ORIGINAL ARTICLE
A Randomized Comparison Between Single- and Triple-Injection Subparaneural Popliteal Sciatic Nerve Block Worakamol Tiyaprasertkul, MD,* Francisca Bernucci, MD,† Andrea P. González, MD,† Prangmalee Leurcharusmee, MD,‡ Murray S. Yazer, MD, FRCPC,‡ Wallaya Techasuk, MD,‡ Vanlapa Arnuntasupakul, MD,‡ Daniel Chora de la Garza, MD,‡ Roderick J. Finlayson, MD, FRCPC,‡ and De QH Tran, MD, FRCPC‡ Background and Objectives: This prospective randomized trial compared ultrasound-guided single-injection (SI) and triple-injection (TI) subparaneural popliteal sciatic nerve block. We hypothesized that multiple injections are not required when local anesthetic (LA) is deposited under the paraneurium because the latter entraps LA molecules, ensuring circumferential spread around the nerve. Therefore, in addition to comparable success rates, we also expected similar total anesthesia-related times (sum of performance and onset times) and designed this study as an equivalency trial. Methods: Ultrasound-guided subparaneural posterior popliteal sciatic nerve block was carried out in 100 patients. In the SI group, LA was deposited at a single location between the tibial and peroneal nerves. In the TI group, LA was injected between the tibial and peroneal divisions, medial to the tibial nerve, and lateral to the common peroneal nerve. The total LA volume (15 mL) and mixture (lidocaine 1%–bupivacaine 0.25%– epinephrine 5 μg/mL) were identical in all subjects. The performance time, number of needle passes, and adverse events (paresthesia, neural edema) were recorded by the (nonblinded) investigator supervising the block. A blinded observer evaluated the success rate (sensorimotor composite score ≥6/8 points at 30 minutes) as well as the onset time and contacted patients 7 days after the surgery to inquire about persistent numbness or motor deficit. Results: Both techniques provided comparable success rates (92%) and total anesthesia-related times (17.1–19.7 minutes). Expectedly, the SI group required fewer needle passes (1 vs 3; P < 0.001) and a shorter needling time (3.0 ± 2.3 minutes vs 4.0 ± 2.3 minutes; P = 0.025). The TI group displayed a shorter onset time (12.5 ± 7.9 minutes vs 15.8 ± 7.9 minutes; P = 0.027). The performance time, procedural discomfort, and incidence of paresthesia (14%–20%) were similar between the 2 groups. Sonographic neural swelling was detected in 2 subjects in the SI group. In both cases, the needle was carefully withdrawn and the injection was completed uneventfully. Follow-up of the 100 subjects 1 week after surgery revealed no residual numbness or motor deficit. Conclusions: Ultrasound-guided SI and TI subparaneural popliteal sciatic nerve blocks result in comparable success rates and total anesthesiarelated times. Expectedly, the SI technique requires fewer needle passes. (Reg Anesth Pain Med 2015;40: 315–320)
From the *Maharaj Nakorn Chiang Mai Hospital, Department of Anesthesia, Chiang Mai University, Chiang Mai, Thailand; †Department of Anesthesia, Hospital de Carabineros, Santiago, Chile; and ‡Montreal General Hospital, Department of Anesthesia, McGill University, Montreal, Quebec, Canada. Accepted for publication February 27, 2015. Address correspondence to: De QH Tran, MD, FRCPC, Montreal General Hospital, Department of Anesthesia 1650 Ave Cedar, D10-144, Montreal, Quebec, Canada H3G-1A4 (e‐mail: [email protected]). The authors declare no conflict of interest. Funding: None Copyright © 2015 by American Society of Regional Anesthesia and Pain Medicine ISSN: 1098-7339 DOI: 10.1097/AAP.0000000000000253
F
or sciatic nerve block, 2 randomized trials have thus far demonstrated that circumferential injection of local anesthetic (LA) around the nerve provides a higher success rate and shorter onset time than LA deposition at a single location next to the nerve.1,2 In recent years, multiple studies have described a new method for sciatic block, whereby LA is injected under the paraneurium, a fascial layer that surrounds the sciatic nerve from its origin to its division into common peroneal and tibial branches.3 Cumulated evidence suggests that subparaneural LA injection provides a reliable sciatic nerve block.4–9 Furthermore, in our practice, we have also observed that circumferential injection is seldom necessary when LA is deposited inside the paraneural sheath: the paraneurium seems to entrap LA molecules, thus ensuring circumferential spread around the nerve. The aim of this prospective randomized trial was to compare for the first time single-injection (SI) and triple-injection (TI) techniques for ultrasound (US)-guided subparaneural popliteal sciatic nerve block. In keeping with our empirical experience, we expected similar success rates as well as comparable total anesthesia-related times (sum of performance and onset times) and designed the current study as an equivalency trial.
