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.

The level of partial pressure of carbon dioxide affects organ perfusion in respiratory failure patients undergoing pressure support ventilation with venovenous extracorporeal membrane oxygenation: a prospective study.

BACKGROUND: We evaluated the influence of different partial carbon dioxide pressure (PaCO2) levels on organ perfusion in patients with respiratory failure receiving pressure-support ventilation with veno-venous extracorporeal membrane oxygenation (V-V ECMO). METHODS: In this twelve patients prospective study, ECMO gas-flow was decreased from baseline (PaCO2 < 40 mmHg) until PaCO2 increased by 5-10 mmHg (High-CO2 phase). Resistance indices of gut, spleen, and snuffbox artery, the peripheral perfusion index (PPI), and heart rate variability were measured at baseline and High-CO2 phase. RESULTS: When PaCO2 increased from 36 (36-37) mmHg at baseline to 42 (41-43) mmHg in the High-CO2 phase (p < 0.001), PPI decreased significantly (p = 0.026). The snuffbox artery (p = 0.022), superior mesenteric artery (p = 0.042), and spleen (p = 0.012) resistance indices increased significantly. The root mean square of successive differences (RMSSD) decreased from 19.5(18.1-22.7) to 15.9(14.4-18.6) ms (p = 0.034), and the ratio of low-frequency to high-frequency components(LF/HF) increased from 0.47 ± 0.23 to 0.70 ± 0.38 (p = 0.013). CONCLUSIONS: High PaCO2 might cause decreased peripheral tissue and visceral organ perfusion through autonomic nervous system in patients with respiratory failure undergoing PSV with V-V ECMO.

The level of partial pressure of carbon dioxide affects respiratory effort in COVID-19 patients undergoing pressure support ventilation with extracorporeal membrane oxygenation.

BACKGROUND: Patients with COVID-19 undergoing pressure support ventilation (PSV) with extracorporeal membrane oxygenation (ECMO) commonly had high respiratory drive, which could cause self-inflicted lung injury. The aim of this study was to evaluate the influence of different levels of partial pressure of carbon dioxide(PaCO2) on respiratory effort in COVID-19 patients undergoing PSV with ECMO. METHODS: ECMO gas flow was downregulated from baseline (respiratory rate < 25 bpm, peak airway pressure < 25 cm H2O, tidal volume < 6 mL/kg, PaCO2 < 40 mmHg) until PaCO2 increased by 5 - 10 mmHg. The pressure muscle index (PMI) and airway pressure swing during occlusion (ΔPOCC) were used to monitor respiratory effort, and they were measured before and after enforcement of the regulations. RESULTS: Ten patients with COVID-19 who had undergone ECMO were enrolled in this prospective study. When the PaCO2 increased from 36 (36 - 37) to 42 (41-43) mmHg (p = 0.0020), there was a significant increase in ΔPOCC [from 5.6 (4.7-8.0) to 11.1 (8.5-13.1) cm H2O, p = 0.0020] and PMI [from 3.0 ± 1.4 to 6.5 ± 2.1 cm H2O, p < 0.0001]. Meanwhile, increased inspiratory effort determined by elevated PaCO2 levels led to enhancement of tidal volume from 4.1 ± 1.2 mL/kg to 5.3 ± 1.5 mL/kg (p = 0.0003) and respiratory rate from 13 ± 2 to 15 ± 2 bpm (p = 0.0266). In addition, the increase in PaCO2 was linearly correlated with changes in ΔPOCC and PMI (R2 = 0.7293, p = 0.0003 and R2 = 0.4105, p = 0.0460, respectively). CONCLUSIONS: In patients with COVID-19 undergoing PSV with ECMO, an increase of PaCO2 could increase the inspiratory effort.

End-Tidal to Arterial Pco2 Ratio as Guide to Weaning from Venovenous Extracorporeal Membrane Oxygenation.

