Fluid management in surgical patients

BASICS OF FLUID
MANAGEMENT IN
SURGICAL PATIENTS
DEPT OF UROLOGY
GOVT ROYAPETTAH HOSPITAL AND KILPAUK MEDICAL COLLEGE
CHENNAI

Moderators:
Professors:
 Prof. Dr. G. Sivasankar, M.S., M.Ch.,
 Prof. Dr. A. Senthilvel, M.S., M.Ch.,
Asst Professors:
 Dr. J. Sivabalan, M.S., M.Ch.,
 Dr. R. Bhargavi, M.S., M.Ch.,
 Dr. S. Raju, M.S., M.Ch.,
 Dr. K. Muthurathinam, M.S., M.Ch.,
 Dr. D. Tamilselvan, M.S., M.Ch.,
 Dr. K. Senthilkumar, M.S., M.Ch.
Dept of Urology, GRH and KMC, Chennai.
2

TOTAL BODY WATER DISTRIBUTION
 Total body water (TBW) - 60% of body weight
 ICF – 2/3rd
 ECF – 1/3rd
3

ELECTRONEUTRALITY
4

NORMAL WATER BALANCE
INTAKE
 Oral or IV fluid intake
 Insensible fluid input = 300ml water due to
oxidation
OUTPUT
 Urine output
 Insensible fluid loss
 Skin = 500 ml
 Lung = 400 ml
 Intestine = 100 ml
NORMAL DAILY INSENSIBLE FLUID LOSS = 1000 – 300 ML = 700 ML
NORMAL DAILY FLUID REQUIREMENT = URINE OUTPUT + 700 ML
5

VARIATIONS IN FLUID CALCULATION
 Main reason – variability in the amount of fat tissue
 The variability of TBW related to body weight is about 45%–70%
 Ideal for fluid management - Lean body mass, rather than total body weight.
 Women have somewhat lower TBW in relation to body weight due to more subcutaneous fat.
 With increasing age TBW decreases, mainly reflecting tissue atrophy (cell mass reduction).
6

FLUID CALCULATION BASED ON
BODY WEIGHT
 1000 mL for the first 10 kg actual body weight
 +50 mL fluid/kg for the next 10 kg actual body weight (or 1500 mL for the first 20 kg of
body weight)
 +15 mL fluid/kg for each additional kg over 20 kg (add this to the base of 1500 mL)
 This formula can be used for older adults who are normal weight, underweight, or
overweight.
7

RATE OF FLUID ADMINISTRATION
ROUTINE IV SET
 RATE OF FLUID MAINTANENCE:
 Volume in Litres /24 hrs x 10 = Drops rate / min
 Ex: 3 Litres/24 hrs → 30 drops /min
 EFFECTIVE RATE OF FLUID REPLACEMENT /
HOUR :
 50 -100ML +
 Urine output / hour +
 Ongoing losses / hour
 Volume in ml/hr / 4 = Drops rate / min
 Ex: Fluid replacement 100 ml/hr → 25 drops /min
MICRODRIP SET
 Volume in ml / hr = drops / min
Routine IV set →15 drops = 1ml
Microdrip set → 60 drops = 1ml
8

TYPES FLUID THERAPY
 RESUSCITATION
 REPLACEMENT
 MAINTANENCE
9

MAINTANENCE
 25–30 ml/kg/day of water and
 approximately 1 mmol/kg/day of potassium, sodium and chloride and
 approximately 50–100 g/day of glucose to limit starvation ketosis
 Replaces fluid lost from lungs, skin, urine and faeces
 Losses are poor in salt
 Maintenance fluid should be hypotonic to plasma sodium
 Routinely used : 5% D, Dextrose with 0.45%NaCl
10

RESUSCITATION
 If patients need IV fluid resuscitation, use crystalloids that contain sodium in the range
130–154 mmol/l, with a bolus of 500 ml over less than 15 minutes
 Balanced crystalloids are the fluids of choice for fluid resuscitation in the perioperative
setting, and the use of 0.9% saline should be reserved for specific conditions such as
treatment of hypochloremic metabolic alkalosis.
11

