Ultrasound assessment of diaphragm thickness, contractility, and strain in healthy pediatric patients

Background Ultrasound-based diaphragmatic assessments are becoming more common in pediatric acute care, but baseline pediatric diaphragm thickness and contractility values remain unknown.Methods We conducted a prospective, observational study of healthy children aged <18 years undergoing elective surgery. Diaphragm thickness at end-expiration (Tdi-exp), thickening fraction (DTF) and excursion were measured by ultrasound during spontaneous breathing and during mechanical ventilation. Diaphragm strain and peak strain rate were ascertained post hoc. Measurements were compared across a priori specified age groups (<1 year, 1 to <3, 3 to <6, 6 to <12, and 12 to <18 years) and with versus without mechanical ventilation.Results Fifty subjects were evaluated (n = 10 per age group). Baseline mean Tdi-exp was 0.19 +/- 0.04 cm, DTF 0.19 +/- 0.09, excursion 1.69 +/- 0.97 cm, strain -10.3 +/- 4.9, peak strain rate -0.48 +/- 0.21 s-1. No significant difference in Tdi-exp or DTF was observed across age groups (p > .05). Diaphragm excursion increased with age (p < .0001). Diaphragm strain was significantly greater in the 12-17-year age group (-14.3 +/- 6.4), p = .048, but there were no age-related differences in peak strain rate (p = .08). During mechanical ventilation, there were significant decreases in DTF 0.12 +/- 0.04 (p < .0001), excursion 1.08 +/- 0.31 cm (p < .0001), strain -4.60 +/- 1.93 (p < .0001), and peak strain rate -0.20 +/- 0.10 s-1 (p < .0001) while there was no change in Tdi-exp 0.18 +/- 0.03 cm (p = .25) when compared to baseline values.Conclusion Pediatric Tdi-exp, DTF, and diaphragm peak strain rate were similar across age groups. Diaphragm excursion and strain varied across age groups. All measures of diaphragm contractility were diminished during mechanical ventilation.