PCO2 Difference Research Articles

Indices of Tissue Perfusion: Triggers of Targets of Resuscitation?

Circulatory shock is characterized by a decrease in oxygen delivery to the tissues associated with impairment in oxygen metabolism and tissue hypoxia. Clinical and biological signs of impaired tissue perfusion and tissue hypoxia are used as bedside to detect circulatory failure and trigger resuscitation procedures. The most popular signs of tissue hypoperfusion include mean arterial pressure, capillary refill time and mottling score, central venous oxygen saturation (ScvO2), veno-arterial difference in PCO2 (PvaCO2), microcirculation assessment, and lactate. Both the severity and duration of the alterations in any of these variables are associated with a poor outcome so that it sounds logical to trigger therapy based on these. Using these variables as target for therapy is much more complex. Some of the limits for using some of these variables as targets include an incertitude about the target to reach (should we aim at normalizing or improving the variable, and by how much?) and the time lag between resolution of impaired tissue perfusion/hypoxia and normalization of the variable. The ideal target variable should have a well-defined end point and a rapid response time. Interestingly, hemodynamic resuscitation targeting these variables gave variable results. In this review, we will discuss the interest and limitations of the above-mentioned indices of tissue perfusion and hypoxia as trigger as well as end point of resuscitation in critically ill patients.

Effect of acetazolamide on susceptibility to central sleep apnea in chronic spinal cord injury.

Spinal cord injury (SCI) is an established risk factor for central sleep apnea. Acetazolamide (ACZ), a carbonic anhydrase inhibitor, has been shown to decrease the frequency of central apnea by inducing mild metabolic acidosis. We hypothesized that ACZ would decrease the propensity to develop hypocapnic central apnea and decrease the apneic threshold. We randomized 16 participants with sleep-disordered breathing (8 SCI and 8 able-bodied controls) to receive ACZ (500 mg twice a day for 3 days) or placebo with a 1-wk washout before crossing over to the other drug arm. Study nights included polysomnography and determination of the hypocapnic apneic threshold and CO2 reserve using noninvasive ventilation. For participants with spontaneous central apnea, CO2 was administered until central apnea was abolished, and CO2 reserve was measured as the difference in end-tidal Pco2 () before and after. Steady-state plant gain, the response of end-tidal Pco2 to changes in ventilation, was calculated from and V̇e ratio during stable sleep. Controller gain, the response of ventilatory drive to changes in end-tidal Pco2, was defined as the ratio of change in V̇e between control and hypopnea to the ΔCO2 during stable non-rapid eye movement sleep. Treatment with ACZ for three days resulted in widening of the CO2 reserve (-4.0 ± 1.2 vs. -3.0 ± 0.7 mmHg for able-bodied, -3.4 ± 1.9 vs. -2.2 ± 2.2 mmHg for SCI, P < 0.0001), and a corresponding decrease in the hypocapnic apnea threshold (28.3 ± 5.2 vs. 37.1 ± 5.6 mmHg for able-bodied, 29.9 ± 5.4 vs. 34.8 ± 6.9 mmHg for SCI, P < 0.0001), respectively. ACZ significantly reduced plant gain when compared with placebo (4.1 ± 1.7 vs. 5.4 ± 1.8 mmHg/L min for able-bodied, 4.1 ± 2.0 vs. 5.1 ± 1.7 mmHg·L-1·min for SCI, P < 0.01). Acetazolamide decreased apnea-hypopnea index (28.8 ± 22.9 vs. 39.3 ± 24.1 events/h; P = 0.05), central apnea index (0.6 ± 1.5 vs. 6.3 ± 13.1 events/h; P = 0.05), and oxyhemoglobin desaturation index (7.5 ± 8.3 vs. 19.2 ± 15.2 events/h; P = 0.01) compared with placebo. Our results suggest that treatment with ACZ decreases susceptibility to hypocapnic central apnea due to decreased plant gain. Acetazolamide may attenuate central sleep apnea and improve nocturnal oxygen saturation, but its clinical utility requires further investigation in a larger sample of patients.NEW & NOTEWORTHY Tetraplegia is a risk factor for central sleep-disordered breathing (SDB) and is associated with narrow CO2 reserve (a marker of susceptibility to central apnea). Treatment with high-dose acetazolamide for 3 days decreased susceptibility to hypocapnic central apnea and reduced the frequency of central respiratory events during sleep. Acetazolamide may play a therapeutic role in alleviating central SDB in patients with cervical spinal cord injury, but larger clinical trials are needed.

