High central venous-to-arterial CO2 difference/arterial-central venous O2 difference ratio is associated with poor lactate clearance in septic patients after resuscitation

A review of using CO2-derived variables to detect tissue hypoperfusion during cardiopulmonary bypass

Complications after cardiac surgery with cardiopulmonary bypass (CPB) are associated with increased morbidity and mortality. Early detection and prompt reversion of tissue hypoperfusion during CPB are key factors to reduce organ dysfunction after cardiac surgery. CO2 (carbon dioxide)-derived variables which are easy to assess and routinely available to evaluate the adequacy of macro- and microcirculation may offer important information on the adequacy of the perfusion during CPB. However, since some practical issues remain unsolved in providing a reliable measurement of CO2 removal from the patient, CO2-derived variables are not widely monitoring during CPB. This review aims to demonstrate the basic principles of CO2-derived variables during CPB, the available techniques to assess CO2-derived variables on CPB and the clinically relevant applications.

Venoarterial Partial Pressure of Carbon Dioxide Difference: Let's Trend It!

How to cite this article: Ravisankar NR. Venoarterial Partial Pressure of Carbon Dioxide Difference: Let's Trend It! Indian J Crit Care Med 2024;28(4):323-325.

Use of CO2-Derived Variables in Cardiac Intensive Care Unit: Pathophysiology and Clinical Implications

Shock is a life-threatening condition, and its timely recognition is essential for adequate management. Pediatric patients with congenital heart disease admitted to a cardiac intensive care unit (CICU) after surgical corrections are particularly at risk of low cardiac output syndrome (LCOS) and shock. Blood lactate levels and venous oxygen saturation (ScVO₂) are usually used as shock biomarkers to monitor the efficacy of resuscitation efforts, but they are plagued by some limitations. Carbon dioxide (CO₂)-derived parameters, namely veno-arterial CO₂ difference (ΔCCO₂) and the VCO₂/VO₂ ratio, may represent a potentially valuable addition as sensitive biomarkers to assess tissue perfusion and cellular oxygenation and may represent a valuable addition in shock monitoring. These variables have been mostly studied in the adult population, with a strong association between ΔCCO₂ or VCO₂/VO₂ ratio and mortality. In children, particularly in CICU, few studies looked at these parameters, while they reported promising results on the use of CO₂-derived indices for patients' management after cardiac surgeries. This review focuses on the physiological and pathophysiological determinants of ΔCCO₂ and VCO₂/VO₂ ratio while summarizing the actual state of knowledge on the use of CO₂-derived indices as hemodynamical markers in CICU.

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.

Techniques for Oxygenation and Ventilation in Coronavirus Disease 2019

This paper discusses mechanisms of hypoxemia and interventions to oxygenate critically ill patients with COVID-19 which range from nasal cannula to noninvasive and mechanical ventilation. Noninvasive ventilation includes continuous positive airway pressure ventilation (CPAP) and high-flow nasal cannula (HFNC) with or without proning. The evidence for each of these modalities is discussed and thereafter, when to transition to mechanical ventilation (MV). Various techniques of MV, again with and without proning, and rescue strategies which would include extra corporeal membrane oxygenation (ECMO) when it is available and permissive hypoxemia where it is not, are discussed.

Ratio of carbon dioxide veno-arterial difference to oxygen arterial-venous difference is not associated with lactate decrease after fluid bolus in critically ill patients with hyperlactatemia: results from a prospective observational study

BACKGROUND

High ratio of the carbon dioxide veno-arterial difference to the oxygen arterial-venous difference (P_vaCO₂/C_avO₂) is associated with fluid bolus (FB) induced increase in oxygen consumption (VO₂). This study investigated whether P_vaCO₂/C_avO₂ was associated with decreases in blood-lactate levels FB in critically ill patients with hyperlactatemia.

METHODS

This prospective observational study examined adult patients in the intensive care unit (ICU) with lactate levels > 1.5 mmol/L who received FBs. Blood-lactate levels were measured before and after FB under unchanged metabolic, respiratory, and hemodynamic conditions. The primary outcome was blood-lactate levels after FB. Significant decreases in blood-lactate levels were considered as blood-lactate levels < 1.5 mmol/L or a decrease of more than 10% compared to baseline.

RESULTS

The study enrolled 40 critically ill patients, and their median concentration of blood lactate was 2.6 [IQR:1.9 - 3.8] mmol/L. There were 27 (68%) patients with P_vaCO₂/C_avO₂ ≥ 1.4 mmHg/ml, and 10 of them had an increase in oxygen consumption (dVO₂) ≥ 15% after FB, while 13 (32%) patients had P_vaCO₂/C_avO₂ < 1.4 mmHg/ml before FB, and none of them had dVO₂ ≥ 15% after FB. FB increased the cardiac index in patients with high and low preinfusion P_vaCO₂/C_avO₂ (13.4% [IQR: 8.3 - 20.2] vs. 8.8% [IQR: 2.9 - 17.4], p = 0.34). Baseline P_vaCO₂/C_avO₂ was not found to be associated with a decrease in blood lactate after FB (OR: 0.88 [95% CI: 0.39 - 1.98], p = 0.76). A positive correlation was observed between changes in blood lactate and baseline P_vaCO₂/C_avO₂ (r = 0.35, p = 0.02).

CONCLUSIONS

In critically ill patients with hyperlactatemia, P_vaCO₂/C_avO₂ before FB cannot be used to predict decreases in blood-lactate levels after FB. Increased P_vaCO₂/C_avO₂ is associated with less decrease in blood-lactate levels.

