Measurement Of Venous Oxygen Saturation Research Articles

Oxygen Extraction and Mortality in Patients Undergoing Chronic Haemodialysis Treatment: A Multicentre Study.

Patients on haemodialysis (HD) suffer a high mortality rate linked to developing subclinical hypoxic parenchymal stress during HD sessions. The oxygen extraction ratio (OER), an estimate of the oxygen claimed by peripheral tissues, might represent a new prognostic factor in HD patients. This study evaluated whether the intradialytic change in OER (ΔOER) identified patients with higher mortality risks. We enrolled chronic HD patients with permanent central venous catheters with available central venous oxygen saturation (ScvO2) measurements; the arterial oxygen saturation was measured with peripheral oximeters (SpO2). We measured OER before and after HD at enrolment; deaths were recorded during two-years of follow-up. In 101 patients (age: 72.9 ± 13.6 years, HD vintage: 9.6 ± 16.6 years), 44 deaths were recorded during 11.6 ± 7.5 months of follow-up. Patients were divided into two groups according to a 40% ΔOER threshold (ΔOER < 40%, n = 56; ΔOER ≥ 40%, n = 45). The ΔOER ≥ 40% group showed a higher incidence of death (60% vs. 30%; p = 0.005). The survival curve (log-rank-test: p = 0.0001) and multivariate analysis (p = 0.0002) confirmed a ΔOER ≥ 40% as a mortality risk factor. This study showed the intradialytic ΔOER ≥ 40% was a mortality risk factor able to highlight critical hypoxic damage. Using a ΔOER ≥ 40% could be clinically applicable to characterise the most fragile patients.

Dual wavelength retinal vessel oximetry – influence of fundus pigmentation

BackgroundClinical methods examining oxygenation parameters in humans have been used in many different care settings, but concerns have been raised regarding their clinical utility when assessing people with darker skin pigmentation. While saturation values can be crucial in emergency medicine, they are equally valuable in assessing disease mechanisms and monitoring change in disease progression. Retinal pigmentation varies across individuals and hence, can impact on retinal oxygen parameters. The objective of this study was to quantify and eliminate the impact of retinal pigmentation on retinal vessel oxygen saturation parameters measured in the superficial retinal arterioles and venules.Methods105 healthy individuals of varying skin colour, iris colour and heritage were included. Following a full eye exam to exclude any ocular abnormality, all participants underwent intraocular pressure, systemic blood pressure measurements and dilated dual wavelength retinal photography. Rotation matrices were employed to minimise the dependency of retinal pigmentation on arterial and venous oxygen saturation measurements determined in a concentric measurement annulus.ResultsRetinal oxygen saturation in venules showed a linear correlation with retinal pigmentation (y = 0.34 × x + 38.598), whereas arterial saturation followed a polynomial pattern (y = 0.0089 × x2 + 0.7499 × x + 85.073). Both arterial and venous saturation values were corrected using local fundus pigmentation. Pre-correction retinal arterial and venous oxygen saturation were 89.0% (±13.1) and 43.7% (±11.5), respectively, and post- correction values were 94.8% (±8.7) for arteries and 56.3% (±7.0) veins.ConclusionsWhen assessing multi-ethnic cohorts, it is important to consider the impact of pigmentation on imaging parameters and to account for it prior to clinical interpretation.

Abstract 10557: A Case of Cardiogenic Shock in a Woman With a Mitochondrial Cardiomyopathy

