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Topic: Pediatric arthrogryposis - intraop difficulty ventilating, hyperthermia
A wheelchair-bound 7 y/o 17 kg male with arthrogryposis multiplex congenital (AMC) was scheduled for elective release of contractures of his right arm and both feet (involvement of hips, arms and bilateral clubfoot). He was induced with sevoflurane and given 15 mg intravenous succinylcholine for endotracheal intubation with a 5.0 cuffed tube. Baseline HR 140/min. Sevoflurane was supplemented with a remifentanil infusion. No non-depolarizing muscle relaxant (NDMR) was given after sux. 1 hour into the case, noted progressive decrease in tidal volume and decreased compliance (150 cc tidal volume with 18 cm PIP initially; with decrease in tidal volume to 80 cc and increase PIP up to 50).
1) Which of the following is NOT a possible cause of decreased compliance or increased airway resistance?
A) Endobronchial intubation
B) Secretions in the tube
C) Patient too lightly anesthetized
D) Bronchospasm
E) Excessive leak around endotracheal tube cuff
F) Pneumothorax
G) Chest wall rigidity
The end-tidal CO2 progressively increased > 70 mm and the esophageal temperature increased from 37.5° C. to 38.5°C.
2) With the above data, which of these statements is correct?
A) The hypercarbia and temperature increase confirm the diagnosis of malignant
hyperthermia.
B) The hypercarbia and temperature increase are due to inadequate ventilation
and iatrogenic overheating.
C) Without knowledge of the cause of difficult ventilation and accurate
measurement of total minute ventilation, one cannot confirm excessive CO2
production.
D) Decreased lung compliance is not a typical presenting sign of acute MH.
The child had been warmed with a Bair Hugger (both over and under him) that was now turned off.
3) One should observe a prompt decrease in temperature after turning off the Bair Hugger.
A) True
B) False
Caller confirmed that tube was correctly positioned, without external kinking or internal occlusion. The child was treated with dantrolene 60 mg i.v. with prompt resolution of hypercarbia followed by a decrease in temperature.
4) Which of these statements may be correct?
A) Prompt improvement following dantrolene was due to decreased muscle
hypermetabolism.
B) Prompt improvement following dantrolene was due to muscle relaxation
independent of any decrease in metabolic rate.
5) If 10 mg rocuronium was given instead of 60 mg dantrolene, and one observed prompt reduction in PIP to normal with resolution of hypercarbia followed by a decrease in temperature, this would strongly suggest that the patient did not have an acute MH episode.
A) True
B) False
An ABG obtained after dantrolene treatment did not show any metabolic acidosis. Urine was clear and serum potassium level was normal. The child was extubated in the PACU about 1 hour after stable. CK levels obtained 6 and 14 hours later were within normal limits. The child was maintained on 20 mg iv dantrolene q 6 hours for 36 hours.
Answers:
1. E
2. C & D
3. B
4. A & B
5. A
Narrative:
Arthrogryposis multiplex congenita (AMC) is characterized by multiple joint contractures present at birth related to sustained lack of fetal movement in utero. Causes may be classified under: 1) neurologic disorders, 2) neuromuscular junction disorders, 3) primary muscular disorders, or 4) maternal factors, e.g. oligohydramnios. In addition to the underlying causes, important anesthetic considerations include: 1) potential difficult direct laryngoscopy due to limited range-of-motion, micrognathia or microstomia; 2) difficult intravenous access; 3) potential intraoperative and postoperative pulmonary complications associated with restrictive pulmonary disease, scoliosis, muscle weakness, or aspiration; 3) occasional association with genito-urinary or cardiac anomalies; or 4) hyperthermia typically not associated with hypercarbia, lactic acidosis or rhabdomyolysis. While there are some anecdotal reports of MH in children with AMC, the series by Baines et al (Anaesth Intensive Care, 1986, 14:370-372) reported no episodes of MH in 67 patients undergoing a total of 396 anesthetics with triggering agents. Because of the frequent presence of challenging airway management and difficult intravenous access and the rare occurrence of anesthetic-induced MH in this population, inhalational anesthesia with sevoflurane or halothane may be very useful. Because of potential underlying myopathy, one must consider the risk of exaggerated hyperkalemia following succinylcholine. Martin and Tobias have a recent review article in Pediatric Anesthesia 2006, 16:31-37.
One should suspect MH with progressive or persistent hypercarbia despite an easily delivered minute ventilation that should produce a normal (or low) end-tidal CO2. In AMC, an acute MH episode may or may not cause rigidity beyond that due to baseline flexion contractures. Although generalized rigidity (despite adequate anesthetic depth and full muscle relaxation) is the most specific sign of MH, chest wall rigidity with difficulty ventilation is not a typical presentation of MH. Prompt relief of increased inflation pressures and hypercarbia following muscle relaxant would strongly suggest that the patient did not have MH. Given baseline muscle atrophy, it is unclear that large elevations in CK would be observed following an MH episode. Muscle biopsy for contracture testing may be impractical in the absence of suitable healthy muscle.
If hyperthermia is due to warming with a Bair Hugger or similar device, simply turning the device off and leaving it on the patient will not result in prompt cooling. One would need to put the device on “cool” (if possible), or take the Bair Hugger off of the patient and expose them to cooler air.
________________________________________
MH Hotline Consultant
Professor of Anesthesiology
UCLA School of Medicine
Los Angeles CA 90095-1778