Pcv-aCO2 and procalcitonin levels for the early diagnosis of bloodstream infections caused by gram-negative bacteria

BACKGROUND

The central venous-to-arterial carbon dioxide difference (Pcv-aCO₂) is a biomarker for tissue perfusion, but the diagnostic value of Pcv-aCO₂ in bacteria bloodstream infections (BSI) caused by gram-negative (GN) bacteria remains unclear. This study evaluated the expression levels and diagnostic value of Pcv-aCO₂ and procalcitonin (PCT) in the early stages of GN bacteria BSI.

METHODS

Patients with BSI admitted to the intensive care unit at Guangdong Provincial People's Hospital between August 2014 and August 2017 were enrolled. Pcv-aCO₂ and PCT levels were evaluated in GN and gram-positive (GP) bacteria BSI patients.

RESULTS

A total of 132 patients with BSI were enrolled. The Pcv-aCO₂ (8.32 ± 3.59 vs 4.35 ± 2.24 mmHg p = 0.001) and PCT (30.62 ± 34.51 vs 4.92 ± 6.13 ng/ml p = 0.001) levels were significantly higher in the GN group than in the GP group. In the diagnosis of GN bacteria BSI, the area under the receiver operating characteristic curve (AUROC) for Pcv-aCO₂ was 0.823 (95% confidence interval (CI): 0.746-0.900). The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were 71.90%, 88.00%, 74.07% and 78.21%, respectively. The AUROC for PCT was 0.818 (95% CI: 0.745-0.890). The sensitivity, specificity, PPV and NPV were 57.90%, 94.67%, 71.93% and 74.67%, respectively.

CONCLUSIONS

Pcv-aCO₂ and PCT have similar and high diagnostic value for the early diagnosis of BSI caused by GN bacteria.

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.

Elevated Venous to Arterial Carbon Dioxide Gap and Anion Gap Are Associated with Poor Outcome in Cardiogenic Shock Requiring Extracorporeal Membrane Oxygenation Support

Optimal management of cardiogenic shock requiring extracorporeal membrane oxygenation (ECMO) is still an evolving area in which assessment and optimization of the microcirculation may be critically important. We hypothesized that the venous arterial carbon dioxide gap (P(v-a)CO2 gap); the ratio of this gap to arterio-venous oxygen content (P(v-a)CO2/C(a-v)O2 ratio) and the anion gap would be early indicators of microcirculatory status and useful parameters for outcome prediction during ECMO support. We retrospectively reviewed 31 cardiogenic shock patients requiring veno-arterial ECMO, calculating P(v-a)CO2 gap and P(v-a)CO2/C(a-v)O2 ratios in the first 36 hours and the final 24 hours of ECMO support. Sixteen patients (52%) survived and 15 (48%) died. After 24 hours of ECMO support, the P(v-a)CO2 gap (4.9 ± 1.5 vs. 6.8 ± 1.9 mm Hg; p = 0.004) and anion gap (5.2 ± 1.8 vs. 8.7 ± 2.7 mmol/L; p < 0.001) were significantly higher in non-survivors. In the final 24 hours of ECMO support, the P(v-a)CO2 gap (3.5 ± 1.6 vs. 10.5 ± 3.2 mm Hg; p < 0.001), P(v-a)CO2/C(a-v)O2 ratio (1.1 ± 0.5 vs. 2.7 ± 1.0; p < 0.001), anion gap (5.1 ± 3.0 vs. 9.3 ± 5.9 mmol/L; p = 0.02), and lactate (median 1.0 [interquartile range {IQR}: 0.7-1.5] vs. 2.8 [IQR: 1.7-7.7] mmol/L; p = <0.001) were all significantly lower in survivors. Increasing P(v-a)CO2 gap and increasing anion gap were significantly associated with increased risk of mortality. Optimum cut-points for prediction of mortality were 6 mm Hg for P(v-a)CO2 gap in combination with an anion gap above 6 mmol/L in the first 24 hours of ECMO in patients with cardiogenic shock requiring ECMO.

Acute hyperventilation increases oxygen consumption and decreases peripheral tissue perfusion in critically ill patients

PURPOSE

This study aimed to evaluate the effects of acute hyperventilation on central venous-to-arterial carbon dioxide tension difference (Pv-aCO₂), central venous oxygen saturation (ScvO₂), central venous-to-arterial CO₂ difference/arterial-central venous O₂ difference ratio (CO₂GAP-Ratio), and peripheral perfusion index (PI) in hemodynamically stable critically ill patients.

METHODS

Fifty-four mechanically ventilated patients were evaluated. The cardiac index, Pv-aCO₂, ScvO₂, CO₂GAP-Ratio, PI, and arterial and venous blood gas parameters were measured in the first set of measurements. Then, alveolar ventilation was increased by raising the respiratory rate (10 breaths/min). After a 30 min hyperventilation period, the second set of measurements was recorded.

