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COMPARISON OF RENAL VENOUS BLOOD FLOW BETWEEN NORMAL PREGNANT WOMEN AND NON-PREGNANT WOMEN BY COLOUR AND DUPLEX DOPPLER SONOGRAPHY.

Byline: Shamrez Khan, Rabia Waseem Butt, Riffat Masoud, M. Najmul Hasnat, Muhammad Umar and Usman Shakil

Abstract

Objectives: To investigate whether normal pregnancy has a significant effect on intra!renal venous blood flow and to assess whether the physiological maternal pyelocaliectasis causes a measurable change in venous impedance indices in pregnant women.

Study Design: Cross sectional comparative study.

Place and duration of study: Radiology Departments, KRL Hospital Islamabad and Combined Military Hospital Lahore from Jan 2010 to Jul 2010

Patients and Methods: A total of 50 normal pregnant women in their second and third trimester and 50 controls, i.e. normal non-pregnant married healthy women of childbearing age were included in the study. Confounding variables were controlled by excluding subjects having recent or previous renal calculi, pathological renal conditions or congenital renal anomalies or generalized disorders affecting haemodynamics ruled out by history, clinical examination and ultrasound examination in both pregnant and non-pregnant women.

Results: After grading the degree of hydronephrosis, venous impedance index was obtained from the interlobar veins. Overall the collecting system dilatation was present in 60 % of 50 right kidneys and 42 % of 50 left kidneys in the pregnant women. The venous impedance indices were significantly lower in 50 pregnant women than the values in non-pregnant subjects (p less than 0.001 for the right and the left kidney). The overall difference in venous impedance indices between right and left kidneys was not significant in pregnant women (p = 0.11). There was an inverse correlation between the grade of pelvicalyceal dilatation and the venous impedance indices in both kidneys in 50 pregnant women.

Conclusion: Normal pregnancy causes dilatation of the pelvicalyceal system and significant reduction in renal venous impedance index values in second and third trimesters. Therefore one should be careful in interpretation of an abnormally reduced venous impedance index and hydronephrosis as a sign of pathological ureteral obstruction in pregnant women.

Article

INTRODUCTION

Normal maternal kidneys undergo marked hemodynamic and hormonal changes in pregnancy1 related maternal hydronephrosis2. These changes can both hide and mimic renal disease1. The higher incidence of urinary symptoms in the patients attending obstetric and gynecological clinics3 in our community requires a non invasive, quick, safe and cost effective diagnostic tool since x-ray, contrast studies and CT scan are generally contraindicated in pregnancy. The differentiation between true renal obstruction and physiological maternal hydronephrosis is also important, since renal colic is the most common painful non-obstetric condition for which pregnant women are hospitalized2.

Changes in resistive index of the renal blood vessels can be measured by colour and duplex Doppler ultrasonography differentiating between renal obstructive4 and non-obstructive diseases. Doppler ultrasonography can be safely recommended for the pregnant women5 of both intra-renal arteries and veins. Renal obstruction affects the venous flow more than the arterial flow and comparing the venous flow in obstructed and unobstructed kidneys may improve diagnostic accuracy6 and instead of resistive index the term impedance index7 is preferred for the veins. In acute ureteric obstruction, there is an elevation in renal interstitial pressure and hence a reduced venous impedance index. Assessment of maternal hydronephrosis by grey scale ultrasonography and measurement of renal venous impedance index values by Doppler ultrasonography may be helpful in evaluating renal haemodynamics8 in normal pregnant women.

The study was carried out to study the effect of pregnancy on intrarenal venous blood flow.

SUBJECTS AND METHODS

This cross sectional study was carried out at Radiology Departments, KRL Hospital Islamabad and CMH Lahore from Jan 2010 to Jul 2010. Fifty normal pregnant women in their second and third trimester and 50 controls i.e normal non-pregnant married healthy women of child bearing age were included in the study through non-probability convenience sampling. Confounding variables were controlled by excluding subjects having recent or previous renal calculi, pathological renal conditions or congenital renal anomalies or generalized disorders affecting haemodynamics ruled out by history, clinical examination and ultrasound examination in both pregnant and non pregnant women. All subjects were examined by grey scale and Doppler ultrasonography using a colour Doppler scanner (Voluson 730.pro V of GE) with a 2.0-5.0 MHz variable frequency convex probe. Both kidneys were scanned in all women in lateral decubitus position in a state of normal hydration and urinary bladder filling.