METHODS After obtaining ethics committee approval (McGill University Health Center, Montreal, Canada; Hospital de Carabineros, Department of Anesthesia, Santiago, Chile; and Department of Anesthesia, Chiang Mai University, Chiang Mai, Thailand) and written informed consent, patients undergoing surgery of the ankle or foot were prospectively enrolled in 3 teaching hospitals (Montreal General Hospital, Hospital de Carabineros, and Maharaj Nakorn Chiang Mai Hospital). Inclusion criteria were age between 18 and 70 years, American Society of Anesthesiologists (ASA) status I to III, and body mass index between 20 and 35 kg/m2. Exclusion criteria were inability to consent to the study, preexisting neuropathy, coagulopathy, hepatic or renal failure, allergy to LA, pregnancy, and prior surgery in the popliteal fossa. After arrival in the induction room, an 18- or 20-gauge intravenous catheter was placed in the upper limb, and standard intravenous premedication (0.03 mg/kg of midazolam and 0.6 μg/kg of fentanyl) was administered to all patients. Supplemental oxygen (nasal cannulae at 4 L/min) and standard ASA monitoring were applied throughout the procedure. Using a computer-generated sequence of random numbers and a sealed envelope technique, 100 patients were randomly allocated to receive an US-guided SI or TI subparaneural popliteal sciatic nerve block. All blocks were performed by residents, fellows, or staff anesthesiologists. Independently of their status, operators were considered experts if, before the start of the study, they possessed an experience level equal or superior to 60 US-guided subparaneural popliteal sciatic nerve blocks (SI or TI technique). Otherwise, they were considered trainees.10 All blocks were supervised by one of the
Regional Anesthesia and Pain Medicine • Volume 40, Number 4, July-August 2015
315
Copyright © 2015 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Tiyaprasertkul et al
Regional Anesthesia and Pain Medicine • Volume 40, Number 4, July-August 2015
coauthors. The portable US machine (M-Turbo; Sonosite, Bothell, Washington), 6- to 13-MHz linear probe, and LA mixture (lidocaine 1%–bupivacaine 0.25%–epinephrine 5 μg/mL) were identical in all subjects. For both techniques, patients were placed in the prone position. In the popliteal fossa, at the level of the skin crease, the tibial nerve was first identified with US. Subsequently, it was followed rostrally until it merged with the common peroneal nerve. The neural bifurcation was identified as the point where both branches, situated contiguously, displayed a bilobular pattern4,8,9 (Fig. 1A). An initial skin wheal was raised with 3 mL of lidocaine 1%. Using an out-of-plane technique, a 22-gauge 5-cm block needle (StimuQuick Echo; Arrow International Inc, Reading, Pennsylvania) was advanced until its tip was positioned between the tibial and peroneal nerves inside the paraneural sheath (Fig. 1B). In the SI group, the entire LA volume (15 mL) was injected. In the TI
group, only 5 mL was deposited between the 2 nerves; using an out-of-plane technique, 2 additional 5-mL aliquots were injected medial to the tibial nerve and lateral to the common peroneal nerve (Fig. 1B). For both groups, care was taken to ensure that neural swelling (defined as an increase in the cross-sectional surface of the nerve) did not occur during the injection process.11 If neural swelling was detected by US, the needle was carefully withdrawn before resuming the injection. During the performance of the block, the imaging time (defined as the temporal interval between contact of the US probe with the patient and the acquisition of a satisfactory picture) and the needling time (defined as the temporal interval between the start of the skin wheal and the end of LA injection through the block needle) were recorded by the (nonblinded) investigator supervising the block. Performance time was defined as the sum of imaging and needling times. The number of needle passes
FIGURE 1. A, Neural bifurcation. B, Ultrasonographic targets. CP indicates common peroneal nerve; S, single-injection technique; T, triple-injection technique; Tb, tibial nerve.
