A comparative study of serum sodium and potassium levels between pre-eclamptic patients and normal pregnant women

 

V Naga Guhan¹, Sarita Basu^2*, K Prabhakara Rao³, Mary Daniel⁴, S Arul Vijaya Vani⁵,

S Priyadharshini⁶

 

{¹Assistant Professor, Department of Biochemistry} {⁶Assistant Professor, Department of Anatomy}

Al Azhar Medical College and Super Specialty Hospital, Thodupuzha, INDIA.

²Associate Professor, Department of Biochemistry, Meenakshi Medical College Hospital and Research Institute, Kanchipuram, INDIA.

{³Professor and Head, Department of Biochemistry} {⁴Professor and Head, Department of Obstetrics and Gynaecology}

Pondicherry Institute of Medical Sciences (PIMS), Pondicherry, INDIA.

⁵Assistant Professor, Department of Biochemistry, Mahatma Gandhi Medical College, Pondicherry, INDIA.

Email: guhan.nagu@gmail.com

 

Abstract               Background: Hypertensive disorders in pregnancy are one of the major causes of maternal and perinatal mortality and morbidity. Though various factors like placental ischemia, immunological maladaptations, genetics and susceptible endothelium have been shown to play etiological role, the exact pathogenesis and complications of preeclampsia still remains undivulged. Of late, electrolyte imbalance is gaining prominence in the aetiopathogenesis of preeclampsia. Aim: To estimate and compare the serum levels of electrolytes like sodium and potassium between preeclamptic patients and normal pregnant women Materials and Methods: This was a case control study done in Pondicherry Institute of Medical Sciences with 50 preeclamptic patients as cases and 50 gestationally age matched normal pregnant women as controls. After getting informed consent, serum sodium and potassium levels were measured from both cases and controls. Results: Serum potassium levels were significantly decreased (p < 0.001) in cases when compared to controls. Further hyponatremia (p- 0.003) and hypokalemia (p- 0.001) were strongly associated with preeclampsia. Conclusion: Hyponatremia and hypokalemia were more prevelant in preeclamptic women. Proper monitoring and appropriate correction of these parameters during early pregnancy can prevent hypertensive complications in pregnancy.

Key Words: Potassium, preeclampsia, sodium

 

 

 

 

INTRODUCTION

About 830 women die from pregnancy related complications around the world every day¹.The major causes that account for 80% of all maternal deaths are severe bleeding, infections, hypertensive disorders followed by unsafe abortions. In developed countries like India, almost one fourth of maternal deaths are due to pre eclampsia and eclampsia.²  Preeclampsia is defined as high blood pressure (≥ 140/90 mmHg) and proteinuria(>300mg/day) after 20 weeks of pregnancy in a previously normotensive woman.³ Whereas eclampsia is defined as, seizures that cannot be attributed to other causes in a woman with pre-eclampsia.⁴ Though various theories have been proposed for the aetiopathogenesis of pregnancy induced hypertension, the most convincing among them is poor placentation. Inappropriate syncytiotrophoblast invasion and poor remodeling of uterine vessels leads to placental insufficiency. This triggers the complex mechanisms resulting in systemic endothelial dysfunction and the clinical syndrome of preeclampsia.⁵ Very recently, electrolyte imbalance is also gaining focus in the evolution of preeclampsia.⁶ The role of electrolytes like sodium and potassium in maintaining the normal vasculature and regulating the blood pressure is established by various researches⁷. So we measured the serum sodium and potassium levels in preeclamptic patients and compared with normal pregnant women to figure out their role in the pathogenesis and prevention of preeclampsia.

 

MATERIALS AND METHODS

1. Type of study: Case Control Study.
2. Setting: Pondicherry Institute of Medical Sciences
3. Duration: Jan 2012 – Aug 2013
4. Sample size: 50 cases and 50 controls (Calculated by allowing alpha error-0.05 and beta error 10%)
5. Inclusion Criteria:

Cases: Pregnancy Patients after 20 weeks of gestation with

Controls: Gestational age matched normal pregnant women.