RESULTS

Acute hyperventilation induces an increase in Pv-aCO₂ (from 3.87 ± 1.31 to 8.44 ± 1.81 mmHg, P < 0.001) and a decrease in ScvO₂(from 71.78 ± 4.82 to 66.47 ± 5.74%, P < 0.001). The CO₂GAP-Ratio was significantly increased(from 0.97 ± 0.40 to 1.74 ± 0.46, P < 0.001), and the PI showed a remarkable decrease caused by acute hyperventilation(from 1.82 ± 1.14 to 1.40 ± 0.99，P = 0.04). Hyperventilation-induced ∆_Pv-aCO₂ was negatively correlated with ∆PaCO₂(r = -0.572, P<0.001). The change in ∆_PaCO₂ was correlated with ∆_ScvO₂(r = 0.450, P<0.001). However, the left ventricular outflow tract velocity time integral (LVOT-VTI) remained unchanged during hyperventilation.

CONCLUSIONS

Acute hyperventilation induced an increase in oxygen consumption and decreased peripheral tissue perfusion in patients. For critical care patients, it is necessary to pay attention to the influence of hyperventilation on peripheral tissue perfusion indices and oxygen consumption indices.

Ratio of venous-to-arterial PCO2 to arteriovenous oxygen content difference during regional ischemic or hypoxic hypoxia

The purpose of the study was to evaluate the behavior of the venous-to-arterial CO₂ tension difference (ΔPCO₂) over the arterial-to-venous oxygen content difference (ΔO₂) ratio (ΔPCO₂/ΔO₂) and the difference between venous-to-arterial CO₂ content calculated with the Douglas’ equation (ΔCCO_2D) over ΔO₂ ratio (ΔCCO_2D/ΔO₂) and their abilities to reflect the occurrence of anaerobic metabolism in two experimental models of tissue hypoxia: ischemic hypoxia (IH) and hypoxic hypoxia (HH). We also aimed to assess the influence of metabolic acidosis and Haldane effects on the PCO₂/CO₂ content relationship. In a vascularly isolated, innervated dog hindlimb perfused with a pump-membrane oxygenator system, the oxygen delivery (DO₂) was lowered in a stepwise manner to decrease it beyond critical DO₂ (DO_2crit) by lowering either arterial PO₂ (HH-model) or flow (IH-model). Twelve anesthetized and mechanically ventilated dogs were studied, 6 in each model. Limb DO₂, oxygen consumption (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}\text{O}}_{2}$$\end{document}V˙O2), ΔPCO₂/ΔO₂, and ΔCCO_2D/ΔO₂ were obtained every 15 min. Beyond DO_2crit, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}\text{O}}_{2}$$\end{document}V˙O2 decreased, indicating dysoxia. ΔPCO₂/ΔO₂, and ΔCCO_2D/ΔO₂ increased significantly only after reaching DO_2crit in both models. At DO_2crit, ΔPCO₂/ΔO₂ was significantly higher in the HH-model than in the IH-model (1.82 ± 0.09 vs. 1.39 ± 0.06, p = 0.002). At DO_2crit, ΔCCO_2D/ΔO₂ was not significantly different between the two groups (0.87 ± 0.05 for IH vs. 1.01 ± 0.06 for HH, p = 0.09). Below DO_2crit, we observed a discrepancy between the behavior of the two indices. In both models, ΔPCO₂/ΔO₂ continued to increase significantly (higher in the HH-model), whereas ΔCCO_2D/ΔO₂ tended to decrease to become not significantly different from its baseline in the IH-model. Metabolic acidosis significantly influenced the PCO₂/CO₂ content relationship, but not the Haldane effect. ΔPCO₂/ΔO₂ was able to depict the occurrence of anaerobic metabolism in both tissue hypoxia models. However, at very low DO₂ values, ΔPCO₂/ΔO₂ did not only reflect the ongoing anaerobic metabolism; it was confounded by the effects of metabolic acidosis on the CO₂–hemoglobin dissociation curve, and then it should be interpreted with caution.

Biochemical markers for clinical monitoring of tissue perfusion

The assessment and monitoring of the tissue perfusion is extremely important in critical conditions involving circulatory shock. There is a wide range of established methods for the assessment of cardiac output as a surrogate of oxygen delivery to the peripheral tissues. However, the evaluation of whether particular oxygen delivery is sufficient to ensure cellular metabolic demands is more challenging. In recent years, specific biochemical parameters have been described to indicate the status between tissue oxygen demands and supply. In this review, the authors summarize the application of some of these biochemical markers, including mixed venous oxygen saturation (S_vO₂), lactate, central venous–arterial carbon dioxide difference (PCO₂ gap), and PCO₂ gap/central arterial-to-venous oxygen difference (C_a–vO₂) for hemodynamic assessment of tissue perfusion. The thorough monitoring of the adequacy of tissue perfusion and oxygen supply in critical conditions is essential for the selection of the most appropriate therapeutic strategy and it is associated with improved clinical outcomes.

Observational study of therapeutic bronchoscopy in critical hypoxaemic ventilated patients with COVID-19 at Mediclinic Midstream Private Hospital in Pretoria, South Africa

Background

Flexible fibreoptic bronchoscopy (FFB) has been used for years as a diagnostic and therapeutic adjunct for the diagnosis of potential airway obstruction as a cause of acute respiratory failure or in the management of hypoxaemia ventilated patients. In these circumstances, it is useful to evaluate airway patency or airway damage and for the management of atelectasis.

Objectives

To evaluate the use of FFB as a rescue therapy in mechanically ventilated patients with severe hypoxaemic respiratory failure caused by COVID-19.

Methods

We enrolled 14 patients with severe and laboratory confirmed COVID-19 who were admitted at Mediclinic Midstream Private Hospital intensive care unit in Pretoria, South Africa, in July 2020.

