Relation Between Multiplication of Venous Carbon Dioxide Partial Pressure (PvCO2) and the Ratio of Gas Flow to Pump Flow (Ve/Q) with Hyperlactatemia During Cardiopulmonary Bypass.

BACKGROUND: The incidence of hyperlactatemia due to hypoperfusion during cardiopulmonary bypass (CPB) increases morbidity. Carbon dioxide production during CPB is one of the lactate production markers, in addition to other markers such as delivery oxygen (DO2), oxygen consumption (VO2), mixed vein oxygen saturation (SvO2), and oxygen extraction ratio (O2ER). METHOD: This observational analytic study was conducted on 40 adult cardiac surgery patients using a CPB machine. Initial lactate is taken when entering CPB and final lactate is examined 15 min after coming off bypass. The values of DO2, VO2, SvO2, VCO2, respiratory quotient (RQ), DO2/VCO2, PvCO2 × Ve/Q were calculated from the results of blood and venous gas analysis 1 h after entering CPB in the nadir of core temperature and lowest pump flow. RESULT: The multivariate test showed that the value of PvCO2 × Ve/Q was more effective than other oxygenation and carbon dioxide parameters in predicting an increase in the percentage of lactate. Each increase of 1 mmHg PvCO2 ×× Ve/Q can predict a final lactate increase of 29% from the initial lactate. The high PvCO2 × Ve/Q value is also the strongest correlation factor for the incidence of hyperlactatemia after CPB (final lactate >3 mmol/L). The cutoff value of this marker is >19.3 mmHg, which has a sensitivity of 100% and a specificity of 55.6% with a strong correlation value. CONCLUSION: The PvCO2 × Ve/Q value proved to be one of the significant markers in predicting hyperlactatemia during cardiac surgery using CPB.

A prospective observation study of the dynamic monitoring of transcutaneous arterial blood oxygen saturation and carbon dioxide during bronchoscopy.

BACKGROUND AND AIMS: Because bronchoscopy is an invasive procedure, sedatives and analgesics are commonly administered, which may suppress the patient's spontaneous breathing and can lead to hypoventilation and hypoxemia. Few reports exist on the dynamic monitoring of oxygenation and ventilation during bronchoscopy. This study aimed to prospectively monitor and evaluate oxygenation and ventilation during bronchoscopy using transcutaneous arterial blood oxygen saturation and carbon dioxide. METHODS: We included patients who required pathological diagnosis using fluoroscopic bronchoscopy at our hospital between March 2021 and April 2022. Midazolam was intravenously administered to all patients as a sedative during bronchoscopy, and fentanyl was administered in addition to midazolam when necessary. A transcutaneous blood gas monitor was used to measure dynamic changes, including arterial blood partial pressure of carbon dioxide (tcPCO2), transcutaneous arterial blood oxygen saturation (SpO2), pulse rate, and perfusion index during bronchoscopy. Quantitative data of tcPCO2 and SpO2 were presented as mean ± standard deviation (SD) (min-max), while the quantitative data of midazolam plus fentanyl and midazolam alone were compared. Similarly, data on sex, smoking history, and body mass index were compared. Subgroup comparisons of the difference (Δ value) between baseline tcPCO2 at the beginning of bronchoscopy and the maximum value of tcPCO2 during the examination were performed. RESULTS: Of the 117 included cases, consecutive measurements were performed in 113 cases, with a success rate of 96.6%. Transbronchial lung biopsy was performed in 100 cases, whereas transbronchial lung cryobiopsy was performed in 17 cases. Midazolam and fentanyl were used as anesthetics during bronchoscopy in 46 cases, whereas midazolam alone was used in 67 cases. The median Δ value in the midazolam plus fentanyl and midazolam alone groups was 8.10 and 4.00 mmHg, respectively, indicating a significant difference of p < 0.005. The mean ± standard deviation of tcPCO2 in the midazolam plus fentanyl and midazolam alone groups was 44.8 ± 7.83 and 40.6 ± 4.10 mmHg, respectively. The SpO2 in the midazolam plus fentanyl and midazolam alone groups was 94.4 ± 3.37 and 96.2 ± 2.61%, respectively, with a larger SD and greater variability in the midazolam plus fentanyl group. CONCLUSION: A transcutaneous blood gas monitor is non-invasive and can easily measure the dynamic transition of CO2. Furthermore, tcPCO2 can be used to evaluate the ventilatory status during bronchoscopy easily. A transcutaneous blood gas monitor may be useful to observe regarding respiratory depression during bronchoscopy, particularly when analgesics are used.