Potassium disorders in pediatric emergency department: Clinical spectrum and management

IntroductionPotassium abnormalities are frequent in intensive care but their incidence in the emergency department is unknown. AimWe describe the spectrum of potassium abnormalities in our tertiary-level pediatric emergency department. MethodsRetrospective case-control study of all the patients admitted to a single-center tertiary emergency department over a 2.5-year period. We compared patients with hypokalemia (<3.0mEq/L) and patients with hyperkalemia (>6.0mEq/L) against a normal randomized population recruited on a 3:1 ratio with potassium levels between 3.5 and 5mEq/L. ResultsBetween January 1, 2013 and August 31, 2016 we admitted 108,209 patients to our emergency department. A total of 9342 blood samples were tested and the following potassium measurements were found: 60 cases of hypokalemia (2.8±0.2mEq/L) and 55 cases of hyperkalemia (6.4±0.6mEq/L). In total, 200 patients with normokalemia were recruited (4.1±0.3mEq/L). The main causes of the disorders were non-specific: lower respiratory tract infection (23%) and fracture (15%) for hypokalemia, lower respiratory tract (21.8%) and ear–nose–throat infections (20.0%) for hyperkalemia. Patients with hyperkalemia had an elevated creatinine level (0.72±1.6 vs. 0.40±0.16mg/dL, P<0.0001) with lower bicarbonate (19.4±3.8 vs. 21.8±2.8mmol/L, P=0.0001) and higher phosphorus levels (1.95±0.6 vs. 1.42±0.27mg/dL, P=0.0001). Patients with hypokalemia had an elevated creatinine level (0.66±0.71 vs. 0.40±0.16mg/dL, P<0.0001) and a lower phosphorus level (1.12±0.31 vs. 1.42±0.27mg/dL, P=0.0001). We did not observe significant differences in pH, PCO2, base excess and lactate, or in the mean duration of hospitalization in general wards and pediatric intensive care units according to the PIM and PRISM scores. DiscussionDyskalemia is rare in emergency department patients: 0.64% for hypokalemia and 0.58% for hyperkalemia. This condition could be explained by a degree of renal failure due to transient volume disturbance. The main mechanism is dehydration due to digestive losses, polypnea in young patients, and poor intake. In the case of hypokalemia, poor intake and digestive losses could be the main explanation. These disorders resolve easily with feeding or perfusion and do not impair development. ConclusionDyskalemia is rare in emergency department patients and is easily resolved with feeding or perfusion. A plausible etiological mechanism is a transient volume disturbance. Dyskalemia is not predictive of poor development in the emergency pediatric population.

Exercise training session-induced metabolic acidosis in barrel racing horses

ABSTRACT: In horses, acid-base balance disorders are common after intense exercise, with metabolic acidosis being the most common after high intensity and short duration exercise. Understanding the processes that cause them is fundamental for procedures, which aimed to improve the physical fitness of horses for athletic purposes, with fewer changes in homeostasis. The present study assessed the effect of barrel racing on acid base balance in Quarter Horse, at the following times: T0 - immediately before training; T1 - immediately after the end of the second course; T2 - one hour after the end of the second course. In T1, there was decrease (P&lt;0.05) in the pH, HCO3 -, pCO2, cBase, tCO2 and strong ion difference concentrations, while the plasma lactate and anion gap increased (P&lt;0.05). It was concluded that barrel racing training caused transient metabolic acidosis in the horses, and hyperlactatemia was still present after an hour of rest.

Role of central venous - Arterial pCO2 difference in determining microcirculatory hypoperfusion in off-pump coronary artery bypass grafting surgery.

