Topic: Pediatric tonsillectomy - postop tachycardia, hypercarbia, fever

The hotline consultant received the following call from a hospital pediatric ICU:

A 5 y/o girl was airlifted to them following tonsillectomies and adenoidectomy at a free-standing ambulatory surgery center.  The child was induced with sevoflurane, intubated when deeply anesthetized, and anesthesia was maintained with sevoflurane/nitrous oxide and supplemented with 2 mcg/kg iv fentanyl.  Surgery was described as uneventful and surgery time was 25 minutes.  During emergence and following extubation, heart rate increased to 160/minute with end-tidal CO₂ >80 mm via face mask.  Rectal temperature was 38.8° C.  The child was promptly reintubated. 

1)      Which of the following data is the MOST important when considering MH as a possible cause of the high end-tidal CO₂?

A)    Arterial blood gas

B)     Venous blood gas

C)    Minute Ventilation (Respiratory rate X Tidal volume)

D)    Tachycardia

E)     Absence of rigidity

2)      Which of the following details would also be helpful in interpreting the hypercarbia?

A)    Observation if child was extubated awake or deep.

B)     History of confirmed or suspected obstructive sleep apnea.

C)    Post-reintubation CXR demonstrating collapsed left lung.

D)    Presence or absence of laryngospasm or stridor following extubation.

E)     ALL of the above.

3)      Which of the following details might be useful in evaluating the temperature 38.8° C.?

A)    History of recent URI in patient or family member.

B)     WBC with differential.

C)    Intra-operative use of warming device (e.g. Bair-Hugger).

D)    Preoperative temperature.

E)     ALL of the above.

4)      After re-intubation, the patient is given a total of 4 mg/kg iv Dantrolene, sedated with lorazepam, and transferred via helicopter to the nearest hospital with a pediatric ICU.  The successful reduction in end-tidal CO₂ with a brief period of hyperventilation following re-intubation but PRIOR to dantrolene administration is irrelevant when considering whether or not to refer the child (and her family) for future evaluation of MH susceptibility. 

A)    True

B)     False

5)      If you suspect MH, have given dantrolene with improvement of respiratory acidosis, which of the following is CRITICAL to diagnose and treat prior to transport?

A)    Myoglobinuria

B)     EKG signs of hyperkalemia

C)    Thrombocytopenia

D)    Hypocalcemia

6)      Reduction of temperature following dantrolene occurs only when MH is the cause of hyperthermia.

A)    True

B)     False

The child arrived in the PICU.  Sedation was maintained with a propofol infusion.  Temperature was 36.4° C.  A central venous catheter was placed.  With lightening of sedation, the child moved all extremities on command.  Venous blood gas, WBC, serum potassium, platelets, and PT, PTT were all within normal limits.  Urine output is good, and the urine is negative dipstick for heme pigment. The CK level was 159 eight hours following admission.

7)      The normal labs and CK level exclude the diagnosis of MH.

A)    True

B)     False

8)      The caller wants to know if they should obtain a muscle biopsy for MH diagnosis while the child is still intubated and sedated.  Which of the following is appropriate advice?

A)    Yes, obtain muscle biopsy at your hospital. Any hospital pathology lab can determine the diagnosis of MH.

B)     Do NOT obtain a muscle biopsy for MH evaluation.  The test requires that the muscle remain viable, and can be performed only at a designated diagnostic center.

C)    Yes, obtain a muscle biopsy, freeze the specimen, and ship it via FedEx to the closest MH Biopsy Center.

The child did well, was awakened and extubated.

Answers:

1.  C

2.  E

3.  E

4.  B

5.  B

6.  B

7.  B

8.  B

Narrtive:

The questions highlight the importance of recording and communicating data during the ongoing treatment, evaluation, and subsequent review of information of a suspected MH episode.  The anesthesiologist or nurse anesthetist who cared for the child in the OR is best able to determine whether the post-extubation hypercarbia was due to hypoventilation, or due to increased CO₂ production with hypercarbia despite increased minute ventilation.  His or her assessment will help determine whether or not future evaluation of the patient and her family for MH susceptibility is warranted.  A blood gas, whether arterial or venous, will confirm the presence of hypercarbia, and may also demonstrate metabolic acidosis.  If possible, blood should be placed in a heparinized syringe and placed on ice for blood gas and potassium determination upon arrival to the hospital.  Factors contributing to hypoventilation (e.g., respiratory depressants, history of sleep apnea, increased airway resistance, previous endobronchial intubation, aspiration of blood, pulmonary edema) should be recorded.  Mild-to-moderate temperature elevation after ENT procedures is quite common, reflecting inflammation or infection. 

When treating acute MH at a freestanding surgery center, administration of dantrolene with reduction in hypermetabolism is crucial prior to transport.  Observing for EKG signs of hyperkalemia is also critical because acute hyperkalemia may suddenly result in ventricular tachycardia or fibrillation, or asystole.

Temperature reduction following dantrolene is NON-specific and is often seen in conditions other than anesthetic-induced MH.

Significant rises in CK level, serum potassium or persistent myoglobinuria are NOT consistently observed following prompt and successful treatment of an acute MH episode. 

Muscle biopsy for determination of MH susceptibility should not be performed during acute rhabdomyolysis.  Halothane-caffeine contracture testing can only be performed at a designated MH Biopsy Center; these are listed on www.mhaus.org.  The muscle must be viable, NOT frozen.  The biopsy is therefore almost always performed at the MH Biopsy Center.