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?
“Pay no attention to the man behind the curtain”
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.
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).
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.
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
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.
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.
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.
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”.
Scenario #1– Elective Cesarean delivery—
a uniquely social surgery
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.
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.
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).
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.
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.
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!
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.
Spinal / epidural causes
sympathectomy– dilation of resistance
arterioles and capacitance veins.
www.cvphysiology.com/Blood%20Pressure/BP019.htm
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.
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.
“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.
Colman-Brochu S 2004
When IVC is not compressed,
venous return is easy. Cardiac
output stays high.
http://www.manbit.com/OA/f28-1.htm
Manbit
images
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
Chestnut chap. 2
How much LUD is enough?
Now we judge by maternal BP and FHR.
Is there a better way?
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
Minutes
S
0
R90
L90
R90
L90
S
33
Archer, Suresh and Ballas 2011
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
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
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?”
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.
One more “equation”:
• Neuraxial anesthesia +
• Aortocaval compression +
• Unreplaced blood loss =
• Disaster
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?
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.
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”.
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.
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!
Spinal Anatomy
Vertebral Body
Nerves from
spinal cord
Spinal sack
Or Dura
Nerve to body
Bump on the back
Slide courtesy of Alex Pue, MD
40
Spinal
Anesthetic is
deposited inside
the spinal sack
and quickly acts
on the nerves
spinal needle
Slide courtesy of Alex Pue, MD
41
Epidural
Spinal sack
Epidural
needle &
catheter are
outside the
spinal sack
(dura)
Epidural catheter
Slide courtesy of Alex Pue, MD
42
Anesthetic initially
deposited inside the
spinal sack and acts
directly on the nerves
Combined
spinalepidural
spinal needle
epidural needle
Slide courtesy of Alex Pue, MD
spinal needle
43
Ultrasound for spinal block placement: first, midline is marked (“shadow” of spinous
processes in middle of probe).
http://www.usra.ca/sb_neuraxial
Then vertical level is marked between spinous processes, where we can
see reflection from vertebral body.
http://www.usra.ca/sb_neuraxial
Ultrasound (US) can be useful in obese patients or patients with scoliosis
or other spine pathology. We use the standard OB curved US probe.
Needle insertion point is intersection of midline (y-axis) and proper
horizontal level (x-axis).
http://www.usra.ca/sb_neuraxial
Combined Spinal-Epidural
spinal needle
epidural needle
Spinal fluid
coming from
spinal needle
Slide courtesy of Alex Pue, MD
49
Anesthesia for CS—
Complications
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Sympathectomy / hypotension
Nausea
Bradycardia
High spinal / respiratory paralysis
Aspiration
Difficult intubation
Local anesthetic toxicity (IV “epidural”)
Failed regional anesthesia GA
Persistent neurological deficit
“Uterine hypertonic syndrome”
• Rapid pain relief with CSE or epidural can cause
“fetal distress” due to uterine hypertonus.
• We must be aware to avoid unnecessary CS.
• Dx is palpate uterus.
• Rx is SC terbutaline or SL NTG.
• Mechanism: loss of epinephrine beta agonism?
Scenario #2: Examination for
postpartum hemorrhage (PPH)
• Woman postpartum with hemorrhage.
• You need to explore birth canal and repair
laceration or remove retained placenta.
• Epidural catheter in place.
• How do we proceed?
Scenario #2: In PPH,
we are worried about:
•
•
•
•
•
Airway (GA is always Plan B)
Adequate IV access
Volume status (in shock RRHRBP).
Blood availability
Keep patient warm and warm all fluids
(especially blood) – prevent “fatal triad” of
hypothermia, acidosis and coagulopathy.
Scenario #2: Examination for
postpartum hemorrhage
• Anesthesiologist should be reluctant to
use epidural catheter in presence of
uncorrected hypovolemia.
• Even riskier with de novo spinal (faster
onset).
• Go to OR for exam / repair. Correct
volume status and use neuraxial or GA.
Scenario #3: STAT CS
for “fetal distress”
• We are thinking: Airway, airway, airway.
• STAT CS is one reason we need advance
knowledge of difficult airways. You tell us,
or better, we take a peak at everybody.
• Minimal History: allergies, meds, heart and
lung disease, other major med problems.
Scenario #3: STAT CS
for “fetal distress”
• If airway is sketchy and no neuraxial
available, we all have a big problem.
Nervous anesthesiologist
• If you want to make an anesthesiologist
uptight and ornery, ask her to use her
wonderful and dangerous drugs when the
airway cannot be secured.
• Don’t put someone to sleep unless you are
sure you can breathe for them.
• For us, this is absolutely fundamental.
“STAT CS”
•
•
•
•
•
•
Often “a flail”.
“We’ve got to go. NOW!”
Egos and emotions run high.
Does the patient know what is happening?
Talk to patient. Informed consent.
Don’t endanger the mother to “save” the
baby.
• Anesthesia needs to know when and how to
say “no” to the OB.
• Stay calm.
• Cover the basics (H&P, IV access, airway,
informed consent, patient asleep before
How do we kill patients
in OB anesthesia?
• Rush to the OR, pressure to “put the patient
down” to save the baby.
• IV induction, paralysis.
• Panic, confusion, inexperience, bad luck
• “Can’t intubate, can’t ventilate” death or brain
damage.
“The AIRWAY—
Anesthesia’s #1 concept”
• Just exactly what does it mean?
• An anatomical and functional concept
which means “We can ensure that the
patient will breathe on her own or we can
breathe for her.”
