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.

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).

Relative Severity of Human Performance Decrements Recorded in Rapid vs. Gradual Decompression.

INTRODUCTION: Cabin decompression presents a threat in high-altitude-capable aircraft. A chamber study was performed to compare effects of rapid (RD) vs. gradual decompression and gauge impairment at altitude with and without hypoxia, as well as to assess recovery.METHODS: There were 12 participants who completed RD (1 s) and Gradual (3 min 12 s) ascents from 2743-7620 m (9000-25000 ft) altitude pressures while breathing air or 100% O2. Physiological indices included oxygen saturation (SPo2), heart rate (HR), respiration, end tidal O2 and CO2 partial pressures, and electroencephalography (EEG). Cognition was evaluated using SYNWIN, which combines memory, arithmetic, visual, and auditory tasks. The study incorporated ascent rate (RD, gradual), breathing gas (air, 100% O2) and epoch (ground-level, pre-breathe, ascent-altitude, recovery) as factors.RESULTS: Physiological effects in hypoxic "air" ascents included decreased SPo2 and end tidal O2 and CO2 partial pressures (hypocapnia), with elevated HR and minute ventilation (V˙E); SPo2 and HR effects were greater after RD (-7.3% lower and +10.0 bpm higher, respectively). HR and V˙E decreased during recovery. SYNWIN performance declined during ascent in air, with key metrics, including composite score, falling further (-75% vs. -50%) after RD. Broad cognitive impairment was not recorded on 100% O2, nor in recovery. EEG signals showed increased slow-wave activity during hypoxia.DISCUSSION: In hypoxic exposures, RD impaired performance more than gradual ascent. Hypobaria did not comprehensively impair performance without hypoxia. Lingering impairment was not observed during recovery, but HR and V˙E metrics suggested compensatory slowing following altitude stress. Participants' cognitive strategy shifted as hypoxia progressed, with efficiency giving way to "satisficing," redistributing effort to easier tasks.Beer J, Mojica AJ, Blacker KJ, Dart TS, Morse BG, Sherman PM. Relative severity of human performance decrements recorded in rapid vs. gradual decompression. Aerosp Med Hum Perform. 2024; 95(7):353-366.

Hypocapnia in women with fibromyalgia.

OBJECTIVES: The purpose of this study was to investigate whether people with fibromyalgia (FM) have dysfunctional breathing by examining acid-base balance and comparing it with healthy controls. METHODS: Thirty-six women diagnosed with FM and 36 healthy controls matched for age and gender participated in this cross-sectional study. To evaluate acid-base balance, arterial blood was sampled from the radial artery. Carbon dioxide, oxygen, bicarbonate, base excess, pH and lactate were analysed for between-group differences. Blood gas analyses were performed stepwise on each individual to detect acid-base disturbance, which was categorized as primary respiratory and possible compensation indicating chronicity. A three-step approach was employed to evaluate pH, carbon dioxide and bicarbonate in this order. RESULTS: Women with FM had significantly lower carbon dioxide pressure (p = 0.013) and higher lactate (p = 0.038) compared to healthy controls at the group level. There were no significant differences in oxygen pressure, bicarbonate, pH and base excess. Employing a three-step acid-base analysis, 11 individuals in the FM group had a possible renally compensated mild chronic hyperventilation, compared to only 4 among the healthy controls (p = 0.042). CONCLUSIONS: In this study, we could identify a subgroup of individuals with FM who may be characterized as mild chronic hyperventilators. The results might point to a plausible dysfunctional breathing in some women with FM.

The relation of lactate level and carbon dioxide pressure discrepancies between transcutaneous and arterial measurements.

