors). Gastrointestinal discomfort was analyzed qualitatively. Compared with placebo (pH 7.37 ± 0.02, [HCO3]: 27.5 ± 2.6 mmol·L), the NaHCO3 ingestion resulted in a preexercise blood alkalosis (pH +0.06 ± 0.04, [HCO3]: +4.4 ± 2.0 mmol·L, P < 0.05), whereas NH4Cl resulted in a blood acidosis (pH -0.05 ± 0.03, [HCO3]: -4.8 ± 2.1 mmol·L, P < 0.05). Anaerobic energy expenditure rate and PO were reduced throughout the trial in NH4Cl compared with placebo and NaHCO3, resulting in a lower total anaerobic work and impaired performance (P < 0.05). Plasma lactate, V˙CO2, and end-tidal CO2 partial pressure were lower and the V˙E/V˙CO2 higher throughout the trial in NH4Cl compared with placebo and NaHCO3 (P < 0.05). There was no difference between NaHCO3 and placebo for any of these variables (P > 0.05). Minimal gastrointestinal distress was noted in all conditions. Preexercise acidosis, but not alkalosis, affects anaerobic metabolism and PO during a 4-km cycling TT.

P6185How do peak oxygen consumption, ventilator efficiency slope and end-tidal carbon dioxide partial pressure perform in the short-, long- and very long-term risk stratification in heart failure?

P6185How do peak oxygen consumption, ventilator efficiency slope and end-tidal carbon dioxide partial pressure perform in the short-, long- and very long-term risk stratification in heart failure?

Effects of Hypercapnia on Myocardial Blood Flow in Healthy Human Subjects.

Elevation of the end-tidal partial pressure of CO2 (PETco2) increases cerebral and myocardial blood flow (MBF), suggesting that it may be a suitable alternative to pharmacologic stress or exercise for myocardial perfusion imaging. The purpose of this study was to document the pharmacodynamics of CO2 for MBF using prospective end-tidal targeting to precisely control arterial Pco2 and PET to measure the outcome variable, MBF. Methods: Ten healthy men underwent serial 82Rb PET/CT imaging. Imaging was performed at rest and during 6-min hypercapnic plateaus (baseline; PETco2 at 50, 55, and 60 mm Hg; repeat of PETco2 at 60 mm Hg; and repeat of baseline). MBF was measured using 82Rb injected 3 min after the beginning of hypercapnia and a 1-tissue-compartment model with flow-dependent extraction correction. Results were compared with those obtained during an adenosine stress test (140 μg/kg/min). Results: Baseline PETco2 was 38.9 ± 0.8 (mean ± SD) mm Hg (range, 35-43 mm Hg). All PETco2 targets were sustained, with SDs of less than 1.5 mm Hg. Heart rate, systolic blood pressure, rate × pressure product, and respiratory frequency increased with progressive hypercapnia. MBF increased significantly at each level of hypercapnia to 1.92-fold over baseline (0.86 ± 0.24 vs. 0.45 ± 0.08 mL/min/g; P = 0.002) at a PETco2 of 60 mm Hg. MBF after the administration of adenosine was significantly greater than that with the maximal hypercapnic stimulus (2.00 vs. 0.86 mL/min/g; P < 0.0001). Conclusion: To our knowledge, this study is the first to assess the response of MBF to different levels of hypercapnia in healthy humans with PET. MBF increased with increasing levels of hypercapnia; MBF at a PETco2 of 60 mm Hg was double that at baseline.

Sex-specific cardiopulmonary exercise testing parameters as predictors in patients with idiopathic pulmonary arterial hypertension.