• “Protected airway” means that stomach
contents can’t get into the lungs.
Intubating a
dolphin would
be very easy.
They have a
“blowhole”.
We would be
out of a job.
Unlike
dolphins,
humans
have a
breathing
orifice that is
hard to get
to.
Cuffed endotracheal tube (ETT)– gold standard of airway maintenance and
protection.
http://www.healthsystem.virginia.edu/Internet/AnesthesiologyElective/images/anesth0018.jpg
Laryngeal mask airway (“LMA”)– gold standard of airway rescue / maintenance
device when ETT not possible.
LMA sits behind larynx and epiglottis. Provides limited airway protection. Can be a
life-saving device.
www.anecare.com/.../QED-spontaneous-brief.html
Oral airway plus lift mandible and tongue (“jaw thrust”)– basic airway
maintenance maneuver. Provides no airway protection but can be lifesaving. Do this in seizing patient, plus turn her onto her side.
What are the threats to the airway?
• You and I are the primary threats!
• We want to help!
• We want to “save the baby”!
• Will we choose to induce anesthesia without
ensuring the airway?
General anesthesia for CS
• Recent anesthesia grads will have limited
experience with GA for CS because of our
success with neuraxial.
• And we all get “flustered”.
• A good topic for drills, practice.
Protocol for
general anesthesia for CS
Abdomen is prepped, draped, OBs have
knife in hand, ready to cut, prior to
induction.
• Clear, calm, specific communication.
• “Patient is awake”, “Patient is asleep”,
“You can cut now”.
Protocol for
general anesthesia for CS
Two to three minutes of “preoxygenation” (patient breathes 100% O2
to fill lungs).
Pre-oxygenation provides a reserve of O2
for period of apnea after induction and
paralysis and before ventilation.
Functional residual capacity (FRC) is our “air tank” for apnea.
www.picture-newsletter.com/scuba-diving/scuba... from Google images
Pregnant Mom has a smaller “air tank”.
Non-pregnant
woman
www.pyramydair.com
/blog/images/scubaweb.jpg
This is why we
“pre-oxygenate” the patient.
Wikipedia
It gives us more time to get the tube in before she gets low on oxygen.
“Ramping up”
the obese
patient to
facilitate
intubation.
Cephalad
retraction of
pannus can
interfere with
breathing.
Obese patient:
disaster waiting
to happen.
www.airpal.com/ramp.htm
Awake fiberoptic intubation can be lifesaving,
but it takes time and skill.
We need to know about “difficult airways” in
advance, so we evaluate patient and make
plans.
Weight and Wellness Program
(Dr. Lacoursiere)
• Integrated approach to obese parturient:
• OB, Anesthesia, Nursing, equipment,
training, patient buy-in, etc.
• Protocols, bundles, etc.
• In development…
Scenario #4:
Severe pre-eclampsia
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Anesthesia worries:
Platelets (also PT, PTT, fibrinogen?)
Airway swelling / pulmonary edema
Stroke / MI / CHF due to hypertension
Magnesium effects (uterine atony,
potentiates neuromuscular blocking
agents, patient on ventilator postop?).
Scenario #4:
Severe pre-eclampsia
• Our approach: neuraxial unless platelets
are low (50-100K is the number). Look at
venipuncture sites for oozing, under BP
cuff for bruising.
• Neuraxial will “help” lower BP– but don’t
let us overdo it!
• Early epidural?
Scenario #4:
Severe pre-eclampsia
• Get epidural in before the platelets go
down in HELLP?
• Maybe, but then removal of catheter
becomes a problem (same requirement for
50-100K).
Scenario #4:
Severe pre-eclampsia
• How recent does platelet count have to be
in pre-eclampsia? Communicate with your
anesthesiologist.
• 2-6 hours in truly severe pre-eclampsia
and florid HELLP? I have no firm answer.
• 27 gauge spinal?
Scenario #4:
Severe pre-eclampsia
• We should NOT be more worried than
usual about catastrophic hypotension with
neuraxial anesthesia in pre-eclampsia.
• This used to be taught but is less common
in pre-eclampsia than in normal patients.
Scenario #4:
Severe pre-eclampsia
• If GA required (low platelets, abruption,
severe “fetal distress”, DIC):
• Prevent extreme hypertension with
laryngoscopy by using IV fentanyl and / or
labetalol before induction of GA.
• Magnesium will potentiate nondepolarizing NMB agents (curare-like,
vecuronium, rocuronium).
Scenario #4:
Severe pre-eclampsia
• Arterial line VERY useful in severe preeclampsia for:
• BP, but also mag levels, other blood
draws, ABGs in case of pulmonary edema
or ventilator care.
• A little extra work (and nurses may be
unfamiliar) but very helpful.
Summary
• Neuraxial and general anesthesia are both
threats to breathing.
• “Airway” is the fundamental concept of
anesthesia and our greatest obsession.
• Prevention of aspiration of gastric contents
is another of our obsessions.
Summary
• Neuraxial anesthesia is best in OB, but GA
is always the backup.
• Neuraxial anesthesia + blood loss + IVC
compression = disaster.
• In OB, we need to get the uterus off the IVC,
but knowing how much LUD is enough may
be difficult. EC may help with this.
Summary
• OB anesthesiologist needs to
communicate well with rest of OB team.
• Obesity requires communication and
planning (“systems approach”).
• Spinal or epidural best in pre-eclampsia,
but check platelets. GA in pre-E requires
special care.
The End