Transcript Fluid and electrolyte in surgical patients - NUS

Department of Surgery
Yong Loo Lin School of Medicine
National University of Singapore
Total Body Water
total
intracellular
extracellular
intravas
interstitial
body wt%
Total body
water%
60
40
20
5
15
100
67
33
8
25
Composition of Fluids
plasma
interstitial
intracellular
Cations
Na
K
Ca
Mg
140
4
5
2
146
4
3
1
12
150
10
7
Anions
Cl
HCO
SO4
HPO4
Protein
103
24
1
2
16
104
27
1
2
5
3
10
116
40
Control of Volume
Kidneys maintain constant volume and
composition of body fluids
• Filtration and reabsorption of Na
• Regulation of water excretion in response to ADH
Water is freely diffusible
• Movement of certain ions and proteins between
compartments restricted
Osmoregulation
 osmolality 289 mOsm/kg H20
 osmoreceptor cells in paraventricular/
supraoptic nuclei
 osmoreceptors control thirst and ADH
 small changes in Posm - large response
Osmoregulation
Excess free water (Posm 280)
 thirst inhibited
 ADH declines
 urine dilutes to Uosm 100
Osmoregulation
Decreased free water (Posm 295)
 thirst increased
 ADH increases
 urine concentrates to Uosm 1200
Volume Control

osmoreceptors - day to day control

baroreceptors - respond to pressure change
neural and hormonal efferents
hormonal mediators
Baroreceptors

Hormonal mediators
aldosterone
renin
ANP
dopamine

Hormonal effect
 ECF  Na and water reabsorption
Baroreceptors

Neural mechanism
Autonomic nervous system
Renin-angiotensin
Renin secreted when

drop BP

drop Na delivery to kidney

increased sympathetic tone
Renin-Angiotensin
Angiotensin II
Increases vascular tone

increases catecolamine release

decrease renal blood flow

increases Na reabsorption

stimulates aldosterone release
Aldosterone
Release stimutlated by



Angiotensin II
increased K
ACTH
Effect


Na and water absorption
in distal tubular segments
Control of Volume
Effective circulating volume
• Portion of ECF that perfuses organs
• Usually equates to Intravascular volume
Third space loss
• Abnormal shift of fluid for Intravascular to
tissues eg bowel obst, i/o, pancreatitis
Normal Water Exchange
Avg daily ml
Min daily ml
Sensible
urine
800-1500
300
intestinal up to 10,000
sweat
up to litres
500
Insensible
lungs/skin 600-900
600-900
8-10 mls/kg/D -  10%/ o rise in Temp
Normal Intake of Water
2000mls - 1300 free water
700 bound to food
additional water comes from catabolism
Water and Eletrolyte Exchange
Surgical patients prone to
disruption
 nil orally
 anaesthesia
 trauma
 sepsis
Fluid and Electrolyte Therapy
Surgical patients need
Maintenance
volume requirements
On going losses
Volume excess/deficits
Maintenance electrolyte requirements
Electrolyte excess/deficits
1. Maintenance Requirements
This includes:
Body weight
0-10Kg
next 10-20Kg
subsequent Kg
insensible
urinary
stool losses
Fluid required
100ml/kg/d
50 ml/kg/d
20ml/kg/d
15ml/Kg/d for elderly
70 Kg Man Needs
1st 10kg x 100mls = 1000mls
2nd 10kg x 50mls =
500mls
Next 50kg x 20mls= 1000mls
TOTAL
2500 mls /d
2. On Going Losses

NG

drains

fistulae

third space losses
Concentration is similar to plasma
Replace with isotonic fluids
3. Volume Deficit - Acute
 vital
•
•
•
signs changes
Blood pressure
Heart rate
CVP
 tissue
changes not obvious
 urine
output low
3. Volume Deficit - Chronic
Decreased
Sunken
skin turgor
eyes
Oliguria
Orthostatic
hypotension
High
BUN/Creatine ratio
HCT
increases 6-8 points per litre deficit
Plasma
Na may be normal
4. Volume Excess

