A kidney stone can stay inside the kidney for long, before it breaks free and passes down. Stones may pass on their own without any symptoms over a period of few days to few weeks. Red, pink or brown colour to the urine, which is normal may be observed during the course of passing a kidney stone. There may be difficulty in passing a large stone causing severe symptoms for a prolonged period.
Sharp pain in the back and side, often with nausea and vomiting are symptomatically common when the stone breaks free and begins to move down the ureter. Symptoms fade and stop as the stone reaches the bladder. Once in the bladder, the kidney stone as a whole may pass through the urethra again causing pain while urinating. If the stone breaks in to smaller fragments in the bladder before being passed out, urinating with fragmented stones is normally painless and unnoticed.
Most kidney stones eventually pass through the urinary tract on their own within 48 hours to few days, with ample fluid intake. While size is the main factor in whether stones will pass on their own, stone location in the ureter also makes a difference. Symptoms experienced during an acute episode of passing a kidney stone correlate clinically to the three distinct stages.
Stage 1 of Passing Kidney stone
The physiology behind this stage is that the effects of the inflammatory process due to the accumulation of deposits forming a stone, cause a progressive rise in renal blood flow and renal pelvis and ureteral pressure. This is the situational circumstance where the afferent arteriole, called the faucet of the kidney opens maximally to push the stone out of the kidney. Despite that, urine from the kidney can no longer pass to the bladder and as a result builds up and stretches the upper end of the ureter and renal collecting system. This stretch activates sensory nerve fibres of the neuronal network located in the kidney and ureters.
This stage lasts for approximately 1 to 1 and half hours. The obstruction caused by the stone at the renal tubules classically correlates with the onset of pain or spasm. This is when a person presents at the casualty seeking medical care.
Stage 2 of Passing Kidney stones
The sensory nerve fibres transmit afferent signals to corresponding levels of the spinal cord which the body interprets as pain at the site of neuronal activation. Pain usually shifts downwards along with the stone that migrates from the kidney down the ureter and towards the bladder. The stone when lodged at the upper end of the ureter is sensed at a level as high as the upper flank and when down the ureter, almost near the junction at the entry to the bladder is felt as low as the labia or testicle. efferent arteriolar vasoconstriction which causes a decrease in overall renal blood flow but an increase in ureteral pressure for up to five hours. The faucet is opened and the end clamp is tightened. The pain classically persists at a severe level for several hours.
Other symptoms in addition to pain may also be experienced while passing a stone. Nerves involved in the process of sensing the renal obstruction are closely linked to nervous supply of adjacent organs like the gastrointestinal tract. Nausea and vomiting which so often accompany an acute episode of renal colic are proposed to be due to cross activation of the associated sensory nerve fibres. Patients have even reported alternative symptoms without any pain. The stone which is at the uretero-vesical junction nearing the bladder, may in certain cases exhibit predominant urinary symptoms and the only noticeable symptoms could be increased urinary frequency, urgency and discomfort while voiding. These symptoms often are mistaken for urinary infection and is repeatedly treated with temporary antibiotics until the point of correct diagnosis.
Stage 3 of Passing Kidney stones
Persistent stone obstruction and sustained increase in renal pressure causes a release of prostaglandin E2. This is a chemical mediator of injury response and produces severe symptoms of pain. It causes hyperperistalsis of the ureters where increased intensity of ureteral contractions in a coordinated wave form, drive urine down to the bladder and eventually even lead to ureteral spasm. The tiny resistance vessels known the renal afferent arterioles which control the flow of blood into the capillaries of the kidneys also get dilated.
There is increased blood flow to the kidney due to arteriolar dilatation. This chain of events promotes a condition of temporary diuresis which is increased production of urine. As a consequence, spasm tightens the ureter around the stone and obstruction is further worsened. Lactic acid build up, which is normal reaction to any muscle being over-worked, also with ureter in spasm, sets off an inflammatory sequence that itself often worsens pain.
With such circumstantial prolonged time, there is reduced blood flow to the affected kidney, even though the arterioles which allow blood into the renal capillaries remain dilated. This happens because the efferent arterioles, which promote blood out of the capillaries, begin to constrict. Efferent arteriolar vasoconstriction increases filtration by renal glomerulus, the urine filtration site of nephrons being controlled by capillary blood supply. The increased filtration continues and can even elevate vascular pressures.
Subsequently, renal blood flow further decreases to the affected kidney and ultimately decreases ureteral pressure such that filtration and urine production begin to fall. At this point, pain subsides at least partially. Intermittent obstruction activating the above chain of physiological events each time urinary flow is obstructed, explains the wave pattern of pain experienced in most cases. This is derived to happen through a combination of the stone moving and the pressure within the ureter with increasing or decreasing muscle spasm.
The fall in blood flow may be minimally injurious during an acute renal attack, but over prolonged periods, it can cause renal failure. This marks the importance of relieving the urinary pathway of an obstructing stone. There is nothing as simple and easy if stones pass of themselves. Medical attention and immediate evacuation of the stone is absolutely needed if the stone continues to obstruct the urinary tract. Interestingly, though not physiologically understood, non-obstructive kidney stones also cause pain and removal can cure it. Kidney stone management and non-invasive stone removal techniques not only has the potential to alleviate pain but may also decrease the risk of future stone growth or spontaneous passage at a later date.
It is advisable to get kidney test done once every 6 months as advised by best urologist in Chennai. As they say, “prevention is better than cure”, you can have a heads up on your kidney’s health before bigger and expensive damage happens.