REPLACEMENT FOR
ONGOING LOSSES
CALCULATION OF FLUID REPLACEMENT
• To correct body fluid deficit caused
by ongoing fluid loss
• Commonly used : Isotonic saline, DNS,
RL, Isolyte M, P and G
12

PARAMETERS FOR ASSESSING
ADEQUATE FLUID REPLACEMENT
 Regaining weight loss due to fluid loss
 Skin – Warm extremities, normal elasticity, moist tongue
 Urine output : >30-50ml/hr in adults or 0.5 – 1.0 ml/kg/hr in children
 Pulse rate, BP, Decreasing hematocrit
 Blood urea and serum creatinine will be normal
 Urinary sodium excretion >25mEq/L
 Normal ABG, CVP, PAWP
13

14

INTRAVENOUS FLUIDS
CRYSTALLOIDS
 Water + Electrolytes
 Expands intravascular volume to a lesser
degree than colloids.
 Replenishes interstitial compartment
 Leaves intravascular space faster - T ½ 20-30
min.)
 Less antigenic as compared to colloids
COLLOIDS
 Volume expanders
 Antigencity present – Anaphylactic Reaction
may occur
 Never exceed 1-1.5ltr / day (20ml/kg / day)
 Expands intravascular volume more than
crystalloids
15

0.9% NaCl
 Contains 154 mmol/L each of sodium and chloride
 100 ml contains 0.9 gms of NaCl
 Indications:
 Water & salt depletion ( diarrhoea, vomiting, excessive diuresis or perspiration)
 Hypovolemic shock
 Alkalosis with dehydration
 Initial fluid therapy in DKA
 Contraindications:
 CHF, Renal disease, Cirrhosis
 Dehydration with severe hypokalemia
 Higher concentration of chloride → hyperchloremia metabolic acidosis both in healthy volunteers and surgical
patients
 Hyperchloremia has also been associated with decreased renal blood flow and glomerular filtration rate
16

RINGER’S LACTATE
INDICATIONS
 Severe hypovolemia
 Replacing fluid in postoperative patients,
burns, fractures
 Diarrhoea induced hypokalemic metabolic
acidosis
 For maintaining normal ECF fluid and
electrolyte balance during and after surgery
CONTRAINDICATIONS
 Liver disease, severe hypoxia, shock – lactate
metabolism is severely impaired → lactic
acidosis
 CHF, Addison’s disease
 Vomiting / continuous NGA (hypovolemia
with metabolic alkalosis)
 Along with blood transfusion (calcium binds
with citrate anticoagulant)
ONE LITRE = Na+ -130; K+-4; CHLORIDE – 109; CALCIUM – 3; BICARBONATE – 28 mEq
17

5% DEXTROSE – BEST AGENT FOR INTRACELLULAR DEHYRDATION
INDICATIONS
 Dehydration due to inadequate water intake or
excessive water loss
 Pre & postoperative fluid replacement
 Provide adequate calories
 Treatment and prevention of ketosis in
starvation, diarrhea, vomiting and high grade
fever
 Correction of hypernatremia due to pure water
loss
CONTRAINDICATIONS
 Cerebral edema
 Neurosurgical procedures
 Hypovolemic shock
 Hyponatremia & water intoxication
 Blood transfusion
 Uncontrolled diabetes & severe
hyperglycemia
ONE LITRE = WATER + 50 GMS OF GLUCOSE
18

5% DEXTROSE WITH 0.45% NaCl
INDICATIONS
 Fluid therapy in pediatrics
 Sever hypernatremia (gradual correction –
avoids cerebral edema)
 Maintanence fluid therapy
 Early postoperative period
CONTRAINDICATIONS
 Hyponatremia
 Severe dehydration due to diarrhea and
vomiting
[when there is requirement of larger salt
replacement]
ONE LITRE = 77 mEq OF SODIUM AND CHLORIDE + 50 GMS OF DEXTROSE
19