316
© 2015 American Society of Regional Anesthesia and Pain Medicine
Copyright © 2015 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Regional Anesthesia and Pain Medicine • Volume 40, Number 4, July-August 2015
TABLE 1. Patient Characteristics
Age, y Sex (male/female) BMI, kg/m2 ASA physical status (I/II/III) Types of surgery (ankle/foot)
Single Injection (n = 50)
Triple Injection (n = 50)
P
40.3 ± 15.3 28/22 26.2 ± 3.6 26/24/0
41.4 ± 14.6 28/22 25.4 ± 3.3 32/18/0
0.709 >0.999 0.250 0.224
27/23
32/18
0.309
Continuous variables are presented as mean ± SD; categorical variables are presented as counts. BMI indicates body mass index.
was also recorded by the same investigator. The initial needle insertion counted as the first pass. Any subsequent needle advancement that was preceded by a retraction of at least 10 mm counted as an additional pass.12 The incidences of vascular puncture and sonographic swelling were also noted by the supervising coauthor. Measurements of sciatic nerve blockade were carried out every 5 minutes, until 30 minutes, by a blinded observer. Sensory blockade was graded according to a 3-point scale using ice: 0 = no block; 1 = analgesia (patient can feel touch, not cold); 2 = anesthesia (patient cannot feel touch). Sensory blockade of the tibial and peroneal nerves was assessed on the plantar and dorsolateral aspects of the foot, respectively.4,8,9 Motor blockade was also graded with a 3-point scale: 0 = no block; 1 = paresis; 2 = paralysis. Motor blockade of the tibial and peroneal nerves was assessed using plantar and dorsiflexion, respectively.4,8,9 Overall, the maximal composite score was 8 points. The block was considered a success if a minimal composite score of 6 points was achieved within 30 minutes of LA injection.9 Onset time was defined as the time needed to obtain a successful block. Thus, the total anesthesia-related time was equal to the sum of
Subparaneural Popliteal Block
performance and onset times. The blinded observer also recorded the patient’s age, gender, height, and weight, as well as the occurrence of paresthesia and the level of procedural pain during block placement using a 10-cm visual analog scale (0 cm = no pain; 10 cm = worst, imaginable pain). Because thigh tourniquets are routinely used by our surgeons, patients also received general or neuraxial anesthesia. If continuous LA infusion was required to manage postoperative pain (as decided by the treating anesthesiologist), perineural catheters were inserted with US using a 17-gauge Tuohy needle and a standard kit (StimuCath; Teleflex Medical, Research Triangle Park, North Carolina). Placement of popliteal catheters did not impact the recording of data because it was carried out during the 5-minute interval between the end of LA injection through the 22-gauge block needle and the first sensorimotor assessment of the block. During the insertion of the perineural catheter, no additional LA (or saline) was injected. Furthermore, procedure-related pain and occurrence of paresthesia were assessed prior to skin puncture with the 17-gauge Tuohy needle. If the surgery involved the medial aspect of the foot or ankle, a US-guided saphenous nerve block was also performed.13 One week after the surgery, all patients were contacted by the blinded investigator to inquire about complications such as persistent numbness/paresthesia or motor deficit.
Statistical Analysis Our working hypothesis was that multiple injections are not required when LA is deposited inside the paraneural sheath. Thus, in addition to comparable success rates, we also expected similar total anesthesia-related times (sum of performance and onset times) and designed the current study as an equivalency trial. In a previous study, the SI technique provided a total anesthesia-related time of 23.1 ± 8.8 minutes.9 We deemed that a 30% difference in total time (6.9 minutes) carries little clinical significance. Thus, a calculated sample size of 44 patients per group was required for a statistical power of 0.90 and a type I error of 0.025. Because onset and total times can only be
TABLE 2. Block Performance Data Single Injection (n = 50)
Triple Injection (n = 50)
Imaging time, min Needling time, min Performance time, min Onset time, min Total anesthesia-related time, min
1.0 ± 1.1 3.0 ± 2.3 3.9 ± 2.9 15.8 ± 7.9 19.7 ± 9.0
0.7 ± 0.9 4.0 ± 2.3 4.8 ± 2.9 12.5 ± 7.9 17.1 ± 9.2
Success at 30 min, n (%) Composite score at 30 min Operator’s experience level (trainees/experts) No. passes Block-related pain (scale 0–10) Paresthesia, n (%) Vascular puncture, n (%) Neural edema, n (%)
46 (92) 7 (4–8) 17/33 1 (1–6) 2 (0–7) 7 (14) 0 (0) 2 (4)
46 (92) 8 (5–8) 18/32 3 (3–8) 3 (0–7) 10 (20) 0 (0) 0 (0)
P 0.084 0.025 0.157 0.027 0.166 95% CI of the difference of the means (−1.1 to 6.4) >0.999 0.112 0.834
