RRT IN
CRITICALLY ILL
When?
How?
How much?
A 43 year old male presented to emergency
department with confusion
 History
 Recurrent attacks of difficulty in passing urine ,
urine volume was decreasing over the last
month together with sever burning sensation.
 Recurrent attacks of fever during the last 2
weeks with incomplete antibiotic courses.
 History of acute lumbar disc prolapse with
severe back ache & heavy use of analgesics (
diclofenac, ketorlac, feldine……) over the last 3
months.
On examination
 Vitals: BP







80/50 mmHg
HR
135 bpm, regular
Temp.
35˚C
RR
30/ min.
Cold ,pale peripheral extremities
Delayed capillary filling
Weak peripheral pulsations
Chest exam.: Bilateral harsh vesicular breathing
bilateral fine basal crepetation
Pupils equal medium size & reactive
No lateralizing manifestation
Patient is confused, not cooperative, not communicating
Laboratory data
Complete blood count (CBC)
 Hemoglobin (g/dl) 10.5
Hematocrit (%) 29
 Platelet count 86,000
 WBC (cells/ml) 20,000
Segmented neutrophils 85%
Band forms
10%
Chemistry
 BUN (mg/dl)






60
Creatinine (mg/dl)
7.5
Lactic acid (meq/L)
7
Potassium (mEq/L )
5.9
Sodium(mEq/L)
132
Magnesium (mEq/L) 3
Phosphorous (mg/dL)
4.5
Arterial Blood Gases





