PBLD4: Non-Obstetric Surgery During Pregnancy

Little is known about the prognosis of poorly differentiated thyroid carcinomas (medullary, anaplastic) during pregnancy. It is generally recommended to proceed with surgery during pregnancy if a large primary tumor or extensive metastatic disease is present. (1,2)

References

1. Yasmeen S, Cress R, Romano PS, Xing G, Berger-Chen S, Danielsen B, Smith LH. Thyroid cancer in pregnancy. Int J Gynaecol Obstet 2005;91:15–20.
2. Nam KH, Yoon JH, Chang HS, Park CS. Optimal timing of surgery in well-differentiated

Elective procedures should be postponed until after delivery. (3) If a procedure must occur during pregnancy, whenever possible non-urgent surgeries should be performed during the second trimester.  Organogenesis occurs during the first trimester and fetal exposures should be limited if possible.  Once in the third trimester, the risk of preterm labor following surgery and anesthesia is increased.  When anesthesia is required, however, it is important to note that no particular anesthetic drugs have been shown to be teratogenic in human studies.  Early evidence in animal models has shown that general anesthesia may cause neuronal apoptosis and behavior deficits later in life, but this has yet to be demonstrated in humans. (4)

References

3. Non-obstetric surgery during pregnancy. Committee Opinion No. 474. American College of Obstetricians and Gynecologists. Obstet Gynecol 2011;117:420-1.
4. Reitman E, Flood P. Anaesthetic considerations for non-obstetric surgery during pregnancy. Br J Anaesth 2011;107(s1):i72-78.

The American College of Obstetricians and Gynecologists as well as the American Society of Anesthesiologists recommend obstetric consultation for all patients undergoing non-obstetric surgery during pregnancy.

The ACOG Committee Opinion on Non-obstetric Surgery During Pregnancy (3) makes the following recommendations regarding fetal heart rate monitoring:

1. If the fetus is considered previable, it is generally sufficient to ascertain the fetal heart rate by Doppler before and after the procedure
2. At a minimum, if the fetus is considered to be viable, simultaneous electronic fetal heart rate and contraction monitoring shod be performed before and after the procedure to assess fetal well-being and the absence of contractions

Reference

3. Non-obstetric surgery during pregnancy. Committee Opinion No. 474. American College of Obstetricians and Gynecologists. Obstet Gynecol 2011;117:420-1.

While not universally agreed upon, ACOG guidelines recommend that intraoperative monitoring should be used only once the fetus is viable, with the intent that emergent delivery is a feasible option in the event of severe fetal distress.(4)

Additionally, procedures involving the thorax and abdomen do not specifically preclude intraoperative FHR monitoring. Monitoring can be used as long as it is physically possible to perform.

Reference

4. Reitman E, Flood P. Anaesthetic considerations for non-obstetric surgery during pregnancy. Br J Anaesth 2011;107(s1):i72-78.

In non-laboring patients, gastric emptying has been shown in multiple studies not to be delayed during pregnancy, even at full term. (5,6) Similar studies performed in obese parturients also demonstrated no change in gastric emptying. (7) Thus NPO guidelines are unchanged in pregnant patients compared to non-pregnant patients. Patients must be NPO for clear liquids for two hours and solids for 6-8 hours depending on the composition of the meal. If additional risk factors for aspiration exist – such as morbid obesity, diabetes, or potential difficult airway – further restrictions may be considered on a case-by-case basis.

References

5. Wyner J, Cohen SE. Gastric volume in early pregnancy: effect of metoclopramide. Anesthesiology 1982;57:209–12.
6. Wong CA, Loffredi M, Ganchiff JN, Zhao J, Wang Z, Avram MJ. Gastric emptying of water in term pregnancy. Anesthesiology 2002;96:1395–400.
7. Wong CA, McCarthy RJ, Fitzgerald PC, Raikoff K, Avram MJ. Gastric emptying of water in obese pregnant women at term. Anesth Analg 2007;105:751–5.

