Use of central venous oxygen saturation to guide therapy

Oxygenation heterogeneity facilitates spatiotemporal flow pattern visualization inside human blood vessels using photoacoustic computed tomography

Hemodynamics can be explored through various biomedical imaging techniques. However, observing transient spatiotemporal variations in the saturation of oxygen (sO2) within human blood vessels proves challenging with conventional methods. In this study, we employed photoacoustic computed tomography (PACT) to reconstruct the evolving spatiotemporal patterns in a human vein. Through analysis of the multi-wavelength photoacoustic (PA) spectrum, we illustrated the dynamic distribution within blood vessels. Additionally, we computationally rendered the dynamic process of venous blood flowing into the major vein and entering a branching vessel. Notably, we successfully recovered, in real time, the parabolic wavefront profile of laminar flow inside a deep vein in vivo-a first-time achievement. While the study is preliminary, the demonstrated capability of dynamic sO2 imaging holds promise for new applications in biology and medicine.

Continuous positive airway pressure combined with small-tidal-volume ventilation on arterial oxygenation and pulmonary shunt during one-lung ventilation in patients undergoing video-assisted thoracoscopic lobectomy: A randomized, controlled study

BACKGROUND

One-lung ventilation (OLV) is frequently applied during video-assisted thoracoscopic surgery (VATS) airway management to collapse and isolate the nondependent lung (NL). OLV can give rise to hypoxemia as a result of the pulmonary shunting produced. Our study aimed to assess the influence of continuous positive airway pressure (CPAP) combined with small-tidal-volume ventilation on improving arterial oxygenation and decreasing pulmonary shunt rate (QS/QT) without compromising surgical field exposure during OLV.

METHODS

Forty-eight patients undergoing scheduled VATS lobectomy were enrolled in this research and allocated into three groups at random: C group (conventional ventilation, no NL ventilation intervention was performed), LP group (NL was ventilated with lower CPAP [2 cmH2O] and a 40-60 mL tidal volume [TV]), and HP group (NL was ventilated with higher CPAP [5 cmH2O] and a 60-80 mL TV). Record the blood gas analysis data and calculate the QS/QT at the following time: at the beginning of the OLV (T0), 30 min after OLV (T1), and 60 min after OLV (T2). Surgeons blinded to ventilation techniques were invited to evaluate the surgical fields.

RESULTS

The demography data of the three groups were consistent with the surgical data. At T1, PaO2 in the HP group was substantially higher compared to the C group (P < 0.05), while there was no significant difference in the LP group (P > 0.05). At T1-T2, PaCO2 in the LP and HP groups was significantly less than that in the C group (P < 0.05). At T1, the QS/QT values of groups C, LP, and HP were 29.54 ± 6.89%, 22.66 ± 2.08%, and 19.64 ± 5.76%, respectively, and the QS/QT values in the LP and HP groups markedly reduced (P < 0.01). The surgical field's evaluation by the surgeon among the three groups was not notable (P > 0.05).

CONCLUSION

CPAP combined with small-tidal-volume ventilation effectively improved arterial oxygenation and reduced QS/QT and PaCO2 without compromising surgical field exposure during OLV. Among them, 5 cmH2O CPAP + 60-80 ml TV ventilation had a better effect on improving oxygenation.

Intraoperative haemodynamic monitoring and management of adults having non-cardiac surgery: Guidelines of the German Society of Anaesthesiology and Intensive Care Medicine in collaboration with the German Association of the Scientific Medical Societies

Haemodynamic monitoring and management are cornerstones of perioperative care. The goal of haemodynamic management is to maintain organ function by ensuring adequate perfusion pressure, blood flow, and oxygen delivery. We here present guidelines on "Intraoperative haemodynamic monitoring and management of adults having non-cardiac surgery" that were prepared by 18 experts on behalf of the German Society of Anaesthesiology and Intensive Care Medicine (Deutsche Gesellschaft für Anästhesiologie und lntensivmedizin; DGAI).

PERSUADE Survey-PERioperative AnestheSia and Intensive Care Management of Left VentricUlar Assist DevicE Implantation in Europe and the United States

OBJECTIVE

To comprehensively assess relevant institutional variations in anesthesia and intensive care management during left ventricular assist device (LVAD) implantation.

DESIGN

The authors used a prospective data analysis.

SETTING

This was an online survey.

PARTICIPANTS

Participants were from LVAD centers in Europe and the US.

INTERVENTIONS

After investigating initial interest, 91 of 202 European and 93 of 195 US centers received a link to the survey targeting institutional organization and experience, perioperative hemodynamic monitoring, medical management, and postoperative intensive care aspects.

MEASUREMENTS AND MAIN RESULTS

The survey was completed by 73 (36.1%) European and 60 (30.8%) US centers. Although most LVAD implantations were performed in university hospitals (>5 years of experience), significant differences were observed in the composition of the preoperative multidisciplinary team and provision of intraoperative care. No significant differences in monitoring or induction agents were observed. Propofol was used more often for maintenance in Europe (p < 0.001). The choice for inotropes changed significantly from preoperatively (more levosimendan in Europe) to intraoperatively (more use of epinephrine in both Europe and the US). The use of quantitative methods for defining right ventricular (RV) function was reported more often from European centers than from US centers (p < 0.05). Temporary mechanical circulatory support for the treatment of RV failure was more often used in Europe. Nitric oxide appeared to play a major role only intraoperatively. There were no significant differences in early postoperative complications reported from European versus US centers.

CONCLUSIONS

Although the perioperative practice of care for patients undergoing LVAD implantation differs in several aspects between Europe and the US, there were no perceived differences in early postoperative complications.

New Noninvasive Method for the Assessment of Central Venous Oxygen Saturations in Critically Ill Patients

OBJECTIVES

To compare noninvasive external jugular vein oxygen saturations (SjvO2) and central venous oxygen saturation (ScvO2) from a blood sample in patients admitted to the intensive care unit.

DESIGN

A prospective, comparative, monocentric clinical trial design was used.

SETTING

The study was performed in the Department of Anaesthesiology, Pharmacology, Intensive Care and Emergency Medicine, University Hospitals of Geneva (Switzerland).

PARTICIPANTS

A total of 79 patients were enrolled; patients with confirmed COVID-19 infection requiring invasive mechanical ventilation (patients with COVID-19, n = 36) and patients after liver transplantation (posttransplant patients, n = 43).

INTERVENTIONS

Simultaneous measurement of SjvO2 by near-infrared spectroscopy and ScvO2 from central venous blood samples using a blood gas analyzer in stable hemodynamic conditions.

MEASUREMENTS AND MAIN RESULTS

A strong linear correlation was evidenced in both the COVID-19 and posttransplant patient groups between the 2 modalities. The Bland-Altman analysis showed low bias in accordance with low percentage error in both groups (0.57% and 8.09% for patients with COVID-19; 0.00% and 13.72% for posttransplant patients).

CONCLUSIONS

Central venous oxygen saturation can be estimated reasonably by the continuous noninvasive measurement of SjvO2 using near-infrared spectroscopy.

Management of Acutely Decompensated Pulmonary Hypertension

Pulmonary arterial hypertension is a severe life-threatening condition associated with increased pulmonary vascular resistance and resulting right heart dysfunction. Admission to intensive care unit with acutely decompensated right heart failure is a significant negative prognostic event with a high risk of multisystem organ dysfunction and death. Presentations are heterogenous and may combine signs of both diastolic and systolic dysfunction complicating management. Renal dysfunction is often present, but other organ systems can be involved resulting in findings such as acute hepatic dysfunction or bowel wall congestion and ischemia. The goals of therapy are to rapidly reverse ventriculo-arterial decoupling and reduce right ventricular afterload to prevent progression to refractory or irreversible right heart failure. Triggering events must be investigated for and addressed urgently if identified. Volume status management is critical and both noninvasive and invasive testing can aid in prognostication and guide management, including the use of inotropes and vasopressors. In cases of refractory right heart dysfunction, consideration of urgent lung transplantation and mechanical circulatory support is necessary. These patients should be managed at expert centers in an intensive care setting with a multidisciplinary team of practitioners experienced in the management of right heart dysfunction given the high short- and long-term mortality resulting from acute decompensated right heart failure.

Extracorporeal Life Support in Pulmonary Hypertension: Practical Aspects

Extracorporeal life support (ECLS), in particular veno-arterial extracorporeal membrane oxygenation, has emerged as a potentially life-saving treatment modality in patients presenting with pulmonary hypertension and right heart failure refractory to conventional treatment. Used mainly as a bridge to lung transplantation, ECLS is also being used occasionally as a bridge to recovery in patients with treatable causes of right heart failure. This review article describes indications, contraindications, techniques, and outcomes of the use of ECLS in patients with PH, focusing on practical aspects in the management of such patients.

