The effect of spinal anaesthesia on blood volume in man

Abstract

HYPOTENSION resulting from vasodilatation secondary to sympathetic blockade is a problem which may be associated with the use of spinal anaesthesia. In most eases, it can be readily controlled by either parenteral fluids or a vasopressor. Hydration sufficient to fill a dilated vaseular tree may present a hazard to the cardiac patient when the block wears off, whereas the use of a prophylactic vasopressor does not give rise to this partieular problem.The effect of spinal anaesthesia on the whole blood volume is not dearly documented. Results from previous studies 1-5 are conflicting due to variations in species studied, premedieation, types and dosages of anaesthetic agents, associated surgical procedures, and techniques used for blood volume measurements. This study therefore seeks to evaluate the effect on the plasma and red cell volumes of a widely used method of anaesthesia, employing a prophylactic vasopressor under standardized conditions for measurements. METHODS PatientsNineteen previously ambulatory male patients, 59 to 87 years of age, had an observation eystoscopy performed under spinal anaesthesia, with each study begun at 10 A.M. These patients were free of significant respiratory or metabolic disease, and their cardiovascular status was stable, with no clinical signs of heart failure. None were receiving digitalis or diuretics. They were not premedicated, and had been fasting for 10 to 12 hours. AnaesthesiaAnaesthesia was administered at the L 3--4 or L 4-5 intervertebral space, using a 26-gauge needle and a 21-gauge introducer. Depending upon the patient's height, and with the intent of producing sensory blockade to the level of the xiphoid, 10 to 15 rag. of 1 per cent tetraeaine hydroehloride, and an equal volume of 10 per cent dextrose, were injected into the subaraehnoid space. 6 This was followed immediately by the injection of a vasopressor, in the form of 8 to 16 rag. of methamphetamine hydroehloride, 7 into the paravertebral muscles adjacent to the lumbar puncture site. The patient was immediately turned supine. The level of sensory anaesthesia at twenty minutes varied from T 4 to T 10. One patient

Estimating allowable blood loss with correction for variations in blood volume

“…Although this factor is lower in pregnant women and infants, a number of studies show that it varies very little in normal man (14). The haematocrit factor has been found to be constant over a haematocrit range from 9 to 82% (15), and seems to be unaltered by spinal anaesthesia (16) and bleeding of between 10 to 20% of the blood volume ( 17).…”

Volume effect of Ringer's solution in the blood during general anaesthesia

“…The ‘haemoglobin dilution method’ is based on the fact that changes in B‐Hb concentration reflect changes in blood volume provided that account is taken of losses of red blood cells [3]. The calculations also require that erythrocyte mobilization from non‐circulating reservoirs does not occur in man [11] and that the haematocrit factor is stable under a wide range of clinical conditions, including anaemia and moderate blood loss [12– 14]. The haematocrit factor was widely studied in the 1950s and should be introduced into the calculations, although what the factor represents is somewhat unclear.…”