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Electrolytes, Fluids, Acid Base Balance and Shock

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Title: Electrolytes, Fluids, Acid Base Balance and Shock


1
Electrolytes, Fluids, Acid Base Balance and Shock
  • Gwynne Jones
  • Critical Care

2
Electrolytes, Fluids, Acid Base Balance and Shock
  • Correct Fluid Management faqcilitatescrucial
    Homeostasis.
  • This permits
  • Optimum Cardio-vascular perfusion
  • Optimum Organ Function
  • Optimum Cellular Function

3
Electrolytes, Fluids, Acid Base Balance and Shock
  • Knowledge of the Compartmentalisation of Body
    Fluids forms the basis for
  • Understanding the Pathological Shifts in these
    Fluid Spaces in Varying Disease States
  • Quantifying Deficiencies or Excesses in these
    Spaces
  • Informs Choice of Fluid Type and Quantity

4
Electrolytes, Fluids, Acid Base Balance and Shock
  • Knowledge of the Compartmentalisation of Body
    Fluids forms the basis for
  • Understanding the Effects of Sodium Concentration
    on Interstitial and Cellular Volume and Function
  • Understanding Acid-Base Homeostasis
  • Understanding specific Patient Needs in Renal
    Failure, Brain Disease, Liver, Heart and Lung
    Diseases.

5
Electrolytes, Fluids, Acid Base Balance and Shock
  • Body Fluid Compartments
  • Water Contributes 50-70 of Body Weight.
  • Fat has Little Water, thus Lean People have
    greater Body Water as weight
  • Water is distributed EVENLY throughout all body
    compartments but will follow Osmotic Gradients

6
Electrolytes, Fluids, Acid Base Balance and Shock
  • Body Fluid Compartments
  • Total Cations Must Equal Total Cations
  • Sodium is Predominently Extracellular and
    determines Extracellular Fluid Volume.
  • Cell Volume is Controlled mainly by Cell Membrane
    Ion Pumps

7
Electrolytes, Fluids, Acid Base Balance and Shock
  • Electrolyte Concentration is usually expressed in
    terms of chemical combining activity, or
    equivalents.
  • Equivalent Atomic Wt (g)/valence

8
Electrolytes, Fluids, Acid Base Balance and Shock
  • Body Fluid Compartments
  • Total Cations Must Equal Total Cations
  • The Physiological Activity of Electrolytes in
    Solution depends on the Number of Particles per
    Unit Volume (milli-mols/Liter, mMol/L
  • The Number of Electric Charges per Unit Volume
    (milli-equivalents per Liter, mEq/L
  • The Number of Osmotically Active Ions per unit
    Volume (milli-osmoles per Liter, mOsm/L)

9
Electrolytes, Fluids, Acid Base Balance and Shock
  • Body Fluid Compartments
  • Total Cations Must Equal Total Cations
  • Sodium is predominently Extracellular and
    determines Extracellular Fluid Volume.
  • Cell Volume is Controlled mainly by Cell Membrane
    Ion Pumps

10
Electrolytes, Fluids and Shock
11
Electrolytes, Fluids and Shock
50 Total body Water
80 Total Body Water
12
Electrolytes, Fluids and Shock
13
Electrolytes, Fluids and Shock
  • Two Thirds of the body Water is in the cells.
  • This is between 30L to 40 L.
  • Is has an Electrolyte composition very different
    from the Extra-cellular water.
  • What is this difference?

14
Electrolytes, Fluids and Shock
  • Two Thirds of the body Water is in the cells.
  • Electrolyte composition
  • Cations
  • Potassium 150 mMol/L
  • Sodium 10 mMol/L
  • Magnesium 40 mMol/L.
  • Calcium and Hydrogen nanoMols/L
  • Anions
  • Phosphate and Sulphate 150 mMol/L.
  • Proteinate 40 mMol/L
  • Bicarbonate 10 mMol/L

15
Electrolytes, Fluids and Shock
  • Two Thirds of the body Water is in the cells.
  • This is between 30L to 40 L.
  • Is has an Electrolyte composition very different
    from the Extra-cellular water.
  • How is it maintained?

