Evaluation of Propofol Anesthesia in Morbidly Obese Children and Adolescents

Vidya Chidambaran; Senthilkumar Sadhasivam; Jeroen Diepstraten; Hope Esslinger; Shareen Cox; Beverly M Schnell; Paul Samuels; Thomas Inge; Alexander A Vinks; Catherijne A Knibbe

Disclosures

BMC Anesthesiol. 2013;13(8) 

In This Article

Results

Demographics

Patient and surgical characteristics are presented in Table 1. Of 23 patients enrolled, 20 were fully evaluable. One patient withdrew shortly before the procedure (no samples); and two patients were excluded because of difficulty obtaining blood samples from existing intravenous lines. 19 patients met criteria for morbid obesity.

Propofol and Opioid Doses

Hourly propofol and fentanyl equivalent doses, as well as calculated induction doses, are presented in Table 2. Data from four patients were excluded from the calculation of propofol induction dose, due to the use of boluses and protocol deviations from standardized infusion for induction. Only linear regression of induction dose and weight scalars was found to be significant. They are depicted in Figure 1. LBM were the most highly correlated to the induction dose with least root MSE. Means and standard deviations (SD) of administered propofol maintenance rates and rates corresponding to BIS 40–60 based on TBW (Figure 2A) and ABW (Figure 2B) are presented. Number of paired observations for the latter calculation from data of 8 patients, was 116; evaluable BIS values 0.5–3 minutes apart were included to maximize available data in that BIS range. Infusion rates administered were consistently higher than those that were found to correlate with BIS 40–60.

Figure 1.

Linear regression of propofol induction dose to weight scalars. Linear regression trendlines for correlation of posthoc calculated induction dose of propofol (titrated to loss of verbal contact) with weight scalars are shown. The correlation coefficients, Root Mean Square Errors (Root MSE) and p-values for the correlations were found to be R2 = 0.58, Root MSE = 45.92, p = 0.0068 for Lean Body Mass (LBM), R2 = 0.54, Root MSE = 47.82, p = 0.01 for Adjusted Body Weight (ABW) and R2 = 0.5, Root MSE = 49.61, p = 0.0143 for Total Body Weight (TBW).

Figure 2.

Maintenance propofol infusion rates. Data analysis of propofol infusion rates used during the maintenance phase (in μg kg−1 h−1 on the left Y-axis and mg kg−1 h−1 on the right Y-axis) based on total body weight (TBW) and adjusted body weight (ABW) are depicted in (A) and (B) respectively. The red solid circles and the grey shaded area within the error bands (red dotted lines) represent the means and SD of actual administered infusion rates over time, while the green dots and vertical lines represent the means and SD of infusion rates corresponding to BIS values of 40–60.

Hemodynamics

Figure 3 shows the mean and SD of the percentage difference from baseline for HR (1A), DBP (1B), SBP (1C) and MAP (1D) from 5 minutes prior to start of propofol to 200 minutes of propofol anesthesia. SBP, MAP and DBP values declined by about 20%, reaching a nadir at about 15 minutes after induction and returning to baseline values in 30–40 minutes. Overall, average percentage variability from baseline was 20%. Labetolol was used in one patient and the data from this patient were excluded from this analysis.

Figure 3.

Variability of hemodynamic parameters over time during propofol anesthesia. In this figure, time profiles of variability of heart rate (A), diastolic blood pressure (DBP) (B), systolic blood pressure (SBP) (C) and mean blood pressure (MAP) (D) are presented as the mean (black solid circles) and standard deviation (SD) {grey shaded area between error bands (black dotted lines)} of the % change from baseline for the stated parameter, plotted every 5 minutes during 200 minutes of propofol anesthesia. The first dot on the timeline represents the start of propofol induction (baseline) and hence % variability is 0%.

Intraoperative Propofol Plasma Concentrations and BIS Scores

An average of 14 venous samples was collected per patient. In Figure 4A, the means ± SD of propofol concentrations during different phases of anesthesia are shown. BIS data were not retrievable for one patient due to software malfunction. Figure 4B shows the means and SD of BIS values recorded every 5 minutes during the maintenance phase of propofol anesthesia (excluding 1st ten minutes after induction and the last ten minutes of emergence for every patient). It is noteworthy that the BIS values were in the range of 20–40 for 89.4% and less than 20 for another 3.9% of the maintenance phase. Nineteen of twenty patients had BIS levels less than 40 for at least 20 minutes of maintenance.

Figure 4.

Summary of propofol concentrations during different phases of propofol anesthesia and BIS values over time. (A) represents the means (black solid circles for induction phase, squares for maintenance and inverted triangles for emergence phase) and standard deviations (SD) (black vertical lines) of propofol concentrations during different phases of anesthesia; The propofol concentration during the induction phase (first 15 minutes) was 7.0 ± 4.1 mg.l−1 (n = 16). The mean (SD)(number of samples) for propofol concentrations collected during 15–30, 30–60, 60–90, 90–120 and >120 minute time intervals of maintenance anesthesia were 6.8(1.8)(26), 6.9(2.5)(41), 5.8(2.2)(36), 5.4(2.7)(15) and 6.1(3.2)(29) mg.l−1 respectively. (B) shows the means (black solid circles) and SD (black vertical lines) of blinded BIS values during 10–200 minutes of maintenance phase of propofol anesthesia. Grey shaded areas depict range of propofol concentrations reported to be associated with BIS 50 in children (A) (3.2–5.4 mg.l-1: Riguozzo et. al, 2010) and BIS values generally considered to infer adequate depth of anesthesia (B) (46–60) for this population.

Postoperative Propofol Concentrations and RSS

Propofol concentrations declined to 2.4(1.2) mg.l−1 during the first hour of emergence and remained at 1.1(0.6) mg.l−1 during the second hour after the discontinuation of propofol infusion (Figure 4A). Ramsay sedation scores > 4 were present up to 30 minutes after arrival to the PACU, which indicates deep sedation. Spearman Rank correlation between RSS and the propofol concentrations was found to be 0.65 (p < 0.0001).

Other Clinical Data

Time to induction, eye opening and incidence of awareness are presented in Table 2. Six patients had RAE in the PACU – one patient had airway obstruction requiring airway manipulation to correct mild hypoxemia, and five others had an extended requirement for oxygen (>120 minutes) to maintain saturation > 90%. BMI was significantly associated with the likelihood of having an adverse respiratory event in the PACU (p = 0.05). For every unit increase in BMI, there was a corresponding increase of 14% in the odds of having an adverse respiratory event.

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