Effect of mannitol on the performance of the isolated canine heart after fibrillatory arrest

Pretreatment with hyperosmolal mannitol has been shown to improve performance of the heart in which there are areas of regional ischemia and to diminish the evidence of ischemic damage. In the present study, mannitol was administered during the recovery period following acute ischemic arrest of the canine isovolumic left ventricle. Performance was examined before, during, and after the period of hyperosmolality. Each heart was subjected to three arrest periods of identical duration (1.5 to 3.0 min). Heart rate and aortic pressure were held constant except during arrest periods. During the first 2 min following defibrillation and reestablishment of coronary perfusion, saline or 25% mannitol was administered in the sequence saline mannitol saline for respective ischemic periods. The osmolality during saline was 315 ± 4.8 mOsm (S.E.) and during mannitol 347 ± 5.9 mOsm. Peak isovolumic pressure and dp/dt demonstrated improved performance during and following hyperosmolality induced by mannitol when compared to saline. Similar results were obtained with the sequence mannitol saline mannitol. Hypertonic mannitol without prior ischemia resulted in improved performance which was limited to the period of hyperosmolality. Thus a brief increase in osmolality with mannitol after fibrillatory arrest provided a relative improvement in myocardial performance, possibly by decreasing the amount of ischemic injury to functioning myocardium.