Enhancing the estimation of PaCO2 from etCO2 during ventilation through non-invasive parameters in the ovine model.

BACKGROUND: In mechanically ventilated neonates, the arterial partial pressure of CO 2 ( PaCO 2 ) is an important indicator for the adequacy of ventilation settings. Determining the PaCO 2 is commonly done using invasive blood gas analyses, which constitute risks for neonates and are typically only available infrequently. An accurate, reliable, and continuous estimation of PaCO 2 is of high interest for medical staff, giving the possibility of a closer monitoring and faster reactions to changes. We aim to present a non-invasive estimation method for PaCO 2 in neonates on the basis of end-tidal CO 2 ( etCO 2 ) with inclusion of different physiological and ventilation parameters. The estimation method should be more accurate than an estimation by unaltered etCO 2 measurements with regard to the mean absolute error and the standard deviation. METHODS: Secondary data from 51 preterm lambs are used, due to its high comparability to preterm human data. We utilize robust linear regression on 863 PaCO 2 measurements below or equal to 75 mmHg from the first day of life. etCO 2 along with a set of ventilation settings and measurements as well as vital parameters are included in the regression. Included independent variables are chosen iteratively by highest Pearson correlation to the remaining estimation deviation. RESULTS: The evaluation is carried out on 12 additional neonatal lambs with 246 PaCO 2 measurements below or equal to 75 mmHg from the first two days of life. The estimation method shows a mean absolute error of 3.80 mmHg with a 4.92 mmHg standard deviation of differences and a standard error of 0.31 mmHg in comparison to measured PaCO 2 by blood gas analysis. CONCLUSIONS: The estimation of PaCO 2 by the proposed equation is less biased than unaltered etCO 2 . The usage of this method in clinical practice or in applications like the automation of ventilation needs further investigation.

Preventive effects of transcutaneous CO2 application on disuse osteoporosis and muscle atrophy in a rat hindlimb suspension model.

We previously demonstrated that transcutaneous CO2 application promotes muscle fiber-type switching, fracture healing, and osteogenesis by increasing blood flow and angiogenesis. Here, we aimed to investigate the preventive effects of transcutaneous CO2 application on disuse osteoporosis and muscle atrophy in a rat hindlimb suspension model. Eleven-week-old male Sprague-Dawley rats were divided into hindlimb suspension (HS), HS with transcutaneous CO2 application (HSCO2), and control groups. HSCO2 rats were administered transcutaneous 100 % CO2 gas in their bilateral hindlimbs, five times a week for 20 min. After 3 weeks, we harvested the gastrocnemius, femur, and tibia for assessment. Histological analysis revealed a significant decrease in the gastrocnemius myofiber cross-sectional area in HS rats compared to the control rats, whereas HSCO2 rats exhibited a significant increase compared to HS rats. Micro-computed tomography showed significant bone atrophy in the trabecular and cortical bones of the femur in HS rats compared to those of the control rats, whereas significant improvement was noted in HSCO2 rats. Histological analysis of the proximal tibia revealed more marrow adipose tissue in the HS rats than in the control rats. However, in the HSCO2 rats, fewer marrow adipose tissue and osteoclasts were observed. Moreover, HSCO2 rats had more osteoblasts and higher expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and vascular endothelial growth factor (VEGF) than the HS rats. The gastrocnemius and distal femur of HSCO2 rats also exhibited elevated PGC-1α and VEGF expression and upregulation of the myogenesis markers and osteogenesis markers compared to those of HS rats. This treatment effectively prevented disuse osteoporosis and muscle atrophy by promoting local angiogenesis and blood flow. PGC-1α is crucial for promoting this angiogenic pathway. Transcutaneous CO2 application may be a novel preventive procedure for disuse osteoporosis and muscle atrophy, complementing medication and rehabilitation.

Accuracy and Interpretation of Transcutaneous Carbon Dioxide Monitoring in Critically Ill Children.

