M. Cruz - Academia.edu (original) (raw)
Papers by M. Cruz
Anesthesiology, 2009
Noisy pressure support ventilation has been reported to improve respiratory function compared to ... more Noisy pressure support ventilation has been reported to improve respiratory function compared to conventional assisted mechanical ventilation. We aimed at determining the optimal level of pressure support variability during noisy pressure support ventilation. Twelve pigs were anesthetized and mechanically ventilated. Acute lung injury was induced by surfactant depletion. At four levels of pressure support variability (coefficients of variation of pressure support equal to 7.5, 15, 30, and 45%, 30 min each, crossover design, special Latin squares sequence), we measured respiratory variables, gas exchange, hemodynamics, inspiratory effort, and comfort of breathing. The mean level of tidal volume was constant among variability levels. Compared to conventional pressure support ventilation, different levels of variability in pressure support improved the elastance of the respiratory system, peak airway pressure, oxygenation, and intrapulmonary shunt. Oxygenation and venous admixture benefited more from intermediate (30%) levels of variability, whereas elastance and peak airway pressure improved linearly with increasing variability. Heart rate as well as mean arterial and pulmonary arterial pressures decreased slightly at intermediate to high (30-45%) levels of variability in pressure support. Inspiratory effort and comfort of breathing were not importantly influenced by increased variability in pressure support. In a surfactant depletion model of acute lung injury, variability of pressure support improves lung function. The variability level of 30% seems to represent a reasonable compromise to improve lung functional variables during noisy pressure support ventilation.
Anesthesiology, 2009
BACKGROUND: Evidence exists that during pressure support ventilation (PSV), the addition of an ex... more BACKGROUND: Evidence exists that during pressure support ventilation (PSV), the addition of an extrinsic (ie, ventilator-generated) breath-to-breath variability (BBV) of breathing pattern improves respiratory function. If BBV is beneficial per se, choosing the PS level that maximizes it could be considered a valid strategy for conventional PSV. In this study, we evaluated the effect of different PS levels on intrinsic BBV in acutely ill, mechanically ventilated subjects to determine whether a significant relationship exists between PS level and BBV magnitude. METHODS: Fourteen invasively mechanically ventilated subjects were prospectively studied. PS was adjusted at 20 cm H 2 O and sequentially reduced to 15, 10, and 5 cm H 2 O. Arterial blood gas analysis and pressure at 0.1 s after the onset of inspiration (P 0.1 ) were measured at each PS level. Airway and esophageal pressure and air flow were continuously recorded. Peak inspiratory flow, tidal volume (V T ), breathing frequency, and pressure-time product (PTP) were calculated on a breath-by-breath basis. The breathing pattern variability was assessed by the coefficient of variation of the time series of V T , peak inspiratory flow, and breathing frequency from ϳ60 consecutive breath cycles at each PS level. A general linear model for repeated measures was applied, with PS as an independent factor. A significance level of .05 was considered. RESULTS: Despite a large inter-individual difference in all measured variables (P < .001), the coefficient of variation was as low as 30%, and no significant differences in the coefficient of variation of peak inspiratory flow, breathing frequency, and V T between PS levels were observed (P > .15). Additionally, a significant increase in P 0.1 , PTP, and breathing frequency (P < .01) and a reduction in V T (P < .001) were observed with PS reduction. CONCLUSIONS: Despite a significant increase in spontaneous activity with PS reduction, BBV was not influenced by the PS level and was as low as 30% for all evaluated parameters. Key words: pressure support ventilation; breath-to-breath variability; patient-ventilator interaction; coefficient of variation. [Respir Care 2014;59(12):1-•. © 2014 Daedalus Enterprises] RESPIRATORY CARE • DECEMBER 2014 VOL 59 NO 12 rich3/zrk-rcare/zrk-rcare/zrk01214/zrk6560d14a guidts S01؍ 7/31/14 11:43 4/Color Figure(s): 1 Art: RC-02853 Input-EAS