EXPLORING THE ROLE OF CENTRAL VENOUS OXYGEN SATURATION IN THE EVALUATION AND MANAGEMENT OF SEVERE HYPOXEMIA IN MECHANICALLY VENTILATED PATIENTS

ABSTRACT

Background: Although central venous oxygen saturation (ScvO 2 ) has been used as an endpoint for the treatment of circulatory shock, its role in guiding the evaluation and treatment of patients with severe hypoxemia remains to be assessed. The aim of this study was to assess the incidence of low ScvO 2 in a cohort of hypoxemic patients and the association of this finding with differences in clinical management and patient outcomes. Methods: Retrospective review of data from adult intensive care unit patients with hypoxemia who required invasive mechanical ventilation for over 24 h and had at least one ScvO 2 measured within 6 h of a PaO 2 /FiO 2 ratio <200. Results: Of 442 mechanically ventilated patients with severe hypoxemia, 249 (56%) had an ScvO 2 <70%. When compared with patients with ScvO 2 ≥70%, those with low ScvO 2 had worse systemic oxygenation and hemodynamic parameters and were more likely to receive red blood cell transfusions (31.7% vs. 18.1%, P = 0.001), epinephrine (27.3% vs. 16.6%, P = 0.007), and inodilators. Outcomes such as median intensive care unit length of stay (7.5 vs. 8.3 days, P = 0.337) and hospital mortality (39.8% vs. 35.7%, P = 0.389) were not different between groups. When stratified by the central venous-to-arterial CO 2 difference (∆PCO 2 ), patients with a low ScvO 2 and normal ∆PCO 2 had lower median PaO 2 and hemoglobin levels and received more red blood cell transfusions, whereas those with an increased ∆PCO 2 had a lower pulse pressure and cardiac index and were more likely to receive epinephrine and milrinone. Conclusion: Low ScvO 2 is frequently observed in mechanically ventilated patients with severe hypoxemia, and these patients receive different interventions. Clinicians often use therapies targeting systemic oxygen delivery to correct low ScvO 2 . Prospective research is needed to identify patients with severe hypoxemia that might benefit from interventions targeting systemic oxygen delivery.

The ∆Pv-aCO2/∆Ca-vO2 ratio as a predictor of mortality in patients with severe acute respiratory distress syndrome related to COVID-19

OBJECTIVE

To evaluate the central venous-to-arterial carbon dioxide difference combined with arterial-to-venous oxygen content difference (∆Pv-aCO2/∆Ca-vO2 ratio) as a predictor of mortality in patients with COVID-19-related severe acute respiratory distress syndrome (ARDS).

METHODS

Patients admitted to the intensive care unit with severe ARDS secondary to SARS-CoV-2, and invasive mechanical ventilation were included in this single-center and retrospective cohort study performed between April 18, 2020, and January 18, 2022. The tissue perfusion indexes (lactate, central venous oxygen saturation [ScvO2], and venous-to-arterial carbon dioxide pressure difference [∆Pv-aCO2]), anaerobic metabolism index (∆Pv-aCO2/∆Ca-vO2 ratio), and severity index (Simplified Acute Physiology Score II [SAPSII]) were evaluated to determine its association with the mortality through Cox regression analysis, Kaplan-Meier curve and receiver operating characteristic (ROC) curve.

RESULTS

One hundred fifteen patients were included in the study and classified into two groups, the survivor group (n = 54) and the non-survivor group (n = 61). The lactate, ScvO2, ∆Pv-aCO2, and ∆Pv-aCO2/∆Ca-vO2 ratio medians were 1.6 mEq/L, 75%, 5 mmHg, and 1.56 mmHg/mL, respectively. The ∆Pv-aCO2/∆Ca-vO2 ratio (Hazard Ratio (HR) = 1.17, 95% confidence interval (CI) = 1.06-1.29, p = 0.001) was identified as a mortality biomarker for patients with COVID-19-related severe ARDS. The area under the curve for ∆Pv-aCO2/∆Ca-vO2 ratio was 0.691 (95% CI 0.598-0.774, p = 0.0001). The best cut-off point for ∆Pv-aCO2/∆Ca-vO2 ratio was >2.14 mmHg/mL, with a sensitivity of 49.18%, specificity of 85.19%, a positive likelihood of 3.32, and a negative likelihood of 0.6. The Kaplan-Meier curve showed that survival rates were significantly worse in patients with values greater than this cut-off point.

CONCLUSIONS

The ∆Pv-aCO2/∆Ca-vO2 ratio could be used as a predictor of mortality in patients with severe ARDS secondary to SARS-CoV-2.

The effect of inhaled nitric oxide on shunt fraction in mechanically ventilated patients with COVID-19 pneumonia

Background

Studies in patients with severe acute respiratory distress syndrome (ARDS) with refractory hypoxaemia suggest that inhaled nitric oxide (iNO) can be added to ventilatory strategies as a potential bridge to clinical improvement. However, the potential role of iNO as a management strategy in severe COVID-19 pneumonia remains unclear. The authors describe their clinical findings of using iNO for severe COVID-19 pneumonia in 10 patients with refractory hypoxaemia in a tertiary respiratory intensive care unit. The results showed an improvement in shunt fraction, P/F ratio, PaO2 and arterial oxygen saturation but the improvements did not translate into a mortality benefit. This report adds to the current body of literature indicating that the correct indications, timing, dose and duration of iNO therapy and how to harness its pleiotropic effects still remain to be elucidated.

What the study adds

This brief report adds to the body of literature exploring the potential use of inhaled nitric oxide as a management strategy in patients with severe COVID-19 pneumonia with refractory hypoxaemia.

What are the implications of the findings

The findings of the report shows that there is a beneficial role of using inhaled nitric oxide to improve respiratory parameters, but that it does not translate to a mortality benefit. It adds to the investigation of establishing which patients, the duration and at what dose, inhaled nitric oxide should be used to gain maximum benefit for this subgroup of patients.

Predictive value of extubation failure by decrease in central venous oxygen saturation: A systematic review and meta-analysis

Background

The predictive power of extubation failure diagnosed by decrease in central venous oxygen saturation (ΔScvO2) varies by studies. Here we summarized the diagnostic value of extubation failure tested by ΔScvO2.

Methods

A comprehensive online search was performed to select potentially eligible studies that evaluated the predictive power of extubation failure tested by ΔScvO2. A manual search was also performed to identify additional studies. Data were extracted to calculate the pooled sensitivity, specificity, positive likelihood ratio (LR), negative LR, diagnostic odds ratio (DOR), and area under the receiver operating characteristic curve (AUC) to evaluate the predictive power of extubation failure.

Results

Overall, five studies including 353 patients were included in this review, of whom 105 (30%) were extubation failure. The cutoff values of ΔScvO2 varied across studies, ranging from 3.8% to 5.4%. Heterogeneity between studies was assessed with an overall Q = 0.007, I² = 0%, and P = 0.498. The pooled sensitivity and specificity for the overall population were 0.83 (95% CI: 0.74-0.90) and 0.88 (95% CI: 0.83-0.92), respectively. The pooled positive LR and negative LR were 7.2 (95%CI: 4.6-11.2) and 0.19 (95%CI: 0.12-0.31), respectively. The DOR was 38 (95% CI: 17-86). Overall, the pooled AUROC was 0.92 (95% CI: 0.90-0.94).

Conclusions

The ΔScvO2 performed well in predicting extubation failure in adult mechanical ventilation patients. Further studies with a larger data set and well-designed models are required to confirm the diagnostic accuracy and utility of ScvO2 in predicting extubation outcomes in mechanical ventilation patients.

Variation in central venous oxygen saturation to evaluate fluid responsiveness: a systematic review and meta-analysis

BACKGROUND

Since oxygen content and oxygen consumption typically remain unchanged within a short period, variation in central venous oxygen saturation (ΔScvO₂) during fluid challenge can theoretically track the changes in cardiac output (CO). We conducted this meta-analysis to systematically assess the diagnostic performance of ΔScvO₂ during a fluid challenge for fluid responsiveness in mechanically ventilated patients receiving volume expansion.

METHODS

Electronic databases were systematically searched to identify relevant studies published before October 24, 2022. As the cutoff value of ΔScvO₂ was expected to vary across the included studies, we estimated the area under the hierarchical summary receiver operating characteristic curve (AUHSROC) as the primary measure of diagnostic accuracy. The optimal threshold of ΔScvO₂ and the corresponding 95% confidential interval (CI) were also estimated.

RESULTS

This meta-analysis included 5 observational studies comprising 240 participants, of whom 133 (55%) were fluid responders. Overall, the ΔScvO₂ during the fluid challenge exhibited excellent performance for defining fluid responsiveness in mechanically ventilated patients receiving volume expansion, with an AUHSROC of 0.86 (95% CI 0.83-0.89), a pooled sensitivity of 0.78 (95% CI 0.69-0.85), a pooled specificity of 0.84 (95% CI 0.72-0.91), and a pooled diagnostic odds ratio of 17.7 (95% CI 5.9-53.2). The distribution of the cutoff values was nearly conically symmetrical and concentered between 3 and 5%; the mean and median cutoff values were 4% (95% CI 3-5%) and 4% (95% CI not estimable), respectively.