Rationale: Weaning from venovenous extracorporeal membrane oxygenation (VV-ECMO) is based on oxygenation and not on carbon dioxide elimination. Objectives: To predict readiness to wean from VV-ECMO. Methods: In this multicenter study of mechanically ventilated adults with severe acute respiratory distress syndrome receiving VV-ECMO, we investigated a variable based on CO2 elimination. The study included a prospective interventional study of a physiological cohort (n = 26) and a retrospective clinical cohort (n = 638). Measurements and Main Results: Weaning failure in the clinical and physiological cohorts were 37% and 42%, respectively. The main cause of failure in the physiological cohort was high inspiratory effort or respiratory rate. All patients exhaled similar amounts of CO2, but in patients who failed the weaning trial, [Formula: see text]e was higher to maintain the PaCO2 unchanged. The effort to eliminate one unit-volume of CO2, was double in patients who failed (68.9 [42.4-123] vs. 39 [20.1-57] cm H2O/[L/min]; P = 0.007), owing to the higher physiological Vd (68 [58.73] % vs. 54 [41.64] %; P = 0.012). End-tidal partial carbon dioxide pressure (PetCO2)/PaCO2 ratio was a clinical variable strongly associated with weaning outcome at baseline, with area under the receiver operating characteristic curve of 0.87 (95% confidence interval [CI], 0.71-1). Similarly, the PetCO2/PaCO2 ratio was associated with weaning outcome in the clinical cohort both before the weaning trial (odds ratio, 4.14; 95% CI, 1.32-12.2; P = 0.015) and at a sweep gas flow of zero (odds ratio, 13.1; 95% CI, 4-44.4; P < 0.001). Conclusions: The primary reason for weaning failure from VV-ECMO is high effort to eliminate CO2. A higher PetCO2/PaCO2 ratio was associated with greater likelihood of weaning from VV-ECMO.

Effect of doxofylline on pulmonary inflammatory response and oxidative stress during mechanical ventilation in rats with COPD.

OBJECTIVE: To evaluate the effects of doxofylline on inflammatory responses and oxidative stress during mechanical ventilation in rats with chronic obstructive pulmonary disease (COPD). METHODS: Eight-week-old male Sprague Dawley rats were selected, and the COPD rat model was constructed. The rats were randomly divided into a model group (group M), a model + normal saline group (group N), a doxofylline group (group D), and a control group fed with conventional chow and given normal oxygen supply (group C) (n = 12 in each group). Tracheal intubation and mechanical ventilation were conducted in the rats in each group after anesthesia. A real-time intravenous infusion with 50 mg/kg of doxofylline was conducted in group D, and there was no drug intervention in groups C, N and M. Pathological manifestations of the pulmonary tissues were observed and compared among the groups. And some indicators were evaluated. RESULTS: (1) The pulmonary tissues of the rats in groups M, N, and D exhibited typical pathological histological changes of COPD. (2) Groups M, N, and D showed increased Ppeak, PaCO2, total white blood cell count in BALF, and IL-8, TNF-α, and MDA levels in the pulmonary tissue and BALF, and decreased PaO2 and IL-10 and SOD levels, compared with group C. (3). Group D showed decreased Ppeak, PaCO2, total white blood cell count in BALF, and IL-8, TNF-α, and MDA levels in the pulmonary tissue, and increased PaO2 and IL-10 and SOD levels, compared with group N or M. CONCLUSION: Doxofylline was shown to improve ventilation and air exchange during mechanical ventilation in rats with COPD, reduce the inflammatory response and oxidative stress, and mitigate the degree of pulmonary tissue injury.

Optimal Targets of the First 24-h Partial Pressure of Carbon Dioxide in Patients with Cerebral Injury: Data from the MIMIC-III and IV Database.

