Nonobstetric Surgery During Pregnancy

Nonobstetric Surgery During Pregnancy

Anesthetic relevance	Medium
Anesthetic management	Nonobstetric anesthesia and surgery in pregnant women involves managing surgical procedures and anesthesia administration with specific considerations for both maternal and fetal safety. A complete discussion with patient, surgeon and obstetrician about timing, urgency and intraoperative monitoring is important.
Specialty	Anesthesiology, Obstetric Anesthesiology
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Nonobstetric anesthesia and surgery in pregnant women involves managing surgical procedures and anesthesia administration with specific considerations for both maternal and fetal safety. It's crucial due to the complexity of balancing the health needs of the pregnant patient with minimizing potential risks to the developing fetus. This topic underscores the importance of specialized medical care and interdisciplinary collaboration to ensure optimal outcomes for both mother and child during nonobstetric surgical interventions.

Surgical Considerations

Timing of Surgery

Emergency surgery, which is urgently needed, should be performed irrespective of the trimester of pregnancy.

Nonurgent surgeries, such as cholecystectomy for recurrent biliary obstruction without infection, are typically scheduled during the second trimester whenever feasible.

According to societal guidelines, elective surgeries that are not urgent should generally be postponed until after delivery.

Rationale

It's advisable to limit fetal exposure to surgery and medications during the first trimester of pregnancy, particularly during organogenesis, due to the inconclusive certainty surrounding the safety of many drugs in pregnancy. Additionally, caution is warranted because common adverse outcomes in the first trimester, such as miscarriage, vaginal bleeding, or fetal structural anomalies, could mistakenly be attributed to surgery and anesthesia without clear alternative causes.

Anesthetic implications

Preoperative optimization

Pregnant patients needing surgery should undergo preoperative evaluation akin to nonpregnant patients. This involves documenting medical and obstetric history comprehensively, alongside a detailed airway assessment during physical examination. Additional laboratory tests should be conducted based on the patient's medical conditions and the planned surgery; however, uncomplicated pregnancies typically do not necessitate extra preoperative testing.

Preoperative aspiration mitigation

Based on the anatomic and hormonal changes that occur, pregnant patients may be at increased risk of aspiration during induction of (or emergence from) general anesthesia, especially in cases of difficult or failed intubation when mask ventilation may be required. The risk of aspiration may be reduced by preoperative fasting and use of pharmacologic prophylaxis. However, no specific intervention has been shown to improve clinical outcomes, and decision to administer prophylaxis should be individualized.

Intraoperative management

Fetal Monitoring

One purpose of fetal monitoring is to identify concerning changes in the fetal heart rate (FHR) that may be influenced by reversible maternal factors not detectable through maternal monitoring alone. Even slight decreases in maternal blood pressure, oxygen levels, or uteroplacental blood flow can potentially affect fetal well-being. Interventions may include administering intravenous fluids, increasing oxygen levels, administering medications to raise maternal blood pressure, or adjusting maternal positioning. However, interpreting FHR patterns can be challenging during general anesthesia, as there is typically a decrease in beat-to-beat variability. Moreover, not all nonobstetric surgeries can be paused to facilitate emergency cesarean delivery, thus the exact benefit to the fetus remains uncertain.

When to perform

The decision to perform intra-operative monitoring should be a group decision between the Patient, Attending Surgeon, Anesthesiologist, and Obstetrician. It should be based on factors such as gestational age, type of surgery, and available resources. It should be recognized that in certain situations: specific surgeries, anesthetics or medications may need to be given that can have negative effects on the FHR, but the ability to stop, pause of reverse the effects may not be possible to facilitate an emergency cesarean delivery.

Society Guidelines recommend continuous monitoring of FHR in all viable fetuses (greater than 23 to 24 weeks of gestation) throughout surgery. The can be done via electronic FHR monitor or Doppler ultrasound. This is not always technically feasible due to positioning, type of surgery and location. At a minimum the FHR should be monitored preoperatively an post operatively for a period of time regardless of the gestational age. It should be recognized continuous FHR monitoring has not been shown conclusively to improve fetal outcome in women under general anesthesia.

If the decision is made to perform Intraoperative, qualified personnel are required to be available to monitor and interpret the FHR throughout the surgery. This must be an obstetrician or clinician experienced in reading and evaluation FHR strips and under almost no circumstances should be the Anesthesiologist directing the patients anesthetic. If continuous monitoring is performed after 23 to 24 weeks gestation, Appropriate resources should be immediately available, including and obstetrician or clinician capable of performing an emergency C-Section.

