Anesthetic Management for a Morbidly Obese Patient (with OSA) Undergoing THR
Preoperative Considerations & Preparation
Why is a morbidly obese patient at increased risk for aspiration?
In morbidly obese patients, the esophageal sphincter tone is reduced and intra-abdominal pressures are increased. Both of these criteria, along with the position of the patient, can result in an increased risk for aspiration. Therefore, acid prophylaxis is an important preoperative criteria.
How should you preoxygenate a morbidly obese patient, and why is it so important?
Preoxygenation, or denitrogenation, is very important in a morbidly obese patient because their functional residual capacity (FRC) and total lung capacity are already reduced.
We can preoxygenate the patient either by asking them to take four to six vital capacity breaths initially, then by applying a well-fitting mask and giving 100% oxygen for 6 to 8 minutes.
What is the goal of preoxygenation (denitrogenation)?
The goal of denitrogenation is to remove the nitrogen from the lungs and fill them with 100% oxygen.
What additional monitoring equipment is necessary for this case?
An intra-arterial BP monitoring setup should be arranged. A temperature probe is also essential to maintain normothermia.
Why is a temperature probe specifically needed for this patient?
It is essential to maintain normothermia. If the patient becomes hypothermic, it may delay our extubation criteria and the action of the drugs, meaning we may not be able to extubate the patient.
Intraoperative & Anesthetic Plan
What type of anesthesia is preferred for this patient undergoing a major procedure like THR?
For this patient, because of the major procedure and anticipated blood loss, I would like to have hypotensive anesthesia.
Extubation & Post-Operative Care
What are your specific extubation criteria for this patient?
Before extubation, we must take an ABG to ensure there is no electrolyte imbalance and check the acid-base status. The specific extubation criteria include:
- The patient should be completely awake and alert.
- Head holding for more than 5 seconds.
- Hemodynamically stable.
- Respiratory rate between 10 to 30.
- SpO2 of more than 90%.
- A complete reversal of the neuromuscular blockade with a TOF score of more than 0.9.
What is the immediate post-operative plan for shifting the patient?
This patient needs to be shifted to a high-dependency unit with high monitoring. We would shift the patient in an ICU bed to the post-operative care unit.
Why is careful monitoring in the ICU necessary for this patient?
In the ICU, we need careful monitoring because there is a high chance of desaturation, BP fluctuations, infections, and DVT.
What DVT prophylaxis measures will you take?
For DVT prophylaxis, we can use pneumatic compression stockings or start on LMWH postoperatively.
What are the criteria for discharging the patient from the ICU to the ward?
The modified Aldrete score is used. A score of more than or equal to 9 is the criteria for shifting the patient from ICU to the room. This score checks:
- Activity: Ability to move four, two, or no extremities.
- Respiration: Ability to take deep breaths, or presence of dyspnea/apnea.
- Circulation: BP fluctuations (e.g., ±20 mmHg or ±50 mmHg).
- Consciousness: Patient is conscious, oriented, awake, and alert.
- Oxygen Saturation: Able to maintain SpO2 >90% on room air, with O2, or unable to maintain it.
What other complications can be expected in the post-operative period?
- Rapid desaturation: Due to OSA risk.
- Hypotension and BP fluctuations: Especially if the patient is hypertensive.
- Surgical site infections: There is an increased risk, so prophylactic antibiotics should be started.
In addition to DVT prophylaxis, incentive spirometry and deep breathing exercises should be started in post-operative care. CPAP may also be required.