There is Controversy about what is more critical volume or concentration to achieve an optimum analgesic treatment with quadratus lumborum block. From the experiences of the authors, the regular dose of 20 ml of Bupivacaine at 0.375% concentration could not be enough in some cases to produce an optimum analgesic treatment, especially in hip arthroplasties. What is proposed in this study is to evaluate whether the volume injected in the quadratus lumborum block is more important than the concentration of the local anesthetic in terms of control of pain during the next 24 hours after surgery and opioid consumption.

The Quadratus Lumborum Block (QLB) was originally described by Blanco in 2007 as a posterior variation of the Transversus Abdominis Plane block. It is now, however, recognized as a unique, alternative, and separate interfascial plane block. The QLB has been studied and compared with other types of blocks and it may offer several advantages such as simplicity, safety, and avoidance of hypotension. Additionally, dermatomal coverage may be greater than for other types of blocks. In cadaveric studies the paravertebral spread of dye was found from T7-L5 , although an vivo study in healthy volunteers showed the paravertebral spread of the contrast solution only between T10-L1 at 1 hour after the block. It is noted that while these anatomical studies invariably show the spread of contrast or dye extending to the paravertebral space that spread may be limited in degree. Thus follows a point of significant controversy as to whether the paravertebral space is in fact the block's primary site of action or whether it acts primarily on nerves, radicular and sympathetic, situated in the thoracolumbar fascia. Questions of mechanism and site of action notwithstanding, the safety and clinical efficacy of this block has been clearly demonstrated in multiple types of surgeries including abdominal laparoscopic , open laparotomy , urologic , and general surgery with analgesia lasting roughly 24 hours, decreased consumption of opioids, decreased time to ambulation, and decreased hospital length of stay. In recent studies, QL block employment was shown to produce a significant reduction in length of stay during hip surgery as well as similar analgesia to Lumbar Plexus blockade.

The quadratus lumborum block has since 2016 become standard of care for abdominal and hip surgeries at our institution, replacing paravertebral and lumbar plexus blocks respectively, and as part of a broader multimodal analgesia institutional ERAS (Enhanced Recovery After Surgery) protocol. Coincident with its implementation we have seen significant reductions in opiate and PCA use as well as hospital length of stay. Similar results have been reported by other institutions.

Since the first description of this technique, several approaches to and anatomic targets within the quadratus lumborum plane have been described although their mechanism of action, spread, and relative clinical effectiveness remain areas of some debate. There remain many unanswered questions regarding this block and its subtypes. It is, for example, unknown if one technique would be better than another for different types of surgery. Likewise little is known of the relative importance of local anesthetic concentration and injectate volume - the principal question addressed by this proposed study.

Inclusion Criteria:

Patients 18-80 years old Patients undergoing total hip arthroplasty BMI 19-45, >50 kg Male and Female All races American Society of Anesthesiologists physical status classification I, II, III Spinal Anesthesia Provided

Exclusion Criteria:

Pregnancy Non english speaking or inability to participate in the study Patients with coagulopathy or With INR >1.5 the day of the surgery. pharmacologic coagulopathy: patients on xarelto, plavix, or any kind of "Blood Thinners" Chronic steroid use: patients with consumption of steroid for more than 3 months.

Chronic pain: pain for more than 3 months Chronic opiate use : consumption of opioids for more than 3 months.

There is no plan to share individual participant data

An envelope will contain the randomized concentration and volume of ropivacaine to be administered to the patient. Once the anesthesiologist knows which volume he is going to administer, he will reseal the envelope and return it to the research team. This process will allow only the anesthesiologist performing the block to have knowledge of the volume he is administering, keeping both the patients and outcome assessor of the research team blinded.

The anesthesiologist will fill the syringe with the appropriate volume of medication. Immediately after, he will cover the numbers on the syringe with a piece of opaque tape, preventing any others from visualizing the volume to be administered.