Abstract

Spinal anesthesia is a commonly performed regional technique by a majority of the anesthesiologists worldwide. This technique is learnt early during training and relatively easy to master. Despite being the oldest regional anesthesia technique, it continues to evolve and develop in various aspects. This review attempts to highlight the recent advances in this “almost–perfect” technique with respect to indications, procedure, drugs, and strategies to minimize side effects. Understanding the finer aspects and knowledge gaps will help postgraduates and practicing anesthesiologists in designing patient specific techniques and interventions.

Keywords

conduction anesthesia, regional anesthesia, spinal anesthesia

---

Introduction

Spinal anesthesia is a perhaps the most commonly performed regional technique by majority of the anesthesiologists across the world. The technique is learnt early during training and technical competence is acquired quickly, after 40–70 supervised attempts. ¹ The procedure is relatively easy to perform, has a definite endpoint, the results are predictable, surgical conditions are acceptable and safe for the patient when performed with due diligence. Still, this “almost–perfect” technique is continuously evolving with newer indications, novel drugs, and innovative strategies to mitigate side effects. This narrative review attempts to analyze the recent trends and updates in spinal anesthesia and its implications upon practice.

Methods

A literature search was made in the following databases—PubMed, Cochrane central, Embase, Scopus, and Google scholar with the keywords—spinal anesthesia or anesthesia, subarachnoid block, and central neuraxial blockade. Review articles, randomized trials, systematic reviews, meta-analysis, and clinical trials were included. Articles within the last 10 years were analyzed for a description or evaluation of spinal anesthesia with respect to these 4 major domains—indications, technical description, drugs, and strategies for minimizing side effects. Abstracts were reviewed and those relevant to the queries were chosen, no attempts were made to grade the evidence. The results are presented as a narrative review.

Newer Indications

Spinal anesthesia is originally a technique for lower abdominal and lower limb procedures, but it has evolved into an acceptable option for upper abdominal surgeries also. More recently spinal anesthesia is being utilized for various surgeries, for which traditionally general anesthesia was considered as the technique of choice.

Laparoscopic Surgeries

General anesthesia with cuffed endotracheal tube and controlled ventilation is the preferred technique for laparoscopic surgeries. While spinal anesthesia is a feasible option, concerns about the adequacy of ventilation, possibility of shoulder pain, and patient discomfort due to head-low position remain. On the other hand, spinal anesthesia might even offer some benefits like cost effectiveness, lesser post-operative nausea, and vomiting, better post-operative analgesia to name a few. As the patient is spontaneously breathing, PaCO₂ levels are maintained. A meta-analysis by Longo et al.² evaluating the use of spinal in laparoscopic cholecystectomies suggests that in healthy individuals, compared to general anesthesia spinal anesthesia may not offer any extra benefits. The shoulder pain is troublesome, and a 3.2% of patients might require conversion to general anesthesia. The post-operative pain is less, but the incidence of post dural puncture headache is higher. In extra peritoneal inguinal mesh repairs, spinal anesthesia caused lesser post-operative pain and quicker recovery, but offset by the higher incidence of headache, longer procedural times, hypotension, and urinary retention.³ Spinal anesthesia may be an option in selected patients with significant risks associated with general anesthesia.

Spine Surgeries

While it is an acceptable option for surgeries like a single level discectomy, spinal anesthesia has been successfully used in more complex surgeries like multi-level instrumentation without serious adverse events. In a retrospective study involving 497 spine surgeries done under spinal anesthesia, the incidence of hypertension and tachycardia was much lesser when compared to general anesthesia.⁴ The study population included patients with severe degenerative spinal disorders, lumbar spinal stenosis, etc., which are relative contraindications to spinal anesthesia. The blood loss and analgesic consumption may not significantly decrease, though.⁵ However, if there is a need for endotracheal intubation or conversion to general anesthesia, the process is cumbersome with the possibility of sterility breach. The risk benefit balance of spinal anesthesia should always be considered especially in prolonged surgeries. Spinal anesthesia is not an option if intraoperative neurophysiological monitoring is planned.

