The effect of changing transfusion practice on rates of perioperative stroke and myocardial infarction in patients undergoing carotid endarterectomy: a retrospective analysis of 1114 Mayo Clinic patients. Mayo Perioperative Outcomes Group.

OBJECTIVE: To evaluate changes in the institution's red blood cell (RBC) transfusion practice during the past 15 years and the influence of these changes on neurologic or cardiac morbidity after carotid endarterectomy. PATIENTS AND METHODS: Based on a retrospective analysis of the Mayo Clinic database, 1,114 patients who underwent carotid endarterectomy were stratified into 1 of 2 groups: (1) 1980 to 1985 (ie, pre-human immunodeficiency virus screening, early-practice group [n=552]) and (2) 1990 to 1995 (ie, recent-practice group [n=562]). Data were compared between time periods using the chi2 test for categorical variables and the rank sum test for continuous variables. Logistic regression was used to assess the association between perioperative transfusion practice and the occurrence of stroke or myocardial infarction. Two-tailed P values < or = 05 were considered statistically significant. RESULTS: Patients in the recent-practice group were significantly older (mean +/- SD age, 69.6 +/- 8.7 years) vs 65.9 +/- 8.3 years in the early-practice group (P<.001). The proportion of patients receiving perioperative RBC transfusion decreased dramatically from 72.9% in 1980-1985 to 8.7% in 1990-1995 (P<.001). Additionally, the mean +/- SD number of RBC units transfused decreased from 1.10 +/- 1.30 U in 1980-1985 to 0.27 +/- 1.22 U in 1990-1995 (P<.001). Mean +/- SD discharge hemoglobin concentration decreased from 13.7 +/- 1.4 g/dL in 1980-1985 to 11.8 +/- 1.5 g/dL in 1990-1995 (P<.001). Rates of perioperative stroke and myocardial infarction did not differ between the 2 time periods (early-practice group vs recent-practice group: stroke, 5.1% vs 3.6% [P=.22]; myocardial infarction, 1.5% vs 2.3% [P=.29]). CONCLUSIONS: Our results suggest that elderly patients undergoing carotid endarterectomy (ie, individuals known to be at high risk for cerebral and cardiac ischemia) can tolerate modest perioperative anemia despite a considerable change in the institution's transfusion practice (lower "transfusion trigger," the hemoglobin concentration or hematocrit value below which RBC transfusion is indicated).

Densities of cerebrospinal fluid and spinal anaesthetic solutions in surgical patients at body temperature.

PURPOSE: To determine the densities of cerebrospinal fluid (CSF) in patients for surgery under spinal anaesthesia. The densities of the CSF were compared with the densities of local anaesthetic solutions and their mixtures with commonly used spinal opioids. METHOD: One ml of CSF was collected from 131 consecutive patients that consented to the study at the time of spinal anaesthesia. Densities were measured at 37 degrees C in a Density Meter that displayed density to the fourth decimal point and was accurate to 0.00003 g.ml-1. The densities of a selection of spinal anaesthetic drugs were also measured. RESULTS: The mean CSF density in the study population was 1.00059 +/- SD 0.00020. In men of all ages, the mean CSF density was 1.00067 +/- 0.00018 g.ml-1; in postmenopausal women 1.00060 +/- 0.00015 g.ml-1; in premenopausal non-pregnant women 1.00047 +/- 0.00076 g.ml-1; and in pregnant women 1.00033 +/- 0.00010 g.ml-1. There were differences between the CSF densities in pregnant women compared with men (P = 0.0001), postmenopausal women (P = 0.0001) and non-pregnant premenopausal women (P = 0.03). Local anaesthetic solutions that contain sugar (glucose or dextrose) were all hyperbaric. In the absence of sugar, all local anaesthetic solutions were hypobaric except for lidocaine CO2 which was slightly hyperbaric. Opioids were all hypobaric except meperidine which was hyperbaric. CONCLUSION: Pregnant women have slightly lower CSF densities than do men and postmenopausal women, and non-pregnant premenopausal women. In the absence of sugar all spinal anaesthetic solutions measured were hypobaric except for lidocaine CO2 and meperidine, both of which were hyperbaric.