Venous Oxygen Content Research Articles

Prognostic value of arterial lactate combined with central venous-to-arterial carbon dioxide difference to arterial-to-central venous oxygen content difference ratio in septic shock patients

To evaluate the prognostic value of arterial lactate (Lac) combined with central venous-to-arterial carbon dioxide difference to arterial-to-central venous oxygen content difference ratio (Pcv-aCO2/Ca-cvO2) in patients with septic shock following early fluid resuscitation. A total of 97 patients with septic shock admitted to intensive care unit (ICU) of Lanzhou University Second Hospital from January 2017 to December 2019 were enrolled. The Pcv-aCO2/Ca-cvO2 ratio was calculated from blood gas analysis of radial artery and superior vena cava which was performed before resuscitation and at 6 hours of resuscitation at the same time. The patients were divided into death group and survival group according to the 28-day prognosis. The baseline data, acute physiology and chronic health evaluation II (APACHE II) score, sequential organ failure score (SOFA), clinical therapy, lactate clearance rate (LCR) at 6 hours, the length of ICU stay, hemodynamics and oxygen metabolism parameters before and after resuscitation were compared between the two groups. Risk factors were analyzed by multivariate Cox regression for 28-day mortality of patients with septic shock. The receiver operating characteristic (ROC) curve was plotted to assess the prognostic values of these factors for 28-day mortality. (1) Compared with the survival group, the patients in the death group showed significantly higher levels of APACHE II score (23.96±4.31 vs. 17.70±3.92) and SOFA score (12.74±2.80 vs. 9.23±2.43, both P < 0.01), significantly higher proportions of mechanical ventilation [85.2% (23/27) vs. 50.0% (35/70)] and continuous renal replacement therapy [CRRT; 51.9% (14/27) vs. 25.7% (18/70), both P < 0.05], a significantly more fluid replacement at 6 hours (L: 2.92±0.24 vs. 2.63±0.25, P < 0.01), a significantly lower level of LCR at 6 hours [(11.61±7.76)% vs. (27.67±13.71)%, P < 0.01], and a shorter length of ICU stay (days: 6.37±2.70 vs. 7.67±2.31, P < 0.05). (2) Compared with the survival group, the patients before resuscitation in the death group showed a significantly lower level of mean arterial pressure [MAP (mmHg, 1 mmHg = 0.133 kPa): 52.63±4.35 vs. 55.74±3.01, P < 0.01], significantly higher levels of Lac and Pcv-aCO2/Ca-cvO2 ratio [Lac (mmol/L): 7.13±1.75 vs. 5.22±1.36, Pcv-aCO2/Ca-cvO2 ratio: 1.67±0.29 vs. 1.48±0.22, both P < 0.01]; and the patients at 6 hours of resuscitation in the death group showed a significantly lower level of MAP (mmHg: 62.59±4.80 vs. 66.71±3.91, P < 0.01), significantly higher levels of central venous pressure (CVP), Lac, Pcv-aCO2 and Pcv-aCO2/Ca-cvO2 ratio [CVP (mmHg): 10.74±1.40 vs. 8.80±0.75, Lac (mmol/L): 6.36±1.86 vs. 3.90±1.95, Pcv-aCO2 (mmHg): 7.59±2.02 vs. 4.34±1.37, Pcv-aCO2/Ca-cvO2 ratio: 1.87±0.51 vs. 1.03±0.27, all P < 0.01]. (3) Multivariate Cox regression analysis showed that the independent risk factors for 28-day mortality in patients with septic shock were Lac and Pcv-aCO2/Ca-cvO2 ratio whether before or at 6 hours of resuscitation [Lac before resuscitation: relative risk (RR) = 1.434, 95% confidence interval (95%CI) was 1.070-1.922, P = 0.016; Lac at 6 hours of resuscitation: RR = 1.564, 95%CI was 1.202-2.035, P = 0.001; Pcv-aCO2/Ca-cvO2 ratio before resuscitation: RR = 2.828, 95%CI was 1.108-4.207, P = 0.038; Pcv-aCO2/Ca-cvO2 ratio at 6 hours of resuscitation: RR = 4.386, 95%CI was 2.842-5.730, P = 0.000]. (4) ROC curve analysis showed that Lac and Pcv-aCO2/Ca-cvO2 ratio at 6 hours of resuscitation had predictive value for the prognosis of patients with septic shock, the area under ROC curve (AUC) was 0.849 (95%CI was 0.762-0.914) and 0.905 (95%CI was 0.828-0.955), respectively. However, the predictive value of Lac combined with Pcv-aCO2/Ca-cvO2 ratio in patients with septic shock was significantly higher than Lac [AUC (95%CI): 0.976 (0.923-0.996) vs. 0.849 (0.762-0.914), Z = 3.354, P = 0.001], the sensitivity was 97.14%, and the specificity was 88.89%. Lac and Pcv-aCO2/Ca-cvO2 ratio are independent risk factors for predicting 28-day mortality in patients with septic shock. Lac combined with Pcv-aCO2/Ca-cvO2 ratio can assess the prognosis of patients with septic shock more accurately.

Central venous minus arterial carbon dioxide pressure to arterial minus central venous oxygen content ratio as an indicator of tissue oxygenation: a narrative review.