DNS [5%DEXTROSE+0.9%NaCl]
INDICATIONS
 Correction of salt depletion and hypovolemia
with supply of energy
 Correction of vomiting or nasogastric
aspiration induced alkalosis and
hypochloremia
 Compatible with blood transfusion
CONTRAINDICATIONS
 Cardiac, hepatic, renal failure
 Hypovolemic shock [hyperglycemia &
osmotic diuresis → aggravates fluid deficit]
ONE LITRE = 154 mEq OF SODIUM AND CHLORIDE + 50 GMS OF DEXTROSE
20

COMPOSITION ISOLYTE G (Gastric
replacement
solution)
ISOLYTE M
(Maintenance
solution with 5%D)
ISOLYTE P (Pediatric
Maintenance fluid)
ISOLYTE E
(Extracellular
replacement fluid)
GLUCOSE (gms) 50 50 50 50
Sodium (mEq) 65 40 25 140
Potassium (mEq) 17 35 20 10
Chloride (mEq) 150 38 22 103
Other Ammonium - 69 Phosphate -15
Acetate – 20
Acetate – 23
Phosphate – 3
Magnesium – 3
Acetate – 47
Calcium - 5
Magnesium -3
Citrate - 8
INDICATIONS Replace gastric
juice loss,
Metabolic alkalosis
Maintenance fluid
Hypokalemia
Pediatric
maintenance fluid,
Diabetes insipidus
Diarrhoea,
Metabolic acidosis,
maintenance of
ECF volume
CONTRAINDICATIO
NS
Hepatic failure,
Renal failure,
Metabolic
acidosis, severe
vomiting with
shock
Renal failure,
hyponatremia,
water intoxication,
Adrenocortical
insufficiency, Burns
Hyponatremia,
renal failure,
Hypovolemic
shock
Vomiting, NGA,
Metabolic alkalosis
21

HYPERTONIC CRYSTALLOIDS
1. 3% NaCl (hypertonic saline)
Na+ 513 mEq/L, Cl- 513 mEq/L (1026 mOsm/L)
2. 5% NaCl (hypertonic solution)
Na+ 855 mEq/L, Cl- 855 mEq/L (1710 mOsm/L)
 Used to increase ECF volume, decrease cellular swelling
 Used only in critical situations to treat hyponatremia (<115mEq/L)
 Must be administered slowly because it can cause intravascular volume overload and
pulmonary edema
 Supplies no calories
22

CHARACTERISTICS OF IV FLUIDS
CHARACTERISTIC TYPE OF FLUIDS
Most physiological RL
Rich in sodium 0.9%NS, DNS
Rich in chloride 0.9%NS, DNS, Isolyte-G
Rich in potassium Isolyte M, P and G
Corrects acidosis RL, IsolyteE, P & M
Corrects alkalosis Isolyte G
Cautious use in renal failure RL, Isolyte M, G, P & E
Avoided in liver failure RL, Isolyte G
Glucose free RL, NS
Sodium free 5%, 10%, 20%, 25%, Dextrose
Potassium free NS, DNS, Dextrose solutions
23

COLLOIDS
 Macromolecules retained within the vascular system → Plasma volume expanders
 Characteristics of IV colloid fluids per 100 ml infusion
TYPE OF FLUID EFFECTIVE PLASMA
VOLUME EXPANSION (ml)
DURATION OF
EXPANSION (Hrs)
5% ALBUMIN 70 – 130 16
25% ALBUMIN 400 – 500 16
6% HETASTARCH 100 -130 24
10% PENTASTARCH 150 8
10% DEXTRAN 40 100 – 150 6
6% DEXTRAN 70 80 12
24

COLLOIDS
 Contain both electrolytes and large organic macromolecules (usually >40 kDa)
 Increased endothelial permeability in critically ill patients may accelerate movement into the interstitial
space, thereby reducing the efficacy of volume expansion, increasing tissue edema, and potentially
promoting end-organ damage.
 Almost all colloid solutions have an osmolality similar to that of plasma. However, colloid osmotic (oncotic)
pressure, which represents a small percentage of osmolality, varies greatly.
 Sodium content, the primary cationic determinant of osmolality, of commercially available colloid solutions
is similar to that of crystalloid solutions, while the potassium, chloride, and calcium concentrations differ.
25

