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In Response

Mirzakhani, Hooman MD, MMSc, PhD; Nozari, Ala MD, PhD

doi: 10.1213/ANE.0000000000001476
Letters to the Editor: Letter to the Editor
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Published ahead of print August 22, 2016.

Department of Anesthesia and Critical Care, Massachusetts General Hospital, Boston, Massachusetts, Anesthesia, Critical Care and Pain Medicine, Harvard Medical School, Boston, Massachusetts, hoomi@post.harvard.edu

Published ahead of print August 22, 2016.

We thank Li et al for sharing their important observations on the variability of the required succinylcholine dose for electroconvulsive therapy (ECT). Consistent with our findings, their group reports a mean required succinylcholine dose of 0.9 mg/kg (approximately 0.86 mg/kg in our study), but considerably larger and sometimes smaller dose requirements in 5.8% of the ECT patients. We are intrigued that their recommended dose from >500 ECT patients is in accord with our findings, and we agree with their insightful comment regarding the importance of considering a significant variability in response to this neuromuscular blocking agent (NMBA). We did find that 6.4% of the patients needed doses greater or smaller than 2× the standard deviation. Accordingly, we propose that a clinically relevant initial dose of succinylcholine or rocuronium (eg, their minimum effective doses [MEDs]: MED50 or MED90) be administered during the first ECT session but that this dose is subsequently adjusted with 0.05 to 0.2 mg/kg increments or decrements until optimally induced seizure activities are achieved in each patient.

We conducted additional analyses of the NMBA doses in our study and calculated the interindividual coefficient of variation (COV) of the MEDs. Consistent with a calculated COV of 27% (based on the reported mean and standard deviation) by Li et al, the COV for succinylcholine in our study was 26% (95% confidence interval, 21–29), which was 1.24 times larger than that of rocuronium (21%; 95% confidence interval, 20–27). This observed interindividual variability is in line with previously published data from non-ECT studies that showed the COV for the median effective dose (ED50) was 22% (range, 15%–27%).1

A small MED variability is especially important if it is critical to avoid suboptimal neuromuscular blockade, eg, in patients with increased risk for skeletal injury. If rocuronium is the preferred NMBA, however, it should be kept in mind that the duration of the induced neuromuscular blockade may be longer and largely variable when higher doses are administered.2 Consequently, longer recovery times that can extend beyond the ECT treatment should be anticipated, and quantitative monitoring of the neuromuscular transmission should be employed. Alternatively, sugammadex can be used to reverse the rocuronium-induced neuromuscular blockade, although this approach is currently not cost-effective nor might reliably preclude residual blockade. This unpredictable response to sugammadex may be particularly relevant after a brief procedure, such as ECT, given that it has to be administered shortly after neuromuscular blockade with rocuronium.3

Hooman Mirzakhani, MD, MMSc, PhDAla Nozari, MD, PhDDepartment of Anesthesia and Critical CareMassachusetts General HospitalBoston, MassachusettsAnesthesia, Critical Care and Pain MedicineHarvard Medical SchoolBoston, Massachusettshoomi@post.harvard.edu

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REFERENCES

1. Kopman AF, Lien CA, Naguib M. Neuromuscular dose-response studies: determining sample size. Br J Anaesth. 2011;106:194198.
2. Arain SR, Kern S, Ficke DJ, Ebert TJ. Variability of duration of action of neuromuscular-blocking drugs in elderly patients. Acta Anaesthesiol Scand. 2005;49:312315.
3. Kotake Y, Ochiai R, Suzuki T, et al. Reversal with sugammadex in the absence of monitoring did not preclude residual neuromuscular block. Anesth Analg. 2013;117:345351.
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