Case Presentation: A 35-year-old woman with nonischemic cardiomyopathy, with a left ventricular ejection fraction &lt;20% on home dobutamine, and chronic weakness was referred to our institution for heart transplantation evaluation. She was directly admitted to the hospital for suspected cardiogenic shock after her labs revealed a lactate level of 5.4 mmol/L. Her hospital course was complicated by persistently undulating lactate levels (0.2 - 8.6 mmol/L) that increased with exertion, despite normal mixed venous oxygen saturation measurements obtained from a pulmonary artery catheter. Serologic genetic testing was negative, and electromyography revealed the presence of a proximal and axial myopathy. A deltoid muscle biopsy was obtained, and genetic testing of the specimen revealed two mitochondrial deoxyribonucleic acid deletions, and electron microscopy revealed mitochondrial paracrystalline inclusions. She subsequently underwent left ventricular assist device placement and was started on carnitine, arginine, creatine, thiamine, and coenzyme Q10 supplementation. Despite left ventricular assist device placement, the patient has continued to decline due to progressive right heart failure and is currently being considered for cardiac transplantation. Discussion: Mitochondrial cardiomyopathy (MCM) is an alteration in cardiac structure and function caused by genetic defects of the mitochondrial respiratory chain, in the absence of other causes of heart failure. The true prevalence of MCM is unknown. Clinical manifestations in those with MCM present on a spectrum, ranging from asymptomatic cases to those with signs and symptoms typical of heart failure. Extra-cardiac features commonly include chronic weakness and fatigue. Diagnosis is made with prompt genetic testing and microscopic evaluation of a skeletal muscle biopsy specimen. Outcomes in patients who receive a left ventricular assist device are unknown and warrant further investigation.

Effect of the Fraction of Inspired Oxygen on Intermittent Central Venous Oxygen Saturation Measurements.

Central venous oxygen saturation (ScvO2) is an essential test readily performed both by medical and nursing personnel in a critical care setting. It gives information on the patient's oxygen supply, oxygen consumption, and cardiac output. It plays an important role in early goal-directed treatment. This study was planned to assess the effect of different fractions of inspired oxygen (FiO2) levels on central venous oxygen saturation for consideration during the evaluation of central venous oxygen saturation. This interventional cross-over study enrolled 60 critically ill, nonmechanically ventilated patients. Blood samples were repeatedly drawn from the distal end of the central venous catheter for blood gas analysis after administration of 30%, 40%, and 50% FIO2 respectively. The results showed that increasing FiO2 from 30% to 40% resulted in a mean increase in ScvO2 of 6.2%. While increasing FiO2 from 40% to 50% resulted in a mean increase in ScvO2 of 3.2%. A significant increase in ScvO2 with changes in FiO2 level was recorded among patients in shock or patients with pneumonia (from 30% to 50%, p=0.002 in shock patients and from 30% to 40%, p=0.02 in patients with pneumonia). Increasing FiO2 resulted in a substantial rise in ScvO2. ScvO2 changes in response to a therapeutic challenge should be interpreted at constant FiO2 level, especially in patients with pneumonia.

Retinal oxygen saturation, vessel diameter and flicker response in eyes with specific subtypes of neovascular age-related macular degeneration during aflibercept treatment.

PurposeTo evaluate the effect of intravitreal aflibercept monotherapy on arterial and venous oxygen saturation, retinal vessel diameter and flicker response in patients with newly diagnosed specific subtypes of exudative maculopathy.MethodsThis prospective study included forty-four eyes of 44 patients with treatment-naïve polypoidal choroidal vasculopathy (PCV, n = 12), hemorrhagic choroidal neovascularization (hCNV, n = 12), pigment epithelium detachment (PED, n = 9) and type 3 MNV (RAP, n = 11). All patients received three initial aflibercept 2mg/0.05ml injections (Eylea®) in monthly intervals (loading phase) and were subsequently treated until month 12. Measurements of arterial and venous oxygen saturation, vessel diameters and flicker response were performed using the Dynamic Vessel Analyzer (DVA; IMEDOS, Jena, Germany). Statistical analysis was performed on the total population at baseline, after loading dose and at the last follow-up visit.ResultsThe arterial oxygen saturation was 94.01±2.14% and showed no change after loading dose (93.94±2.88%, p = 0.4; estimated difference [confidence interval] -0.38 [-1.24; 0.48]) and at the last visit (95.48±1.90%; p = 0.1; -1.29 [-0.34; 2.91]). The venous oxygenation during treatment was 78.49±6.93% at baseline, 80.94±7.71% after 3-monthly injections (p = 0.7; -0.43 [-2.72; 1.86]) and 80.56±7.33% at month 12 (p = 0.5; 1.07 [-2.10; 4.24). The arterial and venous vessel diameters were 94±22μm and 131±19μm at baseline, and remained unchanged following aflibercept loading dose and at the last follow-up visit (p-value: p = 0.5; 2.30 [-5.00; 9.59] p = 0.8; 0.59 [-3.17; 4.34]). During stimulation with flicker light, arterial diameter changed by +1.24±4.93% at baseline and remained stable at month 3 (+2.70±5.95%; p = 0.5; 1.43 [-2.54; 5.41]) while the change in venous diameter during flicker stimulation was +4.52±4.45% at baseline and +4.13±3.65% after loading dose (p = 0.4, 5.18 [1.73; 8.63]).ConclusionDuring intravitreal aflibercept treatment oxygen saturation, vessel diameter and flicker response did not change in the total population of patients with specific subtypes of exudative maculopathy.

