• Return of Motor Function of the Thigh and Lower Leg [ Time Frame: Postoperative day 0 (day of surgery) ]
  time to return of motor function of the thigh and lower leg
• Number of Patients With Dizziness Events [ Time Frame: Postoperative day 2 ]
  number of patients with dizziness when transitioning from lying down to sitting or standing
• Number of Patients With Urinary Retention Events [ Time Frame: postoperative day 1 ]
  number of patients with inability to urinate within 8 hours of surgery OR a report of distended or painful bladder occurring on postoperative day 0 or 1, either by patient report or on palpation by nursing
• Number of Patients With Transient Neurological Symptoms (TNS) [ Time Frame: Postoperative days 0-2 ]
  Number of patients with TNS events occurring. Transient neurological symptoms were defined as new onset of back, buttock, or thigh pain occurring after spinal anesthesia.
• Hospital Stay [ Time Frame: hospital stay (0-3 days) ]
  length of hospital stay

• return of motor function of the thigh and lower leg [ Time Frame: Postoperative day 0 (day of surgery) ]
  time to return of motor function of the thigh and lower leg
• return of sensory function of the thigh and lower leg [ Time Frame: Postoperative day 0 (day of surgery) ]
  time to return of sensory function of the thigh and lower leg
• incidence of orthostatic hypotension [ Time Frame: Postoperative day 2 ]
  incidence of low blood pressure when transitioning from lying down to sitting or standing
• Incidence of Dizziness [ Time Frame: Postoperative day 2 ]
  incidence of dizziness when transitioning from lying down to sitting or standing
• Incidence of Urinary Retention [ Time Frame: postoperative day 1 ]
  incidence of patients with inability to urinate within 8 hours of surgery OR a report of distended or painful bladder occurring on postoperative day 0 or 1, either by patient report or on palpation by nursing
• Transient Neurological Symptoms (TNS) [ Time Frame: Postoperative day 2 ]
  incidence of TNS
• Hospital Stay [ Time Frame: 0-30 days after surgery ]
  length of hospital stay
• Percentage of Patients in Each Group Meeting Discharge Readiness Criteria [ Time Frame: 0-30 days after surgery ]
  The percentage of patients in each group that meets discharge readiness criteria will be compared.

Total hip replacement is often performed under spinal anesthesia, which is the standard at Thomas Jefferson University Hospital (TJUH) and Rothman Orthopedic Specialty Hospital (ROSH) for patients without contraindications. Spinal anesthesia involves injecting a numbing medicine (local anesthetic) into the cerebrospinal fluid that bathes the spinal cord through a space between two bones in the back. This causes temporary numbness of the legs and hips and allows surgery to take place without patients feeling pain during surgery. Different local anesthetics can be used for spinal anesthesia and each works for a different duration of time. Another factor that affects how spinal anesthesia medications work is the baricity of the medication, which refers to how dense it is compared to cerebrospinal fluid (CSF). Medications that are less dense than CSF are hypobaric, those with same density are isobaric, and those with greater density are hyperbaric. For clinical purposes, this really only comes into play when positioning the patient immediately after spinal placement as patient position has different effects on the dermatomal level attained depending on baricity of the local anesthetic. Bupivacaine is a long-acting local anesthetic that has been used for several decades for total hip replacement. It is available in both hyperbaric form (with dextrose added) and isobaric form (with no dextrose added). Mepivacaine is another local anesthetic that has a shorter duration of action and is also used for spinal anesthesia in total hip replacement at many centers. All three drugs are used routinely at different centers in the United States. Despite the differences in duration that have been described from pharmacokinetic studies, a randomized, controlled study comparing the three drugs in terms of important outcomes, such as the ability to walk after surgery, has not been published yet. Therefore, the investigators want to compare the three local anesthetics in a randomized, controlled fashion to see if more patients are able to walk sooner after receiving mepivacaine spinal anesthesia than either form of bupivacaine spinal anesthesia.

Patients who are eligible will be called the night prior to surgery and the study will be explained over the phone. Patients who express interest will be recruited on the day of their scheduled surgery in the short-procedure unit. Patients will be given consent forms and time to read them and ask questions.

