Spinal Opioids in Anesthetic Practice

Anatomy and Physiology

The spine is made up of vertebral bones and intervertebral discs. There are seven cervical, twelve thoracic, and five lumbar vertebrae plus the sacrum. Posterior elements of the vertebra include the vertebral arch, spinous process, pedicles, and laminae. The vertebral body forms the anterior element. The thoracic spinous processes are angulated steeply and project inferiorly, while lumbar spinous processes are nearly horizontal. At each vertebral level, paired spinal nerves exit the central nervous system (CNS).

The spinal cord occupies the vertebral column, surrounded by the pia mater, arachnoid mater, and dura mater. It is widely taught that the spinal cord extends from the foramen magnum to L1 in adults and L3 in children, moving cephalad with age. Therefore, a lumbar puncture below L1 in an adult and L3 in children should avoid needle trauma to the spinal cord. Cerebrospinal fluid (CSF) resides in the subarachnoid or intrathecal (IT) space. Layers from outermost to innermost to reach the IT space include skin, subcutaneous fat, supraspinous ligament, interspinous ligament, ligamentum flavum, dura mater, subdural space, arachnoid mater, and subarachnoid space.

CSF is found in the cerebral ventricles, cisterns, and subarachnoid space surrounding the brain and spinal cord. It cushions the CNS from trauma and helps clear waste products. Most CSF is formed by the choroid plexuses of the lateral ventricles, some by the ventricles' ependymal cell linings, and smaller quantities formed from fluids leaking into perivascular space from surrounding cerebral vessels. CSF production in adults is 21 mL/hr, with a total volume of about 150 ml. CSF flows from lateral ventricles through the intraventricular foramina into the third ventricle, through the cerebral aqueduct into the fourth ventricle, and through the foramen of Magendie and the foramina of Luschka into the cerebellomedullary cistern. CSF enters the subarachnoid space from the cerebellomedullary cistern, circulating the brain and spinal cord before being absorbed in arachnoid granulations. CSF is isotonic with plasma despite lower potassium, bicarbonate, and glucose concentrations. Its protein content is limited. Absorption of CSF is the principal means by which perivascular and interstitial protein is returned to the blood due to a lack of lymphatics in the CNS.

Pharmacology

Morphine is the neuraxial opioid used most often due to its long duration of action compared with fentanyl and sufentanil. Morphine mainly binds to mu-opioid receptor subtypes.[2] It acts via G-protein subcategories, mu1 and mu2.[2] Binding to mu receptors results in decreased excitability of neurons via G-protein coupled inhibition of adenylate cyclase. This results in potassium channels' excitation with dampening of voltage-dependent calcium channels, increasing the threshold for pain signals to be triggered.[3] Morphine stimulates the opioid receptors in the substania gelatinosa of the posterior spinal cord.[4] Its hydrophilic nature results in the slow rostral spread and prolonged duration of action, and it provides effective analgesia even when injected at the lumbar level.[5] Intrathecal morphine (ITM) provides approximately 18 to 24 hours of postoperative analgesia. Its hydrophilic nature makes crossing the blood-brain barrier more difficult and delays the onset of action to 45 to 75 minutes after injection. Depending on the indication, ITM is usually administered in doses of 0.15 to 0.3 mg in adults. In contrast, IT fentanyl (10 to 20 mcg) and IT sufentanil (2.5 to 5 mcg) are often used to improve intraoperative analgesia.[6] Their onset of action, 5 to 20 minutes, is more rapid than morphine due to their hydrophobic nature. The duration of action is 1 to 4 hours for fentanyl and 2 to 6 hours for sufentanil. Although injected IT, the most analgesic effect of hydrophobic opioids (fentanyl and sufentanil) is due to movement to plasma and their effect on sedation and respiratory depression in the brainstem. Morphine's hydrophilic nature results in slower uptake and greater bioavailability at the spinal cord's dorsal horn.

Indications

Perioperative

When combined with a local anesthetic, spinal opioids improve the block's quality and reduce the need for systemic opioids postoperatively. For procedures that begin rapidly after a spinal injection such as caesarian section, fentanyl (10 to 20 mcg) is often added due to its rapid onset to improve analgesia during surgery, while intrathecal morphine (ITM) is added to provide postop analgesia. During the caesarian section, the addition of spinal opioids to the local anesthetic helps block discomfort due to the manipulation of the uterus. For surgeries that require large incisions or median sternotomy, fentanyl may or may not be added, and ITM is added to provide postop analgesia.