Spinal Anesthesia in Cardiac Surgeries

High spinal anesthesia, a complication of accidental drug overdose is intentionally used in cardiac surgeries along with general anesthesia. The stress response and inflammatory mediators are lesser,⁶ and it is possible to extubate the patient earlier.⁷ The technique has been successfully used in bypass and valve replacement surgeries.

Pediatric Spinal Anesthesia

With the advent of ultrasound, pediatric regional techniques have gained universal acceptance. Spinal anesthesia has been successfully used in infants for various surgeries like duodenal atresia, laparoscopic pyloromyotomy, meningomyelocele repair, etc., where general anesthesia was considered necessary.⁸ While a brief exposure to general anesthetic is probably safe,⁹ concerns about long term effects upon cognitive and behavioral functions remain. This has reinforced the value of regional techniques, including spinal anesthetics. The advantages include better hemodynamic stability, faster recovery of gastrointestinal functions, and shorter post-anesthesia recovery stay.¹⁰

Anti-Platelets and Anticoagulants

Spinal anesthesia is usually deferred in patients taking antiplatelet drugs due to the risk of spinal hematomas and subsequent neurological deficits. According to current recommendations, aspirin is no longer a contraindication, and clopidogrel should be stopped 5–7 days before a spinal, but the real risk of spinal hematomas is unknown. A systematic review involving more than 300 patients who received neuraxial anesthesia with uninterrupted antiplatelet drugs showed no instances of hematoma or neurological deficit.¹¹ In patients undergoing lumbar puncture, the incidence of bloody tap was 3% within a week and 5% after 4 weeks of stopping antiplatelet and no difference was observed whether patient received aspirin alone or dual antiplatelets.¹² The risk of hematoma seems multifactorial—including age, gender, renal dysfunction, difficult anatomy, multiple attempts, and catheter insertion. In a recent Danish cohort study, the risk of spinal hematoma was 0.23% in patients with preexisting coagulopathy 0.20% without.¹³ Similarly, in obstetric patients receiving low molecular weight heparin (LMWH), uneventful spinal anesthetics have been administered. A systematic review based on data from 28 obstetric patients who received spinal before the minimum recommended time for discontinuing LMWH and 52 patients who received the same without discontinuing them found no reports of spinal or epidural hematomas, which was considered encouraging.¹⁴ Despite these encouraging reports, till better evidence emerge, it is safe to follow the current the American Society of Regional Anesthesia and Pain Medicine (ASRA) recommendations of withholding antiplatelet and LMWH before spinal anesthesia. However, a new recommendation (evidence level grade 2C) by ASRA¹⁵ allows for exceptions or modifications of ASRA guidelines in obstetric patients under special circumstances. A single attempt with an atraumatic needle without catheters may be considered in such exceptional scenarios. Direct acting anticoagulants represent a special scenario owing to their long action, ASRA’s recent guidelines address this issue.

Day Care Spinal Anesthesia

Traditionally general anesthesia with short acting drugs and motor sparing nerve blocks are preferred for day care surgeries. The possibility of residual motor blockade, voiding difficulties, and fear of post dural puncture head ache deter the use of spinal anesthesia for day care surgeries. Strategies to address these issues include using low doses of local anesthetics, unilateral spinal anesthesia, and using newer short acting drugs. Even though it is possible, bupivacaine is not an ideal choice for day care surgeries, as the dose range ensuring both reliable anesthesia and early ambulation is narrow.¹⁶ Two drugs of interest are prilocaine and articaine. About 2% hyperbaric prilocaine, is associated with significantly faster motor recovery than 0.5% ropivacaine.¹⁷ Readiness for discharge can be achieved in 4 hours.¹⁸ Articaine, widely used by dentists, has a thiophene ring with an ester linkage leading to faster metabolism (elimination half-life 27 mins vs. 90 mins of other amides).¹⁹ Articaine is an acceptable choice for day care procedures of about an hour duration.²⁰ However, the incidence of hypotension may be more and probability of transient neurological symptoms are a concern.²¹

Technical Advances

Continuous Spinal Anesthesia (CSA)