Introduction: Partial carbondioxide pressure of the arterial blood (PaCO2) is used to evaluate alveolar ventilation. Transcutaneous carbon dioxide pressure (TcCO2) monitoring has been developed as a non-invasive (NIV) alternative to arterial blood gas analysis (ABG). Studies have shown that decreased tissue perfusion leads to increased carbondioxide (CO2). The use of transcutaneous capnometry may be unreliable in patients with perfusion abnormalities. In this study, we aimed to evaluate the relation between TcCO2-PaCO2 and lactate level which is recognized as a marker of hypoperfusion. Materials and Methods: In this prospective cohort study in critical care patients with hypercapnic respiratory failure (PaCO2 ≥45 mmHg) who received NIV between April 2019 and January 2020 in the intensive care unit were enrolled in the study. Patients' simultaneously measured TcCO2 and PaCO2 values of hypercapnic patients were recorded. Each paired measurement was categorized into two groups; normal lactate (<2 mmol/L) and increased lactate (≥2 mmol/L). Result: A total of 116 paired TcCO2 and PaCO2 measurements of 29 patients were recorded. Bland-Altman analysis showed the mean bias between the TcCO2 and PaCO2 and 95% limits of agreement (LOA) in all measurements (1.75 mmHg 95% LOA -3.67 to 7.17); in the normal lactate group (0.66 mmHg 95% LOA -1.71 to 3.03); and in the increased lactate group (5.17 mmHg 95% LOA -1.63 to 11.97). The analysis showed a correlation between lactate level and the difference between TcCO2 and PaCO2 (r= 0.79, p< 0.001) and a negative correlation between mean blood pressure and the difference between TcCO2 and PaCO2 (r= -0.54, p= 0.001). Multiple regression analysis results showed that lactate level was independently associated with increased differences between TcCO2 and PaCO2 (Beta= 0.875, p< 0.001). Conclusions: TcCO2 monitoring may not be reliable in patients with increased lactate levels. TcCO2 levels should be checked by ABG analysis in these patients.

Evaluation of agreement between a noninvasive method for real-time measurement of critical blood values with a standard point-of-care device.

The purpose of this work was to investigate the degree of agreement between two distinct approaches for measuring a set of blood values and to compare comfort levels reported by participants when utilizing these two disparate measurement methods. Radial arterial blood was collected for the comparator analysis using the Abbott i-STAT® POCT device. In contrast, the non-invasive proprietary DBC methodology is used to calculate sodium, potassium, chloride, ionized calcium, total carbon dioxide, pH, bicarbonate, and oxygen saturation using four input parameters (temperature, hemoglobin, pO2, and pCO2). Agreement between the measurement for a set of blood values obtained using i-STAT and DBC methodology was compared using intraclass correlation coefficients, Passing and Bablok regression analyses, and Bland Altman plots. A p-value of <0.05 was considered statistically significant. A total of 37 participants were included in this study. The mean age of the participants was 42.4 ± 13 years, most were male (65%), predominantly Caucasian/White (75%), and of Hispanic ethnicity (40%). The Intraclass Correlation Coefficients (ICC) analyses indicated agreement levels ranging from poor to moderate between i-STAT and the DBC's algorithm for Hb, pCO2, HCO3, TCO2, and Na, and weak agreement for pO2, HSO2, pH, K, Ca, and Cl. The Passing and Bablok regression analyses demonstrated that values for Hb, pO2, pCO2, TCO2, Cl, and Na obtained from the i-STAT did not differ significantly from that of the DBC's algorithm suggesting good agreement. The values for Hb, K, and Na measured by the DBC algorithm were slightly higher than those obtained by the i-STAT, indicating some systematic differences between these two methods on Bland Altman Plots. The non-invasive DBC methodology was found to be reliable and robust for most of the measured blood values compared to invasive POCT i-STAT device in healthy participants. These findings need further validation in larger samples and among individuals afflicted with various medical conditions.

Standard vs. carbone dioxide adapted kidney replacement therapy in hypercapnic ARDS patients: a randomized controlled pilot trial (BigBIC).