Non-invasively Measured Venous Oxygen Saturation as Early Marker of Impaired Oxygen Delivery in Preterm Neonates.

IntroductionAdequate oxygen supply for preterm neonates may be defined through non-invasive measurement of venous oxygen saturation (SvO2) and fractional oxygen extraction using near-infrared spectroscopy (NIRS). We investigated whether there was a difference in peripheral muscle SvO2 (pSvO2) and peripheral fractional oxygen extraction (pFOE) in preterm neonates with early inflammation/infection compared to healthy subjects during the first 72 h after birth.Materials and MethodsWe retrospectively analyzed secondary outcome parameters of prospective observational studies, including preterm neonates at risk of infection in whom peripheral NIRS measurements were performed in combination with venous occlusions. Early neonatal inflammation/infection was diagnosed by clinical signs and laboratory parameters. Peripheral muscle tissue oxygenation index (pTOI) was measured using either NIRO 300 or NIRO 200-NX (both Hamamatsu Photonics, Japan) on the patients' lower legs. Using 20-s venous occlusions, pSvO2 and pFOE were calculated incorporating simultaneous measurements of arterial oxygen saturation (SpO2).ResultsWe analyzed measurements from 226 preterm neonates (median gestational age 33.9 weeks), 64 (28.3%) of whom were diagnosed with early neonatal inflammation/infection. During the first 24 h after birth, pSvO2 (66.9% [62.6–69.2] vs. 69.4% [64.6–72.0]; p = 0.04) and pTOI (68.6% [65.3–71.9] vs. 71.7% [67.3–75.1]; p = 0.02) were lower in those neonates with inflammation/infection, while there was no such difference for measurements between 24–48 and 48–72 h.DiscussionNIRS measurement of pSvO2 and pFOE is feasible and may be utilized for early detection of impaired peripheral oxygen delivery. As pTOI was also significantly lower, this parameter may serve as substitute for diminished regional oxygen supply.

MRI evaluation of cerebral metabolic rate of oxygen (CMRO2) in obstructive sleep apnea

Patients with obstructive sleep apnea (OSA) are at elevated risk of developing systemic vascular disease and cognitive dysfunction. Here, cerebral oxygen metabolism was assessed in patients with OSA by means of a magnetic resonance-based method involving simultaneous measurements of cerebral blood flow rate and venous oxygen saturation in the superior sagittal sinus for a period of 10 minutes at an effective temporal resolution of 1.3 seconds before, during, and after repeated 24-second breath-holds mimicking spontaneous apneas, yielding, along with pulse oximetry-derived arterial saturation, whole-brain CMRO2 via Fick’s Principle. Enrolled subjects were classified based on their apnea-hypopnea indices into OSA (N = 31) and non-sleep apnea reference subjects (NSA = 21), and further compared with young healthy subjects (YH, N = 10). OSA and NSA subjects were matched for age and body mass index. CMRO2 was lower in OSA than in the YH group during normal breathing (105.6 ± 14.1 versus 123.7 ± 22.8 μmol O2/min/100g, P = 0.01). Further, the fractional change in CMRO2 in response to a breath-hold challenge was larger in OSA than in the YH group (15.2 ± 9.2 versus 8.5 ± 3.4%, P = 0.04). However, there was no significant difference in CMRO2 between OSA and NSA subjects. The data suggest altered brain oxygen metabolism in OSA and possibly in NSA as well.

