Carbon dioxide narcosis caused by midazolam in a patient with myotonic dystrophy

Risk factors for perioperative adverse events in children with myotonic dystrophy

BACKGROUND

This study was conducted to identify patient-related, surgical, and anesthetic factors that would help predict adverse events and allow for better planning of perioperative care in children with myotonic dystrophy.

METHODS

This is a retrospective chart review from a large tertiary pediatric hospital. Data were collected on demographics, disease severity, surgical procedure, and anesthetic technique. Perioperative adverse events were recorded.

RESULTS

Records on 27 patients having 78 anesthetics over a 17.5-year period were reviewed. The overall frequency of postoperative respiratory complications was 10%. Significant risk factors were high muscular impairment rating scale (MIRS) grade (P = 0.007), at least 2300 cytosine, thymine, guanine (CTG) repeats on the protein kinase gene of chromosome 19q (P = 0.009), a longer duration of surgery (RR = 14.0 for surgery lasting at least 1 h; P = 0.002), perioperative morphine use (RR = 7.7, 95% CI 2.2-12.8; P = 0.005), intubation (P = 0.02), and the use of muscle relaxant without reversal (RR = 15.5, P = 0.0002). Using a multivariate risk model, only MIRS grade and the use of muscle relaxant without reversal were shown to be significant independent risk factors (RR = 24.9, P < 0.0001).

CONCLUSIONS

The MIRS is a statistically significant and clinically useful tool for predicting high perioperative risk. Patients with a high MIRS grade should therefore be considered for postoperative intensive care. The use of muscle relaxant without reversal was also shown to be a significant risk factor. Patients who require morphine infusions postoperatively might also be most safely managed in a high dependency unit.

The influence of changes in end-tidal carbon dioxide upon the Bispectral Index

Carbon dioxide is known to affect consciousness in animals and humans. We surmised that changes in end-tidal carbon dioxide during anaesthesia might affect the Bispectral Index. Twenty-four patients due to undergo surgery were anaesthetised with fentanyl and a propofol infusion. The Bispectral Index, pulse rate and blood pressure were recorded while end-tidal carbon dioxide levels were changed. The patients acted as their own controls as they were subjected to high, normal and low levels of end-tidal carbon dioxide (3-12 kPa) according to a randomised sequence. There were no changes in the Bispectral Index or haemodynamic variables resulting from manipulation of the end-tidal carbon dioxide. At the level of hypnosis involved in this study, changes in end-tidal carbon dioxide, within the range tested, do not result in changes in the Bispectral Index.