OBJECTIVES: Transcutaneous carbon dioxide (Tc co2 ) monitoring can noninvasively assess ventilation by estimating carbon dioxide ( CO2 ) levels in the blood. We aimed to evaluate the accuracy of Tc co2 monitoring in critically ill children by comparing it to the partial pressure of arterial carbon dioxide (Pa co2 ). In addition, we sought to determine the variation between Tc co2 and Pa co2 acceptable to clinicians to modify patient care and to determine which patient-level factors may affect the accuracy of Tc co2 measurements. DESIGN: Retrospective observational cohort study. SETTING: Single, quaternary care PICU from July 1, 2012, to August 1, 2020. PATIENTS: Included participants were admitted to the PICU and received noninvasive ventilation support (i.e., continuous or bilevel positive airway pressure), conventional mechanical ventilation, or high-frequency oscillatory or percussive ventilation with Tc co2 measurements obtained within 15 minutes of Pa co2 measurement. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Three thousand four hundred seven paired arterial blood gas and Tc co2 measurements were obtained from 264 patients. Bland-Altman analysis revealed a bias of -4.4 mm Hg (95% CI, -27 to 18.3 mm Hg) for Tc co2 levels against Pa co2 levels on the first measurement pair for each patient, which fell within the acceptable range of ±5 mm Hg stated by surveyed clinicians, albeit with wide limits of agreement. The sensitivity and specificity of Tc co2 to diagnose hypercarbia were 93% and 71%, respectively. Vasoactive-Infusion Score (VIS), age, and self-identified Black/African American race confounded the relationship between Tc co2 with Pa co2 but percent fluid overload, weight-for-age, probe location, and severity of illness were not significantly associated with Tc co2 accuracy. CONCLUSIONS: Tc co2 monitoring may be a useful adjunct to monitor ventilation in children with respiratory failure, but providers must be aware of the limitations to its accuracy.

The ontogeny of white leghorn chicken (Gallus domesticus) blood chemistry changes in response to acute exposure to 10 % O2.

The embryonic chicken is a valuable model for studying the maturation of cardiovascular physiology and the responses of this organ system to environmental manipulations such as acute hypoxia. Hypoxia determines not only the general cardiovascular response but also is a tool to determine the system's maturation of reflexive control. Several studies suggest embryonic chicken's regulation of the cardiovascular response to hypoxia, but no studies have measured the blood chemistry changes that accompany these responses. To clarify the changes in blood parameters accompanying cardiovascular function changes during acute hypoxia, we designed a study to investigate the blood chemistry (pO2, pCO2, pH, lactate, glucose, and blood ions) in developing embryos during acute hypoxia (O2 = 10 %). Embryos ranging from day 13 to 21 of incubation were sampled during a control period and at the end of a 5-min of hypoxia. Hypoxia caused bradycardia on all days of incubation. The maximal blood hypoxic response occurred on day 15, with lactate increasing 7-fold (2.5 to 16.6 mmol/l) while glucose levels decreased by 50 % (136 to 63 mg/dl). Furthermore, hypoxia reduced pH (7.40 to 7.26), which peaked on day 15. These data indicate that a 5-min exposure to 10 % O2 is sufficient to induce dramatic changes in blood chemistry however chorioallantoic arterial blood pO2 was unchanged on most days of the study. Therefore, given the cardiovascular response to hypoxia and the increase in blood lactate prior to airbreathing in the chicken embryo, the embryonic tissues experienced an acute stress that may be the basis for the change in cardiovascular function during the exposure.

Acute renal response to changes in carbon dioxide in mechanically ventilated female pigs.

Kidney response to acute and mechanically induced variation in ventilation associated with different levels of PEEP has not been investigated. We aimed to quantify the effect of ventilatory settings on renal acid-base compensation. Forty-one pigs undergoing hypo- (<0.2 Lkg-1 min-1, PEEP 25 cmH2O), intermediate (0.2-0.4 Lkg-1 min-1 with either PEEP 5 or 25 cmH2O), or hyper-ventilation (>0.4 Lkg-1 min-1, PEEP 5 cmH2O) for 48 h were retrospectively included. The decrease in pH paralleled the decrease in plasma strong ion difference (SID) in hyper- and intermediately ventilated groups with lower PEEP. In contrast, the plasma SID remained nearly constant in hypo- and intermediately ventilated groups with higher PEEP. Changes in plasma chloride concentration accounted for the changes in plasma SID (conditional R2 = 0.86). The plasma SID changes were paralleled by mirror changes in urinary SID. Higher PEEP (25 cmH2O), compared to lower PEEP (5 cmH2O) dampened or abolished the renal compensation through its effect on hemodynamics (higher central venous and mean pulmonary pressures), irrespective of minute ventilation. During mechanical ventilation, the compensatory renal response to respiratory derangement is immediate and progressive but can be dampened by high PEEP levels.

The independent effects of hydrostatic pressure and hypercapnic breathing during water immersion on ventilatory sensitivity and cerebrovascular reactivity.