Capnodynamics—Measuring cardiac output via ventilation

Recent studies have identified stable hemodynamics as a contributing factor to improve outcome in pediatric anesthesia. So far, most of the hemodynamic monitoring methods applied in children have been complex to apply and often not satisfactory validated. Standard mainstream carbon dioxide analysis in combination with real-time mathematical analysis of the measured capnography data has enabled the development of dynamic capnography, a non-invasively cardiac output monitoring method that can be applied without user practice or need for calibrations. Capnodynamic cardiac output assessment has been extensively validated against gold standard reference methods, both in experimental and clinical settings. This review will describe the principle behind dynamic capnography measurement of cardiac output and mixed venous oxygen saturation. Additionally, the methods limitations and challenges when applied in children will be delineated.

Accuracy, Precision, and Trending Ability of Perioperative Central Venous Oxygen Saturation Compared to Mixed Venous Oxygen Saturation in Unselected Cardiac Surgical Patients

To determine whether central venous oxygen saturation (ScvO2) measurements could be used interchangeably with mixed venous oxygen saturation (SvO2) measurements in adult cardiac surgery patients. A single-center prospective observational study. A university hospital. Eighty-five adult patients undergoing cardiac surgery. The study authors compared the oxygen saturations in 590 pairs of venous blood samples drawn from the pulmonary artery catheter (PAC) at three different time points during surgery and four different time points in the intensive care unit. They compared samples obtained from the distal pulmonary artery line (SvO2) to those drawn from the proximal central venous line of the PAC (ScvO2) with the Bland-Altman test and the four-quadrant method. The mean bias between SvO2 and ScvO2 was -1.9 (95% confidence interval [CI], -2.3 to -1.5) and the limits of agreement (LOA) were -11.5 to 7.6 (95% CI, -12.5 to -10.7 and 6.8-8.5, respectively). The percentage error (PE) was 13.2%. Based on the four-quadrant plot, only 50% of the measurement pairs were in agreement, indicating deficient trending ability. ScvO2 values showed acceptable accuracy as the mean bias was low. The precision was inadequate; although the PE was acceptable, the LOA were wide. Trending ability was inadequate. The authors cannot recommend the use of ScvO2 values interchangeably with SvO2 measurements in the management of adult cardiac surgery patients.

Impact of red blood cell transfusion on oxygen transport and metabolism in patients with sepsis and septic shock: a systematic review and meta-analysis.

Red blood cell transfusion is thought to improve cell respiration during septic shock. Nevertheless, its acute impact on oxygen transport and metabolism in this condition remains highly debatable. The objective of this study was to evaluate the impact of red blood cell transfusion on microcirculation and oxygen metabolism in patients with sepsis and septic shock. We conducted a search in the MEDLINE®, Elsevier and Scopus databases. We included studies conducted in adult humans with sepsis and septic shock. A systematic review and meta-analysis were performed using the DerSimonian and Laird random-effects model. A p value < 0.05 was considered significant. Nineteen manuscripts with 428 patients were included in the analysis. Red blood cell transfusions were associated with an increase in the pooled mean venous oxygen saturation of 3.7% (p < 0.001), a decrease in oxygen extraction ratio of -6.98 (p < 0.001) and had no significant effect on the cardiac index (0.02L/minute; p = 0,96). Similar results were obtained in studies including simultaneous measurements of venous oxygen saturation, oxygen extraction ratio, and cardiac index. Red blood cell transfusions led to a significant increase in the proportion of perfused small vessels (2.85%; p = 0.553), while tissue oxygenation parameters revealed a significant increase in the tissue hemoglobin index (1.66; p = 0.018). Individual studies reported significant improvements in tissue oxygenation and sublingual microcirculatory parameters in patients with deranged microcirculation at baseline. Red blood cell transfusions seemed to improve systemic oxygen metabolism with apparent independence from cardiac index variations. Some beneficial effects have been observed for tissue oxygenation and microcirculation parameters, particularly in patients with more severe alterations at baseline. More studies are necessary to evaluate their clinical impact and to individualize transfusion decisions.

