title: Haemodynamic effects of inspiratory and expiratory resistances in anaesthetic breathing systems during induced hypotension.
abstract: This study was aimed at determining the haemodynamic effects of various flow resistances in the anaesthetic breathing system in 15 patients under induced hypotension. The breathing pattern, arterial blood gases and haemodynamics were analysed during spontaneous breathing with three systems with different flow resistance as compared with a low-resistance control system. One was made up of a Digby-Leigh valve with an inspiratory resistance of 7 cmH2O l-1s and a high expiratory resistance of 25 cmH2O l-1s (DLS); the other two had an added inspiratory resistive load of 12 cmH2O l-1s (IRS1) and 25 cmH2O l-1s (IRS2) respectively. Whichever system was used, blood gases did not change. With DLS, pulmonary arterial and wedge pressures increased. With the two high inspiratory resistance systems, stroke volume (SV) increased and heart rate (HR) decreased. In six patients, SV was increased only with IRS2, whereas the increase seen with IRS1 in the other nine subjects disappeared with IRS2. It is concluded that the expiratory resistance should be as low as possible in order to avoid pulmonary haemodynamic consequences. An inspiratory resistive load, carefully adapted to each individual case, produced an increase in SV probably by enhancing the venous return. This latter effect could be beneficial in reducing bleeding during middle ear micro-surgery.
mesh_terms: D000136:Acid-Base Equilibrium; D000293:Adolescent; D000328:Adult; D000403:Airway Resistance; D000758:Anesthesia; D001784:Blood Gas Analysis; D004562:Electrocardiography; D005260:Female; D006439:Hemodynamics; D006801:Humans; D007023:Hypotension, Controlled; D008297:Male; D012119:Respiration