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What the obstetrician needs to know about anesthesia

What the obstetrician needs to know about anesthesia. Tom Archer, MD, MBA Director, Obstetric Anesthesia UCSD July 13, 2011. The black box of anesthesia– Useful, but what is it really all about?. ANESTHESIA. What ARE those men and women doing BEHIND THE CURTAIN?.

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What the obstetrician needs to know about anesthesia

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  1. What the obstetrician needs to know about anesthesia Tom Archer, MD, MBA Director, Obstetric Anesthesia UCSD July 13, 2011

  2. The black box of anesthesia– Useful, but what is it really all about? ANESTHESIA

  3. What ARE those men and women doing BEHIND THE CURTAIN? “Pay no attention to the man behind the curtain”

  4. Anesthesia in one sentence: • You can put the nervous system to sleep with all kinds of drugs, and the patient will do fine, as long as she keeps breathing.

  5. Two more sentences: • Most “anesthesia” drugs can interfere with breathing. • Anesthesia drugs can cause loss of consciousness, intended or unintended, and this can allow stomach contents to get into the lungs (aspiration).

  6. Our drugs interfere with breathing: • Narcotics decrease respiratory rate (to zero!) • Propofol, midazolam cause “upper airway obstruction” (tongue falls back and obstructs). • Severe hypotension causes medullary ischemia and apnea (commonest cause of respiratory arrest after spinal). • High spinal or epidural can paralyze phrenic nerve (less common). • Seizures due to local anesthetic toxicity interfere with breathing.

  7. Our drugs allow aspiration: • Loss of consciousness (LOC) is associated with loss of gag, swallow and cough • Any LOC can allow aspiration of regurgitated gastric contents

  8. Now you understand what we do all day: • Mess up nervous system • Keep patient breathing • Worry about stomach contents getting into the lungs The rest is details.

  9. Two details: • Anesthesia can make the blood pressure go down a lot. That is bad. • Sticking needles into the backs of people whose blood can’t clot is not a good idea.

  10. Anesthetic agents and uterus • Inhaled sevoflurane and desflurane relax uterus. This effect goes away fast (don’t blame sevo for atony once patient is awake). N2O does not relax uterus. • IV and neuraxial anesthesia drugs (LA, narcotics, sedatives, hypnotics, propofol, etomidate, low-dose ketamine, etc.) have little to no direct effect on uterus.

  11. Epidural test dose • “Epidurals” can cause seizures if local anesthetic goes into a vein. • This is one reason for the “test dose”. • Other reason is to detect intrathecal catheter and prevent “high spinal”.

  12. Scenario #1– Elective Cesarean delivery— a uniquely social surgery

  13. Let’s teach our residents the proper approach to a unique operation in a unique setting. • We are “on stage” (what we say, do, body language, staff interactions are closely observed and judged). • You know this. Our residents may not. • As anesthesiologists we may not be accustomed to awake patients, presence of family, etc. Help us when we forget.

  14. Scenario #1: Elective C-section • Neuraxial anesthesia (NA, spinal or epidural) is good from multiple points of view: • Mother experiences birth, protects her own airway, baby gets minimal drug exposure. • NA allows morphine to be given for post-op pain control.

  15. Scenario #1: Elective C-section • NPO, famotidine (Pepcid), metoclopramide (Reglan), sodium citrate (Bicitra). • Despite attempts to empty stomach, we assume full stomach in pregnancy (decreased LES tone, delayed gastric emptying).

  16. Routine after spinal/epidural: • Left uterine displacement (how much is enough?). • Vasopressors to increase SVR and venous return (CO). • Decreased emphasis on IV fluid “preloading” than in the past.

  17. One equation: • (MAP - CVP) = CO x SVR. • Remember Ohm’s Law? V = IR. • Voltage = Current x Resistance • CVP is small, so MAP = CO x SVR, more or less.

  18. Neuraxial anesthesia tends to decrease the MAP, because it • Decreases tone of < 0.1 mm diameter resistance arterioles (SVR), and • Dilates lower body capacitance veins which decreases venous return, and • Venous return = Cardiac output. • And MAP = SVR x CO!

  19. Autonomic nervous system. T1 L2 Sympathetics go to internal organs and to veins and arterioles. Blocking sympathetics decreases venous tone (CO) and arteriolar tone (SVR). Blood pressure falls, vagal tone dominates and bradycardia may occur, making situation even worse.

  20. Spinal / epidural causes sympathectomy– dilation of resistance arterioles and capacitance veins. www.cvphysiology.com/Blood%20Pressure/BP019.htm

  21. 38 y.o. female, repeat c/s, 420 #, gestational hypertension, continuous spinal: fall in systemic vascular resistance (SVR), rise in cardiac output (CO) with onset of block. Increased SVR with phenylephrine.

  22. Neuraxial anesthesia is dangerous in OB because: • Inferior vena cava compression by gravid uterus exacerbates decrease in venous return due to sympathectomy. • Hence, supine OB patient and fetus can “crash” after NA. Hence, routine LUD and pressor agents.

  23. “High or total spinal” • Respiratory AND circulatory disaster. • Assist ventilation AND support CV system with vasopressors. • Getting baby out promptly will HELP with both breathing and venous return / cardiac output.

