The baseline clinical characteristics of the patients are presented in Table 1. Twenty-three (25.3%) patients experienced bradycardia during their surgery using spinal anesthesia and intravenous dexmedetomidine. The remaining 68 patients were included in the comparison group.
Table 1. Univariable analysis of baseline characteristics
|
Bradycardia
(n=23)
|
Without bradycardia
(n=68)
|
P value
|
Sex
Male
Female
|
13 (56.5%)
10 (43.5%)
|
45 (66.2%)
23 (33.8%)
|
0.561
|
Age (years)
|
30 [25; 55]
|
47.5 [33; 56]
|
0.059
|
BMI (kg/m2)
|
25.2±3.1
|
24.9±3.0
|
0.647
|
ASA PS
1
2
|
19 (82.6%)
4 (17.4%)
|
47 (69.1%)
21 (30.9%)
|
0.326
|
Previous medical history
Hypertension
Diabetes
Liver disease
|
1 (4.3%)
1 (4.3%)
4 (17.4%)
|
11 (16.2%)
5 (7.4%)
8 (11.8%)
|
0.274
0.987
|
Abnormal ECG
|
5 (21.7%)
|
17 (25.0%)
|
0.973
|
Baseline SBP (mmHg)
|
125.0 [116.5; 132.5]
|
130.0 [122.5; 140.0]
|
0.051
|
Baseline DBP (mmHg)
|
75.0 [67.5; 82.0]
|
80.0 [73.5; 85.0]
|
0.123
|
Baseline HR (bpm)
|
65.0 [56.5; 69.5]
|
75.0 [65.0; 82.0]
|
0.000
|
Sensory level
>T6 level
<T7 level
|
5 (21.7%)
18 (78.3%)
|
8 (11.8%)
60 (88.2%)
|
0.403
|
Duration of surgery (min)
|
85.0 [60.0; 105.0]
|
65.0 [40.0; 97.5]
|
0.144
|
Duration of anesthesia (min)
|
130.0 [107.5; 155.0]
|
107.5 [82.5; 145.0]
|
0.104
|
Tourniquet time (min)
|
85.0 [60.0; 107.5]
|
62.5 [35.0; 87.5]
|
0.004
|
Recovery time (min)
|
35.0 [27.0; 61.0]
|
42.0 [32.0; 56.0]
|
0.483
|
Dexmedetomidine
Loading dose (mcg/kg)
Maintenance dose (mcg/kg/h)
Total infused dose (mcg/kg)
|
0.7 [ 0.7; 0.7]
0.3 [ 0.3; 0.3]
28.6 [20.8; 37.4]
|
0.7 [ 0.7; 0.7]
0.3 [ 0.3; 0.3]
23.4 [14.7; 33.0]
|
0.724
0.507
0.191
|
Values are presented as numbers (%), medians with [interquartile ranges], or mean±standard deviation. BMI, body mass index; ASA PS, American Society of Anesthesiologists physical status; ECG, electrocardiography; SBP, systolic blood pressure; DBP, diastolic blood pressure; HR, heart rate; bpm, beats per minute
In univariate analysis, there were no differences in sex; age; body mass index; ASA physical status; previous medical history of hypertension, diabetes, or liver disease ECG abnormality; baseline SBP and DBP; sensory blockade level; surgery and anesthesia duration; recovery time; and loading, maintenance, or total infused dose of dexmedetomidine between patients with and without bradycardia. A significant difference was observed in the baseline HR and tourniquet time between patients with and without bradycardia (P<0.05).
In addition to these two significant variables, six additional variables were identified as potential effect modifiers in a multivariable logistic regression analysis model (Table 2). Only baseline HR and tourniquet time were found to be significant independent risk factors of bradycardia during spinal anesthesia combined with dexmedetomidine infusion. The lower the baseline HR, the greater the risk of developing bradycardia (OR 0.89, 95% CI 0.82–0.96, P=0.005). A longer tourniquet time was a significant risk factor for bradycardia (OR 1.06, 95% CI 1.02–1.1, P=0.004).
Table 2. Logistic regression analysis of selected variables
|
Odd ratio (95% CI)
|
P value
|
Age
|
0.97 (0.92–1)
|
0.099
|
Baseline SBP
|
0.98 (0.92–1.03)
|
0.388
|
Baseline DBP
|
1.01 (0.93–1.09)
|
0.871
|
Baseline HR
|
0.89 (0.82–0.96)
|
0.005*
|
Duration of surgery
|
1.05 (0.99–1.13)
|
0.118
|
Duration of anesthesia
|
0.97 (0.94–1)
|
0.061
|
Tourniquet time
|
1.06 (1.02–1.1)
|
0.004*
|
Total infused dose of dexmedetomidine
|
0.88 (0.75–1.04)
|
0.123
|
SBP, systolic blood pressure; DBP, diastolic blood pressure; HR, heart rate; CI, confidence interval
Our study also showed a correlation between low baseline HR and bradycardia development. In terms of age, patients who developed bradycardia had a median age of 30 years, which was lower than that of patients who did not develop bradycardia; however, the difference was not statistically significant. High sensory block levels >T6 were identified in 21.7% and 11.8% of patients with and without bradycardia, respectively, but there was no statistical significance.
Patients with bradycardia had longer surgery and anesthesia duration than those who did not develop bradycardia, but the difference was not statistically significant. The total infused dose of dexmedetomidine was higher in patients with bradycardia than in those without.
In this study, a long tourniquet time was demonstrated to be a significant risk factor for the development of bradycardia during spinal anesthesia combined with dexmedetomidine sedation (OR 10.6, P=0.004).
We performed a receiver operating curve analysis and found that the optimal baseline HR threshold for predicting bradycardia was < 73 bpm (sensitivity, 91.3%; specificity, 57.4%). The AUC for a cutoff value of 73 bpm was moderately accurate for predicting bradycardia (AUC, 0.764; 95% CI 0.663–0.865, P<0.001) (Figure 1). The tourniquet time threshold for estimating the development of bradycardia was >72.5 min (sensitivity 69.6%; specificity 61.8%). A cut-off value of 72.5 min was moderately accurate for estimating the risk of bradycardia (AUC, 0.701; 95% CI 0.577–0.826; P=0.004) (Figure 2).