Exclusion Criteria

Patients with Renal diseases, Diabetes mellitus/Gestational DM, Chronic hypertension, Gestational hypertension(without proteinuria), Adrenal and other endocrine disorders and any other systemic illnesses. Blood samples were acquired from cases and controls after securing informed consent. After centrifuge, serum was separated and was assayed for sodium and potassium levels using electrolyte analyser which worked under the principle of potentiometry using ion selective electrode⁸. All data were expressed as mean ± SD. To compare the mean value of the parameters between cases and controls, ‘Student t Test’ was used whereas Chi square test was used to study the association between two variables. SPSS 17.0 software was used for all statistical analyses and ‘p’ value of ≤ 0.05 was considered as statistically significant.

                                              

RESULTS

In our current study, there was no significant difference in age and gestational age between cases and controls.

 

Figure 1: Comparison of age (yrs) of cases and control

 

Figure 2: Comparison of Gestational Age(weeks) of cases and controls

 

There was no significant difference in serum sodium levels between cases and controls whereas serum potassium levels falls significantly in preeclamptic women than compared to those in control group (Table 1).

 

Figure 3: Comparison of serum sodium(mmol/L) of cases and controls

Figure 4: Comparison of serum potassium(mmol/L) of cases and controls

 Further serum sodium < 135 mmol/L (p value – 0.003) and serum potassium < 3.5mmol/L (p value – 0.001) were found to be strongly associated with preeclampsia.

 

Table 1: Association between hyponatremia and preeclampsia

Chi square test *; p value <0.05 – statistically significant

 

Table 1: Association between hypokalemia and preeclampsia

Chi square test *; p value <0.05 – statistically significant

 

DISCUSSION

This research was carried out to compare the serum levels of sodium and potassium between gestational-age matched preeclampsia and normal pregnancy. In our study we observed that preeclampsia was found to be more common in primigravida (78% of preeclamptic women were primigravida). This contention is strongly supported by Kirsten Duckitt et al, who in their study, found that nulliparity triples the risk of preeclampsia.⁹ In preeclampsia group, 42 % of babies were born as low birth weight whereas in control group only 6% were low birth weights. We have a study by Xiong X et al, supporting the relation between preeclampsia and low birth weight, which states that women with preeclampsia were also at markedly higher risk of having low-birth-weight (adjusted odds ratio, 4.14; 95% confidence interval, 3.32-5.15)¹⁰ Serum sodium is postulated by various studies to play a trivial role in the pathogenesis of preeclampsia. There were contrasting reports stating that both hyponatremia and hypernatremia could be associated with preeclampsia. May N Yussif et al found that the serum sodium was significantly higher in preeclamptic women.¹¹ Neeru Bhaskar et al found that dietary restriction of sodium could decrease the incidence of preeclampsia.¹² But Indumathi V et al in their clinical trial proposed that decreased serum sodium lead to hypertension.¹³ Likewise, in our study too, hyponatremia (Na < 135 mmol/L) was found to be strongly associated with preeclampsia. There was a significant fall in serum potassium levels among cases in our study. Our findings are in accordance with those reported by other authors. Anjum K Sayyed et al in their clinical trial found that hypokalemia may have a key role in the pathogenesis of preeclampsia.¹⁴ Magna Manjareeka et al. found that the preeclamptic women of South India exhibit significantly lower serum potassium levels¹⁵ Extracellular sodium and potassium levels are maintained by the uninterrupted actions of Na+/K+ pump and Na+/K+ cotransporter across the cell membranes. Ulrich S et al, in his research work, accomplished that, in pre eclamptic patients, the net sodium extrusion by Na+/K+ cotransporter was abnormally low.16 This was further substantiated by a study done by Arumanayagam M et al.17 This could be the probable explanation for hyponatremia and hypokalemia encountered in our study among the preeclamptic women. Hyponatremia and hypokalemia increases the renin production and enhances the sensitivity of blood vessels to vasoconstrictors like angiotensin II and aldosterone. Further serum potassium mediates vasodilation through polarisation of vascular smooth muscle membrane. So any decline in serum sodium and potassium can cause vasoconstriction and hypertension.¹⁸

 

 

CONCLUSION

Hyponatremia and hypokalemia documented in our study among the preeclamptic women has both diagnostic and therapeutic implications on the disease. In high risk population, estimation of these parameters in the early pregnancy can be done and its ability to predict the development of preeclampsia in the later pregnancy can be studied further. Proper monitoring and appropriate correction of these parameters during early pregnancy can be used as a preventive tool in preeclampsia.

 

 

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