Influence of arterial dissolved oxygen level on venous oxygen saturation: don't forget the PaO2!

Hypoxische, anämische und kardial bedingte Hypoxämie: Wann beginnt die Hypoxie im Gewebe?

Bei einer Hypoxämie ist oft der Sauerstoffgehalt noch im unteren Normbereich, sodass keine Hypoxie im Gewebe vorliegt. Wird die Hypoxie-Schwelle im Gewebe bei einer hypoxisch, anämisch und auch kardial bedingten Hypoxämie erreicht, kommt es im Zellstoffwechsel, unabhängig von der Genese, zu identischen Gegenregulationen. Im klinischen Alltag wird diese pathophysiologische Tatsache mitunter ignoriert, obwohl je nach Hypoxämie-Ursache die Beurteilung und die Therapie stark unterschiedlich sind. Während für die anämische Hypoxämie restriktive und allgemein akzeptierte Regeln in den Transfusionsrichtlinien festgelegt sind, wird bei einer hypoxischen Hypoxie früh die Indikation zu einer meist invasiven Beatmung gestellt. Die klinische Beurteilung und Indikationsstellung fokussiert dabei auf die Parameter Sauerstoffsättigung, Sauerstoffpartialdruck und Oxygenierungsindex. Während der Corona-Pandemie sind Fehlinterpretationen der Pathophysiologie sichtbar geworden und haben vermutlich zu überflüssigen Intubationen geführt. Für die Behandlung einer hypoxischen Hypoxie mittels invasiver Beatmung aber gibt es keine Evidenz. Im vorliegenden Review wird auf die Pathophysiologie der verschiedenen Hypoxieursachen unter besonderer Berücksichtigung der Intubation und Beatmung auf der Intensivstation eingegangen.

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

Background:

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.

Objectives:

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.

Methods:

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.

Results:

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).

Conclusion:

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.

Preoxygenation: from hardcore physiology to the operating room

If we define the human body by the mass of the elements that compose it, we could say that we are oxygen and other elements. Oxygen, in addition to being fundamental in our composition, is an element that we constantly need to support cellular respiration and, therefore, life. Interestingly, despite its importance, humans have not developed mechanisms that allow us to store it and, therefore, we are unable to sustain life if we are deprived of ventilation, even for brief periods. Accordingly, the ability to induce the cessation of ventilation in a patient must be accompanied by different technical and non-technical skills that allow the patient's safety to be maintained in this highly vulnerable state. Through the use of basic mathematical tools and comparative physiology, we hereby propose to review the physiological foundations of preoxygenation to understand the reasons behind the clinical recommendations in this field.

Intraoperative mild hyperoxia may be associated with improved survival after off-pump coronary artery bypass grafting: a retrospective observational study

Background

The effect of hyperoxia due to supplemental oxygen administration on postoperative outcomes in patients undergoing cardiac surgery remains unclear. This retrospective study aimed to evaluate the relationship between intraoperative oxygen tension and mortality after off-pump coronary artery bypass grafting (OPCAB).

Methods

The study included adult patients who underwent isolated OPCAB between July 2010 and June 2020. Patients were categorised into three groups based on their intraoperative time-weighted average arterial oxygen partial pressure (PaO₂): normoxia/near-normoxia (< 150 mmHg), mild hyperoxia (150–250 mmHg), and severe hyperoxia (> 250 mmHg). The risk of in-hospital mortality was compared using weighted logistic regression analysis. Restricted cubic spline analysis was performed to analyse intraoperative PaO₂ as a continuous variable. The risk of cumulative all-cause mortality was compared using Cox regression analysis.

Results

The normoxia/near-normoxia, mild hyperoxia, and severe hyperoxia groups included 229, 991, and 173 patients (n = 1393), respectively. The mild hyperoxia group had a significantly lower risk of in-hospital mortality than the normoxia/near-normoxia (odds ratio [OR], 0.12; 95% confidence interval [CI], 0.06–0.22) and severe hyperoxia groups (OR, 0.06; 95% CI, 0.03–0.14). Intraoperative PaO₂ exhibited a U-shaped relationship with in-hospital mortality in the non-hypoxic range. The risk of cumulative all-cause mortality was significantly lower in the mild hyperoxia group (hazard ratio, 0.72; 95% CI, 0.52–0.99) than in the normoxia/near-normoxia group.