BACKGROUND: It is generally believed that hypercapnia and hypocapnia will cause secondary injury to patients with craniocerebral diseases, but a small number of studies have shown that they may have potential benefits. We assessed the impact of partial pressure of arterial carbon dioxide (PaCO2) on in-hospital mortality of patients with craniocerebral diseases. The hypothesis of this research was that there is a nonlinear correlation between PaCO2 and in-hospital mortality in patients with craniocerebral diseases and that mortality rate is the lowest when PaCO2 is in a normal range. METHODS: We identified patients with craniocerebral diseases from Medical Information Mart for Intensive Care third and fourth edition databases. Cox regression analysis and restricted cubic splines were used to examine the association between PaCO2 and in-hospital mortality. RESULTS: Nine thousand six hundred and sixty patients were identified. A U-shaped association was found between the first 24-h PaCO2 and in-hospital mortality in all participants. The nadir for in-hospital mortality risk was estimated to be at 39.5 mm Hg (p for nonlinearity < 0.001). In the subsequent subgroup analysis, similar results were found in patients with traumatic brain injury, metabolic or toxic encephalopathy, subarachnoid hemorrhage, cerebral infarction, and other encephalopathies. Besides, the mortality risk reached a nadir at PaCO2 in the range of 35-45 mm Hg. The restricted cubic splines showed a U-shaped association between the first 24-h PaCO2 and in-hospital mortality in patients with other intracerebral hemorrhage and cerebral tumor. Nonetheless, nonlinearity tests were not statistically significant. In addition, Cox regression analysis showed that PaCO2 ranging 35-45 mm Hg had the lowest death risk in most patients. For patients with hypoxic-ischemic encephalopathy and intracranial infections, the first 24-h PaCO2 and in-hospital mortality did not seem to be correlated. CONCLUSIONS: Both hypercapnia and hypocapnia are harmful to most patients with craniocerebral diseases. Keeping the first 24-h PaCO2 in the normal range (35-45 mm Hg) is associated with lower death risk.

Successful treatment of linezolid-induced severe lactic acidosis with continuous venovenous hemodiafiltration: A case report.

Linezolid is an oxazolidinone antibiotic. Linezolid-associated lactic acidosis has been reported in 6.8% of linezolid-treated patients. Lactic acidosis is associated with poor clinical outcomes, with high blood lactate levels resulting in organ dysfunction and mortality. This case report describes the development of lactic acidosis in a 64-year-old Chinese woman who had received 33 days of treatment with antituberculosis drugs and 28 days of treatment with oral linezolid for tuberculous meningitis. Severe lactic acidosis was reversed by withdrawing antituberculosis drugs and using continuous venovenous hemodiafiltration (CVVH). When the patient's condition was stable, she was transferred to the infectious disease department, and antituberculosis drugs, with the exception of linezolid, were reintroduced. This did not result in recurrence of lactic acidosis. The causal relationship between lactic acidosis and linezolid was categorized as 'probable' on the Adverse Drug Reaction Probability Scale. This case demonstrates that CVVH has potential as an alternative to discontinuation of linezolid alone for rapid reversal of linezolid-associated severe lactic acidosis.

Effects of hypercapnia in sepsis: A scoping review of clinical and pre-clinical data.

BACKGROUND: Perform a scoping review of (1) pre-clinical studies testing the physiological effects of higher PaCO2 levels in the setting of sepsis models and (2) clinical investigations testing the effects of hypercapnia on clinical outcomes in mechanically ventilated patients with sepsis. METHODS: We performed a search of CENTRAL, PUBMED, CINAHL, and EMBASE. Study inclusion criteria for pre-clinical studies were: (1) bacterial sepsis model (2) measurement of PaCO2 , and (3) comparison of outcome measure between different PaCO2 levels. Inclusion criteria for clinical studies were: (1) diagnosis of sepsis, (2) receiving invasive mechanical ventilation, (3) measurement of PaCO2 , and (4) comparison of outcomes between different PaCO2 levels. We performed a qualitative analysis to collate and summarize the physiological and clinical effects of hypercapnia according to the recommended methodology from the Cochrane Handbook. RESULTS: Fifteen pre-clinical and nine clinical studies were included. Among pre-clinical studies, the individual studies found higher PaCO2 augments tissue blood flow and oxygenation, and attenuates inflammation and lung injury; however, all pre-clinical studies were found to have some degree of risk of bias. Six of the nine clinical studies were deemed to be good quality. Among clinical studies hypercapnia was associated with increased cerebral perfusion and oxygenation; however, there were conflicting results testing the association between hypercapnia and mortality. CONCLUSION: While individual pre-clinical studies identified potential mechanisms by which changes in PaCO2 levels could affect pathophysiology in sepsis, there is a paucity of clinical data as to the optimal PaCO2 range, demonstrating a need for future research. REGISTRATION: PROSPERO number CRD42018086703.