Cardiopulmonary exercise testing (CPET) has been used for prognosis in idiopathic pulmonary arterial hypertension (IPAH). We explored whether sex differences had an impact on prognostic assessments of CPET in IPAH. Data were retrieved from 21 male and 36 female incident IPAH patients who underwent both right heart catheterization and CPET from 2010 to 2016 at Shanghai Pulmonary Hospital. Cox proportional hazards analysis was used to assess the prognostic value of CPET. The mean duration of follow-up was 22±15 months. Nine men and 15 women had an event. The differences in clinical parameters in the whole population were not the same as the inter-subgroup differences. Event-free women had significantly higher cardiac output, lower pulmonary vascular resistance and percentage of predicted FVC compared with event men (all P<0.05). Event-free men had significantly higher end-tidal partial pressure of CO2 (PETCO2) at anaerobic threshold (AT), peak workload, PETCO2, maximum oxygen consumption (VO2)/minute ventilation (VE), and oxygen uptake efficiency slope and lower end-tidal partial pressure of O2 (PETO2) at AT, peak PETO2, and lowest VE/VCO2 compared with event men. Event-free women had dramatically higher peak VO2, VCO2, VE and O2 pulse than event women (all P<0.05). Peak PETCO2 was the independent predictor of event-free survival in all patients and males, whereas peak O2 pulse was the independent predictor of event-free survival in females. Men with peak PETCO2⩾20.50 mm Hg, women with peak O2 pulse ⩾6.25 ml per beat and all patients with peak PETCO2⩾27.03 mm Hg had significantly better event-free survival. Sex-specific CPET parameters are predictors of poor outcomes. Decreased peak PETCO2 in men and peak O2 pulse in women were associated with lower event-free survival in IPAH.

Effect of Exercise Training on Cerebral Microcirculation in Men with and without Type 1 Diabetes

PURPOSE: Effects of regular exercise on cerebral microcirculation in diabetes are unknown. We examined if exercise training leads to similar adaptations in cerebral microcirculation in men with and without type 1 diabetes (T1D). METHODS: Eight men with T1D (33±6 yrs) and eight healthy men (HC; 38±7 yrs) matched for age, anthropometry, and peak O2 uptake (VO2peak) (p>0.05), completed a 1-year individualized exercise training intervention. Individually collected data on training were similar in T1D vs. HC (mean±SD per month; p>0.05): 13±4 vs. 15±6 endurance training sessions, 3±1 vs. 3±3 resistance training sessions, 57±5 vs. 55±8 % of heart rate reserve, 16:58±6:07 vs. 16:52±4:39 h:min, 7759±4540 vs. 7762±3812 kcal, respectively. Before and after the intervention, the subjects performed step incremental cycling exercise to volitional fatigue. During exercise, alveolar gas exchange (mass spectrometry) and normalized relative concentration changes in deoxygenated hemoglobin (%Δ[HHb]) in the prefrontal cerebral cortex (near-infrared spectroscopy) were monitored; %Δ[HHb] reflects imbalance between local O2 delivery and utilization. RESULTS: Training increased VO2peak and peak work rate similarly in T1D (45±5 to 49±6 mL/min/kg fat-free mass [FFM], p<0.01; 237±34 to 254±27 W, p<0.05) and HC (48±3 to 52±5 mL/min/kg FFM, p<0.05; 255±17 to 282±36 W, p<0.05). Training also decreased minute ventilation at 160W (in T1D and HC) and 200W (in HC) (p<0.05) but had no effect on end-tidal CO2 partial pressure, which estimates arterial CO2 pressure affecting cerebral blood flow. Cerebral %Δ[HHb] did not change at any work rate in T1D but decreased at 200W in HC (p<0.05). No differences were observed between T1D and HC in the reported parameters before the intervention. CONCLUSION: Exercise training did not improve exercise-induced imbalance between local O2 delivery and utilization in prefrontal microcirculation in T1D but did so at high exercise intensity (200 W) in HC. This between-group difference was not due to different respiratory adaptations and must thus be explained by other diabetes-related mechanisms (e.g., impaired cerebrovascular autoregulation, CO2 reactivity, or neocapillarization) influencing cerebral blood flow. Supported by: Tekes, Ministry of Education and Culture, Finnish Medical Foundation.

Automated control of mechanical ventilation during general anaesthesia: study protocol of a bicentric observational study (AVAS)

IntroductionAutomated control of mechanical ventilation during general anaesthesia is not common. A novel system for automated control of most of the ventilator settings was designed and is available on an...

Investigating hyperventilation syndrome in patients suffering from empty nose syndrome.