Conclusions

Maintaining intraoperative PaO₂ at 150–250 mmHg was associated with a lower risk of mortality after OPCAB than PaO₂ at < 150 mmHg and at > 250 mmHg. Future randomised trials are required to confirm if mildly increasing arterial oxygen tension during OPCAB to 150–250 mmHg improves postoperative outcomes.

Extracorporeal Membrane Oxygenation Blood Flow and Blood Recirculation Compromise Thermodilution-Based Measurements of Cardiac Output

The contribution of veno-venous (VV) extracorporeal membrane oxygenation (ECMO) to systemic oxygen delivery is determined by the ratio of total extracorporeal blood flow () to cardiac output (). Thermodilution-based measurements of may be compromised by blood recirculating through the ECMO (recirculation fraction; Rf). We measured the effects of and Rf on classic thermodilution-based measurements of in six anesthetized pigs. An ultrasound flow probe measured total aortic blood flow () at the aortic root. Rf was quantified with the ultrasound dilution technique. was set to 0-125% of and was measured using a pulmonary artery catheter (PAC) in healthy and lung injured animals. PAC overestimated () at all settings compared to . The mean bias between both methods was 2.1 L/min in healthy animals and 2.7 L/min after lung injury. The difference between and increased with an of 75-125%/ compared to QEC <50%/. Overestimation of was highest when resulted in a high Rf. Thus, thermodilution-based measurements can overestimate cardiac output during VV ECMO. The degree of overestimation of depends on the EC/ ratio and the recirculation fraction.

Right Heart Catheterization in Patients with Advanced Heart Failure: When to Perform? How to Interpret?

Right heart catheterization is an established cornerstone of advanced heart failure management, as a clear understanding of the patient's hemodynamic status offers insight into diagnosis, prognosis, and management. In this review, the authors will describe the role of right heart catheterization in the diagnosis and management of shock, in the context of left ventricular assist devices, in the assessment of heart transplant candidacy, and also explore future directions of implantable monitoring devices for pulmonary artery and left atrial pressure monitoring.

Early Lactate-Guided Resuscitation of Elderly Septic Patients

BACKGROUND

Early lactate-guided resuscitation was endorsed in the guidelines of the Surviving Sepsis Campaign as a key strategy to decrease the mortality of patients admitted to the ICU department with septic shock. However, its effectiveness in elderly Asian patients is uncertain.

METHOD

We conducted a single-center trial to test the effectiveness of the early lactate-guided resuscitation of older Asian patients at the Second Hospital of Hebei Medical University. Eligible septic shock patients who consented to participation in the study were randomly assigned to receive early lactate-guided treatment or regular treatment as controls.

RESULT

A total of 82 patients met the hyperlactatemia criteria and participated in the trial. Forty-two patients received early lactate-guided treatment (lactate group) and 40 received regular treatment (control group). The lactate group received more fluids at initial 6 hours (3.3 ± 1.4 vs 2.4 ± 1.7 L, P = 0.01), but similar proportions of patients in both groups required the use of vasopressors and vasodilators. Patients in the lactate group showed significantly reduced ICU needs compared to the control group, which were weaned from mechanical ventilation more quickly (median 7, IQR 4 to 14 vs median 9, IQR 4.3 to 17.8, P = 0.02) and transferred out of the ICU earlier (median 4.5, IQR 2.8 to 7.3 vs median 6, IQR 3.2 to 8, P = 0.01). However, the hospital mortality (35.7% vs 42.5%, P = 0.35) and ICU mortality (31.0% vs 37.5%, P = 0.38) for both groups were not reduced.

CONCLUSION

For critically ill patients (elderly Asian patients) admitted to the ICU department with hyperlactatemia, early lactate-guided treatment reduced ICU needs but did not reduce mortality.

Peripheral measurements of venous oxygen saturation and lactate as a less invasive alternative for hemodynamic monitoring

Background

Peripheral measurement of venous oxygen saturation and lactate is a less invasive alternative to monitor tissue oxygenation as compared to measurements from a central venous catheter. However, there is a lack of evidence to support the use of peripheral measurements. In this study, we investigated the agreement between central and peripheral venous oxygen saturation and lactate.

