Effect of alpha-stat versus pH-stat strategy on oxyhemoglobin dissociation and whole-body oxygen consumption during hypothermic cardiopulmonary bypass.

To determine whether alpha-stat or pH-stat strategy should be used, 20 patients undergoing coronary artery bypass grafting during moderate hypothermic hemodilutional cardiopulmonary bypass were studied. The carbon dioxide management during bypass was randomly done according to alpha-stat strategy in 10 patients (i.e., temperature-uncorrected PaCO2 was kept near 40 mm Hg and uncorrected pHa was kept at about 7.4) and according to pH-stat strategy in the other 10 patients (i.e., temperature-corrected PaCO2 was kept near 40 mm Hg and uncorrected pHa was kept at about 7.4). In both groups, when the central venous temperature was stable at 26.5 +/- 2.5 degrees C, the perfusion flow was altered sequentially from 2.4 to 1.8 and 1.2 L.min-1.m-2. The mixed venous oxyhemoglobin saturation at the different perfusion flows was monitored by the Oxy-Stat meter and was correlated with the corresponding mixed venous oxygen tension to construct an oxyhemoglobin dissociation curve. Also, the whole-body oxygen consumption at the different perfusion flows was computed. The whole-body oxygen consumption and the oxyhemoglobin dissociation were not significantly different between the alpha-stat and the pH-stat groups. In both groups, the dissociation curve is shifted to the left, but the oxygen consumption per unit time does not significantly change despite decreasing the perfusion flow from 2.4 to 1.2 L.min-1.m-2. The results suggest that oxygen delivery is not impaired during moderate hypothermic cardiopulmonary bypass independent of whether alpha-stat or pH-stat strategy is used.

The hemodynamic effects of intravenous norepinephrine versus epinephrine and phenylephrine in patients with ischemic heart disease.

The hemodynamic effects of an intravenous bolus of norepinephrine 10 micrograms, phenylephrine 100 micrograms and epinephrine 10 micrograms were investigated in 30 patients scheduled for coronary artery bypass grafting. The hemodynamic changes following norepinephrine were similar to those achieved by phenylephrine. Both drugs increased the mean blood pressure and systemic vascular resistance without any significant change of cardiac output. In contrast, epinephrine increased the mean arterial pressure and cardiac output without a significant change of systemic vascular resistance. The results suggest that intravenous norepinephrine acts similar to phenylephrine as an alpha-adrenergic agonist, while epinephrine acts predominantly as a beta-adrenergic agonist.

Differential lung ventilation during thoracotomy.

The effect of differential lung ventilation on arterial PO2 and PCO2 was compared to that achieved during one-lung ventilation in 8 patients undergoing thoracotomy. In all patients, OLV of the dependent lung, while collapsing the nondependent lung, was associated with lowering of the arterial PO2. DLV using a special double-lumen tube adaptor was then initiated; the dependent lung was preferentially ventilated by 75-80% of the tidal volume, while the nondependent lung on the operative side was only ventilated by 20-25% of the tidal volume. DLV improved oxygenation and maintained adequate carbon dioxide elimination, with minimal inflation of the nondependent lung into the surgical field. DLV may be used to increase oxygenation whenever conventional OLV is associated with hypoxemia despite the use of 100% oxygen.