Positioning

Beyond 18 to 20 weeks of gestation, patients should be positioned with a 15 to 30 degree left lateral tilt when supine, to reduce aortocaval compression and cardiovascular compromise. The efficacy and need for left uterine displacement (LUD) for healthy parturients at cesarean delivery have been questioned. However, the preponderance of evidence suggests that LUD should be used for nonobstetric surgery.

LUD can be accomplished by tilting the operating table or by placing a wedge under the patient's right hip. Most operations can be successfully performed with LUD. If LUD compromises surgery and the supine level position is required, blood pressure may fall and should be maintained with intravenous (IV) fluid and vasopressor therapy.

Postoperative management

Maternal monitoring

Similar to any postoperative monitoring, close monitoring of the airway and respiratory system is essential during the recovery from anesthesia, as significant anesthetic complications can arise during emergence or shortly after surgery. See other specific Post Anesthesia General Adult Recovery texts

Fetal assessment

The FHR should be monitored in the recovery room, intermittently for previable fetuses, and continuously for the viable fetus. Uterine activity should also be monitored in cases in which the fetus is viable, as contractions are most likely to occur proximate to the procedure and as any tocolytic effect of general anesthetics wears off

Left Uterine Displacement

Left lateral position or uterine displacement should be maintained until the patient is fully awake, alert, and able to adjust her own position.

Postoperative pain control

A multimodal analgesia should be used for postoperative pain control for all patients. This should include nonpharmacologic methods of pain control, acetaminophen, regional anesthesia techniques, and local anesthetic infiltration. Opioids should be used on an as-needed basis.

Nonsteroidal anti-inflammatory drugs (NSAIDs) should not be used routinely during pregnancy (particularly in the early first and late third trimesters) because of potential fetal effects.

Pathophysiology

Physiological Changes of Pregnancy

Cardiovascular

Cardiac output (CO) rises significantly during normal pregnancy. CO reaches approximately 35 percent above baseline by the end of the first trimester, and plateaus at approximately 50 percent above baseline at 30 to 32 weeks gestation when patients are maintained in the left lateral decubitus position. At term, the supine position can reduce CO by 25 to 30 percent compared with left lateral decubitus position, due to compression of the inferior vena cava by the gravid uterus. In a subset of patients, this caval compression can produce significant maternal hypotension, labeled "supine hypotensive syndrome."

Pulmonary

Starting in the first trimester, resting minute ventilation increases, counterintuitively due to increased Tidal Volume not Respiratory Rate, up to nearly 1.5x pre-pregnancy MV by term. Thus pregnancy is associated with a compensated respiratory alkalosis, with pH = 7.42 to 7.44 and partial pressure of carbon dioxide (PaCO2) = 28 to 32 mmHg. Progesterone stimulates this increase in ventilation and causes the common dyspnea symptoms in pregnant women.

With growing uterine size there is a compensatory decrease in FRC. Beyond 20 weeks of gestation there is a noticeable 20 percent FRC decrease

Oxygen consumption is increased by 20 percent.

Hematologic

There is an increase in plasma volume compared to red cell mass causing a concentration decrease in hemoglobin, known as physiologic anemia of pregnancy or a dilutional anemia. normal hemoglobin may be as low as 11 g/dL by the end of the first trimester and approximately 10.5 g/dL in the second trimester.

Pregnancy creates a relatively hypercoagulable state, which persists into the postpartum period primarily due to an increase in concentrations of the vitamin K-dependent clotting factors and type 1 and 2 plasminogen activator inhibitor, and decreases in levels of free protein S, the cofactor of the endogenous anticoagulant activated protein C. Return to baseline thromboembolic risk generally occurs after 12 weeks postpartum.

Gastrointestinal

Gastroesophageal reflux in pregnancy is associated with a decreased lower esophageal sphincter tone throughout pregnancy and an increase in intraabdominal pressure due to the enlarging uterus. 40 to 85 percent of women describe being symptomatic during pregnancy. Gastric emptying is normal during pregnancy. Gastric acid secretion is unchanged or decreased in pregnant women.

For this reason women are considered a Full Stomach during preoperative considerations of anesthesia and for endotracheal intubation and Rapid sequence intubation considerations.