Results

FFB demonstrated the presence of extensive mucus plugging in 64% (n=9/14) of patients after an average of 7.7 days of mechanical ventilation. Oxygenation improved significantly in these patients following FFB despite profound procedural hypoxaemia.

Conclusion

Patients with severe COVID-19 pneumonia who have persistent hypoxaemia despite the resolution of inflammatory parameters may respond to FFB with removal of mucus plugs. We propose consideration of an additional pathophysiological acute phenotype of respiratory failure, the mucus type (M-type).

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.

Methylene blue administration in patients with refractory distributive shock - a retrospective study

Hemodynamic effectiveness of methylene blue (MB) was tested in patients with refractory distributive shock. A retrospective analysis of 20 critically-ill patients who developed refractory shock was performed. Patients were divided into two study groups as responders with positive hemodynamic response to MB administration (defined as 10% decrease of norepinephrine dose) and non-responders. Hemodynamic, outcome data and baseline tissue hypoxia-related parameters including ratio of central venous-to-arterial carbon dioxide tension to arterio-venous oxygen content (P(v-a)CO₂/C(a-v)O₂) were compared between the groups. There were 9 (45%) responders and 11 (55%) non-responders to single bolus of MB administration. Dose of MB did not differ between responders and non-responders (1.3 ± 0.5 vs. 1.3 ± 0.4 mg/kg respectively, P = 0.979). MB responders had lower baseline P(v-a) CO₂/C(a-v)O₂ (1.79 ± 0.73 vs. 3.24 ± 1.18, P = 0.007), higher pH (7.26 ± 0.11 vs. 7.16 ± 0.10, P = 0.037) and lower lactate levels at 12 hours post MB administration (3.4 ± 2.7 vs. 9.9 ± 2.2 mmol/L, P = 0.002) compared to non-responders. Methylene blue represents a non-adrenergic vasopressor with only limited effectiveness in patients with refractory distributive shock. Profound tissue hypoxia with high degree of anaerobic metabolism was associated with the loss of hemodynamic responsiveness to its administration.

Regional capnometry to evaluate the adequacy of tissue perfusion

Tissue hypoperfusion is a major cause of morbidity and mortality in critically ill patients but cannot always be detected by measuring standard whole-body hemodynamic and oxygen-related parameters (e.g., blood pressure, cardiac output, and central venous oxygen saturation). Preclinical and clinical studies have demonstrated that low-flow states are consistently associated with large increases in venous and tissue PCO₂. Monitoring regional PCO₂ with gastric tonometry (PgCO₂) is known to have independent prognostic value for predicting postoperative complications and mortality. The PgCO₂ gap might also be of value as a treatment target (endpoint) in critically ill patients. However, this tool has several limitations and has not yet been developed commercially, thus restricting its use. Regional capnography with sublingual and transcutaneous sensors might be an alternative noninvasive option for evaluating the adequacy of tissue perfusion in critically ill patients. However, further studies are needed to determine whether or not this monitoring technique is of value-particularly as an endpoint for guiding resuscitation. Bladder PCO₂, has only been evaluated in animal studies, and so remains to be validated in patients.

Relationship of relevant factors to P(v-a)CO2/C(a-v)O2 ratio in critically ill patients

Objective

This study investigated the factors related to the ratio of the venoarterial carbon dioxide tension difference [P(v-a)CO₂] to the arteriovenous oxygen content difference [C(a-v)O₂] (hereafter termed “Ratio”).

Methods

We retrospectively studied 1294 pairs of arterial and central venous blood gas measurements in 352 critically ill patients. A high Ratio was defined as > 1.68 based on published literature. Measurements were divided into four groups: Group I [P(v-a)CO₂ ≤ 6 mmHg/central venous oxygen saturation (ScvO₂) < 70%], Group II [P(v-a)CO₂ ≤ 6 mmHg/ScvO₂ ≥ 70%], Group III [P(v-a)CO₂ > 6 mmHg/ScvO₂ ≥ 70%], and Group IV [P(v-a)CO₂ > 6 mmHg/ScvO₂ < 70%].

Results

The Ratio’s strongest correlation was with P(v-a)CO₂ when compared with ScvO₂ and hemoglobin in all data. The P(v-a)CO₂ and ScvO₂ were significantly higher and the hemoglobin and arterial oxygen saturation were significantly lower in the high Ratio measurements (>1.68) than low Ratio measurements (≤1.68). The P(v-a)CO₂ was best for predicting a high Ratio. A P(v-a)CO₂ threshold of 7 mmHg was associated with a sensitivity of 41.77% and specificity of 90.62% for predicting a high Ratio.

Conclusions

A high P(v-a)CO₂ is the most relevant contributor to a high Ratio among all related factors in critically ill patients.

Combination of O2 and CO2-derived variables to detect tissue hypoxia in the critically ill patient

Oxygen-derived parameters have been traditionally used to guide resuscitation during shock states. Nevertheless, normalization of venous oxygen saturation does not exclude the persistence of tissue hypoperfusion and tissue hypoxia. Combination of O₂ and CO₂-derived variables has consistently demonstrated to be related with clinical outcomes and its variations could anticipate changes in lactate and also predict fluid responsiveness in terms of oxygen consumption. Here we discuss the potential mechanisms leading to increase the venous-to-arterial CO₂ (Cv-aCO₂) to arterial-to-venous O₂ content difference (Ca-vO₂), i.e., the Cv-aCO₂/Ca-vO₂ ratio, its potential clinical application, limitations and uncertainties. Finally, although biologically plausible, the potential applications of the Cv-aCO₂/Ca-vO₂ ratio in the clinical practice require to be confirmed.