Both nonparticulate antacids and H2 receptor antagonists have been shown to increase gastric pH, but neither has a significant effect on gastric volume. (8,9,10)  Additionally, because of its rare occurrence and paucity of data, no literature exists demonstrating any worsened patient outcomes when low pH gastric contents are aspirated.  Metoclopramide has been studied mainly in the context of cesarean deliveries, where it has been shown to decrease the incidence of both nausea and vomiting when compared to placebo in double blind, randomized trials. (11,12)

References

8. Dewan DM, Floydh M, Thistlewood JM, Bogardt D, Spielman FJ. Sodium citrate pretreatment in elective cesarean section patients. Anesth Analg 1985;64:34–7.
9. Jasson J, Lefèvre G, Tallet F, Talafre ML, Legagneux F, Conseiller C. Oral administration of sodium citrate before general anesthesia in elective cesarean section: Effect on ph and gastric volume. Ann Fr Anesth Reanim 1989;8:12–8.
10. Lin CJ, Huang CL, Hsu hW, Chen TL. Prophylaxis against acid aspiration in regional anesthesia for elective cesarean section: A comparison between oral single-dose ranitidine, famotidine and omeprazole assessed with fiberoptic gastric aspiration. Acta Anaesthesiol Sin 1996;34:179–84.
11. Lussos SA, Bader AM, Thornhill ML, Datta S. The anti- emetic efficacy and safety of prophylactic metoclopramide for elective cesarean delivery during spinal anesthesia. Reg Anesth 1992;17:126–30.
12. Pan PH, Moore CH. Comparing the efficacy of prophylactic metoclopramide, ondansetron, and placebo in cesarean section patients given epidural anesthesia. J Clin Anesth 2001;13:430–5.

Because of this patient’s non-reassuring airway exam and tracheal compression on imaging, rapid sequence induction should not be performed in order to avoid a cannot ventilate/cannot intubate situation.  Awake fiberoptic intubation is the safest option to secure the airway.

In 1946, Dr. Mendelson initially described the phenomenon of aspiration of gastric contents in pregnant patients undergoing general anesthesia. This was postulated to be due to hormonally-mediated reductions in gastric emptying and mechanical distortions of the stomach due to the gravid uterus. (13) Recent publications, however, have failed to show decreases in gastric emptying in pregnant patients. (6,14) In addition, neither rapid sequence induction nor the addition of cricoid pressure has been shown to decrease aspiration risk. (6,14,15,16) While RSI for parturients may still be considered the standard of care for most, recent studies have called this into question if the patient is appropriately fasted and presenting for elective surgery. Furthermore, RSI should be avoided if difficult airway is anticipated.

References

6. Wong CA, Loffredi M, Ganchiff JN, Zhao J, Wang Z, Avram MJ. Gastric emptying of water in term pregnancy. Anesthesiology 2002;96:1395–400.
13. De Souza DG, Doar LH, Mehta SH, Tiouririne M. Aspiration prohylaxis and rapid sequence induction for elective cesarean delivery: Time to reassess old dogma? Anes Analg 2010;110:1503-1505.
14. Macfie AG, Magides AD, Richmond MN, Reilly CS. Gastric empyting in pregnancy. Br J Anaesth 1991;67:54-57.
15. Neilpovitz DT, Crosby ET. No evidence for decreased incidence of aspiration after rapid sequence induction, Can J Anaesh 2007;54:748-64.
16. Smith KJ, Dobranowki J, Yip G, Dauphin A, Choi PT. Cricoid pressure displaces the esophagus: An observational study using magnetic resonance imaging. Anesthesiology 2003;99:60-4.

Left uterine displacement is recommended after 18-20 weeks gestation, when the uterus has exited the pelvic region and is capable of producing aortocaval compression. (4) Compression of the maternal IVC and aorta can ultimately result in maternal systemic hypotension and decreased placental perfusion. Most studies recommend a tilt of at least 15 degrees, as parturients placed in > 15 degree tilt have less dramatic hemodynamic changes compared to those tilted at less acute angles. (17) In certain scenarios resulting in greater than usual uterine volume (polyhydramnios, multiple gestation, greater gestational ages), even greater tilt may be required to maintain vessel patency.

Reference

4. Reitman E, Flood P. Anaesthetic considerations for non-obstetric surgery during pregnancy. Br J Anaesth 2011;107(s1):i72-78.
17. Lee SWY, Khaw KS, Ngan Kee WD, et al: Haemodynamic effects from aortocaval compression at different angles of lateral tilt in non-labouring term pregnant women. Br Journ of Anaes 2012;1-7.

