The Effects of Ventilatory Pattern on Hyperinflation, Airway Pressures, and Circulation in Mechanical Ventilation of Patients with Severe Air-Flow Obstruction

Abstract

Patients with severe air-flow obstruction receiving mechanical ventilation are at risk of inadvertent pulmonary hyperinflation with morbidity and mortality caused by pneumothorax and circulatory depression. Nine patients with severe air-flow obstruction (5 asthma, 4 chronic air-flow obstruction) requiring mechanical ventilation were studied while sedated and therapeutically paralyzed. Pulmonary hyperinflation during steady-state ventilation was quantified by measuring total exhaled volume during 20- to 40-s apnea (end-inspiratory lung volume, VEI). Patients were studied at 3 levels of minute ventilation (VE) (10, 16, and 26 L/min) and at each VE, 3 levels of tidal volume (VT) (0.6, 1.0, and 1.6 L) and 3 levels of inspiratory flow (VI) (40, 70, and 100 L/min for VT = 1.0 L). There were progressive increases in VEI when VT was increased or when expiratory time (TE) was decreased either by an increase in rate (and hence VE) or by a decrease in VI (at a constant VE) reaching lung volumes as high as 3.6 +/- 0.4 L above FRC. Alveolar, central venous, and esophageal pressure rose in parallel with lung volumes, and hypotension was seen in most patients at highest lung volumes. Peak airway pressure (Ppk) was predominantly related to inspiratory flow and did not reflect changes in lung volume. Levels of ventilation required for normocapnia prior to paralysis (15.7 +/- 2.3 L/min) were associated with hypotension in 7 patients and probable hyperinflation in excess of 1.96 +/- 0.17 L above FRC. VEI is a simple, reproducible measurement of pulmonary hyperinflation and may be more important than Ppk in the causation of barotrauma.(ABSTRACT TRUNCATED AT 250 WORDS)

Bronchodilator delivery with metered-dose inhalers in mechanically-ventilated patients

“…As a result, the lung volume at end-expiration remains higher than functional residual capacity. The volume of trapped gas can be measured with a spirometer by allowing exhalation of sufficient duration until all airflow ceases [58]. BERNASCONI et al [50] showed that administration of fenoterol by a nebulizer reduced end-expiratory lung volume in patients with COPD undergoing mechanical ventilation for respiratory failure.…”

Assessment of Factors Related to Auto-PEEP

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] In our study, we investigated auto-PEEP from an epidemiological point of view and examined how much, and not how, auto-PEEP is associated with factors that are involved in the development of auto-PEEP. Surprisingly, we observed that in our sample of mechanically ventilated subjects, the variables that characterized the breathing pattern (f, T E , V T , and minute ventilation) appeared to have a marginal role in auto-PEEP in the absence of predisposing factors of the subjects (flow limitation, RS , R RS , BMI, and aging).…”

“…A reduction in V T and increase in T E have been advocated as a strategy to decrease dynamic hyperinflation in obstructive patients. 1,9 However, in some instances, carrying out both options could be unpractical because of the risk of severe hypoventilation. Our results suggest that in those cases, auto-PEEP could be more effectively reduced by increasing T E (ie, increasing inspiratory flow or reducing breathing frequency) to increase T E / RS than by decreasing V T .…”

“…These conditions include increased airway resistance, a short expiratory time (T E ), a long time constant of the respiratory system ( RS ), high minute ventilation, tidal expiratory flow limitation, chronic pulmonary disease, acute respiratory failure, and obesity. 1,[8][9][10][11][12][13] Despite the known role of these causes, the quantitative effects on auto-PEEP values are unknown. Therefore, the contribution of each of the determinants of auto-PEEP is unknown, as well as which of them are associated with the risk of high auto-PEEP levels.…”

Ventilación mecánica invasiva. Puesta al día para el médico pediatra

“…58 Se debe monitorear la PEEPi (resistencia al flujo en espiración), el gradiente PIP-P m (resistencia al flujo en inspiración) y la presión diferencial. 59,60 Ventilación mecánica en los pacientes con cardiopatía congénita e hipertensión pulmonar La VM causa cambios cíclicos en los volúmenes pulmonares y las presiones intratorácicas, y origina modificaciones en el tono del sistema nervioso autónomo, la resistencia vascular pulmonar y el retorno venoso, y efectos opuestos sobre la poscarga biventricular, fenómenos englobados como interacciones corazón-pulmón. Ante la falla ventricular izquierda (VI), la VM es beneficiosa al corregir la hipoxia y la ventilación logrando una disminución del VO 2 y de la poscarga ventricular (entendida como presión transmural del VI), que permite mejorar el volumen eyectivo.…”