Patients with empty nose syndrome (ENS) following turbinate surgery often complain about breathing difficulties. We set out to determine if dyspnea in patients with ENS was associated with hyperventilation syndrome (HVS). We hypothesized that lower airway symptoms in ENS could be explained by HVS. Observational prospective study. All consecutive patients referred to our center for ENS over 1 year were invited to participate. Patients completed the Nijmegen score and underwent a hyperventilation provocation test (HVPT) and arterial blood gas and cardiopulmonary tests. HVS was defined by a delayed return of the end-tidal partial pressure of carbon dioxide in the expired gas to baseline during HVPT. Patients with HVS were asked to complete the Sinonasal Outcome Test (SNOT)-16 questionnaire before and after a specific eight-session respiratory rehabilitation program. Twenty-two of the 29 patients referred for ENS during the study period were eligible for inclusion and underwent a complete workup. HVS was diagnosed in 17 of these patients (77.3%). In the five patients who completed the SNOT-16, the score was significantly lower after rehabilitation. This study suggests that HVS is frequent in patients with ENS, and that symptoms can be improved by respiratory rehabilitation. Pathophysiological links between ENS and HVS deserve to be further explored. 2b Laryngoscope, 127:1983-1988, 2017.

Middle cerebral artery blood flow velocity during a 4km cycling time trial.

This study sought to describe middle cerebral artery blood flow velocity (MCAv) during a 4km cycling time trial, and relate it to different pacing strategies adopted by participants. After familiarisation and a standardised exercise protocol, 15 male trained cyclists rode a 4km time trial on a cycling ergometer. MCAv was assessed via transcranial Doppler ultrasound in the right hemisphere at resting baseline, and throughout the time trial. Mean arterial pressure, end-tidal partial pressure of carbon dioxide (PetCO2) and heart rate were assessed alongside MCAv. Plasma lactate was assessed post time trial. Data were compared depending upon whether participants completed the time trial with a positive (first half faster than the last) or negative pacing profile although there was no difference in the time to completion with either pacing strategy (positive 344±23s, negative 334±14s; p=0.394). Lower mean MCAv (positive pacing -7.6±14.2%, negative pacing +21.2±15.0% compared to resting baseline measures; p=0.004) and lower PetCO2 (significant interaction p<0.001) towards the end of the time trial were observed with positive compared to negative pacing. Heart rate and lactate did not differ between pacing strategies. Changes in MCAv appear to depend on the pacing strategy adopted, with a positive pacing strategy likely to contribute to a hyperventilatory drop in PetCO2 and subsequent reduction in MCAv. Although lower cerebral blood flow cannot be directly linked to an inability to raise or maintain power output during the closing stages of the time trial, this potential contributor to fatigue is worth further investigation.

Application of end-tidal carbon dioxide monitoring via distal gas samples in ventilated neonates

Previous research has suggested correlations between the end-tidal partial pressure of carbon dioxide (PETCO2) and the partial pressure of arterial carbon dioxide (PaCO2) in mechanically ventilated patients, but both the relationship between PETCO2 and PaCO2 and whether PETCO2 accurately reflects PaCO2 in neonates and infants are still controversial. This study evaluated remote sampling of PETCO2 via an epidural catheter within an endotracheal tube to determine the procedure's clinical safety and efficacy in the perioperative management of neonates. Abdominal surgery was performed under general anesthesia in 86 full-term newborns (age 1-30days, weight 2.55-4.0kg, American Society of Anesthesiologists class I or II). The infants were divided into 2 groups (n=43 each), and carbon dioxide (CO2) gas samples were collected either from the conventional position (the proximal end) or a modified position (the distal end) of the epidural catheter. The PETCO2 measured with the new method was significantly higher than that measured with the traditional method, and the difference between PETCO2 and PaCO2 was also reduced. The accuracy of PETCO2 measured increased from 78.7% to 91.5% when the modified sampling method was used. The moderate correlation between PETCO2 and PaCO2 by traditional measurement was 0.596, which significantly increased to 0.960 in the modified sampling group. Thus, the PETCO2 value was closer to that of PaCO2. PETCO2 detected via modified carbon dioxide monitoring had a better accuracy and correlation with PaCO2 in neonates.

A new modulation technique and compensation algorithm for mainstream CO[formula omitted] capnography

Carbon dioxide, as a metabolic product of human, is correlated with a patient’s perfusion and ventilation. In medicine, the end-tidal carbon dioxide partial pressure refers to the measurement of exhaled carbon dioxide, and end-tidal carbon dioxide partial pressure monitoring has become an important tool in clinical monitoring. However, there are some aspects needed to be improved. So, the low-frequency modulation is used to reliably acquire the respiration information. The measurement method is improved based on the Lambert–Beer Law. Also, we compensate the initial absorbance because of the light absorbance of the sensor at different wavelengths. The influence of the temperature change is analyzed on the measurement. All of these methods make the end-tidal carbon dioxide partial pressure accurate and convenient.

