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Nephrology > Haemodialysis and Complications > Flashcards

Haemodialysis and Complications Flashcards

1
Q

What are the components in haemodialysis procedure?

A
  1. Dialysis machine
    - Blood pump, safety monitoring
    - Dialysate pump, dialysate monitoring - temperature, electrolytes
    - Air trap - prevents air from entering blood circuit
    - Dialyser membrane
  2. Patient’s access
    - Tunneled catheter
    - Central venous catheter
    - AVF or AVG
  3. Treated water to make dialysate
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2
Q

AV fistula is a __ between __ with adjacent __

What is the Rule of 6 for AV fistula maturity

A

Surgical anastomosis, artery, vein

  1. Period of 6-8 weeks for maturity - increased pressure exposed to vein from the artery causes vein dilatation and thickened vessel wall
  2. Blood flow rate > 600mL/min
  3. Vein diameter > 6mm
  4. Vein depth < 6mm
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3
Q

Synthetic graft is created by surgical interposition of __ between artery and vein

Why is AV fistula preferred over AV graft?

A

Synthetic blood vessel

AV fistula is preferred because:
1. Fewer complications
2. Longer primary patency rate (intervention free access survival)
3. Longer secondary patency rate (access survival until abandonment)
4. Lesser intimal hyperplasia at vein anastomosis
(which may cause stenosis, obstruction, thrombosis)
5. Lower infection rates (no foreign body)

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4
Q

Sadly, about __ of fistulas that are placed are abandoned prior to use due to __, __, __

A

30-50%
Thrombosis
Inadequate blood flow
Complications from access placement

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5
Q

A catheter can be placed for haemodialysis when patient requires dialysis __ and __, or __

It is least desirable, has higher rate of __ and __

Sites:
- Permanent: __
- Temporary: __

A

Acutely and does not have functional AV fistula/graft, or
No suitable site for AV fistula/graft

Higher rate of mortality and morbidity

Permanent catheter (tunneled catheter) through IJV into SVC via subcutaneous tunnel to reduce risk of infection

Temporary cather into IJV or femoral vein, removed within 7 days

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6
Q

A dialyser is a container with __ that separates dialysate from blood that has been removed from the patient.

Hollow fibrer dialyser is most commonly used, containing more than __ hollow fibres made of semipermeable material.

Blood travels __ the hollow fibres, with dialysate flows __ of the hollow fibres in a __ from the blood.

Size of dialyser measured by surface area of semipermeable membrane and expressed in square meters, ranging __ for adults and __ for paediatrics.

A

Semi-permeable membrane

More than 10,000 hollow fibres

Blood travels through hollow fibres
Dialysate flows around the outside of hollow fibres
Countercurrent direction

Adult 1.5 - 2.5 m2
Paediatrics < 1m2

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7
Q

Dialysate is a __ solution consisting of __ and __.

__ and __ is usually physiologic
__ and __ are lesser than physiologic to allow removal of these substances on dialysis.
__ is higher than physiologic to allow for treatment of metabolic acidosis
__ and __ are available at varying concentrations to adjust to rate of removal

A

Physiologic solution, inorganic irons, glucose

Sodium and chloride is physiologic
Magnesium and phosphorus are lesser than physiologic
Bicarbonate is higher than physiologic
Potassium and calcium are varying concentration

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8
Q

Dialysis prescription
Blood flow (Qb) and dialysate flow (Qd)
Dialysate temperature
Dialysate calcium and glucose
Dialyser size and flux
Heparin

A

Blood flow (Qb)
- Usually 250 to 300 (150 in SLED)

Dialysate flow (Qd)
- Flow in countercurrent direction at rate 1 to 1.5x Qb
- Usually at 500 to 800 (300 in SLED)

Dialysate temperature
- Set below patient’s body temperature to allow for vasoconstriction and minimising hypotension with volume removal on dialysis
- 36 degree for normal patient, 35.5 degree for haemodynamically unstable

Dialysate calcium
- 1.25g for neutral calcium balance, 1.5g for hypocalcaemic, haemodynamic unstable

Dialysate glucose
- 2g

Dialyser size and flux
- 15L for smaller size patient, newly initiated dialysis
- 17L for larger size patient
- Low flux for normal, high flux to remove excess toxins

Heparin
- Full: 500 units bolus then 500 units/hr infusion
- Tight: 250 units bolus then 250 units/hr infusion
- Heparin free if active bleeding

