outlines the first drainage hole. Chest tubes are also provided in right angle, trocar, flared, and tapered configurations for different drainage needs. As well, some chest tubes are coated with heparin to help prevent thrombus formation, though the effect of this is disputed. Chest tube have an end hole (proximal, toward the patient) and a series of side holes. The number of side holes is generally 6 on most chest tubes. The length of tube that has side holes is the effective drainage length (EDL). In chest tubes designed for pediatric heart surgery, the EDL is shorter, generally by only having 4 side holes. Channel style chest drains, also called Blake drains, are so-called silastic drains made of silicone and feature open flutes that reside inside the patient. Drainage is thought to be achieved by capillary action, allowing the fluids to travel through the open grooves into a closed cross section, which contains the fluid and allows it to be suctioned through the tube. Though these chest tubes are more expensive than conventional ones, they are theoretically less painful. Chest drainage system A chest drainage system is typically used to collect chest drainage (air, blood, effusions). Most commonly, drainage systems use three chambers which are based on the three-bottle system. The first chamber allows fluid that is drained from the chest to be collected. The second chamber functions as a "water seal", which acts as a one way valve allowing gas to escape, but not reenter the chest. Air bubbling through the water seal chamber is usual when the patient coughs or exhales but may indicate, if continual, a pleural or system leak that should be evaluated critically. It can also indicate a leak of air from the lung. The third chamber is the suction control chamber. The height of the water in this chamber regulates the negative pressure applied to the system. A gentle bubbling through the water column minimizes evaporation of the fluid and indicates that the suction is being regulated to the height of the water column. In this way, increased wall suction does not increase the negative pressure of the system. Newer drainage systems eliminate the water seal using a mechanical check-valve, and some also use a mechanical regulator to regulate the suction pressure. Systems which employ both these are dubbed "dry" systems, whereas systems that retain the water seal but use a mechanical regulator are