Saddle Block Anesthesia

CHAPTER 175 Saddle Block Anesthesia



Peter W. Grigg


Saddle block anesthesia provides pain relief in the area of the perineum, buttocks, and inner thigh by using an intrathecal (spinal) injection of local anesthetic. A saddle block may be confused with a caudal block (injection of local anesthetic into the sacral canal through the sacral hiatus) because the resultant anesthesia may be similar, but the technique is different. This chapter describes the low-spinal saddle block technique. An ideal “saddle block” anesthetizes the area that would touch a saddle if the patient were riding a horse.


With the advent of more complex techniques for producing analgesia and anesthesia, including single-dose intrathecal opiates and combined spinal epidural and continuous spinal infusions, traditional saddle block (low spinal) is used less often.


Saddle block anesthesia has been used for many years for both surgical procedures and obstetric deliveries. Past problems with profound motor paralysis can be avoided by using lower doses of bupivacaine (e.g., 1 to 2 mL 0.25% bupivacaine [Sensorcaine-MPF] with or without a narcotic). Therefore, variations of saddle block anesthesia can be used midlabor or near delivery.


Clinicians administering saddle block anesthesia must have a good understanding of the anatomy, needle placement techniques, pharmacology, and physiology involved, particularly with regard to the obstetric patient. They must be familiar and experienced with the diagnosis and management of possible complications. A review of the updated American Society of Anesthesiologists (ASA) Guidelines for Obstetric Anesthesia (2006) and the ASA Difficult Airway Algorithms is highly recommended for medical professionals anesthetizing obstetric patients.


Saddle blocks should be performed only in hospitals, surgical centers, or facilities where drugs, equipment, and adequately trained personnel are available to manage any and all possible complications. The equipment available should be comparable with that of the main operating rooms.



Indications



• For use in obstetrics when time or other circumstances do not allow the use of continuous catheter spinal or epidural anesthetic techniques (e.g., routine delivery, assisted delivery [forceps, vacuum], episiotomy or perineal repair, or other obstetric procedures).

• To provide quick relief so that a laboring patient can remain stationary for epidural catheter placement.

• Genital surgery (e.g., dilation and curettage, hysteroscopy, vaginal surgery, adult circumcision, orchiectomy, or complicated vasectomy).

• Anorectal surgery (e.g., hemorrhoidectomy, fistulectomy, or rectal-anal biopsy).

• As part of a combined spinal epidural technique, when the spinal needle is placed through an epidural needle that is in the epidural space.


Contraindications



Absolute



• Patient declines.

• Lack of proper resuscitative equipment, skills, or trained staff.

• Allergy to specific local anesthetics.

• Active systemic infection.

• Moderate to severe hypovolemia.

• Blood dyscrasias; coagulopathy; prolonged international normalized ratio, prothrombin time, or activated partial thromboplastin time; thrombocytopenia.

• Anticoagulant therapy (e.g., heparin, warfarin, enoxaparin [Lovenox], clopidogrel [Plavix]).


Relative



• Cutaneous lesions of the lower back.

• Spinal abnormalities, including scoliosis and other structural abnormalities.

• Preexisting neurologic diseases (amyotrophic lateral sclerosis, other degenerative nerve diseases, poliomyelitis).

• Preoperative headache.


Equipment and Supplies



• Disposable sterile gloves

• Equipment for the clinician to observe universal blood and body fluid precautions

• Disposable spinal tray containing the following
• Appropriate prep solutions, swabs, and sterile 4 × 4 gauze pads

• Disposable drapes

• Syringes
3-mL plastic Luer-Lok for local infiltration of lidocaine 1%

5-mL procedural syringe for administration of intrathecal agent

• Needles
image-inch, 25-gauge spinal needle (pencil point instead of cutting bevel)

20-gauge introducer needle

19-gauge filter needle for drawing solutions into the syringes

25- or 27-gauge skin wheal needle

• Medications
Lidocaine 1% (available in 5-mL vial) for local infiltration

Hyperbaric anesthetic
Lidocaine 5% (preservative free) in 7.5% dextrose for intrathecal administration (2-mL vial), or

Tetracaine 1% (2-mL vial) mixed at the time of use with an equal volume of dextrose 10% (5-mL vial) to make the solution hyperbaric, or