16
Electrolytes, Fluids and Shock
  • Two Thirds of the body Water is in the cells.
  • Electrolyte composition
  • Cations
  • Potassium 150 mMol/L
  • Sodium 10 mMol/L
  • Magnesium 40 mMol/L.
  • Calcium and Hydrogen nanoMols/L
  • Anions
  • Phosphate and Sulphate 150 mMol/L.
  • Proteinate 40 mMol/L
  • Bicarbonate 10 mMol/L

These differences are maintained by various cell
membrane ion pumps. Na/K ATPase driven exchangers
are most important
17
Electrolytes, Fluids and Shock
  • Two Thirds of the body Water is in the cells.
  • Electrolyte composition
  • Cations
  • Potassium 150 mMol/L
  • Sodium 10 mMol/L
  • Magnesium 40 mMol/L.
  • Calcium and Hydrogen nanoMols/L
  • Anions
  • Phosphate and Sulphate 150 mMol/L.
  • Proteinate 40 mMol/L
  • Bicarbonate 10 mMol/L

These differences are maintained by various ion
pumps. Na/K ATPase driven exchangers are most
important After Severe Shock 20 of Oxygen/fuel
consumption is used just to pump the Sodium out
of the cells.
18
Electrolytes, Fluids and Shock
  • Two Thirds of the body Water is in the cells.
  • Electrolyte composition
  • Cations
  • Potassium 150 mMol/L
  • Sodium 10 mMol/L
  • Magnesium 40 mMol/L.
  • Calcium and Hydrogen nanoMols/L
  • Anions
  • Phosphate and Sulphate 150 mMol/L.
  • Proteinate 40 mMol/L
  • Bicarbonate 10 mMol/L

These differences are maintained by various ion
pumps. Na/K ATPase driven exchangers are most
important. Cell volume fluctuates a little in
shock and has some influence on resuscitation
fluid choice. In the presence of shock (the ebb
phase) they swell. In more chronic severe illness
(after shock/flow phase) they shrink.
19
Electrolytes, Fluids and Shock
  • Two Thirds of the body Water is in the cells.
  • Electrolyte composition
  • Cations
  • Potassium 150 mMol/L
  • Sodium 10 mMol/L
  • Magnesium 40 mMol/L.
  • Calcium and Hydrogen nanoMols/L
  • Anions
  • Phosphate and Sulphate 150 mMol/L.
  • Proteinate 40 mMol/L
  • Bicarbonate 10 mMol/L

These differences are maintained by various ion
pumps. Na/K ATPase driven exchangers are most
important. Cell volume fluctuates a little in
shock and has some influence on resuscitation
fluid choice. 1. Smaller cells switch off protein
production and thus contribute to nitrogen loss.
20
Electrolytes, Fluids and Shock
  • Two Thirds of the body Water is in the cells.
  • Electrolyte composition
  • Cations
  • Potassium 150 mMol/L
  • Sodium 10 mMol/L
  • Magnesium 40 mMol/L.
  • Calcium and Hydrogen nanoMols/L
  • Anions
  • Phosphate and Sulphate 150 mMol/L.
  • Proteinate 40 mMol/L
  • Bicarbonate 10 mMol/L

These differences are maintained by various ion
pumps. Na/K ATPase driven exchangers are most
important. Cell volume fluctuates a little in
shock. Cells are smaller in recovering shock. 2.
Insulin and certain Amino Acids stimulate protein
synthesis . The re-feeding syndrome is associated
with this. How?
21
Electrolytes, Fluids and Shock
  • Two Thirds of the body Water is in the cells.
  • Electrolyte composition
  • Cations
  • Potassium 150 mMol/L
  • Sodium 10 mMol/L
  • Magnesium 40 mMol/L.
  • Calcium and Hydrogen nanoMols/L
  • Anions
  • Phosphate and Sulphate 150 mMol/L.
  • Proteinate 40 mMol/L
  • Bicardonate 10 mMol/L