Carbon Dioxide Sensing-Biomedical Applications to Human Subjects.

Carbon dioxide (CO2) monitoring in human subjects is of crucial importance in medical practice. Transcutaneous monitors based on the Stow-Severinghaus electrode make a good alternative to the painful and risky arterial "blood gases" sampling. Yet, such monitors are not only expensive, but also bulky and continuously drifting, requiring frequent recalibrations by trained medical staff. Aiming at finding alternatives, the full panel of CO2 measurement techniques is thoroughly reviewed. The physicochemical working principle of each sensing technique is given, as well as some typical merit criteria, advantages, and drawbacks. An overview of the main CO2 monitoring methods and sites routinely used in clinical practice is also provided, revealing their constraints and specificities. The reviewed CO2 sensing techniques are then evaluated in view of the latter clinical constraints and transcutaneous sensing coupled to a dye-based fluorescence CO2 sensing seems to offer the best potential for the development of a future non-invasive clinical CO2 monitor.

Temporal Evolution of the PcvCO2-PaCO2/CaO2-CcvO2 Ratio vs Serum Lactate during Resuscitation in Septic Shock.

BACKGROUND: Lactate as a target for resuscitation in patients with septic shock has important limitations. The PcvCO2-PaCO2/CaO2-CcvO2 ratio may be used as an alternative for the same. The primary outcome of the study is to evaluate the correlation between serum lactate and PcvCO2-PaCO2/CaO2-CcvO2 ratio measured at various time points to a maximum of 24 hours in patients with septic shock [mean arterial pressure (MAP) <65 mm Hg]. The secondary outcomes were to study the (1) relationship between the PcvCO2-PaCO2/CaO2-CcvO2 ratio and lactate clearance at 6, 12, and 24 hours as compared to the initial serum lactate, (2) to ascertain whether the PcvCO2-PaCO2/CaO2-CcvO2 ratio and the arterial lactate levels in the first 24 hours are able to predict mortality at day 28 of enrollment, and (3) to determine whether the PcvCO2-PaCO2/ CaO2-CcvO2 ratio and arterial lactate are useful in discriminating survivors from nonsurvivors. MATERIALS AND METHODS: Thirty patients with sepsis-induced hypotension who were being actively resuscitated were enrolled. Paired arterial and central venous blood samples were obtained 0.5 hourly till stabilization of MAP and 6 hourly thereafter for the first 24 hours. Patients were followed up to day 28 of enrollment for mortality and organ system failure. RESULTS: A positive correlation was observed between arterial lactate and PcvCO2-PaCO2/CaO2-CcvO2 ratio at 0, 6, 12, and 18 hours (R = 0.413, p = 0.02; R = 0.567, p = 0.001; R = 0.408, p = 0.025; R = 0.521, p = 0.003, respectively). No correlation was seen between PcvCO2-PaCO2/CaO2-CcvO2 ratio and lactate clearance. The subgroup analysis showed that PcvCO2-PaCO2/CaO2-CcvO2 ratio >1.696 at 24 hours of resuscitation predicted 28-day mortality (sensitivity: 80%, specificity 69.2%, area under the receiver operating characteristic curve 0.82). CONCLUSION: The PcvCO2-PaCO2/CaO2-CcvO2 ratio and lactate are positively correlated during the first 24 hours of active resuscitation from sepsis-induced hypotension, and a threshold of 1.696 mm Hg/mL/dL at 24 hours significantly differentiates survivors from nonsurvivors (CTRI/2017/11/010342). HOW TO CITE THIS ARTICLE: Madabhushi S, Trikha A, Anand RK, Ramachandran R, Singh PM, Rewari V. Temporal Evolution of the PcvCO2-PaCO2/CaO2-CcvO2 Ratio vs Serum Lactate during Resuscitation in Septic Shock. Indian J Crit Care Med 2021; 25(12):1370-1376.

