| 1.
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A
vascular access : a portal through which blood can be drawn from
and returned to the individual’s systemic circulation. |
| 2.
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A dialysis
machine that pumps blood through the extracorporeal circulation,
monitors and provides for safe dialysis, assists in waste and ?uid
removal with features permitting control of the dialysis procedure. |
| 3.
|
The haemodialyser
or arti?cial kidney which actually performs the cleansing process
with removal wastes. The contemporary dialysers, comprise of membranes
drawn into hollow ?bres which are externally bathed by a ?uid
of dialysate of appropriate composition so that the waste removal
is achieved and appropriate corrective changes are brought about
in the blood. |
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|
| VASCULAR
ACCESS |
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|
The
need for a vascular access may be either temporary (ranging from
several hours to several weeks) or permanent (months to years).
Temporary access involves percutaneous insertion of a cannula into
a large vein (femoral, subclavian or jugular). These cannulae have
either a single or a doublelumen (one lumen functions as the ‘arterial
blood pathway that carries blood away from the body (vein) to the
dialyser and the other ‘venous’ blood pathway returns
blood to the blood stream. When one single lumen catheter is used
for dialysis, the extracorporeal dialysis circuitry as well as the
single patient dialysis system need to be adapted/modi?ed. Temporary
access placement, has its share of complications which range from
complications that arise at the time of catheter placement (haemorrhage
due to puncture of neighbouring vessels, pneumothorax or haemothorax)
or subsequently (infection, catheter clotting, vessel thrombosis
or stricture). A newer access Permacath, constructed from silicone,
incorporating a Dacron cuff and requiring either surgical or percutaneous
placement technique, has become available. The subcutaneous Dacron
cuff location lowers the infection rates and permits longer residence
of the catheter at the implantation site. The Quinton- Scribner
arteriovenous shunt has been rendered obsolete by the new venous
cannulae mentioned above. The shunts, connecting externally the
artery and the vein, are located in the forearm or just above the
ankle. The disadvantage of this access is related to the fact that
two good vessels need to be permanently sacri?ced. The shunt being
external, infection, clotting and accidental dislodgement
of the shunt with exsanguinating haemorrhage is possible. |
| |
|
| Permanent
vascular access may be obtained by anastomosing the artery and the
vein, usually the radial artery and cephalic vein subcutaneously
in the forearm. Occasionally, such a ?stula is constructed more
proximally between the brachial artery and the cephalic vein. The
non-dominant arm is usually selected. Needles are placed in two
arterialised veins to gain ‘access’ to the bloodstream
in readying the patient for dialysis. Poor ?ows, thrombosis, ischaemia
of the hand, oedema, pseudoaneurysm of the venous limb, infections
and congestive heart failure (in large ?stulae) are observed complications.
The native arteriovenous ?stula is the ?rst choice for permanent
access placement. In instances wherein, a native AV fistula cannot
be constructed (poor veins in forearm), it becomes necessary to
use grafts (autogenous saphenous vein graft or PTFE grafts). The
long term patency rates of grafts ismuch inferior to that of native
AV ?stulae. These grafts may be placed in the forearm as either
loop or straight grafts. Graft infection, stenosis and thrombosis,
aneurysm or pseudoaneurysm, limb ischaemia, oedema and congestive
heart failure may complicate matters. |
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| Dialysis
Machines |
| |
|
|
The modern dialysis machine comprises a blood pump, a dialysis solution
delivery system and appropriate safety monitors. The blood pump
aids in the circulation of blood in the extracorporeal circuit -
from access site to dialyser and back to access. The appropriate
dialysate is prepared within the machine using concentrate solutions
admixed with treated and puri?ed water. The more sophisticated machine
have facilities to modify the dialysate solution for individual
patient needs. Dialysis machines can provide variable sodium, bicarbonate
and on-line monitoring of dialysis delivered. The machine is also
capable of determining the rate and quantity of ?uid removed during
a dialysis session by varying pressures within the internal circuitry
through strategically located pumps. Dialysis has become safer because
of the built-in monitoring devices that monitor the temperature,
rate of ?uid removal, the pressures, the presence of air in the
blood circuit, the appropriateness of the dialysate and the occurrence
of blood leak due to the loss of integrity of the dialyser. |
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| Haemodialyser |
| |
|
| The
rotating drum, the coil dialyser, Kill dialyser, the plate dialyser
have all given way to the contemporary dialyser - the hollow ?bre
or capillary dialyser. The dialyser has two compartments: the blood
compartment (blood passing through the capillary lumen) and the
dialysate compartment wherein the dialysate flows. The outside of
the hollow-?bres is bathed by the dialysate solution and exchange
takes place across the hollow-?bres is bathed by the dialysate solution
and exchange takes place across the hollow-fibre membrane. These
hollow fibres, numbering thousands, are |
| |
|
| manufactured
from materials which in initial days comprised cellulose-based materials
but in recent times is made up of synthetic materials that are more
biocompatible and efficient. Though the manufacturers label the
product (dialyser) for ‘single-use only’, reuse of dialysers
has been practised widely. The reuse practices have advantages and
disadvantages. Though standardized, there needs to be quality control
and quality assurance practices in place in the dialysis unit. The
performance of various dialysers is available from the manufacturers.