The cell is thus a rich sauce. It is the lean
body mass that we survive on. For the rest of the
talk/life we leave them in the background. We
forget them at our peril.
22
Electrolytes, Fluids and Shock
23
Electrolytes, Fluids and Shock
The extracellular space is one third of the
total Body Water. Blood plasma is a quarter of
this ( 5L in an adult). Interstitial fluid is
the other three quarters ( 15L in an adult) How
is this difference maintained when the
endothelium is fully permeable to salt water?
24
Electrolytes, Fluids and Shock
There is a subtle difference between blood/plasma
and interstitial fluid. This is mainly the
difference in protein. As Albumin is a small
protein (MW66,000kD), it has the greatest number
of osmotically active molecules. These are able
to exert an osmotic activity across a
semi-permeable membranes.
25
Electrolytes, Fluids and Shock
There is a subtle difference between blood/plasma
and interstitial fluid. Sodium passively
determines the extracellular space volume. Why?
26
Electrolytes, Fluids and Shock
Sodium passively determines the extracellular
space volume. Total body sodium is around
3000mMol. (20L X 140mMol/L). Anyone with edema
has a high body sodium (and the water it
craves). This, unfortunately, does not mean that
the Blood/Plasma volume is low/normal/high!
27
Electrolytes, Fluids and Shock
Whose Law determines the mechanism by which these
intravascular /interstitial volumes are
maintained?
28
Electrolytes, Fluids and Shock
Whose Law determines the mechanism by which this
intravascular /interstitial process is
maintained? Starlings Law.
Jv Ks (Ppl - Pis) - s (ppl - pis)
29
Electrolytes, Fluids and Shock
Jv Ks (Ppl - Pis) - s (ppl - pis)
30
Electrolytes, Fluids and Shock
Jv Ks (Ppl - Pis) - s (ppl - pis)
31
Electrolytes, Fluids, Acid Base Balance and Shock
  • What is s and why is it important?

32
Electrolytes, Fluids, Acid Base Balance and Shock
  • What is s and why is it important?
  • s is the Protein Reflection Co-efficient
  • s is 0.3 in skin (ie very tight endothelium)
  • s is 0.6 in the lung and Kidney
  • s is 0.9 in the Gut and Liver (ie very Leaky for
    Protein)

