Mechanism and the Effect of Midodrine on Portal Pressures in Patients With Cirrhosis

The pathophysiology of ascites is complex and various mechanisms have been proposed. Splanchnic and systemic vasodilation related to excess nitric oxide has been associated with systemic hypotension and increased portal flow.(8-10) This is associated with hemodynamic compensatory mechanisms, including activation of the renin-angiotension aldosterone system (RAAS), sympathetic nervous system (SNS), and non osmotic release of anti-diuretic hormones (ADH).(11, 12) These ultimately result in renal dysfunction, associated with sodium and fluid retention.(13) Several studies have shown reversal of HRS and decreased circulatory dysfunction when vasoconstrictors are administered. Various vasoconstrictors (noradrenaline, teleperessin, octreotide and midodrine) have been used in the management of hepato renal syndrome (HRS). (14-17) Midodrine appears to have some advantages, including the benefit of being an oral medication. (18) The beneficial effects have been noted as early as 6 hours after the use of midodrine in patients with ascites with or without HRS (2) with decreased plasma renin activity (PRA), antidiuretic hormone (ADH), nitrite and nitrate activity (NOx), increased renal plasma flow (RPF), glomerular filtration rate (GFR), increased urine sodium concentration (UNa) and volume, increased mean atrial pressure (MAP), decreased heart rate (HR) and cardiac output (CO). There was also decreased aldosterone in non-azotemic cirrhotic patients with or without ascites in patients studied for 7 days. (3) The renal function improvement was not substantiated in other studies. In patients treated for a month along with octreotide there was no significant improvement of renal function but marginal reversible liver dysfunction with decreased body weight (paracentesis adjusted weight),(19) A similar significant weight reduction was also noted in another study.(7) Midodrine has been shown to be safe and effective in patients when used to prevent dialysis induced hypotension, and has improved systolic pressure, without a significantly increased volume of fluid filtered by dialysis and no change in body weight in patients studied.(20, 21) The beneficial effects have been attributed to its modulating effects on autonomic function and increasing peripheral vessel resistances.(22) The drug has been found to effective and safe in acute and chronic use (21, 23) with minimal side effects.(24) Vasoconstrictors in patients with ascites and hydrothorax In non azotemic cirrhotic patients with ascites, the addition of octreotide improved diuresis and decreased renin, increased MAP, decreased CO and improved renal function by increasing GFR, increased urine sodium and volume excretion.(25) In patient with massive hydrothorax with mild ascites and no azotemia, addition of midodrine to octreotide improves MAP, increases GFR, RPF and urine sodium and volume; and prevents recurrence of hydrothorax. Vasoconstrictors have been recommended as treatment for hydrothorax (4-6)and has been found beneficial in refractory ascites.(26) Significance Vasoconstrictors like midodrine have been shown to be beneficial, with improvement of circulatory dysfunction in various groups of patients including patients with HRS type 1, type 2, non azotemic patients and in patients requiring hemodialysis. There are suggestions of decreased body weight in some of these patients. In patients with hydrothorax, addition of vasoconstrictors has helped in relieving the symptoms. The investigators suggest that midodrine could also benefit patients with refractory ascites. By decreasing the rate of ascitic fluid accumulation, it may be possible to decrease the volume of ascites drained or lengthen the interval between paracentesis, giving comfort to the patients. The beneficial effect on portal pressures and ascites could be due to other mechanisms (such as autonomic function) rather than their effect on renal hemodynamics as they are not sustained. There are no studies where this has been systematically analyzed.