Continuing Education Activity

Thoracic segmental spinal anesthesia is a technique of regional anesthesia that can potentially be a suitable alternative to general anesthesia for certain cases such as laparoscopic surgeries, particularly in patients who are considered at high risk while under general anesthesia. Although not routinely used, the procedure has been shown as beneficial in maintaining hemodynamic stability for these patients and reducing side effects encountered with general anesthesia. This activity describes the procedure of thoracic segmental spinal anesthesia and explains the role of the interprofessional team in managing patients who have undergone this procedure.

Objectives:

• Identify the type of patient that would be considered for undergoing thoracic segmental spinal anesthesia.
• Describe the anatomy of the thoracic spine and the physiological process occurring when thoracic segmental spinal anesthesia is performed.
• Review the most common complications associated with thoracic segmental spinal anesthesia.
• Explain the importance of monitoring patients for adverse effects intraoperatively and postoperatively by the interprofessional team.

Introduction

Thoracic segmental spinal anesthesia is typically utilized for patients undergoing surgery with major medical problems where they are considered a greater risk for general anesthesia. General anesthesia is the standard for most surgeries; however, some drawbacks can include negative drug side effects, prolong recovery, and inadequate pain control. There is currently renewed attention to thoracic segmental spinal anesthesia for several common surgeries. Injection of anesthetics intrathecally into the preferred body height and above where the spinal cord terminates has been revealed to be valuable in these certain circumstances.

Anesthesiologists are hesitant to perform spinal anesthesia above the termination of the conus medullaris due to fear of injuring the spinal cord. However, thoracic spinal anesthesia has been demonstrated as a safe and effective method for various surgeries, including laparoscopic cholecystectomies, breast cancer lumpectomies, and abdominal cancer surgery.[1][2][3] 

Giving thoracic spinal anesthesia may provide another option for these common surgeries: improved patient safety, reduced postanesthesia care stay, and better postoperative pain relief. This review aims to describe the technique, indications, contraindications and highlight the role of the interprofessional team in the management of these patients undergoing thoracic segmental spinal anesthesia.

Anatomy and Physiology

The anatomy of the thoracic and lumbar regions of the spine is similar but has some distinct differences that are important for giving anesthetic in the thoracic spine. Anatomical studies have been performed using MRI to better define the space within the spine for regional anesthesia. These MRI images have shown that the mid to lower thoracic segment of the cord lies anteriorly, where there is a CSF-filled space between the dura and the cord. In contrast, the spinal cord and the cauda equina are touching the dura mater posteriorly in the lumbar region. This has demonstrated there is a greater depth of the posterior subarachnoid space in the thoracic spinal cord. In one MRI imaging study with 50 patients, the space between the dura mater and spinal cord in the thoracic spine measured at 7.75 mm at T5 and 5.88 mm at T10.[4] Intrathecal injections at mid-thoracic levels may have a minimum safe distance before the spinal needle contacts the spinal cord tissue.

Next, the interlaminar spaces in the thoracic spine are narrow and more challenging to access with a needle due to overlap from the vertebral lamina. In contrast, the lamina of the lumbar vertebra do not overlap, and the space between them is larger. Furthermore, the spinous processes of the thoracic vertebra point inferiorly versus the lumbar vertebra pointing posteriorly.[5] This angled position of the thoracic spinal processes will alter the angle of the needle if a midline approach is used and possibly make it difficult for the procedure.

When performing thoracic segmental spinal anesthesia, the layers of anatomy traversed are the same as those in the lumbar region where spinal anesthesia is traditionally performed. When the midline approach is used, the layers the needle goes through first are the skin, followed by subcutaneous fat, supraspinous ligament, interspinous ligament, ligamentum flavum, dura mater, subdural space, arachnoid mater, and lastly, the subarachnoid space. When the paramedian technique is used, the needle goes through the skin, subcutaneous fat, paraspinous muscles, ligamentum flavum, dura mater, subdural space, arachnoid mater, and finally, the subarachnoid space.[6] 

A smaller number of nerve roots are covered by anesthetic within the subarachnoid space in thoracic segmental spinal anesthesia, providing anesthesia in the necessary surgical field dermatomes. Further, since there is less of a block of the lower extremities, a larger portion of the body does not experience venous dilation, which may compensate for adverse effects in blood pressure intraoperatively.[2]

Indications

Thoracic segmental spinal anesthesia is currently best suited for select procedures and patient populations. These typically include shorter procedures with patients considered at high risk of perioperative morbidity and mortality while under general anesthesia or patients unwilling to undergo general anesthesia.[2] In addition, patients who are unable to undergo the traditional method of spinal anesthesia in the lumbar region can benefit as well. Individuals at risk tend to be older patients who decline in physiological reserves, comorbidities, polypharmacy, cognitive dysfunction, and frailty.

Operations that have been performed with success include abdominal cancer surgeries, breast cancer surgeries, and laparoscopic cholecystectomies. In some of these surgeries, the procedure was performed in healthy individuals with excellent outcomes, so, in the future, the procedure may provide benefits for healthy patients as well. The safety of this technique needs to be confirmed by further studies involving a larger number of patients before it can be advised for routine use. 