33
Electrolytes, Fluids and Shock
Jv Ks (Ppl - Pis) - s (ppl - pis)
34
Electrolytes, Fluids and Shock
Jv Ks (Ppl - Pis) - s (ppl - pis)
35
Electrolytes, Fluids and Shock
Jv Ks (Ppl - Pis) - s (ppl - pis)
The endothelium is more complex than initially
imagined. The endothelium is covered by a
glyco-calyx. These two barriers the Endothelium
and the Glycocalyx are co-operative. Damage to
either one is not associated with an increase in
fluid flux. Damage to both is associated with
severe leaky vessels (capillaries)
36
Electrolytes, Fluids and Shock
Jv Ks (Ppl - Pis) - s (ppl - pis)
The endothelium is more complex than initially
imagined. The endothelium is covered by a
glyco-calyx. These two barriers are
co-operative The endothelium is damaged
particularly by Reactive Oxygen Species (ROS) The
glyco-calyx is damaged particularly by proteases.
37
Electrolytes, Fluids and Shock
Jv Ks (Ppl - Pis) - s (ppl - pis)
The endothelium is more complex than initially
imagined. The endothelium is covered by a
glyco-calyx. These two barriers are co-operative.
They allow a flow of interstitial fluid enriched
by sugar and electrolytes. The ¼ Blood/Plasma ¾
interstitial fluid ratio in health is
maintained. Excess is taken up by lymphatics and
returned to the blood via the thoracic duct.
38
Electrolytes, Fluids and Shock
Blood Volume is 5L in the adult. 45 is
RBCs The rest is an aqueous solution of
electrolytes and proteins. The proteins are
functional Immunoglobulins Coagulation
factors Complement Albumin Hormones Etc.
39
Electrolytes, Fluids and Shock
Blood Volume is 5L in the adult. Blood Volume
is highly regulated by What?
40
Electrolytes, Fluids and Shock
Blood Volume is 5L in the adult. Blood Volume
is highly regulated by Pressure Sensors. Volume
Sensors. Osmo-receptors.
41
Electrolytes, Fluids and Shock
Blood Volume is 5L in the adult. Blood Volume
is highly regulated by Pressure
Sensors Carotid Sinus, Renal Vessels. Volume
Sensors Large Veins/Atria. Osmo-receptors Hypo
thalamus.
42
Electrolytes, Fluids and Shock
Blood Volume is 5L in the adult. Blood Volume
is highly regulated by Pressure
Sensors Carotid Sinus, Renal Vessels. Volume
Sensors Large Vein/Atria. Osmo-receptors Hypot
halamus.
These act via the Autonomic Nervous system, the
hypothalamic-Pituitary Axis and adrenal glands to
stimulate thirst, Sodium and Water Retention,
Vaso-constriction etc.
43
Electrolytes, Fluids and Shock
Blood Volume is 5L in the adult. Blood Volume
is highly regulated by Pressure
Sensors Carotid Sinus, Renal Vessels. Volume
Sensors Large Vein/Atria. Osmo-receptors Hypot
halamus.
These act via the Autonomic Nervous system, the
hypothalamic-Pituitary Axis and adrenal glands to
stimulate thirst, Water Retention,
Vaso-constriction etc.
Tell me about the hormones!
44
Electrolytes, Fluids and Shock
ADH CATECHOLAMINES ANGIOTENSIN CORTISOL ALDOSTERON
E ATRIAL NATRIURETIC HORMONE ENDOTHELIN
45
Electrolytes, Fluids and Shock
This is going to get Harder!
46
Electrolytes, Fluids and Shock
Acid-Base Balance. Hydrogen is in Nano-Molar
quantities
47
Electrolytes, Fluids and Shock
Acid-Base Balance.
Hydrogen is in Nano-Molar quantities. It all has
to do with the dissociation of water. Most of the
water is not dissociated (55mMol/L.) 10-14 nMol/L
of water is dissociated into Hand OH- If all is
H the pH is zero. If all is OH- the pH is
14. The pH scale is zero to 14, neutral is a pH
of 7
48
Electrolytes, Fluids and Shock
Acid-Base Balance. Hydrogen is in Nano-Molar
quantities. It all has to do with the
dissociation of water. Most of the water is not
dissociated. 10-14 nMol/L is dissociated into
Hand OH- If all is H the pH is zero. If all is
OH- the pH is 14. The pH scale is zero to 14,
neutral is a pH of 7
There are three independent variables that affect
pH or H ion concentration The
bicarbonate/carbon dioxide system The
dissociation of proteins The Strong Ion
difference (SID
49
Electrolytes, Fluids and Shock
Acid-Base Balance. Hydrogen is in Nano-Molar
quantities. It all has to do with the
dissociation of water. Most of the water is not
dissociated. 10-14 nMol/L is dissociated into
Hand OH- If all is H the pH is zero. If all is
OH- the pH is 14. The pH scale is zero to 14,
neutral is a pH of 7
The Strong Ion difference (SID). This is the
difference between fully dissociated anions and
cations. Na K Cl La- 40 in
health. This is the bath in which your
bicarbonate and proteinate buffers work.
50
Electrolytes, Fluids and Shock
  • The Bicarbonate System

CO2 H2O H HCO3
51
Electrolytes, Fluids and Shock
How long does it take?
1 for 10 acutely.
HCO3
25
40
80
pCO2
52
Pulmonary Ventilation and Gas Exchange
3 for 10 chronically. How long does it take?
HCO3
25
40
80
pCO2
53
Electrolytes, Fluids and Shock
Mr. S. P SBO with Shock
  • A 47 yr old man develops has evident bowel
    obstruction on the background of severe Crohns
    disease.
  • His Blood work shows
  • Hb 90G/L WBC 18,000
  • His Na is 150, Cl-110, K 3.2, HCO3 10.
    Creatinine 320
  • pH 7.2, pCO2 30, HCO3, 10 pO2 90 on nasal oxygen,
    Lactate 5

How are you going to resuscitate him?
54
Electrolytes, Fluids and Shock
VCO2
________
pCO2