Sensitivity to anesthetic medications

The physiologic changes of pregnancy alter sensitivity to many anesthetic medications and may affect drug metabolism. Minimum alveolar concentration is reduced for volatile anesthetics during pregnancy

Effects of Anesthetics of the Fetus and the Pregnancy

There is no compelling evidence that any specific anesthetic agent is teratogenic in humans or that a specific anesthetic-related medication should be avoided during the perioperative care of a pregnant patient. See Other Pages for specific advice and information on the developing fetus. Briefly:

Fetal brain development

Laboratory and animal studies, including studies in nonhuman primates, have reported histologic changes of the brain and adverse neurodevelopmental effects after exposure to most anesthetics during periods of rapid brain development. Human clinical studies involving young children have reported mixed results, although the most robust studies are reassuring that a single anesthetic exposure does not adversely affect neurodevelopment

In 2016, the US Food and Drug Administration (FDA) announced warnings about potential risks of negative effects on the developing brain from administration of anesthetics and sedative drugs to third trimester pregnant women and children under age three, especially for repeated exposures or procedures lasting more than three hours. The FDA recommends that health care providers discuss with pregnant patients the benefits, risks, and appropriate timing of surgery requiring anesthesia that will take longer than three hours. However, the degree of risk remains unclear.

Teratogenicity

Theoretically, any medication could be teratogenic if given in a high enough dose, for a long enough duration of time, and at precisely the right time of development. Although many drugs used in anesthesia have been associated with teratogenic effects in animal studies, such findings are extremely difficult to extrapolate to humans due to interspecies variation and the high dose of agents used in the animal studies. Some medications, such as opioids, have been associated with congenital malformations when used chronically throughout pregnancy. In contrast, the use of all anesthetic medications in the perioperative setting in clinically relevant doses and concentrations has not been associated with teratogenicity.

Benzodiazepines

Some early reports suggested that diazepam use in early pregnancy may be associated with cleft palate. Subsequent studies have failed to demonstrate this association or a definite risk of other anomalies, although a small increase in risk could not be excluded. Benzodiazepines that are commonly used in the perioperative setting (eg, midazolam) have never been associated with congenital malformations. These are however frequently avoided clinically in these cases.

Nitrous oxide

Nitrous oxide has been shown to be a weak teratogen in animal models. Because of its effect of inhibiting methionine synthetase and impairing DNA production, there is concern about nitrous oxide use during pregnancy, particularly in the first trimester during organogenesis. However, no human study has shown any increase in the rate of congenital malformations with nitrous oxide use. This includes a study of over 2000 women who underwent surgery in the first trimester, most with the use of nitrous oxide. Despite this reassuring evidence, it is clinically frequent to avoid nitrous oxide during the first trimester if there are reasonable alternatives.

Medications

Of the clinically relevant medications, All medications cross the Uterine/Placenta barrier except (Heparin, Insulin, Glycopyrrolate, NDNMB, Succinylcholine). Known by the mnemonic (He Is Going Nowhere Soon).

Induction agents

The selection of the anesthesia induction agent (eg, propofol, ketamine, etomidate) should be based on patient factors and provider preference. No agents has been clearly shown to be teratogenic or to have adverse effects on human brain development. Propofol is the preferred induction agent for routine induction in otherwise healthy pregnant patients.

Pregnant patients may be more sensitive to the effects of neuromuscular blocking agents (NMBAs) than nonpregnant patients. As for all patients who receive NMBAs, at a minimum, neuromuscular monitoring with peripheral nerve stimulation should be used to guide dosing and recovery from neuromuscular block in pregnant patients. Quantitative measurements are preferable to qualitative, if possible.

Succinylcholine

The duration of action of succinylcholine is unpredictable in pregnant patients, though this is usually of no clinical significance. This is due to 2 factors: the decrease in pseudocholinesterase, which metabolizes succinylcholine, is reduced during pregnancy, and the increase in the volume of distribution causing a lower plasma level for a given dose.

Nondepolarizing NMBAs

The initial dose of nondepolarizing NMBA should be based on ideal body weight and further doses should be based on neuromuscular monitoring.

Maintenance anesthetics

Choice of maintenance anesthetic agents should be based on the considerations that apply to nonpregnant patients, as none of the standard anesthetic agents have been proven teratogenic or to have relatively increased adverse effects on human brain development. All general anesthetic drugs cross the placenta and may result in minimal or absent FHR variability

A systematic review of four studies including 155 pregnant women undergoing nonobstetric surgery reported minimal or absent FHR variability in most tracings and a decrease in FHR baseline of 10 to 25 beats per minute for women under general anesthesia. Additional criteria are necessary to identify non-reassuring fetal heart rate (FHR) patterns, such as persistent tachycardia without maternal fever, recurrent or prolonged FHR decelerations, repeated late decelerations, or a sinusoidal pattern. Before determining that an FHR tracing warrants emergency delivery, potential drug-induced causes should be ruled out. For instance, opioids and magnesium sulfate can reduce heart rate variability, butorphanol may produce a sinusoidal pattern, and beta blockers and atropine can elevate the FHR. The presence of moderate variability and/or FHR accelerations effectively rules out metabolic acidemia.