The Metaboreflex and the Peripheral Chemoreflex Interact for the Regulation of Ventilation in Patients with Chronic Heart Failure

Patients with chronic heart failure (CHF) tipically present exacerbated ventilation (VE) response to exercise. This phenomenon is associated with exercise intolerance and worse prognosis, and seems to be mediated, at least in part, by abnormalities in the neural control of VE, such as enhanced VE response to activation of muscle afferents sensitive to metabolites (i.e., enhanced metaboreflex), as well as enhanced VE response to inhalation of hypoxic air at rest (i.e., enhanced peripheral chemoreflex). However, the interaction between these reflexes remains unknown in CHF. Then, we sought to test the hypothesis that the activation of the metaboreflex could enhance the contribution of the peripheral chemoreflex for the regulation of VE in patients with CHF. Six men with CHF under optimal pharmacological treatment (New York Heart Association class II‐III, mean ± SD age of 55 ± 6 years and left ventricular ejection fraction (Simpson) 33.7 ± 2.9%) were submitted to 4 steady‐state cycling sessions at 60% of maximal power output for 4 minutes. Then, they recovered for 2 minutes under either 1) post exercise ischemia (PEI) plus normoxia (21% O2), 2) PEI plus hyperoxia (100% O2), 3) free flow plus normoxia, or 4) free flow plus hyperoxia. PEI was used to trap metabolites in the lower limbs, and, consequently, activate the metaboreflex, while hyperoxia was used to inhibit the peripheral chemoreceptors. Patients were blinded to the O2 concentration in the inhaled air. A rebreathing circuit was used during recovery to match the end tidal partial pressure of CO2 (PetCO2) among conditions. Breath‐by‐breath data recorded at peak and throughout recovery were averaged in 20‐s windows for statistical analyses. Peak VE was similar among conditions. As expected, end tidal partial pressure of O2 was higher during hyperoxia than normoxia throughout the recovery period. VE decayed during recovery in all conditions. Of note, hyperoxia augmented the VE decay versus normoxia at 21–40 s (hyperoxia: 16.7 ± 2.3 L/min vs. normoxia: 22.7 ± 2.9 L/min, P &lt; 0.001) and 41–60 s (hyperoxia: 17.1 ± 1.5 L/min vs. normoxia: 20.5 ± 2.2 L/min, P = 0.01) of recovery during PEI. However, hyperoxia did not change VE decay versus normoxia during free flow recovery. Collectively, our findings indicate that the activation of the metaboreflex enhances the peripheral chemoreflex regulation of VE in patients with CHF, which confirms the interaction between these reflexes. This interaction may, consequently, mediate part of the exaggerated VE response to exercise, which is a hallmark of patients with CHF.Support or Funding InformationSão Paulo Research Foundation (FAPESP), National Counsel of Technological and Scientific Development (CNPq), and Research Support Foundation of the State of Rio de Janeiro (FAPERJ).

Mapping the pharmacological modulation of brain oxygen metabolism: The effects of caffeine on absolute CMRO2 measured using dual calibrated fMRI

This study aims to map the acute effects of caffeine ingestion on grey matter oxygen metabolism and haemodynamics with a novel MRI method. Sixteen healthy caffeine consumers (8 males, age=24.7±5.1) were recruited to this randomised, double-blind, placebo-controlled study. Each participant was scanned on two days before and after the delivery of an oral caffeine (250mg) or placebo capsule.Our measurements were obtained with a newly proposed estimation approach applied to data from a dual calibration fMRI experiment that uses hypercapnia and hyperoxia to modulate brain blood flow and oxygenation. Estimates were based on a forward model that describes analytically the contributions of cerebral blood flow (CBF) and of the measured end-tidal partial pressures of CO2 and O2 to the acquired dual-echo GRE signal. The method allows the estimation of grey matter maps of: oxygen extraction fraction (OEF), CBF, CBF-related cerebrovascular reactivity (CVR) and cerebral metabolic rate of oxygen consumption (CMRO2). Other estimates from a multi inversion time ASL acquisition (mTI-ASL), salivary samples of the caffeine concentration and behavioural measurements are also reported.We observed significant differences between caffeine and placebo on average across grey matter, with OEF showing an increase of 15.6% (SEM±4.9%, p<0.05) with caffeine, while CBF and CMRO2 showed differences of −30.4% (SEM±1.6%, p<0.01) and −18.6% (SEM±2.9%, p<0.01) respectively with caffeine administration. The reduction in oxygen metabolism found is somehow unexpected, but consistent with a hypothesis of decreased energetic demand, supported by previous electrophysiological studies reporting reductions in spectral power with EEG.Moreover the maps of the physiological parameters estimated illustrate the spatial distribution of changes across grey matter enabling us to localise the effects of caffeine with voxel-wise resolution. CBF changes were widespread as reported by previous findings, while changes in OEF were found to be more restricted, leading to unprecedented mapping of significant CMRO2 reductions mainly in frontal gyrus, parietal and occipital lobes.In conclusion, we propose the estimation framework based on our novel forward model with a dual calibrated fMRI experiment as a viable MRI method to map the effects of drugs on brain oxygen metabolism and haemodynamics with voxel-wise resolution.