BACKGROUND: Current continuous kidney replacement therapy (CKRT) protocols ignore physiological renal compensation for hypercapnia. This study aimed to explore feasibility, safety, and clinical benefits of pCO2-adapted CKRT for hypercapnic acute respiratory distress syndrome (ARDS) patients with indication for CKRT. METHODS: We enrolled mechanically ventilated hypercapnic ARDS patients (pCO2 > 7.33 kPa) receiving regional citrate anticoagulation (RCA) based CKRT in a prospective, randomized-controlled pilot-study across five intensive care units at the Charité-Universitätsmedizin Berlin, Germany. Patients were randomly assigned 1:1 to the control group with bicarbonate targeted to 24 mmol/l or pCO2-adapted-CKRT with target bicarbonate corresponding to physiological renal compensation. Study duration was six days. Primary outcome was bicarbonate after 72 h. Secondary endpoints included safety and clinical endpoints. Endpoints were assessed in all patients receiving treatment. RESULTS: From September 2021 to May 2023 40 patients (80% male) were enrolled. 19 patients were randomized to the control group, 21 patients were randomized to pCO2-adapted-CKRT. Five patients were excluded before receiving treatment: three in the control group (consent withdrawal, lack of inclusion criteria fulfillment (n = 2)) and two in the intervention group (lack of inclusion criteria fulfillment, sudden unexpected death) and were therefore not included in the analysis. Median plasma bicarbonate 72 h after randomization was significantly higher in the intervention group (30.70 mmol/l (IQR 29.48; 31.93)) than in the control group (26.40 mmol/l (IQR 25.63; 26.88); p < 0.0001). More patients in the intervention group received lung protective ventilation defined as tidal volume < 8 ml/kg predicted body weight. Thirty-day mortality was 10/16 (63%) in the control group vs. 8/19 (42%) in the intervention group (p = 0.26). CONCLUSION: Tailoring CKRT to physiological renal compensation of respiratory acidosis appears feasible and safe with the potential to improve patient care in hypercapnic ARDS. TRIAL REGISTRATION: The trial was registered in the German Clinical Trials Register (DRKS00026177) on September 9, 2021 and is now closed.

Effects of extracorporeal CO2 removal on gas exchange and ventilator settings: a systematic review and meta-analysis.

PURPOSE: A systematic review and meta-analysis to evaluate the impact of extracorporeal carbon dioxide removal (ECCO2R) on gas exchange and respiratory settings in critically ill adults with respiratory failure. METHODS: We conducted a comprehensive database search, including observational studies and randomized controlled trials (RCTs) from January 2000 to March 2022, targeting adult ICU patients undergoing ECCO2R. Primary outcomes were changes in gas exchange and ventilator settings 24 h after ECCO2R initiation, estimated as mean of differences, or proportions for adverse events (AEs); with subgroup analyses for disease indication and technology. Across RCTs, we assessed mortality, length of stay, ventilation days, and AEs as mean differences or odds ratios. RESULTS: A total of 49 studies encompassing 1672 patients were included. ECCO2R was associated with a significant decrease in PaCO2, plateau pressure, and tidal volume and an increase in pH across all patient groups, at an overall 19% adverse event rate. In ARDS and lung transplant patients, the PaO2/FiO2 ratio increased significantly while ventilator settings were variable. "Higher extraction" systems reduced PaCO2 and respiratory rate more efficiently. The three available RCTs did not demonstrate an effect on mortality, but a significantly longer ICU and hospital stay associated with ECCO2R. CONCLUSIONS: ECCO2R effectively reduces PaCO2 and acidosis allowing for less invasive ventilation. "Higher extraction" systems may be more efficient to achieve this goal. However, as RCTs have not shown a mortality benefit but increase AEs, ECCO2R's effects on clinical outcome remain unclear. Future studies should target patient groups that may benefit from ECCO2R. PROSPERO Registration No: CRD 42020154110 (on January 24, 2021).

[Research progress of diagnostic and therapeutic value of carbon dioxide-derived indicators in patients with sepsis].

Effectively assessing oxygen delivery and demand is one of the key targets for fluid resuscitation in sepsis. Clinical signs and symptoms, blood lactic acid levels, and mixed venous oxygen saturation (SvO2) or central venous oxygen saturation (ScvO2) all have their limitations. In recent years, these limitations have been overcome through the use of derived indicators from carbon dioxide (CO2) such as mixed veno-arterial carbon dioxide partial pressure difference (Pv-aCO2, PCO2 gap, or ΔPCO2), the ratio of mixed veno-arterial carbon dioxide partial pressure difference to arterial-mixed venous oxygen content difference (Pv-aCO2/Ca-vO2). Pv-aCO2, PCO2 gap or ΔPCO2 is not a purely anaerobic metabolism indicator as it is influenced by oxygen consumption. However, it reliably indicates whether blood flow is sufficient to carry CO2 from peripheral tissues to the lungs for clearance, thus reflecting the adequacy of cardiac output and metabolism. The Pv-aCO2/Ca-vO2 may serve as a marker of hypoxia. SvO2 and ScvO2 represent venous oxygen saturation, reflecting tissue oxygen utilization. When oxygen delivery decreases but tissues still require more oxygen, oxygen extraction rate usually increases to meet tissue demands, resulting in decreased SvO2 and ScvO2. But in some cases, even if the oxygen delivery rate and tissue utilization rate of oxygen are reduced, it may still lead to a decrease in SvO2 and ScvO2. Sepsis is a classic example where tissue oxygen utilization decreases due to factors such as microcirculatory dysfunction, even when oxygen delivery is sufficient, leading to decrease in SvO2 and ScvO2. Additionally, the solubility of CO2 in plasma is approximately 20 times that of oxygen. Therefore, during sepsis or septic shock, derived variables of CO2 may serve as sensitive markers for monitoring tissue perfusion and microcirculatory hemodynamics. Its main advantage over blood lactic acid is its ability to rapidly change and provide real-time monitoring of tissue hypoxia. This review aims to demonstrate the principles of CO2-derived variables in sepsis, assess the available techniques for evaluating CO2-derived variables during the sepsis process, and discuss their clinical relevance.

