The relationship between the orientation of the lateral decubitus position for spinal anesthesia and positioning pain in patients with a femoral neck fracture: randomized non-inferiority trial

Study design

This prospective randomized non-inferiority trial in a single-center was approved by the Ethics Committee of Aidu Chuo Hospital (approval number: 2013, Aizuwakamatsu, Japan), and the trial was registered at the University Hospital Medical Information Network Clinical Trials Registry (UMIN000043694, https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000049892, registered on March 24, 2021) prior to patient recruitment. The trial was conducted and reported according to the Consolidating Standards of Reporting Trials (CONSORT) 2010 statement [15].

The study was conducted at the Department of Anesthesiology in Aidu Chuo Hospital, Aizuwakamatsu, Japan. Seventy-eight patients who were scheduled for unilateral femoral neck fracture surgery, that is, femoral head prosthetic replacement, between March 2021 and August 2022 gave written informed consent to participate in the study. The inclusion criteria were (1) an age of ≥ 20 years; and (2) scheduled to undergoing surgery under spinal anesthesia. The exclusion criteria were (1) judgement by the orthopedic surgeon that the metastasis of the fracture was so severe that the position may lead to exacerbation of metastasis; (2) atrial fibrillation; (3) taking a beta blocker; (4) little-to-no pain in the fracture area (e.g., use of analgesics within 6 h of the beginning of surgery, sensory paralysis at the fracture site); (5) inability to get into the left lateral decubitus position for reasons other than pain; (6) trauma other than the unilateral hip fracture; and/or (7) judgement by the attending anesthesiologist that spinal anesthesia impossible.

Randomization

To the best of our knowledge, there is no left-right difference in the incidence of femoral neck fractures. Thus, by performing spinal anesthesia in the left lateral position in all 66 patients, randomization of the patients regarding whether the fracture side was up or down was natural. Due to the design of this study, it could not be blind.

Spinal anesthesia protocol

Anesthetic and surgical procedures were performed in the usual manner at our hospital. No patient was administered premedication. A peripheral or central venous line was secured in the ward before surgery. After the patient was brought into the operating room on a stretcher, standard monitors, such as a pulse oximeter, electrocardiograph, and non-invasive blood pressure, were applied in the supine position, and the measurements were recorded every 2.5 min.

All enrolled patients were placed in the left lateral decubitus position by 4–5 staff members (an anesthesiologist, an orthopedic surgeon, and 2 or 3 operating room nurses), paying as much attention to the fractured part as possible. When changing the position, the patient’s head was held by the anesthesiologist, and the fractured lower limb was held by the orthopedic surgeon. Then, an operating room nurse flexed the patient’s neck and held the patient in the left lateral decubitus position with the non-fractured side hip flexed.

After disinfection of the puncture site and draping, local anesthesia was applied to the puncture site with around 3 mL of 1% lidocaine using a 25-guage needle. All patients received spinal anesthesia with around 15 mg (3.0 mL) of 0.5% isobaric bupivacaine by either of the two experienced right-handed authors (I.H. or Y.N.). Spinal anesthesia was performed from the intervertebral space of L3/4 or L2/3 in the left lateral decubitus position by using a 25-guage needle (TOP Spinal Needle, TOP Corp., Tokyo, Japan). Three minutes after spinal injection, an anesthetic effect range was confirmed by evaluating the loss of cold sensation, after confirming that the range reached around T10 bilaterally. Then, the patient was placed in the surgical position and the surgery was started. The anesthetic effect range was also confirmed at the end of surgery.

Outcome measures

Each patient’s pain score and heart rate were recorded by an operating room nurse at four time points: (1) when entering the room in the supine position (baseline); (2) when changing position to the left lateral decubitus position; (3) when local anesthesia was started; and (4) when puncturing spinal injection was successful. The pain score used was based on a scale reported by Lee et al. [14], that is, a scale of from 0 to 4 (0, calm; 1, facial grimacing; 2, moaning; 3, screaming; and 4, unable to proceed because of restlessness or agitation). In addition, the quality of patient position for spinal anesthesia performance (1, unsatisfactory; 2, satisfactory; 3, good; and 4, very good) was evaluated by the anesthesiologist performing it [10]. Moreover, preoperative patient cognitive dysfunction was assessed (0, none; 1, mild; 2, moderate, and 3: severe).

The primary outcome of this study was the percentage of patients who were assessed to have a pain score of intense pain defined as a pain score of 3 or 4 when changing position from the supine to the lateral decubitus position. The secondary outcomes were pain score and heart rate at the four time points, the quality of patient position for spinal anesthesia performance, and the time required for spinal anesthesia (from the start of local anesthesia to the injection of bupivacaine).

Statistical analysis and sample size calculation

Sample size calculation and all statistical analyses were performed using EZR (ver. 1.41, Saitama Medical Center, Jichi Medical University, Saitama, Japan) [16], which is a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria). Although Lee et al. reported that 76.2% of patients with a hip fracture using fentanyl and dexmedetomidine experienced severe pain when changing positions [14], and the patient population of our hospital is elderly, we estimated the percentage of patients who were assessed to have a pain score of intense pain at the time of lateral positioning to be 50% when the conventional method (fracture side up) was performed, and 60% when the fracture side was down. In setting a non-inferiority margin, i.e., the smallest clinical difference that is acceptable between the two groups, we have relied on our own and outside experts’ clinical judgment to determine that a margin of inferiority of 20% for the difference of the percentage of patients of intense pain between the group is not a significant difference. Because there are no data from previous trials to help define the clinical difference between the positioning pain with the fracture side up and that with the fracture side down. Non-inferiority is demonstrated within the margin of 20% at a one-sided significance level of 0.05 and a power of 80%, with a sample size of 34 per group (68 cases in total). In the present study, assuming a drop-out rate of 15% per side, the final sample size was a set of 78 cases in total.

The data were stored as numerical or categorical data. Continuous variables were summarized as means with standard deviations and medians with interquartile ranges, and categorical data as frequencies with percentages. The patient characteristics and anesthesia/surgical characteristics were assessed using an independent t test or the Mann–Whitney U test as appropriate, or chi-squared tests. We used chi-squared tests to analyze the primary outcome; an independent t test to compare means between the two groups for normally distributed, continuous data (i.e., heart rate, the time required for spinal anesthesia); and a Mann–Whitney U test to compare medians for skewed endpoints (i.e., the quality of patient position for spinal anesthesia performance, pain score at the four time points). A value of p < 0.05 was considered to indicate a statistically significant difference. All reported p values as results are two-sided.

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