CONCLUSIONS

In mechanically ventilated patients receiving volume expansion, the ΔScvO2 during the fluid challenge is a reliable indicator of fluid responsiveness. Clinical trial registration PROSPERO, https://www.crd.york.ac.uk/prospero/ , registry number: CRD42022370192.

Management of two circulations in a COVID-19 patient with secondary superinfection

Optimal oxygenation in the intensive care unit requires adequate pulmonary gas exchange, oxygen-carrying capacity in the form of hemoglobin, sufficient delivery of oxygenated hemoglobin to the tissue, and an appropriate tissue oxygen demand. In this Case Study in Physiology, we describe a patient with COVID-19 whose pulmonary gas exchange and oxygen delivery were severely compromised by COVID-19 pneumonia requiring extracorporeal membrane oxygenation (ECMO) support. His clinical course was complicated by a secondary superinfection with staphylococcus aureus and sepsis. This case study is provided with two goals in mind (1) We outline how basic physiology was used to address life-threatening consequences of a novel infection-COVID-19. (2) We describe a strategy of whole-body cooling to lower the cardiac output and oxygen consumption, use of the shunt equation to optimize flow to the ECMO circuit, and transfusion to improve oxygen-carrying capacity when ECMO alone failed to provide sufficient oxygenation.

Mixed venous oxygen tension is a crucial prognostic factor in pulmonary hypertension: a retrospective cohort study

BACKGROUND

The prognostic value of mixed venous oxygen tension (PvO2) at pulmonary hypertension diagnosis treated with selective pulmonary vasodilators remains unclear. This study sought to investigate the association of PvO2 with long-term prognosis in pulmonary arterial hypertension (PAH) and medically treated chronic thromboembolic pulmonary hypertension (CTEPH) and to identify the distinct mechanisms influencing tissue hypoxia in patients with CTEPH or PAH.

METHODS

We retrospectively analyzed data from 138 (age: 50.2 ± 16.6 years, 81.9% women) and 268 (age: 57.4 ± 13.1 years, 72.8% women) patients with PAH and CTEPH, respectively, diagnosed at our institution from 1983 to 2018. We analyzed the survival rates of patients with/without tissue hypoxia (PvO2 < 35 mmHg) and identified their prognostic factors based on the pulmonary hypertension risk stratification guidelines.

RESULTS

Survival was significantly poorer in patients with tissue hypoxia than in those without it for PAH (P = 0.001) and CTEPH (P = 0.017) treated with selective pulmonary vasodilators. In patients with PAH, PvO2 more strongly correlated with prognosis than other hemodynamic prognostic factors regardless of selective pulmonary vasodilators usage. PvO2 was the only significant prognostic factor in patients with CTEPH treated with pulmonary hypertension medication. Patients with CTEPH experiencing tissue hypoxia exhibited significantly poorer survival than those in the intervention group (P < 0.001). PvO2 more strongly correlated with the cardiac index (CI) than the alveolar-arterial oxygen gradient (A-aDO2) in PAH; whereas in CTEPH, PvO2 was more strongly correlated with A-aDO2 than with CI.

CONCLUSIONS

PvO2 may represent a crucial prognostic factor for pulmonary hypertension. The prognostic impact of tissue hypoxia affects different aspects of PAH and CTEPH, thereby reflecting their distinct pathogenesis.

Renal Oxygen Saturation as an Early Indicator of Shock in Children

Background

Shock is a life-threatening syndrome in which tissue perfusion and oxygen delivery are inadequate. Near-infrared spectroscopy (NIRS) has been suggested as a noninvasive tool for monitoring and detecting the state of inadequate tissue perfusion. Renal and mesenteric oximetry show decreased cardiac output earlier than systemic or global parameters of tissue oxygenation or cerebral oximetry. However, until now there has been no study on the validity of regional renal oxygen saturation (rRSO₂) by NIRS for diagnosing shock in children.

Purpose

To analyze the validity of rRSO₂ by NIRS to diagnose shock in children.

Patients and Methods

This cross-sectional study was conducted in critically ill children (aged 1 month–18 years) who were admitted to the pediatric intensive care unit (PICU), from September to November 2020, consecutively. Patients were classified into two groups: shock and non-shock. The diagnosis of shock is based on clinical criteria (tachycardia, sign of hypoperfusion and decrease systolic blood pressure <P5 according to age). Measurement of rRSO₂ by NIRS was performed by the doctor in charge when the patient came to PICU. The baseline rRSO₂ value (%) made a receiver operating characteristic (ROC) curve and was used to find the optimal cut-off value and calculated sensitivity and specificity.

Results

We enrolled 20 critically ill patients. The baseline rRSO₂ in the shock (n=10) and non-shock (n=10) groups were, 44.00±4.95 vs 78.70±4.52 (p 0.003). The optimal cutoff value of the baseline rRSO₂ to predict shock is less than 58.5% with area under the curve (AUC) value is 94.4% (95% CI of 84.4–100%), p 0.001, sensitivity 90% and specificity 90% in critically ill children.

Conclusion

The rRSO₂ value by NIRS can differentiate between shock and non-shock in critically ill patients accurately.

A randomised controlled trial on roles of prostaglandin E1 nebulization among patients undergoing one lung ventilation

Background

Prostaglandin E1 (PGE1) has been reported to maintain adequate oxygenation among patients under 60% FiO₂ one-lung ventilation (OLV). This research aimed to explore whether PGE1 is safe in pulmonary shunt and oxygenation under 40% FiO₂ OLV and provide a reference concentration of PGE1.

Methods

Totally 90 esophageal cancer patients treated with thoracotomy were enrolled in this study, randomly divided into three groups (n = 30/group): Group A (60% FiO₂ and 0.1 µg/kg PGE1), Group B (40% FiO₂ and 0.1 µg/kg PGE1), and Group C (40% FiO₂, 0.2 µg/kg PGE1). Primary outcomes were oxygenation and pulmonary shunt during OLV. Secondary outcomes included oxidative stress after OLV.

Results

During OLV, patients in Group C and B had lower levels of PaO₂, SaO₂, SpO₂, MAP, and Qs/Qt than those in Group A (P < 0.05). At T2 (OLV 10 min), patients in Group C and B exhibited a lower level of PaO₂/FiO₂ than those in Group A, without any statistical difference at other time points. The IL-6 levels of patients in different groups were different at T8 (F = 3.431, P = 0.038), with IL-6 in Group C being lower than that in Group B and A. MDA levels among the three groups differed at T5 (F = 4.692, P = 0.012) and T7 (F = 5.906, P = 0.004), with the MDA level of Group C being lower than that of Group B and A at T5, and the MDA level of Group C and B being lower than that of Group A at T7. In terms of TNF-α level, patients in Group C had a lower level than those in Group B and A at T8 (F = 3.598, P = 0.033). Compared with patients who did not use PGE1, patients in Group C had comparable complications and lung infection scores.

Conclusion

The concentration of FiO₂ could be reduced from 60 to 40% to maintain oxygenation. 40% FiO₂ + 0.2 µg/kg PGE1 is recommended as a better combination on account of its effects on the inflammatory factors.

Trial registration: Chictr.org.cn identifier: ChiCTR1800018288, 09/09/2018.

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

INTRODUCTION

Adequate 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 METHODS

We 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).

RESULTS

We 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.

DISCUSSION

NIRS 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.

Performance of a Risk Analytic Tool (Index of Tissue Oxygen Delivery "IDO2") in Pediatric Cardiac Intensive Care Unit of a Developing Country

OBJECTIVE

To determine the performance of a commercially available risk analytic tool (IDO2) to estimate the risk for SVO2 < 40% in patients admitted in cardiac intensive care unit (CICU).

METHODS

Medical and T3 records of all patients (aged 1 day to 12 years, weight >2 kg) who received care in the CICU between October 1st, 2019 and October 1st, 2020, had SvO2 lab(s) drawn during CICU course and whose data was transmitted to T3, were included. The average IDO2 Index was computed in the 30-min period immediately prior to each SvO2 measurement and used as a predictor score for SvO2 < 40%.

RESULTS

A total of 69 CICU admissions from 65 patients, median age 9.3 months (interquartile range 20.8) were identified. Surgical and medical patients were 61 (88%) and 8 (12%) respectively; 4 (5.7%) patients had single ventricle physiology. Tetralogy of Fallot n = 23 (33.3%) and ventricular septal defects 17 (24.6%) were major cardiac diagnosis. Sixty-one (89.9%) of the admissions were successfully discharged from the hospital. Of the 187-total included SvO2 labs, 17 (9%) were <40%. The AUC of estimating SvO2 < 40% IDO2 was 0.87 [confidence interval (CI): 0.79-0.94]. Average IDO2 above 75 had the highest absolute risk (42.11, CI: 20.25-66.50) and highest RR (4.63, CI: 2.31-9.28, p-value < 0.0001) of SvO2 < 40%.

