Assisting the Anesthesia Provider with Peripheral Nerve Blocks

Historical Foundations and Evolutionary Growth of Regional Anesthesia

The utilization of peripheral nerve blocks (PNBs) has a long history, with surgeon-led efforts beginning in the late 1900s. These early practitioners popularized regional anesthesia primarily as a means to block what was then termed "surgical shock." In the modern era, particularly over the past decade, there has been a significant surge in interest and the practical application of peripheral nerve block regional anesthesia. This growth is driven by the realization that PNBs are an exceptionally versatile tool for anesthesia providers, offering a comprehensive solution that spans the entire perioperative period. They are capable of providing intraoperative anesthesia, intraoperative analgesia, and extending their benefits well into the postoperative phase to provide continuous relief from pain.

Pain Management Philosophy and Clinical Importance

Modern perioperative care places a significant emphasis on the prevention and treatment of acute pain. This is necessitated by the complex, subjective, and multifactorial nature of pain itself, which requires a multimodal and multifaceted pharmacological approach rather than a single-modality solution. Clinical research and various meta-analyses have established a direct, critical link between the intensity of postoperative pain and the subsequent duration of patient recovery and overall functional outcomes. Historically, conventional pain management techniques often failed to provide adequate relief, with approximately $40\%$ of patients undergoing ambulatory orthopedic surgeries reporting poor pain control within the first 48 hours following their procedure. Consequently, the adoption of PNBs is viewed as a vital strategy for improving these outcomes through superior analgesia.

Systemic Benefits and Complication Reduction

Peripheral nerve blocks provide superb anesthesia and analgesia while maintaining a lower complication rate compared to alternative methods. Their use is associated with better overall patient recovery and high levels of patient satisfaction, while also remaining a cost-effective choice for modern healthcare facilities. A primary physiological benefit of PNBs is the ability to avoid or prevent airway manipulation and the hemodynamic consequences often associated with general, spinal, or epidural anesthesia. Furthermore, they allow patients to bypass the common side effects of narcotic analgesics, which include nausea, vomiting, profound sedation, and respiratory depression. By isolating the anesthetic effect to the operative limb, the systemic burden on the patient is greatly minimized.

Detailed Classification of Upper Extremity Peripheral Nerve Blocks

There are several distinct types of upper extremity blocks, each tailored to specific surgical sites. The interscalene block is typically employed for surgeries involving the shoulder, arm, and elbow. The supraclavicular block is highly effective for procedures involving the entire upper extremity. For elbow, forearm, and hand surgery, providers may choose the infraclavicular block or the axillary block, which specifically targets the forearm and hand. Hand and finger surgeries can be managed via a wrist block or a digital nerve block. Finally, the intravenous regional block, also known as the Bier Block, is used for wrist, hand, and finger surgery, though it is currently not as common as its counterparts. Key anatomical structures involved in these blocks include the brachial plexus roots and trunks, the axillary nerve, the musculocutaneous nerve, the radial nerve, the ulnar nerve, and the median nerve, as famously illustrated in anatomical dissections by Netter for CIBA-GEIGY.

Detailed Classification of Lower Extremity Peripheral Nerve Blocks

Lower extremity procedures utilize a specific set of blocks depending on the operative limb's location. The lumbar plexus block is used for the hip, anterior thigh, and knee. The sciatic nerve block targets the knee, tibia, ankle, and foot, while the femoral nerve block specifically focuses on the anterior thigh and knee. Detailed femoral nerve structures include the iliacus, psoas major, lateral femoral cutaneous nerve, inguinal ligament, fascia lata, fascia iliaca, and the femoral sheath containing the femoral artery and vein. For the ankle and foot, the popliteal nerve block or a standard ankle block may be used. The fascia iliac block is primarily for hip procedures, and the adductor canal block is common for total knee, tibia, and fibula repairs. These blocks provide precise surgical conditions and long-lasting postoperative comfort.

Contraindications and Limitations in PNB Application

While peripheral nerve blocks are widely applicable, several contraindications exist that may preclude their use. An uncooperative, combative, or demented patient may not be a suitable candidate for a block performed while awake. In the case of pediatric patients, general anesthesia (GA) is often required alongside or instead of the block. Medical contraindications include significant blood coagulation disorders, which increase the risk of hematoma, and pre-existing neuropathy or nerve injury at the site of the intended block. Evaluation of these factors is a critical step in the preoperative planning phase to ensure patient safety.

Continuous Peripheral Nerve Blocks (CPNB) and Institutional Requisites

Continuous peripheral nerve blocks provide a prolonged duration of postoperative analgesia, typically lasting $48-72\,\text{hours}$, although it is possible to extend this well past the $72\,\text{hour}$ mark. This technique is particularly beneficial for mobilization and physical therapy, as it maintains the patient's mental acuity while minimizing narcotic-related side effects. Implementing a CPNB program requires significant resources, including an experienced anesthesia provider, the education of technologists and nursing staff, and patient education. Furthermore, it demands specific equipment, dedicated block areas, additional time for placement, and well-trained ancillary support. Despite the cost and resource intensity, the high levels of patient satisfaction make it a growing trend in many medical facilities.