Methods

We conducted a prospective observational study including 115 patients who underwent elective cardiac surgery between April and May 2015 at Rigshospitalet, Copenhagen, Denmark. Measurements were obtained simultaneously at induction of anaesthesia, upon arrival in the ICU and 3–4 h postoperatively. Bias and trending ability was identified using Bland-Altman analysis and a four-quadrant plot.

Results

Bias was 13.37% for venous oxygen saturation preoperatively (95% CI: 11.52–15.22, LoA: ±19.10, PE: 22.08%), 11.29% at arrival to the ICU (95% CI: 8.81–13.77, LoA: ±25.10, PE: 32.39%) and 16.49% at 3–4 h postoperatively (95% CI: 14.16–18.82, LoA: ±21.20, PE: 26.82%). A four-quadrant plot demonstrated an 89% concordance. Central and peripheral lactate showed a bias of 0.14 mmol/L preoperatively (95% CI: 0.11–0.17, LoA: ±0.30, PE: 32.08%), 0.16 mmol/L at arrival to ICU (95% CI: 0.09–0.23, LoA: ±0.70, PE: 38.88%) and 0.23 mmol/L at 3–4 h postoperatively (95% CI: 0.11–0.35, LoA: ±0.50, 25.18%).

Discussion

Measurements of peripheral oxygen saturation and lactate may be valuable in an emergency setting, avoiding unnecessary and time consuming application of a CVC.

Conclusion

We found a high bias but an acceptable trending ability between central and peripheral venous oxygenation. Central and peripheral lactate had excellent agreement. Further studies are necessary to validate the use of peripheral venous samples to identify patients at risk of impaired tissue oxygenation.

Measurement of Oxygen Consumption Variations in Critically Ill Burns Patients: Are the Fick Method and Indirect Calorimetry Interchangeable?

OBJECTIVES

To evaluate the interchangeability of oxygen consumption variations measured with the Fick equation (ΔVO2Fick) and indirect calorimetry (ΔVO2Haldane) in critically ill burns patients.

METHODS

Prospective observational single-center study conducted in a university hospital. Twenty-two consecutive burns patients with circulatory insufficiency and hyperlactatemia (>2 mmol/L) who required a fluid challenge (FC) were included. All patients had cardiac output monitoring (transpulmonary thermodilution technique) and were ventilated and sedated. Simultaneous measurements of VO2Fick and VO2Haldane were performed before and immediately after the FC, at rest, and in hemodynamic conditions stabilized for at least 1 h. VO2Fick and VO2Haldane were measured, respectively, with the standard formulae (using arterial and central venous saturation measured with a blood gas analyzer) and with a metabolic monitor.

RESULTS

Forty-four paired measurements of VO2 were obtained. At each timepoint, the median (interquartile range, 25-75) VO2Haldane values were significantly higher than the median VO2Fick values (126 (103-192) vs. 90 (66-149) mL O2/min/m (P = 0.004) before FC and 129 (105-189) vs. 80 (54-119) mL O2/min/m (P = 0.001) after FC). Correlation between the ΔVO2Fick and the ΔVO2Haldane (%) measurements was poor, with an r = 0.06, (P = 0.77). The mean bias was 8.6% [limits of agreement (LOA): -75.7%, 92.9%].

CONCLUSIONS

Analysis of agreement showed poor concordance for the ΔVO2Haldane and the ΔVO2Fick (%) with a low mean bias but large and clinically unacceptable LOA. ΔVO2Haldane and ΔVO2Fick (%) are not interchangeable in these conditions.

Influence of Fraction of Inspired Oxygen on Noninvasive Hemoglobin Measurement: Parallel Assessment of 2 Monitors

BACKGROUND

Previous reports have brought specific attention to the relationship between oxygenation of the patient and the accuracy of noninvasive measurement of hemoglobin (Hb) using an optical sensor. This study aimed to assess prospectively the relationship between fraction of inspired oxygen (FIO2) and the bias of the measurement of Hb by the use of 2 different noninvasive monitors compared with the classic invasive technique.

