Bioimpedance spectroscopy for assessment of volume status in patients before and after general anaesthesia

BackgroundTechnically assisted assessment of volume status before surgery may be useful to direct intraoperative fluid administration. We therefore tested a recently developed whole-body bioimpedance spectroscopy device to determine pre- to postoperative fluid distribution.MethodsUsing a three-compartment physiologic tissue model, the body composition monitor (BCM, Fresenius Medical Care, Germany) measures total body fluid volume, extracellular volume, intracellular volume and fluid overload as surplus or deficit of 'normal' extracellular volume. BCM-measurements were performed before and after standardized general anaesthesia for gynaecological procedures (laparotomies, laparoscopies and vaginal surgeries). BCM results were blinded to the attending anaesthesiologist and data analysed using the 2-sided, paired Student's t-test and multiple linear regression.ResultsIn 71 females aged 45 ± 15 years with body weight 67 ± 13 kg and Duration of anesthesia 154 ± 69 minutes [corrected] duration of anaesthesia 154 ± 68 min, pre- to postoperative fluid overload increased from -0.7 ± 1.1 L to 0.1 ± 1.0 L, corresponding to -5.1 ± 7.5% and 0.8 ± 6.7% of normal extracellular volume, respectively (both pConclusionsRoutine intraoperative fluid administration results in a significant, and clinically meaningful increase in the extracellular compartment. BCM-measurements yielded plausible results and may become useful to guide intraoperative fluid therapy in future studies

Demographic characteristics of the study population.

<p>Continuous variables are reported as mean ± standard deviation, (5^th and 95^th percentile); categorical variables are presented as counts and frequencies. Abbreviations: ASA = American Society of Anaesthesiologists’ physical status classification system, NYHA = New York Heart Association functional classification, PONV = postoperative nausea and vomiting, IV = intravenous. Net perioperative fluid balance = total perioperative intravenous fluid volume, corrected for urinary excretion and blood loss. *In 5 cases, the interval between the BCM-measurements was >60 minutes longer than the duration of anaesthesia, due to logistical reasons.</p><p>Demographic characteristics of the study population.</p

Association between net perioperative fluid balance and changes in pre- to postoperative extracellular volume, with multiple levels of adjustments.

<p>Multiple regression analysis: After stepwise adjustment the coefficients of determination (r²), the p-value¹ for the combined effect of all predictors for each model, the p-value² for the individual effect of a predictor and the correlation coefficient (Beta) represent the association between the outcome and the predictor variables. Boldface indicating statistical significance (p<0.05).</p><p>Association between net perioperative fluid balance and changes in pre- to postoperative extracellular volume, with multiple levels of adjustments.</p

Associations between pre- to postoperative changes in volume status and net perioperative fluid balance.

<p>Scatter plots. Regression equations are as follows: <b>A</b> Change in Extracellular Volume = 0.73×Net Perioperative Fluid Balance –0.37. <b>B</b> Change in Total Body volume = 0.91×Net Perioperative Fluid Balance –0.43. <b>C</b> No linear correlation between Change in Intracellular Volume and Net Perioperative Fluid Balance. <b>D</b> No linear correlation between Change in Intracellular Volume and Change in Extracellular Volume. Pearson correlation test. R² = Coefficient of determination.</p

Vital signs, volume status and body composition before and after anaesthesia.

<p>Delta was calculated by subtracting any patient’s preoperative value from the postoperative value. Significance was determined by Student’s t-test (p<0.05). Italics: Data were incomplete for body temperature (number of missing values: N = 7 [pre], N = 20 [post], N = 20 [delta]), serum protein (number of missing values: N = 15 [pre], N = 39 [post], N = 46 [delta]), serum albumin (number of missing values: N = 42 [pre], N = 40 [post], N = 54 [delta]), C-reactive protein (number of missing values: N = 11 [pre], N = 39 [post], N = 42 [delta]) and Capillary Leak Index (number of missing values: N = 43 [pre], N = 43 [post], N = 55 [delta]), despite significant findings. Note that postoperative laboratory measurements were usually performed on the day after surgery (not simultaneous to the postoperative BCM-measurement). Bold: findings with p<0.05. Abbreviations: ECV = Extracellular Volume, ICV = Intracellular Volume, TBV = Total Body Fluid Volume.</p><p>Vital signs, volume status and body composition before and after anaesthesia.</p