November Case Of The Month
URGENT CORONARY ARTERY BYPASS GRAFTING: TO PROCEED OR NOT?
A 75 year old gentleman presents for urgent coronary artery bypass grafting using endoscopic vein harvesting and bilateral internal mammary arteries. The cardiac catheterization results revealed left main coronary artery equivalent disease resistant to medical therapy. He has a history of well-controlled hypertension with an ACE-inhibitor and metoprolol and diabetes mellitus type II. and no know drug adverse reactions. The patient does not take any statin-type medications. Previous general anesthesia administered without sequellae for a variety of surgical procedures as recently as March of 2007.
After induction of general anesthesia with midazolam, fentanyl, propofol, and pancuronium to facilitate endotracheal intubation, the patient was maintained with isoflurane, fentanyl, and oxygen. Pre-cardiopulmonary bypass ABG revealed was 7.39/41/400 BE 0. End-tidal carbon dioxide level was 35. After median sternotomy for take-down of the internal mammary arteries, endoscopic vein harvest started. One hour into the case, a rising end-tidal carbon dioxide level was noted at level of 59. An ABG was drawn which revealed 7.13/75/380 BE -4. No change in blood pressure nor heart rate which has consistently been in the 70s. At no time was the patient hyperthermic.
Question 1
How should the anesthesiologist proceed at this point considering the urgency of the patient’s coronary artery disease?
1- Cancel the case and evaluate for MH
2- Automatically assume the patient has MH and treat with dantrolene 2.5 mg/kg
3- Look for other causes of hypercarbia in the pre-bypass period
4- Assume that the cause may possibly be MH and discontinue isoflurane, change breathing circuits, soda lime and continue with non-triggering agents as well as careful rewarming during separation from cardiopulmonary bypass
5- Assume that the cause is not MH
Since endoscopic vein harvesting requires insufflation of carbon dioxide into the wound,
the anesthesiologist and surgeon agreed to continue the harvest of the saphenous veins using an the traditional open technique and abandon the endoscopic technique eliminating exogenous causes of hypercarbia. Unfortunately, the end tidal carbon dioxide level did not dramatically improve.
Question 2
At this time, prior to initiating cardiopulmonary bypass, what other diagnostic tests should be performed?
1- Arterial blood gas
2- Serum electrolytes
3- Coagulation studies
4- Urine for myoglobin
5- CPK and Tropinin Levels
Prior to initiating cardiopulmonary bypass and awaiting the results of the tests mentioned in question 2, the anesthesiologist empirically administered dantrolene 2.5 mg/kg. During cardiopulmonary bypass, the entire anesthesia breathing circuit, bellows, scavenging system, and machine were meticulously inspected for leaks and malfunction although none were found. The cardiopulmonary bypass machine was also inspected for problems with carbon dioxide insufflation into the bypass circuit. Blood gases on bypass were measured by alpha stat technique. No further derangements in arterial blood gas were noted during bypass. CPK was within normal limits prior to separation from bypass.
Separation from cardiopulmonary bypass was uneventful. Coagulation studies, additional CPK levels, and well as tropinin levels were normal. No myoglobin in the urine was detectable. No further dantrolene was administered.
Question 3
Did this patient have malignant hyperthermia?
1- Definitely not
2- Not likely
3- Probably
4- Absolutely
Question 4
What do you tell the patient and the family?
1- The patient should have a muscle biopsy when they have safely recovered from their cardiac surgery
2- The patient may be MHS and should be administered a non-triggering anesthetic
3- It is very unlikely that the patient had MH and the cause of the hypercarbia may have been related to other factors
4- The patient should take prophylactic dantrolene prior to his next anesthetic
Narrative:
This patient required urgent CABG due to left main coronary artery equivalent disease. The attending anesthesiologist made wise choices in recommending the suspension of the endoscopic harvesting of the saphenous veins. He was also correct in obtaining the appropriate blood gas and chemical studies prior to initiation of cardiopulmonary bypass as well as changing all breathing circuit tubing and checking all equipment for exogenous causes of carbon dioxide. It was difficult to argue with the administration of dantrolene to the patient at the time since many of the studies were not available.
The purpose of this Hotline Case was to illustrate that the carbon dioxide from the device used to endoscopically harvest saphenous veins may be an unusual source or at least a contributory factor.
Answers:
- 3 & 4
- All are the correct answers
- 2
- 3
Andrew Herlich, MD
Mercy Hospital of Pittsburgh
Dept of Anesthesiology
Pittsburgh, PA