Head-out water immersion (HOWI) induces ventilatory and hemodynamic changes, which may be a result of hydrostatic pressure, augmented arterial CO2 tension, or a combination of both. We hypothesized that the hydrostatic pressure and elevated CO2 tension that occur during HOWI will contribute to an augmented ventilatory sensitivity to CO2 and an attenuated cerebrovascular reactivity to CO2 during water immersion. Twelve subjects [age: 24 ± 3 yr, body mass index (BMI): 25 ± 3 kg/m2] completed HOWI, waist water immersion with CO2 (WWI + CO2), and WWI, where a rebreathing test was conducted at baseline, 10, 30, and 60 min, and postimmersion. End-tidal pressure of carbon dioxide ([Formula: see text]), minute ventilation, expired gases, blood pressure, heart rate, and middle cerebral artery blood velocity were recorded continuously. [Formula: see text] increased throughout all visits (P ≤ 0.011), was similar during HOWI and WWI + CO2 (P ≥ 0.264), and was greater during WWI + CO2 versus WWI at 10, 30, and 60 min (P < 0.001). When HOWI vs. WWI + CO2 were compared, the change in ventilatory sensitivity to CO2 was different at 10 (0.59 ± 0.34 vs. 0.06 ± 0.23 L/min/mmHg; P < 0.001), 30 (0.58 ± 0.46 vs. 0.15 ± 0.25 L/min/mmHg; P < 0.001), and 60 min (0.63 ± 0.45 vs. 0.16 ± 0.34 L/min/mmHg; P < 0.001), whereas there were no differences between conditions for cerebrovascular reactivity to CO2 (P ≥ 0.163). When WWI + CO2 versus WWI were compared, ventilatory sensitivity to CO2 was not different between conditions (P ≥ 0.642), whereas the change in cerebrovascular reactivity to CO2 was different at 30 min (-0.56 ± 0.38 vs. -0.30 ± 0.25 cm/s/mmHg; P = 0.010). These data indicate that during HOWI, ventilatory sensitivity to CO2 increases due to the hydrostatic pressure, whereas cerebrovascular reactivity to CO2 decreases due to the combined effects of immersion.NEW & NOTEWORTHY Although not fully elucidated, the ventilatory and hemodynamic alterations during water immersion appear to be a result of the combined effects of immersion (i.e., elevated [Formula: see text], central hypervolemia, increased cerebral perfusion, increased work of breathing, etc.). Our findings demonstrate that an augmented ventilatory sensitivity to CO2 during immersion may be due to the hydrostatic pressure across the chest wall, whereas an attenuated cerebrovascular reactivity to CO2 may be due to the combined effects of immersion.

Temperature effects on blood gases in embryonic American alligators (Alligator mississippiensis).

Numerous studies report on the influence of temperature on blood gases in ectothermic vertebrates, but there is merely a cursory understanding of these effects in developing animals. Animals that develop in eggs are at the mercy of environmental temperature and are expected to lack the capacity to regulate gas exchange and may regulate blood gases by means of altered conductance for gas exchange. We, therefore, devised a series of studies to characterize the developmental changes in blood gases when embryonic alligators were exposed to 25, 30 and 35 °C. To determine how blood parameters were impacted by changes in embryonic temperature, blood was sampled from the chorioallantoic membrane artery. The blood in the chorioallantoic membrane artery is a mixture of oxygen-poor and oxygen-rich blood, which based on the embryonic vascular anatomy may reflect blood that perfuses the chemoreceptors of the developing animal. Our findings indicate that following a 48 h exposure to 25 °C or 35 °C, there was a positive relationship between CAM artery blood PO2, PCO2 and glucose. However, blood pH suggests embryonic alligators lack an acute regulatory mechanism for adjusting blood pH.

The complexity of cerebral blood flow regulation: the interaction of posture and vasomotor reactivity.

