case 57 - anesthesia for nonobstetric surgery during pregnancy

Question 1

what are the physiologic changes in pregnancy and anesthesia implications for respiratory and cardiac?

Answer 1

1) respiratory

• inc MV (inc TV and RR), inc O2 consumption
• dec FRC (dec ERV and RV) -> uterus pushing diaphragm
• anes -
  
  • inc MV + dec FRC
    
    • rapid uptake and excretion of volatile anes
  • dec FRC + inc o2 consumption
    
    • quicker develop of arterial hypoxemia during apnea
  • edema + weight gain -> difficult intubation

2) Cards

• inc CO (inc SV and HR), dec SVR (progesterone)
• inc plasma volume > inc red blod cell volume
  
  • (relative anemia of pregnancy)
• aortocaval compression 2/2 uterus -> hypotension
• Anes
  
  • left uterine displacement
  • inc CO = inc speed of IV induction of anes

Question 2

what are the physiologic changes in pregnancy and anesthesia implications for GI, hepatic, heme?

Answer 2

3) GI

• inc gastric presure (2/2 gravid uterus pushing up on stomach)
• dec lower esopha sphincter tone
• ?? delayed gastric emptying
• Anes
  
  • inc risk of aspiration
    
    • pre-tx with metoclopramide, sodium bicit, H2 blocker
    • RSI&I + cricoid

4) hepatic

• dec psuedocholinesterase activity (hemodilution)
• anes
  
  • prolong affect of sux (rarely an issue)

5) Heme

• inc clotting factor and fibrinogen concentration
• anes
  
  • hypercoaguable state -> risk of thrombsis (DVT, PE)
  • VTE prophylaxis

Question 3

what are the physiologic changes in pregnancy and anesthesia implications for Renal & CNS?

Answer 3

6) Renal
* inc RBF, inc GFR, Dec BUN/Scr

7) CNS

• progesterone - > decrease MAC + inc sens to LA
• gravid uterus -> compreses IVC -> engorgement of epidural veins
  
  • decreases size of epidural and intrathecal spaces due to epidural venous engorgement
• Anes
  
  • Progesterone
    
    • decrease MAC to avoid anesthetic overdose
  • epidural veins + LA sensitivity
    
    • dec volume + dose of LA during neuraxial anesthesia

Question 4

what is a teratogen, are there any anes meds that are teratogenic?

Answer 4

teratogen

• substance that produces congenital defects
• weeks 3-8 of fetal development

anes meds

• Most anes meds are NOT tertagoenic
  
  • almost all are category B or C classification (category ratings of drugs during pregnancy)
  • Class B = no evidence of risk in humans
  • Class C = risk cannot be ruled out

NO and BZD = controversial

• BZD - class D - potential evidence of risk
  
  • best to avoid during pregnancy
  • cleft palate
• NO
  
  • oxidizes Vit B12 -> needed for methionine synthetase (develop thymidine molecule for DNA)
  • not been found to be assoc with congential abnormalities in humans

Question 5

OR nurse comes to you and asks if she is at risk for complicated pregnancy due to volatile anes gases, what do you say?

Answer 5

OR personnel exposed to volatile anes

• higher risk of spont abortion and congential abnormalities
• scavanging system in place -> removes gases

Question 6

what precautions should be taken to avoid intrauterine fetal asphyxia during nonobstetric surgery?

Answer 6

goals

• maintain normal maternal PaO2
• maintain normal PaCo2
• maintaine uterine blood flow

1) PaO2

• increase Fio2 to maintain adeqauate SaO2
• maternal hypoxemia -> fetal hypoxemia
• avoid high spinal/epidural
• general anes -> apnea assoc with quick desat

2) PaCo2

• severe hypocapnia (dec PacO2) assoc with vasoconstriction of uterine blood vessels
  
  • dec blood flow to fetus
• alkalosis shift oxyhemoblogin dissoc curve to left
• monitor TV, RR

3) uterine blood flow

• UBF = perfusion pressure / vasc resistance
  
  • prefusion pressure = MAP - CVP
• PP
  
  • aortocaval compression -> Left uterine displacement
  • maternal hypotension (anes overdose, hypovolemia, blood loss)
• vasc resistance
  
  • alpha adrenergic drugs, dec PaCo2, inc catechoalmines (light anes, pain) -> all inc vasc resistance -> decrease UBF

Question 7

is pre-term a possiblity during nonobstetric surgery in a pregnant patient?

Answer 7

pre-term labor

• high risk of preterm assoc with procedures manipulating the uterus (abd procedures)
• anes does not affect pre-term labor risk
• lowest risk of preterm labor -> 2nd trimester
  
  • if urgent surgery necessary, push for 2nd trimester

Question 8

is there any additional monitoring needed for anesthetizing a pregnant patient undergoin nonobstetric surgery?

Answer 8

YES

prior to surgery, consultant OB/GYN:

• FHR pre-procedure
• FHR intra-op if feasible
• FHR post-procedure
• create a plan for emergent c/s and fetal distress

Question 9

any speical considerations for pregnant pts underoging laproscopic surgery?

Answer 9

• maintain normocarbia
  
  • pneumoperitoneum can increase PaCO2 levels
• cautious placement of surgical trocars
• main low pneumoperitoneum pressure (<15 mmHg) to allow uterine perfusion

Question 10

Pregnant patient comes for non-obstetric surgery, how would you handle this patient from seeing her pre-op till induction of surgery?

Answer 10

1) avoid surgery during 1st trimester if possible
2) consult Ob/GYN

• document FHR pre-op, intra-op (if possible), and post-op
• create plan for fetal distress and emergent c/s
• **inform pt no known risk of fetal congenital defects, but inc risk of miscarriage or premature labor

3) monitor FHR intra-op if possible
4) avoid pre-medication (risk of aspiration)
5) admin aspiration prophylaxis after 1st trimester
* sodium bicitrate, H2 blocker, metoclopramide
6) LUD if > 16 weeks
* avoid aortocaval compression
7) regional vs general

• provide regional if possible -> avoid irsk of aspiration, difficult intubation, decrease fetal exposure of anes meds
  
  • tx hypotension 2/2 sympathetcomy immeditely with fluids and pressors
• if general:
  
  • RSI&I
  • various emergency meds and airway equip on standby, suction readily avialable

Question 11

Pregnant patient comes for non-obstetric surgery, what are your anes concerns for regional and general anes? Do you have post-op concerns?

Answer 11

regional

• provide unless contraindicated
• avoids intubation, risk of aspiratoin, dec fetal exposure to meds
• sympathetcomy -> hypotension -> dec fetal perfusoin
  
  • tx immedietly with fluids and pressors (phenyl, ephedrine)
• avoid oversedation, monitor EtCo2

general

• aspiration prophylaxis
• difficult intubation -> variety of airway equipment
• RSI&I
• EtCo2 - pregnant levles - 30-35 mmHg
• SaO2 > 95% -> inc FIO2 as necessary
• maintain uterine blood flow

Post-OP

• FHR monitoring
• maintain uterine blood flow (ie avoid hypotension)
• avoid hypotension, hypoxemia, hypercarbia, hypothermia