Pregnant patients have an increased sensitivity to potent inhaled anesthetics, seen as a decrease in the Minimum Alveolar Concentration (MAC). Several studies have reported up to a 30 percent reduction in the minimum alveolar concentration for isoflurane starting in early pregnancy , compared with nonpregnant patients. In contrast, a small study found no difference in the electroencephalographic measures of anesthetic effect between pregnant patients during cesarean delivery and gynecologic patients .

Potent inhalation agents decrease uterine tone during the operative procedure. This is overall advantageous, particularly for abdominal procedures in the second and third trimester, as it may reduce the incidence of pre-term contractions and pre-term labor. However, in the event of emergency delivery, higher doses of uterotonic agents may be required (eg, oxytocin, methylergonovine, carboprost tromethamine) for patients who are receiving these inhalation agents than patients who have neuraxial anesthesia.

Inhaled nitrous oxide (either alone or as a 50 percent mixture with oxygen) has no effect on uterine tone, maternal hemodynamic status, or FHR variability. See above for recommendation of developing fetus.

Neuromuscular Blocking Reversal

Sugammadex

Used to reverse the effects of neuromuscular blocking agents.

Sugammadex has a mechanism of action that encapsulates progesterone and reduces free progesterone levels in pharmacologic simulation studies . This effect could be consequential, since progesterone is required for endometrial decidualization and uterine growth early in pregnancy, and myometrial quiescence and cervical structural integrity later in pregnancy. There is insufficient evidence to conclude that sugammadex is safe during pregnancy, and the decision to use sugammadex should be individualized until more evidence on hormonal and teratogenic effects is available.

At this time the Society of Obstetric Anesthesia and Perinatology has recommended avoiding routine sugammadex use during pregnancy, and instead recommends other reversal agents

Neostigmine and Atropine

Used to revere the effects of neuromuscular blocking agents.

Neostigmine reverses the effects of neuromuscular blocking agents by inhibiting acetylcholinesterase, thereby increasing the availability of acetylcholine at the neuromuscular junction and facilitating muscle contraction. However, it can lead to side effects such as bradycardia due to increased cholinergic activity

Atropine is often co-administered with neostigmine to counteract its cholinergic effects, including bradycardia, by blocking muscarinic receptors and preventing excessive parasympathetic stimulation. This combination helps maintain a balanced autonomic response during recovery from anesthesia

Glycopyrrolate is not typically used in pregnant patients because it crosses the placenta poorly, resulting in limited effectiveness in the fetus. This could lead to fatal bradycardia in the fetus due to unopposed actions of the neostigmine. Therefore, alternative medications such as atropine are preferred.

Antibiotics

Whether antibiotic prophylaxis is required depends on the particular procedure being performed.

Safe antibiotic options for pregnant women include cephalosporins, penicillins, erythromycin (excluding estolate), azithromycin, and clindamycin due to their favorable safety profiles. Aminoglycosides are generally safe but pose risks of fetal and maternal ototoxicity and nephrotoxicity.

Thromboprophylaxis

The hypercoagulable state of pregnancy increases the risk of a thromboembolic event in the postsurgical period

Pneumatic compression devices should be used or considered for all surgeries

Tailor the decision to administer pharmacological prophylaxis according to the anticipated scope and duration of the procedure, as well as the patient's risk factors for venous thrombosis, including factors related to pregnancy (such as thrombophilia, prolonged immobilization, previous venous thrombosis, malignancy, diabetes mellitus, varicose veins, paralysis, maternal age, or obesity).

Glucocorticoid administration

Administration of a course of antenatal glucocorticoids 24 to 48 hours prior to surgery for patients between 24 and 34 weeks of gestation can reduce perinatal morbidity/mortality if preterm birth occurs.

The decision to give glucocorticoids, and potentially delay surgery for 24 to 48 hours, must balance the urgency of the surgery with the obstetrician's estimate of the risk of preterm birth because of the underlying disease or the planned procedure.