Interpretation of venous-to-arterial carbon dioxide difference in the resuscitation of septic shock patients

Correlation and Agreement Between the CO2 Gap Obtained From Peripheral Venous Blood and From Mixed Venous Blood in Mechanically Ventilated Septic Patients

BACKGROUND

Venous-arterial CO2 difference (Pv-aCO2) is a valuable marker that can identify a subset of patients in shock with inadequate cardiac output to meet tissue metabolic requirements. Some authors have found that Pv-aCO2 levels calculated from mixed vs central venous blood demonstrate a linear relationship. The purpose of this study is to determine whether there is a linear relationship between Pv-aCO2 obtained with peripheral venous blood (Pv-aCO2p) and with mixed venous blood, and the agreement between the 2 measures.

METHODS

This was a prospective, single-center, observational clinical study enrolling mechanically ventilated patients in septic shock during the first 24 hours following admission to the intensive care unit.

RESULTS

The Bravais-Pearson r-coefficient between Pv-aCO2 and Pv-aCO2p was .70 in 38 determinations (95%CI .48-.83; P-value = 1.25 x 10^-6). The Bland-Altman bias was 4.11 mmHg (95%CI 2.82-5.39), and the repeatability coefficient was 11.05. Using the Taffe approach, the differential and proportional biases were 2.81 (95%CI .52-5.11) and 1.29 (95%CI .86-1.72), respectively.

CONCLUSION

There was linear correlation between Pv-aCO2p and Pv-aCO2 in mechanically ventilated patients with septic shock. The bias showed a gradual increase in high Pv-aCO2 values in an upward trend.

Conservative versus conventional oxygen therapy in type I acute respiratory failure patients in respiratory intensive care unit, Zagazig University

The present study aimed to assess the effect of a conservative (permissive hypoxemia) versus conventional (normoxia) protocol for oxygen supplementation on the outcome of type I respiratory failure patients admitted to respiratory intensive care unit (ICU). This randomized controlled clinical trial was carried out at the Respiratory ICU, Chest Department of Zagazig University Hospital, for 18 months, starting in July 2018. On admission, 56 enrolled patients with acute respiratory failure were randomized in a 1:1 ratio into the conventional group [oxygen therapy was supplied to maintain oxygen saturation (SpO2) between 94% and 97%] and the conservative group (oxygen therapy was administered to maintain SpO2 values between 88% and 92%). Different outcomes were assessed, including ICU mortality, the need for mechanical ventilation (MV) (invasive or non-invasive), and ICU length of stay. In the current study, the partial pressure of oxygen was significantly higher among the conventional group at all times after the baseline reading, and bicarbonate was significantly higher among the conventional group at the first two readings. There was no significant difference in serum lactate level in follow-up readings. The mean duration of MV and ICU length of stay was 6.17±2.05 and 9.25±2.22 days in the conventional group versus 6.46±2.0 and 9.53±2.16 days in the conservative group, respectively, without significant differences between both groups. About 21.4% of conventional group patients died, while 35.7% of conservative group patients died without a significant difference between both groups. We concluded that conservative oxygen therapy may be applied safely to patients with type I acute respiratory failure.

Central Venous-to-Arterial CO2 Difference-Assisted Goal-Directed Hemodynamic Management During Major Surgery-A Randomized Controlled Trial

BACKGROUND

Different goals have guided goal-directed therapy (GDT). Protocols aiming for central venous-to-arterial carbon dioxide gap (DCO2) <6 mm Hg have improved organ function in septic shock. Evidence for use of DCO2 in the perioperative period is scarce. We aimed to determine if a GDT protocol using central venous saturation of oxygen (SCvo2) and DCO2 reduced organ dysfunction and intensive care unit (ICU) stay in American Society of Anesthesiologist (ASA) I and II patients undergoing major surgeries compared to pragmatic goal-directed care.

METHODS

One hundred patients were randomized. Arterial and venous blood-gas values were recorded every 2 hours perioperatively for all patients. Intervention group (GrI) with access to both values was managed per protocol based on DCO2 and SCvo2. Dobutamine infusion 3 to 5 µg/kg/min started if DCO2 >6 mm Hg after correcting all macrocirculatory end points. Control group (GrC) had access only to arterial-gas values and managed per "conventional" goals without DCO2 or SCvo2. Patients were followed for 48 hours after surgery. Organ dysfunction, sequential organ failure assessment (SOFA) scores-primary outcome, length of stay in ICU, and duration of postoperative mechanical ventilation and hospital stay were recorded. The patient, surgeons, ICU team, and analyzer were blinded to group allocation.