Arterial carbon dioxide ([Formula: see text]) and posture influence the middle (MCAv) and posterior (PCAv) cerebral artery blood velocities, but there is paucity of data about their interaction and need for an integrated model of their effects, including dynamic cerebral autoregulation (dCA). In 22 participants (11 males, age 30.2 ± 14.3 yr), blood pressure (BP, Finometer), dominant MCAv and nondominant PCAv (transcranial Doppler ultrasound), end-tidal CO2 (EtCO2, capnography), and heart rate (HR, ECG) were recorded continuously. Two recordings (R) were taken when the participant was supine (R1, R2), two taken when the participant was sitting (R3, R4), and two taken when the participant was standing (R5, R6). R1, R3, and R5 consisted of 3 min of 5% CO2 through a mask and R2, R4, and R6 consisted of 3 min of paced hyperventilation. The effects of [Formula: see text] were expressed with a logistic curve model (LCM) for each parameter. dCA was expressed by the autoregulation index (ARI), derived by transfer function analysis. Standing shifted LCM to the left for MCAv (P < 0.001), PCAv (P < 0.001), BP (P = 0.03), and ARI (P = 0.001); downward for MCAv and PCAv (both P < 0.001), and upward for HR (P < 0.001). For BP, LCM was shifted downward by sitting and standing (P = 0.024). For ARI, the hypercapnic range of LCM was shifted upward during standing (P < 0.001). A more complete mapping of the combined effects of posture and arterial CO2 on the cerebral circulation and peripheral variables can be obtained with the LCM over a broad physiological range of EtCO2 values.NEW & NOTEWORTHY Data from supine, sitting, and standing postures were measured. Modeling the data with logistic curves to express the effects of CO2 reactivity on middle cerebral artery blood velocity (MCAv), posterior cerebral artery blood velocity (PCAv), heart rate, blood pressure (BP), and the autoregulation index (ARI), provided a more comprehensive approach to study the interaction of arterial CO2 with posture than in previous studies. Above all, shifts of the logistic curve model with changes in posture have shown interactions with [Formula: see text] that have not been previously demonstrated.

Oximetry and carbon dioxide screening for ventilatory requirements in children with spinal muscular atrophy type 1-3.

INTRODUCTION: Despite disease modifying treatments (DMT), assisted ventilation is commonly required in children with Spinal Muscular Atrophy (SMA). Guidelines suggest screening with oximetry and transcutaneous carbon dioxide (TcCO2) for sleep disordered breathing (SDB). AIM: To determine the utility of pulse oximetry and TcCO2 as a screen for SDB and the need for Non-Invasive Ventilation (NIV) in children with SMA type 1-3. METHODS: A prospective cohort study was conducted in Queensland, Australia. Full diagnostic PSG was completed in DMT naïve children with SMA. Pulse oximetry and TcCO2 were extracted from PSG. Apnoea-hypopnoea indices (AHI) criteria were applied to PSG results to define the need for NIV. Abnormal was defined as: ≤3 months of age [mo] AHI≥10 events/hour; >3mo AHI ≥5 events/hour. Receiver operating characteristic curves were calculated for abnormal PSG and pulse oximetry/TcCO2 variables, and diagnostic statistics were calculated. RESULTS: Forty-seven untreated children with SMA were recruited (type 1 n = 13; 2 n = 21; 3 n = 13) ranging from 0.2 to 18.8 years old (median 4.9 years). Oxygen desaturation index ≥4 % (ODI4) ≥20events/hour had sensitivity 82.6 % (95 % CI 61.2-95.0) and specificity of 58.3 % (95 % CI 36.6-77.9). TcCO2 alone and combinations of oximetry/TcCO2 had low diagnostic ability. The same methodology was applied to 36 children who were treated (type 1 n = 7; type 2 n = 17; type n = 12) and oximetry±TcCO2 had low diagnostic ability. CONCLUSION: ODI4 ≥20events/hour can predict the need for NIV in untreated children with SMA. TcCO2 monitoring does not improve the PPV. If normal however, children may still require a diagnostic PSG. Neither oximetry nor TcCO2 monitoring were useful screening tests in the children treated with DMT.

Extracorporeal Carbon Dioxide Removal With the Hemolung in Patients With Acute-on-Chronic Respiratory Failure: A Multicenter Retrospective Cohort Study.

Extracorporeal carbon dioxide removal (ECCO2R) devices are increasingly used in treating acute-on-chronic respiratory failure caused by chronic lung diseases. There are no large studies that investigated safety, efficacy, and the independent association of prognostic variables to survival that could define the role of ECCO2R devices in such patients. This multicenter, multinational, retrospective study investigated the efficacy, safety of a single ECCO2R device (Hemolung) in patients with acute on chronic respiratory failure and identified variables independently associated with intensive care unit (ICU) survival. The primary outcome was improvement in blood gasses with the use of Hemolung. Secondary outcomes included reduction in tidal volume, respiratory rate, minute ventilation, survival to ICU discharge, and complication profile. Multivariable regression analysis was used to identify variables that are independently associated with ICU survival. A total of 62 patients were included. There was a significant improvement in pH and partial pressure of carbon dioxide in arterial blood (PaCO2) along with a reduction in respiratory rate, tidal volume, and minute ventilation with Hemolung therapy. The complication profile did not differ between survivors and nonsurvivors. Multivariable analysis identified the duration of Hemolung therapy to be independently associated with survival to ICU discharge (adjusted odds ratio = 1.21; 95% confidence interval [CI] = 1.040-1.518; p = 0.01).

