[Mean airway pressure during pressure-controlled ventilation with static vs. dynamic positive end-expiratory pressure]. / Presión media de la vía aérea con la aplicación de presión positiva al final de la espiración estática vs. dinámica.

BACKGROUND: Positive end-expiratory pressure increases mean airway pressure (Paw) in patients with mechanical ventilation. We undertook this study to compare mean airway pressure (Paw) generated with static PEEP (sPEEP) vs. dynamic PEEP (dPEEP) at the same level of total PEEP (tPEEP) in the same patient with pressure-controlled mechanical ventilation (PC). METHODS: We conducted a prospective clinical trial at the Intensive Care Unit of a university-affiliated hospital. Consecutive patients in PC with SaO2>90%; FiO2<50%; sPEEP of 4 cm H2O and inspiration-expiration ratio (I:E ratio) 1:2 were included in the study. After a basal period of time of 15 min, Paw was registered (phase one of the study protocol). In phase 2 with the ventilator settings constant, only the I:E ratio was switched to 2:1 to generate dPEEP, and after 15 min Paw and total PEEP (tPEEP) were registered (tPEEP=sPEEP+dPEEP). In phase 3, the I:E ratio was switched back to 1:2 substituting the dPEEP generated in the second phase of the study by sPEEP to maintain the same level of tPEEP of phase 2. After 15 min, Paw was again registered. Friedman and Wilcoxon's test were used, p value<0.05 was considered statistically significant. RESULTS: Thirty eight patients were admitted to the study protocol, tPEEP was 4, 8 and 8 cm H2O and median of the Paw 8.7, 13.8, and 11.4 cm H2O, respectively, with a p value<0.05 in the first, second and third phases of the study. CONCLUSIONS: During pressure control ventilation, mean airway pressure is affected by the level of total PEEP and its composition. Paw is higher when dynamic PEEP participates in the composition of total PEEP.

Presión media de la vía aérea con la aplicación de presión positiva al final de la espiración estática vs. dinámica / Mean airway pressure during pressure-controlled ventilation with static vs. dynamic positive end-expiratory pressure

Introducción: la presión positiva al final de la espiración (PEEP) incrementa la presión media de la vía aérea (Paw) en pacientes con ventilación mecánica. Con el objetivo de comparar la presión media de la vía aérea que se obtiene en un mismo paciente con ventilación mecánica controlada por presión al aplicar presión positiva al final de la espiración estática (PEEPe) y al aplicar presión positiva al final de la espiración dinámica (PEEPd), se realizó un estudio prospectivo, longitudinal, experimental, comparativo y de grupos relacionados. Material y métodos: se incluyeron pacientes con ventilación mecánica controlada por presión con SaO2 > 90 % y FiO2 < 50%, con PEEPe de 4 cm de H2O y relación inspiraciónespiración de 1:2. Después de 15 minutos se midió la presión media de la vía aérea (fase 1). Posteriormente se modificó la relación inspiración-espiración a 2:1 por 15 minutos, con el fin de generar PEEPd (fase 2). Una vez registrada la presión media de la vía aérea, en la fase 3 se regresó de nuevo a la relación inspiración-espiración 1:2, sustituyendo la PEEPd obtenida en la fase 2 por PEEPe para mantener la misma presión positiva al final de la espiración total (PEEPt) de la fase 2 (PEEPt = PEEPe + PEEPd). Concluidos los 15 minutos de estabilización, se registró de nuevo la presión media de la vía aérea y la PEEPt. Se utilizaron las pruebas de Friedman y Wilcoxon, considerando una p < 0.05 como estadísticamente significativa. Resultados: se estudiaron 38 pacientes. La PEEPt fue de 4, 8 y 8 cm de H2O, y las medianas de la presión media de la vía aérea fueron de 8.7, 13.8 y 11.4 cm de H2O en las fases 1, 2 y 3 respectivamente (p < 0.05). Conclusiones: en un mismo paciente con ventilación mecánica controlada por presión y con los mismos niveles de PEEPt, la presión media de la vía aérea es mayor al utilizar PEEPd que PEEPe.