Chronic Pain Management

Intrathecal (IT) opioids have a place in treating cancer pain refractory to systemic opioids, non-opioid analgesics, and other nonpharmacologic pain treatments. IT administration is preferred over the epidural route as drug doses required via epidural are approximately ten times higher and increase systemic side effects.[7] Implantable IT infusion systems are available that deliver drugs to the CNS. The IT catheter is typically placed below L1 under fluoroscopy. The decision to implant a pump is made based on priorities of patient care and life expectancy. In patients with severe chronic pain, comfort should be the priority. If life expectancy is weeks to months, a catheter may be tunneled under the skin and connected to a subcutaneous port. If life expectancy is longer, fully implanted catheters and infusion pumps are selected. Both fixed-rate and programmable pumps that provide as-needed bolus doses are available. If an IT infusion pump is considered, a trial is often performed first with a single-shot technique.[8]

The decision to administer spinal opioids for chronic pain management should be made after confirmation that more conventional treatments are ineffective.[9] Furthermore, as with all chronic pain management, the provider must perform a thorough assessment of the source of pain and its impact on daily living activities. Imaging studies may aid the decision regarding the pain management technique to be selected and are vital to rule out sources of pain that should be treated surgically, such as a tumor compressing a nerve.

Benefits

Neuraxial blockade applied for surgery has been shown to reduce postoperative mortality and additional serious complications after surgery. These include deep vein thrombosis, pulmonary embolism, pneumonia, and respiratory depression, as well as transfusion requirements.[10] Inadequate analgesia during the postoperative period can also lead to numerous adverse consequences, including hemodynamic instability (tachycardia, hypertension, vasoconstriction), increased catabolism, impaired immune response, and altered platelet activation.[11][12] These are particularly undesirable in patients with numerous pre-existing comorbidities or following cardiac surgery.

The addition of opioids to local anesthetic intensifies the quality of the sensory block produced by local anesthetic alone. When used properly, IT opioids provide analgesia that is often superior to that achieved via the epidural and intravenous (IV) routes. Furthermore, when used in appropriate (low) doses, IT opioids result in a side effect profile similar to that of systemic opioids with one exception; pruritus tends to occur more commonly with IT opioids. Finally, spinal is easier to perform than an epidural.

Contraindications

Absolute

Absolute contraindications to spinal include patient refusal, a congenital or acquired bleeding disorder, ingestion of anticoagulants, antiplatelet or thrombolytic agents, or infection at the needle insertion site. Spinal is also contraindicated in patients with increased intracranial pressure, such as that due to an intracranial mass, as this has the potential to result in brainstem herniation.[13]

Before performing spinal, history should be performed to ask about mucosal bleeding, unusual bleeding after trauma, dental work, or surgery, significant nosebleeds, or heavy menses. If petechiae or ecchymoses, or a history of bleeding are present, hematology consultation should be obtained before performing a spinal. Suppose there is no history of bleeding episodes. In that case, spinal may be performed if prothrombin time (PT), activated partial thromboplastin time (APTT), and platelet count is normal, as these rule out the vast majority of bleeding disorders. However, mild Von Willebrand disease may still be present.

There is no definitive platelet count below which providers will not perform a spinal; it differs between providers, centers, and populations. Older literature recommends a platelet count of at least 100 X 10^9/L. However, many will perform spinal with a lower platelet count, depending upon the indication and the patient. Benefits could be considered to outweigh the risks, for example, in a cancer patient with severe pain or an obstetric patient in whom general anesthesia is considered inadvisable due to morbid obesity and abnormal airway anatomy. It has been proposed that in the absence of other problems, a platelet count of 75 X 10^9/L is sufficient in parturients. Douglas et al. 2001 and Tanaka et al. reported spinal performed with platelet counts less than 75 X 10^9/L in patients with idiopathic thrombocytopenic purpura (ITP) or gestational thrombocytopenia who were not pre-eclamptic. Furthermore, they suggest the lower safe limit of platelet count for non-preeclamptic parturients with no history or signs of bleeding is 50 X 10^9/L.[14]

Choi et al. reviewed 507 neuraxial techniques in patients at risk for bleeding, including patients with ITP with platelet counts less than 50 X 10^9/L.[15] In this series, patients with hemophilia and von Willebrand disease whose factor levels were decreased had their factor levels supplemented before the spinal performance. Permanent paraplegia occurred in one patient in whom the diagnosis of hemophilia was unknown when spinal was performed.

