10.1055/a-0732-4899We read with interest the paper by Massimiliano et al [1] which described a technique of “pulling-out of abdominal drain,” which was placed
close to the fistula site in patients with refractory Bergmann’s type A leak to facilitate
closure of fistula. Bile leak occurs in approximately 1 % to 4 % of patients after
laparoscopic cholecystectomy and cystic duct stump is the most common site of leak
[2]
[3].
Endoscopic retrograde cholangiopancreatography (ERCP) is the preferred therapeutic
modality for management of bile duct leaks [4]
[5]. Endoscopic stenting with or without sphincterotomy decreases biliary pressure and
minimizes flow through the leak. The technique of pulling out the drain tube described
by the authors is effective and also a common practice at our center. However, we
take two additional measures in patients with persistent leak after adequate endotherapy:
1. Replace the drain tube with a smaller-diameter tube (e. g. 16F nasogastric tube);
and 2. Convert gravity-assisted drainage to a colostomy bag drainage to remove the
effect of gravity.
These measures help close the fistula in almost all patients. Let’s understand the
physical principles of fluid dynamics behind these measures: (i) Fluid or air flows
from high pressure zone to low pressure zone; and (ii) Compartments that are contiguous
with each other have same pressure.
Fluid (bile) flow in health and disease
In homeostasis
Bile normally flows from bile duct to duodenum: hence biliary pressure (Pbil = 5 – 10 cm of H2O) is higher than duodenal pressure (Pduo). Because the alimentary canal is contiguous with external atmosphere, duodenal pressure
will be similar or slightly higher than atmospheric pressure (Patm) probably due to presence of some peristaltic contractions in the duodenum. Air normally
flows from duodenum to abdominal cavity in perforation peritonitis and intraperitoneal
pressure is normally considered negative, i. e. intraabdominal pressure (Pabd) is lower than duodenal pressure ([Fig. 1]).
Fig. 1 In Homeostasis Pbil > Pduo ≥ Patm > Pabd.
Hence, Pbil > Pduo ≥ Patm > Pabd
In case of bile duct injury
Since ΔPbil–Pabd is higher than ΔPbil–Pduo, bile flows from biliary tract to the peritoneal cavity. But if it is undrained,
intra-abdominal pressure increases gradually and pressure difference decreases.
When biliary sphincterotomy is performed with biliary stenting, biliary pressure decreases
and ΔPbil–Pabd also decreases. Stenting helps in bypassing the leak site and allows it to heal.
This is because the biliary tract is contiguous with the duodenum (after sphincterotomy)
and also with abdominal cavity (fistula site), Pbil = Pduo = Pabd ([Fig. 2]).
Fig. 2 Bile leak post-sphincterotomy and stenting Pbil = Pduo = Pabd.
Drain placement close to the biliary fistula in case of Bergmann’s type A leak
The drain acts as a conduit between the biliary tract and atmosphere and because ΔPbil – Patm will always be higher than ΔPbil –Pduo, the bile leak won’t subside despite stenting, resulting in refractory bile leak
([Fig. 3]).
Fig. 3 When the, drain is close to the fistulous site, Δ Pbil – Patm will always be higher than Δ Pbil – Pduo.
Farther drain displacement
The drain acts as a conduit between the external atmosphere and abdominal cavity,
and flow of fluid between the two compartments results from the pressure difference
between the two. The resultant pressures in the compartments become equal i. e. Pbil = Pduo = Pabd, hence the bile leak ceases ([Fig. 4]).
Fig. 4 When the drain is farther from the fistulous site, Pbil = Pduo = Pabd.
Drain size
Drain size also matters because the flow of fluid is proportional to the 4th power
of the radius (r4) of the drain tube
(Poiseuile’s law). Therefore, in patients with persistent leak despite sphincterotomy
and/or stenting, a larger tube should be replaced by a small-diameter tube.
Effect of gravity
Gravity is an important determinant of drainage of fluid collections that is often
ignored. When a patient is in bed with an abdominal drain hanging by the side to a
lower level (close to the ground), the force of (9.8 m/sec2 × height) will add to external drainage. This can be eliminated if the drain is placed
at the same level as the fistula by converting a drainage bag to an ostomy bag.
Thus, these two additional measures, i. e. replacing the drain tube with a smaller-diameter
tube (e. g. 16F nasogastric tube) and eliminating gravity-assisted drainage by converting
to colostomy bag drainage help close the fistula in almost all patients.