COLLOIDS
 The physiological actions, volume expansion properties, and potential morbidities of these solutions are
determined by multiple factors, including oncotic pressure, molecular weight, plasma half-life, metabolism,
and tissue accumulation
 The plasma half-life of a colloid depends on its molecular weight, elimination route, and function of the
metabolizing or excreting organ.
 The molecular weight mainly determines the degree of volume expansion, whereas intravascular
persistence is determined by elimination.
 When compared to crystalloids, colloids induce greater PV expansion for the same administered volume.
26

27

28

PERIOPERATIVE FLUID
MANAGEMENT
 The factors that determine an appropriate dose of perioperative fluid:
 preoperative physical status of a patient
 anesthetic administration
 use of positive pressure ventilation
 surgical circumstances, especially the type and duration of the surgery and expected blood loss.
 Aim of intraoperative fluid therapy – to maintain an adequate circulating volume to
ensure end-organ perfusion and oxygen delivery to the tissues.
29

PERIOPERATIVE FLUID MANAGEMENT
 Traditional fluid therapy was based on four now-controversial pathophysiologic assumptions:
1. Preoperative fasting results in hypovolemia because of ongoing insensible losses.
2. Evaporative losses increase when surgery compromises the dermal barrier.
3. Surgery-induced fluid shifts into a “third space” require generous replacement.
4. Moderate hypervolemia is well tolerated because the kidneys regulate the overload
 Recent studies of perioperative fluid management challenge those concepts and suggest that
significant benefit can be achieved by individualizing therapy based on patient responses
 Both under-resuscitation and over-resuscitation can have deleterious effects and lead to
increased morbidity and mortality
30

GUIDELINES FOR PREOPERATIVE
FASTING
 The Practice Guidelines for Preoperative Fasting published by the American Society of
Anesthesiologists recommends
 minimum fasting period of 2 hours for clear liquids
 4 hours for breast milk
 6 hours for a light meal
 These recommendations were based on meta-analysis of randomized controlled trials that
show smaller gastric volumes and increased gastric pH in patients who are given clear
fluids 2–4 hours preoperatively versus fluids greater than 4 hours preoperatively
31

PREOPERATIVE FLUID THERAPY
 CORRECTION OF HYPOVOLEMIA - Isotonic NS, RL, colloids, whole blood
 CORRECTION OF ANEMIA – Packed cell is preferred to avoid volume overload
 CORRECTION OF ELECTROLYTE ABNORMALITIES
 REPLACEMENT = FLUID DEFICIT + MAINTENANCE FLUID REQUIREMENT
DEHYDRATION FEATURES FLUID DEFICIT
MILD Thirst, concentrated urine 4% OF BODY WEIGHT
MODERATE Dizziness, weakness, oliguria (<400ml/day),
postural hypotension >20 mmHg, Low JVP
6-8%
SEVERE Confusion, stupor, systolic BP <100 mmHg,
tachycardia, low pulse volume, cold
extremities, poor capillary return, reduced skin
turgor
10%
32

INTRAOPERATIVE FLUID THERAPY
Volume of fluid replacement
1. Correction of fluid deficit due to starvation =
duration of starvation (hrs) X 2ml /kg BW
2. Maintenance during intraoperative period =
duration of surgery (hrs) x 2ml /kg BW
3. Fluid loss – dissection / hemorrhage
Ex: 50 kg male, NPO for 10 hrs, appendectomy (1hr)
Fluid requirement during intraoperative period =
(10x2x50) + (1x2x50) + (6x50x1) = 1400ml
Types of
surgery
Examples Fluid loss
(ml/kg/hr)
Least trauma Opthalmic
surgery,
cystoscopy
Nil
Minimal trauma Tonsillectomy,
plastic surgeries
4
Moderate
trauma
Hernia repair,
appendectom
y, etc
6
Severe trauma Intestinal
resection,
radical
surgeries, THR
10
33

POSTOPERATIVE FLUID THERAPY
 GOALS
 To maintain BP >100/70 mmHg
 Pulse rate <120/min
 Hourly urine output – 30 – 50ml
 Normal temperature, warm skin, normal respiration and sensorium.
34

