Recent Insights into the Measurement of Carbon Dioxide Concentrations for Clinical Practice in Respiratory Medicine

In the field of respiratory clinical practice, the importance of measuring carbon dioxide (CO2) concentrations cannot be overemphasized. Within the body, assessment of the arterial partial pressure of CO2 (PaCO2) has been the gold standard for many decades. Non-invasive assessments are usually predicated on the measurement of CO2 concentrations in the air, usually using an infrared analyzer, and these data are clearly important regarding climate changes as well as regulations of air quality in buildings to ascertain adequate ventilation. Measurements of CO2 production with oxygen consumption yield important indices such as the respiratory quotient and estimates of energy expenditure, which may be used for further investigation in the various fields of metabolism, obesity, sleep disorders, and lifestyle-related issues. Measures of PaCO2 are nowadays performed using the Severinghaus electrode in arterial blood or in arterialized capillary blood, while the same electrode system has been modified to enable relatively accurate non-invasive monitoring of the transcutaneous partial pressure of CO2 (PtcCO2). PtcCO2 monitoring during sleep can be helpful for evaluating sleep apnea syndrome, particularly in children. End-tidal PCO2 is inferior to PtcCO2 as far as accuracy, but it provides breath-by-breath estimates of respiratory gas exchange, while PtcCO2 reflects temporal trends in alveolar ventilation. The frequency of monitoring end-tidal PCO2 has markedly increased in light of its multiple applications (e.g., verify endotracheal intubation, anesthesia or mechanical ventilation, exercise testing, respiratory patterning during sleep, etc.).

Features of cerebral oximetry indicators in different types of combined anesthesia in children with congenital surgical pathology

Background. In the past decade, near-infrared spectroscopy has gained popularity in neonatal wards. Taking into account modern international experience, the presented work assesses the features of cerebral oximetry in children with surgical congenital malformations under various types of combined anesthesia. The purpose of the study was to assess the state of cerebral oxygenation in newborns and infants with congenital malformations in various types of anesthetic support. Materials and methods. A retrospective study included 150 newborns and infants with surgical congenital malformations, depending on the anesthesia (inhalation + regional anesthesia; inhalation + intravenous and total intravenous anesthesia). The parameters of cerebral oximetry were analyzed in comparison with peripheral saturation, blood pressure, partial pressure of CO2, O2 in the blood, and pH. Results. The minimum index of cerebral oximetry was observed in the left brain hemisphere of children in group I — 50.57 ± 16.66 that may be an unfavorable prognostic factor for further recovery and influence on the cognitive functions of the brain. One hour after the operation, the children of the first group, who received combined anesthesia with sevorane and regional anesthesia, showed the worse indicators of cerebral oxi­metry compared to groups II and III (rSO2 of the right hemisphere in the first group — 56.84 ± 12.27, rSO2 of the left hemisphere in the first group — 57.53 ± 13.32, p = 0.0001; 0.0028), while the differences in this indicator between groups II and III were not found (p = 0.4167; 0.4029). Conclusions. Near-infrared spectroscopy has proven to be a simple, feasible and useful method for monitoring the oxygen saturation of the brain. When choosing a combined anesthesia by inhalation and regional anesthesia in child­ren with congenital malformations for surgical treatment, cerebral oxyge­nation should be more carefully monitored with additional control of peripheral saturation, blood pressure, partial pressure of CO2, O2 in the blood and pH.