Value of combined lactate and central venous oxygen saturation measurement in patients with sepsis: a retrospective cohort study

Introduction. Lactate and central venous oxygen saturation (ScvO2) reflect tissue hypoperfusion but each measure is confounded by many additional factors. These confounding factors differ between lactate and ScvO2. Objectives. We postulated that combined assessment of lactate and ScvO2 may yield information beyond that of each measure alone. Specifically we sought to determine whether lactate has different characteristics and predictive value at different levels of ScvO2. Material and methods. We conducted a retrospective analysis of a Derivation cohort and a Validation Cohort of sepsis patients with lactate and ScvO2 measured within the first 4 hours of intensive care unit admission and 12 hours after resuscitation. Patients were grouped according to: 1) ScvO2 &lt; 60 %; 2) 60 % ≤ ScvO2 &lt; 80 %; 3) ScvO2 ≥ 80 %. Results. Lactate was negatively correlated with ScvO2 in the ScvO2 &lt; 60 % group in both cohorts but was not correlated with ScvO2 in the other ScvO2 groups. Using receiver operator characteristic analysis in the Derivation Cohort, in the ScvO2 ≥ 80 % group lactate was predictive of 28-day mortality with an area under the ROC curve (AUC) of 0.94 and an optimal threshold lactate of 3.0 mmol/L. Using this threshold in the ScvO2 ≥ 80 % groups, 28-day mortality was 32.7 %. Conclusions. Lactate has different characteristics and predictive value at different levels of ScvO2. When ScvO2 &lt; 60 % correlation between lactate and ScvO2 is consistent with a degree of oxygen supply limitation. When ScvO2 ≥ 80 % lactate &gt; 3.0 mmol/L is predictive of mortality.

Measurement of mixed venous oxygen saturation (svo2) in high risk cardiac surgery patient

Our study included 112 high risk patients undergoing cardiac surgery in our hospital. Their postoperative hemodynamic parameters were monitored in short intervals using a Swan-Ganz catheter. A ROC curve of SO2 was plotted based on the collected data to evaluate its prognostic performance for patient early postoperative outcome and probability of dying within 30 days after surgery. Results: The best cut-off SO2 value for predicting post-operative complications related to heart failure and the probability of dying within 30 days after surgery in high risk cardiac sugery patients was 55% with a sensitivity of 91.18% and specificity of 31.82%. No death was reported in this study. Conclusions: A SO2value &lt; 55% at the time of admission to ICU indicates poor prognosis for high-risk cardiac surgery patients and more aggressive treatment is required accordingly. This finding is consistent with the results from several studies on patients undergoing surgery for coronary artery disease.

Measurements of venous oxygen saturation in the superior sagittal sinus using conventional 3D multiple gradient-echo MRI: Effects of flow velocity and acceleration.

This work investigates the effects of flow acceleration in the superior sagittal sinus on slice-dependent variations in venous oxygen saturation (SvO2 ) estimations using susceptibility-based MR oximetry. Three-dimensional multiple gradient-echo images, with first-order flow compensation along the anterior-posterior readout direction for the first echo, were acquired twice from 15 healthy volunteers. For all slices, phases within the superior sagittal sinus were fitted using linear regression across four TEs to obtain the Pearson's correlation coefficients (PCCs), the largest of which corresponded to minimum acceleration influence. SvO2 derived from odd echoes on this slice was used to assess interscan difference, and compared with the central 15th slice for slice-dependent difference, both using Bland-Altman analysis. Within-scan interslice SvO2 consistency was examined versus PCC. Multislice-averaged SvO2 values were then computed from slices with PCCs above a certain threshold. Slice-dependent difference in SvO2 varied from -16.2% to 21.5% at two SDs, in agreement with a recent report, and about twice larger than interscan differences for the automatically selected slice (-7.5% to 10.3%) and for the central 15th slice (-8.0% to 8.8%). For slices with PCCs higher than -0.98, interslice SvO2 deviations were all found to be less than 5.0%. Multislice-averaged SvO2 with PCCs higher than -0.98 further reduced interscan difference to -4.7% to 8.2%. Slice-dependent variations in SvO2 may partly be explained by the effects of flow acceleration. Our method may enable conventional 3D multiple gradient echo to be used for SvO2 estimations in the presence of pulsatile flow.

