Is pressure-regulated volume control mode appropriate for severely obstructed patients?

PURPOSE: Management of mechanical ventilation in severely obstructed patients remains controversial. Pressure-regulated volume control ventilation (PRVCV) has been suggested to be the best option, as it should ensure a prefixed tidal volume at the lowest peak inspiratory pressure. We sought to determine the accuracy of the delivered volume, compared with the programmed volume, when using PRVCV. MATERIALS AND METHODS: Experimental work performing ventilation simulations using volume control ventilation (VCV), PRVCV, and pressure control ventilation (PCV). Each mode was tested at tidal volumes (TVs) of 200 and 500 mL at both low and high airway resistance. Evita XL and Servo-i ventilators were used. RESULTS: At 200 ml TV with high resistance, volume delivered with Evita XL was 165 mL (95% confidence interval, 158-169) in VCV, 117 mL (95% confidence interval, 117-120) in PCV, and 120 (95% confidence interval, 115-121) in PRVCV (P<.001). Volume delivered with Servo-i was 133 mL (95% confidence interval, 130-136) in VCV, 108 mL (95% confidence interval, 104-111) in PCV, and 104 (95% confidence interval, 101-108) in PRVCV (P<.001). CONCLUSIONS: In high-resistance simulations, the delivered volume was lower when using PCV or PRVCV modes than VCV mode. Pressure control ventilation or PRVCV may fail to provide programmed TV, ultimately leading to hypoventilation of the patient.

Correlation of oxygen saturation as measured by pulse oximetry/fraction of inspired oxygen ratio with Pao2/fraction of inspired oxygen ratio in a heterogeneous sample of critically ill children.

PURPOSE: Oxygen saturation as measured by pulse oximetry (Spo2)/fraction of inspired oxygen (Fio2) (SF) ratio has demonstrated to be an adequate marker for lung disease severity in children under mechanical ventilation. We sought to validate the utility of SF ratio in a population of critically ill children under mechanical ventilation, noninvasive ventilation support, and breathing spontaneously. MATERIALS AND METHODS: A retrospective database study was conducted in a pediatric intensive care unit of a university hospital. Children with Spo2 less than or equal to 97% and an indwelling arterial catheter were included. Simultaneous blood gas and pulse oximetry were collected in a database. Derivation and validation data sets were generated, and a linear mixed modeling was used to derive predictive equations. Model performance and fit were evaluated using the validation data set. RESULTS: Three thousand two hundred forty-eight blood gas and Spo2 values from 298 patients were included. 1/SF ratio had a strong linear association with 1/Pao2/Fio2 (PF) ratio in both derivation and validation data sets, given by the equation 1/SF = 0.00164 + 0.521/PF (derivation). Oxygen saturation as measured by pulse oximetry/Fio2 values for PF criteria of 100, 200, and 300 were 146 (95% confidence interval [CI], 142-150), 236 (95% CI, 228-244), and 296 (95% CI, 285-308). Areas under receiver operating characteristic curves for diagnosis of PF ratio less than 100, 200, and 300 with the SF ratio were 0.978, 0.952, and 0.951, respectively, in the validation data set. CONCLUSIONS: Oxygen saturation as measured by pulse oximetry/Fio2 ratio is an adequate noninvasive surrogate marker for PF ratio. Oxygen saturation as measured by pulse oximetry/Fio2 ratio may be an ideal noninvasive marker for patients with acute hypoxemic respiratory failure.