How can CO2-derived indices guide resuscitation in critically ill patients?

Assessing the adequacy of oxygen delivery with oxygen requirements is one of the key-goal of haemodynamic resuscitation. Clinical examination, lactate and central or mixed venous oxygen saturation (S_vO₂ and S_cvO₂, respectively) all have their limitations. Many of them may be overcome by the use of the carbon dioxide (CO₂)-derived variables. The venoarterial difference in CO₂ tension ("ΔPCO₂" or "PCO₂ gap") is not an indicator of anaerobic metabolism since it is influenced by the oxygen consumption. By contrast, it reliably indicates whether blood flow is sufficient to carry CO₂ from the peripheral tissue to the lungs in view of its clearance: it, thus, reflects the adequacy of cardiac output with the metabolic condition. The ratio of the PCO₂ gap with the arteriovenous difference of oxygen content (PCO₂ gap/C_a-vO₂) might be a marker of anaerobiosis. Conversely to S_vO₂ and S_cvO₂, it remains interpretable if the oxygen extraction is impaired as it is in case of sepsis. Compared to lactate, it has the main advantage to change without delay and to provide a real-time monitoring of tissue hypoxia.

Relationship Analysis of Central Venous-to-arterial Carbon Dioxide Difference and Cardiac Index for Septic Shock

To analyze the relationship of the central venous-to-arterial carbon dioxide difference (p(cv-a)CO₂) and cardiac index (CI) in patients with septic shock, an observational study was conducted in intensive care unit (ICU). 66 consecutive patients with septic shock and central venous oxygen saturation (ScvO₂) ≥ 70% were included after early fluid resuscitation. Measurements were taken at a 6 h interval (T0, T6, T12, T18, T24) during first 24 h after their admission into ICU, including heart rate (HR), mean arterial pressure (MAP), central venous pressure (CVP), p(cv-a)CO₂, cardiac index(CI, L/(min•m²)) and ScvO₂. Patients were divided into low p(cv-a)CO₂ group (n = 35) and high p(cv-a)CO₂ group (n = 31) according to a threshold of 6 mmHg for p(cv-a)CO₂ at T0. As a result, at T0, T6, T12, T18 and T24, there were respectively significant differences between low and high p(cv-a)CO₂ groups for CI (4.1 ± 1.4 vs 2.4 ± 0.6, 4.4 ± 0.9 vs 2.8 ± 0.7, 4.1 ± 1.3 vs 2.9 ± 0.6, 4.0 ± 1.3 vs 2.7 ± 0.8, 4.2 ± 1.4 vs 2.9 ± 0.8, p < 0.001 at each time point), 28-day mortality rate was 38.7%(12/31) for high p(cv-a)CO₂ group and 22.8% (8/35) for low p(cv-a)CO₂ group (p > 0.05), there were significant differences for p(cv-a)CO₂ (p < 0.05) between low and high p(cv-a)CO₂ groups, no differences for HR, MAP, CVP, ScvO₂ (p > 0.05). CI was inversely correlated with p(cv-a)CO₂ value (r = −0.804, p < 0.001), but not for ScvO₂(r = 0.08, p > 0.05). Receiver operating characteristic curve analysis confirmed the correlation of p(cv-a)CO₂ with CI (AUC: 0.782;p < 0.001; 95% confidence interval: 0.710–0.853). The cut-off value for the best predictive value of CI ≥ 2.2 L/(min·m²) was p(cv-a)CO₂ of 5.55 mmHg or lower with a sensitivity of 85.7% and specificity of 66.8%. Hence CI measured with USCOM is inversely correlated with p(cv-a)CO₂ values in guiding the resuscitation of patients with septic shock.

Resuscitation incoherence and dynamic circulation-perfusion coupling in circulatory shock

OBJECTIVE

Poor tissue perfusion/cellular hypoxia may persist despite restoration of the macrocirculation (Macro). This article reviewed the literatures of coherence between hemodynamics and tissue perfusion in circulatory shock.

DATA SOURCES

We retrieved information from the PubMed database up to January 2018 using various search terms or/and their combinations, including resuscitation, circulatory shock, septic shock, tissue perfusion, hemodynamic coherence, and microcirculation (Micro).

STUDY SELECTION

The data from peer-reviewed journals printed in English on the relationships of tissue perfusion, shock, and resuscitation were included.

RESULTS

A binary (coherence/incoherence, coupled/uncoupled, or associated/disassociated) mode is used to describe resuscitation coherence. The phenomenon of resuscitation incoherence (RI) has gained great attention. However, the RI concept requires a more practical, systematic, and comprehensive framework for use in clinical practice. Moreover, we introduce a conceptual framework of RI to evaluate the interrelationship of the Macro, Micro, and cell. The RI is divided into four types (Type 1: Macro-Micro incoherence + impaired cell; Type 2: Macro-Micro incoherence + normal cell; Type 3: Micro-Cell incoherence + normal Micro; and Type 4: both Macro-Micro and Micro-cell incoherence). Furthermore, we propose the concept of dynamic circulation-perfusion coupling to evaluate the relationship of circulation and tissue perfusion during circulatory shock.

CONCLUSIONS

The concept of RI and dynamic circulation-perfusion coupling should be considered in the management of circulatory shock. Moreover, these concepts require further studies in clinical practice.