ROUTINE POSTOPERATIV FLUID
MANAGEMENT IN NORMAL
INDIVIDUAL
 In NPO patients
 First 24 hours of surgery : 2L 5% dextrose or 1.5 L 5% dextrose + 500 ml isotonic saline
 Increased ADH & Aldosterone secretion due to stress response
 Low volume, less salt maintenance
 Exceptions: salt losing nephropathy, head injury, to replace NGA/drain output, major surgery to replace third space loss
 II POD : 2L 5% dextrose + 1 L of 0.9% saline
 Tissue trauma, blood transfusion, postoperative metabolic acidosis → potassium release
 III POD : Similar to II POD + 40-60 mEq potassium per day
35

 Maintenance fluids at a steady rate over 24 hours period
 Replacement
 Prolonged vomiting / NGA → Normal saline; After initial 2 days – Isolyte G
 Loss of blood → less volume – 3 times volume of isotonic saline or Ringer’s lactate; Greater –
blood products
 Small bowel fistulas / diarrhea → Ringer’s lactate with additional bicarbonate
36

UNIVERSAL RECOMMENDATIONS IN
PERIOPERATIVE FLUID
MANAGEMENT
37

RECOMMENDATIONS
Because of the risk of inducing hyperchloraemic acidosis in routine practice, when
crystalloid resuscitation or replacement is indicated, balanced salt solutions e.g. Ringer’s
lactate/acetate or Hartmann’s solution should replace 0.9% saline, except in cases of
hypochloraemia e.g. from vomiting or gastric drainage.
38

Solutions such as 4%/0.18% dextrose/saline and 5% dextrose are important sources of free
water for maintenance, but should be used with caution as excessive amounts may cause
dangerous hyponatraemia, especially in children and the elderly. These solutions are not
appropriate for resuscitation or replacement therapy except in conditions of significant
free water deficit e.g. diabetes insipidus.
39

To meet maintenance requirements, adult patients should receive sodium 50-100
mmol/day, potassium 40-80 mmol/day in 1.5-2.5 litres of water by the oral, enteral or
parenteral route (or a combination of routes). Additional amounts should only be given to
correct deficit or continuing losses. Careful monitoring should be undertaken using
clinical examination, fluid balance charts, and regular weighing when possible.
40

In patients without disorders of gastric emptying undergoing elective surgery clear non-
particulate oral fluids should not be withheld for more than two hours prior to the
induction of anaesthesia.
41

In the absence of disorders of gastric emptying or diabetes, preoperative administration of
carbohydrate rich beverages 2-3 h before induction of anaesthesia may improve patient
well being and facilitate recovery from surgery. It should be considered in the routine
preoperative preparation for elective surgery.
42

 Routine use of preoperative mechanical bowel preparation is not beneficial and may
complicate intra and postoperative management of fluid and electrolyte balance. Its use
should therefore be avoided whenever possible.
 Where mechanical bowel preparation is used, fluid and electrolyte derangements
commonly occur and should be corrected by simultaneous intravenous fluid therapy
with Hartmann’s or Ringer-Lactate/acetate type solutions.
43

 Excessive losses from gastric aspiration/vomiting should be treated preoperatively with
an appropriate crystalloid solution which includes an appropriate potassium
supplement. Hypochloraemia is an indication for the use of 0.9% saline, with sufficient
additions of potassium and care not to produce sodium overload.
 Losses from diarrhoea/ileostomy/small bowel fistula/ileus/obstruction should be
replaced volume for volume with Hartmann’s or Ringer-Lactate/acetate type solutions.
 “Saline depletion,” for example due to excessive diuretic exposure, is best managed
with a balanced electrolyte solution such as Hartmann's.
44

 In high risk surgical patients preoperative treatment with intravenous fluid and inotropes should be
aimed at achieving predetermined goals for cardiac output and oxygen delivery as this may improve
survival.
 Preoperative or operative hypovolaemia should be diagnosed by flow-based measurements wherever
possible.
 The clinical context should also be taken into account as this will provide an important indication of
whether hypovolaemia is possible or likely. When direct flow measurements are not possible,
hypovolaemia will be diagnosed clinically on the basis of pulse, peripheral perfusion and capillary
refill, venous (JVP/CVP) pressure and Glasgow Coma Scale together with acid-base and lactate
measurements.
 A low urine output can be misleading and needs to be interpreted in the context of the patient’s
cardiovascular parameters above.
45

