What is Postobstructive Diuresis?
Urinary retention, a condition where you can’t fully empty your bladder, can happen to anyone and in various settings. It can cause lower stomach discomfort and problems peeing. One way of confirming it is by checking how much urine
is left after you’ve gone to the toilet. This can be done using an ultrasound (a machine that uses sound waves to create a picture) on your bladder or by inserting a tube into the bladder.
After emptying a bladder that’s been overstretched because of urinary retention, you may experience something called postobstructive diuresis (POD). This results in urinating a lot and losing too much salt and water. You can tell that it’s happening when you pee 200 mL or more in two consecutive hours after relieving urinary retention, or if you pee more than 3000 mL in one day.
It’s important to quickly spot POD, as it can happen to half of those with urinary retention and can become life-threatening if not treated. This is because you can pee out too much once the blockage is removed, causing problems such as overuse of a Foley catheter (a tube inserted into the bladder to drain pee), percutaneous nephrostomy (another way to drain pee from the kidneys), or double-J stent (a small tube put in the ureters, the tubes that urine travels through from the kidneys to the bladder).
Normally, someone’s bladder can hold up to 450 to 500 mL. If left unchecked, POD can lead to severe health troubles, for example, dehydration, electrolyte imbalances (an irregular level of minerals in the body), low blood pressure, hypovolemic shock (a severe fluid loss), and even death. Treatment often involves a team of healthcare professionals working together to provide immediate care and possibly staying at the hospital.
What Causes Postobstructive Diuresis?
Certain risk factors are associated with post-obstructive diuresis (POD), a condition that causes excessive urination after a blockage in the urinary tract is removed. These risk factors can include symptoms similar to lower urinary tract issues, diabetes, having had multiple bladder catheterizations, an enlarged prostate (prostatic hyperplasia), hardened feces (fecal impaction), and the use of certain medications that affect nerve impulses (anticholinergic medications).
The exact reason why POD occurs isn’t entirely understood, but it likely involves several processes:
* Gradual reduction in the kidney’s ability to concentrate urine due to blood vessels being rinsed out
* Weakening of the sodium transport system in a part of the kidney, known as the thick, ascending loop of Henle
* A decrease in the kidney’s ability to filter blood (glomerular filtration rate or GFR), leading to a reduced blood supply and damage to certain kidney cells (juxtamedullary nephrons)
* Reduced response to a hormone (antidiuretic hormone) that helps control water balance in the body.
Various factors can cause a blockage in the urinary system. These can include a tight foreskin (phimosis), an enlarged prostate, narrowing of the urinary tract outlet (meatal stenosis), urinary stones, abnormal valves in the urethra (posterior urethral valves), blockage at the junction between the kidney and the ureter (ureteropelvic junction obstruction), blocked bladder catheters, prostate cancer, hardened feces, diabetes, nerve-related disorders that affect bladder control like spinal cord disorders and multiple sclerosis, and hardened urine (preputial calculus).
Patients with swelling of the kidneys on both sides (bilateral hydronephrosis) on ultrasound or CT scan and an extended bladder should be assumed to have urinary retention (when you can’t fully empty your bladder) until further investigation proves otherwise.
Risk Factors and Frequency for Postobstructive Diuresis
Post-obstructive diuresis (POD) is a condition that can occur after a urinary obstruction has been fixed; however, the exact number of patients who experience it is unknown. It’s estimated that between 0.5% to 52% of patients might have POD after their obstruction is relieved. Additionally, it’s noted that about 10% of men in their 70s and 30% of men in their 80s might have at least one episode of urinary retention. Compared to women, men are more likely to develop POD and the chances of getting it increase as one gets older.
Chronic retention can either be high-pressure or low-pressure. High-pressure retention is more concerning as it could lead to a condition called vesicoureteral reflux, which could in turn cause damage to the kidneys due to direct harm to nephrons, which are parts of the kidney.
- Post-obstructive diuresis (POD) is a condition seen in some patients following the relief of a urinary obstruction.
- Between 0.5% to 52% of patients might deal with POD after their blockage has been cleared.
- About 10% of men in their 70s and 30% in their 80s may have one or more episodes of urinary retention.
- POD is more common in men and the risk of suffering from it increases with age.
- Chronic retention can be high or low pressure. High pressure is more risky as it could possibly cause kidney damage.