pH 7.27
pCO2 30
pO2 58
HCO3 15
O2 Sat % 93
Urine analysis
Leukocytes
Nitrite
100 HPF
+ve
Imaging
 CXR
 Renal US
hilar congestive shadow
Normal appearance
 What is your diagnosis?
 What is your first line of treatment?
 What further investigation would you
like to request?
 would you like to consult other
specialty(s)?
Management
 Patient admitted to ICU & put on mechanical
ventilation
 Central line was inserted, CVP measured, it was
12 cm H2O. IV crystalloid was initiated guided by
CVP
 Arterial line was inserted & invasive blood
pressure was monitored. BP was 75/40mmHg
 Noradrenalin infusion was started at rate of 150
nanogram /kg/ min.
 Foly’s catheter was inserted , only 20 ml of urine
was there
 Anti biotic was started empirically based on
Antibiotic protocol for treatment of
community acquired UTI ( 4th generation
Cephalosporin started with renal adjustment
of the dose)
 Sepsis screening done as blood & urine
culture was send to microbiology lab.
 Would you initiate any RRT for
this patient?
 Why?
 What type of RRT would you use?
 Nephrologist was consulted & he
recommended initiation of CRRT in the form
of CVVHDF
 CVVHDF was started through RT femoral
venous catheter
 Forty-eight hours after CRRT was started,
patient’s potassium level was 3.5, his
creatinine level was 6.3, and his BUN was 57.
Potassium was added to his intravenous
fluids and his electrolytes continued to trend
toward normal.
After five days of the initiation of
antibiotic, patient’s sepsis was slowly
resolving and he was weaned from both
the ventilator and his vasoactive drips.
IV antibiotics were continued until day 14
of hospitalization.
patient’s renal function returned and he
was discharged from the hospital on day
18
Acute renal failure and renal
replacement therapy in the ICU
 Acute renal failure (ARF) is a sudden and
sustained fall in the glomerular filtration rate
(GFR) associated with a loss of excretory
function and the accumulation of metabolic
waste products and water.
 It leads to rising serum urea and creatinine,
usually with a fall in urine output.
 Up to 10% of all patients admitted to the ICU
receive some form of renal replacement
therapy.
Types of RRT
 RRT classified according to the intended
duration of each treatment (intermittent vs
continuous) and, in the case of continuous,
both the access (arterial vs venous) and the
circuit type (dialysis vs filtration).
 CRRT usually involves the removal and return
of blood through a single cannula placed in a
large vein (venovenous therapy),
arteriovenous Haemofiltration is of historical
interest only.
Intermittent VS
continuous
Venous VS arterial
Dialysis Vs filtration
When?
 Intravascular volume overload unresponsive to
diuretic therapy;
 Hyperkalemia refractory to medical
management.
 Severe metabolic acidosis.
 Persistent oliguria or anuria, unresponsive to
volume administration.
 Overt uremic symptoms (encephalopathy,
pericarditis, bleeding diathesis); and
 Progressive azotemia in the absence of specific
symptoms.
Important considerations
 There is still no generally accepted azotemia
threshold for when to start RRT.
 A better term is acute kidney support as it is
analogous to mechanical ventilatory support;
 Therapy should be considered in patients
with marked impairment in organ function
and not limited to patients with complete
failure.
 There is consensus that therapy should begin
before complications develop.
How?
 What is renal replacement therapy?
There are two main physical processes that are
employed to carry out the kidneys' function of
the removal of solute and water from the body
and thereby maintain a steady state:
* Haemofiltration
* Haemodilaysis
 Renal replacement systems may rely
predominantly on Haemofiltration (convection)
or haemodialysis (diffusion) but there are also
systems that combine the two methods.
Haemofiltration process
 Convection describes a process by which
solutes are transported across a
semipermeable membrane together with the
solvent by means of filtration driven by a
trans-membrane pressure gradient
 Convection removes middle molecular
weight proteins of 5000–50,000 Da.
The transmembrane pressure existing from one side of the hemofilter to the other
leads to the passage of solvent (plasma water), bringing with it the passive flow of
solutes it contains.
 Many of the septic mediators (e.g. cytokines,
complement) lie within this group. These
mediators are absorbed onto the filter
membrane and so removed.
 Interest surrounds the use of high volume
Haemofiltration to remove these inflammatory
mediators to improve outcome from severe
sepsis.
 High volume filtration is defined as
ultrafiltration of over than 2 liters/hour, and there
is evidence that filtrate volumes up to 6
liters/hour are associated with a significantly
lower mortality in septic patients.
Haemodialysis process
 Diffusion describes a process passive transport
of solute across a semi-permeable membrane
driven by a concentration gradient such that the
solute will tend to an equal concentration in the
available distribution space on both sides of the
membrane ( from blood to dialysate)
 Blood flow and dialysate flow rates are set in
order to obtain the best compromise between
maximum diffusion and good hemodynamic
tolerance.
The conventional dialysate flow rate is about 500 mL/min
and the blood flow rate is about 300 to 500 mL/min.
Diagram of a haemodialysis circuit. In green: dialysate. In yellow:
used dialysate.
 Hemodialysis allows the passage of small
molecules (with molecular weights of 500 to
5,000 Da) from blood to dialysate.
 Therefore, it allows the removal of many
metabolic waste products and can maintain
good electrolytic homeostasis.
 The main side effect of IHD is the possibility of
poor hemodynamic tolerance
 Sustained, low-efficiency dialysis (SLED) and
continuous haemodialysis are sub-modalities in
which the duration of dialysis is extended (6 to
12 h or even 24 h), allowing for more gradual
removal of solutes and fluid and hence better
hemodynamic tolerance.
Haemodiafilteration
Diagram of continuous Haemofiltration. In
yellow: ultrafiltrate. In pink: replacement
fluid (post dilution).
Diagram of continuous
heamodiafiltration. In green: dialysate. In
pink: replacement fluid (postdilution). In
yellow: ultrafiltrate plus used dialysate
Why CRRT?
 Reduces hemodynamic instability preventing
secondary ischemia
 Acid base balance
 Electrolyte management
 Allows for improved provision of nutritional
support
 Management of sepsis/plasma cytokine filter
 Safer for patients with head injuries
 Probable advantage in terms of renal recovery
Intermittent Vs continuous
How much?
 For continuous haemofiltration, intensity can be
more readily quantified by the ultrafiltration flow
rate, commonly expressed as ml/kg/h of
ultrafiltrate. Early results from single-center
trials showed that increasing the ultrafiltration
rate was associated with improved survival in
critically ill patients with AKI.
 25 to 30 ml/kg/h be prescribed in the hopes of
achieving the 19 and 22 ml/kg/h is recommended
Dose of CRRT
 Dose = amount of solute clearance
 CRRT
= Effluent flow
 Monitor
 Time-averaged serum urea
Dialysis dose: One size
does not fit all!
 Modifications required based on:
 Protein catabolic rate
 Patient weight
 Interruptions
 Recirculation
Complications
 Circuit and haemofilter thromboses lead to reduced
efficiency of the RRT and possible blood loss.
 During a haemodialysis session, back-diffusion can
be observed if the transmembrane pressure
becomes negative. It means that molecules pass
from the dialysate to the blood compartment. It is
necessary to provide a minimum ultrafiltration flow
rate across the membrane to avoid this
phenomenon.
 The use of heparin can be responsible for bleeding
and heparin-induced thrombocytopenia.
 Poor hemodynamic tolerance may occur. The
main causes include rapid solute removal (IHD)
and hypovolemia induced by the removal of
plasma water from the blood compartment. The
preservation of a relative hemodynamic stability
during the RRT session is probably the most
difficult goal to achieve. Recurrent episodes of
hypotension must be avoided because they can
perpetuate organ injury and likely delay renal
recovery.
 Numerous complications are linked to the use of
the catheter. Depending on the venous site
(femoral, subclavian, or internal jugular),
complications of catheter insertion include
arterial puncture, local bleeding, hematoma,
pneumothorax, hemothorax, retroperitoneal
bleeding, or cardiac arrhythmia. The use of
guided insertion procedures, such as ultrasound,
has reduced both the incidence of these
complications and the rate of catheter insertion
failure. Once inserted, catheters may also result
in several mechanical problems (eg,
malpositioning), thrombosis, and infections.
Drug removal/dosing
Factors to consider
 Drug Molecular Weight
 Volume of distribution
 Protein binding
 Ionic charge
 AN 69 cut-off 56,000 Daltons
 Solute with a molecular weight > 56,000 will not be removed
 Urea= 60
 Creatinine=117
 Albumin=62 000
 Vancomycin=1449
Special Attention
 Close management of laboratory values:
 Potassium
 Phosphate
 Magnesium
 Nutritional assessment due to amino acid and
other nutrient losses during CRRT
 Hypothermia