The Effect of the Supine Position on Renal Function in the Near-Term Pregnant Woman12

Abstract

It has been demonstrated previously that urine flow in the recumbent near-term pregnant woman is appreciably less when she is lying on her back than when she is lying on her side and that without change of position the relative oliguria persists for several hours before it is overcome (1, 2).The present report extends the observations on the effect of position on urine flow to include studies of sodium and potassium excretion, effective renal plasma flow, and glomerular filtration rate in near-term normal pregnant women, in women with eclamptogenic toxemia of pregnancy, and in women with large abdominal neoplasms originating in the pelvis. Attempts have been made to determine the mechanism by which the various observed changes in renal function are produced. METHODSStudies were made 11 times in 10 near-term normally pregnant women and 13 times in 8 women with preeclampsia. In most of these studies the excretion of sodium and potassium, the effective renal plasma flow (RPF) and the glomerular filtration rate (GFR) were measured. In one normal and one preeclamptic pregnant woman the observations were repeated following the insertion of large-bore heavy-walled ureteral catheters into both ureters well above the level of the pelvic brim. Similar renal function studies were made in two women who had large abdominal neoplasms arising from the pelvis, one an ovarian serous cystadenocarcinoma and the other a uterus containing multiple fibromyomas. Both tumors were approximately the size of a uterus at 32 to 34 weeks' gestation. Seven patients who had either delivered 7 or 8 days previously or who had undergone total hysterectomy 9 or 10 days before were also observed. Three subjects of this group had been studied previously while pregnant.All medications were stopped the night before; 2 hours before starting the study, a breakfast of milk, cereal, and 'This study was assisted by a grant from the Cleveland Area Heart Society. toast was allowed. One-half hour later an indwelling catheter was inserted into the bladder and oral hydration consisting of 100 ml. of water every 20 minutes was initiated. At this time in the 17 studies where effective renal plasma flow and inulin clearances were to be measured sodium paraminohippurate and inulin were given intravenously in suitable priming doses, followed by a sustaining infusion of each administered intravenously at a constant rate of 4 to 5 ml. per minute. Urine was collected in periods averaging 20 minutes each. With each collection the bladder was washed with distilled water followed by air. In 14 of the studies only the clearances of endogenous creatinine were determined.Paraminohippurate was measured by the method of Bratton and Marshall (3), inulin by the method of Higashi and Peters (4), and creatinine by the method of Bonsnes and Taussky (5). Sodium and potassium were determined with the Beckman flame photometer.Usually the initial observations were made in the lateral recumbent position. One hour after starting oral hydration and one-half hour before starting the first ...

Effect of hypotonic expansion on sodium, water, and urea excretion in late pregnancy: the influence of posture on these results

“…Previous studies had shown that assumption of a supine posture results in an immediate decrement in urinary sodium excretion (11,31). Our data extend this observation by demonstrating that supine recumbency is antinatriuretic despite considerable volume loading and even when the GFR remained above lateral recumbent control values.…”

“…The decrease in filtered sodium has been mentioned as a causal factor (33), but in this study volume expansion before changing position resulted in a number of instances in which supine recumbency was antinatriuretic despite an increased filtered load. The increase in caval pressure induced by supine recumbency has also been implicated (31,(34)(35)(36), since in man congestion of the inferior vena cava induced by an inflatable balloon consistently reduced urinary sodium excretion (37). We have no data to support or deny this sug-'Lindheimer, M. D., and P. V. Weston.…”

“…Also, an increased filtration fraction has been noted in many situations in which sodium reabsorption increases (38). In one study a small increment in the filtration fraction was noted when pregnant women changed from a lateral to a supine position (31). In another study renal function tests were done with pregnant women on their backs one day and on their sides the preceding or following day, and changes in filtration fraction were equivocal (11).…”

Studies of the Inferior Vena Cava in Late Pregnancy

“…Consequently, obstruction to the inferior vena cava at the level of entry of the renal veins automatically implies increased renal venous pressure. The effects of posture on renal function in late pregnancy have already been described (Pritchard, Barnes, and Bright, 1955), and we are currently pursuing these investigations. Finally, it is apparent that posture has profound effects on the circulation in late pregnancy, and this must be carefully considered in any haemodynamic or renal studies in pregnancy.…”

New vascular system in reptiles: Anatomy and postural hemodynamics of the vertebral venous plexus in snakes

“…In pinnipeds and sloths the spinal veins are normally the only avenue for venous return from some parts of the body (Wislocki, 1928;Harrison and Tomlinson, 1956). The plexus also acts as a vascular bypass during transient increases in thoracoabdominal pressure induced by coughing and defecation (Batson, 1957), micturition (Herlihy, 1948), lifting and the Valsalva maneuver (Batson, 1957;Eckenhoff, 1970), abdominal tumors (Pritchard et al, 1955;Scott, 1963), position of the viscera (Herlihy, 1948), pregnancy (Hirabayashi et al, 1996), activity of the abdominal muscles (Youmans et al, 1963), normal respiration (Reitan, 1941;Herlihy, 1948;Brecher, 1956;Eckenhoff, 1970), and the manual application of external pressure (Batson, 1940(Batson, , 1957Herlihy, 1948;Epstein et al, 1970; but see Worthman, 1956b). Under these various conditions, caval venous pressures rise sharply (e.g., Brigden et al, 1950;Scott, 1963) and blood is forced out of the thoracoabdominal veins and shunted into the plexus.…”