Mechanically assisted cough strategies: user perspectives and cough flows in children with neurodisability.

Background
Mechanical insufflation–exsufflation (MI-E) is used to augment cough in children with neurodisability. We aimed to determine the user comfort and cough flows during three MI-E strategies, and to predict factors associated with improved comfort and cough flows.

Methods
This multicentre, crossover trial was done at four regional hospitals in Norway. Children with neurodisability using MI-E long term via mask were enrolled. In randomised order, they tested three MI-E setting strategies (in-/exsufflation pressure (cmH₂O)/in (In)- versus exsufflation (Ex) time):

1. “A-symmetric” (±50/In=Ex)

2. “B-asymmetric” (+25– +30/−40, In > Ex)

3. “C-personalised”, as set by their therapist.
   The primary outcomes were user-reported comfort on a visual analogue scale (VAS) (0 = maximum comfort) and peak cough flows (PCF) (L·min⁻¹) measured by a pneumotachograph in the MI-E circuit.

Results
We recruited 74 children, median (IQR) age 8.1 (4.4–13.8) years, range 0.6–17.9, and analysed 218 MI-E sequences. The mean ± sd VAS comfort scores were 4.7 ± 2.96, 2.9 ± 2.44 and 3.2 ± 2.46 for strategies A, B and C, respectively (A versus B and C, p < 0.001). The mean ± sd PCF registered during strategies A, B and C were 203 ± 46.87, 166 ± 46.05 and 171 ± 49.74 L·min⁻¹, respectively (A versus B and C, p < 0.001). Using low inspiratory flow predicted improved comfort. Age and unassisted cough flows increased exsufflation flows.

Conclusions
An asymmetric or personalised MI-E strategy resulted in better comfort scores, but lower PCF than a symmetric approach utilising high pressures. All three strategies generated cough flows above therapeutic thresholds and were rated as slightly to moderately uncomfortable.