The central venous minus arterial carbon dioxide pressure to arterial minus central venous oxygen content ratio (Pcv-aCO2/Ca-cvO2) has been proposed as a surrogate for respiratory quotient and an indicator of tissue oxygenation. Some small observational studies have found that a Pcv-aCO2/Ca-cvO2 > 1.4 was associated with hyperlactatemia, oxygen supply dependency, and increased mortality. Moreover, Pcv-aCO2/Ca-cvO2 has been incorporated into algorithms for tissue oxygenation evaluation and resuscitation. However, the evidence for these recommendations is quite limited and of low quality. The goal of this narrative review was to analyze the methodological bases, the pathophysiologic foundations, and the experimental and clinical evidence supporting the use of Pcv-aCO2/Ca-cvO2 as a surrogate for respiratory quotient. Physiologically, the increase in respiratory quotient secondary to critical reductions in oxygen transport is a life-threatening and dramatic event. Nevertheless, this event is easily noticeable and probably does not require further monitoring. Since the beginning of anaerobic metabolism is indicated by the sudden increase in respiratory quotient and the normal range of respiratory quotient is wide, the use of a defined cutoff of 1.4 for Pcv-aCO2/Ca-cvO2 is meaningless. Experimental studies have shown that Pcv-aCO2/Ca-cvO2 is more dependent on factors that modify the dissociation of carbon dioxide from hemoglobin than on respiratory quotient and that respiratory quotient and Pcv-aCO2/Ca-cvO2 may have distinct behaviors. Studies performed in critically ill patients have shown controversial results regarding the ability of Pcv-aCO2/Ca-cvO2 to predict outcome, hyperlactatemia, microvascular abnormalities, and oxygen supply dependency. A randomized controlled trial also showed that Pcv-aCO2/Ca-cvO2 is useless as a goal of resuscitation. Pcv-aCO2/Ca-cvO2 should be carefully interpreted in critically ill patients.

Influences of acute hypervolemic hemodilution on serum levels of S-100β protein, NSE and POCD in elderly patients with spinal surgery

To explore the influences of acute hypervolemic hemodilution(AHH) on serum levels of S-100β protein, neuron specific enolase(NSE) and postoperative cognitive dysfunction POCD in elderly patients with spinal surgery. A total of 80 cases elderly patients requiring elective spinal operation were divided into AHH group and C group according to random digits table, 40 cases in each group, with ASA grade I-II. The patients in AHH group were infused 6% hydroxyethyl starch 130/0.4 at a rate of 20 ml/min after anesthesia induction, and blood volume increased by about 20%, the patients in C group were not received AHH, anesthesia and surgical methods were the same as those in AHH group. Intraoperative blood volume, allogeneic blood transfusion and urine volume were recorded. Mean arterial pressure(MAP), heart rate(HR), central venous pressure(CVP) at preoperative 1 d, 1 h after the start of surgery, end of operation, 12 h after surgery were observed. Arterial blood oxygen content (CaO₂), venous blood oxygen content (CjvO₂), arteriovenous oxygen content difference (Da-jvO₂), and cerebral oxygen uptake(CERO₂) were measured at 1 d before surgery, 15 min after surgery, 45 min after surgery, end of surgery. Mini-mental state examination(MMSE) score and serum levels of S-100β protein, NSE were measured at 1 d before surgery, 1, 3, 7 d after surgery. POCD rates of two groups were recorded. Intraoperative blood loss and allogeneic blood transfusion in AHH group was significantly lower than those in C group(P<0.05), and the urine volume was significantly higher than that in C group (P<0.05). Compared with preoperative 1 day, MAP was decreased and CVP was increased at end of surgery in AHH group, compared with C group at the same time, MAP was lower and CVP was higher in AHH group, but both were in normal range. Compared with preoperative 1 day and C group, the levels of Da-jvO₂ and CERO₂ in AHH group was decreased at 15, 45 min after the start of the operation and end of surgery(P<0.05). Compared with preoperative 1 day, MMSE scores of two groups at 1 day after surgery was decreased (P<0.05), the levels of S-100β protein and NSE were increased(P<0.05), and restored at 3, 7 days after surgery. There was statistical difference in MMSE scores, the levels of S-100β protein, NSE at 1 day after surgery between two groups (P<0.05). There was no statistical difference in POCD rate between two groups(P>0.05). AHH can significantly reduce intraoperative blood loss and blood transfusion in elderly patients with spinal surgery, and decrease the levels of S-100β protein and NSE, does not increase the risk of the occurrence of POCD.

Alterations in Retinal Oxygen Delivery, Metabolism, and Extraction Fraction During Bilateral Common Carotid Artery Occlusion in Rats.

PurposeThe purpose of the current study was to investigate alterations in retinal oxygen delivery, metabolism, and extraction fraction and elucidate their relationships in an experimental model of retinal ischemia.MethodsWe subjected 14 rats to permanent bilateral common carotid artery occlusion using clamp or suture ligation, or they underwent sham procedure. Within 30 minutes of the procedure, phosphorescence lifetime imaging was performed to measure retinal vascular oxygen tension and derive arterial and venous oxygen contents, and arteriovenous oxygen content difference. Fluorescent microsphere and red-free retinal imaging were performed to measure total retinal blood flow. Retinal oxygen delivery rate (DO2), oxygen metabolism rate (MO2), and oxygen extraction fraction (OEF) were calculated.ResultsDO2 and MO2 were lower in ligation and clamp groups compared to the sham group, and also lower in the ligation group compared to the clamp group (P ≤ 0.05). OEF was higher in the ligation group compared to clamp and sham groups (P ≤ 0.03). The relationships of MO2 and OEF with DO2 were mathematically modeled by exponential functions. With moderate DO2 reductions, OEF increased while MO2 minimally decreased. Under severe DO2 reductions, OEF reached a maximum value and subsequently MO2 decreased with DO2.ConclusionsThe findings improve knowledge of mechanisms that can maintain MO2 and may clarify the pathophysiology of retinal ischemic injury.