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9
Q

Haemodialysis processes: __ and __

Diffusion - small and middle molecules move via __ between blood and dialysate compartments of dialyser via __
- Movement from __ (__) to __ (__)
- Removal of molecules that are toxic in high concentrations (__, __, __) and repleting molecules that are deficient (__, __)

Ultrafiltration - removal of water during dialysis via __

A

Diffusion, ultrafiltration

Diffusion
Move via concentration gradient, via semipermeable membrane
- Movement from higher concentration (blood) to lower concentration (dialysate)
- Toxic (K, Phos, Urea), deficient (Ca, Bicarb)

Ultrafiltration via transmembrane hydrostatic pressure

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10
Q

What determines the rate of toxin removal?

A
  1. Higher blood flow rate and dialyser flow rate
  2. Higher efficiency dialyser (larger surgace area) KoA
  3. Longer time on dialysis, with diminishing returns
  4. Frequency of dialysis
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11
Q

What determines the rate of fluid removal?

A
  1. Higher transmembrane hydrostatic pressure
  2. Higher ultrafiltration coefficient (Kuf)
  3. Longer duration of dialysis
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12
Q

What is the definition of dry weight?
How to optimise fluid removal during haemodialysis?

A

Different definitions of dry weight:
1. Weight below which patients become hypotensive on dialysis.
2. Body weight at a physiologic extracellular volume state
3. Euvolaemic on minimal number of blood pressure medication

Dry weight varies over time with change in appetite, diarrhoea
Patient will typically gain 1-5% of body weight from fluid accumulation between dialysis session.

Optimisation of Fluid Status
1. By dry weight
2. US IVC diameter and their decrease on inspiration
3. Bioelectric impedence (BIS) - measures extracellular water, intracellular water and total body water
(difference between normal ECW and measured ECW is the overhydration volume)
4. Intradialyric haematocrit monitoring
5. Trends in NTproBNP (10,000-15,000 for adequate dialysis)

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13
Q

What are the measurements for dose of dialysis?

A
  1. Urea reduction ratio (URR)
    - Takes pre (C2) and post-dialysis (1) urea measurement
    - Disadvantage: does not take into account urea generation, urea removal by convention and contraction of total body water

URR (in %) = (C2-C1) x100 / C2

  1. Kt/V (single pool, equilibrated, standard or weekly)
    - Reflects small molecular clearance
    - K is the dialyser blood water urea clearance (L/hour)
    - t is the dialysis session length (hours)
    - V is the volume of distribution of urea (Litre)
    - Higher K and t and lower V result in higher ratio

For 3 times a week dialysis:
- spKt/V minimum 1.4 per session, minimum treatment time 3 hours
(PD dialysis aim Kt/V 1.7 - different method of calculation)

  1. Fluid status and dry weight
  2. Normalised protein catabolic rate (nPCR)
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14
Q

Why does urea rebound post-dialysis?
Optimal sampling of serum urea post-dialysis

A
  1. Access recirculation
  2. Cardiopulmonary recirculation
  3. Remote compartment rebound

Optimal sampling of serum urea post-dialysis
- Slow flow technique - turn off dialysate flow, blood pump slowed to 100mL/min for 15 seconds before obtaining sample from sampling port
- Alternatively: pump stopped, arterial and venous blood lines clamped prior to obtaining sample

(Nowadays mostly automated with machine urea spectrophotometry or algorithm to estimate Kt/V)

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15
Q

What are the factors that caused reduced dialysis dose / reduced Kt/V?

A

Compromised Urea Clearance
A. Patient related
1. Decreased effective time on dialysis
- Reduced blood flow rate
- Access clot
- Inadequate flow through vascular access

  1. Recirculation
    - Inadequate access
    - Stenosis, clotting of access

B. Staff related
1. Decreased effective time

  1. Decreased blood flow rate
    - Settings less than prescribed
    - Difficult cannulation
  2. Decreased dialysate flow rate
    - Settings less than prescribed or inappropriately set
  3. Dialyser - Inadequate quality control of “reuse”

C. Mechanical Problems
1. Dialyser clotting during reuse
2. Dialysate pump calibration error
3. Dialyser performance difference
4. Variability in blood tubing

Decreased Effective Time on Dialysis
A. Patient
1. Late start or early sign off - new symptoms or social reasons
2. Medical complications (hypotension)
3. No show

B. Staff
1. Late start
2. Time calculated incorrectly, on/off read incorrectly
3. Clinical deficiencies
4. Premature discontinuation - scheduling issue, emergencies
5. Incorrect assumptions of continuous treatment time
(did not account for repositioning needles, accidental removal)

C. Mechanical
1. Clotting of dialyser
2. Dialyser leaks
3. Machine malfunction

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16
Q

What are the common complications related symptoms during haemodialysis?