 Hypovolaemia due predominantly to blood loss should be treated with either a balanced
crystalloid solution or a suitable colloid until packed red cells are available.
 Hypovolaemia due to severe inflammation such as infection, peritonitis, pancreatitis or
burns should be treated with either a suitable colloid or a balanced crystalloid.
 In either clinical scenario, care must be taken to administer sufficient balanced
crystalloid and colloid to normalise haemodynamic parameters and minimise overload.
 The ability of critically ill patients to excrete excess sodium and water is compromised,
placing them at risk of severe interstitial oedema. The administration of large volumes
of colloid without sufficient free water (e.g. 5% dextrose) may precipitate a
hyperoncotic state.
46

POSTOPERATIVE RECOMMENDATIONS
 In patients who are euvolaemic and haemodynamically stable a return to oral fluid
administration should be achieved as soon as possible
 In patients requiring continuing i.v. maintenance fluids, these should be sodium poor
and of low enough volume until the patient has returned their sodium and fluid
balance over the perioperative period to zero. When this has been achieved the i.v. fluid
volume and content should be those required for daily maintenance and replacement of
any on-going additional losses.
 The haemodynamic and fluid status of those patients who fail to excrete their
perioperative sodium load, and especially whose urine sodium concentration is
<20mmol/L, should be reviewed.
47

SPECIAL SITUATIONS IN UROLOGY
48

AKI
 Higher molecular weight hydroxyethyl starch (hetastarch and pentastarch MW ≥ 200 kDa) should be avoided in
patients with severe sepsis due to an increased risk of AKI and in brain dead kidney donors due to reports of osmotic
nephrosis like lesions.
 Balanced electrolyte solutions containing potassium can be used cautiously in patients with AKI closely monitored on
HDU or ICU in preference to 0.9% saline.
 If free water is required 5% dextrose or dextrose saline should be used.
 Patients developing hyperkalaemia or progressive AKI should be switched to non potassium containing crystalloid
solutions such as 0.45% saline or 4%/0.18 dextrose/saline
49

RENAL TRANSPLANT
 Balanced salt solutions that contain potassium have been considered hazardous for
patients with renal failure, diabetic ketoacidosis, and those undergoing renal
transplantation surgery.
 However, the low concentration of potassium in balanced salt solutions, ~4.0 mEq/L, is
small in comparison to total body potassium stores exceeding 4,200 mEq in a 70-kg
adult.
 A randomized controlled trial comparing 0.9% saline to lactated Ringer’s solution in 51
patients undergoing renal transplant surgery demonstrated more frequent clinically
significant hyperkalemia (29% vs. 0%; P < 0.05) and metabolic acidosis (31% vs. 0%; P
< 0.04) in patients receiving saline, presumably because the acidemia produced by 0.9%
saline caused movement of potassium from intracellular to extracellular fluid
50

FLUID MANAGEMENT IN DONOR
 Preoperative hydration - 100 ml/hr crystalloids starting from 2200 the night before surgery
 IV bolus colloids 5ml/kg before induction
 Start Mannitol infusion 0.5 g/kg after induction up to the time of nephrectomy
 Intra-operative infusion of 20ml/kg/hr crystalloids
 Target MAP of normal or plus 20% of patient’s normal
 IV bolus colloids 5ml/kg before institution of pneumo-peritoneum in laparascopic donor
nephrectomy
 If suggested infusion volumes are unable to improve Perfusion Pressures, low dose Dopamine
infusion (1-2 ug/kg/min) should be initiated
 Aim for urine output of at least 100 ml/hr
51