Pcv-aCO2/Ca-cvO2 Combined With Arterial Lactate Clearance Rate as Early Resuscitation Goals in Septic Shock

BackgroundWe aimed to investigate the prognostic significance of central venous-arterial carbon dioxide tension to arterial-central venous oxygen content ratio (Pcv-aCO2/Ca-cvO2) combined with arterial lactate clearance rate (LCR) as early resuscitation goals in septic shock. Materials and MethodsWe enrolled 145 septic shock patients admitted to our department from March 2013 to May 2017 in this study. They all received an initial resuscitation therapy according to the Surviving Sepsis Campaign guideline, and were classified into 4 groups according to Pcv-aCO2/Ca-cvO2 and LCR at 6 hours after resuscitation (T6): Group A: Pcv-aCO2/Ca-cvO2 > 1.8, LCR < 30%; Group B: Pcv-aCO2/Ca-cvO2 > 1.8, LCR ≥ 30%; Group C: Pcv-aCO2/Ca-cvO2 ≤ 1.8, LCR < 30% and Group D: Pcv-aCO2/Ca-cvO2 ≤ 1.8, LCR ≥ 30%. General demographics, hemodynamic parameters, metabolic parameters, Acute Physiology and Chronic Health Evaluation II scores, Sequential Organ Failure Assessment scores, length of intensive care unit stay and 28-day mortality were compared among groups. ResultsGroup D had the lowest Acute Physiology and Chronic Health Evaluation II and Sequential Organ Failure Assessment score at day 3, the shortest intensive care unit stay and the lowest 28-day mortality. Kaplan-Meier survival curves up to day 28 showed group D had the longest median survival time. Pcv-aCO2/Ca-cvO2 and LCR at T6 were independent predictors of 28-day mortality. The area under ROC curve for Pcv-aCO2/Ca-cvO2 combined with LCR was significantly greater than either Pcv-aCO2/Ca-cvO2 or LCR alone (both P < 0.05). ConclusionsCombination of Pcv-aCO2/Ca-cvO2 ratio and LCR is better than either alone to predict the adverse outcomes in septic shock, and may provide useful information for assessing the adequacy of resuscitation in early-stage septic shock.

Studies into the determinants of skeletal muscle oxygen consumption: novel insight from near-infrared diffuse correlation spectroscopy.

Diffuse correlation spectroscopy (DCS) is emerging as a powerful tool to assess skeletal muscle perfusion. Near-infrared spectroscopy (NIRS) is an established technique for characterizing the transport and utilization of oxygen through the microcirculation. Here we compared a combined NIRS-DCS system with conventional measures of oxygen delivery and utilization during handgrip exercise. The data show good concurrent validity between convective oxygen delivery and DCS-derived blood flow index, as well as between oxygen extraction at the conduit and microvascular level. We then manipulated forearm arterial perfusion pressure by adjusting the position of the exercising arm relative to the position of the heart. The data show that microvascular perfusion can be uncoupled from convective oxygen delivery, and that tissue saturation seemingly compensates to maintain skeletal muscle oxygen consumption. Taken together, these data support a novel role for NIRS-DCS in understanding the determinants of muscle oxygen consumption at the microvascular level. Diffuse correlation spectroscopy (DCS) is emerging as a powerful tool to assess skeletal muscle perfusion. Combining DCS with near-infrared spectroscopy (NIRS) introduces exciting possibilities for understanding the determinants of muscle oxygen consumption; however, no investigation has directly compared NIRS-DCS to conventional measures of oxygen delivery and utilization in an exercising limb. To address this knowledge gap, nine healthy males performed rhythmic handgrip exercise with simultaneous measurements by NIRS-DCS, Doppler blood flow and venous oxygen content. The two approaches showed good concurrent validity, with directionally similar responses between: (a) Doppler-derived forearm blood flow and DCS-derived blood flow index (BFI), and (b) venous oxygen saturation and NIRS-derived tissue saturation. To explore the utility of combined NIRS-DCS across the physiological spectrum, we manipulated forearm arterial perfusion pressure by altering the arm position above or below the level of the heart. As expected, Doppler-derived skeletal muscle blood flow increased with exercise in both arm positions, but with markedly different magnitudes (below: +424.3±41.4ml/min, above: +306±12.0ml/min, P=0.002). In contrast, DCS-derived microvascular BFI increased to a similar extent with exercise, regardless of arm position (P=0.65). Importantly, however, the time to reach BFI steady state was markedly slower with the arm above the heart, supporting the experimental design. Notably, we observed faster tissue desaturation at the onset of exercise with the arm above the heart, resulting in similar muscle oxygen consumption profiles throughout exercise. Taken together, these data support a novel role for NIRS-DCS in understanding the determinants of skeletal muscle oxygen utilization non-invasively and throughout exercise.

Respiratory Muscle Work Constrains Locomotor Convective and Diffusive Transport in Heart Failure during Exercise