Background:Cardiac surgery is frequently associated with macro and microcirculatory hypoperfusion. Patients with normal central venous oxygen saturation (Scvo2) also suffer from hypoperfusion. We hypothesized that monitoring central venous-arterial pco2 difference (dCO2) could also serve as additional marker in detecting hypoperfusion in cardiac surgery patient.Methods:This is a prospective observational study. Patients undergoing off-pump coronary artery bypass grafting included in this study. The dCO2 was measured postoperatively. The patients with a ScvO2 ≥70% were divided in to 2 groups, the high-dCO2 group (≥8 mmHg) and the low-dCO2 group (<8 mmHg).Results:The 65 patient had scvO2 ≥70%. Out of these, 20 patients were assigned to the high dCO2 group and 45 patients to the low dCO2 group. Patients with high dco2 had higher lactate levels after ICU admission. They also had significantly prolonged need for mechanical ventilation (14.90 ± 10.33 vs 10 ± 9.65, P = 0.0402), ICU stay (5.05 ± 2.52 d vs 3.75 ± 2.36 d, P = 0.049) and hospital stay (12.25 ± 5.90 d vs 8.57 ± 5.55 d P = 0.018). The overall rate of post-operative complications was similar in both the group.Conclusion:The present study demonstrates dCO2 as an easy to assess and routinely available tool to detect global and microcirculatory hypoperfusion in off-pump CABG patients, with assumed adequate fluid status and ScvO2 as a hemodynamic goal. We observed that high dCO2 (>8 mmHg) was associated with decreased DO2I, increased oxygen extraction ratio, the longer need for mechanical ventilation and longer ICU stay.

Dynamic controls on riverine pCO2 and CO2 outgassing in the Dry-hot Valley Region of Southwest China

Inland waters frequently exhibit carbon dioxide (CO2) supersaturation and potentially serve as CO2 emitters to the atmosphere. However, study on water–air interface CO2 exchange from small rivers remains limited, which causes large uncertainty of local and global carbon budgets. Based on seasonal field measurements, carbonate equilibria (CO2SYS program) and empirical models of gas transfer velocity (k value), we investigated the CO2 partial pressure (pCO2), CO2 emission and its controlling factors in the Longchuan River, a subtropical river in the Dry-hot Valley Region of Southwest China. Over 88% of samples were found to be oversaturated with atmospheric CO2, and the mean pCO2 ranged from 1497 ± 1415 μatm (dry period) to 1734 ± 1648 μatm (post-wet period). With the calibrated k values of 43.4–80.5 cm/h, the CO2 emission rates were estimate at 443–514 mmol/m2/day. We highlighted that long-term gully erosion enhanced the buffering capacity of carbonates in the aquatic environment and resulted in seasonal differences in riverine pCO2. Intensive agricultural practices could alter the pCO2 and further stimulate CO2 emissions. There were positive correlations of pCO2-elevation and pCO2-DOC in the initial-wet period but not in the dry period. This study suggests that extreme soil erosion and anthropogenic activities can regulate environmental variables and thus greatly affect the riverine CO2 outgassing. Our findings provide key insights into the understandings of dynamic controls on riverine pCO2 and CO2 outgassing under global change.

The Spatiotemporal Dynamics of the Sources and Sinks of CO2 in the Global Coastal Ocean

AbstractIn contrast to the open ocean, the sources and sinks for atmospheric carbon dioxide (CO2) in the coastal seas are poorly constrained and understood. Here we address this knowledge gap by analyzing the spatial and temporal variability of the coastal air‐sea flux of CO2 (FCO2) using a recent high‐resolution (0.25°) monthly climatology for coastal sea surface partial pressure in CO2 (pCO2). Coastal regions are characterized by CO2 sinks at temperate and high latitudes and by CO2 sources at low latitude and in the tropics, with annual mean CO2 flux densities comparable in magnitude and pattern to those of the adjacent open ocean with the exception of river‐dominated systems. The seasonal variations in FCO2 are large, often exceeding 2 mol C m−2 year−1, a magnitude similar to the variations exhibited across latitudes. The majority of these seasonal variations stems from the air‐sea pCO2 difference, although changes in wind speed and sea ice cover can also be significant regionally. Globally integrated, the coastal seas act currently as a CO2 sink of −0.20 ± 0.02 Pg C year−1, with a more intense uptake occurring in summer because of the disproportionate influence of high‐latitude shelves in the Northern Hemisphere. Combined with estimates of the carbon sinks in the open ocean and the Arctic, this gives for the global ocean, averaged over the 1998 to 2015 period an annual net CO2 uptake of −1.7 ± 0.3 Pg C year−1.