End-tidal carbon dioxide during spontaneous breathing trial to predict extubation failure: A prospective observational study.

Despite advances in weaning protocols, extubation failure (EF) is associated with poor outcomes. Many predictors of EF have been proposed, including hypercapnia at the end of the spontaneous breathing test (SBT). However, performing arterial blood gases at the end of SBT is not routinely recommended, whereas end-tidal carbon dioxide (EtCO2) can be routinely monitored during SBT. We aimed to evaluate the clinical utility of EtCO2 to predict EF. Patients undergoing planned extubation were eligible. Non-inclusion criteria were tracheostomy and patients extubated after successful T-tube SBT. We recorded clinical data and EtCO2 in 189 patients during a successful one-hour low pressure support SBT. EtCO2 measured before successful SBT was lower in patients with EF compared to those with successful extubation (27 [24-29] vs 30 [27-47] mmHg, p = 0.02), while EtCO2 measured at five minutes and at the end of the SBT was not different between the two groups (26 [22-28] vs. 29 [28-49] mmHg, p = 0.06 and 26 [26-29] vs. 29 [27-49] mmHg, p = 0.09, respectively). Variables identified by multivariable analysis as independently associated with EF were acute respiratory failure as the cause of intubation and ineffective cough. Our study suggests that recording EtCO2 during successful SBT appears to have limited predictive value for EF.

Association of early changes in arterial carbon dioxide with acute brain injury in adult patients with extracorporeal membrane oxygenation: A ten-year retrospective study in a German tertiary care hospital.

PURPOSE: To assess the association between fluctuations of arterial carbon dioxide early after start of extracorporeal membrane oxygenation (ECMO) with intracranial hemorrhage (ICH) or ischemic stroke (IS). MATERIALS AND METHODS: This single-center retrospective study included patients who required ECMO for circulatory or respiratory failure between January 2011 and April 2021 and for whom a cerebral computed tomography (cCT) scan was available. Multivariable logistic regression models were fitted to evaluate the association between the relative change of arterial carbon dioxide (RelΔPaCO2) and ICH, IS or a composite of ICH, IS, and mortality. RESULTS: In 618 patients (venovenous ECMO: n = 295; venoarterial ECMO: n = 323) ICH occurred more frequently in patients with respiratory failure (19.0%) compared with patients with circulatory failure (6.8%). Conversely, the incidence of IS was higher in patients with circulatory failure (19.2%) compared with patients with respiratory failure (4.7%). While patients with ECMO for respiratory failure were more likely to have ICH (OR 3.683 [95% CI: 1.855;7.309], p < 0.001), they had a lower odds for IS (OR 0.360 [95%CI: 0.158;0.820], p = 0.015) compared with patients with circulatory failure. There was no significant association between RelΔPaCO2 and ICH or IS. CONCLUSIONS: Irrespective of the indication for ECMO, we did not find a significant association between the relative change in PaCO2 early after ECMO initiation and acute brain injury. Aside from early PaCO2 decline at cannulation, future studies should address fluctuations of PaCO2 throughout the course of ECMO support and their effect on acute brain injury.

Factors associated with carbon dioxide transfer in an experimental model of severe acute kidney injury and hypoventilation during high bicarbonate continuous renal replacement therapy and oxygenation membrane support.

OBJECTIVE: To investigate the factors influencing carbon dioxide transfer in a system that integrates an oxygenation membrane in series with high-bicarbonate continuous veno-venous hemodialysis in hypercapnic animals. METHODS: In an experimental setting, we induced severe acute kidney injury and hypercapnia in five female Landrace pigs. Subsequently, we initiated high (40mEq/L) bicarbonate continuous veno-venous hemodialysis with an oxygenation membrane in series to maintain a pH above 7.25. At intervals of 1 hour, 6 hours, and 12 hours following the initiation of continuous veno-venous hemodialysis, we performed standardized sweep gas flow titration to quantify carbon dioxide transfer. We evaluated factors associated with carbon dioxide transfer through the membrane lung with a mixed linear model. RESULTS: A total of 20 sweep gas flow titration procedures were conducted, yielding 84 measurements of carbon dioxide transfer. Multivariate analysis revealed associations among the following (coefficients ± standard errors): core temperature (+7.8 ± 1.6 °C, p < 0.001), premembrane partial pressure of carbon dioxide (+0.2 ± 0.1/mmHg, p < 0.001), hemoglobin level (+3.5 ± 0.6/g/dL, p < 0.001), sweep gas flow (+6.2 ± 0.2/L/minute, p < 0.001), and arterial oxygen saturation (-0.5 ± 0.2%, p = 0.019). Among these variables, and within the physiological ranges evaluated, sweep gas flow was the primary modifiable factor influencing the efficacy of low-blood-flow carbon dioxide removal. CONCLUSION: Sweep gas flow is the main carbon dioxide removal-related variable during continuous veno-venous hemodialysis with a high bicarbonate level coupled with an oxygenator. Other carbon dioxide transfer modulating variables included the hemoglobin level, arterial oxygen saturation, partial pressure of carbon dioxide and core temperature. These results should be interpreted as exploratory to inform other well-designed experimental or clinical studies.

