Irrigation Volume During Ureterorenoscopy
During flexible renoscopy and stone lithotripsy there are two contradicting irrigation requirements.
The first is the need to achieve visibility and calls for large amounts of irrigation. The other, is the need to control intrarenal pressure ensuring it is as low as possible, which in turn calls for as little irrigation as possible. The dilemma of renoscopy is how to have great visibility and at the same time prevent the rise in intrarenal pressure?
Intrarenal pressure during ureterorenoscopy is a function of the amount of irrigation fluid entering the kidney over a time period - inflow; and the amount of irrigation fluid draining out of the kidney in the same period of time - outflow. In an ideal world, inflow will equal outflow.
But in the real world, inflow is usually much greater than the outflow. Which means there is potential for overcrowding, like in a house full of people and the kidney can be subjected to high intrarenal pressure.
The best policy is to limit irrigation inflow by matching to the outflow. To prevent distention of the kidney, keep the volume of the irrigation inside the kidney below its maximal capacity. If the kidney is only ¾ full there will be enough space to accommodate a small bolus of irrigation without getting distended.
The Kidney & a Soccer Ball
It is important to recognise that the kidney is a noncompliant organ and behaves like a soccer ball in response to volume. A soccer ball when not completely full will admit some air without increase in pressure. However, when the same soccer ball becomes full, even a small amount of air will produce a very sharp rise in pressure.
It is important to keep the kidney not fully distended, so boluses of irrigation can be accommodated by the increase in volume but keeping it below maximal capacity.
The total capacity of the kidney is not more than 10ml, an amount equivalent to a dessert spoon. Therefore, bolus volume matters. Using very small size bolus 1 – 2ml and allowing time to drain is safer than using large boluses.
Mini Pillow
The low volume of irrigation fluid displaced by Mini Pillow (5 ml max) provides additional safety, preventing large spikes in intrarenal pressure as seen with high volume bolus delivery. Its small size allows it to be very responsive. Even a light compression will produce instant fluid flow.
Injecting 10 ml of irrigation to the kidney represents 10 times more volume than it can accommodate. Whereas injecting 2ml bolus is not more than 20% of the kidney’s capacity.
The degree of kidney distention at the beginning of the bolus delivery will determine the rise of intrarenal pressure in response to the bolus volume. If the kidney is ¾ full it will be able to accommodate 2ml bolus safely.
Peditrol
Peditrol is a foot operated irrigation system that delivers maximally 2.7ml of irrigation fluid and affords good visibility. It can also be used as a tool to find and open ureteric orifice with a short jet of water.
How to achieve best visibility without increasing intrarenal pressure:
The bag with liquid should be suspended not more than 30 - 40cm above the level of patient to avoid constant distension of the kidney from hydrostatic pressure.
Remove air from the device by flushing it in upright position
Only small boluses of 1 -2ml at the time should be used to prevent high peaks in intrapelvic pressure. Good comparison is ½ teaspoon (2ml) as the renal capacity is only 10ml.
Allow time between boluses delivery so drainage from the kidney can take place. It takes about 3 seconds for the intrarenal pressure to return to baseline after a single bolus delivery.
Use shortest possible Ureteric Access Sheath and avoid Trendelenburg position as it increases intrarenal pressures.
Bleeding is frequently a symptom of torn capillaries and increasing pressure by elevating bag or delivering boluses more vigorously will worsen the situation. The bleeding can be prevented by working with lower pressures in the collecting system.
Hand-held irrigation devices should not be used with forced, constant flow generating pumps (electric or pneumatic).