A Simple and Accurate Approach for Determining the VFA Concentration in Anaerobic Digestion Liquors, Relying on Two Titration Points and an External Inorganic Carbon Analysis

A new analytic approach is presented for determining the total volatile fatty acids (VFAT) concentration in anaerobic digesters. The approach relies on external determination of the inorganic carbon concentration (CT) in the analyzed solution, along with two strong-acid titration points. The CT concentration can be determined by either a direct analysis (e.g., by using a TOC device) or by estimating it from the recorded partial pressure of CO2(g) in the biogas (often a routine analysis in anaerobic digesters). The titration is carried out to pH 5.25 and then to pH 4.25. The two titration results are plugged into an alkalinity-mass-based equation and then the two terms are subtracted from each other to yield an equation in which VFAT is the sole unknown (since CT is known and the effect of the total orthophosphate and ammonia concentrations is shown to be small at this pH range). The development of the algorithm and its verification on four anaerobic reactor liquors is presented, on both the raw water and on acetic acid-spiked samples. The results show the method to be both accurate (up to 2.5% of the expected value for VFAT/Alkalinity >0.2) and repetitive when the total orthophosphate and ammonia concentrations are known, and fairly accurate (±5% for VFAT >5 mM) when these are completely neglected. PHREEQC-assisted computation of CT from the knowledge of the partial pressure of CO2(g) in the biogas (and pH, EC and temperature in the liquor) resulted in a very good estimation of the CT value (±3%), indicating that this technique is adequate for the purpose of determining VFAT for alarming operators in case of process deterioration and imminent failure.

Use of the Change in Weaning Parameters as a Predictor of Successful Re-Extubation

Objective: Weaning parameters are well studied in patients undergoing first time extubation. Fewer data exists to guide re-extubation of patients who failed their first extubation attempt. It is reasonable to postulate that improved weaning parameters between the first and second extubation attempt would lead to improved rates of re-extubation success. To investigate, we studied a cohort of patients who failed their first extubation attempt and underwent a second attempt at extubation. We hypothesized that improvement in weaning parameters between the first and the second extubation attempt is associated with successful reextubation. Interventions: Rapid shallow breathing index (RSBI), maximum inspiratory pressure (MIP), vital capacity (VC), and the blood partial pressure of CO2 (PaCO2) were measured and recorded in the medical record prior to extubation along with demographic information. We examined the relationship between the change in extubation and re-extubation weaning parameters and re-extubation success. Measurements and Main results: A total of 1283 adult patients were included. All weaning parameters obtained prior to re-extubation differed between those who were successful and those who required a second reintubation. Those with reextubation success had slightly lower PaCO2 values (39.5 ± 7.4 mmHg vs. 41.6 ± 9.1 mmHg, p = 0.0045) and about 13% higher vital capacity volumes (1021 ± 410 mL vs. 907 ± 396 mL, p = 0.0093). Lower values for RSBI (53 ± 32 breaths/min/L vs. 69 ± 42 breaths/min/L, p < 0.001) and MIP (−41 ± 12 cmH2O vs. −38 ± 13 cm H2O), p = 0.0225) were seen in those with re-extubation success. Multivariable logistical regression demonstrates lack of independent associated between the change in parameters between the 2 attempts and re-extubation success. Conclusions: The relationship between the changes in extubation parameters through successive attempts is driven primarily by the value obtained immediately prior to re-extubation. These findings do not support waiting for an improvement in extubation parameters to extubate patients who failed a first attempt at extubation if extubation parameters are compatible with success.

Chronic Effects of a Training Program Using a Nasal Inspiratory Restriction Device on Elite Cyclists

This study compared the response of a 9-week cycling training on ventilatory efficiency under two conditions: (i) Combined with respiratory muscle training (RMT) using a new nasal restriction device (FeelBreathe) (FB group) and (ii) without RMT (Control group). Eighteen healthy elite cyclists were randomly separated into the FB group (n = 10) or Control group (n = 8). Gas exchange was measured breath by breath to measure ventilatory efficiency during an incremental test on a cycloergometer before (Pre) and after (Post) the nine weeks of training. The FB group showed higher peak power (Δ (95%HDI) (0.82 W/kg (0.49, 1.17)), VO2max (5.27 mL/kg/min (0.69, 10.83)) and VT1 (29.3 W (1.8, 56.7)) compared to Control at PostFINAL. The FB group showed lower values from Pre to PostPRE in minute ventilation (VE) (−21.0 L/min (−29.7, −11.5)), Breathing frequency (BF) (−5.1 breaths/min (−9.4, −0.9)), carbon dioxide output (VCO2) (−0.5 L/min (−0.7, −0.2)), respiratory equivalents for oxygen (EqO2) (−0.8 L/min (−2.4, 0.8)), heart rate (HR) (−5.9 beats/min (−9.2, −2.5)), respiratory exchange ratio (RER) (−0.1 (−0.1, −0.0) and a higher value in inspiratory time (Tin) (0.05 s (0.00, 0.10)), expiratory time (Tex) (0.11 s (0.05, 0.17)) and end-tidal partial pressure of CO2 (PETCO2) (0.3 mmHg (0.1, 0.6)). In conclusion, RMT using FB seems to be a new and easy alternative ergogenic tool which can be used at the same time as day-to-day training for performance enhancement.

