Using pCO2 Gap in the Differential Diagnosis of Hyperlactatemia Outside the Context of Sepsis: A Physiological Review and Case Series

Prehospital blood gas analyses in acute patients treated by a ground-based physician-manned emergency unit: a cohort study

BACKGROUND

The prehospital patients treated by ambulances and mobile emergency care units (MECU) are potentially critically ill or injured. Knowing the risks of serious outcomes in these patients is important for guiding their treatment. Some settings allow for prehospital arterial blood gas analyses. This study aimed to assess the outcomes of prehospital patients in relation to their prehospitally measured lactate, pH, and CO2 levels. The primary outcome was 7-day mortality.

METHODS

This register-based cohort study included patients with one or more prehospital blood gas analyses during their prehospital treatment by a physician-manned MECU, from January 2015 to December 2018. The blood samples were analyzed on an ABL90 Flex analyzer. Absolute values with percentages and odds ratios (OR) with 95% confidence intervals (CI) were calculated for the primary and secondary outcomes within prespecified subgroups.

RESULTS

The study included 745 patients, with an overall 7-day mortality rate of 20.0%.

LACTATE LEVEL

The 7-day mortality rates were 11.5% in patients with normal lactate levels (< 2.0 mmol/L), 14.4% with intermediate lactate levels (2.0-3.9 mmol/L), and 33.0% with high lactate levels (≥ 4.0 mmol/L). This corresponded to an OR of 1.30 (95% CI: 0.75-2.24) in the intermediate lactate group (2.0-3.9 mmol/L) and an OR of 3.77 (95% CI: 2.44-5.85) in the high lactate group (≥ 4.0 mmol/L), compared to the reference group with normal lactate.

PH LEVEL

The ORs of 7-day mortality rates were 4.82 (95% CI: 3.00-7.75) in patients with blood pH of < 7.35 and 1.33 (95% CI: 0.65-2.72) in patients with blood pH > 7.45, compared to the reference group with normal pH (7.35-7.45). CO2 LEVEL : The ORs of 7-day mortality rates were 2.54 (95% CI: 1.45-4.46) in patients with blood CO2 of < 4.3 kPa and 2.62 (95% CI: 1.70-4.03) in patients with blood CO2 > 6.0 kPa, compared to the reference group with normal CO2 (4.3-6.0 kPa).

CONCLUSIONS

This study found a strong correlation between increasing 7-day mortality rates and high blood lactate levels, low levels of pH, and abnormal CO2 blood levels, in prehospital patients undergoing prehospital blood analysis.

Treatment of Hyperlactatemia in Acute Circulatory Failure Based on CO2-O2-Derived Indices: Study Protocol for a Prospective, Multicentric, Single, Blind, Randomized, Superiority Study (The LACTEL Study)

Background

Hyperlactatemia is a biological marker of tissue hypoperfusion with well-known diagnostic, prognostic, and therapeutic implications in shock states. In daily clinical practice, it is difficult to find out the exact mechanism underlying hyperlactatemia. Central venous to arterial CO₂ difference (pCO₂ gap) is a better parameter of tissue hypoperfusion than the usual ones (clinical examination and mixed venous saturation). Furthermore, the ratio between the pCO₂ gap and p(v–a)CO₂/C(a–v)O₂ may be a promising indicator of anaerobic metabolism, allowing for the identification of different causes of tissue hypoxia and hyperlactatemia. The main aim of the study is to demonstrate that initial hemodynamic resuscitation based on an algorithm integrating the pCO₂ gap and p(v–a)CO₂/C(a–v)O₂ ratio vs. usual clinical practice in acute circulatory failure improves lactate clearance.

Methods

LACTEL is a randomized, prospective, multicentric, controlled study. It compares the treatment of hyperlactatemia using an algorithm based on the pCO₂ gap and P(v–a)CO₂/C(a–v)O₂ ratio vs. usual clinical practice in acute circulatory failure. A total of 90 patients were enrolled in each treatment group. The primary endpoint is the number of patients with a lactate clearance of more than 10% 2 h after inclusion. Lactate levels were monitored during the first 48 h of treatment as hemodynamic parameters, biological markers of organ failure, and 28-day mortality.

Discussion

pCO₂ derivate indices may be of better interest than routine clinical indices to differentiate causes of hyperlactatemia and diagnose anaerobiosis. LACTEL results will provide clinical insights into the role of these indices in the early hemodynamic management of acute circulatory failure in the ICU.

Clinical Trial Registration

www.clinicaltrials.gov; identifier: NCT05032521.

Pathophysiology and clinical implications of the veno-arterial PCO2 gap

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2021. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2021 . Further information about the Annual Update in Intensive Care and Emergency Medicine is available from https://link.springer.com/bookseries/8901 .

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.