METHODS

Forty-four patients were included prospectively. In each individual, Hb level was determined noninvasively by monitor Pronto-7™ (Masimo Corporation, Irvine, CA) and by monitor NBM-200MP™ (OrSense Ltd, Petah-Tikva, Israel), with the probe placed on 2 fingers on the same hand of the patient. Three measures were performed, first under breathing air and 2 others when fraction of expired oxygen rose to 50% ± 5% and to 90 ± 5%. Simultaneously, a nurse collected a venous blood sample, which was sent immediately to the hematology laboratory for Hb measurement. The main outcome measurement was the mean bias between noninvasive and invasive measurements.

RESULTS

Results show no change in median bias [interquartile range] with FIO2 for Pronto-7 (from 1.1 g/dL [0.0-2.0] in FIO2 21% to 1.0 g/dL [0.2-1.5] in FIO2 100%), but increasingly negative median bias with increasing FIO2 for NBM-200MP (from -0.3 g/dL [-1.3 to 0.3] in FIO2 21% to -0.8 g/dL [-1.5 to -0.1] in FIO2 100%, P = .04).

DISCUSSION

This study showed that noninvasive measurement of Hb could be influenced by inspired fraction of oxygen when the monitor NBM-200MP is used.

Central venous-to-arterial carbon dioxide difference and the effect of venous hyperoxia: A limiting factor, or an additional marker of severity in shock?

Central venous-to-arterial carbon dioxide difference (P_cvaCO₂) has demonstrated its prognostic value in critically ill patients suffering from shock, and current expert recommendations advocate for further resuscitation interventions when P_cvaCO₂ is elevated. P_cvaCO₂ combination with arterial-venous oxygen content difference (P_cvaCO₂/C_avO₂) seems to enhance its performance when assessing anaerobic metabolism. However, the fact that PCO₂ values might be altered by changes in blood O₂ content (the Haldane effect), has been presented as a limitation of PCO₂-derived variables. The present study aimed at exploring the impact of hyperoxia on P_cvaCO₂ and P_cvaCO₂/C_avO₂ during the early phase of shock. Prospective interventional study. Ventilated patients suffering from shock within the first 24 h of ICU admission. Patients requiring FiO₂ ≥ 0.5 were excluded. At inclusion, simultaneous arterial and central venous blood samples were collected. Patients underwent a hyperoxygenation test (5 min of FiO₂ 100%), and arterial and central venous blood samples were repeated. Oxygenation and CO₂ variables were calculated at both time points. Twenty patients were studied. The main cause of shock was septic shock (70%). The hyperoxygenation trial increased oxygenation parameters in arterial and venous blood, whereas PCO₂ only changed at the venous site. Resulting P_cvaCO₂ and P_cvaCO₂/C_avO₂ significantly increased [6.8 (4.9, 8.1) vs. 7.6 (6.7, 8.5) mmHg, p 0.001; and 1.9 (1.4, 2.2) vs. 2.3 (1.8, 3), p < 0.001, respectively]. Baseline P_cvaCO₂, P_cvaCO₂/C_avO₂ and S_cvO₂ correlated with the magnitude of PO₂ augmentation at the venous site within the trial (ρ -0.46, p 0.04; ρ 0.6, p < 0.01; and ρ 0.7, p < 0.001, respectively). Increased P_cvaCO₂/C_avO₂ values were associated with higher mortality in our sample [1.46 (1.21, 1.89) survivors vs. 2.23 (1.86, 2.8) non-survivors, p < 0.01]. P_cvaCO₂ and P_cvaCO₂/C_avO₂ are influenced by oxygenation changes not related to flow. Elevated P_cvaCO₂ and P_cvaCO₂/C_avO₂ values might not only derive from cardiac output inadequacy, but also from venous hyperoxia. Elevated P_cvaCO₂/C_avO₂ values were associated with higher PO₂ transmission to the venous compartment, suggesting higher shunting phenomena.

A comparative analysis of the effects of sevoflurane and propofol on cerebral oxygenation during steep Trendelenburg position and pneumoperitoneum for robotic-assisted laparoscopic prostatectomy

Purpose

Steep Trendelenburg position and pneumoperitoneum during robotic-assisted laparoscopic prostatectomy (RALP) increase intracranial pressure (ICP) and may alter cerebral blood flow (CBF) and oxygenation. Volatile anesthetics and propofol have different effects on ICP, CBF, and cerebral metabolic rate and may have different impact on cerebral oxygenation during RALP. In this study, we measured jugular venous bulb oxygenation (SjO₂) and regional oxygen saturation (SctO₂) in patients undergoing RALP to evaluate cerebral oxygenation and compared the effects of sevoflurane and propofol. We also verified whether SctO₂ may be an alternative to SjO₂.