IntroductionHeart failure (HF) patients demonstrate augmented ventilation for a given metabolic demand which results in increased respiratory muscle work and subsequent competition for blood flow between the respiratory and locomotor muscle beds. Unloading the respiratory muscles during submaximal exercise has been shown to increase leg oxygen uptake (VO2) in HF patients due increased leg blood flow via increased cardiac output and redistribution of cardiac output from the respiratory to locomotor muscles. It has been suggested that increased leg VO2 following respiratory muscle unloading in HF during submaximal exercise is due to augmented convective O2 transport in HF; however, it is unclear if diffusive O2 transport also increases with respiratory muscle unloading. We hypothesized that respiratory muscle unloading during submaximal exercise will lead to increased leg VO2 due to combined increases in convective and diffusive O2 transport.MethodsTen HF patients with reduced systolic function (6M/4W; 53±15 yrs; BMI: 29±6 kg/m2) were recruited. Patients performed two submaximal exercise bouts (i.e. with and without respiratory muscle unloading (via mechanical ventilator) (RM unloading and control (CTL), respectively)). During exercise, leg blood flow (QL) was measured via thermodilution. Intrathoracic pressure was measured via esophageal balloon. Radial arterial and femoral venous blood gases were measured. Blood gases were used to calculate arterial and venous oxygen content (CaO2 and CvO2, respectively). Leg VO2 was calculated as QL multiplied by the difference between CaO2‐CvO2. Leg O2 delivery was calculated as QL multiplied by CaO2. Leg diffusion capacity (DO2) was calculated as leg VO2 divided by femoral venous partial pressure of O2.ResultsFrom CTL to RM unloading, leg VO2 increased during submaximal exercise (0.7±0.3 vs. 1.0±0.4 L/min, p&lt;0.01, respectively). From CTL to RM unloading, leg O2 delivery increased during submaximal exercise (0.9±0.4 vs. 1.4±0.5 L/min, p&lt;0.01, respectively), whereas CaO2‐CvO2 was not different (14.1±3.0 vs. 14.2±3.2 mL/dL, p=0.57, respectively). From CTL to RM unloading, leg DO2 increased during submaximal exercise (30.4±10.8 vs. 49.7±18.6 mL/mmHg, p&lt;0.01, respectively). There was a negative relationship between the degree of RM unloading (i.e. percent decrease in mean inspiratory esophageal pressure) and percent increase in leg DO2 with RM unloading (r= −0.77, p&lt;0.01).ConclusionOur results demonstrate that unloading the respiratory muscles leads to increased leg VO2 due to convective and diffusive O2 transport during submaximal exercise in HF patients. These findings suggest that the naturally occurring respiratory muscle work in HF compromises convective and diffusive O2 transport and thus constrains leg VO2 during submaximal exercise in HF.Support or Funding InformationNIH HL126638 AHA 18POST3990251This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Decreases in Oral Tissue Blood Flow Induced by Remifentanil Are Not Accompanied by Deterioration of Oral Tissue Oxygen Tension in Rabbits

The purpose of this study was to investigate the effects of remifentanil infusion on tissue blood flow and tissue oxygen tension in the mandibular bone marrow and masseter muscle in rabbits. In addition, changes in tissue oxygen consumption in those tissues during remifentanil infusion were investigated. Sixteen male tracheotomized Japanese White rabbits were anesthetized with sevoflurane under mechanical ventilation. Under oxygen and air inhalation, fraction of inspiratory oxygen was set at 0.4 and remifentanil was infused at a rate of 0.4μg ∙ kg-1 ∙ min-1. Measurements were performed before remifentanil infusion, 20minutes after the start of remifentanil infusion, and 20 and 60minutes after the completion of remifentanil infusion (n=8). The observed variables included heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), mandibular bone marrow tissue blood flow (BBF), masseter muscle tissue blood flow (MBF), mandibular bone marrow tissue oxygen tension (PbO2), and masseter muscle tissue oxygen tension (PmO2). Another 8 rabbits were observed for arterial pH, lactate, base excess (BE), and tissue oxygen consumption in the region from which the retromandibular vein received venous blood. Measurements were performed before remifentanil infusion and 20minutes after the start of remifentanil infusion. HR, SBP, DBP, MAP, BBF, and MBF decreased during remifentanil infusion. PbO2 increased 20minutes after remifentanil infusion and returned to almost the baseline value 60minutes after remifentanil infusion. PmO2 did not change throughout the experiment. The difference between the arterial oxygen content of the femoral artery and the venous oxygen content of the retromandibular vein decreased during remifentanil infusion. Arterial pH, lactate, and BE did not change during remifentanil infusion. Remifentanil decreased BBF and MBF but did not decrease PbO2 and PmO2. It is suggested that tissue oxygen consumption decreased during remifentanil infusion.

Impact of Trendelenburg (head down) and reverse Trendelenburg (head up) position on respiratory and cardiovascular function in anaesthetized horses

ObjectiveTo describe the cardiorespiratory effects of a change in table position in anaesthetized horses. Study designProspective, crossover, randomized, experimental study. AnimalsSix adult horses (mean body weight 621 ± 59 kg, aged 13 ± 4 years). MethodsThe horses were anaesthetized twice in dorsal recumbency. They were either placed in the Trendelenburg position (head down; HD) followed by reverse Trendelenburg position (head up; HU) or in reverse order. Every position was maintained for 90 minutes. The order of positions was randomly assigned at initial anaesthesia. Extensive cardiorespiratory monitoring was performed. Statistical analysis consisted of a mixed model with horses as random effect and time, position, section of anaesthesia and interaction between those as fixed effects (p < 0.05). ResultsWhen HU was applied during the first section of anaesthesia, PaO2, (p = 0.012), oxygen saturation (SaO2, p < 0.01) and oxygen content (CaO2, p < 0.01) were significantly higher, while venous admixture (Q˙s/Q˙t, p < 0.01), mean arterial (p = 0.039), right atrial (p < 0.01) and mean pulmonary arterial pressure (p < 0.01) were lower than in HD. After changing from HU to HD, PaO2 and SaO2 remained higher and Q˙s/Q˙t lower compared to the inverse order. Independent of the order, in the HD position Q˙s/Q˙t (p = 0.019) increased while PaO2 (p < 0.01), SaO2 (p = 0.011), CaO2 (p < 0.01), venous PO2 (Pv¯O2; p = 0.019), venous saturation (p = 0.004) and venous oxygen content (p = 0.010) decreased over time. No significant differences were found for cardiac output, oxygen delivery, oxygen consumption and dobutamine requirement between the two positions. Conclusions and clinical relevanceGas exchange is better preserved in HU compared to HD, especially if applied from the start of the anaesthesia.