CSA is almost a century old technique. Despite notable advantages (titrated dosing, extending duration), it is not widely practiced. The microcatheters (29–32 G) introduced in the 80’s had a high incidence of neurological complications prompting its ban by the United States Food and Drug Administration (FDA). Currently macrocatheters are available which are safer. The possibility of infection, nerve injury and persistent cerebrospinal fluid (CSF) leak are some of the deterrents. Most practitioners use this technique only in the elderly due to concerns about postdural puncture headache (PDPH). However, even in the young, CSA might be an option in certain situations like obstetric patients with heart disease, morbid obesity, previous spine surgeries apart from difficult epidural placements and accidental dural puncture.²² Currently, we have both catheter-through-needle and catheter-over-needle equipment available. The Catheter over the needles seal the dural hole better albeit difficult to insert. In a retrospective study of 318 cases, catheter could not be introduced in 5 cases and no patient had PDPH or neurological sequelae.²³ Compared to continuous epidurals, CSA provided faster onset, better analgesia resulting in more satisfied patients who underwent hip replacements.²⁴ Due to unavailability of spinal catheters, epidural catheters continue to be widely used for this purpose.²⁵

Unilateral Spinal Anesthesia

Lesser hemodynamic disturbances, urinary retention, and early motor recovery are some of the possible advantages of unilateral spinal anesthesia. To achieve a strict unilateral effect, the following recommendations are made—hyperbaric drugs, speed of injection as slow as 0.33 mL/min and keeping the patient in knee chest position for at least 10 minutes.²⁶ To achieve such slow injection speeds syringe pumps can be employed. Real time sympathetic tone monitoring also might help in achieving a strictly unilateral effect.²⁷ The duration of sensory block may be the same while motor block may be prolonged, when compared to conventional spinal anesthesia.²⁸ When compared to CSA, unilateral spinal had longer onset times, lesser need for conversion to general anesthesia and is cost effective.²⁹ For unilateral procedures of appropriate duration, unilateral spinal anesthesia may be preferred.

Segmental Thoracic Spinal Anesthesia

This seemingly dangerous technique involves injecting small volumes of anesthetics at thoracic levels for abdominal surgeries. The justifications for this approach include—the distance between the dura and the spinal cord is maximum at thoracic levels;³⁰ this margin of safety is further increased by the oblique course of the needle, thoracic nerves are thinner requiring smaller doses, absence of lower limb venodilation minimizing the risk of hypotension to name a few. Thoracic and even cervical spinal anesthesia are in fact more than a century old,³¹ and doubts remain about its safety. While the spinal nerves are sensitive to needle contact, the cord itself is insensitive to needle penetration, drug injection, or catheter insertion, and accidental cord damage cannot be detected during the puncture.³² This technique has been analyzed only in few small-scale trials so far. The risks versus benefits of this approach remains to be determined.

Rapid Sequence Spinal Anesthesia

Even though general anesthesia is the technique of choice in category 1 caesarean sections, a socalled rapid sequence spinal anesthesia might be an acceptable choice in selected patients. The technique involves a no-touch technique, avoiding additives, limiting attempts, allowing surgery to start before full establishment of level and preparedness to convert to general anesthesia should the need arise. Initial data from case series suggested that it was possible to achieve satisfactory surgical anesthesia within 3–5 minutes.³³ Careful case selection is important as any technical difficulties can prolong the procedure, and even after a successful spinal anesthesia, the time required to achieve adequate anesthesia is unpredictable.³⁴

Epidural Volume Extension

During combined spinal-epidural anesthesia, injecting saline through the epidural catheter can be used achieving higher levels, faster onset, and dose reduction.³⁵ A recent meta-analysis revealed low quality evidence for sensory levels and hypotension, and shorter motor recovery times may be possible.³⁶ A mean volume of 7.5 mL has been suggested to increase the sensory level by 1 dermatome within 5 minutes.³⁷ A ceiling effect has been observed with volumes of 15 mL.³⁸ Limitations of eve include unpredictable sensory levels, need for supplementary analgesics apart from a lack of clarity regarding a dose effect relationship and factors influencing clinical effects.