FLUID MANAGEMENT IN RECIPIENT
 Infusion of non-potassium containing crystalloids is to be initiated
 Goals of therapy include:
 CVP > 12-15 mmHg (7-9 mmHg for restrictive heart disease)
 Systolic BP of > 130
 Mean Arterial BP of > 80
 Total IV fluids of at least 30-50 ml/kg/hr
 Graft turgidity (250 ml of crystalloids initial bolus and assess; further boluses if required until
turgidity improves)
 Serial monitoring of acid base and electrolyte status
 Mixtures of Ringers Lactate or Balanced Crystalloids may be required if worsening
acidosis is seen with large volumes of saline
52

FLUID MANAGEMENT IN RECIPIENT
 In refractory hypotension, not responsive to crystalloid load (especially after induction
and after reperfusion) colloids may be used to optimize intravascular volume
 Vasopressors to be used ONLY after volume therapy has been optimized. Boluses of
ephedrine or phenylephrine may be given for refractory hypotension during initial stages
PRIOR to transplantation
 IV infusion of 20% Mannitol 0.5g/kg to be initiated 30 minutes prior to unclamping
 Total intra-operative fluid administration should be about 30-50ml/kg/hr
53

POST TRANSPLANT FLUID
MANAGEMENT
 Polyuria in the period immediately following the renal transplantation is a transient
phenomenon, and it usually represents the first sign of progressive recovery of the kidney
function.
 Usually 5–8 L/day and decreases within a few days to normal levels without therapeutic
intervention
 The fluid management starts by replacing the daily insensible losses for the next 24 hours
with dextrose and sodium solution.
 The urinary output volume should be monitored and replaced hourly saline, Ringer's
lactate solutions
 Electrolyte monitoring (4-6 hours on the first day)
URINE
OUTPUR /
HR
IV FLUID
PER HOUR
Upto 300
mL
Replace
100% of
urine
output
301-500
mL
Replace
80% of
urine
output
Greater
than 500
ml
Replace
60% of
urine
output
54

OBSTRUCTIVE UROPATHY
55

PATHOPHYSIOLOGY OF URINARY
TRACT OBSTRUCTION
 The degree of injury to the kidney and the effect on overall renal function depends on the
 severity of the obstruction (partial or complete, unilateral or bilateral)
 chronicity of the obstruction (acute vs. chronic)
 baseline condition of the kidneys
 presence of other mitigating factors such as urinary tract infection (UTI).
 The histologic derangements associated with obstruction are localized primarily to the
interstitial compartment of the kidney and include massive tubular dilation, progressive
interstitial fibrosis, and a loss in renal mass secondary to apoptotic cell death →
collectively referred to as obstructive nephropathy
56

CAUSES FOR OBSTRUCTIVE
UROPATHY
57

HEMODYNAMIC CHANGES WITH
OBSTRUCTION
 GLOMERULAR FILTRATION RATE
 GFR = Kf (PGC − PT − GC)
 Kf is a glomerular ultrafiltration coefficient related to the surface area and permeability of the capillary membrane
 PGC - glomerular capillary pressure, which is influenced by both renal plasma flow (RPF) and the resistance of the
afferent and efferent arterioles
 (PT ) – Pressure within the tubules
 πGC - oncotic pressure of proteins in the glomerular capillary and efferent arteriole.
 RENAL BLOOD FLOW = Aortic pressure - Renal venous pressure / Renal vascular resistance
 RENAL VASCULAR RESISTANCE
 Mediated by changes in the resistance of the afferent and efferent arterioles
 Constriction of the afferent arteriole → Decrease in PGC
 Constriction of the efferent arteriole → Increase PGC.
58

UNILATERAL URETERAL
OBSTRUCTION
 Triphasic pattern of renal blood flow (RBF) and ureteral pressure changes during UUO
 FIRST PHASE:
 Increase in pressure within the renal tubules of the affected kidney secondary to obstruction and
a subsequent decrease in GFR.
 The vasculature of the kidney attempts to compensate for the decreased GFR with an increase
in RBF mediated by the release of vasodilators, such as prostaglandin E2 (PGE2) and nitric
oxide (NO)
 Lasts 1 to 2 hours.
59

