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

Background and objective. The mini volume loading test (mVLT) evaluating hemodilution during goal directed crystalloid infusion was able to discriminate between different hydration levels of healthy volunteers and detect pre-operative dehydration in patients. A 2.5 ml kg-1 and 5 ml kg-1 boluses were used in volunteers and patients, respectively. It was established that the arterio-capillary plasma dilution difference (acPDD) is inversely related to the hydration level of subjects. This study aimed to test if these same findings can be replicated in a perioperative setting using 2.5 ml kg-1 boluses.

Material and methods. The mVLT was part of a revised goal directed therapy (revGDT) protocol in total knee arthroplasty (TKA) patients. Before induction of spinal anesthesia and 24 hours later each subject received six mini fluid challenges. These consisted of 2.5 ml.kg-1 boluses of Ringer’s acetate infused over 2–3 min and followed by a 5 min periods with no fluids. Invasive (arterial) and non-invasive (capillary) measurements of hemoglobin were used to calculate the acPDD before and after each mini fluid challenge.

Results. Fifty four patients were enrolled and of these 48 (41 females and 7 males) completed the study. Pre-operative acPDD was significantly higher than post-operative (0.085 [0.012 to 0.141]) vs. 0.006 [-0.059 to 0.101]), P = 0.000. The perioperative 24-h fluid balance was 1976 [870 to 2545] ml.

Conclusions. The mVLT indicated higher post-operative hydration level in TKA patients. The 2.5 ml kg-1 boluses of crystalloid may be used in mVLT to assess the hydration status in the perioperative setting.

Correspondence to A. Andrijauskas Clinic of Anaesthesiology and Intensive Care, Faculty of Medicine, Vilnius University, Šiltnamių 2, 04130 Vilnius, Lithuania. E-mail address: audrius.andrijauskas@mf.vu.lt