THE Role of the Anesthesia Technologist in Block Assistance

In many facilities, certified anesthesia technologists play an indispensable role in the performance of PNBs. Many providers rely heavily on the expertise of the technologist to facilitate a smooth and safe procedure. Depending on the facility's specific practice guidelines, a technologist may be responsible for prepping the surgical site, preparing the specific nerve block needle of choice, setting up and optimizing the ultrasound (U/S) machine, and occasionally assisting with the injection of local anesthetic. It is essential that technologists are well-trained in these procedures as the use of continuous PNBs continues to rise.

Clinical Monitoring and Essential Emergency Equipment

Success and safety in nerve block placement require a designated block space, which can be a specific preoperative area or the operating room itself. Every patient must have a well-functioning I.V. line and be placed on standard monitors, including $SPO_2$, ECG, and Blood Pressure (BP). Resuscitation equipment must be immediately available, containing oxygen, suction, and devices for intubation and ventilation. Crucially, emergency medications must be on hand, including Intralipids, which are used to treat local anesthetic systemic toxicity. These safety measures ensure that the perioperative care team can respond immediately to any adverse events during the block procedure.

Specifications for Nerve Block Supplies and Hardware

The block cart is a central piece of equipment containing needles, catheters, syringes, sterile skin preparation supplies (such as Chloraprep), and drapes. Local anesthetics, basic intubation equipment, and emergency drugs like atropine, vasopressors, midazolam, propofol, and muscle relaxants are also stored here. Ultrasound machines have become the standard for guidance, although nerve stimulators like the B. Braun Stimuplex HNS 11 or 12 are still utilized. Echogenic insulated needles are favored as they feature reflectors and $1\,\text{cm}$ calibrations for better visibility under ultrasound. These needles often have a short $30^{\circ}$ block bevel to help avoid nerve damage and come in sizes ranging from $2$, $4$, to $6\,\text{inches}$ ($50\,\text{mm}$, $80\,\text{mm}$, $100\,\text{mm}$, or $150\,\text{mm}$).

Technical Parameters of Nerve Stimulation and Charge

When using a nerve stimulator, providers must understand the relationship between stimulation current and pulse width. The Stimuplex HNS units allow for adjustments in $mA$ (current), $ms$ (pulse width), and $Hz$ (frequency). For example, a target stimulation current might be set at $1\,\text{mA}$, with a pulse width of $0.10\,\text{ms}$ and a frequency of $2\,\text{Hz}$. A charge table is used to calculate the electrical charge in nanocoulombs ($nC$) using the formula where charge is a product of amplitude and pulse width. For instance, at $1.0\,\text{mA}$ and $0.1\,\text{ms}$, the charge is $100\,nC$, whereas at $1.0\,\text{ms}$ pulse width, the charge increases to $1000\,nC$. These adjustments allow the provider to precisely locate nerves based on the elicited motor response.

Procedural Steps: Time Out and Patient Positioning

Every procedure begins with a pre-procedural "Time Out," ensuring the correct patient identification through name, ID number, and date of birth, as well as confirming the specific type of block to be performed. During the procedure, the technologist monitors vitals, provides supplemental oxygen, and ensures appropriate sedation is administered by the provider. The patient is typically placed in a supine position with the head turned away from the side being blocked. For upper extremity blocks, the arm should be abducted and flexed at the elbow to maintain anatomical land-marks. It is critical that the extremity is exposed and that the wrist is supported in a way that allows for the clear and unobstructed detection of hand twitches when using a nerve stimulator.

Injection Mechanics and Real-Time Safety Monitoring

Once the needle passes through the skin, the technologist or provider applies gentle aspiration with a fluid-filled syringe. The nerve stimulator is initially set to $1.0-2.0\,\text{mA}$ as the needle advances. Once acceptable stimulation is achieved—typically when the amperage can be lowered to approximately $0.2-0.5\,\text{mA}$ without losing the muscular twitch—the injection begins. The technician or technologist performs slow injection, aspirating every $5\,ml$ to ensure the needle hasn't entered a blood vessel. Concurrent monitoring of the EKG is vital to detect tachycardia from epinephrine or arrhythmias like ventricular fibrillation. The patient should also be observed for any changes in mental status that might indicate systemic absorption.

Recognition and Management of Peripheral Nerve Block Complications

While most PNBs are uneventful with a low complication rate of $0-5\%$, the potential for serious issues exists. Local Anesthetic Systemic Toxicity (LAST) is an early, critical complication characterized by intravascular injection, altered mental status, seizures, respiratory depression, hypotension, and cardiac arrhythmias. Delayed complications may include neurologic issues such as tingling, numbness, persistent painful paresthesia, or motor weakness. Block-specific risks include pneumothorax or phrenic nerve palsy. It is vital to discontinue injection if significant resistance is felt or if the patient experiences significant pain, as this may indicate an intraneural injection. Permanent nerve injury has been documented with injections of only $0.5-1.0\,ml$ under high resistance.

Post-Procedural Care and Discharge Coordination

Following the successful placement of the block, the technologist assists with the application of the dressing and continues to monitor the patient. In cases of continuous blocks, the technologist may coordinate with the pharmacy to obtain the pain pump and assist the provider in connecting it to the patient's catheter. Finally, the team must provide the patient with clear postoperative discharge instructions to ensure they understand how to care for the blocked limb and what signs of complications to watch for once they leave the facility.