Relationship Between Pulmonary-to-Systemic-Blood-Flow Ratio (Qp:Qs) Based on Cardiac Catheterization and Indices Derived from Simultaneously Measured End Tidal CO2 (EtCO2) in Children with Complex Congenital Heart Disease.

CO2 removal by the lungs depends upon ventilation and pulmonary blood flow, with end tidal CO2 (EtCO2) as surrogate for it. We studied indices based on EtCO2 measured routinely during anesthesia for cardiac catheterization, along with simultaneously calculated Qp:Qs (pulmonary-to-systemic-blood-flow ratio) in children with complex congenital heart disease to assess the relationship between these measures. A retrospective, single-center, correlational cohort study was conducted at a tertiary-care, free-standing children's hospital. All included subjects had Qp:Qs calculated as well as EtCO2 and PaCO2 documented during a single cardiac catheterization. Children with stage-1 single ventricle or complex biventricular repair with highly variable Qp:Qs were defined as Group 1, and Group 2 comprised those with stage 2 or 3 repairs with less variable Qp:Qs. Exclusion criteria were uncuffed artificial airway, EtCO2 > PaCO2, and abnormally high Qp:Qs. EtCO2 indices were defined as EtCO2:PaCO2 (alveolar functional fraction) and EtCO2 gap (PaCO2-EtCO2). Correlation coefficients were obtained between Qp:Qs and EtCO2 indices in both groups. A total of 29 patients in Group 1 and 24 in Group 2 underwent final analysis. Even with highly variable Qp:Qs, Group 1 showed a strong correlation between Qp:Qs and EtCO2:PaCO2 (r = 0.83, p < 0.0001). A similarly strong correlation was maintained in Group 2 (r = 0.79, p < 0.0001) and in both groups combined (r = 0.86, p < 0.0001). A very strong negative correlation was present between Qp:Qs and EtCO2 gap (r = - 0.77, p < 0.0001). EtCO2:PaCO2 has a very strong correlation with Qp:Qs simultaneously calculated during catheterization. It can be an additional parameter to estimate Qp:Qs in critical management of children with congenital heart disease. Our results also provide a basis for future prospective studies to assess dynamic changes in EtCO2-based indices and Qp:Qs.

A metabolic hypothesis for the evolution of temperature effects on the arterial PCO2 and pH of vertebrate ectotherms.

Body temperature increases in ectothermic vertebrates characteristically lead to both increases in arterial PCO2  (PaCO2 ) and declines in resting arterial pH (pHa) of about 0.017 pH units per 1°C increase in temperature. This 'alphastat' pH pattern has previously been interpreted as being evolutionarily driven by the maintenance of a constant protonation state on the imidazole moiety of histidine protein residues, hence stabilizing protein structure-function. Analysis of the existing data for interclass responses of ectothermic vertebrates shows different degrees of PaCO2  increases and pH declines with temperature between the classes, with reptiles>amphibians>fish. The PaCO2  at the temperature where maximal aerobic metabolism (V̇O2,max) is achieved is significantly and positively correlated with temperature for all vertebrate classes. For ectotherms, the PaCO2  where V̇O2,max is greatest is also correlated with V̇O2,max, indicating there is an increased driving force for CO2 efflux that is lowest in fish, intermediate in amphibians and highest in reptiles. The pattern of increased PaCO2  and the resultant reduction of pHa in response to increased body temperature would serve to increase CO2 efflux, O2 delivery and blood buffering capacity and maintain ventilatory scope. This represents a new hypothesis for the selective advantage of arterial pH regulation from a systems physiology perspective in addition to the advantages of maintenance of protein structure-function.

Hypercapnia in diving: a review of CO2 retention in submersed exercise at depth.