Is jugular bulb oximetry monitoring associated with outcome in out of hospital cardiac arrest patients?

Cerebral protection against secondary hypoxic-ischemic brain injury is a key priority area in post-resuscitation intensive care management in survivors of cardiac arrest. Nevertheless, the current understanding of the incidence, diagnosis and its’ impact on neurological outcome remains undetermined. The aim of this study was to evaluate jugular bulb oximetry as a potential monitoring modality to detect the incidences of desaturation episodes during post-cardiac arrest intensive care management and to evaluate their subsequent impact on neurological outcome. We conducted a prospective, observational study in unconscious adult patients admitted to the intensive care unit who had successful resuscitation following out of hospital cardiac arrest of presumed cardiac causes. All the patients were treated as per European Resuscitation Council 2015 guidelines and they received jugular bulb catheter. Jugular bulb oximetry measurements were performed at six hourly intervals. The neurological outcomes were evaluated on 90th day after the cardiac arrest by cerebral performance categories scale. Forty patients met the eligibility criteria. Measurements of jugular venous oxygen saturation were performed for 438 times. Altogether, we found 2 incidences of jugular bulb oxygen saturation less than 50% (2/438; 0.46%), and 4 incidences when it was less than 55% (4/438; 0.91%). The study detected an association between SjVO2 and CO2 (r = 0.26), each 1 kPa increase in CO2 led to an increase in SjvO2 by 3.4% + / − 0.67 (p < 0.0001). There was no association between SjvO2 and PaO2 or SjvO2 and MAP. We observed a statistically significant higher mean SjvO2 (8.82% + / − 2.05, p < 0.0001) in unfavorable outcome group. The episodes of brain hypoxia detected by jugular bulb oxygen saturation were rare during post-resuscitation intensive care management in out of hospital cardiac arrest patients. Therefore, this modality of monitoring may not yield any additional information towards prevention of secondary hypoxic ischemic brain injury in post cardiac arrest survivors. Other factors contributing towards high jugular venous saturation needs to be considered.

What matters in shock? Flow or pressure?

Shock is a state of ‘acute circulatory failure’, the key feature of which is an inability for tissues and cells to get enough oxygen to meet their needs, ultimately resulting in cell death1. Shock can be classified as hypovolemic, cardiogenic, obstructive or distributive although many patients will have several types of shock simultaneously1. Although it is important to identify and treat the underlying cause of shock (e.g., antibiotics and source removal for septic shock; thrombolysis or embolectomy for massive pulmonary embolism causing obstructive shock1, hemodynamic support must be started immediately in all cases to provide a minimum perfusion pressure and prevent development or worsening of organ dysfunction. In this context, both “flow” and “pressure” are important components. Indeed, the arterial pressure is determined by blood flow and vascular tone, i.e., blood pressure = cardiac output x systemic vascular resistance. The essential aspects of shock resuscitation can be remembered using the simple VIP mnemonic: ventilate (ensure adequate oxygenation), infuse (provide adequate fluid resuscitation), and pump (administer vasoactive agents). Fluid administration should be guided by repeated fluid challenges so that patients receive enough fluid but not too much, as excess fluid can have multiple harmful effects. If hypotension is severe, vasopressors should be started early, at the same time as fluids, to increase systemic vascular resistance and thus arterial pressure. Prolonged periods of hypotension are associated with worse outcomes2. Importantly, although an initial mean arterial pressure (MAP) target of 65 mmHg may be a useful aim, this will not be optimal for all and target values should be adapted according to the individual patient, taking into account various factors including age and history of chronic hypertension. Indeed, if the MAP target is too low, resultant hypoperfusion may lead to cellular death and organ dysfunction, but a target that is too high may be associated with edema and excessive vasoconstriction as a result of higher amounts of fluid and vasoactive agents3, which may also impair organ function. Patients with circulatory shock must therefore be carefully monitored, including regular assessment of cardiac output, and treatment and targets adapted accordingly. Monitoring organ perfusion at the bedside is difficult without specific tools to assess the microcirculation. As such, we must generally rely on three “windows” that can indicate inadequate perfusion, i.e., impaired cutaneous perfusion, impaired renal function, and impaired mental status1. Plasma lactate levels can also be useful, with changes over time providing some indication of adequacy of tissue oxygenation. Although these changes are too slow to help acutely guide therapy, the trend can provide valuable information about patient status over time. If flow remains inadequate and there is no, or only a poor, response to fluids, an inotropic agent may be considered. Dobutamine is the inotrope of choice. In this context, measurement of mixed (SvO2) or central venous (ScvO2) oxygen saturation can help as it provides an indication of the balance between oxygen delivery and consumption, with low values ( < 70%) suggesting that increasing oxygen delivery could be beneficial4.