Methods

Fifty patients scheduled for RALP were randomly assigned to undergo sevoflurane (group S) or propofol (group P) anesthesia. SjO₂, SctO₂, mean arterial pressure (MAP), heart rate (HR), cardiac index (CI), central venous pressure (CVP), partial pressures of arterial oxygen (PaO₂) and carbon dioxide (PaCO₂), hemoglobin concentration (Hb), Bispectral Index (BIS) and nasopharyngeal temperature (BT) were recorded 5 min before surgery commencement, 5 min after pneumoperitoneum, 5, 30, 60, 90, and 120 min after pneumoperitoneum in a Trendelenburg position, and after desufflation in a supine position.

Results

SjO₂ was significantly higher in group S than in group P at all measurement points [group S vs. group P: 77 % (11) vs. 65 % (13), mean of all measurement points (1SD); p < 0.01]. Linear regression analysis (β = 0.106; r² = 0.065; p = 0.004) shows a weak relationship between SjO₂ and SctO₂.

Conclusions

Sevoflurane maintains higher SjO₂ levels than propofol during RALP. SctO₂ does not accurately reflect SjO₂.

Early goal-directed therapy in severe sepsis and septic shock: insights and comparisons to ProCESS, ProMISe, and ARISE

Prior to 2001 there was no standard for early management of severe sepsis and septic shock in the emergency department. In the presence of standard or usual care, the prevailing mortality was over 40-50 %. In response, a systems-based approach, similar to that in acute myocardial infarction, stroke and trauma, called early goal-directed therapy was compared to standard care and this clinical trial resulted in a significant mortality reduction. Since the publication of that trial, similar outcome benefits have been reported in over 70 observational and randomized controlled studies comprising over 70,000 patients. As a result, early goal-directed therapy was largely incorporated into the first 6 hours of sepsis management (resuscitation bundle) adopted by the Surviving Sepsis Campaign and disseminated internationally as the standard of care for early sepsis management. Recently a trio of trials (ProCESS, ARISE, and ProMISe), while reporting an all-time low sepsis mortality, question the continued need for all of the elements of early goal-directed therapy or the need for protocolized care for patients with severe and septic shock. A review of the early hemodynamic pathogenesis, historical development, and definition of early goal-directed therapy, comparing trial conduction methodology and the changing landscape of sepsis mortality, are essential for an appropriate interpretation of these trials and their conclusions.

Pitfalls in haemodynamic monitoring in the postoperative and critical care setting

Haemodynamic monitoring is a vital part of daily practice in anaesthesia and intensive care. Although there is evidence to suggest that goal-directed therapy may improve outcomes in the perioperative period, which haemodynamic targets we should aim at to optimise patient outcomes remain elusive and controversial. This review highlights the pitfalls in commonly used haemodynamic targets, including arterial blood pressure, central venous pressure, cardiac output, central venous oxygen saturation and dynamic haemodynamic indices. Evidence suggests that autoregulation in regional organ circulation may change either due to chronic hypertension or different disease processes such as traumatic brain injury, cerebrovascular ischaemia or haemorrhage; this will influence the preferred blood pressure target. Central venous pressure can be influenced by multiple pathophysiological factors and, unless central venous pressure is very low, it is rarely useful as a predictor for fluid responsiveness. Central venous oxygen saturation can be easily increased by a high arterial oxygen tension, making it useless as a surrogate marker of good cardiac output or systemic oxygen delivery in the presence of hyperoxaemia. Many dynamic haemodynamic indices have been reported to predict fluid responsiveness, but they all have their own limitations. There is also insufficient evidence to support that giving fluid until the patient is no longer fluid responsive can improve patient-centred outcomes. With the exception in the context of preventing contrast-induced nephropathy, large randomised controlled studies suggest that excessive fluid treatment may prolong duration of mechanical ventilation without preventing acute kidney injury in the critically ill.