Abstract 120: Effects of Therapeutic Hypothermia on Blood Parameters in Rats With Acute Hemorrhagic Shock

Background: Our research group recently observed that therapeutic hypothermia (TH) compared with normothermia improved long-term survival in an experimental model of hemorrhagic shock. The effect of TH on blood counts, blood gases and chemistries during the early phase of recovery from hemorrhagic shock are unknown. Therefore, the purpose of the present study was to examine the effects of TH on blood parameters in the early phase of resuscitation from hemorrhagic shock. Methods and results: Sprague Dawley rats (both genders) were randomly assigned to TH (n= 16) or normothermia group (n= 15). Rats were anesthetized with intraperitoneal ketamine and xylazine. After heparinizing, hemorrhagic shock was induced by withdrawing blood to a fixed mean blood pressure (MBP) of 30 mmHg for 30 minutes and then shed blood was reinfused. TH was started 5 minutes after MBP reached 30 mmHg. Core temperature was maintained at ~ 32 °C until blood volume was fully restored, after which the rats were allowed to warm back to normal temperature. In the normothermia group, body temperature was maintained at ~ 37°C. Arterial blood samples were collected 1 hour after resuscitation with shed blood. We found that pO2 (partial pressure of oxygen) was significantly higher in TH group versus the normothermic group. The rats in normothermic group had significantly elevated potassium, chloride and lactate levels and more negative base excess compared to rats that in TH group (Table). The neutrophil was lower in the TH group; the lymphocyte (%) was higher in the TH group. There were no significantly differences in pH, pCO2, sodium, calcium or glucose between the normothermia and TH groups. Conclusions: pO2 remained normal and levels of potassium, chloride, lactate and neutrophil were lower in TH group. These results may contribute to the protective effect of TH during hemorrhagic shock.

Reassessing Southern Ocean Air-Sea CO2 Flux Estimates With the Addition of Biogeochemical Float Observations.

New estimates of pCO2 from profiling floats deployed by the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project have demonstrated the importance of wintertime outgassing south of the Polar Front, challenging the accepted magnitude of Southern Ocean carbon uptake (Gray et al., 2018, https://doi:10.1029/2018GL078013). Here, we put 3.5 years of SOCCOM observations into broader context with the global surface carbon dioxide database (Surface Ocean CO2 Atlas, SOCAT) by using the two interpolation methods currently used to assess the ocean models in the Global Carbon Budget (Le Quéré et al., 2018, https://doi:10.5194/essd-10-2141-2018) to create a ship‐only, a float‐weighted, and a combined estimate of Southern Ocean carbon fluxes (<35°S). In our ship‐only estimate, we calculate a mean uptake of −1.14 ± 0.19 Pg C/yr for 2015–2017, consistent with prior studies. The float‐weighted estimate yields a significantly lower Southern Ocean uptake of −0.35 ± 0.19 Pg C/yr. Subsampling of high‐resolution ocean biogeochemical process models indicates that some of the differences between float and ship‐only estimates of the Southern Ocean carbon flux can be explained by spatial and temporal sampling differences. The combined ship and float estimate minimizes the root‐mean‐square pCO2 difference between the mapped product and both data sets, giving a new Southern Ocean uptake of −0.75 ± 0.22 Pg C/yr, though with uncertainties that overlap the ship‐only estimate. An atmospheric inversion reveals that a shift of this magnitude in the contemporary Southern Ocean carbon flux must be compensated for by ocean or land sinks within the Southern Hemisphere.

End-tidal carbon dioxide underestimates plasma carbon dioxide during emergent trauma laparotomy leading to hypoventilation and misguided resuscitation: A Western Trauma Association Multicenter Study.