Preoperative Management All patients without contraindications or allergies will receive oral gabapentin and acetaminophen in the short procedure unit prior to surgery per routine practice.

Intraoperative Management The targeted spinal dermatome level to achieve will be T10 (umbilicus). For isobaric drugs, patients will sit after spinal placement for 3-5 minutes to achieve this level. For hyperbaric bupivacaine, patients will be immediately placed supine and in Trendelenberg position for 3-5 minutes to achieve adequate level and confirmed with sensory pinprick testing, which will be performed every 2 minutes beginning at spinal placement time. After spinal is placed, sedation will be titrated at the discretion of the anesthesia team to achieve the American Society of Anesthesiology's definition of moderate sedation (purposeful response to verbal or tactile stimulation, spontaneous ventilation, and no airway intervention needed) using propofol. All patients will receive tranexamic acid unless contraindicated (10 mg/kg bolus), as well as multimodal analgesia with a non-steroidal anti-inflammatory drug (NSAID) and dexamethasone 4 mg IV per routine practice.

Postoperative Management

Sensory and motor assessments will take place every 30 minutes from PACU arrival time until motor strength is 5/5 in both lower extremities in hip flexion, knee extension, and toe dorsiflexion or the patient's motor function returns to baseline. The time of return of motor function will be documented. Physical therapists will visit the patient between 3 and 3.5 hours after spinal placement to assess for ability to ambulate and perform Tinnetti test, which assesses ambulation and gait and gives a score of 0 through 28 (see attached). Urinary retention will be assessed through asking the following on postoperative day 1:

1. At what time did the participant first urinate?
2. Did participant require a Foley catheter or straight catheter to drain urine from his or her bladder?

These questions will be asked along with the following about TNS (transient neurological symptoms):

1. Does the participant have any pain in his or her lower back that goes into his or her buttocks and/or down his or her thigh that was not there before surgery?
2. If yes, how would the participant rate that specific pain from 0 (no pain) to 10 (worst pain imaginable).
3. How would the participant rate his/her overall pain (0 to 10 scale)?
4. How satisfied is the participant with his/her anesthesia experience (0 to 10 scale where 0 is very dissatisfied and 10 is very satisfied)?

TNS will be defined as the new onset (within 24 hours of surgery) of back pain that radiates into the buttocks, thighs, hips, or distally. Localized back pain will not be included.

Urinary retention will be defined by inability to urinate within 8 hours, a report of distended or painful bladder occurring on postoperative days 0 or 1, either by patient report or on assessment by nursing, or the use of a Foley catheter or straight catheter.

Post-discharge phone calls

The following will be asked to patients via phone calls after discharge at 24 and 48 hours after surgery if not still in the hospital (will be asked in-person otherwise):

1. Does the participant have any back pain that was not present before surgery that goes into his/her buttocks, thighs, hips, or lower leg?
2. If yes, how would the participant rate that specific pain from 0 (no pain) to 10 (worst pain imaginable).
3. How would the participant rate his/her overall pain (0 to 10 scale)?
4. How satisfied is the participant with his/her anesthesia experience (0 to 10 scale where 0 is very dissatisfied and 10 is very satisfied)?

Post-discharge data collection Readmissions within 90 days will be recorded for all patients including the reason for readmission.

