July 2007 Case of the Month

July 2007 – Case of the Month

Hypercarbia Following Induction of General Anesthesia

A 30 y/o male is scheduled for an open fixation of right ankle. He does not have any relevant previous medical or surgical history. MH family history is negative. General anesthesia was induced using propofol and fentanyl. Muscle relaxation was achieved with rocuronium. The trachea was intubated without difficulty and general anesthesia was maintained with desflurane. Few minutes following induction, the anesthesiologist noticed that the temperature has increased abruptly from 36.0 to 36.6 º. Simultaneously, ETCO2 increases to 48. Despite increasing minute ventilation by increasing respiratory rate to 20 breaths per minute, ETCO2 did not normalized. Matter in fact; the anesthesiologist noticed that the inspired CO2 was 6-7, and heart rate increased from 80 to 118 b/m.

 

1.  Is this MH?

            A. Yes

            B. No

            C. Likely MH

            D. Unlikely MH

 

2. Should dantrolene be administered?

            A. Yes

            B. No

            C. 0.1 mg/kg only

 

3. Most likely cause of hypercarbia?

            A. MH

            B. Fentanyl

            C. CO2 absorber malfunction

 

4. Does MH increase inspired CO2?

A. Yes

            B. No

            C. Only if it is sever enough

           

5.  What is the next step in managing this patient?

            A. Check ABG

            B. Continue observing hoping the patient will improve

            C. Discontinue desflurane

            D. Call MH hotline consultant

 

 

 

 

 

 

 

Narrative:

 

Follow-up: The anesthesiologist turned off desflurane and continued the surgery using total intravenous anesthesia (TIVA). Intraoperative ABG showed respiratory acidosis without metabolic acidosis. Patient was extubated at the end of the surgery. CK in PACU was normal. Inspiratory CO2 was high to the end of the case.

 

Impression: It is always hard to rule out MH with certainty. That is why it is better to err on the safe side and start by discontinuing the triggering agent. Calling the hotline consultant after obtaining blood gas would be the next step. MH should not increase inspiratory CO2 as long as the CO2 absorber works appropriately. Risks and benefits of dantrolene administration should always be weighed. In this case, MH symptoms were unconvincing and it was felt unnecessary to administer dantrolene till we get more information (ABG, CK….etc).

Patient did well postoperatively with normal CK values.

 

Conclusion: Not MH; most probably hypercarbia due to CO2 absorber malfunction.

 

Answers:

 

  1. D. Unlikely MH (see discussion)
  2. B. No (see discussion)
  3. C. CO2 absorber malfunction (see discussion)
  4. B. No (see discussion)
  5. C. Discontinue desflurane (see discussion)

 

 

 

Mohanad Shukry, MD

Assistant Professor, Anesthesiology

Children’s Hospital of Oklahoma

Oklahoma University

750 NE 17th St. Suite 200

Oklahoma City, OK 73104