From the Guidelines
The recommended dose of intrathecal bupivacaine for morbidly obese patients is typically 10-15 mg (2-3 mL of 0.5% solution), which is similar to non-obese patients. Dosing should be based on ideal body weight rather than actual body weight, as cerebrospinal fluid volume does not increase proportionally with obesity. When administering, patient positioning is crucial; a sitting position may be preferable to facilitate identification of landmarks. Consider adding adjuvants like fentanyl (10-25 mcg) or morphine (100-200 mcg) to enhance analgesia while allowing for lower bupivacaine doses. Careful titration is essential, as morbidly obese patients may experience more extensive cephalad spread of anesthesia due to increased intra-abdominal pressure compressing the epidural space. This can lead to higher blocks and potential respiratory compromise. Monitoring for hypotension is particularly important, as these patients may have baseline cardiovascular issues. The onset of action is typically 5-10 minutes, with duration of 2-3 hours for anesthesia, though sensory effects may last longer.
Key Considerations
- Dosing based on ideal body weight rather than actual body weight is recommended, as supported by the concept of using lean body weight for anesthesia induction to avoid hypotension 1.
- The use of multimodal, opioid-sparing analgesia approaches is highly supported by evidence to improve postoperative recovery 1.
- Regional anaesthetic techniques, such as epidural analgesia and ultrasound-guided transversus abdominis plane block, have been shown to be highly efficient in reducing opioid requirements 1.
- Infiltration of bupivacaine 0.5% before incision results in a reduction in opioid consumption and postoperative pain, suggesting the effectiveness of bupivacaine in managing pain in morbidly obese patients 1.
Administration and Monitoring
- Patient positioning, such as a sitting position, is crucial for facilitating the identification of landmarks during administration.
- Careful titration and monitoring for hypotension are essential due to the potential for increased cephalad spread of anesthesia and baseline cardiovascular issues in morbidly obese patients.
- The use of adjuvants like fentanyl or morphine can enhance analgesia while allowing for lower bupivacaine doses, which is in line with the recommendation for multimodal analgesia approaches 1.
From the Research
Recommended Dose of Intrathecal Bupivacaine for Morbidly Obese Patients
The recommended dose of intrathecal bupivacaine for morbidly obese patients can vary depending on several factors, including the specific procedure being performed and the patient's individual characteristics.
- A study published in Anesthesiology in 2011 found that the effective dose (ED(50)/ED(95)) of intrathecal bupivacaine for cesarean delivery in morbidly obese patients was similar to that of non-obese patients, with an ED(50) of 9.8 mg and an ED(95) of 15.0 mg 2.
- Another study published in Revista brasileira de anestesiologia in 2009 found that the ED(95) of intrathecal bupivacaine for elective cesarean delivery was similar in obese and normal weight women, with an estimated ED(95) of 12.92 mg 3.
- A study published in Medicina (Kaunas, Lithuania) in 2023 found that the suggested dose ranges for favorable block heights were 15-17 mg and 10.5-16 mg for patients aged <60 and ≥60 years, respectively, regardless of BMI 4.
- However, it's worth noting that the optimal dose of intrathecal bupivacaine may depend on various factors, including the baricity of the solution, the volume of epidural extension, and the patient's individual characteristics, as highlighted in a study published in Anesthesia and analgesia in 2008 5.
Key Considerations
When determining the recommended dose of intrathecal bupivacaine for morbidly obese patients, several key considerations should be taken into account, including:
- The patient's body mass index (BMI) and overall health status
- The specific procedure being performed and the desired level of anesthesia
- The potential risks and benefits of different dosing regimens
- The need for individualized dosing and careful monitoring of the patient's response to the anesthesia. A study published in the British journal of anaesthesia in 1990 found that morbidly obese patients may require less local anesthetic for spinal anesthesia, and that the use of plain bupivacaine at the L4-5 interspace may be recommended to avoid extensive spread of the block 6.