Before proceeding, signed informed consent from the patient is necessary for this procedure. The indication for thoracic segmental spinal anesthesia and what to expect during the procedure, as well as the benefits, risks, and alternative procedures should be described in detail for the patient. A patient must be informed of what to expect after the procedure is performed and that they will be awake during surgery. This will cause a great deal of anxiety in many patients, and as such, they should be informed of feeling certain aspects of the procedure, such as tugging or pain from pneumoperitoneum due to insufflation during a laparoscopic case.[7]

Contraindications

There are major known contraindications to all neuraxial anesthesia. The absolute contraindications are patient refusal or lack of consent, local infection at the site of the procedure, a true allergy to drugs given, and elevated intracranial pressure, which increases the risk of uncal herniation when CSF is lost through the needle. In addition, spinal anesthesia is contraindicated when the operation is expected to take longer than the duration of the nerve block. 

The relative contraindications are preexisting neurological diseases (multiple sclerosis and other demyelinating diseases), sepsis, severe hypovolemia, and coagulopathy. In the setting of coagulopathy, performing spinal anesthesia can be considered depending on the level of severity.  Other relative contraindications include severe mitral and aortic stenosis and left ventricular outflow obstruction, as seen with hypertrophic obstructive cardiomyopathy.[8]

Equipment

The performance of thoracic spinal anesthesia is performed under an aseptic technique, and the anesthesiologist is expected to maintain a sterile environment. A surgical hat, masks, and sterile gloves are required to maintain sterility. The patient should be monitored with a blood pressure cuff and/or have an arterial line placed for invasive arterial blood pressure monitoring if the patient is at risk for hemodynamic instability. Routine monitoring with EKG as well as a pulse oximeter for oxygenation is also necessary. If the plan is to use sedation before starting, the tools needed to assist in ventilation, oxygenation, and circulatory support should be in place. Intravenous access should be established before starting.

Prepackaged spinal anesthesia kits are available, which usually include an antiseptic preparation that is bactericidal such as chlorhexidine, a sterile drape, and 1% lidocaine used as a local anesthetic for the site of needle insertion. Other items include the spinal needle, syringes, and the spinal anesthetic solution. Spinal anesthetics can range from a variety of different types; however, the most widely used is bupivacaine (0.5% or 0.75%) due to its potency, its onset of 5 to 8 minutes, with a duration of anesthesia that lasts from 90 to 150 minutes, and lower incidence of transient neurologic symptoms (TNS). Less commonly, 0.5% lidocaine has also been used in the past; however, this fell out of favor due to higher chances of TNS.[9]

Personnel

It is recommended that thoracic segmental spinal anesthesia be performed by highly experienced anesthesiologists who have extensive practice with neuraxial anesthesia and are comfortable performing this procedure. Additional support from other staff such as another anesthesiologist, nurse anesthetist, or nursing staff is also necessary for assistance. The other team members are present to assist with equipment and supplies. In addition, the patient needs someone to ensure they maintain their posture and keep them safe in their position on the operating room table.

Preparation

Pertinent history and physical examination should be performed before starting. The most important for patient history is any allergies, prior adverse effects to anesthetics, or any family history of complications with anesthetics. The physical exam includes evaluating the thoracic spine for any signs of scoliosis, surgery, infection, severely restricted range of motion, or findings that will make thoracic spinal anesthesia more challenging or impossible. In addition, a basic neurologic exam of gross motor and sensory function should be assessed. Lastly, A review of laboratory studies and vital signs (normal blood pressure and absence of fever) should be conducted to identify patients who may be at risk of complications. A procedural time-out is then performed, confirming the patient's name, the procedure, any known allergies, and confirm consent was given.

Technique or Treatment

The initial setup for the procedure is patient positioning which is performed in the sitting or lateral decubitus position. The positioning also includes the height of the OR table, providing blankets for comfort, and sedation for the patient if required. The sitting position is commonly favored because it avoids a potential rotation of the spine that can occur with the lateral decubitus position. The patient should flex the neck and push out the lower back to open up the thoracic intervertebral spaces. For the lateral decubitus position, the ideal positioning consists of having the patient's back in line with the edge of the bed closest to the anesthesiologist, with the patient’s knees flexed up to their abdomen.

Once the patient is positioned correctly, the insertion level is identified by palpation and the use of anatomic landmarks to identify the corresponding spinous process. The space between 2 palpable spinous processes is the site of entry. The inferior angle of the scapula (T7 spinous process) and the 12th rib margin (L1 spinous process) are widely used as landmarks to estimate the level. Each thoracic vertebra articulates with ribs along the lateral border of its vertebral body, which helps determine the lower thoracic and upper lumbar areas. Other interspaces can then be identified, depending on where the needle needs to be inserted, using the ‘counting up method.’