K
Alv. Vent.
Wont or Cant Breath
pCO2
Alveolar Hyperventilation
55
Energy Metabolism in Critically Ill
GLYCOLYSIS
Why does bicarbonate fall, on roughly a mol for
mol basis, when lactic acidosis occurs?
H HCO3 H2CO3 CO2 H2O
56
Energy Metabolism in Critically Ill
GLYCOLYSIS
Why does bicarbonate fall, on roughly a mol for
mol basis, when lactic acidosis occurs?
HLactate NaHCO3 NaLactate H2CO3
H HCO3 H2CO3 CO2 H2O
57
Electrolytes, Fluids and Shock
What are the determinants of Cardiac Output?
58
Electrolytes, Fluids and Shock
Cardiac Output is determined by four
variables Preload Afterload Contractility Hea
rt Rate
59
Electrolytes, Fluids and Shock
Cardiac Output is determined by four
variables 1. Preload This is the force or load
that stretches the cardiac muscle prior to
contraction.
60
Electrolytes, Fluids and Shock
Cardiac Output is determined by four
variables. Afterload This is the impedence to
outflow of the ventricle. This includes the size
of the ventricle (La Place), The SVR, PVR,
compliance of large vessels and the pleural
pressure
61
Electrolytes, Fluids and Shock
Cardiac Output must equal Venous return. Venous
return is determined by five variables Stressed
Vascular Volume Venous Compliance Venous
Resistance Distribution of Blood Flow Right
Atrial Pressure
62
Electrolytes, Fluids and Shock Venous Return
This is hard but worth thinking about!
63
Electrolytes, Fluids and Shock
What is the proportion of blood in the arterial
side of the circulation compared to the Venous
side?
ARTERIOLE
VENULE
Pressure 35 mmHg
Pressure 7 mmHg
X
X
64
Electrolytes, Fluids and Shock
What is the proportion of blood in the arterial
side of the circulation compared to the Venous
side 70. Why?
ARTERIOLE
VENULE
Pressure 35 mmHg
Pressure 7 mmHg
X
X
65
Electrolytes, Fluids and Shock
The Venous Anatomy and Venous Return
  • The Veins are very compliant.
  • The arteries are not.

66
Electrolytes, Fluids and Shock
The Venous Anatomy and Venous Return
  • The Veins are very compliant.
  • The elastic recoil of the compliant capacity
    vessels is a potential energy (filled by the
    arterial pressure).
  • This potential energy of elastic recoil acts to
    transfer blood towards the heart maintaining
    cardiac filling and output.

67
Electrolytes, Fluids and Shock
The Venous Anatomy and Venous Return
  • The Veins are very compliant.
  • The elastic veins have an elasticity that allows
    them to act like an auxiliary pump

68
Electrolytes, Fluids and Shock
The Venous Anatomy and Venous Return
  • There is a progressive drop in pressure within
    the systemic circuit from the highest value, at
    the outlet of the left ventricle to the lowest
    value, at the right atrium.
  • What would happen to these pressures if it were
    possible to switch off the heart, without reflex
    change, for 30 seconds?

69
Electrolytes, Fluids and Shock
The Venous Anatomy and Venous Return
  • What would happen to these pressures if it were
    possible to switch off the heart, without reflex
    change, for 30 seconds?
  • Without flow, the pressure throughout the system
    would equalise to a level determined by the
    compliance of the whole system.
  • As the venous system is hugely compliant, the
    pressure would equalise at a pressure just above
    the RA pressure.
  • This is The Mean Systemic Pressure.

70
Electrolytes, Fluids and Shock
The Venous Anatomy and Venous Return
X
X
ARTERIOLE
VENULE
Pressure 35 mmHg
Pressure 7 mmHg
This is the mean systemic pressure
X
X
71
Electrolytes, Fluids and Shock
The Venous Anatomy and Venous Return
  • Without flow, the pressure throughout the system
    would equalise at all points to a level
    determined by the compliance of the whole system.
  • This is The Mean Systemic Pressure.
  • It is the pressure in the small veins which
    distends the capacitance vessels, thereby
    producing a potential energy for flow to return
    to the RA.
  • The RA pressure is constantly emptied by the RV

72
Electrolytes, Fluids and Shock
The Mean Systemic Pressure.
  • As the venous system is hugely compliant, the
    pressure would equalise at a pressure just above
    the RA pressure. The Mean Systemic Pressure.
  • The Mean Systemic Pressure is the driving
    pressure for venous return.
  • It is 5 to 10 mmHg. in the normal circulation.
  • As RA pressure is less, only - 4 to 4 mmHg.,
    venous return is fine.