Assessment of platelet function with viscoelastic tests might help a provider decide whether to perform spinal in the presence of thrombocytopenia and abnormal platelet function documented with viscoelastic tests such as thromboelastogram (TEG), rotational thromboelastogram, or quantra should probably result in a decision not to perform the spinal.[16] Patients with severe preeclampsia and platelet count less than 100 X 10^9/L have impaired platelet function detectable with TEG-r (mm), maximal amplitude (mm), and alpha angle (degrees), although the platelet function analyzer (PFA-100) may be more sensitive to abnormal platelet function than the TEG in this population.[17]

A survey of international practice that includes discussing the risk of subependymal hemorrhage (SEH) in patients undergoing cardiac surgery has been reported.[18]

Relative

Relative contraindications should be weighed on a case-by-case basis. Spinal stenosis, prior spinal surgery, and spina bifida are relative contraindications, as a deviation from typical anatomy can make access difficult and spread of local anesthetic unpredictable.[19] An association between neuraxial techniques and nerve injury [19] has been reported in patients with spinal stenosis, lumbar disk disease, or a history of prior spine surgery. However, causation cannot be assumed, as this was a retrospective study without a control group that underwent surgery without neuraxial techniques. Also, factors such as disease progression were not considered in the analysis. In patients with multiple sclerosis, response to spinal anesthetic may be variable, resulting in prolonged motor and/or sensory blockade. However, there is no evidence that spinal anesthesia exacerbates the symptoms of multiple sclerosis.[20]

Some consider bacteremia to be a relative contraindication to spinal, due to concern that a needle passing through a vessel might introduce bacteria into the epidural or subarachnoid space. Providers often perform a diagnostic lumbar puncture in patients with fever of unknown origin. Work indicates that the incidence of lumbar puncture-induced meningitis is not greater than that of spontaneous meningitis, and cases that appear to be lumbar puncture-induced meningitis may be due to eventual seeding of the meninges in patients with more severe bacteremia.[21] This suggests spinal can be performed if judged safer than general anesthesia when considering the patient’s overall condition.[22] In such cases, spinal is considered acceptable if antibiotic therapy is initiated before spinal puncture, and there has been a demonstrable response to therapy (Horlocker 2000). Of note, in children under the age of one who underwent diagnostic spinal tap during bacteremia, there was a higher incidence of meningitis after lumbar puncture.[23]

Hemodynamic Considerations

Hypovolemia, hypertrophic obstructive cardiomyopathy, and mitral stenosis are relative contraindications to spinal anesthesia with a local anesthetic. It may significantly reduce systemic vascular resistance, resulting in significant hypotension in these patients who are preload-dependent. Spinal injection of local anesthetics should be considered contraindicated in patients with severe aortic stenosis. These patients have hypertrophied left ventricles with increased oxygen requirements, and myocardial ischemia may result from decreases in diastolic blood pressure and coronary perfusion pressure. Low-dose injection of spinal opioid alone (without local anesthetic) may be tolerated in patients with mild or moderate valvular heart disease. Low-dose opioid injection alone results in a smaller decrease in blood pressure than local anesthetics. Still, spinal techniques are best avoided in patients with severe aortic stenosis, for if these patients develop ventricular fibrillation, they are difficult or impossible to resuscitate.

In particular, it may be necessary to perform an open-chest cardiac massage to have a chance of successfully resuscitating a patient with severe aortic stenosis who has suffered a cardiac arrest. Some have applied spinal anesthesia to patients with aortic stenosis.[24] A number of these patients had aortic valve area 0.8 cm2 (not critical aortic stenosis), as well as continuous infusions of phenylephrine to support blood pressure.[24] Still, we suggest careful assessment of risks versus benefits before applying spinal anesthesia with a local anesthetic to patients with moderate aortic stenosis and believe it is absolutely contraindicated in patients with severe aortic stenosis.

