Diaphragmatic dysfunctionin criticallyill patients undergone mechanical ventilation

INTRODUCTION. Prolonged mechanical ventilation (MV) can cause mus- cle atrophy and adversely affect diaphragmatic force-generating capacity, a con- dition referred to as ventilator-induced diaphragmatic dysfunction (VIDD). Dia- phragmatic ultrasound has been proposed as a bedside daily monitoring of dia- phragm function; however, to date there are no specific serum biomarkers for muscular damage and dysfunction. Foster et al. suggested that skeletal troponin I (sTnI) could be a sensitive marker to detect early signs of muscle injury. OB- JECTIVES. Firstly, to study the trend of a novel biomarker (sTnI) in mechani- cally ventilated ICU patients; secondly, to determine whether this trend was as- sociated with the development of VIDD as assessed with diaphragmatic ultra- sound. METHODS. Serial serum samples were obtained from 24 mechanically ven- tilated ICU patients at 24 (T0), 48 (T1) and 72 (T3) hours after admission. Pa- tients were not considered for inclusion if they had a history of neuromuscular disease or a previously documented diaphragm paralysis. Specimens were ana- lysed and specific isoforms for sTnI (slow (ssTnI) and fast (fsTnI)) were assayed by commercially available ELISA kits (Human TNNI ELISA kit, Mybiosource). Simultaneously, in 16 patients diaphragmatic displacement (DD), thickness at end expiration (T EE ) and thickening fraction (TF) were measured with ultrasound. Data are reported as median [IQR]. Values were compared using Friedman's analysis for repeated measures and Wilcoxon test for paired samples; p < 0.05 was considered statistically significant. RESULTS. Ventilatory variables did not change over time. The two sTnI isoforms had a different behaviour over time: ssTnI levels remained unchanged during the course of MV (p=0.957), while sfTnI significantly decreased over time (p<0.003), with the lowest level after 72 hours from admission (T0 vs T2, p = 0.004). Both DD (p = 0.004) and TF (< 0.0001) decreased over time, while T EE remained stable. We found a statistically significant correlation between the per- cent change from baseline of sfTnI and TF at 72 hours from admission (r = 0.661, p = 0.007). CONCLUSIONS. Our results seem to demonstrate that both sTnI and ultra- sound describe adequately the decrease in diaphragmatic function over time in mechanically ventilated ICU patients. Moreover, fsTnI seems to be better corre- lated with echographical signs of diaphragmatic dysfunction.