Bier's Block Versus Mini-bier's Block in Patients Undergoing Hand Surgery

Introduction:

Several ways of anesthesia can be used to perform hand surgery, being general anesthesia, intravenous regional anesthesia as well as locoregional anesthesia. Locoregional anesthesia and intravenous regional anesthesia are often performed since patients can be discharged from the hospital more rapidly.

A conventional Bier's block is performed using a tourniquet on the upper arm to create a bloodless field and to contain the anesthetics within the surgical area (1). Complications are rare but are often linked to a systemic toxicity reaction after releasing the tourniquet (2). A mini-Bier's block in which the tourniquet is placed on the fore-arm, has been shown to be a safe and effective way of anesthesia to perform hand surgery. By using this type of anesthesia, the dose of the anesthetic can be reduced compared to a conventional Bier's block which reduces the risk of systemic toxicity reactions (3-5).

Currently, studies that made a comparison between the two anesthesia techniques are scarce and inconsistent. Next to that, those studies also used different types of anesthetics and dosages. To see which technique is advantageous in clinical practice, the investigators want to investigate the efficacy of the Bier's block and mini-Bier's block in patients that are planned to undergo hand surgery.

Outcome measures:

The primary aim of this study is to compare the analgesic efficacy of the Bier's block versus the mini-Bier's block. The hypothesis is that there is no difference between the two techniques. A blinded surgeon will determine the analgesic efficacy of these techniques (graded as "complete" or "incomplete") and divide the efficacy in 4 grades. Grade 1 and grade 2 are considered "complete" blockade, while grade 3 and grade 4 are considered "incomplete" blockade. Grade 1: complete motor and sensory blockade, grade 2: partial motor blockade but no pain or deep pressure sensitivity, grade 3: partial motor blockade with mild pain requiring rescue local or opioid analgesia, grade 4: incomplete motor- and sensory blockade requiring sedation/conversion to general anesthesia).

Secondary study outcomes:

• Onset time, which is defined as the time from the injection of the local anesthetic until the complete sensory loss in hand (assessed by the blinded surgeon via "pin prick").
• Patient's pre-, intra- and post-operative pain scores will be measured via an 11-point Numeric Rating Scale (NRS) in which number 0 means "no pain at all", number 5 means "moderate pain" and number 10 means "worst possible pain".
• Tourniquet time: the amount of time that the tourniquet is inflated.
• Tourniquet tolerance time: the amount of time required for the inflated tourniquet to cause a painful sensation (NRS > 3).
• Satisfaction with the surgical field (bloodless field) will be graded by a blinded surgeon, measured using a 5-point scale (1= extremely dissatisfied until 5= extremely satisfied).
• The time spent in the operating room.
• Duration of surgery.
• General patient satisfaction will be assessed using a 7-point Likert Scale, in which number 1 equals "extremely dissatisfied" and number 7 means "extremely satisfied".

Design:

In this monocentric, investigator-initiated, observer-blinded, prospective, randomized, controlled, non-inferiority trial, 2 anaesthetic procedures will be compared in patients that undergo hand surgery (Carpal Tunnel Syndrome, trigger finger, dequervain tenovaginitis, disease of Dupuytren, ganglion cyst).

This study will be performed according to the Declaration of Helsinki and will be approved by the ethics committee of the JESSA Hospital, Hasselt, Belgium before the start of the study. A written informed consent will be obtained before participation in the study.

Randomization will be performed using a computer-generated random allocation sequence. Allocation numbers will be sealed in opaque envelopes, which will be opened in sequence by an independent anesthesiologist who is not involved in the assessment of outcomes.

Both the surgeon and the researcher will be blinded for the used type of anesthesia. Since the clear difference between an upper arm and forearm tourniquet, all patients will receive a second tourniquet which will not be inflated. That is, patients receiving the Bier's block will receive an additional forearm tourniquet which will not be inflated and patients in group of the mini-Bier's block will receive an additional upperarm tourniquet which will not be inflated. In this way, a possible de-blinding of the surgeon and researcher is minimized.

Study Procedures:

The patient will first receive information about this study. Before the start of the study, written informed consent will be obtained, after which the patient will be randomized to one of the 2 treatment groups. Before surgery, all patients will receive an intravenous catheter in the contralateral arm with infusion of 0.9% Natriumchloride (NaCl), paracetamol 1g and standard monitoring (non-invasive blood pressure, electrocardiogram and O2 saturation measurements).

In the Bier's block group:

An intravenous catheter will be placed in the dorsal vein of the hand that will undergo surgery. Afterwards, a tourniquet will be placed on the upper arm and inflated, after which the anesthetic can be administered via the dorsal vein catheter (40ml Lidocaine 0.5%). The tourniquet remains inflated for 25 minutes to reduce systemic toxicity reactions postoperatively.

In the mini-Bier's block group:

An intravenous catheter will be placed in the dorsal vein of the hand that will undergo surgery. Afterwards, a tourniquet will be placed on the forearm and inflated, after which the anesthetic can be administered via the dorsal vein catheter (25ml lidocaine 0.5%). The tourniquet remains inflated for 10 minutes to reduce systemic toxicity reactions postoperatively.

Before the start of the surgery, the blinded surgeon will assess the quality of the block (primary outcome) using a forceps. The quality of the block will be graded "complete" or "incomplete" as described above. In case of grade 1 or grade 2, the surgical procedure can start. In case of grade 3, the blockade will be enhanced (local anesthetic or intravenous opioid administration (alfentanil or sufentanil)). In case of grade 4, sedation/conversion to general anesthesia will be performed.

All secondary outcome measures will be investigated by the blinded researcher.

Statistical analysis:

Sample size was determined for the primary study outcome with the aim to reject the non-inferiority of the mini-Bier's block. Based on a meta-analysis (unpublished data) we expect a 98.5% complete blockade in the experimental group (mini-Bier's block) and a 100% complete blockade in the control group (Bier's block). With a difference of 5% between the 2 groups and a binary outcome (complete/incomplete), we calculated that 135 patients are needed per group (α=0.05, power=0.80). Considering a drop-out rate of 3.5%, the total number of patients is 140 per group.

Descriptive statistics will be presented as frequencies and percentages of the total amount of patients for categorical variables, while numerical variables will be presented as mean. Group comparison will be performed using Chi-square test (or a Fisher's Exact test when necessary) for frequencies. Depending on normality, a Mann-Whitney U test or a Student's t-test will be used. Corrections will be applied for multiple measurements of the Numerical Rating Scale (NRS) for pain scores. An average difference of 1.3 points or more on the NRS pain score is considered clinical relevant. A p-value <0.05 is considered statistical significant, while p<0.10 is considered a tendency.