73
Electrolytes, Fluids and Shock
The Mean Systemic Pressure.
  • As the venous system is hugely compliant, the
    pressure would equalise at a pressure just above
    the RA pressure. The Mean Systemic Pressure.
  • The Mean Systemic Pressure is the driving
    pressure for venous return.
  • It is 5 to 10 mmHg. in the normal circulation.
  • As RA pressure is less, only - 4 to 4 mmHg.,
    venous return is fine.

The Job of the Right Ventricle is to keep the
Right Atrium empty. It does the job amazingly
well as long as the RV afterload is low (ie the
lungs are OK).
74
Electrolytes, Fluids and Shock
The Mean Systemic Pressure.
Imagine the pressure change as you fill a
collapsed bag. Until filled, there will be no
pressure change The bag is very compliant. It has
a large unstressed volume
This is how the veins are with a blood volume of
4L.
75
Electrolytes, Fluids and Shock
The Mean Systemic Pressure.
  • Now the bag has filled, the pressure will
    increase in proportion to the compliance of the
    wall of the bag, together with the rate at which
    fluid is entering the bag.
  • You have reached the bags stressed volume.

This is how the veins are with a blood volume of
5L.
76
Electrolytes, Fluids and Shock
The Mean Systemic Pressure.
Imagine the pressure change as you fill a
collapsed bag. Until filled, there will be no
pressure change The bag is very compliant. It has
a large unstressed volume
This is how the veins are with a blood volume of
4L.
77
Electrolytes, Fluids and Shock
The Mean Systemic Pressure.
Imagine the pressure change as you fill a
collapsed bag. Until filled, there will be no
pressure change The bag is very compliant. It has
a large unstressed volume
Fluid Resuscitation would be Good. Which Fluid
would you Choose?
78
Electrolytes, Fluids and Shock
Venous Return and Cardiac Function
Venous return will be zero when RA pressure
equals mean systemic pressure
Mean Systemic Pressure
Venous Return
RA Pressure
79
Are We Treating The Right Ventricle?
Venous Return and Cardiac Function
Venous return can be increased in three ways
2. Increase PMS
Cardiac output
or
Venous Return
1. Reduce Atrial Pressure
RA Pressure
80
Electrolytes, Fluids and Shock
The Mean Systemic Pressure (PMS).
INFUSED VOLUME
Systemic Vascular volume
INCREASED PMS
Mean systemic pressure
INCREASED PMS
INCREASED PMS
DECREASE IN COMPLIANCE
REDUCTION IN UNSTRESSED VOLUME
81
Electrolytes, Fluids and Shock
  • The systolic and diastolic dysfunction after
    acute MI produces LV failure.
  • Pre-load recruitable stroke work (move up the
    Frank-Starling Curve) increases LV end-diastolic
    pressure.
  • LV end-diastolic pressure (the wedge/PAOP) was
    measured at 28mm Hg.
  • This high wedge/PAOP induces pulmonary
    hypertension, thereby increasing RV afterload.
  • The RV is failing also, as indicated by the high
    right atrial pressure.
  • Sympathetic activation at low levels mostly
    produces a decrease in venous capacity.
  • This produces the equivalent of a blood
    transfusion.
  • This volume load increases venous return and
    right ventricular dilation.
  • RV volume increase may increase RV ejection
    fraction, although the high RV afterload may not
    permit this increase, The RV being excellent at
    increasing output if impedence is low but poor
    when impedence to outflow is high, as in
    pulmonary hypertension.

82
Electrolytes, Fluids and Shock
Effect of Sympathetic activation on preload and
afterload
Venous Capacity


SVR
Systemic Vascular Resistance
VC
Sympathetic Nervous System Output
83
Electrolytes, Fluids and Shock
The Venous Innervation
Sympathetic Nerve
Sympathetic Nerve
a1a1a1
a2a2
a1a1a1
a2a2
a2a2
a2a2
a2a2
a2a2
Artery
a1a1a1
Vein
a1a1a1
84
Electrolytes, Fluids and Shock
The Venous Innervation
Sympathetic Nerve
Phosphodiesterase 3
Cyclic AMP
Adenyl Cyclase
Protein Kinase G
a1 or a2
Artery
or
Vein
Vaso-constriction
Multiple Kinases
iCa
85
Electrolytes, Fluids and Shock
The Mean Systemic Pressure.
  • The venous system has a potentially huge
    unstressed volume which is controlled by many of
    the humoral and neural networks we have been
    discussing.
  • You know the difficulty in maintaining BP in
    someone in neurogenic shock. Large amounts of
    volume are initially needed to increase pressure.
  • Although some of this BP fall is secondary to
    loss of arteriolar tone, until the venous tank is
    filled, arterial constrictors are poorly
    effective.