CONCLUSION

IDO2 performed well in estimating low SvO2 (<40%) in pediatric patients presenting to a CICU in a low resource setting. Future work is needed to determine the effect of this risk analytic tool on clinical outcomes in such a setting.

Multitargeted interventions to reduce dialysis-induced systemic stress

Hemodialysis (HD) is a life-sustaining therapy as well as an intermittent and repetitive stress condition for the patient. In ridding the blood of unwanted substances and excess fluid from the blood, the extracorporeal procedure simultaneously induces persistent physiological changes that adversely affect several organs. Dialysis patients experience this systemic stress condition usually thrice weekly and sometimes more frequently depending on the treatment schedule. Dialysis-induced systemic stress results from multifactorial components that include treatment schedule (i.e. modality, treatment time), hemodynamic management (i.e. ultrafiltration, weight loss), intensity of solute fluxes, osmotic and electrolytic shifts and interaction of blood with components of the extracorporeal circuit. Intradialytic morbidity (i.e. hypovolemia, intradialytic hypotension, hypoxia) is the clinical expression of this systemic stress that may act as a disease modifier, resulting in multiorgan injury and long-term morbidity. Thus, while lifesaving, HD exposes the patient to several systemic stressors, both hemodynamic and non-hemodynamic in origin. In addition, a combination of cardiocirculatory stress, greatly conditioned by the switch from hypervolemia to hypovolemia, hypoxemia and electrolyte changes may create pro-arrhythmogenic conditions. Moreover, contact of blood with components of the extracorporeal circuit directly activate circulating cells (i.e. macrophages-monocytes or platelets) and protein systems (i.e. coagulation, complement, contact phase kallikrein-kinin system), leading to induction of pro-inflammatory cytokines and resulting in chronic low-grade inflammation, further contributing to poor outcomes. The multifactorial, repetitive HD-induced stress that globally reduces tissue perfusion and oxygenation could have deleterious long-term consequences on the functionality of vital organs such as heart, brain, liver and kidney. In this article, we summarize the multisystemic pathophysiological consequences of the main circulatory stress factors. Strategies to mitigate their effects to provide more cardioprotective and personalized dialytic therapies are proposed to reduce the systemic burden of HD.

Ultrasound and Other Advanced Hemodynamic Monitoring Techniques in the Intensive Care Unit

The ideal device for hemodynamic monitoring of critically ill patients in the intensive care unit (ICU) or the operating room has not yet been developed. This would need to be affordable, consistent, have a very low margin of error (<30%), be minimally or noninvasive, and allow the clinician to make a reasonable therapeutic decision that consistently led to better outcomes. Such a device does not yet exist. This article will describe the distinct options we, as critical care physicians, currently possess for this Herculean endeavor.

The use of near-infrared spectroscopy for the evaluation of a 4-week rehabilitation program in patients with COPD

BACKGROUND

Near-infrared spectroscopy (NIRS) technology can evaluate muscle metabolism and oxygenation. NIRS-based oximeters can measure skeletal muscle oxygen delivery and utilization during static and dynamic work non-invasively. Our goal was to assess the value and usability of NIRS technology in chronic obstructive pulmonary disease (COPD) rehabilitation program.

METHODS

Forty patients with COPD participated in a 4-week inpatient rehabilitation program that included breathing exercises and personalized cycle/treadmill training adjusted to the functional capacity, physical activity and comorbidities of the patients. A NIRS muscle oxygen monitor was used to measure tissue oxygenation and hemoglobin levels. Total hemoglobin index, average muscle oxygenation, minimal and maximal muscle oxygenation were recorded before and after the rehabilitation program.

RESULTS

Rehabilitation resulted improvement in 6 min walking distance (6MWD:335.3 ± 110. vs. 398.3 ± 126.2 m; P < 0.01), maximal inspiratory pressure (MIP: 57.7 ± 22.7 vs. 63.6 ± 18.0 cmH2O; P < 0.01), chest wall expansion (CWE: 2.84 ± 1.26 vs, 4.00 ± 1.76 cm; P < 0.01), breath hold time (BHT: 25.8 ± 10.6 vs. 29.2 ± 11.6 s; P < 0.01) and grip strength (GS: 24.9 ± 11.9 vs. 27.0 ± 11.4 kg; P < 0.01). Quality of life improvement was monitored by COPD Assessment Test (CAT: 17.00 ± 8.49 vs. 11.89 ± 7.3, P < 0.05). Total hemoglobin index (tHb: 12.8 ± 1.3% vs. 12.8 ± 1.4), average muscle oxygenation (SmO2: 67.5 ± 14.4% vs. 65.2 ± 20.4%) showed a tendency for improvement. Maximal muscle oxygenation decreased (SmO2 max: 98.0 ± 20.5% vs. 90.1 ± 14.3%; P < 0.01). Minimal muscle oxygenation increased (SmO2 min: 42.6 ± 12.6% vs. 54.8 ± 14.3%; P < 0.01).

CONCLUSIONS

NIRS results showed that muscle oxygenation and microcirculation can be described as a high-risk factor in COPD patients. The 4-week rehabilitation improves functional parameters, quality of life and tissue oxygenation levels in COPD patients.

The Value of Combining Carbon Dioxide Gap and Oxygen-Derived Variables with Lactate Clearance in Predicting Mortality after Resuscitation of Septic Shock Patients

Background

Achieving hemodynamic stabilization does not prevent progressive tissue hypoperfusion and organ dysfunction during resuscitation of septic shock patients. Many indicators have been proposed to judge the optimization of oxygen delivery to meet tissue oxygen consumption.

Methods

A prospective observational study was conducted to evaluate and validate combining CO₂ gap and oxygen-derived variables with lactate clearance during early hours of resuscitation of adults presenting with septic shock.

Results

Our study included 456 adults with a mean age of 63.2 ± 6.9 years, with 71.9% being males. Respiratory and urinary infections were the origin of about 75% of sepsis. Mortality occurred in 164 (35.9%) patients. The APACHE II score was 18.2 ± 3.7 versus 34.3 ± 6.8 (p < 0.001), the initial SOFA score was 5.8 ± 3.1 versus 7.3 ± 1.4 (p=0.001), while the SOFA score after 48 hours was 4.2 ± 1.8 versus 9.4 ± 3.1 (p < 0.001) in the survivors and nonsurvivors, respectively. Hospital mortality was independently predicted by hyperlactatemia (OR: 2.47; 95% CI: 1.63-6.82, p=0.004), PvaCO₂ gap (OR: 2.62; 95% CI: 1.28-6.74, p=0.026), PvaCO₂/CavO₂ ratio (OR: 2.16; 95% CI: 1.49-5.74, p=0.006), and increased SOFA score after 48 hours of admission (OR: 1.86; 95% CI: 1.36-8.13, p=0.02). A blood lactate cutoff of 40 mg/dl at the 6th hour of resuscitation (T6) had a 92.7% sensitivity and 75.3% specificity for predicting hospital mortality (AUROC = 0.902) with 81.6% accuracy. Combining the lactate cutoff of 40 mg/dl and PvaCO₂/CavO₂ ratio cutoff of 1.4 increased the specificity to 93.2% with a sensitivity of 75.6% in predicting mortality and with 86.8% accuracy. Combining the lactate cutoff of 40 mg/dl and PvaCO₂ gap of 6 mmHg increased the sensitivity to 93% and increased the specificity to 98% in predicting mortality with 91% accuracy.

Conclusion

Combining the carbon dioxide gap and arteriovenous oxygen difference with lactate clearance during early hours of resuscitation of septic shock patients helps to predict hospital mortality more accurately.

Investigating spectroscopic measurement of sublingual veins and tissue to estimate central venous oxygen saturation

BACKGROUND

Venous oxygen saturation reflects venous oxygenation status and can be used to assess treatment and prognosis in critically ill patients. A novel method that can measure central venous oxygen saturation (ScvO2) non-invasively may be beneficial and has the potential to change the management routine of critically ill patients.

OBJECTIVE

The study aims to evaluate the potential of sublingual venous oxygen saturation (SsvO2) to be used in the estimation of ScvO2.

METHODS

We have developed two different approaches to calculate SsvO2. In the first one, near-infrared spectroscopy (NIRS) measurements were performed directly on the sublingual veins. In the second approach, NIRS spectra were acquired from the sublingual tissue apart from the sublingual veins, and arterial oxygen saturation was measured using a pulse oximeter on the fingertip.