The use of venous blood gas in assessing arterial acid-base and oxygenation status - an analysis of aggregated data from multiple studies evaluating the venous to arterial conversion (v-TAC) method.

BACKGROUND: Several methods exist to reduce the number of arterial blood gases (ABGs). One method, Roche v-TAC, has been evaluated in different patient groups. This paper aggregates data from these studies, in different patient categories using common analysis criteria. RESEARCH DESIGN AND METHODS: We included studies evaluating v-TAC based on paired arterial and peripheral venous blood samples. Bland-Altman analysis compared measured and calculated arterial values of pH, PCO2, and PO2. Subgroup analyses were performed for normal, chronic hypercapnia and chronic base excess, acute hyper- and hypocapnia, and acute and chronic base deficits. RESULTS: 811 samples from 12 studies were included. Bias and limits of agreement for measured and calculated values: pH 0.001 (-0.029 to 0.031), PCO2 -0.08 (-0.65 to 0.49) kPa, and PO2 0.04 (-1.71 to 1.78) kPa, with similar values for all sub-group analyses. CONCLUSION: These data suggest that v-TAC analysis may have a role in replacing ABGs, avoiding arterial puncture. Substantial data exist in patients with chronic hypercapnia and chronic base excess, acute hyper- and hypocapnia, and in patients with relatively normal acid-base status, with similar bias and precision across groups and across study data. Limited data exist for patients with acute and chronic base deficits.

A Summed Score From Cardiopulmonary Exercise Test Parameters Predicts 1-Year Mortality in Newly Diagnosed Interstitial Lung Disease.

BACKGROUND: Cardiopulmonary exercise testing (CPET) is a unique diagnostic tool that assesses the functional capacity of the heart, lungs, and peripheral oxidative system in an integrated manner. However, the clinical utility of CPET for evaluating interstitial lung disease (ILD) remains uncertain. The objective of this study was to determine the predictive value of CPET for mortality in subjects with ILD. METHODS: We prospectively enrolled subjects with ILD who underwent CPET at a tertiary medical center in Taiwan and followed up their survival status for 12 months. Mortality prediction was based on comparing CPET parameters between subjects who survived and those who died. We further analyzed CPET parameters that showed significant differences using receiver operating characteristic curves to identify their optimal cutoff values. RESULTS: A total of 106 newly diagnosed subjects with ILD underwent CPET, and the 1-y mortality rate was 7.5%. Six CPET variables were found to be significant predictors of mortality: peak oxygen consumption, oxygen pulse, end-tidal partial pressure of carbon dioxide, heart rate recovery 1 min after CPET, minute ventilation to carbon dioxide output slope, and functional aerobic impairment. We calculated a summed score by adding the number of CPET variables that exceeded their cutoff values. Subjects with a summed score of 6 had a 1-y survival rate of only 25%, whereas subjects with scores of 0-5 had a survival rate of 98%. CONCLUSIONS: In conclusion, the summed score represents a useful tool for screening patients with ILD who can undergo a CPET to determine their prognosis.

The physiological significance of plasma-accessible carbonic anhydrase in the respiratory systems of fishes.

Carbonic anhydrase (CA) activity is ubiquitously found in all vertebrate species, tissues and cellular compartments. Most species have plasma-accessible CA (paCA) isoforms at the respiratory surfaces, where the enzyme catalyzes the conversion of plasma bicarbonate to carbon dioxide (CO2) that can be excreted by diffusion. A notable exception are the teleost fishes that appear to lack paCA at their gills. The present review: (i) recapitulates the significance of CA activity and distribution in vertebrates; (ii) summarizes the current evidence for the presence or absence of paCA at the gills of fishes, from the basal cyclostomes to the derived teleosts and extremophiles such as the Antarctic icefishes; (iii) explores the contribution of paCA to organismal CO2 excretion in fishes; and (iv) the functional significance of its absence at the gills, for the specialized system of O2 transport in most teleosts; (v) outlines the multiplicity and isoform distribution of membrane-associated CAs in fishes and methodologies to determine their plasma-accessible orientation; and (vi) sketches a tentative time line for the evolutionary dynamics of branchial paCA distribution in the major groups of fishes. Finally, this review highlights current gaps in the knowledge on branchial paCA function and provides recommendations for future work.