Carbon dioxide (CO2) retention, or hypercapnia, is a known risk of diving that can cause mental and physical impairments leading to life-threatening accidents. Often, such accidents occur due to elevated inspired carbon dioxide. For instance, in cases of CO2 elimination system failures during rebreather dives, elevated inspired partial pressure of carbon dioxide (PCO2) can rapidly lead to dangerous levels of hypercapnia. Elevations in PaCO2 (arterial pressure of PCO2) can also occur in divers without a change in inspired PCO2. In such cases, hypercapnia occurs due to alveolar hypoventilation. Several factors of the dive environment contribute to this effect through changes in minute ventilation and dead space. Predominantly, minute ventilation is reduced in diving due to changes in respiratory load and associated changes in respiratory control. Minute ventilation is further reduced by hyperoxic attenuation of chemosensitivity. Physiologic dead space is also increased due to elevated breathing gas density and to hyperoxia. The Haldane effect, a reduction in CO2 solubility in blood due to hyperoxia, may contribute indirectly to hypercapnia through an increase in mixed venous PCO2. In some individuals, low ventilatory response to hypercapnia may also contribute to carbon dioxide retention. This review outlines what is currently known about hypercapnia in diving, including its measurement, cause, mental and physical effects, and areas for future study.

Restoring heat stress-associated reduction in middle cerebral artery velocity does not reduce fatigue in the heat.

Heat-induced hyperventilation may reduce PaCO2 and thereby cerebral perfusion and oxygenation and in turn exercise performance. To test this hypothesis, eight volunteers completed three incremental exercise tests to exhaustion: (a) 18 °C ambient temperature (CON); (b) 38 °C (HEAT); and (c) 38 °C with addition of CO2 to inspiration to prevent the hyperventilation-induced reduction in PaCO2 (HEAT + CO2 ). In HEAT and HEAT + CO2 , rectal temperature was elevated prior to the exercise tests by means of hot water submersion and was higher (P < 0.05) than in CON. Compared with CON, ventilation was elevated (P < 0.01), and hence, PaCO2 reduced in HEAT. This caused a reduction (P < 0.05) in mean cerebral artery velocity (MCAvmean ) from 68.6 ± 15.5 to 53.9 ± 10.0 cm/s, which was completely restored in HEAT + CO2 (68.8 ± 5.8 cm/s). Cerebral oxygenation followed a similar pattern. V ˙ O 2   m a x was 4.6 ± 0.1 L/min in CON and decreased (P < 0.05) to 4.1 ± 0.2 L/min in HEAT and remained reduced in HEAT + CO2 (4.1 ± 0.2 L/min). Despite normalization of MCAvmean and cerebral oxygenation in HEAT + CO2 , this did not improve exercise performance, and thus, the reduced MCAvmean in HEAT does not seem to limit exercise performance.

Correlation of end tidal and arterial carbon dioxide levels in critically Ill neonates and children.

AIM OF THE STUDY: End tidal carbon dioxide (EtCO2) monitoring is considered to reflect real-time estimation of partial pressure of carbon dioxide in arterial blood (PaCO2) noninvasively. However, knowledge about its relationship with PaCO2 in critically ill pediatric and neonatal patients is limited. The primary objective was to evaluate predictive capability of end tidal carbon dioxide monitoring and secondary objective was to determine the influence of severity of lung disease on EtCO2 and PaCO2 relationship. MATERIALS AND METHODS: This was a prospective, nonrandomized, consecutive enrollment study carried out in neonatal and pediatric intensive care units of a tertiary care children hospital. It was conducted in 66 neonates and 35 children receiving mechanical ventilation. Severity of lung disease was estimated by ventilation index and PaO2/FiO2 (P/F) ratio. Simultaneous recording of EtCO2 and PaCO2 levels was done and data were analyzed for correlation and agreement. RESULTS: In neonates, 150 EtCO2 and PaCO2 pairs were recorded. The mean weight ± SD of patients was 2.1 ± 0.63 kg. PaCO2 had a positive correlation with EtCO2 (r = 0.836, 95% CI = 0.78-0.88). P/F ratio <200 adversely affected relationship. In infants and children, 96 pairs were recorded. Mean age ± SD of patients was 4.20 ± 4.92 years and mean weight ± SD was 13.1 ± 9.49 kg. PaCO2 had an excellent correlation with EtCO2 (r = 0.914, 95% CI = 0.87 and 0.94). P/F ratio <200 adversely affected relationship. CONCLUSION: EtCO2 monitoring displayed a good validity to predict PaCO2. Correlation was affected by low P/F ratio (<200); hence, it is recommended that blood gases be measured in these patients until such time that a good relation can be established between end tidal and arterial CO2 values.