Over hydration

Mobilisation of third space losses
Signs
 weight
gain
 pulmonary edema
 peripheral edema
 S3 gallop
Fluid and Electrolyte Therapy
Goal
 normal haemodynamic parameters
 normal electrolyte concentration
Method
replace
normal maintenance requirements
ongoing losses
deficits
Fluid and Electrolyte Therapy
Normal maintenance requirements
 use BW formula
On going losses
 measure all losses in I/O chart
 estimate third space losses
Deficits
 estimate using vital signs
 estimate using HCT
Fluid and Electrolyte Therapy
The best estimate of the volume required
is the patients response
After therapy started observe
vital
signs
Urine output (0.5mls/Kg/hr)
Central venous pressure
Maintenance Electrolyte Requirements
Na 1-2mEq/Kg/d
K
0.5 - 1 mEq/Kg/d

Usually no K given until after urine output is
adequate and U/E done.

Always give K with care, in an infusion slowly
- never bolus

Ca, PO4, Mg not required for short term
Time Frame for Replacement

Usually correct over 24 hours

For ill patients calculate over
shorter period and reassess e.g. 1, 2
hours or 3 hours for e op cases

Deficits - correct half the amount
over the period and reassess
Postoperative Fluid Therapy

Check i/v regime ordered in op form

Assess for deficits by checking I/O chart and
vital signs

Maintenance requirements calculated

Usually K not started

Monitor carefully vital signs and urine output
Postoperative Fluid Therapy

Urine specific gravity may be used
(1.010 - 1.012)

CVP useful in difficult situations
(5-15 cm H20)

Body weight measured in special
situation e.g. burns
Concentration Changes

changes in plasma Na are indicative of
abnormal TBW

losses in surgery are usually isotonic

hypoosmolar condition usually caused by
replacement with free water
Hyponatremia Usually Excess Free Water

Free water replacement of isotonic losses

Increased ADH secretion

Low intravascular volume states like cirrhosis
/low albumin

Excess solute e.g. glucose - intracellular water
shifts to ECF
Hyponatremia Usually Excess Free Water

Features - depends on rapidity
acute drop below 120
weakness
fatigue
confusion
cramps
nausea/vomiting
headache/delirium/seizures/coma
permanent CNS damage
Diagnosis of Hyponatremia

assess circulating volume

exclude hyperosmolar states

check for losses

check for excess free water replacement

In difficult situations measure urine Na
(> <20mEq/L)
Treatment of Hyponatremia

replace volume deficits in dehydration

restrict free water in overload
Na required = [desired Na] - [actual Na] x (TBW)
TBW = 0.6xWt
Correct half the deficit over 12 hours and
reassess
Hyperkalaemia

Fatal if undiagnosed

Trauma, burns, septic, acidotic patient

ECG-Peak T, widened QRS, ST depressed

Repeat serum K

Insulin/dextrose, correct acidosis with HCO3,
calcium IV infusion, oral calcium resonium,
dialysis
Hypokalaemia

Depressed neuromuscular function

Dietary, excess loss – vomiting, diuretics

Related to alkalosis

Repeat serum K

Correct primary problem, replace orally or IV
st
Fit pt lap cholecystectomy 1 POD
Na
K
 Cl
 HCO3
 Urea
 Creat

121 mmol/l (135-145)
4.6 mmol/l (3.5-5.0)
90 mmol/l (98-108)
22 mmol/l (23-33)
3.5 mmol/l (3.0 to 8.0)
50 umol/l (60 to 120)
st
60 yr colectomy 1 POD
Na
K
 Cl
 HCO3
 Urea
 Creat
 HCT

121 mmol/l (135-145)
2.6 mmol/l (3.5-5.0)
50 mmol/l (98-108)
12 mmol/l (23-33)
1.5 mmol/l (3.0 to 8.0)
40 umol/l (60 to 120)
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