Screening Strategies for Sleep-Disordered Breathing in Patients With Spinal Cord Injury in a Tertiary Care Rehabilitation Center.

BACKGROUND: Sleep-disordered breathing (SDB) is frequent in patients with spinal-cord injury (SCI). However, SDB is frequently underdiagnosed due to limited access to diagnostic testing and knowledge about the condition. Moreover, SDB heterogeneity (sleep apnea, obstructive sleep apnea or central sleep apnea and nocturnal alveolar hypoventilation) implies complex evaluation of both nocturnal respiratory effort and hypercapnia. The aim of this study was to compare different screening strategies for an SDB diagnosis in patients with SCI. METHODS: This was a retrospective analysis of data from subjects with SCI followed up in a tertiary-care rehabilitation center with a specialized sleep unit. Subjective (questionnaires) and objective data (polysomnography [PSG]), [Formula: see text] extracted from the PSG, morning blood gases, and nocturnal transcutaneous CO2 (PtcCO2 ) were collected and analyzed. A retrospective comparison of different strategies for SDB screening was carried out. Each strategy was compared (alone and in combination) with the standard of care for sleep apnea (PSG) and nocturnal alveolar hypoventilation (PtcCO2 ) diagnosis. The performance of the usual cutoff and visual analysis was studied. RESULTS: Among 190 subjects with SCI who underwent a full night's PSG, data were available for 104 questionnaires and 162 with oximetry. Nocturnal alveolar hypoventilation was screened by PtcCO2 and blood gases in 52 subjects with SCI. Questionnaires (the modified Screening for Obstructive Sleep Apnea in Tetraplegia and the Epworth Sleepiness Scale) had poor performance for identifying sleep apnea and did not identify nocturnal alveolar hypoventilation. [Formula: see text] (oxygen desaturation index score ≥ 13) and visual analysis of [Formula: see text] were good at identifying sleep apnea but insufficient to identify nocturnal alveolar hypoventilation. Diurnal blood gases were poor predictors of nocturnal alveolar hypoventilation. CONCLUSIONS: Questionnaires were of limited use in subjects with SCI, but the oxygen desaturation index derived from oximetry performed well for sleep apnea screening. Both diurnal blood gases and oximetry visual analysis were insufficient for nocturnal alveolar hypoventilation screening. PtcCO2 monitoring should be mandatory and ideally combined with PSG given the heterogeneity of SDB phenotypes and associated sleep comorbidities of patients with SCI.

Arterial blood gas analysis or venous blood gas analysis for adult hospitalised patients with respiratory presentations: a systematic review.

BACKGROUND: Identification of hypoxaemia and hypercapnia is essential for the diagnosis and treatment of acute respiratory failure. While arterial blood gas (ABG) analysis is standard for PO2 and PCO2 measurement, venous blood gas (VBG) analysis is increasingly used as an alternative. Previous systematic reviews established that VBG reporting of PO2 and PCO2 is less accurate, but the impacts on clinical management and patient outcomes are unknown. AIMS: This study aimed to systematically review available evidence of the clinical impacts of using ABGs or VBGs and examine the arteriovenous difference in blood gas parameters. METHODS: A comprehensive search of the MEDLINE, Embase and Cochrane Library databases since inception was conducted. Included studies were prospective or cross-sectional studies comparing peripheral ABG to peripheral VBG in adult non-critical care inpatients presenting with respiratory symptoms. RESULTS: Of 15 119 articles screened, 15 were included. No studies were found that examined clinical impacts resulting from using VBG compared to ABG. Included studies focused on the agreement between ABG and VBG measurements of pH, PO2, PCO2 and HCO3 -. Due to the heterogeneity of the included studies, qualitative evidence synthesis was performed. While the arteriovenous difference in pH and HCO3 - was generally predictable, the difference in PO2 and PCO2 was more significant and less predictable. CONCLUSIONS: Our study reinforces the notion that VBG is not comparable to ABG for physiological measurements. However, a key revelation from our research is the significant lack of data regarding the clinical implications of using VBG instead of ABG, a common scenario in clinical practice. This highlights a critical knowledge gap.