Equipment

Equipment required for spinal injection of opioids is the same as for spinal anesthesia performed with local anesthetic alone and includes:

• Sterile gloves, a mask, and a sterile hat
• Antiseptic solution
• Sterile overlay of the procedure field
• Monitors including a pulse oximeter, electrocardiogram (ECG), and blood pressure cuff
• Spinal anesthesia kit containing spinal needle(s), a local anesthetic for subcutaneous injection at the site, and local anesthetic for spinal injection to produce surgical anesthesia. (Some kits contain labels and a sterile surgical marker)
• Resuscitation equipment
• If the patient is pregnant, depending on the circumstances, fetal monitoring may be advisable

Personnel

Neuraxial opioids procedures are typically performed by an anesthesiologist, a provider who has completed a fellowship in pain management, or a spine specialist (either orthopedist or neurosurgeon). A nurse is advisable to assist, such as to hand the provider items as needed, in a sterile fashion.

Preparation

As noted above, history and coagulation tests should exclude the possibility of a bleeding disorder. Questions related to drug ingestion should be asked as well, as medications may increase bleeding risk. The provider should inquire about large-volume alcohol ingestion, as alcohol potentiates aspirin-induced and nonsteroidal anti-inflammatory drug-induced prolonged bleeding time for up to two days.[25] Spinal can usually be performed safely if patients take 325 mg of aspirin daily or a low dose of a nonsteroidal anti-inflammatory drug. Of note, the number of days drugs should be discontinued before the performance of regional anesthesia varies for different anti-coagulant, anti-platelet, and herbal agents, based upon their pharmacology. Therefore, the provider should refer to the 2018 guidelines of the American Society of Regional Anesthesia and Pain Medicine to ensure a safe amount of time has passed.[26]

Day of Procedure

Steps before and performance of spinal are the same, whether opioids are added to local anesthetic for surgery, or administered for chronic pain in a clinic. Informed consent must be obtained and should include a discussion of the risks and benefits of spinal. Side effects and complications should be discussed. While side effects such as nausea and pruritus may be mentioned, headache and neurologic complications must be carefully explained. Post-dural puncture headache (PDPH) incidence is often stated to be 1.5% to 2% among young, pregnant women (though some newer studies report incidences up to 4%), and persistent PDPH has resulted in medical-legal action. Therefore, it is wise to carefully explain to parturients that spinal for caesarian section has been determined to be safer than general anesthesia and that if PDPH occurs, treatments are available. Indeed, a good relationship formed with the patient at this time is likely to result in a request for such treatment, up to and including a blood patch, while a lack of informed consent will lead to a patient who is both in pain and angry. The risk of rare complications such as neurologic deficits should be mentioned, with an incidence of 1:10,000 – 1:25,000 and the fact that these deficits usually resolve in time. These estimates may be conventional, based on the Third National Audit Project of the Royal College of Anaesthetists. The interested reader is referred to this in-depth study that sought to quantify the major complications associated with neuraxial blocks.[27]

Some feel the risk of subependymal hemorrhage (SEH) is sufficiently rare that it need not be discussed. It may be more prudent to discuss this risk while also stating it may be as rare as 1 in 100,000 to 1 in 200,000 in patients without bleeding. In some institutions, consent for anesthesia is included within the surgical consent. At these centers, a note should be written confirming the conversation about spinal with the patient.

The healthcare team must be prepared for unexpected occurrences. Therefore, intravenous access should be established, and vital sign monitors (ECG, pulse oximetry, and blood pressure) applied throughout the performance of a spinal.[28][29] Equipment for advanced airway protection must be available and staff trained in its use.[28][29] A procedure timeout is performed, and a checklist is verified by staff before starting the procedure.

Technique or Treatment

When spinal is performed to supplement general anesthesia for major surgery, it is usually performed while the patient is awake, allowing the patient to inform the anesthesiologist of pain or paresthesia experienced during the spinal. Such notice would warn the provider the needle may be in a nerve root, which would result in a slight withdrawal of the needle. Some believe the prevention of an intraneural injection may minimize the risk of a postoperative neurologic complication. Still, evidence for this is inconclusive. Indeed, spinal anesthesia is often performed in anesthetized children, and there is no convincing evidence this increases the risk of neurologic complications.