A Randomized Comparison Between Single- and Triple-Injection Subparaneural Popliteal Sciatic Nerve Block Worakamol Tiyaprasertkul, MD,* Francisca Bernucci, MD,† Andrea P. González, MD,† Prangmalee Leurcharusmee, MD,‡ Murray S. Yazer, MD, FRCPC,‡ Wallaya Techasuk, MD,‡ Vanlapa Arnuntasupakul, MD,‡ Daniel Chora de la Garza, MD,‡ Roderick J. Finlayson, MD, FRCPC,‡ and De QH Tran, MD, FRCPC‡ Background and Objectives: This prospective randomized trial compared ultrasound-guided single-injection (SI) and triple-injection (TI) subparaneural popliteal sciatic nerve block. We hypothesized that multiple injections are not required when local anesthetic (LA) is deposited under the paraneurium because the latter entraps LA molecules, ensuring circumferential spread around the nerve. Therefore, in addition to comparable success rates, we also expected similar total anesthesia-related times (sum of performance and onset times) and designed this study as an equivalency trial. Methods: Ultrasound-guided subparaneural posterior popliteal sciatic nerve block was carried out in 100 patients. In the SI group, LA was deposited at a single location between the tibial and peroneal nerves. In the TI group, LA was injected between the tibial and peroneal divisions, medial to the tibial nerve, and lateral to the common peroneal nerve. The total LA volume (15 mL) and mixture (lidocaine 1%–bupivacaine 0.25%– epinephrine 5 μg/mL) were identical in all subjects. The performance time, number of needle passes, and adverse events (paresthesia, neural edema) were recorded by the (nonblinded) investigator supervising the block. A blinded observer evaluated the success rate (sensorimotor composite score ≥6/8 points at 30 minutes) as well as the onset time and contacted patients 7 days after the surgery to inquire about persistent numbness or motor deficit. Results: Both techniques provided comparable success rates (92%) and total anesthesia-related times (17.1–19.7 minutes). Expectedly, the SI group required fewer needle passes (1 vs 3; P < 0.001) and a shorter needling time (3.0 ± 2.3 minutes vs 4.0 ± 2.3 minutes; P = 0.025). The TI group displayed a shorter onset time (12.5 ± 7.9 minutes vs 15.8 ± 7.9 minutes; P = 0.027). The performance time, procedural discomfort, and incidence of paresthesia (14%–20%) were similar between the 2 groups. Sonographic neural swelling was detected in 2 subjects in the SI group. In both cases, the needle was carefully withdrawn and the injection was completed uneventfully. Follow-up of the 100 subjects 1 week after surgery revealed no residual numbness or motor deficit. Conclusions: Ultrasound-guided SI and TI subparaneural popliteal sciatic nerve blocks result in comparable success rates and total anesthesiarelated times. Expectedly, the SI technique requires fewer needle passes. (Reg Anesth Pain Med 2015;40: 315–320)
From the *Maharaj Nakorn Chiang Mai Hospital, Department of Anesthesia, Chiang Mai University, Chiang Mai, Thailand; †Department of Anesthesia, Hospital de Carabineros, Santiago, Chile; and ‡Montreal General Hospital, Department of Anesthesia, McGill University, Montreal, Quebec, Canada. Accepted for publication February 27, 2015. Address correspondence to: De QH Tran, MD, FRCPC, Montreal General Hospital, Department of Anesthesia 1650 Ave Cedar, D10-144, Montreal, Quebec, Canada H3G-1A4 (e‐mail: [email protected]). The authors declare no conflict of interest. Funding: None Copyright © 2015 by American Society of Regional Anesthesia and Pain Medicine ISSN: 1098-7339 DOI: 10.1097/AAP.0000000000000253
F
or sciatic nerve block, 2 randomized trials have thus far demonstrated that circumferential injection of local anesthetic (LA) around the nerve provides a higher success rate and shorter onset time than LA deposition at a single location next to the nerve.1,2 In recent years, multiple studies have described a new method for sciatic block, whereby LA is injected under the paraneurium, a fascial layer that surrounds the sciatic nerve from its origin to its division into common peroneal and tibial branches.3 Cumulated evidence suggests that subparaneural LA injection provides a reliable sciatic nerve block.4–9 Furthermore, in our practice, we have also observed that circumferential injection is seldom necessary when LA is deposited inside the paraneural sheath: the paraneurium seems to entrap LA molecules, thus ensuring circumferential spread around the nerve. The aim of this prospective randomized trial was to compare for the first time single-injection (SI) and triple-injection (TI) techniques for ultrasound (US)-guided subparaneural popliteal sciatic nerve block. In keeping with our empirical experience, we expected similar success rates as well as comparable total anesthesia-related times (sum of performance and onset times) and designed the current study as an equivalency trial.
