Anesthesiology
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The effect of cerebral blood flow (CBF) and cerebrospinal fluid pressure (CSFP) of mechanical ventilation with positive end-expiratory pressure (PEEP) at 5, 10, and 15 cm H2O was studied in 23 paralyzed, ventilated goats which were divided into three treatment groups. Group I received no volume expansion agent to counteract the hemodynamic effects of PEEP. Group II received normal saline to maintain a constant arterial blood pressure (BP), and Group III received a mannitol solution for BP maintenance. ⋯ Thus, when PEEP therapy is associated with substantial decreases in BP and CO, CBF may decrease as well. Maintenance of BP and CO by volume expansion with a crystalloid solution resulted in a greater reduction in CBF than in the untreated group but maintenance of BP and CO by mannitol infusion resulted in maintenance of CBF at the baseline, pre-PEEP level. The authors conclude that brain interstitial fluid pressure is an important variable in the determination of cerebral blood flow during ventilation with PEEP.
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Positive end-expiratory pressure (PEEP) has little beneficial effect in improving gas exchange in canine left lower lobe (LLL) pneumonia. This is true because while PEEP improves lobar gas exchange, it also increases relative perfusion (QL) to the diseased lobe. The authors hypothesized that PEEP administered to only the diseased lung would avoid the increased QLLL. ⋯ QLLL per cent did not increase during PEEP. These results suggest that unilateral PEEP improves regional gas exchange within the pneumonia lobe, probably by ventilating units which were previously perfused but not ventilated. Further, this improvement in regional gas exchange occurred without the diversion of blood flow towards consolidated lung that occurs with whole-lung PEEP, and so resulted in a substantial net improvement in overall gas exchange.