BACKGROUND: Positive end-expiratory pressure increases mean airway pressure (Paw) in patients with mechanical ventilation. We undertook this study to compare mean airway pressure (Paw) generated with static PEEP (sPEEP) vs. dynamic PEEP (dPEEP) at the same level of total PEEP (tPEEP) in the same patient with pressure-controlled mechanical ventilation (PC). METHODS: We conducted a prospective clinical trial at the Intensive Care Unit of a university-affiliated hospital. Consecutive patients in PC with SaO2>90%; FiO2<50%; sPEEP of 4 cm H2O and inspiration-expiration ratio (I:E ratio) 1:2 were included in the study. After a basal period of time of 15 min, Paw was registered (phase one of the study protocol). In phase 2 with the ventilator settings constant, only the I:E ratio was switched to 2:1 to generate dPEEP, and after 15 min Paw and total PEEP (tPEEP) were registered (tPEEP=sPEEP+dPEEP). In phase 3, the I:E ratio was switched back to 1:2 substituting the dPEEP generated in the second phase of the study by sPEEP to maintain the same level of tPEEP of phase 2. After 15 min, Paw was again registered. Friedman and Wilcoxon's test were used, p value<0.05 was considered statistically significant. RESULTS: Thirty eight patients were admitted to the study protocol, tPEEP was 4, 8 and 8 cm H2O and median of the Paw 8.7, 13.8, and 11.4 cm H2O, respectively, with a p value<0.05 in the first, second and third phases of the study. CONCLUSIONS: During pressure control ventilation, mean airway pressure is affected by the level of total PEEP and its composition. Paw is higher when dynamic PEEP participates in the composition of total PEEP.

[Pulmonary mechanics, oxygenation index, and alveolar ventilation in patients with two controlled ventilatory modes. A comparative crossover study]. / Mecánica pulmonar, índice de oxigenación y ventilación alveolar en pacientes con dos modalidades de ventilación mecánica controlada. Un estudio comparativo de tipo cruzado.

OBJECTIVE: To compare in a crossover study pulmonary mechanics, oxigenation index (PaO(2)/FiO(2)), and partial pressure of CO(2) in arterial blood (PaCO(2)) in patients with mechanical ventilation in two controlled ventilatory modes. SETTING: Intensive care unit of a university affiliated hospital. DESIGN: Prospective crossover clinical trial. PATIENTS AND METHODS: A total 114 consecutive patients were admitted to the intensive care unit (ICU) under controlled mechanical ventilation with SaO(2) >90% and FiO(2) <0.5 and assigned by random allocation to either volume control (VC) and constant inspiratory flow (square flow curve) (group I) or pressure control mode (PC) (group II). Both groups were ventilated with tidal volume (Vt) of 7 ml/kg, respiratory rate (RR) 14/min, inspiratory-expiratory ratio 1:2 (I:E), PEEP 5 cm H(2)O, and FiO(2) 0.4. After 15 min of mechanical ventilation, pulmonary mechanics, oxygenation index (OI), and PaCO(2) were measured and registered, and ventilatory mode was switched to PC mode in group I and to VC in group II, maintaining the same ventilator settings. Pulmonary mechanics, OI, and PaCO(2) were again registered after 15 min of ventilation. RESULTS: Peak inspiratory pressure (PIP) was higher in VC than in PC (31.5 vs 26 cm H(2)O), which resulted in a significant increase in transpulmonary pressure amplitude difference (DP) (25 vs 19 cm H(2)O). Mean airway pressure (MAP) and OI were lower in VC than in PC (11.5 vs 12 cm H(2)O, and 198.5 vs 215, respectively). Dynamic compliance (DynC) was lower in VC than in PC (20 vs 26 ml/cm H(2)O), p < 0.05 for all values. At constant ventilator settings in the same patient, PC and not VC ventilation decreases PIP (which results in smaller transpulmonary pressure amplitude difference), increases MAP, and DynC and improves the oxygenation index.