METHODS After obtaining ethics committee approval (McGill University Health Center, Montreal, Canada; Hospital de Carabineros, Department of Anesthesia, Santiago, Chile; and Department of Anesthesia, Chiang Mai University, Chiang Mai, Thailand) and written informed consent, patients undergoing surgery of the ankle or foot were prospectively enrolled in 3 teaching hospitals (Montreal General Hospital, Hospital de Carabineros, and Maharaj Nakorn Chiang Mai Hospital). Inclusion criteria were age between 18 and 70 years, American Society of Anesthesiologists (ASA) status I to III, and body mass index between 20 and 35 kg/m2. Exclusion criteria were inability to consent to the study, preexisting neuropathy, coagulopathy, hepatic or renal failure, allergy to LA, pregnancy, and prior surgery in the popliteal fossa. After arrival in the induction room, an 18- or 20-gauge intravenous catheter was placed in the upper limb, and standard intravenous premedication (0.03 mg/kg of midazolam and 0.6 μg/kg of fentanyl) was administered to all patients. Supplemental oxygen (nasal cannulae at 4 L/min) and standard ASA monitoring were applied throughout the procedure. Using a computer-generated sequence of random numbers and a sealed envelope technique, 100 patients were randomly allocated to receive an US-guided SI or TI subparaneural popliteal sciatic nerve block. All blocks were performed by residents, fellows, or staff anesthesiologists. Independently of their status, operators were considered experts if, before the start of the study, they possessed an experience level equal or superior to 60 US-guided subparaneural popliteal sciatic nerve blocks (SI or TI technique). Otherwise, they were considered trainees.10 All blocks were supervised by one of the
Regional Anesthesia and Pain Medicine • Volume 40, Number 4, July-August 2015
315
Copyright © 2015 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Tiyaprasertkul et al
Regional Anesthesia and Pain Medicine • Volume 40, Number 4, July-August 2015
coauthors. The portable US machine (M-Turbo; Sonosite, Bothell, Washington), 6- to 13-MHz linear probe, and LA mixture (lidocaine 1%–bupivacaine 0.25%–epinephrine 5 μg/mL) were identical in all subjects. For both techniques, patients were placed in the prone position. In the popliteal fossa, at the level of the skin crease, the tibial nerve was first identified with US. Subsequently, it was followed rostrally until it merged with the common peroneal nerve. The neural bifurcation was identified as the point where both branches, situated contiguously, displayed a bilobular pattern4,8,9 (Fig. 1A). An initial skin wheal was raised with 3 mL of lidocaine 1%. Using an out-of-plane technique, a 22-gauge 5-cm block needle (StimuQuick Echo; Arrow International Inc, Reading, Pennsylvania) was advanced until its tip was positioned between the tibial and peroneal nerves inside the paraneural sheath (Fig. 1B). In the SI group, the entire LA volume (15 mL) was injected. In the TI
group, only 5 mL was deposited between the 2 nerves; using an out-of-plane technique, 2 additional 5-mL aliquots were injected medial to the tibial nerve and lateral to the common peroneal nerve (Fig. 1B). For both groups, care was taken to ensure that neural swelling (defined as an increase in the cross-sectional surface of the nerve) did not occur during the injection process.11 If neural swelling was detected by US, the needle was carefully withdrawn before resuming the injection. During the performance of the block, the imaging time (defined as the temporal interval between contact of the US probe with the patient and the acquisition of a satisfactory picture) and the needling time (defined as the temporal interval between the start of the skin wheal and the end of LA injection through the block needle) were recorded by the (nonblinded) investigator supervising the block. Performance time was defined as the sum of imaging and needling times. The number of needle passes
FIGURE 1. A, Neural bifurcation. B, Ultrasonographic targets. CP indicates common peroneal nerve; S, single-injection technique; T, triple-injection technique; Tb, tibial nerve.
