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Topic: Increased TECO2
An otherwise healthy teenager is having an ACL repair. The patient is without a personal or family history of problems with anesthesia or neuromuscular disease. The procedure is performed with an LMA using Desflurane, Propofol and fentanyl. Towards the end of the procedure Dilaudid is titrated for post op pain relief (0.02 mg/kg). The ETCO2 rises to 70 mmhg and would not decrease despite assisted ventilation (TV 500, RR 15). ETCO2 trace is normal without signs of rebreathing. ABGs: ph 7.16, PCO2 72, PO2 200, BE -1 HR 90's. BP normal. T 37.5. There is no rigidity.
1. Is this MH?
A. Yes
B. No
B. Likely MH
C. Unlikely MH
2. Should dantrolene be given?
A. Yes
B. No
3. Most likely cause of hypercarbia?
A. MH
B. LMA malpositioning
C. Fentanyl/Dilaudid
Narrative:
Follow-up: The child was carefully watched for 2 hours. Dantrolene was not given. A repeat ABG was ph 7.3; PCO2 54. Vital signs remained normal. Post op CK was normal.
Impression: It is always hard in the "heat of battle" to say that something is not MH. However, there are certain parts of the presentation of this patient that suggest that this is not MH.
1) The timing of the increased ETCO2 occurred after Dilaudid was given. It is possible that either a large dose of Dilaudid was given or the patient was sensitive to its effect. A patient having MH should have a high respiratory rate as they attempt to blow off CO2. The low respiratory rate of 15 without spontaneous breathing over the ventilator is more suggestive of narcotic affect then MH. In support of this, the ABG which only showed a respiratory acidosis without any metabolic component.
2) The patient had assisted ventilation through an LMA. It can be very difficult to aggressively assist ventilation through an LMA without inflating the stomach. Thus the increased CO2 may have been due to ineffective ventilation.
3) Although not always present the lack of tachycardia, fever or muscle rigidity points away from MH.
Conclusion: Not MH; most probably hypoventilation due to narcotic sensitivity.
Answers:
1. C. Unlikely MH (See discussion above)
2. B. No (See discussion)
3. C. Most likely C (See discussion)
________________________________________
Richard F. Kaplan, MD
Professor and Chief
Division of Anesthesiology and Pain Medicine
Children's National Medical Center
111 Michigan Ave N.W.
Washington, DC 20010
Tele: 202-884-2025
Fax: 202-884-4922 or 202-884-5999
