Changes in carbon dioxide production and oxygen uptake evaluated using indirect calorimetry in mechanically ventilated patients with sepsis

Background Several clinical guidelines recommend monitoring blood lactate levels and central venous oxygen saturation for hemodynamic management of patients with sepsis. We hypothesized that carbon dioxide production (VCO2) and oxygen extraction (VO2) evaluated using indirect calorimetry (IC) might provide additional information to understand the dynamic metabolic changes in sepsis. Methods Adult patients with sepsis who required mechanical ventilation in the intensive care unit (ICU) of our hospital between September 2019 and March 2020 were prospectively enrolled. Sepsis was diagnosed according to Sepsis-3. Continuous measurement of VCO2 and VO2 using IC for 2 h was conducted within 24 h after tracheal intubation, and the changes in VCO2 and VO2 over 2 h were calculated as the slopes by linear regression analysis. Furthermore, temporal lactate changes were evaluated. The primary outcome was 28-day survival. Results Thirty-four patients with sepsis were enrolled, 26 of whom survived 76%. Significant differences in the slope of VCO2 (− 1.412 vs. − 0.446) (p = 0.012) and VO2 (− 2.098 vs. − 0.851) (p = 0.023) changes were observed between non-survivors and survivors. Of note, all eight non-survivors and 17 of the 26 survivors showed negative slopes of VCO2 and VO2 changes. For these patients, 17 survivors had a median lactate of − 2.4% changes per hour (%/h), whereas non-survivors had a median lactate of 2.6%/hr (p = 0.023). Conclusions The non-survivors in this study showed temporal decreases in both VCO2 and VO2 along with lactate elevation. Monitoring the temporal changes in VCO2 and VO2 along with blood lactate levels may be useful in predicting the prognosis of sepsis.

Intraoperative hyperglycemic stress response and tissue perfusion in cardiac surgery

Background and aim of the study Approximately 30% of patients undergoing cardiac surgery have a history of diabetes and 60-80% of patients without diabetes have stress hyperglycemia. We examined patients undergoing cardiac surgery to determine the presence of stress hyperglycemia and its relationship to tissue perfusion. Methods Hemodynamic parameters, central venous oxygen saturation, lactate,oxygen delivery and consumption, oxygen extraction rate were analyzed at four intraoperative time points. Results The stress-induced hyperglycemic response during cardiac surgery was more severe in patients without diabetes. When focusing on the oxygen extraction rate in terms of tissue oxygenation, diabetic patients had 1.22 times higher and significant oxygen extraction rate than non-diabetic patients. Conclusions Although lactate values were slightly higher and central venous oxygen saturation were slightly lower in the diabetic group, considering the fact that oxygen extraction rate reflects the total outcome of small changes in all these parameters, we can emphasize the conclusion that diabetic patients undergoing cardiac surgery have greater tissue oxygen demand/supply imbalance compared to non-diabetic patients. In our study, this tissue oxygenation defect in diabetic patients was not found to be directly correlated with blood glucose levels. Perhaps, even if the disease is under control, the negative effects of diabetes on all systems have accumulated and led to such a result.

Changes in central venous-to-arterial carbon dioxide tension induced by fluid bolus in critically ill patients

Background In this prospective observational study, we evaluated the effects of fluid bolus (FB) on venous-to-arterial carbon dioxide tension (PvaCO2) in 42 adult critically ill patients with pre-infusion PvaCO2 > 6 mmHg. Results FB caused a decrease in PvaCO2, from 8.7 [7.6−10.9] mmHg to 6.9 [5.8−8.6] mmHg (p < 0.01). PvaCO2 decreased independently of pre-infusion cardiac index and PvaCO2 changes during FB were not correlated with changes in central venous oxygen saturation (ScvO2) whatever pre-infusion CI. Pre-infusion levels of PvaCO2 were inversely correlated with decreases in PvaCO2 during FB and a pre-infusion PvaCO2 value < 7.7 mmHg could exclude a decrease in PvaCO2 during FB (AUC: 0.79, 95%CI 0.64–0.93; Sensitivity, 91%; Specificity, 55%; p < 0.01). Conclusions Fluid bolus decreased abnormal PvaCO2 levels independently of pre-infusion CI. Low baseline PvaCO2 values suggest that a positive response to FB is unlikely.

Hemodynamic Perspectives in Anemia

Oxygen delivery in normal physiologic states is determined by cardiac output, hemoglobin, oxygen saturation, and to a lesser extent, dissolved oxygen in the blood. Compensatory mechanisms such as an increase in stroke volume, heart rate, and re-distribution of blood flow helps in scenarios with increased oxygen demand. In cases of acute hemodynamic decompensation, this pre-existing physiologic relation between oxygen delivery and oxygen consumption is altered, resulting in tissue hypoxia and resultant anaerobic metabolism. A persistent state of sub-critical O2 delivery correlates with increased mortality. Oxygen consumption itself is usually independent of delivery unless a critical threshold is unmet. We can use various parameters such as serum lactate, oxygen extraction, and central venous oxygen saturation to determine this pathology. A basic understanding of this physiology will help better tailor therapy to improve outcomes in critically ill patients.

Central venous-to-arterial PCO2 difference as a marker to identify fluid responsiveness in septic shock

Defining the hemodynamic response to volume therapy is integral to managing critically ill patients with acute circulatory failure, especially in the absence of cardiac index (CI) measurement. This study aimed at investigating whether changes in central venous-to-arterial CO2 difference (Δ-ΔPCO2) and central venous oxygen saturation (ΔScvO2) induced by volume expansion (VE) are reliable parameters to define fluid responsiveness in sedated and mechanically ventilated septic patients. We prospectively studied 49 critically ill septic patients in whom VE was indicated because of circulatory failure and clinical indices. CI, ΔPCO2, ScvO2, and oxygen consumption (VO2) were measured before and after VE. Responders were defined as patients with a > 10% increase in CI (transpulmonary thermodilution) after VE. We calculated areas under the receiver operating characteristic curves (AUCs) for Δ-ΔPCO2, ΔScvO2, and changes in CI (ΔCI) after VE in the whole population and in the subgroup of patients with an increase in VO2 (ΔVO2) ≤ 10% after VE (oxygen-supply independency). Twenty-five patients were fluid responders. In the whole population, Δ-ΔPCO2 and ΔScvO2 were significantly correlated with ΔCI after VE (r = − 0.30, p = 0.03 and r = 0.42, p = 0.003, respectively). The AUCs for Δ-ΔPCO2 and ΔScvO2 to define fluid responsiveness (increase in CI > 10% after VE) were 0.76 (p < 0.001) and 0.68 (p = 0.02), respectively. In patients with ΔVO2 ≤ 10% (n = 36) after VE, the correlation between ΔScvO2 and ΔCI was 0.62 (p < 0.001), and between Δ-ΔPCO2 and ΔCI was − 0.47 (p = 0.004). The AUCs for Δ-ΔPCO2 and ΔScvO2 were 0.83 (p < 0.001) and 0.73 (p = 0.006), respectively. In these patients, Δ-ΔPCO2 ≤ -37.5% after VE allowed the categorization between responders and non-responders with a positive predictive value of 100% and a negative predictive value of 60%. In sedated and mechanically ventilated septic patients with no signs of tissue hypoxia (oxygen-supply independency), Δ-ΔPCO2 is a reliable parameter to define fluid responsiveness.

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.