Anesthesiology, 2009
Noisy pressure support ventilation has been reported to improve respiratory function compared to ... more Noisy pressure support ventilation has been reported to improve respiratory function compared to conventional assisted mechanical ventilation. We aimed at determining the optimal level of pressure support variability during noisy pressure support ventilation. Twelve pigs were anesthetized and mechanically ventilated. Acute lung injury was induced by surfactant depletion. At four levels of pressure support variability (coefficients of variation of pressure support equal to 7.5, 15, 30, and 45%, 30 min each, crossover design, special Latin squares sequence), we measured respiratory variables, gas exchange, hemodynamics, inspiratory effort, and comfort of breathing. The mean level of tidal volume was constant among variability levels. Compared to conventional pressure support ventilation, different levels of variability in pressure support improved the elastance of the respiratory system, peak airway pressure, oxygenation, and intrapulmonary shunt. Oxygenation and venous admixture benefited more from intermediate (30%) levels of variability, whereas elastance and peak airway pressure improved linearly with increasing variability. Heart rate as well as mean arterial and pulmonary arterial pressures decreased slightly at intermediate to high (30-45%) levels of variability in pressure support. Inspiratory effort and comfort of breathing were not importantly influenced by increased variability in pressure support. In a surfactant depletion model of acute lung injury, variability of pressure support improves lung function. The variability level of 30% seems to represent a reasonable compromise to improve lung functional variables during noisy pressure support ventilation.
Anesthesiology, 2009
BACKGROUND: Evidence exists that during pressure support ventilation (PSV), the addition of an ex... more BACKGROUND: Evidence exists that during pressure support ventilation (PSV), the addition of an extrinsic (ie, ventilator-generated) breath-to-breath variability (BBV) of breathing pattern improves respiratory function. If BBV is beneficial per se, choosing the PS level that maximizes it could be considered a valid strategy for conventional PSV. In this study, we evaluated the effect of different PS levels on intrinsic BBV in acutely ill, mechanically ventilated subjects to determine whether a significant relationship exists between PS level and BBV magnitude. METHODS: Fourteen invasively mechanically ventilated subjects were prospectively studied. PS was adjusted at 20 cm H 2 O and sequentially reduced to 15, 10, and 5 cm H 2 O. Arterial blood gas analysis and pressure at 0.1 s after the onset of inspiration (P 0.1 ) were measured at each PS level. Airway and esophageal pressure and air flow were continuously recorded. Peak inspiratory flow, tidal volume (V T ), breathing frequency, and pressure-time product (PTP) were calculated on a breath-by-breath basis. The breathing pattern variability was assessed by the coefficient of variation of the time series of V T , peak inspiratory flow, and breathing frequency from ϳ60 consecutive breath cycles at each PS level. A general linear model for repeated measures was applied, with PS as an independent factor. A significance level of .05 was considered. RESULTS: Despite a large inter-individual difference in all measured variables (P < .001), the coefficient of variation was as low as 30%, and no significant differences in the coefficient of variation of peak inspiratory flow, breathing frequency, and V T between PS levels were observed (P > .15). Additionally, a significant increase in P 0.1 , PTP, and breathing frequency (P < .01) and a reduction in V T (P < .001) were observed with PS reduction. CONCLUSIONS: Despite a significant increase in spontaneous activity with PS reduction, BBV was not influenced by the PS level and was as low as 30% for all evaluated parameters. Key words: pressure support ventilation; breath-to-breath variability; patient-ventilator interaction; coefficient of variation. [Respir Care 2014;59(12):1-•. © 2014 Daedalus Enterprises] RESPIRATORY CARE • DECEMBER 2014 VOL 59 NO 12 rich3/zrk-rcare/zrk-rcare/zrk01214/zrk6560d14a guidts S01؍ 7/31/14 11:43 4/Color Figure(s): 1 Art: RC-02853 Input-EAS