Pcv-aCO2/Ca-cvO2 Combined With Arterial Lactate Clearance Rate as Early Resuscitation Goals in Septic Shock

BACKGROUND

We aimed to investigate the prognostic significance of central venous-arterial carbon dioxide tension to arterial-central venous oxygen content ratio (Pcv-aCO₂/Ca-cvO₂) combined with arterial lactate clearance rate (LCR) as early resuscitation goals in septic shock.

MATERIALS AND METHODS

We enrolled 145 septic shock patients admitted to our department from March 2013 to May 2017 in this study. They all received an initial resuscitation therapy according to the Surviving Sepsis Campaign guideline, and were classified into 4 groups according to Pcv-aCO₂/Ca-cvO₂ and LCR at 6 hours after resuscitation (T6): Group A: Pcv-aCO₂/Ca-cvO₂ > 1.8, LCR < 30%; Group B: Pcv-aCO₂/Ca-cvO₂ > 1.8, LCR ≥ 30%; Group C: Pcv-aCO₂/Ca-cvO₂ ≤ 1.8, LCR < 30% and Group D: Pcv-aCO₂/Ca-cvO₂ ≤ 1.8, LCR ≥ 30%. General demographics, hemodynamic parameters, metabolic parameters, Acute Physiology and Chronic Health Evaluation II scores, Sequential Organ Failure Assessment scores, length of intensive care unit stay and 28-day mortality were compared among groups.

RESULTS

Group D had the lowest Acute Physiology and Chronic Health Evaluation II and Sequential Organ Failure Assessment score at day 3, the shortest intensive care unit stay and the lowest 28-day mortality. Kaplan-Meier survival curves up to day 28 showed group D had the longest median survival time. Pcv-aCO₂/Ca-cvO₂ and LCR at T6 were independent predictors of 28-day mortality. The area under ROC curve for Pcv-aCO₂/Ca-cvO₂ combined with LCR was significantly greater than either Pcv-aCO₂/Ca-cvO₂ or LCR alone (both P < 0.05).

CONCLUSIONS

Combination of Pcv-aCO₂/Ca-cvO₂ ratio and LCR is better than either alone to predict the adverse outcomes in septic shock, and may provide useful information for assessing the adequacy of resuscitation in early-stage septic shock.

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

BACKGROUND

Central venous oxygen saturation (ScvO₂), venous-arterial blood carbon dioxide partial pressures difference (Pv-aCO₂), venous-arterial blood carbon dioxide partial pressures difference/arterial-venous oxygen difference ratio (Pv-aCO₂/Ca-vO₂) and lactate are important parameters employed during shock resuscitation. We designed this study to confirm the effects of time delay and body temperature on measurements of these four parameters.

METHODS

Arterial and central venous blood samples were simultaneously drawn by plastic syringes via indwelling intra-arterial and central venous catheters from critically ill patients. Blood gas analyses were performed on both samples and repeated after 10, 20, 30, 40, 50 and 60 min. Patients were divided into a control group and a high temperature group according to whether the body temperature was greater than 38 °C.

RESULTS

A total of 30 critically ill patients were enrolled. There was a trend of increasing values for ScvO₂, Pv-aCO₂, Pv-aCO₂/Ca-vO₂ and lactate over time (P < 0.001). The ScvO₂ differences were all lower in high temperature group after 10, 20, 30, 40, 50 and 60 min when compared to the corresponding differences in the control group (P < 0.05). The differences in lactate values were slightly higher in the high temperature group, relative to the control group after 20, 30, 40, 50 and 60 min (P < 0.05).

CONCLUSIONS

Measurements of ScvO₂, Pv-aCO₂, lactate and Pv-aCO₂/Ca-vO₂ were affected by time delay or body temperature. We recommend that arterial and central venous blood gas samples be analyzed quickly within 10 min, especially for patients with body temperature <38 °C.

TRIAL REGISTRATION

ChiCTR, ChiCTR1800014484 . Registered 16 January 2018.

Oxygen-Flow-Pressure Targets for Resuscitation in Critical Hemodynamic Therapy

Far from traditional "vital signs," the field of hemodynamic monitoring (HM) is rapidly developing. However, it is also easy to misunderstand hemodynamic therapy as merely HM and some concrete bundles or guidelines for circulation support. Here, we describe the concept of "critical hemodynamic therapy" and clarify the concepts of the "therapeutic target" and "therapeutic endpoint" in clinical practice. Three main targets (oxygen delivery, blood flow, perfusion pressure) for resuscitation are reviewed in critically ill patients according to the sepsis guidelines and hemodynamic consensus. ScvO2 at least 70% has not been recommended as a directed target for initial resuscitation, and the directed target of mean arterial pressure (MAP) still is 65 mmHg. Moreover, the individual MAP target is underlined, and using flow-dependent monitoring to guide fluid infusion is recommended. The flow-directed target for fluid infusion might be a priority, but it remains controversial in resuscitation. The interpretation of these targets is necessary for adequate resuscitation and the correction of tissue hypoxia. The incoherence phenomenon of resuscitation (macrocirculation and microcirculation, tissue perfusion, and cellular oxygen utilization) is gaining increased attention, and early identification of these incoherences might be helpful to reduce the risk of over-resuscitation.

