“OPOCUS” – Obstetric Point-of-Care Ultrasound: An Essential Tool for the Obstetric Anesthesiologist

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Point-of-care ultrasound (POCUS) has emerged as a transformative tool in modern medicine, enabling bedside imaging and real-time clinical decision-making; it has proved to be an effective clinical tool even in the hands of non-radiologists.[1,2] In the context of obstetric anesthesia, POCUS provides significant advantages, such as streamlining procedures, enhancing maternal and fetal safety, and improving outcomes.[3–5] We propose the term “OPOCUS” (Obstetric Point-Of-Care UltraSound) as a standard diagnostic and therapeutic tool in the domain of the obstetric anesthesiologist. Point-of-care ultrasound is a non-invasive, non-harmful, easily available, and affordable imaging modality with a myriad of uses. Applications of OPOCUS in pregnant patients include airway evaluation, neuraxial block guidance, cardiovascular and pulmonary assessment, abdominal nerve blocks, vascular access, and evaluation of obstetric emergencies, making it a cornerstone of care in obstetric anesthesiology.[6–9] Airway assessment with ultrasound in cases of difficult airway has been gaining popularity.[10] Pregnancy-induced physiological changes such as weight gain, edema, and increased breast size complicate airway management. Ultrasound assessment facilitates a detailed evaluation of airway anatomy, including tongue size, epiglottis visibility, and the prediction of difficult intubation.[10] It can be used to mark the cricoid (which is difficult to manually palpate in pregnancy with obesity) in preparation for front-of-neck access if required, and also for confirming the success of intubation.[9,11] Other applications described include visualizing the endotracheal tube cuff (if filled with saline) to rule out endobronchial intubation and predicting post-extubating stridor by measuring the amount of cuff leak.[12] This proactive approach enables anesthetists to prepare alternative airway strategies, reducing the risk of complications when administering emergent general anesthesia to these parturients. Neuraxial techniques like epidural and spinal anesthesia are fundamental in obstetric anesthesia for labor analgesia and cesarean sections. Traditional “blind” techniques rely on anatomical landmarks, which may be obscured by obesity or musculoskeletal disorders.[13] Ultrasound guidance improves success rates by providing real-time visualization of the spine, interspinous spaces, and the epidural space.[4] This reduces multiple attempts, patient discomfort, and procedural time while lowering the risk of complications such as accidental dural punctures. Most studies have utilized a low-frequency curvilinear probe, and most techniques involve counting upward from the sacrum; this has been proven to be more accurate than the classic landmark technique.[4] It also estimates the depth of needle insertion required and overall increases the safety of neuraxial access.[4] One study showed that, when compared to the radiological gold standard, ultrasound-based assessment was precise in 71% of patients (vs. 31% by palpation), and within one spinal level difference in all others.[13] Any intervention that improves procedural quality, success, and safety should be taken seriously, and we recommend that this assessment be a standard tool utilized in all women at term or in labor. Of late, ultrasound is being used for gastric volume assessment both in adults and in children; though still in its initial stages, it can be a useful tool for optimizing airway protection strategies in laboring women who are likely to need cesarean sections.[14–16] Aspiration is an important cause of airway-related mortality and morbidity, and all measures to reduce this risk should be considered.[17,18] Identifying patients at high risk of aspiration can ensure proactive airway management, such as prophylactic oral antacid therapy, appropriate positioning, and the judicious use of cricoid pressure during induction. A low-frequency (2–5 MHz) probe is ideal to provide the penetration required for gastric imaging.[14] The gastric antrum is the primary target due to its superficial location; qualitative information about the type of content (solid/liquid/gas), as well as quantitative estimates of gastric volume based on measurements and formulas, can directly advise clinical management.[14] However, it should be noted that the pregnant state can add difficulty in procuring images of the gastric antrum due to displacement by the enlarged uterus, fetal movements, and positioning challenges, as well as discomfort in a woman in active labor. Nonetheless, the added safety and prevention of complications may counterbalance these technical challenges. Further, for the delivery of parturients with complex pregnancies and for emergencies with severe maternal or fetal compromise, invasive hemodynamic monitoring is often needed. Proficiency in ultrasound-guided evaluation of fluid status, cardiac function and venous filling can help tailor vasoactive therapy and improve maternal and fetal outcomes. For an obstetric anesthesiologist, this competency would be of tremendous help in achieving optimal patient care without needing the assistance of colleagues from cardiac anesthesia or critical care medicine. Ultrasound techniques have also been used for the assessment of obstetric emergencies.[5,19,20] Obstetric complications such as postpartum hemorrhage, uterine rupture, and amniotic fluid embolism demand immediate diagnosis and intervention. Point-of-care ultrasound aids in assessing uterine and pelvic anatomy, detecting retained products of conception, and guiding transabdominal procedures.[5] In emergencies like amniotic fluid embolism and pulmonary embolism, lung and cardiac ultrasound support rapid diagnosis and critical decision-making. Lastly, although fetal monitoring primarily falls under obstetric care, anesthesiologists using ultrasound can evaluate fetal positioning, placental location, and amniotic fluid levels when rapid assessment is required, such as in labor or surgical emergencies. Many obstetric ultrasound assessments make use of the transvaginal ultrasound probe; although currently outside the scope of an anesthesiologist, with time and familiarity this modality may also be used by the OPOCUS-trained anesthesiologist to help the surgical team (who may be scrubbing up) during an emergency where minutes are precious. The advantages of OPOCUS include accuracy, whereby there is less reliance on anatomical assumptions, leading to more precise interventions; real-time visualization, allowing immediate adjustments during a procedure or changes in management based on findings; and reduced complications, due to early detection as well as a reduced number of procedural attempts. All of the above can lead to cost-effective healthcare, while enhancing the training pathways of obstetric anesthesiologists. The basic skills needed in OPOCUS training should therefore encompass airway assessment, neuraxial block placement, gastric ultrasound, cardiopulmonary evaluation, assessment of obstetric emergencies, and monitoring fetal wellbeing. There are also likely to be many challenges in incorporating OPOCUS into any obstetric fellowship or residency program. There may be technical difficulties to learn as well as practice in this patient cohort, as obesity, uterine enlargement, and fetal positioning can obscure imaging, thus complicating the assessment. Another factor is the steeper learning curve faced by an accomplished attending anesthesiologist compared to a young resident who may have learned the use of ultrasound early in training; though with regular use and familiarity, this can be mitigated. Equipment availability is another concern, as an increased frequency of OPOCUS utilization will require more ultrasound machines available simultaneously; this may have significant implications in smaller healthcare centers. There are also likely to be time concerns in emergent situations, especially in the early learning phases. How

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