Densities of cerebrospinal fluid and spinal anaesthetic solutions in surgical patients at body temperaturePurpose: 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 anaesthestic 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~ in a Density Meter that displayed density to the fourth decimal point and was accurate to 0.00003 g-ml -l. The densities of a selection of spinal anaesthetic drugs were also measured, Results: The mean CSF density in the study population was 1.00059 ___ 5D 0.00020. In men of all ages, the mean CSF density was I .00067 ---0.00018 g'ml-l; in postmenopausal women I .00060 -0.00015 g-ml-l; in premenopausal non-pregnant women I .00047 +-0.00076 g'ml-l; and in pregnant women 1.00033 ___ 0.00010 g.ml -I . 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 CO 2 which was slightly hyperbaric. Opioids were all hypobaric except meperidine which w~ hyperbaric. Conclusion: Pregnant women have slightly lower CSF densities than do men and postmenopausal women, and non-pregnant premanopausal women. In the absence of sugar all spinal anaesthetic solutions measured were hypobaric except for lidocaine CO 2 and meperidine, both of which were hyperbanc.

The effect of anemia on the coronary microcirculation was studied in young male rats. Chronic anemia resulted in increased left ventricular end-diastolic pressure and decreased functional reserve. Cardiac mass in anemic animals increased by 25%. Capillary and arteriolar densities in these hearts remained unchanged, indicating angiogenesis in this experimental situation (estimated aggregate capillary length in the left ventricle of anemic hearts was 3.06 km compared with 2.35 km in control hearts). Capillary hematocrit was decreased in chronic anemia less than systemic hematocrit: from 25 to 18% in anemia versus 45 to 28% in controls. Capillary hematocrit and red blood cell spacing were also studied after acute blood withdrawal. Here, capillary hematocrit was preserved even more: 22 versus 24% in systemic hematocrit. Finally, the same was studied in isolated hearts perfused with solutions of various hematocrits. After perfusion with low-hematocrit solution (14%), the capillary hematocrit (24%) was even higher than the perfusate hematocrit! In conclusion, we found evidence of angiogenesis in cardiomegaly induced by chronic anemia. Microvascular growth was accompanied by advantageous regulation of red blood cell spacing within these vessels. This was even more pronounced during acute hemodilution and in isolated perfused hearts.

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