A mini volume loading test (mVLT) using 2.5-mL kg−1 boluses of crystalloid for indication of perioperative changes in hydration status

Abstract

Background and objective: A mini volume loading test (mVLT) evaluating hemodilution during step-wise crystalloid infusion has established that the arterio-capillary plasma dilution difference is inversely correlated to the body hydration level of subjects. This observational study aimed to test whether this can be replicated in a perioperative setting using a 2.5-mL kg−1 boluses. Materials and methods: The mVLT was performed before induction of regional anesthesia and 24 h later. Step-wise infusion implied six mini fluid challenges. These consisted of 2.5-mL kg−1 boluses of Ringer's acetate infused during 2–3 min and followed by 5-min periods with no fluids. Invasive (arterial) and noninvasive (capillary) measurements of hemoglobin were performed before and after each mini fluid challenge, as well as after a 20-min period without fluid following the last bolus. Hemoglobins were used to calculate the arterio-capillary plasma dilution difference which is used as an indication of changes in body hydration level. The 24-h fluid balance was calculated. Results: Subjects were 69.5 (6.0) years old, their height was 1.62 m (1.56–1.65), weight was 87.0 kg (75.5–97.5) and body mass index (BMI) was 33.5 kg/m2 (31.0–35.1). Preoperative arterio-capillary plasma dilution difference was significantly higher than postoperative (0.085 [0.012–0.141] vs. 0.006 [−0.059 to 0.101], P = 0.000). The perioperative 24-h fluid balance was 1976 mL (870–2545). Conclusions: The mVLT using 2.5-mL kg−1 boluses of crystalloid was able to detect the higher postoperative body hydration level in total knee arthroplasty patients.

Keywords

• Mini volume loading test
• Hydration level
• Perioperative fluid balance
• Noninvasive hemoglobin
• Stroke volume