Respiratory quotient estimations as additional prognostic tools in early septic shock

Central venous-to-arterial carbon dioxide difference (P_cvaCO₂), and its correction by the arterial-to-venous oxygen content difference (P_cvaCO₂/C_avO₂) have been proposed as additional tools to evaluate tissue hypoxia. Since the relationship between pressure and content of CO₂ (CCO₂) might be affected by several factors, some authors advocate for the use of C_cvaCO₂/C_avO₂. The aim of the present study was to explore the factors that might intervene in the difference between P_cvaCO₂/C_avO₂ and C_cvaCO₂/C_avO₂, and to analyze their association with mortality. Observational study in a 30-bed mixed ICU. Fifty-two septic shock patients within the first 24 h of ICU admission were studied. After restoration of mean arterial pressure, hemodynamic and metabolic parameters were evaluated. A total of 110 sets of measurements were performed. Simultaneous P_cvaCO₂/C_avO₂ and C_cvaCO₂/C_avO₂ values were correlated, but agreement analysis showed a significant proportional bias. The difference between P_cvaCO₂/C_avO₂ and C_cvaCO₂/C_avO₂ was independently associated with pH, S_cvO₂, baseline C_cvaCO₂/C_avO₂ and hemoglobin. A stepwise regression analysis showed that pH was the single best predictor for the magnitude of such difference, with very limited effect of other variables. At inclusion, variables associated with ICU-mortality were lactate, pH, P_cvaCO₂/C_avO₂, and the difference between P_cvaCO₂/C_avO₂ and C_cvaCO₂/C_avO₂. Initial S_cvO₂, P_cvaCO₂, C_cvaCO₂/C_avO₂, and cardiac index were not different in survivors and non-survivors. In a population of early septic shock patients, simultaneous values of P_cvaCO₂/C_avO₂ and C_cvaCO₂/C_avO₂ were not equivalent, and the main determinant of the magnitude of the difference between these two parameters was pH. The P_cvaCO₂/C_avO₂ ratio was associated with ICU mortality, whereas C_cvaCO₂/C_avO₂ was not.

Sepsis: A Review of Advances in Management

Infections represent a common health problem in people of all ages. Usually, the response given to them is appropriate and so little treatment is needed. Sometimes, however, the response to the infection is inadequate and may lead to organ dysfunction; this is the condition known as sepsis. Sepsis can be caused by bacteria, fungi or viruses and at present there is no specific treatment; its management basically focuses on containing the infection through source control and antibiotics plus organ function support. This article reviews key elements of sepsis management, focusing on diagnosis, biomarkers and therapy. The main recent advance in therapy is the strategy of personalized medicine, based on a precise approach using biomarkers to identify specific individuals who are likely to benefit from more personalized attention.

Venoarterial PCO2-to-arteriovenous oxygen content difference ratio is a poor surrogate for anaerobic metabolism in hemodilution: an experimental study

Background

The identification of anaerobic metabolism in critically ill patients is a challenging task. Observational studies have suggested that the ratio of venoarterial PCO₂ (P_v–aCO₂) to arteriovenous oxygen content difference (C_a–vO₂) might be a good surrogate for respiratory quotient (RQ). Yet P_v–aCO₂/C_a–vO₂ might be increased by other factors, regardless of anaerobic metabolism. At present, comparisons between P_v–aCO₂/C_a–vO₂ and RQ have not been performed. We sought to compare these variables during stepwise hemorrhage and hemodilution. Since anemia predictably produces augmented P_v–aCO₂ and decreased C_a–vO₂, our hypothesis was that P_v–aCO₂/C_a–vO₂ might be an inadequate surrogate for RQ.

Methods

This is a subanalysis of a previously published study. In anesthetized and mechanically ventilated sheep (n = 16), we compared the effects of progressive hemodilution and hemorrhage by means of expired gases analysis.

Results

There were comparable reductions in oxygen consumption and increases in RQ in the last step of hemodilution and hemorrhage. The increase in P_v–aCO₂/C_a–vO₂ was higher in hemodilution than in hemorrhage (1.9 ± 0.2 to 10.0 ± 0.9 vs. 1.7 ± 0.2 to 2.5 ± 0.1, P < 0.0001). The increase in P_v–aCO₂ was lower in hemodilution (6 ± 0 to 10 ± 1 vs. 6 ± 0 to 17 ± 1 mmHg, P < 0.0001). Venoarterial CO₂ content difference and C_a–vO₂ decreased in hemodilution and increased in hemorrhage (2.6 ± 0.3 to 1.2 ± 0.1 vs. 2.8 ± 0.2 to 6.9 ± 0.5, and 3.4 ± 0.3 to 1.0 ± 0.3 vs. 3.6 ± 0.3 to 6.8 ± 0.3 mL/dL, P < 0.0001 for both). In hemodilution, P_v–aCO₂/C_a–vO₂ increased before the fall in oxygen consumption and the increase in RQ. P_v–aCO₂/C_a–vO₂ was strongly correlated with Hb (R² = 0.79, P < 0.00001) and moderately with RQ (R² = 0.41, P < 0.0001). A multiple linear regression model found Hb, RQ, base excess, and mixed venous oxygen saturation and PCO₂ as P_v–aCO₂/C_a–vO₂ determinants (adjusted R² = 0.86, P < 0.000001).

Conclusions

In hemodilution, P_v–aCO₂/C_a–vO₂ was considerably increased, irrespective of the presence of anaerobic metabolism. P_v–aCO₂/C_a–vO₂ is a complex variable, which depends on several factors. As such, it was a misleading indicator of anaerobic metabolism in hemodilution.