Selected and shared hematological responses to apnea in elite human free divers and northern elephant seals (Mirounga angustirostris).

Despite elite human free divers achieving incredible feats in competitive free diving, there has yet to be a study that compares consummate divers, (i.e. northern elephant seals) to highly conditioned free divers (i.e., elite competitive free-diving humans). Herein, we compare these two diving models and suggest that hematological traits detected in seals reflect species-specific specializations, while hematological traits shared between the two species are fundamental mammalian characteristics. Arterial blood samples were analyzed in elite human free divers (n = 14) during a single, maximal volitional apnea and in juvenile northern elephant seals (n = 3) during rest-associated apnea. Humans and elephant seals had comparable apnea durations (∼6.5 min) and end-apneic arterial Po2 [humans: 40.4 ± 3.0 mmHg (means ± SE); seals: 27.1 ± 5.9 mmHg; P = 0.2]. Despite similar increases in arterial Pco2 (humans: 33 ± 5%; seals: 16.3 ± 5%; P = 0.2), only humans experienced reductions in pH from baseline (humans: 7.45 ± 0.01; seals: 7.39 ± 0.02) to end apnea (humans: 7.37 ± 0.01; seals: 7.38 ± 0.02; P < 0.0001). Hemoglobin P50 was greater in humans compared to elephant seals (29.9 ± 1.5 and 28.7 ± 0.6 mmHg, respectively; P = 0.046). Elephant seals overall had higher carboxyhemoglobin (COHb) levels (5.9 ± 2.6%) compared to humans (0.8 ± 1.2%; P < 0.0001); however, following apnea, COHb was reduced in seals (baseline: 6.1 ± 0.3%; end apnea: 5.6 ± 0.3%) and was slightly elevated in humans (baseline: 0.7 ± 0.1%; end apnea: 0.9 ± 0.1%; P < 0.0002, both comparisons). Our data indicate that during static apnea, seals have reduced hemoglobin P50, greater pH buffering, and increased COHb levels. The differences in hemoglobin P50 are likely due to the differences in the physiological environment between the two species during apnea, whereas enhanced pH buffering and higher COHb may represent traits selected for in elephant seals.NEW & NOTEWORTHY This study uses similar methods and protocols in elite human free divers and northern elephant seals. Using highly conditioned divers (elite free-diving humans) and highly adapted divers (northern elephant seals), we explored which hematological traits are fundamentally mammalian and which may have been selected for. We found differences in P50, which may be due to different physiological environments between species, while elevated pH buffering and carbon monoxide levels might have been selected for in seals.

PaCO2 is nonlinearly associated with NIV failure in patients with hypoxemic respiratory failure.

