Aplicaciones e implicaciones de la pausa al final de la inspiración en ventilación mecánica / Applications and implications of end-inspiratory pause in mechanical ventilation / Aplicações e implicações da pausa ao final da inspiração na ventilação mecânica

Resumen: El uso de la pausa al final de la inspiración (PFI) en ventilación mecánica data de hace más de 50 años y con mayor impulso en la década de los 70, se le atribuye una mejoría en la presión parcial de oxígeno arterial (PaO2) al incrementar la presión media de la vía aérea (Pma), mayor aclaramiento de la presión parcial de dióxido de carbono arterial (PaCO2) y permite la monitorización de la presión meseta (Pmeseta) en la mecánica ventilatoria; sin embargo, los estudios clínicos sobre su uso son escasos y controversiales. En este artículo se abordan los mecanismos fisiológicos, fisiopatológicos y la evidencia sobre el uso de la PFI en ventilación mecánica (VM).

Abstract: The use of the end inspiratory pause (EIP) in mechanical ventilation has been going on for more than 50 years and with greater momentum in the 1970s, an improvement in the partial pressure of arterial oxygen (PaO2) is attributed to the increase mean airway pressure, greater clearance of partial pressure of arterial carbon dioxide and allows monitoring of plateau pressure in ventilatory mechanics; However, the Clinical studies on its use are few and controversial. This article addresses the physiological and pathophysiological mechanisms and the evidence on the use of EIP in mechanical ventilation.

Resumo: A utilização da pausa ao final da inspiração (PFI) na ventilação mecânica remonta a mais de 50 anos e com maior impulso na década de 70, atribui-se uma melhora na pressão parcial de oxigênio arterial (PaO2) pelo aumento da pressão média das vias aéreas (Pma), uma maior depuração da pressão parcial de dióxido de carbono arterial (PaCO2) e permite a monitorização da pressão de platô (Pplateau) na mecânica ventilatória, porém estudos Os dados clínicos sobre seu uso são escassos e controversos. Este artigo aborda os mecanismos fisiológicos e fisiopatológicos e as evidências sobre o uso do PFI na ventilação mecânica (VM).

Investigation of mechanical ventilation pressure parameters' effect on the prognosis of acute respiratory distress syndrome / 中华急诊医学杂志

Objective To find out whether we can get the optimality in the prognosis of acute respiratory distress syndrome (ARDS) by combing the pressure parameters in mechanical ventilation with traditional PaO2/FiO2.Methods This is a retrospective study.Patients included here were diagnosed as ARDS in the Emergency Unit (EICU) of the First Affiliated Hospital of China Medical University fiom January 2018 to December 2018.All the patients were intubated and mechanically ventilated.Patients with a short observation time (＜ 48 h) or unable to cooperate with treatment were excluded.According to the patient's 28-day survival,patients were divided into the survival and non-survival groups.Parameters in the two groups such as basic characteristics,SOFA score,non-respiratory system SOFA score (nR-SOFA),and PaO2/FiO2 were analyzed with LSD-t test or rank sum test.Simultaneously,plateau pressure,driving pressure,mean airway pressure and the ratio of these mechanical ventilation pressure parameters to the PaO2/FiO2 were also analyzed.Results A total of 147 patients were included in the study and 117 of them were analyzed.The overall 28-day mortality was 31.62％ (n=37).There were no significant differences in gender,age,body mass index,initial arterial oxygen partial pressure and carbon dioxide partial pressure between the survival group and non-survival groups (P ＞0.05).But there was a significant difference in SOFA score(6.53 ± 2.96 vs 8.65 ± 3.00) and nR-SOFA(3.44 ± 2.98 vs 5.27 ± 2.86).Among the evaluation indexes,the PPOI obtained the AUC of 0.828,with the sensitivity of 86.5％,and specificity of 71.2％.The AUC of the SOFA score was 0.707,while the AUC of the PPOI combined with the SOFA score was 0.833.Conclusion Mechanical ventilation pressure parameters can be used to predict the prognosis of patients with ARDS.PPOI may evaluate the prognosis of ARDS in a more simple,timely and real-time manner.