Regarding the sitting and lateral decubitus positions, it is unclear if one is superior to the other. However, some anesthesiologists may be more skilled in one position as compared with the other. Still, the midline is generally easier to identify in the sitting position. When sitting, patients are placed with their back perpendicular to the table, their elbows resting on a bedside table or hugging a pillow, and are instructed to flex their spine (like “an angry cat”) open the vertebral spaces. An assistant is beneficial in these cases to help the patient maintain their position and encourage them to “push out” their lower back. Patients lie on their side with the knees flexed in the lateral decubitus position, often referred to as the “fetal position.” They are also encouraged to flex their neck and move their head as close to their knees as possible. Using surface anatomy, the location of introducer placement can be identified. An imaginary line is drawn between the iliac crests, which most often correlates with the L4 spinous process or L4-L5 interspace, although this sometimes results in a spinal puncture at L3-L4, L5-S1, and sometimes L2-L3. Spinous processes identify the midline. If the patient is obese and is difficult to palpate the spinous processes, the intergluteal cleft may also help identify the midline.

Regardless if a single-shot spinal is being performed or a catheter inserted for continuous spinal, the two common choices for needle insertion are the midline or paramedian approach. For either approach, a sterile field is established with an antibacterial solution. A fenestrated drape is applied. The midline is identified as described above, and local anesthetic, most often lidocaine 1% - 2%, is injected at the needle insertion site. The introducer is inserted at a slight cephalad angle of 10 to 15 degrees. After the introducer has been inserted through the skin and subcutaneous tissue, the spinal needle (typically 24-27 gauge) is inserted through the introducer with its bevel parallel to midline. The user can feel texture changes as the needle passes through the supraspinous and interspinous ligaments and ligamentum flavum. A popping sensation is often palpable as the needle completes its course through the epidural space and as the dura is penetrated. The final length needed to achieve this penetration averages roughly 5 cm in adults.[30]

A midline approach may prove unsuccessful due to severe arthritis, kyphoscoliosis before spine surgery, positioning difficulties, a small interspinous space caused by bony calcification, or calcification of spinal ligaments. In such cases, the paramedian approach may be employed, in which the needle is inserted through the skin 1 cm inferior and 1 cm lateral to the caudal tip of the L4 spinous process. The needle is then aimed 10 to 15 degrees cephalad and 10 to 15 degrees toward the midline. This results in dural puncture while avoiding the supraspinous and interspinous ligaments. Both midline and paramedian approaches may be used for either local anesthetic and/or opioid injections. Once in the subarachnoid space, the stylet is removed, and clear CSF should appear at the needle hub. Once CSF fluid is seen flowing through the needle, medications can be injected.[31]

On occasion, a small amount of blood-tinged CSF flows initially, but CSF then clears. This occurs if the spinal needle pierced a vessel during entry and, as long as CSF clears, injection of local anesthetic and/or opioids may proceed.

In patients with no coagulation disorder and an atraumatic tap, the risk of SEH in cardiac surgery is estimated to be between 1 in 220,000 to 1 in 3,600.[32] There is an increased risk with a traumatic tap. Therefore, if a traumatic tap occurs, it may be advisable to postpone surgery for 24 hours, especially if the patient is listed to undergo surgery that requires the administration of an anticoagulant, such as heparin.

When spinal opioids are administered for postoperative pain, a decision is required to perform the spinal before or after surgery. Performance at the end of surgery would prolong the length of postoperative analgesia. It is most common to perform the spinal before surgery, as this will help mitigate the stress response and lower the doses of anesthetics and analgesics required intraoperatively. Furthermore, the benefit of a few additional hours of postoperative analgesia is outweighed by the benefits achieved with preemptive analgesia, which has been demonstrated to result in benefits for up to one-year post-surgery.[33]

Side Effects

Back-ache may occur after spinal due to bruising and/or a localized inflammatory response. Treatment includes cold compresses and oral analgesics such as acetaminophen or NSAIDs. These symptoms usually resolve within several days. Muscle spasm may be treated with a muscle relaxant. Persistent or severe back pain should result in an assessment of more serious complications.

Shivering, a side effect of spinal with a local anesthetic occurs in at least 40% of patients and is believed due to vasodilatation and a decrease in core temperature. While not a side effect of opioids, attempts should be made to pre-warm the patient and use warm IV fluids to minimize discomfort. Effective treatments include IV meperidine, tramadol, and clonidine.