CSF Lavage

A lifesaving technique—after accidental intrathecal administration of epidural drugs is CSF lavage. It involves administration of saline in 15 mL boluses and aspirating an equal amount of CSF, the procedure is repeated few times, helping in diluting the drug and minimizing the adverse effects, hastening the recovery. This technique has successfully been used in accidental intrathecal administration drugs meant for epidural use³⁹ and reversing accidental high spinal anesthesia.^40,41 Some possible side effects include low pressure herniations and introduction of infections.

Ultrasound Guidance

The effectiveness of ultrasound in regional anesthesia has been proven beyond doubt. In central neuraxial blockade, preprocedural ultrasound can result in increased success rates, decreased attempts and ease of performance. In elderly patients for combined spinal-epidural techniques through a paramedian approach, preprocedural ultrasound increased first pass success rates, reduced number of attempts and improved patient satisfaction.⁴² It may be of value in obese parturient and in difficult punctures, but may not increase the first pass success rates in patients with palpable landmarks.⁴³ Whether it improves patient safety also is inconclusive.⁴⁴ The perceived advantages are also operator dependent, as no improvement in ease of procedure when compared to landmark based approach was evident with junior residents.⁴⁵ Hence, in difficult spinal anesthesia a preprocedural ultrasound by an experienced operator is recommended to improve success rates and decrease number of needle passes.

Newer Drugs

Short and ultrashort acting intrathecal drugs have gained special interest due to increasing usage of spinal anesthesia in day care procedures, as previously mentioned. Even though a wide gamut of drugs has been used as additives in spinal anesthesia, consistent, and safe results are obtained with only opioids and α 2 agonists. Whereas opioids have the potential to cause respiratory depression, urinary retention and pruritus, α 2 agonists are known to cause transient bradycardia and hypotension.⁴⁶Concerns were raised regarding neurotoxicity of intrathecal dexmedetomidine, but recent animal studies suggest a single dose is safe⁴⁷ and might even protect against lignocaine induced neuronal death.⁴⁸ A variety of systemically administered drugs can influence the onset and duration of spinal block.⁴⁹

Management of Side Effects

Hypotension

Several drugs and strategies are used to minimize the unavoidable hypotension that accompanies spinal anesthesia. Most of the research involve obstetric patients, in whom maintaining blood pressure is of paramount value. Drugs and interventions like ephedrine, phenylephrine, noradrenaline, metaraminol, colloids, fluid loading techniques, elastic compression stockings have shown to be effective in minimizing hypotension to varying degrees. A recent meta-analysis⁵⁰ ranked these interventions in the following order (most effective to least effective)—metaraminol, norephinephrine, phenylephrine, leg compression, ephedrine, colloid before induction, angiotensin 2, colloid after induction, and lastly crystalloid before induction. The same study has revealed more bradycardia with phenylephrine and lower umbilical artery pH with ephedrine. With respect to the fetal acid base status, noradrenaline, mephentermine, metaraminol, had the least effect on fetal acid base status followed by phenylephrine and ephedrine. Ephedrine was associated with worst outcomes, except bradycardia.⁵¹ Recently drugs like glycopyrrolate and ondansetron also have shown to minimize vasopressor requirements.^52-55 While most of them can minimize the hypotension, none appears to reliably prevent the hypotension.⁵⁶ This is possibly due to multiple mechanisms contributing to the hypotension—arteriolar and venous dilation⁵⁷ apart from decreased cardiac output especially in the elderly.⁵⁸ A genetic basis for exaggerated hypotension is also proposed.⁵⁹ The criteria of hypotension also have been changing as more recent studies indicating maintaining blood pressure above 90% of the baseline values lead to better outcomes. An international consensus statement recommends the same.⁶⁰

Minimizing the local anesthetic dosage—low dose spinal anesthesia, even though effective in minimizing hypotension and vomiting, increase the need for analgesic supplementation.⁶¹ Alternatively, allowing the patient to remain seated for a while after the spinal (seated time) helps in minimizing the hypotension and nausea, secondary to lesser sensory levels but prolong the motor blockade.^62,63