Sickle Cell Hemoglobin C Disease Patient Undergoing Coronary Artery Bypass Grafting with Complete Exchange Blood Transfusion during Cardiopulmonary Bypass

Sickle cell disorders are associated with increased risk of sickling and vaso-occlusive complications when undergoing cardiopulmonary bypass (CPB) surgery. Monitoring of certain parameters such as venous and arterial oxygen content, hematocrit, acid base homeostasis, and body temperature are required for a superior outcome. Furthermore, perioperative exchange transfusion has a positive effect on the outcome of surgery and on the survival of patients undergoing heart surgery. Avoiding intraoperative hypoxia and hypothermia, and minimizing hemoglobin S (HbS) and hemoglobin C (HbC) levels with exchange transfusion make bypass surgery relatively safe with enhanced outcomes in these cases. The exact HbS level for conducting cardiac surgery with CPB is not known, however, a HbS level &lt;30% is considered safe for conducting CPB. By using a “discard” cardiotomy reservoir and priming the oxygenator reservoir with donor blood, we were able to reduce the intraoperative circulating HbS and HbC levels to less than 15% and sequester the plasma and clotting factors from the discarded blood using intraoperative plasmapheresis.

Comparison of different methods to calculate venous admixture in anaesthetized horses

ObjectiveThe aim of this study was to compare different methods to determine venous admixture (Q˙s/Q˙t) in anaesthetized horses. The first objective was to estimate Q˙s/Q˙t using jugular venous blood oxygen content (Q˙s/Q˙t jugular), and a fixed value for the oxygen extraction (F-shunt). The second objective was to assess the influence of blood pressure and positioning on oxygen extraction. The third objective was to perform regression analysis between jugular and mixed venous blood oxygen tensions. Study designProspective, experimental trial. AnimalsThe study was performed with seven warmblood horses that were anaesthetized with detomidine, butorphanol, ketamine, diazepam and isoflurane in oxygen. MethodsMultiple simultaneous arterial, jugular venous and pulmonary arterial blood samples were taken under normotensive and hypotensive conditions in lateral and dorsal recumbency. Arterial, mixed venous, and end-capillary oxygen content were calculated. ResultsA significant correlation between Q˙s/Q˙t and Q˙s/Q˙t jugular was found [intraclass correlation coefficient (ICC) = 0.68, p < 0.001], and Bland–Altman analysis showed a bias of –11.5% and wide limits of agreement (–27.7% to 4.6%). F-shunt significantly correlated with Q˙s/Q˙t (ICC = 0.88, p < 0.001), and Bland–Altman analysis showed a lower bias (–1.97) and narrower limits of agreement (–13.8% to 9.9%). Positioning and blood pressure significantly influenced oxygen extraction. The regression formula was Y = 0.80X + 2.61 (where Y is the calculated mixed venous oxygen tension and X is the jugular venous oxygen tension) when outliers were excluded (ICC=0.82, p < 0.001). Conclusions and clinical relevanceThis study shows that F-shunt provides reasonable estimates of Q˙s/Q˙t but can possibly be improved by using simple algorithms without the need for pulmonary arterial catheterization. These algorithms use blood pressure- and positioning-dependent oxygen extraction and regression analysis between jugular venous and pulmonary arterial oxygen tension. Although promising, the validity of these algorithms needs to be determined in future studies.

Retinal Oxygen Delivery and Metabolism in Healthy and Sickle Cell Retinopathy Subjects.

PurposeReduction in inner retinal oxygen delivery (DO2) can cause retinal hypoxia and impair inner retinal oxygen metabolism (MO2), leading to vision loss. The purpose of the current study was to establish measurements of DO2 and MO2 in healthy subjects and test the hypothesis that DO2 and MO2 are reduced in sickle cell retinopathy (SCR) subjects.MethodsDual wavelength retinal oximetry and Doppler optical coherence tomography were performed in 12 healthy control and 12 SCR subjects. Images were analyzed to measure retinal arterial and venous oxygen content (O2A and O2V), venous diameter (DV), and total retinal blood flow (TRBF). Retinal arteriovenous oxygen content difference (O2AV), DO2, MO2, and oxygen extraction fraction (OEF) were calculated according to the following equations: O2AV = O2A − O2V; DO2 = TRBF * O2A; MO2 = TRBF * O2AV; OEF = MO2/DO2.ResultsRetinal DV and TRBF were higher in the SCR group as compared to the control group, whereas, O2A, O2V, and O2AV were lower in SCR group as compared to the control group. DO2, MO2, and OEF were not significantly different between control and SCR groups. MO2 and DO2 were linearly related, such that higher MO2 was associated with higher DO2. There was an inverse relationship between TRBF and OEF, such that lower TRBF was associated with higher OEF.ConclusionsIncreased blood flow compensated for decreased oxygen content, thereby maintaining DO2, MO2, and OEF at predominately lower stages of SCR. Quantitative assessment of these parameters has the potential to advance knowledge and improve diagnostic evaluation of retinal ischemic conditions.

Central venous-arterial carbon dioxide tension to arterial-central venous oxygen content ratio combined with lactate clearance rate as early resuscitation goals of septic shock