316
© 2015 American Society of Regional Anesthesia and Pain Medicine
Copyright © 2015 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Regional Anesthesia and Pain Medicine • Volume 40, Number 4, July-August 2015
TABLE 1. Patient Characteristics
Age, y Sex (male/female) BMI, kg/m2 ASA physical status (I/II/III) Types of surgery (ankle/foot)
Single Injection (n = 50)
Triple Injection (n = 50)
P
40.3 ± 15.3 28/22 26.2 ± 3.6 26/24/0
41.4 ± 14.6 28/22 25.4 ± 3.3 32/18/0
0.709 >0.999 0.250 0.224
27/23
32/18
0.309
Continuous variables are presented as mean ± SD; categorical variables are presented as counts. BMI indicates body mass index.
was also recorded by the same investigator. The initial needle insertion counted as the first pass. Any subsequent needle advancement that was preceded by a retraction of at least 10 mm counted as an additional pass.12 The incidences of vascular puncture and sonographic swelling were also noted by the supervising coauthor. Measurements of sciatic nerve blockade were carried out every 5 minutes, until 30 minutes, by a blinded observer. Sensory blockade was graded according to a 3-point scale using ice: 0 = no block; 1 = analgesia (patient can feel touch, not cold); 2 = anesthesia (patient cannot feel touch). Sensory blockade of the tibial and peroneal nerves was assessed on the plantar and dorsolateral aspects of the foot, respectively.4,8,9 Motor blockade was also graded with a 3-point scale: 0 = no block; 1 = paresis; 2 = paralysis. Motor blockade of the tibial and peroneal nerves was assessed using plantar and dorsiflexion, respectively.4,8,9 Overall, the maximal composite score was 8 points. The block was considered a success if a minimal composite score of 6 points was achieved within 30 minutes of LA injection.9 Onset time was defined as the time needed to obtain a successful block. Thus, the total anesthesia-related time was equal to the sum of
Subparaneural Popliteal Block
performance and onset times. The blinded observer also recorded the patient’s age, gender, height, and weight, as well as the occurrence of paresthesia and the level of procedural pain during block placement using a 10-cm visual analog scale (0 cm = no pain; 10 cm = worst, imaginable pain). Because thigh tourniquets are routinely used by our surgeons, patients also received general or neuraxial anesthesia. If continuous LA infusion was required to manage postoperative pain (as decided by the treating anesthesiologist), perineural catheters were inserted with US using a 17-gauge Tuohy needle and a standard kit (StimuCath; Teleflex Medical, Research Triangle Park, North Carolina). Placement of popliteal catheters did not impact the recording of data because it was carried out during the 5-minute interval between the end of LA injection through the 22-gauge block needle and the first sensorimotor assessment of the block. During the insertion of the perineural catheter, no additional LA (or saline) was injected. Furthermore, procedure-related pain and occurrence of paresthesia were assessed prior to skin puncture with the 17-gauge Tuohy needle. If the surgery involved the medial aspect of the foot or ankle, a US-guided saphenous nerve block was also performed.13 One week after the surgery, all patients were contacted by the blinded investigator to inquire about complications such as persistent numbness/paresthesia or motor deficit.
Statistical Analysis Our working hypothesis was that multiple injections are not required when LA is deposited inside the paraneural sheath. Thus, in addition to comparable success rates, we also expected similar total anesthesia-related times (sum of performance and onset times) and designed the current study as an equivalency trial. In a previous study, the SI technique provided a total anesthesia-related time of 23.1 ± 8.8 minutes.9 We deemed that a 30% difference in total time (6.9 minutes) carries little clinical significance. Thus, a calculated sample size of 44 patients per group was required for a statistical power of 0.90 and a type I error of 0.025. Because onset and total times can only be
TABLE 2. Block Performance Data Single Injection (n = 50)
Triple Injection (n = 50)
Imaging time, min Needling time, min Performance time, min Onset time, min Total anesthesia-related time, min
1.0 ± 1.1 3.0 ± 2.3 3.9 ± 2.9 15.8 ± 7.9 19.7 ± 9.0
0.7 ± 0.9 4.0 ± 2.3 4.8 ± 2.9 12.5 ± 7.9 17.1 ± 9.2
Success at 30 min, n (%) Composite score at 30 min Operator’s experience level (trainees/experts) No. passes Block-related pain (scale 0–10) Paresthesia, n (%) Vascular puncture, n (%) Neural edema, n (%)
46 (92) 7 (4–8) 17/33 1 (1–6) 2 (0–7) 7 (14) 0 (0) 2 (4)
46 (92) 8 (5–8) 18/32 3 (3–8) 3 (0–7) 10 (20) 0 (0) 0 (0)
P 0.084 0.025 0.157 0.027 0.166 95% CI of the difference of the means (−1.1 to 6.4) >0.999 0.112 0.834