  24. Colman-Brochu S 2004

  25. When IVC is not compressed, venous return is easy. Cardiac output stays high. http://www.manbit.com/OA/f28-1.htm Manbit images

  26. When IVC is compressed, venous return occurs by vertebral plexus and azygos system. CO falls and uterine veins are engorged. http://www.manbit.com/OA/f28-1.htm

  27. Chestnut chap. 2

  28. How much LUD is enough? Now we judge by maternal BP and FHR. Is there a better way?

  29. Cardiac output (venous return) depends on maternal position late in gestation. 34 y.o. pregnant patient at 26 weeks 3 days estimated gestational age. Hospitalized for preterm labor. No contractions or medications at time of measurement. 120 HR 80 80 SI 30 8 CI 3 Position S R90 L90 R90 L90 S Minutes 0 33 Archer, Suresh and Ballas 2011

  30. After epidural, BP and CO fall and don’t respond to phenylephrine or ephedrine. BP and CO increase when patient is placed left side down. Archer, Shapiro, Suresh 2011

  31. Autotransfusion observed: once patient is left side down, blood squeezed out of contracting uterus easily gets back to the heart, causing increased CO, as seen here. Archer, Shapiro, Suresh 2011

  32. Basic CS monitoring • Talk with the patient! • Does her face display anxiety? • “Take a deep breath!” • Have her squeeze your fingers • What is her hand temperature? • Are the hand veins dilated? • “Do your hands feel normal or do they feel a little numb?”

  33. CS red flags • “I don’t feel so good…I think I’m going to throw up…” (Hypotension until proven otherwise). • “Doc, I feel like I’m not getting enough to breathe…” • The “floppy arm sign.” • The “shaking head sign.” • High spinal will need ventilatory help.

  34. One more “equation”: • Neuraxial anesthesia + • Aortocaval compression + • Unreplaced blood loss = • Disaster

  35. Intrathecal and epidural medications: • Neuraxial local anesthetics cause sympathectomy and hypotension. Can cause motor block. • Fentanyl (rarely sufentanil): improves quality of block during CS, esp. visceral pain. No sympathectomy, no hypotension, no motor block. Can cause itching. • Morphine for post-CS pain relief. Itching?

  36. Block level for CS • Need T4 (nipples) to block visceral pain (traction on peritoneum, exteriorize uterus). Numbness in hands is OK (C5-8). • Lower block will allow skin incision and you can probably “get away with it” but expect visceral discomfort. Leave uterus in for repair to decrease peritoneal traction? • Supplement with fentanyl, ketamine prn.

  37. Neuraxial (NA) morphine • Delayed respiratory depression (up to 24 hrs later). With 0.1 mg, very rare (1 per several 1000s). Rx with naloxone (Narcan). • ASA guidelines for post NA morphine monitoring: RR q 1 hr x 12h then q 2h x 12h. • We do a “post CS pain management visit”.

  38. Neuraxial morphine • Can cause: itching, nausea, ileus, urinary retention. Itching Rx’d with nalbuphine (nubain) or diphenhydramine (Benadryl). • We do pain orders 1st 24 hours. Caution with IV + NA narcotics. • “Multimodal analgesia”: NA morphine, NSAID, oral acetaminophen plus narcotic (Percocet), cautious IV opioid.

  39. NSAIDs for post CS pain • Ketorolac commonly used around the country: 30 mg IV q 6h x 4 doses. Maximum of 5 days. • NSAID contraindications: renal problems (includes pre-eclampsia), GI ulcers, bleeding problems. • American Academy of Pediatrics says: Ketorolac OK for breast feeding. Our NICU says yes. Package insert says no!

  40. Spinal Anatomy Nerves from spinal cord Vertebral Body Spinal sack Or Dura Nerve to body Bump on the back Slide courtesy of Alex Pue, MD

  41. spinal needle Spinal Anesthetic is deposited inside the spinal sack and quickly acts on the nerves Slide courtesy of Alex Pue, MD

  42. Epidural Spinal sack Epidural needle & catheter are outside the spinal sack (dura) Epidural catheter Slide courtesy of Alex Pue, MD

  43. Anesthetic initially deposited inside the spinal sack and acts directly on the nerves spinal needle epidural needle spinal needle Combined spinal-epidural Slide courtesy of Alex Pue, MD

  44. Ultrasound for spinal block placement: first, midline is marked (“shadow” of spinous processes in middle of probe). http://www.usra.ca/sb_neuraxial

  45. Then vertical level is marked between spinous processes, where we can see reflection from vertebral body. http://www.usra.ca/sb_neuraxial

  46. Ultrasound (US) can be useful in obese patients or patients with scoliosis or other spine pathology. We use the standard OB curved US probe.

  47. Needle insertion point is intersection of midline (y-axis) and proper horizontal level (x-axis). http://www.usra.ca/sb_neuraxial

  48. spinal needle epidural needle Spinal fluid coming from spinal needle Combined Spinal-Epidural Slide courtesy of Alex Pue, MD

  49. Anesthesia for CS—Complications • Sympathectomy / hypotension • Nausea • Bradycardia • High spinal / respiratory paralysis • Aspiration • Difficult intubation • Local anesthetic toxicity (IV “epidural”) • Failed regional anesthesia GA • Persistent neurological deficit

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