A
  1. Hypotension (intradialytic hypotension) (10-40%)
  2. Cramps (5-30%)
  3. Nausea and vomiting (5-10%)
  4. Headache (5-10%)
  5. Pruritus (1-5%)
  6. Chest pain (1-5%)
  7. Back pain (1-5%)
  8. Fever and chills (<1%)
17
Q

What are the features of intradialytic hypotension

A
  1. Often asymptomatic until BP dropped very low to potentially dangerous level
  2. Lightheadedness
  3. Dizziness
  4. Cramping
  5. Nausea

BP is monitored every 30-60 minutes during dialysis

18
Q

What are the causes of intradialytic hypotension?

A
  1. Volume-related
    - High UF
    - Incorrect low dry weight
    - Low sodium level in dialysate
  2. Inadequate vasoconstriction
    - Anti-hypertensive use prior to dialysis
    - Autonomic neuropathy
    - Dialysate tempereature higher than patient’s body temperature
    - Eating during dialysis
  3. Cardiac factors
    - Cardiac ischaemia, myocardial infarction
    - Heart failure
    - Arrhythmias
  4. Others
    - Dialyser reaction
    - Haemolysis
    - Severe anaemia
    - Air embolism
    - Septicaemia
    - Pericardial tamponade
19
Q

What are the management to minimise IDH?

A
  1. Re-assess dry weight regularly
  2. Avoid large fluid gains between dialysis sessions
  3. Fluid-restricted, low salt diet
  4. Increase dialysis treatment time to reduce hourly UF rate
  5. Decreasing dialysate temperature by 0.5 - 2 degree
  6. Avoid intradialytic food ingestion
  7. Midodrine (in patient without cardiac ischaemia)
    - Does not work if on alpha adrenergic blockers
20
Q

Dialysis dysequilibirium syndrome occurs in __ (levels __) subjected to prolonged haemodialysis session

Pathophysiology: acute increase in __ from abrupt decrease in __ causes movement of water from __ to __

Features:
Mild: __
Severe __

Management of severe DDS
Prevention of DDS

A

Acute uraemia (urea levels >53.5 mmol/L or > 150mg/dL)

Acute increase in brain water content, abrupt decrease in plasma tonicity, movement of water from plasma to brain tissue

Features
Mild: non-specific - restlessness, headache, nausea, vomiting
Severe: seizure, obtundation, coma

Management of severe DDS
1. Stop dialysis
2. Airway and breathing control
3. Consider IV mannitol

Prevention: short HD sessions on initiation (2 - 2.5 hours)

21
Q

What are the life-threatening complications that may occur during dialysis?

A
  1. Arrhythmias
  2. Myocardial infarction
  3. Pericardial effusion
  4. Seizures
  5. Intracranial bleeding
  6. Haemolysis
  7. Air embolism
22
Q

Anaphylactic dialyser reactions and management

A

Type A: anaphylactic reactions
- Causes: allergy to ethylene oxide, AN-69 membrane, contaminated dialysis solution, heparin, dialyser reuse
- Mild: watery eyes, sneezing, cough, abdominal cramps, diarrhoea, itch, urticaria
- Severe: dyspnoea, feeling of warmth, sense of impending catastrophe, cardiac arrest, death
- Onset: first few minutes of dialysis, or delayed more than 30 minutes
- Treatment: stop dialysis, clamp blood line, disconnect patient from circuit, discharge blood lines and dialyser without returning blood to patient. +/- anaphylaxis treatment

Type B: non-specific dialyser reactions
- Manifest as chest or back pain
- Onset: 20-60 minutes
- Treatment: supportive, use different dialyser

23
Q

Acute haemolysis may occur during HD due to __, __or __

Obstruction or narrowing of blood line due to __, __, __ in __ can cause haemolysis.

Dialysate issues such as __, __, __ can also cause haemolysis.