There are varying reports about how often POD happens after a urinary retention has been resolved with some literature indicating it could be as much as 50%. POD can also occur in children after the repair of obstructions in the part where the kidney and ureter (the tube that carries urine from the kidney to the bladder) meet. Sometimes, this can be linked to a kidney disorder known as renal tubular acidosis, but not always. Even in cases where the other kidney is functioning normally, POD can occur.
Signs and Symptoms of Postobstructive Diuresis
Acute urinary retention is a common medical occurrence, usually characterized by lower stomach pain and a complete inability to pee. This condition often follows different urinary symptoms such as a weak urine flow, difficulty in starting urination, and frequent urination. Chronic urinary retention, on the other hand, develops gradually and is usually painless. It’s typically accompanied by small amounts of voided urine and uncontrolled urine leakage. A swollen or heavy feeling in the lower stomach area can be expected but confirmation using bladder ultrasound or catheter is necessary.
When the urinary obstruction gets cleared, there is a boost in urine output. If it exceeds a certain limit, it becomes harmful. In such cases, patients may suffer from symptoms such as extreme and uncontrollable urination, excessive thirst, dehydration, discolored pee indicating blood in urine, profuse sweating, general weakness, leg cramps, confusion, and fainting or sudden loss of consciousness.
During their initial checkup, doctors assess the patient’s level of hydration by measuring aspects like weight and comparing it to their previous weight. Signs of dehydration like skin that doesn’t bounce back when pinched, rapid heart rate, and low blood pressure when standing up can be observed. On the other hand, biochemical changes can lead to weight gain, high blood pressure, and swelling of the lower legs. The Glasgow Coma Scale can be used to determine the level of a patient’s mental function.
- Lower stomach pain and inability to pee
- Weak urine flow, difficulty in starting urination, and frequent urination
- Small amounts of voided urine and uncontrolled urine leakage (in chronic cases)
- Extreme and uncontrollable urination
- Excessive thirst and dehydration
- Discolored pee indicating blood in urine
- Profuse sweating, general weakness, and leg cramps
- Confusion and fainting
- Signs of dehydration or biochemical changes
Testing for Postobstructive Diuresis
When someone has a blocked bladder or ureter, a condition known as Post-obstructive Diuresis (POD) can occur after the blockage is removed. This condition means the person starts to produce an unusually large amount of urine. There isn’t a specific test to predict who will develop POD after their urinary tract obstruction is treated. But, some studies have found initial high levels of a waste product called creatinine, sodium bicarbonate, and urinary retention can increase the risk of developing POD. Other conditions such as kidney issues, dizziness, heart failure, and a depressed central nervous system might also make a person more likely to develop significant POD.
Medical professionals diagnose POD by examining patients who have these risk factors. It’s recommended to closely monitor the person’s overall fluid status, how much urine they produce, and their electrolyte levels. It should also involve daily blood tests and the patient’s weight should be measured every eight hours.
Patients who are at risk of developing POD may need to be admitted to the hospital for monitoring. Their urine output should be measured every two hours, and their vital signs (like heart rate and blood pressure) should be checked every six to eight hours. They should also have certain components of their blood – like, sodium, potassium, phosphate, magnesium, urea, and creatinine – tested every 12 to 24 hours.
If a patient’s urine output exceeds 200 mL per hour for two consecutive hours or if it exceeds 3 liters in 24 hours, this indicates the possibility of severe POD. To differentiate between types of POD, levels of sodium and potassium and the concentration of the urine can be monitored. This information helps in identifying the type of excessive urination – being due to urea (a kind of waste product) or salts. Urea-related excessive urination is usually self-limiting, whereas salt-related one may become problematic, requiring close monitoring of sodium and hydration levels. If the concentration of sodium in the urine is more than 40 mEq/L, it could suggest kidney tubular injury and can result in severe POD if it continues for a long time.
Lastly, one helpful measure is the specific gravity of urine, a measure of its concentration. If the specific gravity is 1.020, that means the urine is concentrated, and POD has settled or is nearly settled. But if the specific gravity is 1.000, the body’s not concentrating the urine enough. This finding is consistent with a dangerous form of POD that involves excessive loss of salt in the urine, and this requires careful monitoring by the healthcare team.
Treatment Options for Postobstructive Diuresis
Previously, it was believed that large amounts of urine in the bladder should be drained slowly or in stages to prevent possible complications like blood in the urine, a sudden drop in heart rate, post-obstructive diuresis (a condition characterized by excessive urine production after a urinary blockage is removed), and low blood pressure. However, new studies have shown that quick and complete drainage of the bladder using a Foley catheter (a tube inserted into the bladder to drain urine) is safe. Also, there’s no increased likelihood for these issues.