RESULTS

Twenty-six healthy subjects were included in the study. In the first and second approaches, average SsvO2 values were 75.0% ± 1.8 and 75.8% ± 2.1, respectively. The results of the two different approaches were close to each other and similar to ScvO2 of healthy persons (> 70%).

CONCLUSION

Oxygen saturation of sublingual veins has the potential to be used in intensive care units, non-invasively and in real-time, to estimate ScvO2.

Pulmonary Vascular Resistance Measurement Remains Keystone in Congenital Heart Disease Management

Pulmonary vascular resistance (PVR) plays a major role in congenital heart management and critical decision. The impact of pulmonary vascular disease in the early and late morbidity and mortality after cardiac surgery and interventional catheterization in congenital heart defect (CHD) highlights the importance of critical evaluation for PVR. Currently, PVR is evaluated with invasive cardiac catheterization for hemodynamic data collection, processing, and analysis. Despite the limitation of hemodynamic evaluation in the setting of CHD, accurate data analysis, and interpretation have significant impact on clinical outcome and procedure success. This article reviews the basic calculation of PVR in the setting of congenital heart disease with diagrammatic illustration for easy understanding of the hemodynamic.

Updates in Hemodynamic Monitoring: A Review for Pharmacists

Vital signs are regularly monitored in hospitalized patients. In the intensive care unit (ICU), traditional non-invasive blood pressure monitoring and telemetry may not provide enough information to determine the etiology of hemodynamic instability or guide intervention. Arterial catheters remain the gold-standard for continuous blood pressure monitoring and are commonly used in ICU patients. Pulmonary artery catheters and central venous catheters are beneficial in select patient populations and provide more advanced and specific information about a patient's hemodynamics. However, neither are benign and can increase risk of complications such as infection, arrhythmias, pneumothorax and vascular or valvular damage. In the past 10 years, the development of reliable non-invasive (NICOM), or minimally-invasive (MICOM), cardiac output monitoring devices has accelerated. The MICOM devices require an arterial catheter to obtain hemodynamic values, whereas NICOM devices do not require any arterial or venous access. These devices have emerged to be particularly useful in evaluating and managing patients with suspected mixed shock. As these devices become more prevalent, it is imperative that clinical pharmacists become familiar with interpreting this data as it may have a substantial impact on medication selection and optimization. This review will discuss the basics of NICOM and MICOM devices, limitations with these methods of monitoring, and clinical application for pharmacists.

Simple equations to predict the effects of veno-venous ECMO in decompensated Eisenmenger syndrome

Adult patients with uncorrected congenital heart diseases and chronic intracardiac shunt may develop Eisenmenger syndrome (ES) due to progressive increase of pulmonary vascular resistance, with significant morbidity and mortality. Acute decompensation of ES in conditions promoting a further increase of pulmonary vascular resistance, such as pulmonary embolism or pneumonia, can precipitate major arterial hypoxia and death. In such conditions, increasing systemic oxygenation with veno‐venous extracorporeal membrane oxygenation (VV‐ECMO) could be life‐saving, serving as a bridge to treat a potential reversible cause for the decompensation, or to urgent lung transplantation. Anticipating the effects of VV‐ECMO in this setting could ease the clinical decision to initiate such therapeutic strategy. Here, we present a series of equations to accurately predict the effects of VV‐ECMO on arterial oxygenation in ES and illustrate this point by a case of ES decompensation with refractory hypoxaemia consecutive to an acute respiratory failure due to viral pneumonia.

Systemic Oxygen Utilization in Severe COVID-19 Respiratory Failure: A Case Series

Background

Management of hypoxemia in patients with severe COVID-19 respiratory failure is based on the guideline recommendations for specific SpO₂ targets. However, limited data exist on systemic O₂ utilization. The objective of this study was to examine systemic O₂ utilization in a case series of patients with this disease.

Patients and methods

Between March 24, and April 9, 2020, 8 patients intubated for severe COVID-19 respiratory failure had near-simultaneous drawing of arterial blood gas (ABG), central venous blood gas (cVBG), and central venous oxygen saturation (ScvO₂) at a mean of 6.1 days into hospitalization. Three patients were managed with indirect cardiac output (CO) monitoring by FloTrac sensor and Vigileo monitor (Edwards Lifesciences, Irvine, CA). The oxygen extraction index (OEI; SaO₂-ScvO₂/SaO₂) and oxygen extraction fraction (OEF; CaO₂-CvO₂/CaO₂ ≥ 100) were calculated. Values for hyperoxia (ScvO₂ ≥ 90%), normoxia (ScvO₂ 71-89%), and hypoxia (ScvO₂ ≤ 70%) were based on the literature. Mean values were calculated.

Results

The mean partial pressure of oxygen (PaO₂) was 102 with a mean fraction of inspired O₂ (FiO₂) of 44%. One patient was hyperoxic with a reduced OEI (17%). Five patients were normoxic, but 2 had a reduced OEF (mean 15.9%). Two patients were hypoxic but had increased systemic O₂ utilization based on OEF or OEI.

Conclusion

In select patients with severe COVID-19 respiratory failure, O₂ delivery (DO₂) was found to exceed O₂ utilization. SpO₂ targets based on systemic O₂ utilization may help in reducing oxygen toxicity, especially in the absence of anaerobic metabolism. Further data are needed on the prevalence of systemic O₂ utilization in COVID-19.

How to cite this article

Garg RK, Kimbrough T, Lodhi W, DaSilva I. Systemic Oxygen Utilization in Severe COVID-19 Respiratory Failure: A Case Series. Indian J Crit Care Med 2021;25(2):215-218.

Effects of impaired microvascular flow regulation on metabolism-perfusion matching and organ function

Impaired tissue oxygen delivery is a major cause of organ damage and failure in critically ill patients, which can occur even when systemic parameters, including cardiac output and arterial hemoglobin saturation, are close to normal. This review addresses oxygen transport mechanisms at the microcirculatory scale, and how hypoxia may occur in spite of adequate convective oxygen supply. The structure of the microcirculation is intrinsically heterogeneous, with wide variations in vessel diameters and flow pathway lengths, and consequently also in blood flow rates and oxygen levels. The dynamic processes of structural adaptation and flow regulation continually adjust microvessel diameters to compensate for heterogeneity, redistributing flow according to metabolic needs to ensure adequate tissue oxygenation. A key role in flow regulation is played by conducted responses, which are generated and propagated by endothelial cells and signal upstream arterioles to dilate in response to local hypoxia. Several pathophysiological conditions can impair local flow regulation, causing hypoxia and tissue damage leading to organ failure. Therapeutic measures targeted to systemic parameters may not address or may even worsen tissue oxygenation at the microvascular level. Restoration of tissue oxygenation in critically ill patients may depend on restoration of endothelial cell function, including conducted responses.

Oxygen metabolism markers as predictors of mortality in severe COVID-19

Objective

To investigate the use of oxygen metabolism markers as predictors of mortality in patients with severe coronavirus disease 2019 (COVID-19).

Methods

A retrospective analysis was undertaken to compare the medical records of patients with severe COVID-19 (53 deceased patients and 50 survivors). The survivors were selected from 222 records using a random number generator. In addition, 28 individuals who considered themselves to be healthy and who had no history of serious illness were included in the study for comparison. Oxygen saturation in arterial blood, oxygen saturation in central venous blood (ScvO₂), arterial partial pressure of oxygen (PaO₂), respiratory index (PaO₂/fraction of inspired oxygen), oxygen delivery, oxygen consumption (VO₂) and oxygen extraction (O₂ER) were compared in all participants. The optimal cut-off point for each oxygen metabolism marker in the prediction of mortality was determined based on the maximum value of the Youden Index in receiver operating characteristic curve analysis.

Results

Significant differences in all studied oxygen metabolism markers were found between survivors compared with deceased patients (p < 0.001). ScvO₂, VO₂ and O₂ER [area under curve (AUC) 1.0] were the strongest predictors of mortality, and PaO₂ was the weakest predictor of mortality (AUC 0.81). ScvO₂ <29%, VO₂ >124.6 ml/min and O₂ER >30.2% were identified as predictors of mortality in patients with COVID-19.

Conclusion

ScvO₂, VO2 and O₂ER are good predictors of mortality in critically ill patients with COVID-19.