End-tidal carbon dioxide (ETCO2) is routinely used during elective surgery to monitor ventilation. The role of ETCO2 monitoring in emergent trauma operations is poorly understood. We hypothesized that ETCO2 values underestimate plasma carbon dioxide (pCO2) values during resuscitation for hemorrhagic shock. Multicenter trial was performed analyzing the correlation between ETCO2 and pCO2 levels. Two hundred fifty-six patients resulted in 587 matched pairs of ETCO2 and pCO2. Correlation between these two values was very poor with an R of 0.04. 40.2% of patients presented to the operating room acidotic and hypercarbic with a pH less than 7.30 and a pCO2 greater than 45 mm Hg. Correlation was worse in patients that were either acidotic or hypercarbic. Forty-five percent of patients have a difference greater than 10 mm Hg between ETCO2 and pCO2. A pH less than 7.30 was predictive of an ETCO2 to pCO2 difference greater than 10 mm Hg. A difference greater than 10 mm Hg was predictive of mortality independent of confounders. Nearly one half (45%) of patients were found to have an ETCO2 level greater than 10 mm Hg discordant from their PCO2 level. Reliance on the discordant values may have contributed to the 40% of patients in the operating room that were both acidotic and hypercarbic. Early blood gas analysis is warranted, and a lower early goal of ETCO2 should be considered. Therapeutic, level IV.

Seasonal variations and intricate diel differences in the physio-chemical parameters and CO2 emissions from a typical karst groundwater-fed reservoir in southern China

The quantification of CO2 flux of water reservoirs is still largely uncertain due to complex temporal variations in physio-chemical parameters and CO2 emissions. To address this issue, the diel-scale characteristics of physio-chemical parameters, δ13CDIC, and CO2 emission flux from Dalongdong reservoir (DLD), a karst groundwater-fed reservoir, in southern China were measured covering July, August, and November of 2014 and March and June of 2015. The results showed that the physio-chemical parameters, δ13CDIC, and CO2 emission flux displayed significant seasonal variations and intricate diel differences in the DLD reservoir. At the seasonal scale, the DLD reservoir is a CO2 source because the mean value of the CO2 emission flux is higher than zero. The highest CO2 emission flux was in November of 2014 due to reservoir overturn and the lowest flux was in August of 2014 due to reservoir thermal stratification. Diel differences in pH, DO, DIC, and pCO2 were inconspicuous during the study periods, while the CO2 emission and δ13CDIC showed higher values during the daytime than the nighttime during July of 2014 and March and June of 2015. In August of 2014, mean differences between the daytime and nighttime CO2 emission were inconspicuous due to a negative CO2 emission flux occurrence. Reservoir overturn in November of 2014 resulted in a higher mean CO2 emission flux and larger data range during the daytime than at nighttime. Future studies that calculate CO2 emissions in water reservoirs should consider monitoring temporal frequencies to obtain more accurate estimations of CO2 emission fluxes.

Improving the prognostic value of ∆PCO2 following cardiac surgery: a prospective pilot study.

Conflicting results have been published on prognostic significance of central venous to arterial PCO2 difference (∆PCO2) after cardiac surgery. We compared the prognostic value of ∆PCO2 on intensive care unit (ICU) admission to an original algorithm combining ∆PCO2, ERO2 and lactate to identify different risk profiles. Additionally, we described the evolution of ∆PCO2 and its correlations with ERO2 and lactate during the first postoperative day (POD1). In this monocentre, prospective, and pilot study, 25 patients undergoing conventional cardiac surgery were included. Central venous and arterial blood gases were collected on ICU admission and at 6, 12 and 24 h postoperatively. High ∆PCO2 (≥ 6 mmHg) on ICU admission was found to be very frequent (64% of patients). Correlations between ∆PCO2 and ERO2 or lactate for POD1 values and variations were weak or non-existent. On ICU admission, a high ∆PCO2 did not predict a prolonged ICU length of stay (LOS). Conversely, a significant increase in both ICU and hospital LOS was observed in high-risk patients identified by the algorithm: 3.5 (3.0–6.3) days versus 7.0 (6.0–8.0) days (p = 0.01) and 12.0 (8.0–15.0) versus 8.0 (8.0–9.0) days (p < 0.01), respectively. An algorithm incorporating ICU admission values of ∆PCO2, ERO2 and lactate defined a high-risk profile that predicted prolonged ICU and hospital stays better than ∆PCO2 alone.

Venous-to-arterial pCO2 difference in high-risk surgical patients.