Clinical practice and effect of carbon dioxide on outcomes in mechanically ventilated acute brain-injured patients: a secondary analysis of the ENIO study.

PURPOSE: The use of arterial partial pressure of carbon dioxide (PaCO2) as a target intervention to manage elevated intracranial pressure (ICP) and its effect on clinical outcomes remain unclear. We aimed to describe targets for PaCO2 in acute brain injured (ABI) patients and assess the occurrence of abnormal PaCO2 values during the first week in the intensive care unit (ICU). The secondary aim was to assess the association of PaCO2 with in-hospital mortality. METHODS: We carried out a secondary analysis of a multicenter prospective observational study involving adult invasively ventilated patients with traumatic brain injury (TBI), subarachnoid hemorrhage (SAH), intracranial hemorrhage (ICH), or ischemic stroke (IS). PaCO2 was collected on day 1, 3, and 7 from ICU admission. Normocapnia was defined as PaCO2 > 35 and to 45 mmHg; mild hypocapnia as 32-35 mmHg; severe hypocapnia as 26-31 mmHg, forced hypocapnia as < 26 mmHg, and hypercapnia as > 45 mmHg. RESULTS: 1476 patients (65.9% male, mean age 52 ± 18 years) were included. On ICU admission, 804 (54.5%) patients were normocapnic (incidence 1.37 episodes per person/day during ICU stay), and 125 (8.5%) and 334 (22.6%) were mild or severe hypocapnic (0.52 and 0.25 episodes/day). Forced hypocapnia and hypercapnia were used in 40 (2.7%) and 173 (11.7%) patients. PaCO2 had a U-shape relationship with in-hospital mortality with only severe hypocapnia and hypercapnia being associated with increased probability of in-hospital mortality (omnibus p value = 0.0009). Important differences were observed across different subgroups of ABI patients. CONCLUSIONS: Normocapnia and mild hypocapnia are common in ABI patients and do not affect patients' outcome. Extreme derangements of PaCO2 values were significantly associated with increased in-hospital mortality.

Prognostic value of arterial carbon dioxide tension during cardiopulmonary resuscitation in out-of-hospital cardiac arrest patients receiving extracorporeal resuscitation.

BACKGROUND: Current guidelines on extracorporeal cardiopulmonary resuscitation (ECPR) recommend careful patient selection, but precise criteria are lacking. Arterial carbon dioxide tension (PaCO2) has prognostic value in out-of-hospital cardiac arrest (OHCA) patients but has been less studied in patients receiving ECPR. We studied the relationship between PaCO2 during cardiopulmonary resuscitation (CPR) and neurological outcomes of OHCA patients receiving ECPR and tested whether PaCO2 could help ECPR selection. METHODS: This single-centre retrospective study enrolled 152 OHCA patients who received ECPR between January 2012 and December 2020. Favorable neurological outcome (FO) at discharge was the primary outcome. We used multivariable logistic regression to determine the independent variables for FO and generalised additive model (GAM) to determine the relationship between PaCO2 and FO. Subgroup analyses were performed to test discriminative ability of PaCO2 in subgroups of OHCA patients. RESULTS: Multivariable logistic regression showed that PaCO2 was independently associated with FO after adjusting for other favorable resuscitation characteristics (Odds ratio [OR] 0.23, 95% Confidence Interval [CI] 0.08-0.66, p-value = 0.006). GAM showed a near-linear reverse relationship between PaCO2 and FO. PaCO2 < 70 mmHg was the cutoff point for predicting FO. PaCO2 also had prognostic value in patients with less favorable characteristics, including non-shockable rhythm (OR, 3.78) or low flow time > 60 min (OR, 4.66). CONCLUSION: PaCO2 before ECMO implementation had prognostic value for neurological outcomes in OHCA patients. Patients with PaCO2 < 70 mmHg had higher possibility of FO, even in those with non-shockable rhythm or longer low-flow duration. PaCO2 could serve as an ECPR selection criterion.

