Median Effective Concentration of Ropivacaine for Femoral Nerve Block Maintaining Motor Function During Knee Arthroscopy in Two Age Groups

Figures & data

Figure 1 Femoral nerve blocking guided by ultrasound. Arrow indicates the femoral nerve, which is surrounded by injected ropivacaine.

Figure 2 Flow diagram for the up-and-down method.

Table 1 Group Characteristics and Demographic Data

	Group 1	Group 2	P-value
	(n=39)	(n=41)
	(18–60)	(>60)
Age (yr)***	37.90±9.31	65.46±4.27	<0.001
Sex (M/F)	20/19	14/27	0.121
BMI (kg/m^2)	26.58±4.61	25.73±2.95	0.332
ASA physical status^a (I/II)***	29/10	14/27	<0.001
Duration of operation (min)	45.00 (10)	45.00 (20)	0.305
Operation subtypes^a			0.395
Partial meniscectomy	28/39	27/41
Meniscus formation and suture	6/39	4/41
Removal of loose bodies	2/39	7/41
Arthroscopic debridement	3/39	3/41

Notes: Data for age and BMI are presented as mean±SD. Data for duration of operation are presented as median (inter-quartile range). ^aData are presented as the number of patients. ***Differences between groups are significant, P <0.001.

Abbreviations: ASA, American Society of Anesthesiologists; BMI, body mass index.

Figure 3 Femoral nerve block responses to predetermined ropivacaine concentrations using the Dixon’s up-and-down method in consecutive Group 1 (in black) and Group 2 (in grey) patients. Only patients from the first negative to positive response crossover in the 2 respective age groups were included. These sequential arrays included seven crossovers from negative to positive responses in 2 groups (Group 1, aged 18–60 years; Group 2, >60 years). Solid circle, negative response concentration; open circle, positive response concentration.

Table 2 Sensory Blockade Data

Variables	Group 1	Group 2	P-value
	(n=39)	(n=41)
	(18–60)	(>60)
Onset time of sensory blockade (min)	5.31±1.88	4.61±2.40	0.153
Resting VAS scores 24 hours after surgery	0 (1.0)	1 (2.0)	0.177
Dynamic VAS scores 24 hours after surgery	3 (2.0)	3 (1.5)	0.448
Duration of sensory blockade (h)	19.00(8.00)	13.00(11.50)	0.111
Number of patients that required supplementary analgesia^a
Ketorolac tromethamine 30 mg^a	16/39	17/41	0.968
Tramadol 100 mg^a	4/39	6/41	0.800

Notes: Data for time-to-onset of sensory block are shown as mean±SD. Data for duration of sensory block and VAS scores are shown as median (inter-quartile range). ^aData are presented as the number of patients.

Abbreviation: VAS, visual analogue scale.

Table 3 Postoperative Analgesic Data in Differential Nerve Block

	Group 1^a	Group 2^b	P-value
Subjects, n	12	12
Resting VAS scores 24 hours after surgery	0 (1.00)	1.5 (2.75)	0.099
Dynamic VAS scores 24 hours after surgery	3 (1.00)	3.5 (1.75)	0.086
Number of patients that required supplementary analgesia^c
Ketorolac tromethamine 30 mg^c	2/12	6/12	0.193
Tramadol 100 mg^c	1/12	3/12	0.590

Notes: ^aGroup 1 defined as patients 18 to 60 years of age; ^bGroup 2 defined as patients older than 60 years. Data for resting and dynamic VAS scores are presented as median (inter-quartile range). ^cData are presented as the number of patients.