Degree of hydronephrosis was graded on a scale from 0 to 3 indicating

0 = No pelvicalyceal dilatation (= 5 mm sinus echo separation)

1 = Mild (6-10 mm sinus echo separation)

2 = Moderate (11-15 mm sinus echo separation)

3 = Severe ( greater than 15 mm sinus echo separation)

Colour flow mapping was used to identify renal interlobar veins. During a brief period in which the subject held her breath a pulsed Doppler sample was positioned over renal interlobar vein and at least three similar, sequential Doppler waveforms were recorded from the middle of the kidney. The angle of incidence of the Doppler ultrasound beam was kept as parallel to the investigated vessel as possible. Colour scale was adjusted by assigning blue colour to venous flow away from the probe and depicting it as negative. The pulse repetition frequency of the Doppler ultrasonography beam was set according to the peak flow velocity avoiding aliasing.

After measuring peak venous flow velocity (A) and least flow velocity (B), venous impedance index [(A-B)/A] value was calculated. To prevent bias all the readings were taken in same position and at same level in both kidneys.

Statistical Analysis:

The statistical analysis was performed with the Statistical Package for Social Sciences (SPSS) version 10.0. The results were expressed as mean +- standard deviation. The ANOVA was used to determine if the venous impedance indices were different between pregnant and non-pregnant women, and whether there were any differences between kidneys of pregnant women without pelvicalyceal dilatation and the kidneys of control group. ANOVA was performed to investigate whether the impedance indices were significantly different between right and left kidneys in pregnant women. Frequency percentages were calculated for trimester of gestation and degree of hydronephrosis in pregnant women. p values [?]0.05 indicated a statistically significant difference.

RESULTS

Fifty pregnant and 50 non-pregnant women were included in the study. Out of 50 pregnant women 21 (42%) were in second trimester. Overall the collecting system dilatation was present in 60 % of the right kidneys in pregnant women and 42 % the left kidneys in pregnant women. It was more frequent and severe on the right side than on the left. Mild collecting system dilatation was seen in one (2%) non-pregnant subject on the right side.

Results showed that the venous impedance indices were significantly lower in pregnant women than the values in non-pregnant subjects (p less than 0.001 for the right kidney) and (p less than 0.001 for the left kidney).

The overall difference in venous impedance indices between right and left kidneys was not significant in pregnant women (p = 0.11) and non-pregnant women (p=1.000) (Table 1).

Table-1: Venous impedance index in pregnant and non-pregnant women.

Group###Venous Impedance index###P-Value

###Right Kidney###Left Kidney

Pregnent women (n=50)###0.35 +- 0.08###0.37 +-0.06###0.110

Non-pregtnent women (n=50) 0.49 +- 0.09###0.49 +- 0.08###1.000

p-value###less than 0.001###less than 0.001

Table-2: Venous impedance index according to digree of hydronephrosis in pregnant women

Degree of###Right Kidney###Left Kidney

Hydronephrosis###Impedance Index###n###Impedance Index

###n###Right

0###20###0.38 +- 0.07###30###038+-0.5

1###22###0.33 +- 0.07###18###0.35+-0.65

2###3###0.29 +- 0.05###2###0.28+-0.07

3###5###0.31 +- 0.11###0###-

p-Value###less than 0.05

Table 2 reveals the mean venous impedance indices for kidneys of pregnant subjects, grouped according to presence and degree of pyelocaliectasis (hydronephrosis). There was an inverse relationship between the grade of pelvicalyceal dilatation and the venous impedance indices in both kidneys in 50 pregnant women.

On duplex doppler sonography there was a measurable increase in sinus echo separation in kidneys of the pregnant females along with a decrease in venous impedance index values. The venous waveform in pregnant women also showed diminished phasic oscillations due to elevated presystolic flow. In comparison with this, no measurable hydronephrosis were seen in non-pregnant females, value of venous impedance index was normal and prominent phasic oscillations were seen in the venous waveforms (Figure).

