From the Guidelines
Ultrasound guidance is the recommended method for performing peripheral nerve blocks and neuraxial anesthesia in morbidly obese patients. This approach offers significant advantages over traditional landmark-based techniques, which can be particularly challenging in this patient population due to obscured anatomical landmarks and increased tissue depth. According to the Association of Anaesthetists of Great Britain and Ireland 1, regional anesthesia is preferred to general anesthesia in morbidly obese patients, and ultrasound might be a useful adjunct to improve success rates.
When performing ultrasound-guided blocks in obese patients, using low-frequency curvilinear probes (2-5 MHz) is often necessary to achieve adequate depth penetration. For neuraxial procedures, a pre-procedural ultrasound scan helps identify the midline, appropriate intervertebral space, and estimate the depth to the epidural or intrathecal space. This information improves first-attempt success rates and reduces complications. Key considerations for neuraxial anesthesia in morbidly obese patients include:
- Using specific equipment such as extra-long spinal or epidural needles, as recommended by the Association of Anaesthetists of Great Britain and Ireland 1
- Positioning the patient in a way that facilitates access, such as the sitting position with the bed tilted towards the operator, allowing the patient to lean forward
- Leaving at least 5 cm of catheter in the epidural space to reduce migration, as suggested by the same guidelines 1
The use of ultrasound guidance improves safety and efficacy by providing real-time visualization of anatomical structures and needle advancement, reducing the risk of vascular puncture, pneumothorax, or inadvertent intravascular injection. By prioritizing ultrasound guidance and adhering to specialized techniques and equipment recommendations, practitioners can enhance the outcomes of peripheral nerve blocks and neuraxial anesthesia in morbidly obese patients, ultimately reducing morbidity, mortality, and improving quality of life.
From the Research
Ultrasound Guidance for Peripheral Nerve Block and Neuraxial Anesthesia in Morbidly Obese Patients
- Ultrasound guidance is a recommended method for peripheral nerve block and neuraxial anesthesia in morbidly obese patients, as it allows for more accurate placement of the block and reduces the risk of complications 2, 3.
- The use of ultrasound guidance can improve the success rate of peripheral nerve blocks in obese patients, even in cases where traditional landmark-based techniques are challenging due to thick subcutaneous tissue 2, 3.
- Ultrasound-guided multiple peripheral nerve blocks can be used as an alternative to general anesthesia in morbidly obese patients, reducing the risk of cardiorespiratory complications 4, 5.
Challenges and Considerations
- Morbidly obese patients pose unique challenges for anesthesiologists, including increased difficulty with neuraxial procedures and a higher risk of complications 4, 6.
- The use of skin landmarks may be challenging in obese patients, and ultrasound techniques can help improve block performance 3.
- The accuracy of anesthesiologists' estimates of the interspinous level in super-obese parturients may be poor, and ultrasound guidance may not always prevent inadvertently high epidural or intrathecal catheter placement 6.
Specific Techniques and Applications
- Ultrasound-guided transversus abdominis plane (TAP) block and lateral femoral cutaneous nerve (LFCN) block can be used for bone marrow aspiration in morbidly obese patients, providing effective analgesia and reducing the need for general anesthesia 5.
- Intercostobrachial nerve block (T2) can be used to prevent pain during injection of bone marrow aspirate into the non-union site 5.
- Dexmedetomidine and ketamine can be used for deep level sedation and analgesia in combination with ultrasound-guided peripheral nerve blocks 5.