Alteration of tissue perfusion is a main contributor to organ dysfunction in high-risk surgical patients. The difference between venous carbon dioxide and arterial carbon dioxide pressure (pCO2 gap) has been described as a parameter reflecting tissue hypoperfusion in critically ill patients who are insufficiently resuscitated. The pCO2 gap/CavO2 ratio has also been described as an indicator of the respiratory quotient, thus the relationship between DO2 and VO2. Most of the knowledge about the pCO2 gap and the pCO2 gap/CavO2 ratio has come from studies in the literature on animal models or intensive care unit (ICU) patients. To date, publications pertaining to the operative setting are sparse. In the present review, we will first discuss the physiological background of the pCO2 gap and CO2-O2 derived parameters used in the operating room. Few studies have focused on the clinical relevance of the pCO2 gap in high-risk non-cardiac surgical patients. Prospective observational studies with a small sample size and retrospective studies have shown that the pCO2 gap may be a useful complementary tool to identify patients who remain insufficiently optimized hemodynamically. In a few studies, a high pCO2 gap was associated with postoperative complications following non-cardiac high-risk surgery. Results of observational studies conducted in patients undergoing cardiac surgery are contradictory. We focused on the divergence between non-cardiac surgery, cardiac surgery, and septic critically ill patients. When analyzing the literature, we can find some explanations for the discrepancies in the published results between cardiac and non-cardiac surgery. Finally, we will discuss the clinical utility of the pCO2 gap in high-risk surgical patients.

Buccal jet streaming and dead space determination in the South American lungfish, Lepidosiren paradoxa

The “jet stream” model predicts an expired flow within the dorsal part of the buccal cavity with small air mixing during buccal pump ventilation, and has been suggested for some anuran amphibians but no other species of air breathing animal using a buccal force pump has been investigated. The presence of a two-stroke buccal pump in lungfish, i.e. expiration followed by inspiration, was described previously, but no quantitative data are available for the dead-space of their respiratory system and neither a detailed description of airflow throughout a breathing cycle. The present study aimed to assess the degree of mixing of fresh air and expired gas during the breathing cycle of Lepidosiren paradoxa and to verify the possible presence of a jet stream during expiration in this species. To do so, simultaneous measurements of buccal pressure and ventilatory airflows were carried out. Buccal and lung gases (PCO2 and PO2) were also measured. The effective ventilation was calculated and the dead space estimated using Bohr equations. The results confirmed that the two-stroke buccal pump is present in lungfish, as it is in anuran amphibians. The present approaches were coherent with a small dead space, with a very small buccal-lung PCO2 difference. In the South American lungfish the dead space (VD) as a percentage of tidal volume (VT) (VD / VT) ranged from 4.1 to 12.5%. Our data support the presence of a jet stream and indicate a small degree of air mixing in the buccal cavity. Comparisons with the literature indicate that these data are similar to previous data reported for the toad Rhinella schneideri.

Is microcirculatory assessment ready for regular use in clinical practice?

The present review discusses the current role of microcirculatory assessment in the hemodynamic monitoring of critically ill patients. Videomicroscopic techniques have demonstrated that microvascular perfusion is altered in critically ill patients, and especially in sepsis. These alterations are associated with organ dysfunction and poor outcome. Handheld microscopes can easily be applied on the sublingual area of critically ill patients. Among the specific limitations of these techniques, the most important is that these can mostly investigate the sublingual microcirculation. The representativity of the sublingual area may be questioned, especially as some areas may sometimes be more affected than the sublingual area. Also, evaluation of the sublingual area may be difficult in nonintubated hypoxemic patients. Alternative techniques include vasoreactivity tests using either transient occlusion or performing a thermal challenge. These techniques evaluate the maximal dilatory properties of the microcirculation but do not really evaluate the actual microvascular perfusion. Focusing on the glycocalyx may be another option, especially with biomarkers of glycocalyx degradation and shedding. Evaluation of the glycocalyx is still largely experimental, with different tools still in investigation and lack of therapeutic target. Venoarterial differences in PCO2 are inversely related with microvascular perfusion, and can thus be used as surrogate for microcirculation assessment. Several limitations prevent the regular use in clinical practice. The first is the difficult use of some of these techniques outside research teams, whereas nurse-driven measurements are probably desired. The second important limitation for daily practice use is the lack of uniformly defined endpoint. The final limitation is that therapeutic interventions affecting the microcirculation are not straightforward. Clinical and biological surrogates of microcirculatory assessment can be used at bedside. The role of microvideoscopic techniques is still hampered by the lack of clearly defined targets as well as interventions specifically targeting the microcirculation.

