Myocardial oxygen consumption, oxygen supply/demand heterogeneity, and microvascular patency in regionally stunned myocardium.

Although oxygen consumption closely parallels mechanical work in the normal heart, previous studies have found that stunned myocardium may have normal or even increased oxygen consumption despite depressed function. In this study we used microspectrophotometry to measure the oxygen saturations within arteries and veins of less than 100 micron diameter in quick-frozen biopsy samples from normal and regionally stunned myocardium of 10 open-chest anesthetized dogs. Regional myocardial blood flow, measured by radioactive microspheres, was similar in stunned and normal regions, as was mean arteriolar oxygen saturation. However, mean venous oxygen saturation was lower in the stunned region (epicardium 38.0% vs 43.8%, p less than .02; endocardium 36.2% vs 39.5%, p = .12), indicating increased oxygen extraction and consumption, despite a marked reduction in mean systolic segmental shortening from 14.4% to 0.5%. In addition, there was greater vein-to-vein heterogeneity of oxygen saturation in the stunned region, with an excess of veins having low saturations (statistically significant in epicardium, nonsignificant trend in endocardium). Microvascular injections studies with Microfil or drafting ink revealed filling of over 95% of arterioles and 85% of capillaries in the stunned region, similar to the findings in the normal region. Our results are consistent with an inefficient transfer of energy into myocyte contraction or an increased use of energy for noncontractile activities in stunned myocardium. In addition, the finding of increased heterogeneity of oxygen extraction suggests that the injury to stunned myocardium may not be uniform to all contractile elements, but instead may be focally and irregularly distributed.

Effect of repeated episodes of drug-induced ventricular dyskinesia on subsequent regional function in the dog: comparison with myocardial stunning produced by repeated coronary occlusions.

Stunned myocardium can be produced by repeated short episodes of ischemia. Histochemical and ultrastructural abnormalities such as sarcomere lengthening and myofiber thinning have been noted in myocardium soon after the onset of ischemia and have been attributed to the mechanical stretching that occurs during ventricular systole. To test whether mechanical forces alone could produce the residual dysfunction seen in stunned myocardium, regional dyskinesia was produced in open chest dogs by six repeated intracoronary infusions of either potassium chloride, 0.2 mEq/min for 2.5 minutes, or lidocaine, a 10 mg bolus followed by 1 to 3 mg/min for 5 minutes. These dogs were matched with dogs that had six repeated coronary occlusions of 2.5 and 5 minutes' duration, respectively. Regional function was analyzed using fractional systolic shortening and the load-independent end-systolic pressure-length relation. Both potassium chloride and lidocaine produced regional dyskinesia that was similar to the dyskinesia produced by coronary occlusion. Although regional ventricular function after repeated coronary occlusions remained significantly reduced, function returned completely to normal within 5 minutes after the last drug-induced dyskinesia. In conclusion, regional dysfunction produced by potassium chloride and lidocaine does not produce residual dysfunction despite mechanical forces during systole similar to those seen during coronary occlusion.

Selective enhancement of function of stunned myocardium by increased flow.

Although augmentation of flow does not improve the performance of normal myocardium, the hyperemic response after brief coronary occlusion is associated with transient hyperfunction in the previously ischemic region. In this study we assessed the effect of vasodilator-enhanced coronary blood flow on the systolic function of postischemic stunned myocardium. In 18 open-chest, anesthetized dogs the anterior descending artery was occluded for 5 min, followed by a 10 min period of reflow, repeated 12 times with a final 90 min recovery period. After the recovery period, either 0.06 mg/min dipyridamole (n = 6), 1 mg/min papaverine (n = 6), or 1.5 micrograms/kg/min nitroglycerin (n = 6) was infused intravenously for 15 min. Regional myocardial blood flow, which had returned to normal before administration of vasodilator, was increased 150% above baseline by dipyridamole and 80% by papaverine, but was unchanged by nitroglycerin. Segmental shortening decreased after repeated occlusions: from 17.5% to 0.9% in the group later treated with dipyridamole, from 18.6% to 6.7% in the papaverine group, and from 19.2% to-1.9% in the nitroglycerin group (p less than .005 for all groups). Segmental shortening increased to 8.8% after dipyridamole, 13.6% after papaverine, and 5.1% after nitroglycerin (p less than .05 for all groups), although the load-independent end-systolic pressure-length relationship (ESPLR) showed a significant shift to the left, reflecting enhanced performance, only after dipyridamole and papaverine. For all dogs combined, the percent improvement in ESPLR was correlated with the percent increase in flow (R = -.73, p less than .001). Performance was unchanged in the control region despite similar augmentation of flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Demystifying critical care management. Part 2.

Management functions are the major responsibility of the CNE. Effective application of these functions to CCUs is a vital element in the total nursing management process because of the resources allocated to this area. Critical care units are geographically designated areas, the complexity of which is heightened by the critical condition of the patients, the advanced technology available, the expertise needed to function in this environment. This complexity is best understood when the unit is analyzed using a systems approach. Although CCUs are distinct geographic areas, they function as multiple systems within and in conjunction with the other hospital and health-care systems. This article has detailed specific aspects of these systems that impact on CCU management. The article has provided this specificity according to the management functions of assessment, planning, implementing, and controlling. Effective management of CCUs provides valuable evidence to administrative and corporate-level personnel that chief nursing executives are, in fact, professional administrators. This acceptance of the CNEs' expertise provides an additional power base that is essential in negotiations for budget allocations and strategic planning if nursing department goals and objectives are to be achieved.

Demystifying critical care management. Part 1.

Many nurse executives avoid an active management role in their hospital's critical care areas, a stance that can result in decreased personal, professional, and institutional efficiency and effectiveness. This article is a guide for applying the management process in critical care units and for helping nurse executives gain control of one of the largest consumers of hospital and nursing resources. This is part 1 of a two-part article.