Assessment of macro- and micro-oxygenation parameters during fractional fluid infusion: A pilot study

PURPOSE

The main goal of this study was to assess whether maximal fluid infusion improves both oxygen delivery (DO₂) and micro-circulatory parameters during hemodilution. The secondary objective was to assess the ability of baseline micro-circulatory parameters to predict oxygen consumption (VO₂) response following fluid infusion.

MATERIALS AND METHODS

In a postoperative cardiac ICU, patients received repeated fluid infusion until stroke volume (SV) was maximized. Before and after each fluid expansion, macro- (DO₂, VO₂) and micro-circulatory oxygenation parameters were recorded [central venous oxygen saturation (ScVO₂), blood lactate, difference in veno-arterial carbon dioxide tension (P(v-a)CO₂), somatic and cerebral oxygen saturation (rSO₂)]. Patients were classified as VO₂-Responders or VO₂-Non-Responders according to an increase in VO₂ above or below 15%, respectively.

RESULTS

After maximal fluid infusion, all patients showed improved macro- and micro-circulatory oxygenation parameters, but VO₂-Responders had lower values (especially for ScVO₂ and cerebral rSO₂). Only baseline ScVO₂ and cerebral rSO₂ were useful to predict the VO₂ response to maximal fluid infusion (ROC_AUC 0.80 (95% CI: 0.54-0.95, P=0.012) and 0.83 (95% CI: 0.57-0.96, P=0.001).

CONCLUSIONS

Maximal fluid infusion improves macro- and micro-circulatory oxygenation parameters. For VO₂-Responders, only ScVO₂ and cerebral rSO₂ could serve as markers of tissue hypoxia.

Persistent hyperlactatemia-high central venous-arterial carbon dioxide to arterial-venous oxygen content ratio is associated with poor outcomes in early resuscitation of septic shock

OBJECTIVE

Several studies reported Pv-aCO₂/Ca-vO₂ ratio as a surrogate of VCO₂/VO₂ to detect global tissue hypoxia. The present study aimed to evaluate the prognostic value of Pv-aCO₂/Ca-vO₂ ratio combined with lactate levels during the early phases of resuscitation in septic shock.

METHODS

A retrospective study was conducted in 144 septic shock patients in a 30-bed mixed ICU. A Pv-aCO₂/Ca-vO₂ ratio>1.4 was considered abnormal. Patients were classified into four predefined groups according to lactate levels and Pv-aCO₂/Ca-vO₂ ratio after the first 6h of resuscitation. Sequential Organ Failure Assessment (SOFA) score at day 3 was assessed. A Kaplan-Meier curve showed the survival probabilities at day 28 using a log-rank test to evaluate the differences between groups. A receiver operating characteristics (ROC) curve evaluated the ability of lactate, Pv-aCO₂/Ca-vO₂ ratio and Pv-aCO₂/Ca-vO₂ ratio combined with lactate to predict mortality at day 28.

RESULTS

Combination of hyperlactatemia and high Pv-aCO₂/Ca-vO₂ ratio was associated with poor SOFA scores and low survival rates at day 28 (P<0.001). The Cox multivariate survival analysis demonstrated that Pv-aCO₂/Ca-vO₂ ratio and lactate at T6 were independent predictors of mortality at day 28. The area under the ROC curve of the Pv-aCO₂/Ca-vO₂ ratio combined with lactate for predicting mortality at day 28 was highest and superior to that of lactate and Pv-aCO₂/Ca-vO₂ ratios.

CONCLUSION

Combination of Pv-aCO₂/Ca-vO₂ ratio and lactate at early stages of resuscitation of septic shock can better predict the prognosis of patients. The Pv-aCO₂/Ca-vO₂ ratio may become a useful parameter supplementary to lactate in the resuscitation of septic shock.

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.

The value of blood lactate kinetics in critically ill patients: a systematic review

BACKGROUND

The time course of blood lactate levels could be helpful to assess a patient's response to therapy. Although the focus of published studies has been largely on septic patients, many other studies have reported serial blood lactate levels in different groups of acutely ill patients.

METHODS

We performed a systematic search of PubMed, Science Direct, and Embase until the end of February 2016 plus reference lists of relevant publications. We selected all observational and interventional studies that evaluated the capacity of serial blood lactate concentrations to predict outcome. There was no restriction based on language. We excluded studies in pediatric populations, experimental studies, and studies that did not report changes in lactate values or all-cause mortality rates. We separated studies according to the type of patients included. We collected data on the number of patients, timing of lactate measurements, minimum lactate level needed for inclusion if present, and suggested time interval for predictive use.

RESULTS

A total of 96 studies met our criteria: 14 in general ICU populations, five in general surgical ICU populations, five in patients post cardiac surgery, 14 in trauma patients, 39 in patients with sepsis, four in patients with cardiogenic shock, eight in patients after cardiac arrest, three in patients with respiratory failure, and four in other conditions. A decrease in lactate levels over time was consistently associated with lower mortality rates in all subgroups of patients. Most studies reported changes over 6, 12 or 24 hrs, fewer used shorter time intervals. Lactate kinetics did not appear very different in patients with sepsis and other types of patients. A few studies suggested that therapy could be guided by these measurements.

CONCLUSIONS

The observation of a better outcome associated with decreasing blood lactate concentrations was consistent throughout the clinical studies, and was not limited to septic patients. In all groups, the changes are relatively slow, so that lactate measurements every 1-2 hrs are probably sufficient in most acute conditions. The value of lactate kinetics appears to be valid regardless of the initial value.