A. De Wolf

Extent of anesthesia and hemodynamic effects after subarachnoid administration of bupivacaine with epinephrine

It has been suggested that the amount of local anesthetic injected into the subarachnoid space is more important than the volume or concentration that is used in determining the extent of anesthesia (1-7). However, this conclusion was based on studies using small volumes of local anesthetic (e.g., 1 4 ml). We have used larger volumes of local anesthetic (10 ml) for subarachnoid anesthesia, with good analgesia and without complications (8). We have now evaluated the effect of using widely disparate volumes (2.5 vs 10 ml) and concentrations (0.5% vs 0.125%) of bupivacaine while maintaining a constant dose (12.5 mg) on the extent of sensory anesthesia and the resultant hemodynamic changes.

Morbidity and mortality in patients with coronary artery disease undergoing orthotopic liver transplantation

Thirty-two patients with coronary artery disease who underwent liver transplantation between 1990 and 1994 were identified. Coronary artery disease was managed medically (n = 9), by angioplasty (n = l), or surgically (n = 22) prior to liver transplantation. Two patients underwent simultaneous coronary artery bypass gralting and liver transplantation. Complete preoperative cardiac evaluation was performed in all patients. Perioperative and postoperative morbidity and mortality were retrospectively determined. Overall mortality was 50%, whereas morbidity was 81 %. Follow-up was between 1 and 3 years after liver transplantation. Subgroup analysis revealed that medically managed patients had a 56% mortality and a 100% morbidity. The patient who underwent angioplasty survived without morbidity. One patient who underwent simultaneous coronary artery bypass grafting and liver transplantation died intraoperatively. The second patient survived but required pace

Monitoring anaesthetic gas concentrations in the exhaust of the cardiopulmonary bypass oxygenator

in the exhaust of the cardiopulmonary bypass oxygenator Editor—Nitzschke and colleagues recently studied sevoflurane plasma concentrations during cardiopulmonary bypass (CPB). The authors found no relationship between sevoflurane plasma concentrations and either sevoflurane concentrations in the exhaust of the oxygenator or bispectral index (BIS) values, prompting them to conclude that ‘Measuring the concentration of sevoflurane in the exhaust from the oxygenator is not useful for monitoring sevoflurane administration during bypass’. However, the authors failed to take into account the consequences of Henry’s law: at aconstant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid. Blood/gas partition coefficient changes for sevoflurane during CPB were not measured, and may have been considerable given the acute changes in blood temperature and haematocrit that routinely occur. For this reason, the partial pressure in the blood remains unknown. This is the important variable, because, like all gases, inhaled anaesthetics are transported down a partial pressure gradient (not a concentration gradient), and because their clinical effects correlate with the partial pressure. The appropriate technique to use is double headspace equilibration of blood samples, as described by many previous authors, which allows simultaneous measurement of partial pressure and solubility. – 6 To summarize, reporting plasma concentrations without blood solubility does not allow meaningful clinical recommendations to be made. By implication, trying to find a relationship between plasma sevoflurane concentration and BIS with these data is futile. Therefore we argue that the conclusions by Nitzschke and colleagues are premature: pending further evidence, it remains reasonable practice to monitor anaesthetic gas concentrations in the exhaust of the oxygenator.