OBJECTIVE: To explore the association between PaCO2 and noninvasive ventilation (NIV) failure in patients with hypoxemic respiratory failure. METHODS: A retrospective study was performed in a respiratory ICU of a teaching hospital. Patients admitted to ICU between 2011 and 2019 were screened. We enrolled the patients with hypoxemic respiratory failure. However, patients who used NIV due to acute-on-chronic respiratory failure or heart failure were excluded. Data before the use of NIV were collected. Requirement of intubation was defined as NIV failure. RESULTS: A total of 1029 patients were enrolled in final analysis. The rate of NIV failure was 45% (461/1029). A nonlinear relationship between PaCO2 and NIV failure was found by restricted cubic splines (p = 0.03). The inflection point was 32 mmHg. The rate of NIV failure was 42% (224/535) in patients with PaCO2 >32 mmHg. However, it increased to 48% (237/494) in those with PaCO2 ≤ 32 mmHg. The crude and adjusted hazard ratio (HR) for NIV failure was 1.36 (95%CI:1.13-1.64) and 1.23(1.01-1.49), respectively, if the patients with PaCO2 >32 mmHg were set as reference. In patients with PaCO2 ≤ 32 mmHg, one unit increment of PaCO2 was associated with 5% reduction of NIV failure. However, it did not associate with NIV failure in patients with PaCO2 >32 mmHg. CONCLUSIONS: PaCO2 and NIV failure was nonlinear relationship. The inflection point was 32 mmHg. Below the inflection point, lower PaCO2 was associated with higher NIV failure. However, it did not associate with NIV failure above this point.

CENTRAL VENOUS-TO-ARTERIAL CARBON DIOXIDE PARTIAL PRESSURE DIFFERENCE AS A GUIDING PARAMETER FOR CARDIOTONIC DRUG ADMINISTRATION IN PATIENTS WITH EARLY-STAGE SEPTIC SHOCK.

ABSTRACT: Objective: This study aimed to investigate the effect of the central venous-to-arterial carbon dioxide partial pressure difference (Pcv-aCO2) on the administration of cardiotonic drugs in patients with early-stage septic shock. Methods: A retrospective study was conducted on 120 patients suffering from septic shock. At admission, the left ventricular ejection fraction (LVEF) and Pcv-aCO2 of the patients were obtained. On the premise of mean arterial pressure ≥ 65 mm Hg, the patients were divided into two groups according to the treatment approaches adopted by different doctors-control group: LVEF ≤50% and observation group: Pcv-aCO2 ≥ 6. Both groups received cardiotonic therapy. Results: The two groups of patients had similar general conditions and preresuscitation conditions ( P > 0.05). Compared with the control group, the observation group had a higher mean arterial pressure, lactic acid clearance rate, and urine output after 6 h of resuscitation ( P < 0.05), but a lower absolute value of lactic acid, total fluid intake in 24 h, and a lower number of patients receiving renal replacement therapy during hospitalization ( P < 0.05). After 6 hours of resuscitation, the percentages of patients meeting central venous oxygen saturation and central venous pressure targets were not significantly different between the control and observation groups ( P > 0.05). There was no difference in the 28-day mortality rate between the two groups ( P > 0.05). Conclusion: Pcv-aCO2 is more effective than LVEF in guiding the administration of cardiotonic drugs in the treatment of patients with septic shock.

Perioperative Evaluation of Arterial and Venous Whole Blood in the Lamb (Ovis aries) Fontan Model.

Whole blood analysis can evaluate numerous parameters, including pH, pCO2, pO2, HCO3 - , base excess, glucose, electrolytes, lactate, blood urea nitrogen, creatinine, bilirubin, and hemoglobin. This valuable tool enables clinicians to make more informed decisions about patient care. However, the current body of literature describing perioperative whole blood analysis in Dorset sheep (Ovis aries) is small, so clinicians lack adequate information to guide their decision-making when evaluating test results. We evaluated arterial and venous whole blood pH, bicarbonate, pCO2, lactate, creatinine, and blood urea nitrogen before and for the first 24 hours after surgery in 2 cohorts of male and female Ovis arie s undergoing one of 2 major cardiovascular procedures, a Single-Stage Fontan or an inferior vena cava to pulmonary artery extracardiac conduit implantation (IP-ECC). The cohort undergoing a Single-Stage Fontan, which is the more complex procedure, exhibited greater deviation from baseline measurements than did the cohort undergoing the IP-ECC for lactate, bicarbonate, and creatinine. The cohort undergoing the IP-ECC showed no significant deviation from baseline for any parameters, potentially indicating a better safety margin than expected when compared with the Single-Stage Fontan. Together, these results indicate the clinical value of arterial and venous whole blood measurements in perioperative management of sheep and can provide a reference for clinicians managing sheep after significant cardiovascular procedures.