Patients who are more prone to developing severe post-obstructive diuresis may need to stay in the hospital for around 24 hours. During this time, medical staff will closely monitor their urine output and levels of various chemicals in the blood, like sodium, potassium, and creatinine. These measurements will be taken every few hours for urine and every 12 hours for the blood chemicals. Doctors will also record the patient’s weight daily and take urine samples to measure different elements present in the urine.
Patients will receive fluids intravenously, or through an IV, and the amount is usually adjusted based on the severity of the post-obstructive diuresis. The most frequent type of IV fluid given is normal saline, but the amount should not exceed 75% of the urine the patient produced in the last 1 or 2 hours. This approach is taken to avoid stimulating more urine production. Essentially, doctors attempt to avoid causing excessive urination by controlling fluid intake. Patients who are mentally capable should continue to drink fluids orally, while those who are not may receive a saline solution through an IV.
Severe post-obstructive diuresis can place patients at risk of complications like low fluid levels inside the body, unstable blood pressure and heart rate, as well as imbalances in the body’s acidity and chemicals. Therefore, it’s important to closely monitor fluid levels inside the body, the patient’s weight, chemicals in the blood, and the functioning of the kidney to achieve a quicker recovery. Once patients show an improvement in condition and their lab results are back to normal, they can be discharged and have a later follow-up appointment with a urologist.
What else can Postobstructive Diuresis be?
If a patient is producing an abnormal amount of urine after their blocked bladder has been treated, they should be tested for the various possible causes. Some of the conditions and factors that may be contributing to the production of too much urine include:
- Cushing syndrome, which makes your body produce too much of certain hormones
- Primary hyperaldosteronism, a disorder that can cause high blood pressure (hypertension)
- Diabetes insipidus, a rare condition that causes frequent, heavy urination
- Use of certain drugs like diuretics, caffeine, acetazolamide, or lithium
- Early-stage kidney failure
- Receiving too much fluid via an intravenous line during treatment
- Drinking too much fluid
- Hypercalcemia (too much calcium in your blood)
- Hyperglycemia (high blood sugar)
- Hypokalemia (low potassium levels)
- Conditions that make it hard for the kidneys to concentrate urine, such as chronic pyelonephritis, sickle cell disease, and amyloidosis
- Taking mannitol, a type of drug used to reduce swelling and pressure inside the eye or around the brain
- Osmotic diuresis, a condition where too much water is drawn into the kidneys from the blood, producing a lot of diluted urine
- Pod, or post-obstructive diuresis, which can happen after a blockage in the urinary system is cleared
- Psychogenic polydipsia, a condition where a person drinks an excessive amount of water due to a mental illness
What to expect with Postobstructive Diuresis
The recovery of the kidneys after an obstruction is removed can depend on several factors. These include how long the blockage has been present, the severity of the obstruction, whether one or both kidneys were affected, and if there was an accompanying infection.
By fixing a blockage in the urinary tract, it could lead to excessive urination. In response to this, a careful management plan is required that may include replacing fluids and electrolytes that were lost. Generally, the outlook for people with “pathological POD” – which refers to certain health conditions that lead to urinary obstructions – is quite good. However, this might not be the case if the person experiences any of the complications mentioned before.
Possible Complications When Diagnosed with Postobstructive Diuresis
Patients with POD (Polydipsia and Overhydration Disorder) may experience several complications. These include:
- Volume Depletion – a lower than normal amount of blood in the body
- Hyponatremia or Hypernatremia – abnormally low or high levels of sodium in the blood
- Hypokalemia – low levels of potassium in the blood
- Hypomagnesemia – low levels of magnesium in the blood
- Metabolic Acidosis – a condition causing the blood to become too acidic
- Hypovolemic Shock – a life-threatening condition that occurs when you lose more than 20 percent of your body’s blood or fluid supply
- Death – in severe cases
Preventing Postobstructive Diuresis
If you or a family member are dealing with urinary retention, it’s important to know that most people who have a procedure to relieve pressure on their bladder (also called bladder decompression) will likely maintain or recover normal kidney function. However, it’s crucial to understand the risks involved in the process, so that you can make a well-informed decision about your health. There are some individuals who are more likely to experience postoperative delirium (POD), a condition that might cause confusion or memory loss after surgery. These patients should be accurately identified and given the right information about how they will be looked after and what complications might arise.