Another approach is to use ultrasound guidance with the ‘counting up' method starting from the 12th rib and moving up until the corresponding vertebral level is found.[5] A skin mark is then made to identify the correct level of the block. Once located, the area is cleaned with antiseptic preparation and is given time to dry. A drape is placed on the area of focus to maintain sterility. The skin of the puncture site is infiltrated with 1% lidocaine in the midline or paramedian location, depending on the approach chosen.

 In the midline approach, the needle is angled more cephalad for thoracic segmental anesthesia as the long thoracic spinous processes point caudally and are most sharply angled between T4 and T9, making insertion of the needle in the midline more difficult in the midthoracic region. Beyond T10, they start to resemble those in the lumbar region.[5] The skin is infiltrated about 2 cm from the midline for the paramedian approach, and the spinal needle advances at an angle toward the midline. In this approach, the supraspinous and interspinous ligaments are not encountered, and there is less resistance before reaching the ligamentum flavum. After needle insertion, which should be slow and cautious, there will be an increase in resistance followed by a characteristic “popping” sensation through the ligamentum flavum.

Once the needle is through the ligamentum flavum, the stylet is removed, and a clear flow of CSF should be seen at the hub of the needle. Once the flow of clear CSF begins, approximately 1 to 2 ml of 0.5% to 0.75% bupivacaine is injected, plus the addition of 15 to 20 ug of fentanyl intrathecally.  Depending on the operative location, a hyper, iso, or hypobaric anesthetic solution can be injected. Alternatively, a combined spinal-epidural (CSE) needle set can be used to first identify the epidural space with the “loss of resistance” method followed by the advancement of the spinal needle through the epidural needle. The CSE system can limit the amount of the needle that projects beyond the tip of the epidural needle, minimizing the risk of injuring the spinal cord.[3]

Once the anesthetic is injected, the spinal needle is removed, and the patient is placed in a supine position. The patients should be assessed for an adequate sensory block to pinprick.[10] If the sensory block is inadequate after 5 to 10 minutes, the patient should go under general anesthesia if possible.

Complications

There are major and minor complications to the thoracic spinal blockade; however, the major complications are rare. The most serious complications of thoracic spinal anesthesia include:[11]

• Direct needle trauma
• Infection (abscess, meningitis)
• Vertebral canal hematoma
• Spinal cord ischemia
• Arachnoiditis
• Total spinal anesthesia
• Cardiovascular collapse
• Death

Minor complications, on the other hand, are common and shouldn’t be disregarded. Some of the more common minor complications include hypotension, nausea/vomiting (typically caused by hypotension), bradycardia, paresthesia, transient mild hearing impairment, backache, urinary retention, and TNS. Lastly, post-dural puncture headaches, which are considered a “minor” complication, can be severely debilitating for patients and are common in occurrence.[12][13][14]

Clinical Significance

Thoracic segmental spinal anesthesia offers many benefits not available with general anesthesia or with lumbar spinal anesthesia in some cases. This technique has made it possible to perform certain major operations on an awake patient at high risk for morbidity and mortality under general anesthesia. Other benefits include better pain control than opioids and a decrease in the opioid requirement during or after a procedure, which lowers the incidence of the side effects with these drugs. Furthermore, there is an earlier recovery of bowel function and decreased complications which result in a shorter length of in-hospital stay and patient satisfaction.[3] 

This procedure can also be valuable for postop pain in combination with other modalities. Lastly, the anesthetic dose is lower, so hemodynamic instability becomes minimal.[15] Administering thoracic spinal anesthesia may allow for the potential that such surgeries, which need a prolonged hospital course, can occur with high-risk patients and safely.

Enhancing Healthcare Team Outcomes

Thoracic spinal anesthesia is a beneficial procedure that is useful for a wide range of surgical procedures. However, there are significant risks that the healthcare team needs to be aware of. Patient selection is an important aspect, and a detailed history and physical examination will determine who is eligible. The indication for thoracic spinal anesthesia needs to match the surgical needs of the patient. After surgery, the post-op team should be aware of the procedure, and the patient needs to be monitored closely for hemodynamic stability. Monitoring in the immediate post-op period should occur until the resolution of the anesthetic.

Both physicians and nurses from other specialties should also be aware of the nature of anesthesia that these patients underwent. Before discharge, the patient should receive a list of possible complications and look out for them. They should be asked about any headaches, backache and evaluated for neurological deficits. Lastly, patients should be reassured and evaluated regarding any complications that may have occurred from this procedure.

Nursing, Allied Health, and Interprofessional Team Interventions

Safe and effective use of thoracic segmental spinal anesthesia requires an interprofessional team approach, including anesthesiologists, nurses, and pharmacists, all collaborating to achieve optimal patient results. The nurse assists the anesthesiologist in performing the procedure and ensures the patient is comfortable and feels safe. Close monitoring of the patient and their vitals by nurses during the procedure and postoperatively is key to safety.

Nursing, Allied Health, and Interprofessional Team Monitoring

The nursing staff monitors vitals postoperatively and ensures patients are stable before discharge.