In mechanically ventilated patients with ALI the breathing of pure oxygen leads to derecruitment, which is prevented by high PEEP.
R, NIKLASSON L, DREFELDT B. Gas exchange during controlled ventilation in children with normal and abnormal pulmonary circulation: a study using the single breath test for carbon dioxide. Anesth Analg 1986;65:645-52. Carbon dioxide single breath tests (SBT-COJ were obtained during anesthesia and controlled ventilation in 42 children about to undergo thoracic surgery. The tests were obtained with a computerized system based on the Servo ventilator. The system made on-line corrections for compressed volume, apparatus deadspace, and rebreathing. Children with normal pulmonary circulation had excellent gas exchange with high Pao, values, a mean alveolar deadspace fraction (VoalviVTalv) of 0.10, and a gently sloping phase 111 of SBT-CO,. Children with pulmonary hyperperfusion (left to right shunting) due to an atrial septal defect or a ventrical septal defect had significantly lower Paoz values, steeper phase 111 slopes, and a greater spead of values for VualvlV?'alv. Children with pulmonary hypoperfusion due to pulmonary stenosis in combination with intracardiac right to left shunting had extremely low Pao, values, and "adult" values for V,alviVTalv. They required increased ventilation to maintain CO, homeostasis. In the pooled material, the airway deadspace was strongly correlated to height, weight, and age. The airway deadspace was unaffected when tidal volume was increased by 37%, and ventilatory frequency simultaneously reduced by 30%, a maneuver that left alveolar ventilation unchanged. This is probably because an endinspiratory pause was used; when frequency is reduced the length of the end-inspiratory pause increases, allowing proximal diffusion of the alveolarlfresh gas interface.Many children presenting for cardiovascular surgery have lesions that affect perfusion of the lung. A patent ductus arteriosus (PDA) will give rise to a small to moderate degree of pulmonary hyperfusion, i.e., left to right (L-R) shunt. Greater degrees of L-R shunt can be seen with an atrial septal defect (ASD) or a ventricular septal defect (VSD), the latter often giving rise to pulmonary hypertension. In these, arterial oxygenation is only moderately reduced.When pulmonary stenosis (PS) occurs as an isolated defect, the circulation is normal or hypokinetic, but PS combined with an intracardiac right to left (R-L) shunt gives rise to pulmonary hypoperfusion with hypoxemia. In transposition of the great arteries (TGA), both the pulmonary and systemic circulations may be hyperkinetic, but the large R-L shunt may Part of this work has been presented in abstract form. Br J Anaesth 1985;57817-8.
Objective: To avoid ventilator induced lung injury, tidal volume should be low in acute lung injury (ALI). Reducing dead space may be useful for example by using a pattern of inspiration that prolongs the time available for gas distribution and diffusion within the respiratory zone, the mean distribution time (MDT). A study was conducted to investigate how MDT affects CO 2 elimination in pigs at health and after ALI.Design and setting: Randomised crossover study in the animal laboratory of Lund University Biomedical Center. Subjects and intervention:Healthy pigs and pigs with ALI, caused by surfactant perturbation and lungdamaging ventilation were ventilated with a computer-controlled ventilator. With this device each breath could be tailored with respect to insufflation time and pause time (T I and T P ) as well as flow shape (square, increasing or decreasing flow). Measurements and results:The single-breath test for CO 2 allowed analysis of the volume of expired CO 2 and the volume of CO 2 re-inspired from Y-piece and tubes. With a long MDT caused by long T I or T P , the expired volume of CO 2 increased markedly in accordance with the MDT concept in both healthy and ALI pigs. High initial inspiratory flow caused by a short T I or decreasing flow increased the re-inspired volume of CO 2 . Arterial CO 2 increased during a longer period of short MDT and decreased again when MDT was prolonged.Conclusions: CO 2 elimination can be enhanced by a pattern of ventilation that prolongs MDT. Positive effects of prolonged MDT caused by short T I and decreasing flow were attenuated by high initial inspiratory flow.
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