Quantifying the Amount of Bleeding and Associated Changes in Intra-Abdominal Pressure and Mean Airway Pressure in Patients Undergoing Lumbar Fixation Surgeries: A Comparison of Three Positioning Systems

STUDY DESIGN: Prospective, randomised controlled, single centre study of 45 patients posted for two level lumbar fixation surgery in the prone position. PURPOSE: To compare intra-abdominal pressure (IAP), mean airway pressure mean airway pressure and blood loss during the spine surgery in prone position using three different positioning systems. OVERVIEW OF LITERATURE: Studies have correlated IAP with the amount of perioperative bleeding. However, IAP and airway pressures while assessing the bleeding comparing two or more prone positioning systems are unclear. METHODS: This prospective study was conducted on a cohort of 45 patients scheduled for two-level lumbar fixation. Patients were randomly allocated to a spine table, Wilson's frame, and thermomodulated pads. Bladder pressure as an indicator of IAP, mean and peak airway pressures, and blood loss were monitored. RESULTS: IAP increased whenever patient position was changed to prone .The increase in pressure was more in the Wilson's frame group but was statistically significant only on prolonged positioning. Adopting the prone position always increased the mean airway pressure, but the increased was significant only in the Wilson's frame group. Mean airway pressure decreased in the spine table group and was statistically significant. The blood loss in the spine table group was significantly less as compared to the other groups. CONCLUSIONS: Positioning on a spine table results in less blood loss and low mean airway pressure. The Wilson's frame results in high IAP, increased mean airway pressure, and more blood loss. The thermomodulated frame increases mean airway pressure and produces a moderate increase in IAP and airway pressure.

Quantifying the Amount of Bleeding and Associated Changes in Intra-Abdominal Pressure and Mean Airway Pressure in Patients Undergoing Lumbar Fixation Surgeries: A Comparison of Three Positioning Systems

STUDY DESIGN: Prospective, randomised controlled, single centre study of 45 patients posted for two level lumbar fixation surgery in the prone position. PURPOSE: To compare intra-abdominal pressure (IAP), mean airway pressure mean airway pressure and blood loss during the spine surgery in prone position using three different positioning systems. OVERVIEW OF LITERATURE: Studies have correlated IAP with the amount of perioperative bleeding. However, IAP and airway pressures while assessing the bleeding comparing two or more prone positioning systems are unclear. METHODS: This prospective study was conducted on a cohort of 45 patients scheduled for two-level lumbar fixation. Patients were randomly allocated to a spine table, Wilson's frame, and thermomodulated pads. Bladder pressure as an indicator of IAP, mean and peak airway pressures, and blood loss were monitored. RESULTS: IAP increased whenever patient position was changed to prone .The increase in pressure was more in the Wilson's frame group but was statistically significant only on prolonged positioning. Adopting the prone position always increased the mean airway pressure, but the increased was significant only in the Wilson's frame group. Mean airway pressure decreased in the spine table group and was statistically significant. The blood loss in the spine table group was significantly less as compared to the other groups. CONCLUSIONS: Positioning on a spine table results in less blood loss and low mean airway pressure. The Wilson's frame results in high IAP, increased mean airway pressure, and more blood loss. The thermomodulated frame increases mean airway pressure and produces a moderate increase in IAP and airway pressure.

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.

Cumulative Effects of Positive Pressure Ventilation on the Development of Chronic Lung Disease in Very Low Birth Weight Infants

PURPOSE: Barotrauma is one of the most important risk factors of chronic lung disease (CLD) in neonates. However, so-often called `high pressure' does not specify the magnitude or duration of positive pressure ventilation in relation to development of CLD. We investigated whether cumulative effect of positive pressure ventilation over time was more closely associated with CLD than the magnitude of maximal peak inspiratory pressure (PIP) or mean airway pressure (MAP). METHODS: Clinical data were collected from 53 very low birth weight (VLBW) infants (24; CLD and 29; non-CLD) who were treated with mechanical ventilation due to respiratory distress syndrome (RDS) at the neonatal intensive care unit (NICU) in Yonsei University Medical Center. Areas under the pressure-time curve for peak inspiratory pressure (AUCPIP), mean airway pressure (AUCMAP), and FiO2 (AUCFiO2) were calculated from hourly changes of the ventilatory parameters plotted against time during the first 5 days of life, and were compared with the magnitudes of episodic, maximum PIP, MAP or FiO2. RESULTS: The AUCMAP and AUCPIP in CLD group was significantly higher than in non-CLD group (639.8+/-142.9 cmH2O hr vs. 474.2+/-148.0 cmH2O hr, P 0.05). After statistical correction for independent factors related to development of CLD, AUCMAP was shown to be most meaningful. CONCLUSION: Our data are suggestive of the importance of cumulative barotrauma over time in CLD rather than episodic barotrauma caused by cross-sectional or intermittent high peak pressures.

