Obstetric Anesthesiology



Obstetric Anesthesiology


Shreya Patel

Caitlin Sutton



GENERAL PRINCIPLES



  • Maternal mortality is rising in the United States. Anesthesia-related mortality accounted for 0.2% of pregnancy-related deaths from 2011.


  • Maternal mortality from anesthesia complications has decreased with advancements in monitoring and establishing standards of care.


  • The primary goals of the obstetric anesthesiologist are the safety and comfort of the pregnant woman and her fetus and are achieved through a variety of anesthetic techniques that are individualized to the patient’s medical condition and preferences.


  • Analgesia refers to a lack of pain perception and is typically sought during labor; anesthesia denotes the absence of all sensation and is the goal during surgical intervention.


  • Epidural injections or catheters are placed in the epidural space deep to the ligamentum flavum but outside the dura mater, whereas spinal injections or catheters are placed in the intrathecal (or subarachnoid) space between the arachnoid mater and the pia mater, where the cerebrospinal fluid is found.


COMMONLY PERFORMED ANESTHETIC PROCEDURES


Neuraxial Techniques



  • Neuraxial procedures allow access to either the epidural or intrathecal space for drug administration. A single injection allows for a onetime dose of medication, whereas a catheter allows for variable onset speed, dosing, and duration of analgesia or anesthesia.


  • Neuraxial procedures can facilitate a safe and comfortable delivery for the majority of patients. Table 3.9.1 compares the advantages and disadvantages of neuraxial analgesia and anesthesia.


  • Preanesthetic evaluation should include assessment of contraindications to neuraxial placement. Table 3.9.2 lists contraindications for neuraxial anesthesia.


  • For placement, experienced personnel, peripheral intravenous access, resuscitative equipment, and monitors should be available.


  • Commonly used neuraxial techniques include epidural catheters, single-shot spinal injections, combined spinal-epidurals (CSE), and dural puncture epidurals (DPE) (Figure 3.9.1A-D). Continuous spinal catheters are occasionally used as well. Table 3.9.3 compares the advantages and disadvantages of the various techniques.
















  • Medication dosing differs significantly depending on the location of administration. Spinal administration of a dose intended for the epidural space can lead to total spinal anesthesia, profound hypotension, bradycardia, or respiratory arrest.


  • Epidural



    • Generally placed in the lumbar region for labor or cesarean delivery (CD), below the termination of the spinal cord at L1 to L2.


    • Often considered the “gold standard” for labor analgesia; less commonly placed de novo for CD. Their use in CD typically follows conversion of a functioning labor epidural to a surgical anesthetic at the time of decision for CD.


    • Technique: The epidural space is identified by a loss of resistance to saline or air as the needle traverses the vertebral ligaments. Once the epidural space is identified, a catheter is threaded blindly and secured.


    • Early labor epidural placement has not been shown to increase the rate of CD or prolong the duration of the first stage of labor (1).


  • Spinal



    • Technique: A small gauge needle is passed into the intrathecal space, and medications are administered into the cerebrospinal fluid and the needle is removed.


    • Pencil-point needles are the standard of care owing to the much lower rate of postdural puncture headache (PDPH) associated with their use.








    • Spinal blockade is most commonly performed as a single-shot technique and has a limited duration.


    • Compared to epidural anesthesia, spinal blockade is rapid and predictable, provides a denser block, and carries a lower risk of local anesthetic systemic toxicity (LAST) (2).


  • Combined Spinal-Epidural



    • Allows for medication administration into both the intrathecal and epidural spaces, offering the advantages of a spinal’s rapid, reliable block and an epidural catheter’s ability to extend block height and duration.


    • Technique: A “needle through needle” technique in which the epidural space is accessed first, followed by a spinal needle through the epidural needle into the subarachnoid space, where the intrathecal injection is administered. The spinal needle is removed, and a catheter is threaded through the remaining epidural needle into the epidural space and secured.










  • Dural Puncture Epidural



    • A variation on the combined spinal-epidural technique without the administration of intrathecal medications often used for labor analgesia owing to the more rapid onset and improved blockade quality compared with a traditional epidural technique.


    • Technique: Similar to the “needle through needle” approach described for CSE is performed, but no intrathecal medication is administered.


    • The presence of free-flowing cerebrospinal fluid (CSF) through the spinal needle can act as a “confirmatory” end point, indicating a higher likelihood of correct epidural positioning.


  • Continuous Spinal Anesthesia



    • Involves the placement of a catheter into the intrathecal space, either intentionally or after unintentional dural puncture during attempted epidural placement.


    • Technique: Similar to that of a single-shot spinal, but the needle must be large enough to accommodate a catheter.