Serum lactate poorly predicts central venous oxygen saturation in critically ill patients: a retrospective cohort study

BackgroundSerum lactate and central venous oxygen saturation (ScvO2) are commonly used and commonly recommended as markers of tissue oxygenation in shock states. Medical literature has both explicitly stated and implied that the two biomarkers are interchangeable in the management of patients with shock. However, there have been relatively few direct comparisons of these tests in clinical circumstances, and the relationship between them is uncertain. The objective of our study was to evaluate whether simultaneous or near-simultaneous measurements of lactate and ScvO2 reveal a consistent relationship between these two biomarkers.MethodsA retrospective cohort study was conducted in an urban, academic US hospital. All adults in ICUs between March 2007 and March 2017 who had a lactate measurement and ScvO2 or mixed venous oxygen saturation (SvO2) measurement made +/− 1 h from the lactate were included. Linear and non-linear correlations of ScvO2 and lactate were assessed in a variety of shock states.ResultsTwo thousand sixty-two patients were included. Lactate and ScvO2 correlated poorly (r2 = 0.0041, p = 0.0019). This was true for patients with ScvO2 ≤ 65% (r2 = 0.0431, p < 0.001), patients with normal kidney and liver function (r2 = 0.0517, p < 0.001), and septic shock patients (r2 = 0.0037, p = 0.17). For patients with an O2 extraction ratio ≥ 50%, lactate and ScvO2 were strongly correlated (r2 = 0.93, p = 0.0019), but these patients represented only 2.8% of patients in whom the ratio could be calculated.ConclusionsLactate can predict ScvO2 when patients are at or below the critical oxygen delivery threshold, but relatively few shock patients meet this criterion. In the overall population of critically ill patients, serum lactate predicts ScvO2 poorly, even after controlling for factors that may affect lactate production. Lactate and ScvO2 should not be assumed to be interchangeable markers of tissue oxygenation/perfusion.

Calibrated fMRI for dynamic mapping of CMRO2 responses using MR-based measurements of whole-brain venous oxygen saturation

Functional MRI (fMRI) can identify active foci in response to stimuli through BOLD signal fluctuations, which represent a complex interplay between blood flow and cerebral metabolic rate of oxygen (CMRO2) changes. Calibrated fMRI can disentangle the underlying contributions, allowing quantification of the CMRO2 response. Here, whole-brain venous oxygen saturation (Y v ) was computed alongside ASL-measured CBF and BOLD-weighted data to derive the calibration constant, M, using the proposed Y v -based calibration. Data were collected from 10 subjects at 3T with a three-part interleaved sequence comprising background-suppressed 3D-pCASL, 2D BOLD-weighted, and single-slice dual-echo GRE (to measure Y v via susceptometry-based oximetry) acquisitions while subjects breathed normocapnic/normoxic, hyperoxic, and hypercapnic gases, and during a motor task. M was computed via Y v -based calibration from both hypercapnia and hyperoxia stimulus data, and results were compared to conventional hypercapnia or hyperoxia calibration methods. Mean M in gray matter did not significantly differ between calibration methods, ranging from 8.5 ± 2.8% (conventional hyperoxia calibration) to 11.7 ± 4.5% (Yv-based calibration in response to hyperoxia), with hypercapnia-based M values between (p = 0.56). Relative CMRO2 changes from finger tapping were computed from each M map. CMRO2 increased by ∼20% in the motor cortex, and good agreement was observed between the conventional and proposed calibration methods.