Relationship between the mixed venous-to-arterial carbon dioxide gradient and the cardiac index in acute pulmonary embolism.

AIMS: Among patients with acute pulmonary embolism (PE) undergoing mechanical thrombectomy, the cardiac index (CI) is frequently reduced even among those without a clinically apparent shock. The purpose of this study is to describe the mixed venous-to-arterial carbon dioxide gradient (CO2 gap), a surrogate of perfusion adequacy, among patients with acute PE undergoing mechanical thrombectomy. METHODS AND RESULTS: This was a single-centre retrospective study of consecutive patients with PE undergoing mechanical thrombectomy and simultaneous pulmonary artery catheterization over a 3-year period. Of 107 patients, 97 had simultaneous mixed venous and arterial blood gas measurements available. The CO2 gap was elevated (>6 mmHg) in 51% of the cohort and in 49% of patients with intermediate-risk PE. A reduced CI (≤2.2 L/min/m2) was associated with an increased odds [odds ratio = 7.9; 95% confidence interval (CI) 3.49-18.1, P < 0.001] for an elevated CO2 gap. There was an inverse relationship between the CI and the CO2 gap. For every 1 L/min/m2 decrease in the CI, the CO2 gap increased by 1.3 mmHg (P = 0.001). Among patients with an elevated baseline CO2 gap >6 mmHg, thrombectomy improved the CO2 gap, CI, and mixed venous oxygen saturation. When the CO2 gap was dichotomized above and below 6, there was no difference in the in-hospital mortality rate (9 vs. 0%; P = 0.10; hazard ratio: 1.24; 95% CI 0.97-1.60; P = 0.085). CONCLUSION: Among patients with acute PE undergoing mechanical thrombectomy, the CO2 gap is abnormal in nearly 50% of patients and inversely related to the CI. Further studies should examine the relationship between markers of perfusion and outcomes in this population to refine risk stratification.

Association of Arterial Carbon Dioxide Tension Following In-Hospital Cardiac Arrest With Survival and Favorable Neurologic Outcome.

BACKGROUND: In-hospital cardiac arrest (IHCA) continues to be associated with high morbidity and mortality. The objective of this study was to study the association of arterial carbon dioxide tension (PaCO2) on survival to discharge and favorable neurologic outcomes in adults with IHCA. METHODS: The study population included 353 adults who underwent resuscitation from 2011 to 2019 for IHCA at an academic tertiary care medical center with arterial blood gas testing done within 24 hours of arrest. Outcomes of interest included survival to discharge and favorable neurologic outcome, defined as Glasgow outcome score of 4-5. RESULTS: Of the 353 patients studied, PaCO2 classification included: hypocapnia (PaCO2 <35 mm Hg, n = 89), normocapnia (PaCO2 35-45 mm Hg, n = 151), and hypercapnia (PaCO2 >45 mm Hg, n = 113). Hypercapnic patients were further divided into mild (45 mm Hg < PaCO2 ≤55 mm Hg, n = 62) and moderate/severe hypercapnia (PaCO2 > 55 mm Hg, n = 51). Patients with normocapnia had the highest rates of survival to hospital discharge (52.3% vs. 32.6% vs. 30.1%, P < 0.001) and favorable neurologic outcome (35.8% vs. 25.8% vs. 17.9%, P = 0.005) compared those with hypocapnia and hypercapnia respectively. In multivariable analysis, compared to normocapnia, hypocapnia [odds ratio (OR), 2.06; 95% confidence interval (CI), 1.15-3.70] and hypercapnia (OR, 2.67; 95% CI, 1.53-4.66) were both found to be independently associated with higher rates of in-hospital mortality. Compared to normocapnia, while mild hypercapnia (OR, 2.53; 95% CI, 1.29-4.97) and moderate/severe hypercapnia (OR, 2.86; 95% CI, 1.35-6.06) were both independently associated with higher in-hospital mortality compared to normocapnia, moderate/severe hypercapnia was also independently associated with lower rates of favorable neurologic outcome (OR, 0.28; 95% CI, 0.11-0.73), while mild hypercapnia was not. CONCLUSIONS: In this prospective registry of adults with IHCA, hypercapnia noted within 24 hours after arrest was independently associated with lower rates of survival to discharge and favorable neurologic outcome.