Objective: To investigate the prognostic significance of central venous-arterial carbon dioxide tension to arterial-venous oxygen content ratio (Pcv-aCO(2)/Ca-cvO(2)) combined with lactate clearance rate (LCR) as early resuscitation goals of septic shock. Methods: One hundred and forty-five septic shock patients admitted to Second Department of Critical Care Medicine of Lanzhou University Second Hospital from March 2013 to May 2017 were enrolled in this study.All septic shock patients received an initial resuscitation therapy according to early goal-directed therapy.The arterial and central venous blood gases were measured simultaneously at baseline (T0) and 6 hours after resuscitation (T6). Pcv-aCO(2)/Ca-cvO(2) and LCR were calculated.Patients were classified into four groups according to Pcv-aCO(2)/Ca-cvO(2) and LCR at T6: group A, Pcv-aCO(2)/Ca-cvO(2)>1.8 and LCR<30%; group B, Pcv-aCO(2)/Ca-cvO(2)>1.8 and LCR≥30%; group C, Pcv-aCO(2)/Ca-cvO(2)≤1.8 and LCR<30%; group D, Pcv-aCO(2)/Ca-cvO(2)≤1.8 and LCR≥30%.General demographics, hemodynamic parameters, oxygen metabolism parameters, acute physiology and chronic health evaluation (APACHE Ⅱ) scores, sequential organ failure assessment (SOFA) scores, length of intensive care unit (ICU) stay, and 28-day mortality rate were compared among the 4 groups.A Kaplan-Meier curve showed the survival probabilities at day 28 using a log-rank test for multiple comparisons.Parameters were introduced into a Cox's proportional hazards regression model to analyze the prediction of 28-day mortality.Receiver operating characteristics (ROC) curves were constructed to evaluate the ability of Pcv-aCO(2)/Ca-cvO(2), LCR, Pcv-aCO(2)/Ca-cvO(2) combined with LCR at T6 to predict 28-day mortality. Results: Compared with patients in group A, patients from group D had the lower APACHE Ⅱ and SOFA score at day 3 (t=-2.909, -3.630, both P<0.05), shorter ICU stay (t=-2.575, P=0.011), and lower mortality rate at day 28 (χ(2)=3.124, P=0.011). Survival curves up to day 28, illustrated by Kaplan-Meier method, showed that group A had the shortest median survival time (χ(2)=10.332, P=0.016), difference between group A and group D was statistically significant (χ(2)=8.304, P=0.004). The Cox regression analysis revealed that Pcv-aCO(2)/Ca-cvO(2) (RR=3.888, 95%CI: 2.443-6.189, P<0.001) and LCR (RR=0.073, 95%CI: 0.008-0.640, P=0.018) at T6 were independent predictors of 28-day mortality.The area under ROC curve for Pcv-aCO(2)/Ca-cvO(2) combined with LCR (0.919, 95%CI: 0.862-0.958) was significantly greater than whether Pcv-aCO(2)/Ca-cvO(2) (0.862, 95%CI: 0.795-0.914) or LCR (0.820, 95%CI: 0.748-0.879) alone (Z=2.032, 2.364, both P<0.05). Conclusion: Combination of Pcv-aCO(2)/Ca-cvO(2) and LCR is better than single parameter to predict the risk of adverse outcomes of septic shock patients, and may provide useful information for assessing the adequacy of resuscitation at early stage of septic shock.

Determining the venous oxygen reservoir: A novel, hypothetical approach to titration of supplemental oxygen in preterm newborns

While normal oxygen saturation is commonly thought to be a marker of normal oxygenation, cutaneous saturation does not account for the sufficiency of oxygen within each cell or that of the system overall. Rather, cutaneous oximetry simply defines the saturation of haemoglobin (Hb) with oxygen in a pulsatile vessel. Assessment of sufficiency is best determined by measurement of the amount of oxygen left over following aerobic respiration. This left over oxygen is ‘stored’ on Hb in the venous compartment and can be calculated as the venous oxygen content. We hypothesize that the development of a venous oxygen content or saturation reference range in a group of well, uninjured very preterm newborns and subsequent application, in a randomised trial, with a structural, functional and molecular outcome will resolve the method for assessment of oxygen sufficiency in preterms by demonstrating both clinical safety and effectiveness. This method could be subsequently used for titration of supplemental oxygen.

Regional cerebral tissue oxygen saturation changes following blood transfusion in neuro-intensive care unit patients-a pilot observational study.

Although central venous oxygen saturation (ScvO2 ) is used to decide on red blood cell (RBC) transfusion, whether its improvement is associated with parallel improvement in cerebral oxygenation is not adequately studied. This study looked at changes in regional cerebral tissue oxygen saturation (rSO2 ) following RBC transfusion in neuro-intensive care unit (ICU) patients. In this prospective observational pilot study, rSO2 was measured in adult neuro-ICU patients before RBC transfusion, at the end and at 6, 12, 18 and 24 h after RBC transfusion. rSO2 measurements were taken using cerebral oximetry on both sides of the hemicraniums. Haemoglobin, central venous pressure, ScvO2 and temperature were recorded during the study period. Arterial oxygen content, central venous oxygen content and cerebral fractional oxygen extraction were calculated. Mann Whitney U test was used to study the changes in variables at baseline and at 24 h following RBC transfusion. Friedman's test was used to study changes in parameters from baseline to 24 h post-transfusion. A P value of <0·05 was considered to be significant. The data from 13 subjects were analysed. rSO2 increased significantly following RBC transfusion on both sides of the brain (P = 0·002, P = 0·007), with a corresponding decrease in cerebral fractional oxygen extraction (P = 0·001, P = 0·007). RBC transfusion increased rSO2 significantly on both sides of the brain. As patients' outcomes were not studied, whether this increase in regional cerebral oxygen saturation is beneficial or if it is because of excess DO2 is still unclear. Further studies are required to clarify this issue.

Validating the Physiologic Model HumMod as a Substitute for Clinical Trials Involving Acute Normovolemic Hemodilution.

