Fever after open heart surgery in a patient with a history of Neuroleptic Malignant Syndrome (NMS)
Hx: The MH hotline received a call regarding a 15 y.o. 70 kg male on his first post operative day following mitral valve repair.
The child had a history of NMS (Neuroleptic Malignant Syndrome) following Haldol (haloperidol) treatment. All psychotropic drugs were stopped 1 week prior to surgery. There were no signs of hypermetabolism during the anesthetic which included Sevoflurane/Desflurane/ Fentanyl/Rocuronium/Midazolam. In particular, end tidal CO2, temperature, HR, BP, arterial and venous blood gases during bypass were all in acceptable ranges. There was a moderate metabolic acidosis without respiratory acidosis after bypass which resolved. Urine was initially pink during bypass which quickly cleared.
On post op day #1 the child failed extubation due to "oversedation" and was reintubated. He developed a fever to 104 after intubation. Heart rate 170 bpm. ABG did not show a metabolic or respiratory acidosis, ABG
PO2 66, PCO2 43, ph 7.39s(TV 600, RR 12). The patient was placed on a cooling blanket and Dantrolene (1 mg/kg) was started. CK 900 IU/L. The condition slowly improved with HR 120 bpm, temperature 37 degrees centigrade. MH Hotline was called for further treatment:
Questions
1. What is the likelihood that this was an MH episode:
a. Definite
b. Likely
c. Unlikely
d. Highly unlikely
2. Could this be an MNS episode?
a. Definite
b. Likely
c. Unlikely
d. Highly unlikely
3. Is the metabolic acidosis coming off bypass related to MH?
a. yes
b. no
c. maybe
4. Was the "failed intubation" due to MH?
a. highly likely
b. highly unlikely
c. maybe
5. Can you have an MH reaction without increased pCO2 on arterial
blood gases?
a. Yes
b. No
6. Was the use of Dantrolene indicated?
a. Yes
b. No
c. Maybe
Answers and Narrative:
1. d. Highly unlikely
MH can occur in the post op period but it usually occurs within minutes to hours unless there are signs of MH during the anesthetic. Some of the signs of MH may be delayed due to cooling and decreased metabolic demands during bypass. The metabolic acidosis during bypass may be due to many causes (low perfusion, ineffective cooling, prolonged bypass, fever). A sensitive sign of MH is decreased saturation and high CO2 in the pump venous blood gases during bypass.
2. d. Highly unlikely
NMS is a hypermetabolic state due to Neuroleptic drugs such as phenothiazines (e.g. Haldol). It can present in the perioperative period and be confused with an MH reaciotn (fever, rigidity, increased CK). A similar state can occur with SSRI's (e.g. Zoloft). It usually occurs upon initiation of neuroleptic drugs. It is thought due to dopamine receptor blockade. Since this patient's medications were stopped for 10 days this episode is not be related to NMS. NMS is not thought to be triggered by drugs that trigger MH. Further, NMS patients do not appear more likely to be susceptible to MH. One must be careful that Neuroleptic drugs were not given in the post op period (e.
metoclopromide).
3. b.
Metabolic acidosis immediately after bypass is common and has many causes (inadequate perfusion, acidosis, poor heart function, hypoxia).
Temperature is usually lowered by bypass and hyperthermia therefore may be even more delayed then without bypass.. Pink urine due to pump hemolysis is also common. A sensitive sign of MH is decreased saturation and high CO2 in the pump venous blood gases during bypass. Since these were not found isolated metabolic acidosis is not related to MH in this patient.
4. b.
The need for reintubation could be due to respiratory failure from the increased metabolic demands of an MH episode. This would be accompanied by increased CO2 production. Unintubated patients would attempt to "hyperventilate" in an effort to blow off the extra CO2. Thus their respiratory rate and tidal volume would ap[pear to increase.
"Oversedated" patients have shallow, slow respirations. Thus the need for reintubation in this patient is inconsistent with MH.
5. c.
Since MH is a hypermetabolic state it should always be associated with increased CO2 production. If mechanical ventilation is set too high then arterial CO2 may be normal or low even if CO2 production is elevated.
Therefore, it is possible to have an MH episode with normal or low arterial blood gas CO2 levels. Arterial CO2 levels will increase as the MH episode gets worse and CO2 production continues to increase and overwhelm minute ventilation.
6. c.
Dantrolene is a life saving drug for MH. The earlier that it is given during an MH episode the better the chances of a full reversal of the episode. In retrospect this patient probably aspirated when he was "over sedated". However, when there is a question of MH and you cannot quickly rule it out then it is appropriate to give Dantrolene. Dantrolene is also effective in reducing fever from many causes other then MH. Even though this wasn't a case of MH you can make an argument for its use.
Refs:
Richard Kaplan, MD
Children's National Medical Center
Washington, DC