Side effects of spinal opioids, nausea, vomiting, urinary retention, pruritus, and respiratory depression, are the same as intravenous opioids, although pruritus may be more severe with the IT route. Older literature contains case reports of severe respiratory depression progressing to respiratory arrest with IT opioids. It is now known that doses used in such cases were excessive. Indeed, most of the side effects are dose-related, with doses greater than 0.5 mg IT morphine resulting in significant side effects.[34] Pruritis is the one side effect that is uniquely worse with IT opioids as compared with IV opioids, and that seen with sufentanil is worse than with fentanyl.[35] This and its higher cost explains why fentanyl is used more often than sufentanil. The severity of pruritis is usually dose-dependent and can be treated effectively with naloxone. Even a small naloxone dose, 40 to 80 mcg, will usually alleviate pruritis, yet not reverse analgesia.[36] Ondansetron, a 5-HT3 receptor antagonist, is not only an effective antiemetic but also reduces the severity of pruritus.[37] Neuraxial opioids can also cause urinary retention via effects at the spinal cord and pontine micturition center.

Respiratory depression is a particularly concerning side effect not only because it is life-threatening but also because it is often insidious. Indeed, patients in whom it occurs are often observed to be comfortable and sleeping and may therefore not attract attention from nurses or providers. Part of this state may be due to hypercarbia. Respiratory depression after ITM most often occurs 6-18 hours after intrathecal injection, though it may occur sooner if significant doses of IV narcotics are administered intraoperatively. Therefore, if ITM has been administered, it is advisable to use low doses of intravenous narcotics intraoperatively and for postoperative intravenous patient-controlled analgesia. Older literature reported respiratory depression as a serious concern when 1.0 mg or more of ITM was administered. Newer literature indicates that as little as 0.15 to 0.3 mg ITM can provide satisfactory pain control for pelvic or abdominal surgery, while as little as 0.3 mg may be adequate for median sternotomy. When low doses of ITM are used, optimal postop pain control will be assured by providing postoperative patient-controlled anesthesia with low dose fentanyl or morphine intravenously. Due to concern for respiratory depression, appropriate monitoring should be provided for patients who receive ITM. Guidelines are discussed below under postoperative monitoring. For same-day surgery, only low-dose fentanyl, 5 to 10 mcg, should be injected IT.

Complications

Failure of a spinal blockade is not a complication per se but needs to be assessed and managed appropriately. Block failure may occur due to the needle's movement during injection, incomplete entry of the needle into the subarachnoid space, or injection into a nerve root. If failure of spinal with a local anesthetic occurs, it is advisable to proceed with general anesthesia, as there may be a partial effect and re-injection of the second dose of local anesthetic may result in a high spinal, with the attendant risks of severe hypotension, bradycardia, respiratory arrest, and cardiac arrest.

Post-dural puncture headache (PDPH), a moderate complication of spinal, is influenced by the size of the spinal needle and patient demographics. It has a higher incidence among women [38], pregnancy [39], prior headaches (either PDPH or chronic headaches), and younger age.[38] In a study of 94 patients undergoing cesarean section in whom spinal was performed with a 24-gauge Quincke needle in all subjects, a significantly higher incidence of PDPH was detected among patients in whom spinal was performed in the sitting position (20.8%), as compared to patients in whom spinal was performed in the lateral decubitus position (4.3%), p = 0.017.[40] In another study of 320 obstetric patients, the incidence of PDPH was 5% in patients in whom a 25-gauge Whitacre needle was used as compared with a 28.12% incidence of PDPH in patients in whom a 25-gauge Quincke needle was used.[41] The high incidence of reported PDPH in the Quincke group may be because patients were asked about symptoms of headache for five days postop.

Major complications are rare, especially when the proper procedure has been followed. They include direct needle trauma, infection, peripheral nerve injury, and SEH. Needle insertion into the spinal cord or nerves can cause neurologic injury. When the patient experiences paresthesia, the needle may be adjacent to or penetrating neural tissue. A retrospective analysis found 6.3% of patients experienced paresthesia with needle insertion, yet only 0.67% of these patients had persistent paresthesia postoperatively.[42] Furthermore, all patients had resolution of symptoms within 24 months.[42]

While the possibility of respiratory depression from spinal opioids is dose-related and is impacted by IV narcotic administration, it needs to be appreciated that local anesthetic used for surgical anesthesia may result in a high spinal and associated bradycardia, hypotension, respiratory arrest, and even cardiac arrest. If these signs occur, they must be treated with atropine, ephedrine or phenylephrine (depending on the heart rate) or epinephrine, with intubation and/or advanced cardiac life support as indicated. Of note, in patients who suffer cardiac arrest after spinal, the most important treatment to prevent the development of brain injury is the rapid administration of epinephrine.