    • The presence of a catheter allows for repeated drug administration to extend the height or duration of the spinal blockade.


    • Owing to the larger gauge needle required for catheter insertion, continuous spinal anesthetics have the major disadvantage of a high risk for PDPH.


  • Neuraxial Procedures in the Setting of Coagulopathy or Anticoagulation



    • Neuraxial anesthesia should not be performed in patients with severe coagulopathy because of the increased risk of spinal or epidural hematoma. A minimum acceptable platelet count has not been standardized, but the risk of hematoma is low in patients with a platelet count of >70,000 ug/dL, provided there is no evidence of functional coagulopathy, platelet dysfunction, or downward trend (4).


    • There is a growing number of pregnant women in whom therapeutic or preventative thromboprophylaxis is indicated. The Society of Obstetric Anesthesiology and Perinatology issued a consensus statement for anesthetic management of pregnant women receiving thromboprophylaxis or higher dose anticoagulants. The recommendations are summarized in Table 3.9.4 (5).











REGIONAL ANESTHESIA TECHNIQUES



  • Regional anesthesia may be used as part of a multimodal postoperative analgesia strategy. Currently available evidence suggests that these blocks are most beneficial in settings where neuraxial opioids are not administered (e.g., CD performed with general anesthesia) or in patients with breakthrough pain despite neuraxial opioid administration (6).

The most commonly performed blocks for obstetric surgical patients include transversus abdominis plane (TAP) blocks and quadratus lumborum (QL) blocks (Figure 3.9.2). Continuous wound infiltration (CWI) offers another method of medication delivery.



  • Transversus Abdominis Plane (TAP) Block



    • Technique: Using ultrasound guidance, a needle is advanced into the plane between the internal oblique and transversus abdominis plane, and medication is administered into the fascial plane. A catheter may be threaded into the plane and left in place.


    • TAP block should be considered after CD especially for patients who do not receive neuraxial morphine (7).


  • Quadratus Lumborum (QL) Block



    • Technique: Using ultrasound guidance, a needle is advanced into the plane lateral, posterior, or anterior to the QL muscle, and medication is administered into the fascial plane. A catheter may be threaded into the plane and left in place.


    • QL blocks are closer to the vertebral column than TAP blocks, possibly contributing to paravertebral spread and thus visceral analgesia. Depending upon which QL block is used and the extent of paravertebral spread, hemodynamic changes and quadriceps weakness may be seen (7).


  • CWI



    • Technique: A multiorifice catheter is placed by the surgeon at the surgical site before closure, preferably deep to the rectus fascia.


    • Medications (most commonly local anesthetics) are delivered continuously by a pump.


ANTEPARTUM AND PREOPERATIVE PLANNING



  • All patients in the labor and delivery suite have the potential to need an anesthetic emergently and should be evaluated by an anesthesia care provider for a focused history and physical examination. Significant anesthetic or obstetric concerns should be discussed with the obstetric team in a regularly scheduled multidisciplinary team “huddle” at every shift change.


  • For patients with high-risk conditions, early referral for antepartum evaluation by an obstetric anesthesiologist allows for timely investigation, specialist referrals, and medical optimization. Management often requires multidisciplinary input and potentially transfer to a facility with a higher level of resources. This approach has been shown to reduce maternal morbidity and mortality (8).


  • Appropriate indications for antepartum and peripartum anesthesiology consultation are included in Table 3.9.5.


  • Preoperative Laboratory Evaluation



    • Obtaining preoperative or intrapartum patient labs beyond routine prenatal labs should be considered based on maternal history and physical examination.


    • Assessment of routine intrapartum platelet count is not necessary before neuraxial procedures in the healthy parturient and should be individualized and based on a patient’s history (e.g., preeclampsia), physical examination, and clinical signs (9).


    • Although blood typing is recommended for all parturients, routine crossmatching is not generally necessary for healthy patients with a history of uncomplicated pregnancy. An example of an algorithm for transfusion laboratory evaluation (e.g., blood type, screen, and crossmatch) for patients admitted to labor and delivery can optimize resource utilization (Table 3.9.6).


ANESTHESIA FOR CESAREAN DELIVERY


Choice of Anesthetic Technique for Cesarean Delivery



  • Neuraxial anesthesia confers a superior safety profile, postoperative analgesia, and patient experience and is considered

    the preferred mode of anesthesia for CD. However, the safety of general anesthesia for CD has improved substantially, and there is no longer a significant difference in mortality rate between the techniques. General anesthesia for CD should not be avoided when indicated (10).












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Sep 8, 2022 | Posted by in OBSTETRICS | Comments Off on Obstetric Anesthesiology

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