Bupivacaine 0.75% in 8.25% dextrose (2-mL vial)

Bupivacaine 0.25% methyl paraben free (MPF; for epidural use) plain

Epinephrine 1:1000 (1-mL vial); addition of 0.2 to 0.3 mg (0.2 to 0.3 mL of 1 : 1000) epinephrine to tetracaine will produce vasoconstriction and prolong the duration of anesthesia by about 50%

Ephedrine 5% (1-mL) in case hypotension develops (the usual dose to treat hypotension is 10 mg [0.2 mL] intravenously [IV])

Fentanyl 50 µg/mL for injection

NOTE: A 1% solution equals 10 mg/mL.


• IV fluids (Ringer’s lactate, normal saline)

• Continuous fetal monitoring equipment if used for labor and delivery

• Patient monitoring equipment, including automated blood pressure (BP) device, continuous electrocardiograph (ECG), and pulse oximeter

• Emergency and resuscitative equipment, including suction, positive-pressure breathing device (Ambu-Bag), oxygen, and defibrillator (Having general anesthesia equipment available may be useful [e.g., endotracheal tubes, laryngoscope].)

• Emergency and other drugs not included in the spinal kit
• Atropine

• Diphenhydramine (Benadryl)

• Ephedrine (not included in all commercial spinal kits)

• Lidocaine for IV injection

• Metoclopramide (Reglan)

• Neo-Synephrine

• Epinephrine

• Phenylephrine

• Succinylcholine

• Propofol, thiopental, and midazolam


Anesthetic Agents and Doses


For saddle block, the three commonly used local anesthetics are lidocaine, tetracaine, and bupivacaine. Lidocaine produces a more rapid onset of anesthesia than tetracaine or bupivacaine; however, it is the shortest acting of the three. Lidocaine generally produces adequate surgical analgesia for 45 to 90 minutes, whereas tetracaine and bupivacaine will last image to 3 hours.


Recently, reports of neurologic sequelae (transient radicular irritation) have raised concerns about the use of lidocaine for intrathecal anesthesia. The risk appears to be reduced if the lidocaine solution is diluted before injection with an equal volume of cerebrospinal fluid (CSF). Tetracaine and bupivacaine are excellent alternatives to lidocaine; however, their increased duration of action requires a longer recovery period.


NOTE: For a rapidly progressing obstetric patient, lidocaine may be the only option that will work quickly enough.


Hyperbaric solutions (solutions more dense than CSF) are used for saddle block anesthesia so that in the sitting position the anesthetic solution travels caudad, affecting only the lower levels of the spinal cord. It is important to remember that during pregnancy, inferior vena cava compression will cause engorgement and distention of the vertebral venous system. As a result, there is a decrease in the CSF capacity of the subarachnoid space; therefore, the dose requirements are generally reduced in the pregnant patient.


Near delivery, the usual dose of lidocaine for a saddle block is 25 to 50 mg of 5% lidocaine in 7.5% dextrose (0.5 to 1.0 mL). It should be mixed with equal amounts of CSF before injecting. The equivalent dose of 1% tetracaine is 4 to 6 mg (0.4 to 0.6 mL) plus an equal volume of 10% dextrose solution. For bupivacaine, 5 to 6 mg (0.66 to 0.8 mL of the 0.75% bupivacaine in 8.25% dextrose) should be used. Epidural bupivacaine 0.25% MPF 1 mL (2.5 mg) with 25 µg fentanyl provides less motor block. In surgical procedures for the nonpregnant patient, the doses should be increased.


Confining the anesthetic to a saddle block distribution depends on the dosage and the time that the patient remains in the sitting position after administration of the anesthetic. Too little time in the sitting position (lying down too soon) may produce a higher level of anesthesia than desired, placing the patient at higher risk of hypotension and a higher level of block.


NOTE: From an anesthetic perspective, the level of anesthesia refers to an anatomic level or segment of effect (e.g., up to the level of the umbilicus [T10], the lower border of the ribs [T8], or the level of the xiphoid [T6]), whereas depth refers to the amount of remaining sensation. With saddle block, both motor and sensation are blocked; however, the level of the sensory block is usually two segments above the motor block.

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May 14, 2017 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on Saddle Block Anesthesia

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