Meningitis may occur after spinal anesthesia. Sources of infection could be contaminated spinal trays and medication, oral flora of the provider performing the spinal, and underlying patient infection. Still, after a diagnostic lumbar puncture, meningitis incidence is not significantly different compared with the spontaneous incidence of meningitis.[21]

The most severe complication of spinal is SEH. If new neurologic symptoms develop after spinal, neurosurgical consultation and an MRI of the spine should be obtained immediately, as patients who develop SEH are more likely to have a favorable outcome if operated on within 24 hours of symptom onset.[43]

In a recent study conducted to assess the risk of SEH after spinal surgery – in patients in whom spinal was not performed- a 50 mm Hg or greater increase in systolic blood pressure after extubation, and high body mass index, were identified.[44]

Clinical Significance

Whether IT opioids are added to local anesthetic to provide surgical anesthesia or injected alone, they result in blunting of the intraoperative stress response, decreased requirement for anesthetic agents, and improved postoperative analgesia. Low-dose fentanyl, 10 – 20 mcg, is often added to the local anesthetic for short or less invasive surgeries. For surgeries with large incisions, ITM is usually administered. Applications for specific types of surgery are discussed below.

IT opioids are also very effective in managing patients with severe chronic pain syndromes in whom patient comfort is not achieved with more conventional treatments.

Foot and Ankle Surgery

Most foot and ankle surgery is done on an outpatient basis. In these cases, fentanyl (5 to 10 mcg) is the IT opioid of choice. It may improve the quality of the spinal block while supplementing postop analgesia for up to four hours. However, since these patients may be sent home quickly, some prefer to avoid IT opioids, as postop nausea, vomiting, or pruritus may delay discharge.

Cesarean Section

Neuraxial anesthesia is the preferred technique for caesarian deliveries in the United States and Canada, used for more than 95% of these procedures.[45] A combination of local anesthetic (most often bupivacaine) and opioid (fentanyl and/or morphine) is often used. A meta-analysis of patients undergoing spinal anesthesia for cesarean section found the need for intraoperative analgesic supplementation decreased from 24 to 4% when opioids were added to the local anesthetic injection.[6] The preference for spinal (or epidural) anesthesia over general anesthesia is that regional techniques preclude the need to manage the airway, which is more challenging in the pregnant population. Furthermore, maternal blood loss is decreased with spinal compared to general anesthesia, due primarily to lower blood pressure.[46] Spinal anesthesia also allows the mother to be awake, have a partner present, and permits rapid bonding with the baby. Fentanyl 10 to 15 mcg is often administered to supplement intraoperative analgesia provided by the local anesthetic, while it is added to 0.100 to 0.150 mg ITM to provide postoperative analgesia.

Orthopedic 

Spinal anesthesia is beneficial for hip fracture surgery, particularly in the elderly, and a 2005 best practice review recommended regional anesthesia whenever possible for this type of surgery.[47] Benefits cited include decreased mortality, deep vein thrombosis, pulmonary complications, and transfusion requirements. ITM has also been used as part of multimodal anesthesia after total knee arthroplasty, with patients having lower pain scores at 12 hours postoperatively and lower systemic opioid use up to 48 hours postoperatively, compared with controls.[48]

Cardiac

Multiple groups have reported the use of ITM in patients undergoing cardiac surgery. Several groups have reported decreased postoperative pain scores with ITM and diminished postoperative systemic opioids than controls who received no intrathecal injection.[49][50] Low-dose ITM has also been shown to facilitate early extubation after cardiac surgery [51][52], including off-pump coronary artery bypass grafting, thereby facilitating fast-track recovery. In a study of 507 balanced pairs created with propensity score matching, patients who received ITM had fewer postoperative pulmonary complications after heart surgery than patients treated with IV analgesia.[53] Besides, fewer patients in the ITM group required prolonged ICU or hospital stays.[53] Another group reported improved pain scores and improved patient satisfaction and decreased catecholamine release at some time points in patients treated with ITM versus controls.[49] In children ages, 3 months to 6 years old undergoing pediatric cardiac surgery, spinal blockade with tetracaine 0.5 to 2.0 mg/kg and morphine 7 mcg/kg has been shown to result in lower postoperative pain scores and lower IV fentanyl PCA requirements versus controls, with no differences in hypotension, bradycardia, oxygen desaturation or pruritus.[54]