Shivering

Shivering is a compensatory mechanism for the fall in core body temperature (thermoregulatory) during anesthesia and non-thermoregulatory shivering is associated to vasodilation and pain.⁶⁴ Inadvertent hypothermia in obstetric patients receiving spinal anesthesia has an incidence of up to 91%.⁶⁵ Apart from patient discomfort, hypertension and increased oxygen consumption, hypothermia is associated with various adverse outcomes. Ingestible telemetric sensors have shown lowered intestinal temperatures reaches a peak after 1 hour of spinal anesthesia and may not return to normal even after 8 hours.⁶⁶ Non-pharmacological methods to minimize shivering like forced air warming and warmed fluids might minimize the incidence⁶⁷ but may not be always effective.^65,68 The optimal strategy for preventing hypothermia remains unknown.⁶⁹ Pharmacological treatment modalities have been employed including intrathecal dexmedetomidine, opioids, intravenous ketamine, tramadol, ondansetron, magnesium⁷⁰, and newer options like dexamethasone and nefopam.⁷¹ While dexmedetomidine, ketamine, and meperidine remain popular choices, a multimodal and individualized approach seems logical.

Neurotoxicity

Neurotoxicity of local anesthetics is influenced by the concentration and duration of exposure. The underlying mechanism with both ester type and amide local anesthetics includes mitochondrial dysfunction due to calcium overload, overproduction of reactive oxygen species, DNA damage, and neuronal apoptosis. Different local anesthetics might cause neurotoxicity via different pathways.⁷² The incidence of transient neurological symptoms is more with lignocaine when compared to bupivacaine, levobupivacaine, ropivacaine, and prilocaine. 2-chlorprocaine has similar neurotoxic profile as lignocaine, based on a recent Cochrane review.⁷³

PDPH

While reduction in needle sizes has significantly reduced the incidence of PDPH, very thin needles (29G and beyond) may be associated with higher failure rates.⁷⁴ Atraumatic needles can reduce the incidence of PDPH, but the evidence is only of moderate quality.⁷⁵ They are costlier than conventional Quincke needles. The correlation with needle size and PDPH rates is not seen in pencil-point needles.⁷⁶ Visual and auditory disturbances due to traction of cranial nerves can accompany⁷⁷ and sometimes the hearing loss can be long lasting.⁷⁸ There seems to be an increased incidence of chronic headache and back ache in these patients.⁷⁹ Bed rest and fluids do not appear to influence the incidence of PDPH.⁸⁰ With respect to pharmacological treatment various drugs like caffeine, gabapentin, theophylline, and hydrocortisone have shown to decrease pain scores, while sumatriptan and ACTH did not show any effect.⁸¹ For prevention of PDPH after an accidental dural puncture, a 2013 Cochrane review found morphine, cosyntropin, and aminophylline effective for treatment, whereas dexamethasone actually increased the risk of PDPH.⁸² Epidural blood patch remains the technique of choice in established PDPH.

Vomiting

Vomiting after spinal anesthesia is multifactorial, influenced by patient factors (e.g., age, sex, obesity, and smoking status), anesthesia factors (e.g., high spinal anesthesia, hypotension, adjuvants [opioids], unopposed vagal activity, and pain) and surgical factors (e.g., orthopedic and obstetric). Among the interventions, maintaining blood pressure, normovolemia, and various antiemetic drugs (e.g., 5HT3 antagonists, dopamine antagonists, dexamethasone, and propofol) have been employed. NICE guidelines⁸³ recommend fluids, vasopressors, aspiration prophylaxis, and antiemetic prophylaxis (e.g., pharmacological or acupressure) for all parturient. Acupressure^84,85 and stimulation of P6 point⁸⁶ have shown to be effective in minimizing vomiting in parturient, though a consensus is lacking. A 2015 Cochrane review found no difference between P6 acupoint stimulation and antiemetics for prevention of postoperative nausea and vomiting (PONV).⁸⁷ Aromatherapy also showed only uncertain benefits in preventing PONV.⁸⁸

In conclusion, spinal anesthesia, an old and commonly performed technique, is still evolving in terms of indications, technical advancements, drugs, and management of side effects. Better understanding of the physiology of spinal anesthesia, pharmacology of local anesthetics, and additives and newer interventions for managing adverse effects will help in designing tailor made techniques for patients. This in turn will help in improving patient safety, quality of perioperative care, and outcomes. Still there is scope for research and improvement in spinal anesthesia, which will continue to be refined in a quest for perfection.

---

References