 SECOND PHASE
 Lasting 3 to 4 hours
 Ureteral pressure remains elevated but RBF begins to decline
 FINAL PHASE
 Both ureteral pressure and RBF flow progressively decline, resulting in a gradual loss in renal
function
 Mediated by an increase in afferent arteriolar resistance
 In addition to impeding RBF, it has been shown that increased afferent arteriolar resistance
causes a decrease in effective glomerular capillary pressure and a resulting decrease in renal
tubular pressure
60

BILATERAL URETERAL
OBSTRUCTION
 Modest initial increase in RBF lasting about 90 minutes, followed by a decrease in bilateral
RBF
 Ureteral pressure remains elevated for at least 24 hours
 Prolonged elevation in intratubular pressure contributes to the decrease in GFR
 During UUO, preglomerular vasodilation is followed by a more prolonged preglomerular
vasoconstriction, and this increase in afferent arteriolar resistance causes a reduction in
glomerular capillary pressure that in turn results in decreased intratubular pressure.
 In contrast, during BUO preglomerular vasodilation is followed by a prolonged postglomerular
vasoconstriction. This increase in efferent arteriolar resistance results in increased PGC and
intratubular pressure despite a decrease in RBF.
 The positive effect of increased PGC on GFR is offset by the persistent elevation in tubular
pressure.
61

VASOACTIVE MEDIATORS IN BUO
 NO
 Patelet activating factor
 Inhibiton of endothelin
 ANP – most important mediator
 Because there is no second renal unit to compensate for the ureteral obstruction, intravascular
volume increases in response to BUO and serves as a stimulus for secretion of ANP.
 ANP in turn increases afferent arteriolar dilation and efferent arteriolar vasoconstriction,
leading to an increase in PGC and intratubular pressure.
62

INTRARENAL DISTRIBUTION OF
BLOOD FLOW
 UUO
 Shift in RBF from the outer cortex to the juxtamedullary region of the kidney and large portions
of the cortical vascular bed become unperfused or underperfused
 Reduced GFR at this stage is therefore not only the result of a reduction in PGC in individual
glomeruli because of increased afferent arteriolar resistance but also occurs because of a global
lack of perfusion of many glomeruli.
 BUO
 Shift of blood flow from the juxtamedullary region of the kidney to the outer cortex in response
to BUO
 These alterations in the distribution of renal cortical blood flow also may contribute to the
differences in GFR observed between BUO and UUO.
63

64

PYELORENAL BACK FLOW
PATHWAYS
 Urine may still egress from kidney in obstruction via
 Pyelotubular – backflow into the terminal collecting ducts
 Pyelointerstitital – rupture of calyceal fornix into the cortex
 Pyelosinus back flow – rupture of calyceal fornix and subsequent extravasation
 Pyelovenous back flow – primary exit pathway in chronic obstruction
 Pyelolymphatic back flow – In acute phases of obstruction
65

POSTOBSTRUCTIVE DIURESIS
 High urine output exceeding >200ml / hr over 12 consecutive hours after the obstruction
is relieved
 Types
 Physiological
 Pathological
 Risk factors
 Hypertension, weight gain, edema, azotemia, volume overload
66

POST OBSTRUCTIVE DIURESIS
PHYSIOLOGICAL
 Self limiting
 Response to solute and water overload
PATHOLOGICAL
 Inappropriate diuresis beyond euvolemic state
 Insensitivity of collecting tubule to ADH and
defects in urinary concentrating ability
 Down regulation of sodium transport channels
 Down regulation of Aquaporin channels
 Altered regulation of ANP
67

Management
 Normally, the diuresis subsides after solute and fluid homeostasis is achieved.
 Pathologic diuresis
 First 24 hours – if urine output > 200ml / hr → 85% of hourly output replaced with 0.45%
saline
 After 24 hours – Total fluids infused about 1L less or < 75% than the previous day’s output,
provided the patient is hemodynamically stable
 If signs of hypovolemia – 0.5 L less (instead od 1L) than the last 24hrs output
 Replacement of electrolytes
 Once the urine output is < 3 L / day – oral fluids
68

INDIVIDUALISEDGOALDIRECTEDFLUIDTHERAPY
NEITHERUNDERRESUSCITATIONNOR
OVER-CORRECTION
69

70

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