Application of Three Factors-Levels Respiratory Parameters in General Anesthesia / 中国微创外科杂志

Objective To study the best combination of respiratory parameters that can maintain good ventilation with a low airway pressure under general anesthesia and CO2 pneumoperitoneum (12 mm Hg) during laparoscopy, which is important for lung protections. Methods Basic respiratory parameters of anesthesia machine, respiratory frequency (f), tidal volume (VT), and respiration ratio (I∶E), were used as three factors A, B, and C. The there levels were set as f=15, 12, and 9 bpm; VT =8, 10, and 12 ml/kg body weight; and I∶E =1∶2.5, 1∶2.0, and 1∶1.5. L9(34) K=3 was adopted for repeated orthogonal experimental design. The effect of different combinations of respiratory parameters on peak inspiratory pressure (PIP), mean airway pressure (Pmean),and end-tidal carbon dioxide partial pressure (PETCO2), were analyzed statistically. Results During the laparoscopy, the vital signs of 27 patients were stable under general anesthesia with 9 combinations of the respiratory parameters, the SpO2 was maintained at 100%, and the PEEP was kept at 1 hPa. The effect of the three levels of VT (factor B) on PIP was not significant (P=0.074). While the effects of f (factor A) on PETCO2 and I∶E on Pmean were significantly different among the three levels (P=0.002 and P=0.017, respectively). Conclusion The best combination of three factors-levels respiratory parameters is not small tidal volume with fast frequency or large tidal volume with slow frequency, but is A2B2C2 (f=12 bpm, VT=10 ml/kg body weight, and I∶E=1∶2.0).

The Effects of Inspiratory Pause on Airway Pressure and Gas Exchange under Same I: E ratio in Volume-controlled Ventilation / 결핵

BACKGROUND: In volume-controlled ventilation, the use of inspiratory pause increases the inspiratory time and thus increases mean airway pressure and improves ventilation But under the same I : E ratio, the effects of in spiratory pause on mean airway pressure and gas exchange are not certain. Moreover, the effects may be different according to the resistance of respiratory system. So we studied the effects of inspiratory pause on airway pressure and gas exchange under the same I : E ratio in volume-controlled ventilation. METHODS: Airway pressure and arterial blood gases were evaluated in 12 patients under volume-controlled mechanical ventilation with and without inspiratory pause time 5%. The I : E ratio of 1 : 3, FiO2, tidal volume, respiratory rate, and PEEP were kept constant. RESULTS: PaCO2 with inspiratory pause was lower than without inspiratory pause (38.6 +/- 7.4 mmHg vs.41.0 +/- 7.7 mmHg. p < 0.01). p(A-a)O2 was not different between ventilation with and without inspiratory pause (185.3 +/- 86.5mm Hg vs. 184.9 +/- 84.9mmHg vs. p=0.766). Mean airway pressure with inspiratory pause was higher than without inspiratory pause (9.7 +/- 4.0 cmH2O vs. 8.8 +/- 4.0 cm H2O, p < 0.01). The resistance of respiratory system inversely correlated with the pressure difference between plateau pressure with pause and peak inspiratory pressure without pause (r=-0.777, p < 0.01), but positively correlated with the pressure difference between peak inspiratory pressure with pause and peak inspiratory pressure without pause (r=0.811, p < 0.01). Thus the amount of increase in mean airway pressure with pause positively correlated with the resistance of respiratory system (r=0.681, p < 0.05). However, the change of mean airway pressure did not correlated with the change of PaCO2. CONCLUSION: In volume-controlled ventilation under the same I : E ratio of 1 : 3, inspiratory pause time of 5% increases mean airway pressure and improves ventilation. Although the higher resistance of respiratory system, the more Increased mean airway pressure, tile increase in mean airway pressure did not correlated with the change in PaCO2.