Association of Preoperative Mixed Venous Oxygen Saturation with Postoperative Segmental Pulmonary Hypertension in Pulmonary Atresia with Ventricular Septal Defect and Major Aortopulmonary Collaterals

In patients with pulmonary atresia with ventricular septal defect and major aortopulmonary collateral arteries (PA/VSD/MAPCAs), segmental pulmonary hypertension is common; however, its pathophysiology remains to be elucidated. This study aimed to identify preoperative hemodynamic factors associated with segmental pulmonary hypertension after intracardiac repair in patients with PA/VSD/MAPCAs. This study included 12 patients with PA/VSD/MAPCAs who underwent unifocalization and intracardiac repair from 2009 at our institution. Hemodynamic measurements of preoperative and postoperative cardiac catheterization were collected. Patients were considered to have pulmonary hypertension if the mean pulmonary pressure measured postoperatively at any peripheral pulmonary artery was ≥ 20 mmHg. The data were compared between patients with and without postoperative segmental pulmonary hypertension; p value < 0.05 was considered statistically significant. Intracardiac repair was performed at the age of 2.1 years (range 0.5-28.2 years). Unifocalization was performed separately prior to intracardiac repair in two patients and concomitantly in 10 patients. Postoperative cardiac catheterization, performed 1.2 years (range 0.2-8.7 years) after intracardiac repair, revealed that five patients had segmental pulmonary hypertension. Patients with postoperative pulmonary hypertension had significantly lower preoperative mixed venous oxygen saturation than those without pulmonary hypertension (57% [55-63%] vs. 65% [53-75%], p < 0.05). No significant differences were found between the groups in terms of age at intracardiac repair, preoperative arterial oxygen saturation, and preoperative peripheral pulmonary arterial mean pressure. Lower preoperative mixed venous oxygen saturation was associated with segmental pulmonary hypertension after intracardiac repair in patients with PA/VSD/MAPCAs.

Excess cerebral oxygen delivery follows return of spontaneous circulation in near-term asphyxiated lambs

Hypoxic-ischaemia renders the neonatal brain susceptible to early secondary injury from oxidative stress and impaired autoregulation. We aimed to describe cerebral oxygen kinetics and haemodynamics immediately following return of spontaneous circulation (ROSC) and evaluate non-invasive parameters to facilitate bedside monitoring. Near-term sheep fetuses [139 ± 2 (SD) days gestation, n = 16] were instrumented to measure carotid artery (CA) flow, pressure, right brachial arterial and jugular venous saturation (SaO2 and SvO2, respectively). Cerebral oxygenation (crSO2) was measured using near-infrared spectroscopy (NIRS). Following induction of severe asphyxia, lambs received cardiopulmonary resuscitation using 100% oxygen until ROSC, with oxygen subsequently weaned according to saturation nomograms as per current guidelines. We found that oxygen consumption did not rise following ROSC, but oxygen delivery was markedly elevated until 15 min after ROSC. CrSO2 and heart rate each correlated with oxygen delivery. SaO2 remained > 90% and was less useful for identifying trends in oxygen delivery. CrSO2 correlated inversely with cerebral fractional oxygen extraction. In conclusion, ROSC from perinatal asphyxia is characterised by excess oxygen delivery that is driven by rapid increases in cerebrovascular pressure, flow, and oxygen saturation, and may be monitored non-invasively. Further work to describe and limit injury mediated by oxygen toxicity following ROSC is warranted.

Haemodynamic monitoring and management in COVID-19 intensive care patients: an International survey

PURPOSE

To survey haemodynamic monitoring and management practices in intensive care patients with the coronavirus disease 2019 (COVID-19).

METHODS

A questionnaire was shared on social networks or via email by the authors and by Anaesthesia and/or Critical Care societies from France, Switzerland, Belgium, Brazil, and Portugal. Intensivists and anaesthetists involved in COVID-19 ICU care were invited to answer 14 questions about haemodynamic monitoring and management.

RESULTS

Globally, 1000 questionnaires were available for analysis. Responses came mainly from Europe (n = 460) and America (n = 434). According to a majority of respondents, COVID-19 ICU patients frequently or very frequently received continuous vasopressor support (56%) and had an echocardiography performed (54%). Echocardiography revealed a normal cardiac function, a hyperdynamic state (43%), hypovolaemia (22%), a left ventricular dysfunction (21%) and a right ventricular dilation (20%). Fluid responsiveness was frequently assessed (84%), mainly using echo (62%), and cardiac output was measured in 69%, mostly with echo as well (53%). Venous oxygen saturation was frequently measured (79%), mostly from a CVC blood sample (94%). Tissue perfusion was assessed biologically (93%) and clinically (63%). Pulmonary oedema was detected and quantified mainly using echo (67%) and chest X-ray (61%).

CONCLUSION

Our survey confirms that vasopressor support is not uncommon in COVID-19 ICU patients and suggests that different haemodynamic phenotypes may be observed. Ultrasounds were used by many respondents, to assess cardiac function but also to predict fluid responsiveness and quantify pulmonary oedema. Although we observed regional differences, current international guidelines were followed by most respondents.

Novel noninvasive estimation of mixed venous oxygen saturation by echocardiography and expired gas analysis

Mixed venous oxygen (O₂) saturation ([Formula: see text]) is an important measure for evaluating the sufficiency of cardiac output (CO) relative to whole body O₂ consumption (V̇o₂), while clinical use is limited to the required invasive catheterization. According to Fick's equation, V̇o₂ (mL/min) = CO (L/min) × Hb (g/dL) × 1.36 (mL/g) × ([Formula: see text] - [Formula: see text])/10 (Hb = hemoglobin concentration, [Formula: see text] = arterial blood O₂ saturation). Because V̇o₂, CO, Hb, and [Formula: see text] can be measured noninvasively with expired gas analysis, echocardiography, a simple blood test, and percutaneous O₂ saturation, respectively, [Formula: see text] can be calculated noninvasively. We hypothesized that noninvasively calculated [Formula: see text] shows a significant correlation and agrees well with invasively measured [Formula: see text]. In 47 patients (29 men; mean age, 70 ± 12 yr) who underwent right heart catheterization, [Formula: see text] was directly measured by sampling pulmonary artery blood. Noninvasively calculated [Formula: see text] was also obtained by the method described above. The calculated [Formula: see text] was significantly correlated with the measured [Formula: see text] (r = 0.79, P < 0.001) and was significantly smaller than the measured [Formula: see text] (70 ± 5.1 vs. 72.1 ± 4.9%, P < 0.001). Bias at [Formula: see text] was -2.2% (95% confidence interval, -3.2 to -1.1%) with limits of agreement from -9.5 to 5.2%, demonstrating acceptable agreement. The optimal cutoff value of calculated [Formula: see text] was 69% for reduced measured [Formula: see text] < 70% with an area under the curve of 0.94. Reduced calculated [Formula: see text] < 69% indicated a sensitivity of 92.9% and a specificity of 90.9% for reduced measured [Formula: see text] < 70%. Noninvasive [Formula: see text] calculated from echocardiography, expired gas analysis, percutaneous arterial blood O₂ saturation, and hemoglobin level significantly correlated and agreed well with direct [Formula: see text] measured by catheterization. This novel method allows for practical evaluation of [Formula: see text] to assess the sufficiency of CO according to whole body metabolism.NEW & NOTEWORTHY Clinical use of mixed venous oxygen saturation ([Formula: see text]) is limited to the required invasive procedure. With Fick's equation, expired gas analysis, echocardiography, simple blood tests, and percutaneous oxygen saturation, [Formula: see text] can be calculated noninvasively. We hypothesized that noninvasively calculated [Formula: see text] shows a significant correlation and agrees well with invasively measured [Formula: see text]. The present study examined the relationship between measured [Formula: see text] and calculated [Formula: see text] in patients who underwent right heart catheterization and demonstrated acceptable agreement. This novel method can expand the indication of evaluating [Formula: see text].

Hemodynamic monitoring with two blood gases: “a tool that does not go out of style”

Introduction. Hemodynamic monitoring of a critically ill patient is an indispensable tool both inside and outside intensive care; we currently have invasive, minimally invasive and non-invasive devices; however, no device has been shown to have a positive impact on the patient's evolution; arterial and venous blood gases provide information on the patient's actual microcirculatory and metabolic status and may be a hemodynamic monitoring tool. Objective. To carry out a non-systematic review of the literature of hemodynamic monitoring carried out through the variables obtained in arterial and venous blood gases. Material and methods. A non-systematic review of the literature was performed in the PubMed, OvidSP and ScienceDirect databases with selection of articles from 2000 to 2019. Results. It was found that there are variables obtained in arterial and venous blood gases such as central venous oxygen saturation (SvcO2), venous-to-arterial carbon dioxide pressure (∆pv-aCO2), venous-to-arterial carbon dioxide pressure/arteriovenous oxygen content difference (∆pv-aCO2/∆Ca-vO2) that are related to cellular oxygenation, cardiac output (CO), microcirculatory veno-arterial flow and anaerobic metabolism and allow to assess tissue perfusion status. Conclusion. The variables obtained by arterial and venous blood gases allow for non-invasive, accessible and affordable hemodynamic monitoring that can guide medical decision-making in critically ill patients.