Central venous-to-arterial PCO2 difference, arteriovenous oxygen content and outcome after adult cardiac surgery with cardiopulmonary bypass: A prospective observational study.

Rapid identification and treatment of tissue hypoxia reaching anaerobiosis (dysoxia) may reduce organ failure and the occurrence of major postoperative complications (MPC) after cardiac surgery. The predictive ability of PCO2-based dysoxia biomarkers, central venous-to-arterial PCO2 difference (ΔPCO2) and ΔPCO2 to arteriovenous oxygen content difference ratio, is poorly studied in this setting. We evaluated the ability of PCO2-based tissue dysoxia biomarkers, blood lactate concentration and central venous oxygen saturation measured 2 h after admission to the ICU as predictors of MPC. A prospective, observational cohort study. Single-centre, academic hospital cardiovascular ICU. We included adult patients undergoing cardiac surgery with cardiopulmonary bypass and measured dysoxia biomarkers at ICU admission, and after 2, 6 and 24 h. The primary endpoint was MPC, a composite of cardiac and noncardiac MPC evaluated in the 48 h following surgery. After univariate analysis of MPC covariates including dysoxia biomarkers measured at 2 h, multivariate logistic regression analyses were performed to identify the association of these biomarkers with MPC for confounders. Areas under the receiver operating characteristic curves were determined for biomarkers which remained independently associated with MPC. MPC occurred in 56.5% of the 308 patients analysed. ΔPCO2, blood lactate concentration and central venous oxygen saturation measured at 2 h, but not ΔPCO2 to arteriovenous oxygen content difference ratio, were significantly associated with MPC. However, only ΔPCO2 was independently associated with MPC after multivariate analysis. The areas under the receiver operating characteristic curves of ΔPCO2 measured at 2 h for MPC prediction was 0.64 (95% CI 0.57 to 0.70, P < 0.001). After cardiac surgery with cardiopulmonary bypass, ΔPCO2 measured 2 h after ICU admission was the only dysoxia biomarker independently associated with MPC, but with limited performance. ClinicalTrials.gov, NCT03107572.

Differences in patient characteristics and care practices between two trials of therapeutic hypothermia.

Background:The Induced Hypothermia (IH) and Optimizing Cooling (OC),trials for HIE had similar inclusion criteria. The rate of death/moderate-severe disability differed for the subgroups treated with TH at 33.5°C for 72 hours (44% vs. 29%, unadjusted p=0.03). We aimed to evaluate differences in patient characteristics and care practices between the trials.Methods:We compared pre/post-randomization characteristics and care practices between IH and OC.Results:There were 208 patients in the IH trial, 102 cooled, and 364 in the OC trial, 95 cooled to 33.5°C for 72 hours. In OC, neonates were less ill, fewer had severe HIE, and the majority were cooled prior to randomization. Differences between IH and OC were observed in the adjusted difference in the lowest PCO2 (+3.08mmHG, p=0.005) and highest PO2 (−82.7 mmHG, p<0.001). In OC compared to IH the adjusted RR of exposure to anticonvulsant prior to randomization was decreased (RR 0.58, (0.40-0.85), p=0.005) and there was increased risk of exposure during cooling to sedatives/analgesia (RR1.86 (1.21-2.86), p=0.005).Conclusion:Despite similar inclusion criteria, there were differences in patient characteristics and care practices between trials. Change in care practices over time should be considered when planning future neuroprotective trials.

A Seasonal to Interannual View of Inorganic and Organic Carbon and pH in Western Lake Superior

