Presentation on theme: "Beginning Neuraxial Anesthesia (an overview) Local Anesthetics (an introduction)"— Presentation transcript:
Beginning Neuraxial Anesthesia (an overview) Local Anesthetics (an introduction)
Neuraxial Anesthesia Indications Any operation in the lower abdomen and below
Contraindications Absolute –Patient doesn’t want it –Infection at site of puncture –Increased ICP –Uncorrected hypovolemia –Uncorrected coagulopathy Relative –Systemic infection –Neuruologic diseases like MS
Spinal vs. Epidural Spinal –More definite endpoint –Easier to do –Faster onset –More intense sensory and motor block –Limited duration –Fewer failures Epidural –Less definite endpoint –More difficult to do –Slower onset –Less intense sensory and motor block possible (labor) –Unlimited duration –Postop analgesia possible –More failures
ABSOLUTELY NO RITUALS!
Where? Spinal - L2-3 and below Epidural - anywhere
Skin anesthesia Do a good intradermal skin wheal Other, deeper soft tissues are not painful The periostium is painful but impossible to anesthetize easily, so don’t try
Please memorize this image. When you are performing an epidural or spinal puncture use the image of the ligaments as a guide to imagine where the needle tip is at all times.
The way the needle is held is unimportant. What is important is that you have control of the needle and that the needle is INSERTED AND MOVED SLOWLY AND DELIBERATELY. Three different ways to hold the needle for the loss of resistance with saline
If at any time you think the plunger is stuck, STOP. Remove the syringe and check that the plunger moves freely. Pay attention to what you are FEELING as the needle advances. If you feel as though the ligamentum flavum has been penetrated but there has been no LOR to injection, STOP. Reassess plunger action and resistance to injection. Pay attention to DEPTH as the needle advances. If you feel as though you should have penetrated the ligamentum flavum by now but there has been no LOR to injection, STOP. Reassess plunger action and resistance to injection.
Please note the following: 1. The syringe is filled with saline and there is NO AIR in the syringe. 2. The syringes shown here are not filled enough to start with. Put 4 – 5 ml of saline in the syringe. 3. Do not inject all of the saline before you have engaged the needle in the interspinous ligament or the ligamentum flavum. 4. Once engaged in a ligament (any ligament) it is impossible to inject the saline 5. Once there is resistance to injection, keep CONSTANT UNREMITTING THUMB PRESSURE ON THE PLUNGER WHILE SLOWLY ADVANCING THE NEEDLE until there is no resistance to injection.
Spinal Anesthesia We do it the same as we do an epidural except we use flimsy needles and we don’t stop in the epidural space
Because the needles are so flimsy, we use an introducer needle
Interspinous lig Epidural space Dura CSF Ligamentum flavum
Epidural injections: What concentration? How much?
Ask your attending
Epidural injections: What concentration? Chloroprocaine – 3% Lidocaine – 1-2% Bupivacaine – % (low conc. for labor) How much? Roughly ml
Spinal injections: What solution? How much?
Ask your attending
Spinal injections: What solution? Chloroprocaine – 2-3% (no dextrose) Lidocaine – 5%/0.75% dextrose Bupivacaine – 0.75%/0.825 dextrose
Spinal injections: How much? Chloroprocaine – 2 ml (40-60 mg) Lidocaine – 1-2 ml ( mg) Bupivacaine – 1-2 ml ( mg)
Conversion of % concentration to mg/ml: 1% solution = 1gm per 100 ml (1000 mg per 100 ml) = 10 mg/ml % solution X 10 = mg/ml e.g., 0.5% bupivacaine X 10 = 5 mg/ml Dose is volume X concentration: 10 ml of 0.5% bupivacaine = 50 mg dose Dose is important in determining toxicity
Manufacturer Maximum Recommended Doses Chloroprocaine –800 mg no epinephrine –1000 mg with epinephrine Lidocaine –300 mg no epinephrine –500 mg with epinephrine Bupivacaine –175 mg no epinephrine –225 mg with epinephrine
Concept of baricity Baricity is the relationship of the density of the local anesthetic solution to the density of the cerebrospinal fluid. If the LA solution is: Less dense than CSF it is hypobaric (floats) Equal in density to CSF it is isobaric (stationary) More dense than CSF it is hyperbaric (sinks) As a concept, baricity refers only to spinal anesthesia and not to epidural anesthesia
Spinal solutions Hyperbaric solutions (with dextrose) –Intra-abdominal operations (including inguinal hernia and vaginal procedures) –All operations can be done with this solution Isobaric solutions (epidural solutions without dextrose) –Lower extremity operations (hip and below) Hypobaric solutions (diluted with DW) –Not really useful
1 ml 5% lido with dextrose during injection 1 ml 5% lido with dextrose immediately after injection
The effect of baricity on the distribution of bupivacaine in spinal model Hyperbaric Isobaric Hypobaric l In spite of the crudeness of this model, the levels of anesthesia predicted by the model are remarkably similar to the levels of anesthesia observed in patients Immediately after injection 20 min. after injection
Hyperbaric Isobaric Hypobaric
What could go wrong?