General Operating Procedures Patients who agree to participate will then be randomized by a computer-generated sequence to one of the three study groups. The anesthesiologist and certified registered nurse anesthetist or resident performing the spinal will be aware of group allocation and will perform spinal anesthesia according to standard operating procedures with the assigned local anesthetic. Intraoperative sedation will be with propofol or dexmedetomidine, at the discretion of the anesthesia team. Patients will remain blinded and surgeons and those performing postoperative assessments will remain blinded as well. As all study drugs are standard spinal anesthesia drugs and readily available, the anesthesia team caring for the patient will be informed of group allocation and the appropriate drug will be selected. These doses of hyperbaric and isobaric bupivacaine are considered "low dose" and are lower than those routinely used at TJUH and ROSH. However, existing evidence shows that low-dose bupivacaine for spinal anesthesia provides adequate anesthesia time for a total joint replacement. Dosing will be as follows: isobaric bupivacaine 12.5 mg (2.5 cc of 0.5%) for < 74" height and 15 mg (3 cc) for > or = 74" height; hyperbaric bupivacaine 10.25 mg (1.5 cc 0.75%) for < 74" height and 13.125 mg (1.75 cc) for > or = 74" height; and isobaric mepivacaine 52.5 mg (3.5 cc of 1.5%) for < 74" height and 60 mg (4 cc) for > or = 74" height. Patients with BMI of 35 or greater will also be given the higher dose of each of the 3 medications listed above.

Intraoperative variables that will be measured include: hypotension (defined as a decrease in baseline blood pressure of 20% or greater), surgeon rating of intraoperative muscle tension (0, 1, 2, or 3 where 0 is the most relaxed and 3 is the tightest), and conversion to general anesthesia.

Postoperative variables that will be measured include: ambulation at 3-3.5 hours (primary endpoint), time to ambulation, attempts needed to ambulate, episodes of orthostatic hypotension while trying to ambulate, urinary retention, opioid consumption, pain, incidence of transient neurological symptoms up to 48 hours postoperatively, discharge readiness, and length of stay.

Post-discharge phone calls

The following will be asked to patients via phone calls after discharge on postoperative days 1 and 2 after surgery if not still in the hospital (will be asked in-person otherwise):

1. Does the participant have any pain in his/her lower back that goes into his/her buttocks and/or down his/her thigh that was not there before surgery?
2. If yes, how would the participant rate that specific pain from 0 (no pain) to 10 (worst pain imaginable).
3. How would the participant rate his/her overall pain (0 to 10 scale)?
4. How satisfied is the participant with his/her anesthesia experience (0 to 10 scale where 0 is very dissatisfied and 10 is very satisfied)?

• Drug: isobaric bupivacaine
  The anesthesiologist and CRNA or resident performing the spinal will perform spinal anesthesia according to standard operating procedures with the randomly assigned local anesthetic.
• Drug: hyperbaric bupivacaine
  TThe anesthesiologist and CRNA or resident performing the spinal will perform spinal anesthesia according to standard operating procedures with the randomly assigned local anesthetic.
• Drug: isobaric mepivacaine
  The anesthesiologist and CRNA or resident performing the spinal will perform spinal anesthesia according to standard operating procedures with the randomly assigned local anesthetic.

• Active Comparator: isobaric bupivacaine
  Isobaric bupivacaine 12.5 mg (2.5 cc of 0.5%) for ≤ 74" height and 15 mg (3 cc) for > 74" height
  Intervention: Drug: isobaric bupivacaine
• Active Comparator: hyperbaric bupivacaine
  hyperbaric bupivacaine 10.25 mg (1.5 cc 0.75%) for ≤ 74" height and 13.125 mg (1.75 cc) for > 74" height
  Intervention: Drug: hyperbaric bupivacaine
• Active Comparator: isobaric mepivacaine
  isobaric mepivacaine 52.5 mg (3.5 cc of 1.5%) for ≤ 74" height and 60 mg (4 cc) for > 74" height
  Intervention: Drug: isobaric mepivacaine

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Inclusion Criteria:

• undergoing elective primary hip replacement surgery
• American Society of Anesthesiologists physical status 1-3

Exclusion Criteria:

• hip fracture
• contraindication to spinal anesthesia (refusal, coagulopathy or recent use of anticoagulant medication that prevents spinal anesthesia, local or systemic infection)
• any other reason deemed significant by attending anesthesiologist
• any patient requiring a wheelchair for ambulation or who cannot walk 25 feet with or without an assist device at time of surgery
• presence of neuropathy in posterior thighs or buttocks
• use of greater than the equivalent of morphine 25 mg IV (oxycodone 30 mg PO) daily
• any patient deemed a poor candidate for spinal anesthesia as determined by the attending anesthesiologist