Blood conservation strategies and transfusion guidelines remain a heavily debated clinical topic. Previous investigational trials have shown that acute isovolemic hemodilution does not limit adequate oxygen delivery; however, a true critical hemoglobin level has never been investigated or defined due to safety concerns for human volunteers. Validated physiologic modeling may be useful to investigate hemodilution at critical hemoglobin levels without the ethical or safety hazards of clinical trials. Our hypothesis is that HumMod, an integrative physiological model, can replicate the cardiovascular and metabolic findings of previous clinical studies of acute isovolemic hemodilution and use coronary blood flow and coronary oxygen delivery in extreme hemodilution to predict a safety threshold. By varying cardiovascular and sizing parameters, unique individuals were generated to simulate a population using HumMod, an integrative mathematical model of human physiology. Hemodilution was performed by simultaneously hemorrhaging 500 mL aliquots of blood while infusing equal volumes of hetastarch, 5% albumin balanced salt solution, or triple volumes of lactated Ringer's solution over 10 minutes. Five hemodilution protocols reported over 3 studies were directly replicated with HumMod to compare and validate essential cardiovascular and metabolic responses to hemodilution in moderately healthy, awake adults. Cardiovascular parameters, mental status, arterial and mixed venous oxygen content, and oxyhemoglobin saturation were recorded after the removal of each aliquot. The outputs of this simulation were considered independent variables and were stratified by hemoglobin concentration at the time of measurement to assess hemoglobin as an independent predictor of hemodynamic and metabolic behavior. The published reports exhibited discrepancies: Weiskopf saw increased heart rate and cardiac index, while Jones and Ickx saw no change in these variables. In HumMod, arterial pressure was maintained during moderate hemodilution due to decreases in peripheral resistance opposing increases in cardiac index. HumMod showed preserved ventilation through moderate hemodilution, compensated for by an increased oxygen extraction similar to the studies of Jones and Ickx. The simulation results qualitatively followed the clinical studies, but there were statistical differences. In more extreme hemodilution, HumMod had a lesser increase in cardiac index, which led to deficiencies in oxygen delivery and low venous saturation. In the simulations, coronary blood flow and oxygen delivery increase up to a critical hemoglobin threshold of 55-75 g/L in HumMod. In this range, coronary blood flow and oxygen delivery fell, leading to cardiac injury. The allowable amount of hemodilution before reaching the critical point is most closely correlated with nonmuscle mass (r = 0.69) and resting cardiac output (r = 0.67). There were significant statistical differences in the model population and the clinical populations, but overall, the model responses lay within the clinical findings. This suggests our model is an effective replication of hemodilution in conscious, healthy adults. A critical hemoglobin range of 5.5-7.5 g/L was predicted and found to be highly correlated with nonmuscle mass and resting cardiac output.

In vivo aerobic metabolism of the rainbow trout gut and the effects of an acute temperature increase and stress event.

The fish gut is responsible for numerous potentially energetically costly processes, yet little is known about its metabolism. Here, we provide the first in vivo measurements of aerobic metabolism of the gut in a teleost fish by measuring gut blood flow, as well as arterial and portal venous oxygen content. At 10°C, gut oxygen uptake rate was 4.3±0.5 ml O2h-1kg-1 (∼11% of whole-animal oxygen uptake). Following acute warming to 15°C, gut blood flow increased ∼3.4-fold and gut oxygen uptake rate increased ∼3.7-fold (16.0±3.3 ml O2h-1kg-1), now representing ∼25% of whole-animal oxygen uptake. Although gut blood flow decreased following an acute stress event at 15°C, gut oxygen uptake remained unchanged as a result of a ∼2-fold increase in oxygen extraction. The high metabolic thermal sensitivity of the gut could have important implications for the overall aerobic capacity and performance of fish in a warming world and warrants further investigation.

Effect of Acute Transfusion on Cerebral Oxygenation in Patients with Sickle Cell Disease

Introduction : The molecular abnormality in sickle hemoglobin (HbS) produces a unique cellular pathology characterized by fragile and rigid red blood cells which block the microcirculation, which, in concert with large vessel vasculopathy and the anemia of sickle cell disease (SCD), compromises oxygen delivery to the brain and other organs. Long-term, periodic transfusions are commonly used to prevent and ameliorate neurologic complications related to vasculopathy, particularly stroke. Despite widespread use of transfusions, little is known about the physiological effects on cerebral O2 delivery, which represents an integration of multiple, potentially opposing processes. While increased hematocrit improves O2 carrying capacity, the consequent elevation of blood viscosity has the potential to impede blood flow to cerebral tissue. Also, 2,3-BPG levels in stored blood are depleted, temporarily impairing O2 delivery. Advances in cerebral oximetry (using near infrared spectroscopy) provide an opportunity to address these issues directly to study cerebral oxygenation following transfusions in SCD. The FORE-SIGHT© cerebral oximeter (CAS Medical Systems) measures cerebral tissue hemoglobin saturation (SCTO2), a mixture of arterial and venous oxygen saturation (30:70) in a voxel of tissue near the gray-white junction in the frontal lobes. Using measured arterial Hb saturation (SaO2) by peripheral pulse oximetry and SCTO2 by cerebral oximetry, cerebral venous Hb saturation (SvO2) can be derived. Additionally, using a measured HbO2 affinity curve derived at the time of SCTO2 determination, SvO2 can be converted to venous oxygen tension, PvO2. PvO2 is in dynamic equilibrium with tissue oxygen tension and represents the best estimate of tissue oxygenation. The primary objective of this study was to use cerebral oximetry to assess and monitor cerebral tissue oxygenation following an elective pre-operative RBC transfusion.Methods : This pilot prospective cohort study enrolled 12 patients with sickle cell anemia (SS, Sb0 thalassemia) in steady-state, who had elective, pre-operative transfusions. Patients who had received transfusion within 3 months or had known cerebral vasculopathy were excluded. Nine patients completed the planned 3 months of study follow up. Two patients were taken off study within a week of enrollment because of difficulties with cerebral oximetry measurements. One did not follow-up after 2 months of participation. Each patient had measurements of SCTO2 prior to the initiation of transfusion, continuously during transfusion, and at predetermined times points post-transfusion, for up to 3 months. Other parameters related to cerebral Hb oxygenation were also measured, including Hb, HbA, HbF, HbS, P50 and 2,3-BPG. The relationship between cerebral oxygenation with age and other predictors of oxygenation was assessed using linear mixed models. The first two post-transfusion measurements (within 96 hours) were compared against pre-transfusion measurements using Wilcoxon signed-rank tests.Results : SCTO2 was significantly associated with age (p=0.02), Hb (p=0.01) and HbA % (p=0.03 (Table 1). Immediately post-transfusion, SCTO2, increased from median values of 58% to 68.5%, p 0.004 (Table 2). Arterial saturation (SaO2) was unchanged post-transfusion, thus the increase in SCTO2 resulted in an increased (calculated) venous saturation (SvO2). P50 fell post transfusion, as expected, and despite increased SvO2, PvO2 remained unchanged. Arterial and venous oxygen content (CaO2, CvO2) increased post transfusion as expected because Hb and SvO2 increased. However, the difference in arterial and venous oxygen content (CdO2 = CaO2 - CvO2) remained unchanged after transfusion. Similar trends in these parameters were observed in second measurements made up to 96 hours after transfusion (Table 2). Since oxygen delivery equals CdO2 × blood flow, cerebral oxygen delivery would only increase if blood flow were increased by transfusion, contrary to reports {Neurology. 1989 Mar;39(3):344-8; Stroke 25:2153-8, 1994}.Conclusion: Although cerebral hemoglobin oxygen saturation (SCTO2) increased after acute transfusion, calculated tissue oxygen tension (PvO2) and apparent oxygen delivery (CdO2) remained unchanged, providing no evidence for acute improvement in cerebral oxygenation after transfusion in SCD. [Display omitted] DisclosuresQuinn:Global Blood Therapeutics: Research Funding.