What could go wrong with spinal anesthesia? It doesn’t work It goes too high (total spinal) It doesn’t go high enough It causes hypotension It doesn’t last long enough It causes a spinal headache
The Two Components of Spinal Headache There must have been a lumbar puncture The headache is related to posture –Worst when standing or sitting –Gone or improved with recumbency
Effect of Age on the Incidence of Spinal Headache Vandam and Dripps, JAMA 1956;161: This and AARP discounts are two of the few advantages to aging!
Needle tip design is important 25 gauge Quincke or cutting needle has 5% incidence of spinal headache in OB patients. 25 gauge Whitacre or pencil tipped needle has <1% incidence of spinal headache in OB patients
What could go wrong with epidural anesthesia? It doesn’t work It goes too high (total spinal) It doesn’t go high enough It causes hypotension It doesn’t last long enough It causes a spinal headache (but it’s not supposed to) It produces spinal anesthesia It goes intravascular causing systemic toxicity
Or the catheter could have penetrated the dura and be located intra-thecally
Epidural Test Dose 3 ml of 1.5% lidocaine with 1:200,000 epi –1:200,000 = 5 ug/ml X 5 ml = 25 ug epi will cause tachycardia and is used to detect and intravascular injection –3 ml X 15 mg/ml = 45 mg lido will cause spinal anesthesia and is used to detect an intrathecal injection
The Local Anesthetic Molecule Local anesthetics consist of an aromatic ring and an amine, separated by a hydrocarbon chain Two types of local anesthetics based on the hydrocarbon chain linkage: Esters have [-CO-O-] linkage Amides have [-N-CO-] linkage
Amide Bupivacaine Analogues
Amide Lidocaine Analogues
Toxicity Directly related to lipid solubility (potency) –Bupivacaine > Lidocaine > Chloroprocaine The more potent the LA, the more toxic the LA is –It takes a lower dose to produce the toxicity Two types of toxicity –Central nervous system –Cardiovascular
Central Nervous System –Earliest signs and symptoms are those of excitation owing to depression of inhibitory cells allowing excitatory cell preponderance Tinnitus Light headedness Confusion Circum-oral numbness Tonic-clonic convulsions
Toxicity of Local Anesthetics Central Nervous System –Excitation is followed by depression l Drowsiness l Unconsciousness l Respiratory Arrest
Recording from a Single Cell Seizure like activity is due to direct excitation, and not depression of inhibitory cells allowing excitatory cell preponderance
Treatment of CNS Toxicity STOP INJECTING If seizure, depress the CNS with benzodiazepines (midazolam, ativan, diazepam), or propofol, or thiopental Support airway and breathing Intubation if necessary Wait until consciousness returns –It is unlikely there will be a good block as the local obviously went intravascular Or convert to general and continue with the operation
Treatment of Bupivacaine Cardiotoxicity Weinberg, GL. RAPM 27:568, 2002 Early Response ABC ACLS Protocol
Treatment of Bupivacaine Cardiotoxicity ii Antiarrhytmic therapy –Benzodiazepines or propofol for seizures and CNS induced arrhythmias –Epinephrine may promote arrhythmias –Amiodarone [now first line ACLS antiarrhythmic] may be useful –Lidocaine may compete with bupivacaine or could be additive (data are mixed on using lidocaine to treat bupivacaine induced VT)
Treatment of Bupivacaine Cardiotoxicity iii Vasopressor support –Epinephrine –Vasopressin 40 U now in ACLS protocol May be less arrhythmogenic than epinephrine Produces greater coronary artery perfusion pressures that last longer than epinephrine Causes less acidosis than repeated doses of epinephrine (Krismer, et al Anesth Analg 2001;93:734–42) –Epinephrine + Vasopressin A combination of epinephrine and vasopressin produces better survival than either epinephrine or vasopressin alone (Mayr, et al Anesth Analg 2004;98:1426 –31)
Treatment of Bupivacaine Cardiotoxicity iiia Contraindications –Calcium channel blockers –Phenytoin –Bretyllium no longer supported
Treatment of Bupivacaine Cardiotoxicity iv Novel therapies –Lipid infusion (soybean oil… ?propofol) Bupivacaine inhibits transport of fatty acids into mitochondria Provides substrate Improves survival and increase dose required for toxicity in rats Sequesters lipid soluble bupivacaine in blood –Insulin/Glucose/Potassium May restore K+ gradients for repolarization May promote ATP source
An Intralipid Protocol Intralipid bag available LA arrest unresponsive to ACLS: 1 ml/kg intralipid IV over one minute Repeat X2 at 3-5 min. intervals 0.25 ml/kg/min intralipid IV until stable Picard J, Meek T: Lipid emulsion to treat overdose of local anaesthetic: the gift of the glob. Anaesthesia 2006; 61: 107-9