DISCUSSION

Colour doppler ultrasound is a useful adjunct to grey scale sonography for studying the vascular behaviour and measuring the flow velocities in various arteries and veins. Afghan et al9, Amin et al4 and Kabala et al10 have utilized colour doppler examination in various studies investigating high risk pregnancies and in renal colic. Kara et al11, Nazarian et al12, Hertzberg et al13 and Liubomirov et al14 have performed duplex and Doppler studied on renal arteries in pregnancy. Bateman et al16, Cox et al15, Rodgers et al16 and Platt et al17 have conducted renal Doppler examination on normal and obstructed kidneys.

In all these studies Doppler ultrasound of kidneys has been directed mostly towards the main and intrarenal arteries. Doppler analysis of intrarenal veins in various renal diseases has not been investigated widely. In a study by Bateman et al6, intrarenal venous flow has shown reduced venous impedance index values on the obstructed side. Spaanderman et al18 and Goodlin19 support the concept that during normal pregnancy there is a fall in total peripheral vascular resistance. In another study carried out on normal pregnant women by Karabulue et al2 there was significant bilateral reduction in renal venous impedance index values. In this study also the venous impedance index values were found to be significantly reduced in both kidneys in normal pregnant women as compared with non-pregnant women. The venous impedance indices in control subjects were similar to the values in previous studies by Karabulut et al2, Oktar et al8 and Bateman et al6.

The venous impedance index values were significantly lower in pregnant women than the values in non-pregnant subjects. This result was in accordance with a similar study carried out by Karabulut et al2 in which the mean venous impedance indices in normal pregnant women were significantly lower than the values in non-pregnant subjects, 0.30+-0.10 versus 0.44+-0.06 in the right (p less than 0.00l), and 0.36+-0.11 versus 0.41+-0.07 in the left kidney (p=0.03).

While evaluating the two theories postulated for explaining the pregnancy induced pyelocaliectasis i.e. the obstructive mechanism and the affect of circulating hormones such as progesterone, Au et al20 supported the mechanical obstruction theory. Ishihara et al21, Grenier et al22 and Croce et al23 concluded that the combined effect of hormones and mechanical obstruction was responsible for the occurrence of pyelocaliectasis. In this study the theory of mechanical obstruction of the ureters seems to be at least in part supported by the presence of more frequent and more severe pyelocaliectasis on right side. However the bilaterality of the hydronephrosis also strengthens the hormonal theory. Hence a multifactorial pathogenesis for pregnancy induced hydronephrosis is supported.

The cardiovascular and haemodynamic changes leading to alteration in blood flow in inferior vena cava24 can also affect the intrarenal veins because of their direct communication through main renal veins. Since in pregnancy blood volume and cardiac output both increase, peripheral vascular resistance should decrease in order to accommodate these changes. During right atrial contraction there is a reversed flow in the inferior vena cava and this must be accommodated by compliance of the veins, manifesting itself as end diastolic flow reduction in the venous waveform. Roobottom et al25 reported decreased hepatic venous pulsatility during pregnancy, which became completely flat with increasing gestational age. This observation was attributed by them to increase in cardiac output and portal velocity as well as the pressure effect caused by the enlarged gravid uterus. Similarly, it can be postulated that the ureters being partly obstructed by the gravid uterus result in increase in interstitial pressure.

Since the renal capsule is rather rigid, this increased interstitial pressure leads to compression over the intrarenal veins. This mechanism also explains mean impedance value being lower and more frequent and severe pelvicalyceal dilatation on the right side as compared to the left since uterus is inclined towards right in majority of females. This fact also supports the inverse correlation between the degree of pelvicalyceal dilatation and venous impedance index.

CONCLUSION

Normal pregnancy causes dilatation of the pelvicalyceal system and significant reduction in renal venous impedance index values in second and third trimesters. Therefore one should be careful in interpretation of an abnormally reduced venous impedance index and hydronephrosis as a signs of pathological ureteral obstruction in pregnant women. These are normal physiological changes of pregnancy in women with normal renal system unless proven otherwise.

Reference

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Article Details
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Author:Khan, Shamrez; Butt, Rabia Waseem; Masoud, Riffat; Hasnat, M. Najmul; Umar, Muhammad; Shakil, Usman
Publication:Pakistan Armed Forces Medical Journal
Article Type:Report
Geographic Code:9PAKI
Date:Mar 31, 2012
Words:2802
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