Bioelectrical impedance analysis of body composition for the anesthetic induction dose of propofol in older patients

Abstract

Background: Older people are currently the fastest growing segment of the worldwide population. The present study aimed to estimate propofol dose in older patients based on size descriptors measured by bioelectrical impedance analysis (BIA).

Methods: A cross sectional study in adult and older patients with body mass index equal to or lower than 35 kg/m² was carried out. BIA and Clinical Frail Scale scoring were performed during pre-operative evaluation. Propofol infusion was started at 2000 mg/h until loss of consciousness (LOC) which was defined by "loss of eye-lash reflex" and "loss of response to name calling". Total dose of propofol at LOC was recorded. Propofol plasma concentration was measured using gas chromatography/ion trap-mass spectrometry.

Results: Forty patients were enrolled in the study. Total propofol dose required to LOC was lower in Age ≥ 65 group and a higher plasma propofol concentration was measured in this group. 60% of old patients were classified as "apparently vulnerable" or "frail" and narrow phase angle values were associated with increasing vulnerability scores. In the Age ≥ 65 group, the correlation analysis showed that the relationship between propofol dose and total body weight (TBW) scaled by the corresponding phase angle value is stronger than the correlation between propofol dose and TBW or fat free mass (FFM).

Conclusions: This study demonstrates that weight-based reduction of propofol is suitable in older patients; however FFM was not seen to be more effective than TBW to predict the propofol induction dose in these patients. Guiding propofol induction dose according to baseline frailty score should also be considered to estimate individualized dosage profiles. Determination of phase angle value appears to be an easy and reliable tool to assess frailty in older patients.

Trial registration: ClinicalTrials.gov Identifier: NCT02713698 . Registered on 23 February 2016.

Keywords: Frailty; Older patients; Phase angle; Propofol induction dose.

Fig. 1

Bland–Altman plots - Janmahasatian formula vs. body impedance analysis in Age < 65 group (a) and Age ≥ 65 group (b). The 95% limits of agreement are shown as dashed lines. BMI | Body mass index (kg/m²)

Fig. 2

Phase angle reference values. a, b and c represent the distribution of phase angle values according to age, BMI and sex. Vertical dashed lines represent lower phase angle reference value in healthy adult population. d shows the distribution of the standardized phase angle, z score, [z score = (observed phase angle-mean reference phase angle)/SD reference phase angle] for specific age, sex and BMI categories. BMI | Body mass index (kg/m²). F | Female. M | Male. SD | Standard deviation

Fig. 3

Standardized phase angle (z-score) and clinical frail scale scores for each patient. CFS | Clinical frail scale

Fig. 4

Propofol dose at LOC. a, b and c show, respectively, the correlations of propofol induction dose with TBW, FFM and TBW•phase angle of Age < 65 group. d, e and f illustrate, respectively, the correlations of propofol induction dose with TBW, FFM and TBW•phase angle of Age ≥ 65 group. Grey line in a and d represents the function equivalent to the standard adult and older propofol dose (2 mg•TBW in a and 1mg•TBW in d), respectively. BMI | Body mass index. FFM | Fat free mass. LOC | Loss of consciousness. TBW | Total body weight