Comparison of the effects of phenylephrine and norepinephrine in patients with restrictive transfusion

Objective To compare the effects of phenylephrine and norepinephrine in patients with restrictive transfusion. Methods 65 patients undergoing laparoscopic resection of rectal cancer were selected.According to the random number table method, the patients were randomly divided into 32 cases of observation group(phenylephrine composite restriction infusion) and 33 cases of control group(norepinephrine combined restrictive transfusion). The operation and hemodynamics of the two groups at different time points were compared.At T0, T1, T2, the central venous blood and arterial blood were collected, the central venous blood saturation(ScvO2), arterial blood lactate(Lac), central venous oxygen partial pressure(PcvO2), PaO2, Hb concentrations, venous oxygen content(CcvO2), arterial oxygen content(CaO2), arteriovenous oxygen content difference(Ca-cvO2) and oxygen uptake rate(ERO2) were compared between the two groups. Results The ASA levels(Ⅰ/Ⅱgrade) of the observation group and the control group were 11 cases/21 cases and 13 cases/20 cases, respectively, the difference was not statistically significant(χ2=5.298, P=0.052). The BMI of the observation group and the control group were (20.61±1.65)kg/m2, (21.57±1.42)kg/m2, respectively, the difference was not statistically significant(t=0.652, P=1.980). The fluid replacement of the observation group and the control group were (1 162±113)mL, (1171±104)mL, respectively, the difference was not statistically significant(t=1.734, P=0.065). The blood loss of the observation group and the control group were (276±41)mL, (294±42)mL, respectively, the difference was not statistically significant(t=0.083, P=1.023). The urine volume of the observation group and the control group were (524±113)mL, (532±109)mL, respectively, the difference was not statistically significant(t=1.834, P=0.053). The operation time of the observation group and the control group were (192±24)min, (197±21)min, respectively, the difference was not statistically significant(t=1.367, P=0.073). The MAP at T1-T2 of the two groups increased, the CVP of the two groups was significantly higher at T1, the HR of the two groups was significantly higher at T2.The MAP, CVP, HR between the two groups had no significant differences(all P>0.05). The levels of ScvO2, PcvO2 and PaO2 at T1 were significantly higher than those at T0, on the contrary, the levels of ScvO2, PcvO2 and PaO2 at T2 were significantly lower than those at T0, and the Hb in the observation group was significantly lower at T1-T2, the Hb in the control group was significantly lower at T1-T2, which in the observation group was lower than the control group, the differences were statistically significant(all P 0.05). There were statistically significant differences in CcvO2, CaO2, Ca-cvO2 and ERO2 between the two groups at different time points(all P<0.05). Conclusion Phenylephrine is more effective than norepinephrine in limiting infusion in elderly patients, and it has more obvious effects on tissue oxygen metabolism. Key words: Infusions, intravenous; Norepinephrine; Deoxyepinephrine

Effects of dexmedetomidine on cerebral oxygen metabolism and postoperative cognitive function during cardiopulmonary bypass of pediatric congenital heart disease surgery

Objective Exploring the effects of dexmedetomidine(Dex) on cerebral oxygen metabolism and postoperative cognitive function during cardiopulmoary bypass of pediatric congenital heart disease(CHD) surgery. Methods Eighty-four children with cardiopulmonary bypass of CHD surgery were randomly divided into observation group and control group(n=42). 2.5% sevoflurane and Dex 0.4 μg·kg-1·h-1 was applied during maintenance of anesthesia in observation group, while only 2.5% sevoflurane was applied in control group. At the time points of before beginning cardiopulmonary bypass(T1), of the ascending aorta was open(T2), of ending cardiopulmonary bypass(T3) and of 6 hours after operation(T4), blood from radial artery and right jugular bulb were harvested for blood gas analysis. The jugular venous oxygen saturation(SjvO2), arterial venous oxygen content difference(Da-jvO2) and cerebral extraction of oxygen(CERO2) were calculated according blood gas analysis. The mini-mental state examination(MMSE) score were evaluated before and 4 day, 3 month and 1 year after surgery. Results The SjvO2 of T2 were higher than SjvO2 of T1 in two groups, but Da-jvO2 and CERO2 were lower than Da-jvO2 and CERO2 of T1. The differences were statistically significant(P 0.05). There were no significant differences in preoperative MMSE scores between two groups(P>0.05). The MMSE scores in observation group at 4 day and 3 month after surgery were (26.5±1.5), (27.6±1.6), which were significantly higher than those in control group[(24.3±1.3), (25.8±1.5)], and the differences were statistically significant(P 0.05). Conclusions Dex could improve cerebral oxygen metabolism and postoperative cognitive function during cardiopulmonary bypass of pediatric CHD surgery. Key words: Dexmedetomidine; Cardiopulmonary bypass; Oxygen metabolism; Cognitive function