European Journal of Cardiovascular Medicine

Lactate is a byproduct of anaerobic metabolism and a recognised biomarker for critical illness. outcomes. Traditionally measured through arterial sampling, lactate is used for diagnosis, prognosis, and treatment response monitoring in critically ill patients (1). However, arterial sampling can be technically challenging and painful, prompting interest in less invasive alternatives like venous sampling. The present study aims to determine the agreement between arterial and venous lactate levels and assess the utility of venous lactate in critical care triage and monitoring. (2) The prognostic significance of lactate in sepsis and critical illness has been well-documented. A notable study by Mahmoodpoor et al. (2019) explored the relationship between arterial and venous lactate levels during the initial six hours of resuscitation in septic shock patients. Their findings revealed a Elevated lactate levels are indicative of tissue hypoperfusion and correlate with poor clinical strong correlation between the two, with venous lactate values consistently higher by a mean bias of 0.684 mmol/L. Importantly, arterial lactate levels ≥3.2 mmol/L combined with a lactate clearance of <20% were shown to be powerful predictors of ICU mortality. These results highlight the clinical value of venous lactate as a less invasive yet dependable surrogate, particularly in emergency settings where timely interventions are critical.(3) A study by Yasufumi Oi et al. (2022) demonstrated a strong correlation (r = 0.93) between peripheral venous lactate (PVL) and arterial lactate (AL) levels in critically ill patients. Although the values did not perfectly align, PVL was highly effective in predicting important arterial lactate thresholds. Notably, a PVL level below 2 mmol/L was found to reliably exclude an AL level above 2 mmol/L, thereby reducing the necessity for invasive arterial sampling. However, the study also noted that this agreement diminished as lactate levels increased, indicating the need for additional research to assess the full clinical utility of venous measurements at higher concentrations.(4) While venous blood gas (VBG) analysis offers a less invasive option for lactate assessment, ongoing debates remain about its accuracy and reliability as a substitute for arterial lactate in all clinical scenarios.(5)

The present study aims to determine the agreement between arterial and venous lactate levels and assess the utility of venous lactate in critical care triage and monitoring.

Study Design & Setting:

A prospective observational study was conducted at AVMC&H, Puducherry, between June 2023 and November 2024 in the Emergency Department and Intensive Care Units.

Participants:

102 critically ill patients aged >16 years, with NEWS scores >5. Exclusion: pregnancy, bleeding diathesis.

Procedure:

Simultaneous ABG and VBG samples were taken at presentation and after 2 hours of resuscitation. ABG was obtained through arterial puncture and VBG at the time of placement of peripheral venous cannula.

Statistics Analysis:

Paired t-tests, Bland-Altman analysis, and linear regression were used. Significance set at p < 0.05.

Demographics: A total of 102 critically ill patients were included in this study. The mean age of participants was 53.1 years with a standard deviation of 14.1 years, indicating a middle-aged to elderly population. The gender distribution showed a predominance of male participants, with 58.8% males and 41.2% females.

Diagnosis distribution: Among the clinical diagnoses, sepsis was the most prevalent, affecting 35.3% of the study population, followed by pulmonary edema (10.8%), septic shock (9.8%), and myocardial infarction (7.8%). Diabetic ketoacidosis (DKA) and lower respiratory tract infections (LRTI) each contributed to 5.9% of cases. Other conditions such as polytrauma, cerebrovascular events, and scrub typhus were less frequently encountered. This variety in diagnoses reflects a broad spectrum of critically ill presentations managed in the emergency department

Most of the patients (90.2%) were initially assessed in the Emergency Medicine Department (EMD), while a smaller proportion (9.8%) were admitted to the Intensive Care Unit (ICU), highlighting the ED's central role in managing acute critical conditions. Vital parameters recorded at presentation revealed a mean respiratory rate of 21.9 breaths per minute, heart rate of 121.3 beats per minute, blood pressure of 90 mmHg, and oxygen saturation (SpO2) of 89%, indicating hemodynamic instability and hypoxia in several cases. The mean body temperature was noted to be 99.91°F.

The level of consciousness assessed by the AVPU scale showed that 54.9% were alert on admission, while 24.5% responded to verbal stimuli, 9.8% to pain, and 10.8% were unresponsive, indicating varying degrees of altered mental status among the critically ill patients.

The NEWS score, which is a composite early warning score, ranged predominantly from 7 to 9. Specifically, 31.4% of patients had a score of 7, 28.4% scored 8, and 11.8% had a score of 9. A minority had scores at the extremes, with 2% scoring 5 and 4.9% scoring the maximum of 15, reflecting the diversity in illness severity.

Initial blood gas analysis showed that the mean arterial lactate level was 2.81 mmol/L with a standard deviation of 2.16, while the venous lactate level was notably higher at 3.98 mmol/L (SD ±2.46). Following 2 hours of resuscitation, there was a marked improvement in both values, with arterial lactate decreasing to 1.81 mmol/L (SD ±1.28) and venous lactate to 2.72 mmol/L (SD ±1.91). These findings indicate a favorable physiological response to resuscitative efforts.

Correlation analysis revealed a strong linear relationship between arterial and venous lactate levels, with a Pearson correlation coefficient of 0.92. Bland-Altman analysis demonstrated a mean bias of 1.1 mmol/L, suggesting that although venous lactate tends to overestimate arterial lactate, the correlation is consistent and clinically significant

The study confirms a strong correlation between arterial and venous lactate values, especially at lower levels (≤2 mmol/L), suggesting venous lactate can be a reliable screening tool. However, divergence increases at higher values, reaffirming the role of ABG in critical lactate interpretation. VBG sampling offers advantages in terms of reduced patient discomfort, procedural simplicity, and efficiency in emergency settings.

The findings align with prior research showing that venous lactate is a practical alternative for initial evaluation, particularly for ruling out hyperlactatemia. Nonetheless, when venous lactate exceeds 2 mmol/L, ABG remains the gold standard.

Venous lactate levels correlate strongly with arterial levels and may serve as a reliable, less invasive initial screening tool in emergency and critical care. However, arterial sampling remains indispensable for accurate diagnosis and management at higher lactate levels.

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