Study of Mixed Venous Oxygen Saturation (SVO2) Measurement in High-Risk Cardiac Surgical Patients

Background: Postoperative haemodynamic complications are the leading cause of mortality in heart surgery. Early prediction of postoperative complications based on haemodynamic parameters is invaluable for timely intervention, and can influence the operative outcome. In developed countries, the use of Swan-Ganz catheter to monitor patients’ postoperative haemodynamic variables for predicting short-term risks has become a gold standard. In Vietnam, there are hundreds cases of cardiac surgery each year; however, there has been no report on monitoring patients’ haemodynamic state and its predictive power for short-term operative outcomes. This study reported using mixed venous oxygen saturation (SVO2) as a prognostic marker for short-term outcome in high-risk cardiac surgical patients at hospitals in Vietnam from 2013–2015.

Effects of time delay and body temperature on measurements of central venous oxygen saturation, venous-arterial blood carbon dioxide partial pressures difference, venous-arterial blood carbon dioxide partial pressures difference/arterial-venous oxygen difference ratio and lactate

BackgroundCentral venous oxygen saturation (ScvO2), venous-arterial blood carbon dioxide partial pressures difference (Pv-aCO2), venous-arterial blood carbon dioxide partial pressures difference/arterial-venous oxygen difference ratio (Pv-aCO2/Ca-vO2) and lactate are important parameters employed during shock resuscitation. We designed this study to confirm the effects of time delay and body temperature on measurements of these four parameters.MethodsArterial and central venous blood samples were simultaneously drawn by plastic syringes via indwelling intra-arterial and central venous catheters from critically ill patients. Blood gas analyses were performed on both samples and repeated after 10, 20, 30, 40, 50 and 60 min. Patients were divided into a control group and a high temperature group according to whether the body temperature was greater than 38 °C.ResultsA total of 30 critically ill patients were enrolled. There was a trend of increasing values for ScvO2, Pv-aCO2, Pv-aCO2/Ca-vO2 and lactate over time (P < 0.001). The ScvO2 differences were all lower in high temperature group after 10, 20, 30, 40, 50 and 60 min when compared to the corresponding differences in the control group (P < 0.05). The differences in lactate values were slightly higher in the high temperature group, relative to the control group after 20, 30, 40, 50 and 60 min (P < 0.05).ConclusionsMeasurements of ScvO2, Pv-aCO2, lactate and Pv-aCO2/Ca-vO2 were affected by time delay or body temperature. We recommend that arterial and central venous blood gas samples be analyzed quickly within 10 min, especially for patients with body temperature <38 °C.Trial registrationChiCTR, ChiCTR1800014484. Registered 16 January 2018.

In vivo validation of cerebral near-infrared spectroscopy: a review.

We summarize the available in vivo validation of cerebral near-infrared spectroscopy (NIRS) oximetry to inform future in vivo validation strategies. In particular, to establish a way forward in the assessment of NIRS instrumentation for future randomized trials, a systematic literature search is performed. The records are screened and abstracts are assessed to select studies fulfilling our inclusion criteria. Twenty-two pediatric and 28 adult studies are analyzed after exclusion of three articles in each group. All studies compare regional cerebral tissue oxygenation measured by cerebral NIRS to invasive measurement of central or jugular venous oxygen saturation. In studies without Bland-Altman plots, we extracted data from scatter plots enabling estimation of mean difference (MD), standard deviation (SD), and limits of agreement (LOA). To assess the agreement between (regional cerebral tissue oxygenation) estimated by NIRS and by blood samples, weighted averages of the MDs and SDs from each study are calculated. We found a fair agreement between the overall mean of cerebral tissue oxygenation and the mean of a reference value measured by co-oximetry whatever NIRS instrument or site of blood sampling used. Cerebral oxygenation overestimates the reference at low values, some instruments apparently more than others. Thus, a high degree of scatter and a lack of a good reference method complicate in vivo validation of NIRS. It is difficult to draw any firm conclusions despite the large number of studies, and the result of this review leaves us questioning if more of such validation studies of cerebral NIRS oximetry are really needed. Furthermore, the combination of lack of validation and poor repeatability is an important issue when designing a randomized clinical trial of implementing cerebral NIRS oximetry into clinical care.