When continuous fetal heart rate (FHR) monitoring is used intraoperatively, most anesthetic agents decrease FHR variability to some degree. This does not indicate fetal acidosis.  Opioids and induction agents may decrease variability to a greater extent than inhalation agents. (18) Overall, neuromuscular blockers (NMB) and reversal agents are safe for both mother and fetus; however, since neostigmine crosses the placenta more readily than glycopyrrolate, fetal bradycardia may result when these medications are administered together for reversal of NMB.  For this reason, some advocate the use of atropine (10-20 mcg/kg) in conjunction with neostigmine for this purpose, as atropine crosses the placenta to a greater extent than glycopyrrolate. (19)

References

18. Liu PL, Warren TM, Ostheimer GE, et al: Foetal monitoring in the parturients undergoing surgery unrelated to pregnancy. Can Anaesth Soc J 1985;32:525-32.
19. Nejdlova M, Johnson T: Anaesthesia for non-obstetric procedures during pregnancy. Contin Educ Anaesth Crit Care Pain 2012;12:203-206.

Pregnant patients who are otherwise healthy tolerate fluid boluses well, and in many clinical scenarios, fluid resuscitation is a reasonable initial treatment for maternal hypotension. (20) However, physiological changes of pregnancy can predispose parturients with significant comorbidities to pulmonary edema, and thus fluid should be cautiously administered to those patients. While no studies have conclusively shown improved outcomes with tight blood pressure control during non-obstetric surgeries, the uteroplacental unit lacks autoregulation capabilities, and therefore maternal blood pressure should ideally remain within 20% of baseline to ensure adequate uteroplacental flow. Studies comparing phenylephrine and ephedrine for the treatment of hypotension in pregnant patients have demonstrated that ephedrine results in lower neonatal pH and higher fetal acidosis. The clinical significance of this is unknown. (21,22)

References

20. Reitman E, Flood P: Anaesthetic considerations for non-obstetric surgery during pregnancy. Br Journ of Anaes 2011;107:i72-i78.
21. Smiley RM: Burden of proof. Anesthesiology 2009;3:470-2.
22. Ngan Kee WD, Lee A, Khaw KS, et al: A randomized double-blinded comparison of phenylephrine and ephedrine infusion combinations to maintain blood pressure during spinal anesthesia for cesarean delivery: the effects on fetal acid-base status and hemodynamic control. Anesth Analg 2008;107:1295-302.

Meta analysis and randomized control trials have demonstrated that neither ephedrine nor phenylephrine is superior in the treatment of hypotension in parturients. (23,24,25,26)  Notably, the majority of these studies have been completed post spinal anesthesia for cesarean delivery.

References

23. King SW, Rosen MA: Prophylactic ephedrine and hypotension associated with spinal anesthesia for cesarean delivery. Int J Obstet Anesth 1998;7:18-22.
24. Ngan Kee WD, Khaw KS, Lee BB, et al: A dose response study of prophylactic intravenous ephedrine for the prevention of hypotension during spinal anesthesia for cesarean delivery. Anesth Analg 2000;90:1390-5.
25. Allen TK, George BB, White WD, et al: A double-blind, placebo-controlled trial of four mixed rate infusion regimens of phenylephrine for hemodynamic support during spinal anesthesia for cesarean delivery. Anesth Analg 2010;111:1221-9.
26. Rolston DH, Schnider SM, DeLorimier AA: Effects of equipotent ephedrine, metaraminol, mephentermine and methoxamine on uterine blood flow in the pregnant ewe. Anesthesiology 1974;4:354-70.

Once a fetus is considered viable, both electronic fetal heart rate monitoring and contraction monitoring should be performed before and after general anesthesia.  Preterm labor is a risk of Non-obstetric surgery during pregnancy, and tocometry may be able to detect contractions that the patient cannot feel.  The risk of preterm labor significantly decreases after the first post-operative week. (27) As pregnancy is a hypercoagulable state which can be compounded by venous stasis post operatively, venous thromboemobolism prophylaxis should always be considered in pregnant patients undergoing surgery. Regional or neuraxial analgesia should be considered for pain control, when applicable, as it may reduce the systemic effects of opioid administration. NSAIDs are considered safe for post-operative analgesia until the second half of pregnancy, when they should be used with caution due to the risk of premature closure of the fetal ductus arteriosus.

References

27. Mhuireachtaigh RN, O’Gorman DA: Anesthesia in pregnant patients for Non-obstetric surgery. Joun of Clin Anes 2006;18:60-66.

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