Postinduction apnoea in dogs premedicated with acepromazine or dexmedetomidine and anaesthetized with alfaxalone or propofol

ObjectiveTo compare incidence and duration of postinduction apnoea in dogs after premedication with methadone and acepromazine (MA) or methadone and dexmedetomidine (MD) followed by induction with propofol (P) or alfaxalone (A). Study designProspective, randomized clinical trial. AnimalsA total of 32 American Society of Anesthesiologists class I dogs (15 females, 17 males), aged between 4 months and 4 years, weighing between 3 and 46 kg. MethodsDogs were randomly allocated to be administered MA+P, MA+A, MD+P or MD+A (methadone 0.5 mg kg−1 and acepromazine 0.05 mg kg−1 or dexmedetomidine 5 μg kg−1). Induction agents were administered intravenously via syringe driver (P at 4 mg kg−1 minute−1 or A at 2 mg kg−1 minute−1) until successful endotracheal intubation and the endotracheal tube connected to a circle system with oxygen flow at 2 L minute−1. Oxygen saturation of haemoglobin (SpO2), end tidal partial pressure of carbon dioxide and respiratory rate were monitored continuously. If apnoea (≥ 30 seconds without breathing) occurred, the duration until first spontaneous breath was measured. If SpO2 decreased below 90% the experiment was stopped and manual ventilation initiated. Data were analysed with general linear models with significance set at p ≤ 0.05. ResultsThere was no statistical difference in the incidence (11 of 16 dogs in A groups and 12 of 16 dogs in P groups), or mean ± standard deviation duration (A groups 125 ± 113 seconds, P groups 119 ± 109 seconds) of apnoea. The SpO2 of one dog in the MD+P group decreased below 90% during the apnoeic period. Conclusions and clinical relevancePropofol and alfaxalone both cause postinduction apnoea and the incidence and duration of apnoea is not influenced by the use of acepromazine or dexmedetomidine in premedication. Monitoring of respiration is recommended when using these premedication and induction agent combinations.

The Application of Biphasic Extrathoracic Cuirass-Assisted Ventilation in Normal Subjects Wearing Chemical-Biological-Radiological-Nuclear (CBRN) Gas Masks.

Mobile RTX (MRTX), a portable light-weighted ventilator, provides noninvasive respiratory support using biphasic extrathoracic cuirass-assisted ventilation. Despite the effectiveness of chemical-biological-radiological-nuclear (CBRN) gas masks, they cause respiratory loading as a result of added dead space and resistance. This prospective comparative pilot study was conducted to investigate the safety and efficacy of assisted ventilation provided by MRTX in healthy adult volunteers wearing CBRN gas masks at rest. Cardiorespiratory parameters were monitored in 11 healthy adult volunteers breathing spontaneously or with assisted ventilation provided by MRTX, freely or with the mask on. Comparisons were made by single-factor analysis of variance. AV significantly increased minute ventilation (p < 0.001). MRTX increased minute ventilation by 6.4 L/min (mean, 95% confidence interval: 3.1, 9.8; p < 0.005) and by 4.7 L/min (1.8, 7.5; p < 0.01) during spontaneous breathing and with the mask on, respectively. Simultaneously, end-tidal carbon dioxide partial pressure decreased by 3.6 mmHg (2.2, 5.1; p < 0.001) and by 6.5 mmHg (3.8, 9.1; p < 0.001). Biphasic extrathoracic cuirass assisted ventilation provided by MRTX is safe and effective in supporting adequate needs at rest even when wearing protective masks. MRTX should be further assessed as a possible adjunct to currently used field ventilation in CBRN scenarios.