|
| |
- Requires intact peritoneum and enough space in peritoneal cavity to
accomodate dialysate
- High glucose concentration in dialysate generates osmotic pressure gradient
which draws fluid into dialysate. Some solute is removed with this
ultrafiltrate by convection but great majority of solute transfer is by
diffusion
- Dialysis membrane quite thick: capillary wall, interstitium and
mesothelium.
Both fluid and solute transfer are slow which limits efficiency of PD
- Volume of ultrafiltrate formed does not increase as rapidly as might be
expected because intraperitoneal fluid is reabsorbed by lymphatics at 05-1.5
ml/min and because glucose is absorbed from dialysate so that its
concentration gradually falls to that of blood. Maximum fluid removal occurs
with a dwell time of approximately 3 h
- Solute removal is greatest when concentration gradient is highest. Clearance
can be maximized by use of dwell times < 2h.
- Typically volume of 2 l is exchanged every hour with inflow, dwell and
outflow times of 10, 30 and 20 mins respectively. Modify as necessary.
Dialysate containing 1.36% glucose most commonly used although may
concentrated solutions may be needed to remove glucose more quickly. Heparin
200-500 U/l may be added to remove risk of blockage of catheter by fibrin
strands
- Heat dialysate to body temperature before use with thermostatically
controlled device
- PD should be restricted to 72 h per catheter as infection risk rises sharply
after this time
Insertion of catheter
- Insert in midline just below umbilicus or in either lower quadrant just
lateral to rectus sheath on a line joining umbilicus to ASIS. RLQ least safe
of these because of risk of caecal injury
- Lie patient flat and examine abdomen to identify any masses or scars. Avoid
these areas
- Wash hands. Gown, gloves, mask
- Prep, drape and infiltrate with LA down to peritoneum
- Insert 14G cannula into peritoneal cavity and rapidly infuse 1-2 l of
dialysate to distend abdomen and to allow space for abdominal contents to
float away from PD catheter during insertion
- Remove cannula and make a small incision at puncture site. Should be large
enough to just admit PD catheter
- Insert catheter with stylet through incision. Ideally patient should be
asked to cough while gentle pressure is exerted on handle of stylet while
position of catheter is stabilized with the other hand. This punctures the
anterior abdominal wall. If patient is unable to cooperate catheter and stylet
should be gently pushed through abdominal wall. Twisting may ease passage
- Advance catheter over stylet until tip is lying in pouch of Douglas
Drug dosage
Clearance of free drug can be predicted approximately by multiplying urea
clearance (20ml/min for a 1h dwell, 8 ml/min for 4h) by ratio of square root of
molecular weight of urea (60 daltons) over square root of drug's molecular
|