AbstractTo investigate the carbon cycle of Lake Superior, Earth's largest freshwater lake by surface area, we performed total organic carbon, dissolved organic carbon, chlorophyll, spectrophotometric pH, total inorganic carbon, and alkalinity measurements on seasonal samples from the western lake. The last three parameters, along with in situ temperature, were used to calculate the partial pressure of carbon dioxide in surface water (pCO2(w)) using the CO2SYS algorithm. There was a strong positive correlation between pH and water temperature and a weaker but significant positive correlation between pH and chlorophyll concentration. Total organic carbon exhibited higher nearshore concentrations (as determined by a negative correlation with total water column depth); such a spatial relationship did not appear in the inorganic carbon parameters (total inorganic carbon, pH, or pCO2(w)). Western Lake Superior exhibited net outgassing in spring, little net gas transfer in summer, and some outgassing in the fall. The pCO2(w) values were negatively correlated with both water temperature and chlorophyll concentration. Seasonal differences in pCO2(w) in Lake Superior appeared more strongly driven by biology and terrestrial inputs as compared to direct effects of temperature on CO2 solubility. Interannual data from the long‐term Great Lakes Environmental Database data set indicated that lake alkalinity has been increasing over the past 20 years, and lake surface water pH appeared relatively stable. Modeling pH change over the same time frame in CO2SYS shows that increases in alkalinity and lake surface water temperature counteract the increase in atmospheric carbon dioxide concentration, leading to a relatively constant pH, consistent with observational data.

Utilization of Neurally Adjusted Ventilatory Assist (NAVA) Mode in Infants and Children Undergoing Congenital Heart Surgery: A Retrospective Review.

We assessed the feasibility and the impact of NAVA compared to conventional modes of mechanical ventilation in ventilatory and gas exchange parameters in post-operative children with congenital heart disease. Infants and children (age < 18years) that underwent congenital heart surgery were enrolled. Patients were ventilated with conventional synchronized intermittent mechanical ventilation (SIMV) and subsequently transitioned to NAVA during their cardiovascular intensive care unit (CVICU) stay. The ventilatory and gas exchange parameters for the 24h pre- and post-transition to NAVA were compared. Additional parameters assessed included pain scores and sedation requirements. Eighty-one patients met inclusion criteria with a median age of 21days (interquartile range 13days-2months). The majority of patients enrolled (75.3%) had complex congenital heart disease with high surgical severity scores. The transition to NAVA was tolerated by all patients without complications. The mean peak inspiratory pressure (PIP) was 1.8cm H2O lower (p < 0.001) and mean airway pressure (Paw) was 0.5cm H2O lower (p = 0.009) on NAVA compared to conventional modes of mechanical ventilation. There was no significant difference in patients' respiratory rate, tidal volume, arterial pH, pCO2, and lactate levels between the two modes of ventilation. There was a decreased sedation requirement during the time of NAVA ventilation. Comfort scores did not differ significantly with ventilator mode change. We concluded that NAVA is safe and well-tolerated mode of mechanical ventilation for our cohort of patients after congenital heart surgery. Compared to conventional ventilation there was a statistically significant decrease in PIP and Paw on NAVA.

Abstract 191: Effects of Anesthetic Agents on Blood Parameters in Rats With Acute Hemorrhagic Shock

Background: Recent studies in our laboratory indicate that isoflurane (ISO) has protective properties including improved survival in rats with hemorrhagic shock compared to ketamine and xylazine (K/X) anesthesia. The effects of these two anesthetic agents upon blood counts, gases and chemistries in the setting of hemorrhagic shock is unknown. The purpose of the present study was to examine the effects of these two commonly used anesthetic regimens on blood parameters in rats with acute hemorrhagic shock. Methods and Results: Sprague Dawley rats (both genders) were anesthetized with either intraperitoneal K/X (90mg/kg and 10mg/kg; n=12) or with isoflurane (5% isoflurane induction and 2% maintenance in room air; n=12). Rats were intubated and ventilated with room air. After heparinization, hemorrhagic shock was induced by withdrawing blood to a fixed mean blood pressure of 30 mmHg for one hour and then shed blood was reinfused. Arterial blood samples were collected at 1 hour after resuscitation with shed blood. We found that K/X was associated with lower PH and lower level of standard bicarbonate concentration (SBC) and oxygen saturation (SO 2 %) and more negative base excess; and had a significantly elevated anion gap, potassium, sodium and chloride levels compared to isoflurane (Table). Platelet counts were preserved and there was less elevation of white blood cell (WBC) in ISO (Table). There were no significant differences in PO 2 , PCO 2 , hematocrit, hemoglobin, glucose and lactate levels between the two types of anesthesia. Conclusions: The anesthesia influenced the levels of blood counts, gases and chemistries in rats with acute hemorrhagic shock, favoring ISO over K/X. Blood parameters remained essentially normal in ISO group, which may help explain the protective role of ISO in hemorrhagic shock.