Contaminants such as __ in water supply, __ or __ to reuse dialysers or inadequate water treatment with excess __, __, __, __.

A

Blood tubing problems, needle problems, dialysate problems

Blood line kinks, manufacturer defect, small-gauge needles in high blood flow rates

Dialysate incorrect electrolyte concentration, too hot, contaminated with chemicals

Chloramine in water supply, formaldehyde or bleach to reuse dialyser
Excess fluoride, nitrate, zinc, copper

24
Q

How is haemolysis in HD detected and managed?

A

Blood in venous line turns port wine in colour
Plasma turns pink in centrifuged samples
Marked drop in Hb without obvious source of bleeding
Hyperkalaemia

Management
Stop dialysis immediately
Blood in dialyser and blood tubing discarded - marked elevated K (haemolysed from erythrocytes)
Treat hyperkalaemia

25
Q

How is air embolism detected and managed?

A

Manifestation depends on positioning
- Seated: air enters cerebral circulation
-> CNS events, LOC, death

  • Recumbent: air enters cardiopulmonary system
    -> Dyspnoea, cough, arrhythmias, chest tightness, acute cardiac and neurologic events

Management
- Immediate clamping of blood line, stop blood pump
- Place patient in recumbent position on left side with head and chest tilted downward
- Administer 100% oxygen by mask, KIV intubation

26
Q

Commonest cause of cardiac arrest in haemodialysis

A

Severe bradycardia

27
Q

Commonest cause of cardiac arrhythmias in haemodialysis

A

Atrial fibrillation

Risk of AF increases with decline in GFR, at least 10 fold in ESRF and on haemodialysis.

28
Q

Water processing for haemodialysis

A

Public water supply
|
Multimedia filter - removes organic materials
|
Carbon filter x2 - removes chloramine - which may acute haemolysis
|
Softener x2 - removes inorganic materials
|
Reverse osmosis machine

Water is checked at every stage to ensure adequate filtration and meeting quality.

Water is sampled for microorganisms by prolonged culture

29
Q

What should you suspect if patient is persistently above dry weight?

A
  1. Intradialysis issue reducing UF
    - Intradialytic hypotension, tachycardia
    - Cramps, chest pain
  2. Compliance to dialysis session
    - Missed dialysis, delinquency
  3. Poor control of interadialytic weight gain (IDWG)
    - Fluid indiscretion
  4. Change of appetite
    - Especially during first 2 years of dialysis, improvement in uraemia leads to improved appetite
30
Q

Types of AV fistula and its common complications

A
  1. Radiocephalic (RC) fistula - anastomosing side of radial artery to end of cephalic vein
    - Complications: JXA stenosis, poro maturation rate (2/3 fail)
    - First choice: lower rates of steal syndrome, preserves future option for proximal fistula
  2. Brachiocephalic (BC) fistula - anastomosing side of brachial artery to end of cephalic vein
    - Complications: cephalic arch stenosis
    - Preferred in DM or with macrovascular disease as better patency rate (distal vessels likely poor)
  3. Brachial-basilic transposition (BBT) fistula - anastomosing side of brachial artery to basilic vein, with basilic vein transposed laterally and elevated superficially (2 stage procedure)
    - Complications: proximal swing segment stenosis, thrombosis
    - Operative risks: high morbidity, site haematoma, wound infection, postoperative arm swelling
31
Q

What are the criterias of adequate haemodialysis? (5)

A

Achieves good control of:
1. Fluid status, BP and cardiovascular health
2. Electrolyte and acid base balance
3. Mineral bone disease
4. Adequate growth and nutrition
5. Quality of life

32
Q

Describe the urea kinetic model

A

Urea is distributed across patient’s total body water both intracellular and extracellular components

1. Urea distribution and movement
Urea is removed from intravascular space during HD,
- Extracellular space can achieve instantaneous equilibrium between extravascular and intravascular component
- Intracellular movement to extracellular limited by cellular transport

Thus intracellular urea equilibrisation with extracellular space occur up to 1 hour after end of HD

2. Urea generation
Urea increases steadily after HD due to protein intake
Amount of urea generation between dialysis treatmetns can be used to calculate nPCR

33
Q

Safe UF rate (mL/kg/hr)

A

12-13mL/kg/hr

Total UF / (kg x duration) (in hour)

Nephrology (9 decks)

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