Monitoring After Administration of Spinal Opioids

Patients who receive ITM should have an hourly assessment of respiratory rate and level of alertness for the first 12 hours and every two hours from hours 12 to 24. If patients have co-morbidities such as hypertension, cardiac or neurologic disease, a body mass index of 40 or greater, receive any other sedatives or general anesthesia, or receive IV magnesium, respiratory rate, and sedation score should probably be measured hourly for twenty-four hours. In high-risk patients, the addition of capnometry and/or pulse oximetry should be considered. However, it should be noted that desaturation may not occur until late in patients receiving supplemental oxygen. Not uncommonly, a slowing respiratory rate and/or increasing sedation will warn of respiratory depression before desaturation. A respiratory rate of ten breaths/min should prompt an in-depth bed-side assessment. Order sets should require a provider to be notified immediately if the respiratory rate decreases to ten breaths per minute or less. Finally, it is important to note that respiratory depression occurs more frequently in obese patients, possibly due to the presence of obstructive sleep apnea.[55]

Enhancing Healthcare Team Outcomes

There is a complex interplay of pain with physiologic implications that impact morbidity and mortality. Psychological implications affect patients’ interpretation of the perioperative experience, quality of recovery, and patient satisfaction. Patients who manifest decreased pain postoperatively and an improved surgical experience assessment are less likely to have acute pain convert to chronic pain.[56] Considering the ongoing opioid epidemic, improving perioperative analgesia is a priority. Spinal opioids can help minimize postoperative opioid use and improve analgesia in patients suffering from chronic pain syndromes. The decreased requirement for oral opioids is better for patients and the healthcare system as a whole. In addition to improved patient experience, earlier extubation and improved postoperative pain control have led to shorter intensive care unit stays, reduced perioperative costs, and resource utilization following surgery, specifically of a cardiac nature.[57]

Clinical Pearls

It has long been taught that the spinal cord ends at L1 in adults. However, ultrasound used to visualize spinal anatomy has shown that the conus medullaris extends below L1 in some patients. Combined with the fact that palpation of the iliac crest – though to represent the L4-5 interspace, may on occasion represent a more cephalad interspace- suggests a possible cause of paresthesia in some patients.

Complaints of nausea, dizziness, or feeling strange sometimes occur shortly after the spinal performance and reflect hypotension that has not yet been measured on the blood pressure monitor. A small dose of phenylephrine or ephedrine, with the preferred agent selected based upon heart rate, can be administered at this time while the blood pressure cuff is recycled. This small dose of vasoconstrictor will help alleviate hypotension and these related symptoms if hypotension is, in fact, present, but will not harm the patient if hypotension is not present. 

The night of surgery, pulse oximetry alone does not ensure patient safety, as patients receiving supplemental oxygen can maintain their saturation with a slow respiratory rate. Indeed, orders should be written to call a provider or provider assistant if the respiratory rate decreases below ten breaths per minute. There should also be a standing order to administer 40 mcg naloxone IV if the respiratory rate decreases to eight per minute and administer an additional 80 mcg IV if the respiratory rate does not climb to at least ten breaths per minute within two minutes of naloxone administration. If a patient’s level of arousal is decreased, an arterial blood gas should be performed. If arterial pressure of carbon dioxide is elevated, a low-dose naloxone infusion and/or some form of ventilatory support (BiPAP or controlled ventilation) may be indicated.

Some prefer to replace the stylet once clear CSF is seen and advance the needle an additional 1 mm. The logic is that the initial visualization of CSF might occur if only part of the needle bevel is inside the spinal canal. The additional 1 mm of distance is believed to ensure the entire bevel is in the spinal canal. This is important for if part of the bevel remains outside the spinal canal, an insufficient dose of medication may be injected, resulting in a failed block.

Some providers will, in a sterile manner, open an additional spinal needle onto the spinal tray. For example, in the elderly, spaces may be narrowed, and the risk of headache is lower; some may place a larger (22-gauge) needle on the spinal tray.

Although it is generally be assumed that an SEH that develops shortly after the spinal performance is due to the spinal, it is interesting to note that spontaneous SEH occurs as well.[58][59]