RESULTS

The groups (44 each) did not significantly differ with respect to baseline characteristics. Perioperative fluids, blood products, and vasopressors used did not significantly differ. The GrI had less organ dysfunction although not significant (79% vs 66%; P = .2). Length of ICU stay in the GrI was significantly less (1.52; standard deviation [SD], 0.82 vs 2.18; SD, 1.08 days; P = .002). Mechanical ventilation duration (0.9 days in intervention versus 0.6 days in control; P = .06) and length of hospital stay did not significantly differ between the groups. Perioperative DCO2 (5.8 vs 8.4 mm Hg; P < .001) and SCvo2 (73.5 vs 68.4 mm Hg; P < .001) were significantly better in the GrI.

CONCLUSIONS

GDT guided by DCO2 did not improve organ function in our cohort. It resulted in greater use of dobutamine, improved tissue oxygen parameters, and decreased length of ICU stay. More evidence is needed for the routine use of DCO2 in sicker patients. In the absence of cardiac output monitors, it may be a readily available, less-expensive, and underutilized parameter for major surgical procedures.

Correlation of central venous-to-arterial carbon dioxide difference to arterial-central venous oxygen difference ratio to lactate clearance and prognosis in patients with septic shock: A prospective observational cohort study

Background

To assess the relationship between the ratio of difference of venoarterial CO₂ tension (P (v-a) CO₂) and difference of arterio-venous oxygen content (C (a-cv) O₂), i.e., ΔPCO₂/ΔCaO₂ with lactate clearance (LC) at 8 and 24 h, to define a cutoff for the ratio to identify LC >10% and >20% at 8 and 24 h, respectively, and its association with prognosis in septic shock.

Methods

Adult patients with septic shock were included in this prospective, observational cohort study. Blood samples for arterial lactate, arterial, and central venous oxygen and carbon dioxide were drawn simultaneously at time zero (T0), 8 h (T8), and 24 h (T24). At T8, patients were divided into Group 8A (LC ≥10%) and Group 8B (LC <10%). At T24, patients were divided into Group 24A (LC ≥20%) and Group 24B (LC <20%).

Results

Ninty-eight patients were included. The area under the curve of ΔPCO₂/ΔCaO₂ at T8 (0.596) and T24 (0.823) was the highest when compared to P(v-a) CO₂ and C(a-v) O₂. The best cutoff of P(v-a) CO₂/C (a-v) O₂ as predictor of LC >10% was 1.31 (sensitivity 70.6% and specificity 53.3%) and for LC >20% was 1.37 (sensitivity 100% and specificity 50%). At both T8 and T24, P(v-a) CO₂/C (a-v) O₂ showed a significant negative correlation with LC. Groups 8A and 24A showed lower intensive care unit mortality than 8B and 24B, respectively. Values of P(v-a) CO₂/C (a-v) O₂ at T8 were comparable, but at T24, there was a significant difference between the survivors and nonsurvivors (P < 0.001).

Conclusion

ΔPCO₂/ΔCaO₂ predicts lactate clearance, and its 24 h value appears superior to the 8-h value in predicting LC and mortality in septic shock patients.

Central venous-to-arterial CO2 difference is a poor tool to predict adverse outcomes after cardiac surgery: a retrospective study

PURPOSE

The venous-to-arterial carbon dioxide partial pressure difference (CO₂ gap) has been reported to be a sensitive indicator of cardiac output adequacy. We aimed to assess whether the CO₂ gap can predict postoperative adverse outcomes after cardiac surgery.

METHODS

A retrospective study was conducted of 5,151 patients from our departmental database who underwent cardiac surgery from 1 January 2008 to 31 December 2018. Lactate level (mmol·L^-1), central venous oxygen saturation (ScVO₂) (%), and the venous-to-arterial carbon dioxide difference (CO₂ gap) were measured at intensive care unit (ICU) admission and on days 1 and 2 after cardiac surgery. The following postoperative adverse outcomes were collected: ICU mortality, hemopericardium or tamponade, resuscitated cardiac arrest, acute kidney injury, major bleeding, acute hepatic failure, mesenteric ischemia, and pneumonia. The primary outcome was the presence of at least one postoperative adverse outcome. Logistic regression was used to assess the association between ScVO₂, lactate, and the CO₂ gap with adverse outcomes. Their diagnostic performance was compared using a receiver operating characteristic (ROC) curve.

RESULTS

There were 1,933 patients (38%) with an adverse outcome. Cardiopulmonary bypass (CPB) parameters were similar between groups. The CO₂ gap was slightly higher for the "adverse outcomes" group than for the "no adverse outcomes" group. Arterial lactate at admission, day 1, and day 2 was also slightly higher in patients with adverse outcomes. Central venous oxygen saturation was not significantly different between patients with and without adverse outcomes. The area under the ROC curve to predict outcomes after CPB for the CO₂ gap at admission, day 1, and day 2 were 0.52, 0.55, and 0.53, respectively.

CONCLUSION

After cardiac surgery with CPB, the CO₂ gap at ICU admission, day 1, and day 2 was associated with postoperative adverse outcomes but showed poor diagnostic performance.

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.