Conductive Polymer/SiO2 Composite as an Anticorrosive Coating Against Carbon Dioxide Corrosion of Mild Steel. A Simulation Study

In this work corrosion of mild steel affected by carbon dioxide was studied using a simulation model developed by Nordsveen M. and Nesic S. Using this comprehensive model of the uniform corrosion made possible to predict of corrosion rate of steel in the carbonic acid medium and the influence of different conditions on the anticorrosive property of coated electrode has been investigated. 1D model of corrosion process includes Butler-Volmer and Tafel equations and takes into account both the kinetics of anodic dissolution of an iron and electrochemical discharge of carbonic acid, water and hydrogen ions. The model has been created in COMSOL Multiphysics software and further improvement of this model allowed studying the influence of parameters such as solution composition, the partial pressure of CO2, temperature and flow velocity of the solution on the corrosion rate of the steel. The results of numerical simulation demonstrate that the use of conductive polymerpolypyrrole/ SiO2 composite as an anti-corrosive resin coating reduces the corrosion rate of mild steel by 7 times or more, depending on pH, temperature and flow rate. Furthermore, increasing of flow velocity from 0.1 to 10 m/s affects to the removal of corrosion products from the surface of mild steel and as a result corrosion rate raises from 0.3 to 0.45 mm/year at a temperature of 80 °C and pH=4.

Photorespiration Enhances Acidification of the Thylakoid Lumen, Reduces the Plastoquinone Pool, and Contributes to the Oxidation of P700 at a Lower Partial Pressure of CO2 in Wheat Leaves

The oxidation of P700 in photosystem I (PSI) is a robust mechanism that suppresses the production of reactive oxygen species. We researched the contribution of photorespiration to the oxidation of P700 in wheat leaves. We analyzed the effects of changes in partial pressures of CO2 and O2 on photosynthetic parameters. The electron flux in photosynthetic linear electron flow (LEF) exhibited a positive linear relationship with an origin of zero against the dissipation rate (vH+) of electrochromic shift (ECS; ΔpH across thylakoid membrane), indicating that cyclic electron flow around PSI did not contribute to H+ usage in photosynthesis/photorespiration. The vH+ showed a positive linear relationship with an origin of zero against the H+ consumption rates in photosynthesis/photorespiration (JgH+). These two linear relationships show that the electron flow in LEF is very efficiently coupled with H+ usage in photosynthesis/photorespiration. Lowering the intercellular partial pressure of CO2 enhanced the oxidation of P700 with the suppression of LEF. Under photorespiratory conditions, the oxidation of P700 and the reduction of the plastoquinone pool were stimulated with a decrease in JgH+, compared to non-photorespiratory conditions. These results indicate that the reduction-induced suppression of electron flow (RISE) suppresses the reduction of oxidized P700 in PSI under photorespiratory conditions. Furthermore, under photorespiratory conditions, ECS was larger and H+ conductance was lower against JgH+ than those under non-photorespiratory conditions. These results indicate that photorespiration enhances RISE and ΔpH formation by lowering H+ conductance, both of which contribute to keeping P700 in a highly oxidized state.