End-tidal CO2: an important parameter for a correct interpretation in functional brain studies using speech tasks.

The aim was to investigate the effect of different speech tasks, i.e. recitation of prose (PR), alliteration (AR) and hexameter (HR) verses and a control task (mental arithmetic (MA) with voicing of the result on end-tidal CO2 (PETCO2), cerebral hemodynamics and oxygenation. CO2 levels in the blood are known to strongly affect cerebral blood flow. Speech changes breathing pattern and may affect CO2 levels. Measurements were performed on 24 healthy adult volunteers during the performance of the 4 tasks. Tissue oxygen saturation (StO2) and absolute concentrations of oxyhemoglobin ([O2Hb]), deoxyhemoglobin ([HHb]) and total hemoglobin ([tHb]) were measured by functional near-infrared spectroscopy (fNIRS) and PETCO2 by a gas analyzer. Statistical analysis was applied to the difference between baseline before the task, 2 recitation and 5 baseline periods after the task. The 2 brain hemispheres and 4 tasks were tested separately. A significant decrease in PETCO2 was found during all 4 tasks with the smallest decrease during the MA task. During the recitation tasks (PR, AR and HR) a statistically significant (p<0.05) decrease occurred for StO2 during PR and AR in the right prefrontal cortex (PFC) and during AR and HR in the left PFC. [O2Hb] decreased significantly during PR, AR and HR in both hemispheres. [HHb] increased significantly during the AR task in the right PFC. [tHb] decreased significantly during HR in the right PFC and during PR, AR and HR in the left PFC. During the MA task, StO2 increased and [HHb] decreased significantly during the MA task. We conclude that changes in breathing (hyperventilation) during the tasks led to lower CO2 pressure in the blood (hypocapnia), predominantly responsible for the measured changes in cerebral hemodynamics and oxygenation. In conclusion, our findings demonstrate that PETCO2 should be monitored during functional brain studies investigating speech using neuroimaging modalities, such as fNIRS, fMRI to ensure a correct interpretation of changes in hemodynamics and oxygenation.

Clinical usefulness of end-tidal CO2 measured using a portable capnometer in patients with respiratory disease.

INTRODUCTION: This study aimed to evaluate the correlation and agreement between end-tidal CO2 (EtCO2 ) measured with the novel portable capnometer (CapnoEye®) and partial pressure of arterial carbon dioxide (PaCO2 ) levels in patients with respiratory diseases and to compare the efficacy of EtCO2 and PvCO2 in predicting PaCO2 levels. METHODS: We analyzed the correlation and the agreement between EtCO2 and PaCO2 and between PvCO2 and PaCO2 using Pearson's moment correlation coefficient in patients with type 1 and type 2 respiratory failure and both groups overall. RESULTS: A total of 100 samples were included that comprised 67 men (67%). The mean age of the subjects was 77 ± 13 years. Chronic obstructive pulmonary disease (COPD) (43%) was the most common disease. There was a high correlation between EtCO2 and PaCO2 (r = 0.88; p < 0.0001). Sixty-six PvCO2 samples were obtained, and there was a high correlation between PvCO2 and PaCO2 (r = 0.81; p < 0.0001). Regarding type 2 respiratory failure, there was a high correlation between EtCO2 and PaCO2 (r = 0.81). The Bland-Altman analysis between PaCO2 and EtCO2 revealed a bias of 5.7 mmHg, with limits of agreement ranging from -5.1 mmHg to 16.5 mmHg. In contrast, the analysis between PaCO2 and PvCO2 revealed a bias of -6.8 mmHg, and the limits of agreement ranged from -22.13 mmHg to 8.53 mmHg. CONCLUSION: EtCO2 measured by CapnoEye® was significantly correlated to PaCO2 levels in patients with respiratory diseases. Moreover, CapnoEye® may be more useful for predicting hypercapnia conditions in which respiratory diseases are compared with measure PvCO2 .