Correlation of Venous Oxygen Saturations from Noninvasive Hematocrit Monitoring Using Blood Gas Measured Oximetry in Chronic Pediatric Hemodialysis Patients

INTRODUCTION

Noninvasive hematocrit monitoring (NIVHM) during pediatric hemodialysis (pedHD) provides data in real time regarding changes in hematocrit and blood volume and also provides venous oxygen saturations. The latter has been proposed to indicate changes in tissue oxygen consumption. It is not known how well NIVHM oxygen saturations (O2sat) approximate blood gas measured oximetry saturation (mO2sat) in the course of pedHD. We aimed to assess the validity and reliability of NIVHM O2sat compared to mO2sat.

METHODS

This is a prospective study in 15 patients <21 years old with >90 days on hemodialysis (HD) without congenital heart disease. HD access was fistula (AVF) in 4 patients and tunneled catheters in the remainder. Pulse oximetry (spO2) was continuously monitored; mO2sat was measured via oximetry in a blood gas analyzer and NIVHM O2sat values collected at the start, middle, and end of HD treatment.

RESULTS

A total of 45 dyad measurements were obtained. NIVHM O2sat correlated well with mO2sat (R = 0.89, p < 0.0001); the same was seen at pre, mid, and post HD time points (R = 0.86-0.95, p < 0.001). NIVHM O2sat was lower than mO2sat; with catheter as access, the difference was 9.3 ± 8.6 (CI: 12.3-6.22, p < 0.0001) and with AVF was 2.1 ± 0.78 (CI: 2.6-1.7, p < 0.0001). Bland-Altman analysis demonstrated the difference but did not show any systematic bias. Continuous monitor of spO2 showed no hypoxia.

DISCUSSION/CONCLUSION

Intradialytic NIVHM O2sat correlates well with mO2sat but yield lower values. Future studies can include NIVHM O2sat changes as a surrogate for central venous O2 saturation changes and potentially yield useful information regarding tissue oxygen consumption in pedHD patients.

Mixed Venous Oxygen Saturation Is a Better Prognosticator Than Cardiac Index in Pulmonary Arterial Hypertension

BACKGROUND

European Society of Cardiology (ESC) and European Respiratory Society (ERS) guidelines include thermodilution cardiac index (TDCI) and mixed venous oxygen saturation (SvO₂) as two of the three hemodynamic determinations used in risk assessment of patients with pulmonary arterial hypertension (PAH). SvO₂ may be a better measurement than TDCI to assess prognosis in patients with either idiopathic or heritable PAH.

RESEARCH QUESTION

What is the concordance between TDCI and SvO₂ ESC/ERS risk group allocation and their prognostic value in patients with PAH?

STUDY DESIGN AND METHODS

In this retrospective study, we assessed the correlation between SvO₂ and TDCI in patients with idiopathic and heritable PAH. We determined concordance in the ESC/ERS risk group allocation and association with survival, both at baseline and follow-up.

RESULTS

A total of 158 patients (mean age, 58 ± 17 years; 72% women) with idiopathic (91%) and heritable (9%) PAH were included. There was moderate association between TDCI and SvO₂ (r = 0.50; 95% CI, 0.37-0.62). Weighted kappa revealed a fair agreement between TDCI and SvO₂ (κ = 0.30; 95% CI, 0.18-0.42), with concordance in risk group allocation in 49% of patients. During a median follow-up of 45 months (interquartile range, 23-105), 62 patients (39%) died. Using Kaplan-Meier analysis, survival was impacted by the SvO₂ (log rank = 0.002) but not by the TDCI risk group allocation (log-rank = 0.51). Using the Cox proportional hazard model, adjusted for age and sex, SvO₂ (but not TDCI) was associated with mortality (hazard ratio per 1% change, 0.94; 95% CI, 0.91-0.97; P < .001).

INTERPRETATION

When using the cutoffs proposed by the ESC/ERS guidelines, we noted poor concordance in risk score allocation between TDCI and SvO₂. In patients with idiopathic or heritable PAH, SvO₂ measurements are superior to TDCI in predicting long-term mortality.

Effects of prostaglandin E1 nebulization of ventilated lung under 60%O2 one lung ventilation on patients' oxygenation and oxidative stress: a randomised controlled trial

Background

High FiO₂ during one-lung ventilation (OLV) can improve oxygenation, but increase the risk of atelectasis and oxidative stress. The aim of this study was to analyze whether Prostaglandin E₁ (PGE₁) can improve oxygenation and attenuate oxidative stress during OLV under a lower FiO₂.

Method

Ninety patients selectively undergoing thoracotomy for esophageal cancer were randomly divided into three groups (n = 30/group): Group P (FiO₂ = 0.6, inhaling PGE₁ 0.1 μg/kg), Group L (FiO₂ = 0.6) and Group C (FiO₂ = 1.0). The primary outcomes were oxygenation and pulmonary shunt during OLV. Secondary outcomes included haemodynamics, respiratory mechanics and oxidative stress in serum.

Results

Patients in Group P had significantly higher PaO₂ and lower shunt fraction in 30 min of OLV compared with Group L. Compared with Group C, patients in Group P had similar levels of PaO₂/FiO₂ in 60 min and higher levels of PaO₂/FiO₂ at 2 h during OLV. The levels of PvO₂ and SvO₂ in Group P and Group L were significantly lower than Group C. Patients in Group P and Group L had significantly higher levels of superoxide dismutase and lower levels of malondialdehyde than Group C. No significant differences were found in SPO₂, ETCO₂, PaCO₂, Paw, HR and MAP among the three groups. The complications in Group C were significantly higher than another two groups.

Conclusion

PGE₁ can maintain adequate oxygenation in patients with low FiO₂ (0.6) during OLV. Reducing FiO₂ to 0.6 during OLV can decrease the levels of oxidative stress and complications after OLV.

Trial registration

chictr.org.cn identifier: ChiCTR1800017100.

Respiratory Physiology for the Anesthesiologist

Respiratory function is fundamental in the practice of anesthesia. Knowledge of basic physiologic principles of respiration assists in the proper implementation of daily actions of induction and maintenance of general anesthesia, delivery of mechanical ventilation, discontinuation of mechanical and pharmacologic support, and return to the preoperative state. The current work provides a review of classic physiology and emphasizes features important to the anesthesiologist. The material is divided in two main sections, gas exchange and respiratory mechanics; each section presents the physiology as the basis of abnormal states. We review the path of oxygen from air to the artery and of carbon dioxide the opposite way, and we have the causes of hypoxemia and of hypercarbia based on these very footpaths. We present the actions of pressure, flow, and volume as the normal determinants of ventilation, and we review the resulting abnormalities in terms of changes of resistance and compliance.

Physiology education for intensive care medicine residents: A 15-minute interactive peer-led flipped classroom session

Introduction

In acute care medicine, knowledge of the underlying (patho)-physiology is of paramount importance. This may be especially relevant in intensive care medicine, where individual competence and proficiency greatly depend on knowledge and understanding of critical care physiology. In settings with time constraints such as intensive care units (ICUs), time allotted to education is often limited. We evaluated whether introduction of a short, interactive, peer-led flipped classroom session is feasible and can provide ICU residents with a better understanding of critical care physiology.

Materials and methods

Using the flipped classroom concept, we developed a 15-minute peer-led interactive “physiology education” session to introduce a total of 44 residents to critical care physiology. Using a nine-item electronic survey with open questions and a five-point Likert scale, we analysed the overall concept with regard to feasibility, motivation, and subjective learning of critical care physiology.

Results

The overall rate of response to the survey was 70.5% (31/44). The residents reported that these sessions sparked their interest (p = 0.005, Chi square 10.52), and that discussion and interaction during these sessions had promoted their knowledge and understanding. Both novice and experienced residents reported that new knowledge was imparted (both p<0.0001, Chi-square 32.97 and 25.04, respectively).

Conclusions

In an environment with time constraints such as the ICU, a 15-minute, interactive, peer-led flipped classroom teaching session was considered feasible and generally appeared useful for teaching critical care physiology to ICU residents. Responses to questions on questionnaires indicated that teaching sessions sparked interest and increased motivation. This approach may theoretically induce a modification in professional behaviour and promote self-directed learning. We therefore support the use of peer-led flipped classroom training sessions in the ICU. Whether these sessions result in improved ICU care should be addressed in subsequent studies.

Central and Mixed Venous O2 Saturation

Mixed and central venous oxygen saturations are commonly used to ascertain the degree of systemic oxygenation in critically ill patients. This review examines the physiological basis for the use of these variables to determine systemic extraction ration, oxygen consumption and tissue oxygenation, and also understand the role they may play in the early treatment of septic individuals.

