Flow Index accurately identifies breaths with low or high inspiratory effort during pressure support ventilation

Table 5 Performance of the FI and other parameters in detecting breaths with low inspiratory effort

	Threshold	Specificity	Sensitivity	PPV	NPV	AUC	P value
Flow index	2.6 (2.2–2.9)	0.76 (0.70–0.82)	0.78 (0.70–0.82)	0.84 (0.81–0.87)	0.66 (0.61–0.71)	0.80 (0.76–0.83)	–
RR (breaths min⁻¹)	24 (23–30)	0.63 (0.44–0.73)	0.53 (0.44–0.75)	0.70 (0.67–075)	0.44 (0.41–0.52)	0.61 (0.57–0.65)	< 0.001
RR/V_T (breaths L⁻¹ min⁻¹)	53 (53–53)	0.55 (0.50–0.62)	0.59 (0.54–0.63)	0.69 (0.66–0.72)	0.44 (0.41–0.48)	0.55 (0.50–0.59)	< 0.001
V_T/IBW (mL kg⁻¹)	8.1 (7.8–10.0)	0.58 (0.52–0.80)	0.50 (0.36–0.56)	0.67 (0.64–0.74)	0.41 (0.38–0.44)	0.50 (0.45–0.54)	< 0.001
P_0.1 (cmH₂O)	1.1 (0.9–1.3)	0.65 (0.56–0.73)	0.70 (0.61–0.80)	0.77 (0.74–0.80)	0.56 (0.51–0.64)	0.72 (0.69–0.76)	0.001

Estimates of sensitivity, specificity, positive predictive value (PPV) and Negative predicted value (NPV) for the best threshold (chosen with by top-left corner in the retrieving operative characteristic curve) for detecting breaths at low inspiratory effort using variables studied as predictors. 95% confidence intervals (95% CI) were obtained by 2000 bootstrapped samples. P values were computed by evaluating bootstrapping tests for the AUC of every variable versus the AUC of the Flow Index. Abbreviation RR, respiratory rate; V_T, tidal volume; IBW, ideal body weight; P_0.1, airway occlusion pressure; PPV, positive predictive value; NPV, negative predictive value; AUC, area under the retrieving operative characteristic curve

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