Choice of a dialyser (material, size, etc) can be individualized. |
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| Other
requirements for Dialysis |
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|
| 1.
Water for Dialysis : Dialysis water needs to be purified, rendered
contaminant-free and sterile, pyrogen-free so that dialysis patients
are not exposed to impure water that could produce long-term complications.
AAMI (Association for the Advancement of Medical Instrumentation)
standards have been prescribed for purity of haemodialysis water. |
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|
| 2.
Dialysis solutions : Dialysis solution concentrates are broadly
bicarbonate containing or acetate-containing. Minor modifications
are possible and utilized in individuals requiring the same. |
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3.
Anticoagulation : To maintain the ?uidity of the blood through the
extracorporeal circulation, anticoagulants such as heparin are used.
Heparin is administered either intermittently after an initial bolus
injection or as a continuous infusion
using the heparin pump present on the dialysis machines. In patients
with bleeding disorders, a regional anticoagulation may be practised.
Regional heparinisation utilizing heparin-protamine or a regional
citrate anticoagulation may be utilized. Another option in patients
with a bleeding tendency is the intermittent saline flushes employed
to clear the blood from the extracorporeal circuit intermittently
and prevent clotting. |
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| Dialysis
prescriptions |
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| Prescriptions
are determined for individual patients though some broad guidelines
exist. The acute haemodialysis prescription differs from that of
a chronic dialysis patient. Factors that are considered other than
that mentioned above include, membrane size and efficiency, fluid
removal, dialysate composition, anticoagulation and duration of
dialysis. The duration of dialysis is usually 4 hours though shorter
or longer dialysis sessions may be prescribed depending on the need,
dialyser used etc. Dialysis prescriptions too may range from sessions
twice a week to short daily dialysis, the common prescription being
thrice a week. |
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| Compications
on haemodialysis |
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| Complications
could be encountered during or post dialysis, early after initiation
of dialysis or late (after many years on dialysis). Hypotension,
dialysis disequilibrium, cramps, nausea and vomiting, headache,
chest pain, back pain, itching and fever and chills comprise the
common complications on dialysis. Some of the complications are
related to the dialyser reactions. Others may be due to ?uid shifts/removal,
pyrogen reactions (contaminated dialysate). Less common complications
include arrhythmias, cardiac tamponade, intracranial bleeding, seizures,
haemolysis, air embolism, dialysis associated neutropenia and complement
activation and dialysis associated hypoxaemia. In patients who have
been on maintenance haemodialysis, bone disease, dialysis dementia,
neuropathy, etc may occur. |
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| Quality-of-life
on dialysis |
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The
adequacy of dialysis may be monitored by periodic laboratory studies
to calculate URR or Kt/V. Since dialysis incompletely replaces
renal function, it becomes essential to provide for the unreplaced
functions viz: active Vitamin D provision, erythropoietin use
in addition to ?uid and diet controls, iron and vitamin supplements,
antihypertensive medications, etc.
With adequate dialysis, disciplined lifestyles, rHuEPO administration,
the quality of life patients has improved tremedously. However,
one may query whether this could be ever achieved in the socioeconomic
conditions existent today in our country.
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