Differences Between Central Venous and Cerebral Tissue Oxygen Saturation in Anaesthetised Patients With Diabetes Mellitus

The brain has high oxygen extraction, thus the regional cerebral tissue oxygen saturation (rSO₂) is lower than the central venous oxygen saturation (ScvO₂). We hypothesised that diabetes widens the physiological saturation gap between ScvO₂ and rSO₂ (gSO₂), and the width of this gap may vary during various phases of cardiac surgery. Cardiac surgery patients with (n = 48) and without (n = 91) type 2 diabetes mellitus (T2DM) underwent either off-pump coronary artery bypass (OPCAB) or other cardiac surgery necessitating cardiopulmonary bypass (CPB) were enrolled. rSO₂ was measured by near-infrared spectroscopy (NIRS) and ScvO₂ was determined simultaneously from central venous blood. rSO₂ was registered before and after anaesthesia induction and at different stages of the surgery. ScvO₂ did not differ between the T2DM and control patients at any stage of surgery, whereas rSO₂ was lower in T2DM patients, compared to the control group before anaesthesia induction (60.4 ± 8.1%[SD] vs. 67.2 ± 7.9%, p<0.05), and this difference was maintained throughout the surgery. After anaesthesia induction, the gSO₂ was higher in diabetic patients undergoing CPB (20.2 ± 10.4% vs. 12.4 ± 8.6%, p < 0.05) and OPCAB grafting surgeries (17.0 ± 7.5% vs. 9.5 ± 7.8%, p < 0.05). While gSO₂ increased at the beginning of CPB in T2DM and control patients, no significant intraoperative changes were observed during the OPCAB surgery. The wide gap between ScvO₂ and rSO₂ and their uncoupled relationship in patients with diabetes indicate that disturbances in the cortical oxygen saturation cannot be predicted from the global clinical parameter, the ScvO₂. Thus, our findings advocate the monitoring value of NIRS in T2DM.

Retrospective analysis of central venous catheters in elective intracranial surgery - Is there any benefit?

Background

It remains unclear whether the use of central venous catheters (CVC) improves a patient's clinical outcome after elective intracranial supratentorial procedures.

Methods

This two-armed, single-center retrospective study sought to compare patients undergoing elective intracranial surgery with and without CVCs. Standard anaesthesia procedures were modified during the study period resulting in the termination of obligatory CVC instrumentation for supratentorial procedures. Peri-operative adverse events (AEs) were evaluated as primary endpoint.

Results

The data of 621 patients in total was analysed in this study (301 with and 320 without CVC). Patient characteristics and surgical procedures were comparable between both study groups. A total of 132 peri-operative AEs (81 in the group with CVC vs. 51 in the group without CVC) regarding neurological, neurosurgical, cardiovascular events and death were observed. CVC patients suffer from AEs almost twice as often as non CVC patients (OR_adjusted = 1.98; 95%CI[1.28–3.06]; p = 0.002). Complications related to catheter placement (pneumothorax and arterial malpuncture) were observed in 1.0% of the cases. The ICU treatment period in patients with CVC was 22 (19;24) vs. 21 (19;24) hours (p = 0.413). The duration of hospital stay was also similar between groups (9 (7;13) vs. 8 (7;11) days, p = 0.210). The total time of ventilation (350 (300;440) vs. 335 (281;405) min, p = 0.003) and induction time (40 (35;50) vs. 30 (25;35) min, p<0.001) was found to be prolonged significantly in the group with CVCs. There were no differences found in post-operative inflammatory markers as well as antibiotic treatment.

Conclusion

The data of our retrospective study suggests that patients undergoing elective neurosurgical procedures with CVCs do not demonstrate any additional benefits in comparison to patients without a CVC.

'Intermittent' versus 'continuous' ScvO2 monitoring in children with septic shock: a randomised, non-inferiority trial

PURPOSE

To compare the effect of 'intermittent' central venous oxygen saturation (ScvO₂) monitoring with 'continuous' ScvO₂ monitoring on shock resolution and mortality in children with septic shock.

METHODS

Primary outcome was the achievement of therapeutic goals or shock resolution in the first 6 h. We randomly assigned children < 17 years' age with septic shock to 'intermittent ScvO₂' or 'continuous ScvO₂' groups. All children were subjected to subclavian/internal jugular line insertion and managed as per Surviving Sepsis Campaign Guidelines. To guide resuscitation, we used ScvO₂ estimated at other clinical and laboratory parameters were monitored similarly in both groups.

RESULTS

We enrolled 75 and 77 children [median (IQR) age: 6 (1.5-10) years] in the 'intermittent' and 'continuous' groups, respectively. Baseline characteristics were comparable between the groups. When compared to the 'continuous' group, fewer children in the 'intermittent' group achieved shock resolution within first 6 h [19% vs. 36%; relative risk (RR) 0.51; 95% CI 0.29-0.89; risk difference - 18.0%; 95% CI - 32.0 to - 4.0]. The lower bound of confidence interval, however, crossed the pre-specified non-inferiority margin. There was no difference in the proportion of children attaining shock resolution within 24 h (63% vs. 69%; RR 0.86; 95% CI 0.68-1.08) or risk of mortality between the groups (47% vs. 43%; RR 1.06; 95% CI 0.74-1.51).

CONCLUSIONS

Given that a greater proportion of children attained therapeutic end points in the first 6 h, continuous monitoring of ScvO₂ should preferably be used to titrate therapy in the first few hours in children with septic shock. In the absence of such facility, intermittent monitoring of ScvO₂ can be used to titrate therapy in these children, given the lack of difference in the proportion of patients achieving shock resolution at 24 h or in risk of mortality between the intermittent and continuous groups.

Optimal norepinephrine-equivalent dose to initiate epinephrine in patients with septic shock

PURPOSE

The specific norepinephrine dose at which epinephrine should be added in septic shock is unclear. This study sought to determine the norepinephrine-equivalent dose at epinephrine initiation that correlated with hemodynamic stability.

METHODS

Septic shock patients receiving both norepinephrine and epinephrine were included in this study. Classification and regression tree analysis was conducted to determine breakpoints in norepinephrine-equivalent dose predicting hemodynamic stability, with two cohorts identified. The primary outcome was hemodynamic stability, and secondary outcomes were shock-free survival, time to achieve hemodynamic stability, and change in SOFA score.

RESULTS

Optimal dose group was identified as initiating epinephrine when norepinephrine-equivalent dose was between 37 and 133 μg/min. A total of 138 and 61 patients were classified in optimal and non-optimal dose groups, respectively. Baseline characteristics were similar between groups except vasopressin use was more frequent in the optimal dose group. More patients in optimal dose group versus non-optimal dose group achieved hemodynamic stability (40 [29%] vs. 9 [14.8%]), absolute risk difference 14.2% [95% CI 2.5-25.9%]; p = .03). On multivariable analysis, initiating epinephrine within the optimal norepinephrine-equivalent dose range was independently associated with higher odds of hemodynamic response (OR 3.06 [95% CI 1.2-7.6]; p = .02). No differences were observed in other secondary outcomes.

CONCLUSIONS

Initiation of epinephrine when patients were receiving norepinephrine-equivalent doses of 37-133 μg/min was associated with a higher rate of hemodynamic stability.

Surviving Sepsis Campaign: Research Priorities for Sepsis and Septic Shock

OBJECTIVE

To identify research priorities in the management, epidemiology, outcome and underlying causes of sepsis and septic shock.

DESIGN

A consensus committee of 16 international experts representing the European Society of Intensive Care Medicine and Society of Critical Care Medicine was convened at the annual meetings of both societies. Subgroups had teleconference and electronic-based discussion. The entire committee iteratively developed the entire document and recommendations.

METHODS

Each committee member independently gave their top five priorities for sepsis research. A total of 88 suggestions (Supplemental Table 1, Supplemental Digital Content 2, http://links.lww.com/CCM/D636) were grouped into categories by the committee co-chairs, leading to the formation of seven subgroups: infection, fluids and vasoactive agents, adjunctive therapy, administration/epidemiology, scoring/identification, post-intensive care unit, and basic/translational science. Each subgroup had teleconferences to go over each priority followed by formal voting within each subgroup. The entire committee also voted on top priorities across all subgroups except for basic/translational science.

RESULTS

The Surviving Sepsis Research Committee provides 26 priorities for sepsis and septic shock. Of these, the top six clinical priorities were identified and include the following questions: 1) can targeted/personalized/precision medicine approaches determine which therapies will work for which patients at which times?; 2) what are ideal endpoints for volume resuscitation and how should volume resuscitation be titrated?; 3) should rapid diagnostic tests be implemented in clinical practice?; 4) should empiric antibiotic combination therapy be used in sepsis or septic shock?; 5) what are the predictors of sepsis long-term morbidity and mortality?; and 6) what information identifies organ dysfunction?

CONCLUSIONS

While the Surviving Sepsis Campaign guidelines give multiple recommendations on the treatment of sepsis, significant knowledge gaps remain, both in bedside issues directly applicable to clinicians, as well as understanding the fundamental mechanisms underlying the development and progression of sepsis. The priorities identified represent a roadmap for research in sepsis and septic shock.