86
Electrolytes, Fluids and Shock
The Mean Systemic Pressure.
  • A fall in arteriolar tone may permit more flow
    into the venous circuit. This will increase the
    mean systemic pressure once the unstressed volume
    is filled.
  • Otherwise mean systemic pressure must be
    increased by reducing the venous capacity or by
    reducing the compliance of the veins. (Reducing
    the size of the bag or making the bag stiffer.)
  • These effects usually occur together in a reflex
    fashion.

87
Electrolytes, Fluids and Shock
The Mean Systemic Pressure
  • The Mean Systemic Pressure may be increased up to
    40mmHg. In exercise or vaso-dilation.
  • The higher the Mean Systemic Pressure, the
    greater will be the venous return.
  • Venous return equals cardiac output.

88
Electrolytes, Fluids and Shock
The Mean Systemic Pressure
  • The Mean Systemic Pressure minus the right Atrial
    pressure is the pressure governing the venous
    return.
  • RVEF increases as RA pressure increases via the
    Frank-Starling mechanism.
  • However, the higher the RA pressure the smaller
    will be the Mean Systemic to RA pressure
    promoting venous return

89
Electrolytes, Fluids and Shock
The Mean Systemic Pressure
  • The higher the RA pressure the smaller will be
    the Mean Systemic to RA pressure promoting venous
    return.
  • There are a family of Venous return curves.

90
Electrolytes, Fluids and Shock
The Venous Anatomy and Venous Return
  • The central venous pressure is dependent upon
  • Blood Volume.
  • Venous Capacity and Resistance.
  • RV performance.
  • This makes the CVP hard to understand.

91
Electrolytes, Fluids and Shock
Venous Return and Cardiac Function
Mean Systemic Pressure
Venous Return and Cardiac Output are equal
Cardiac output
or
Venous Return
RA Pressure
92
Electrolytes, Fluids and Shock
Venous Return and Cardiac Function
Cardiac Output can be increased in three ways
B
Cardiac output
A
or
Venous Return
RA Pressure
Cardiac output increases from A to B from this
increase in PMS
93
Electrolytes, Fluids and Shock
Venous Return and Cardiac Function
3. Increase Cardiac Contractility
  • Cardiac Output can be increased in three ways
  • Increase MSP
  • Increase up the Frank- Starling curve
  • 3. Increase Cardiac Contractility

Cardiac output
or
Venous Return

RA Pressure
94
Electrolytes, Fluids and Shock
95
Electrolytes, Fluids and Shock
Mr. S. P SBO with Shock
  • A 47 yr old man has planned open Right
    Hemi-Colectomy.
  • The Surgery is Uneventful.
  • How would you manage his IV fluids

96
Electrolytes, Fluids and Shock
Mr. S. P SBO with Shock
  • A 47 yr old man has planned Laparoscopic Right
    Hemi-Colectomy.
  • The Surgery is Uneventful.
  • How would you manage his IV fluids

97
Electrolytes, Fluids and Shock
Mr. S. P SBO with Shock
  • A 47 yr old man with no Co-morbidities has
    planned Laparoscopic or Open Right
    Hemi-Colectomy.
  • The Surgery is Uneventful.
  • Why would you manage his IV fluids differently.

98
Electrolytes, Fluids and Shock
Mr. S. P SBO with Shock
  • A 47 yr old man with no Co-morbidities has
    planned Laparoscopic or Open Right
    Hemi-Colectomy.
  • The Surgery is complicated by Fecal Contamination
    and the need for an Ileostomy.
  • Why would you manage his IV fluids differently.

99
Electrolytes, Fluids and Shock
Mr. S. P SBO with Shock
  • A 47 yr old man is admitted with bowel
    obstruction. He has been Vomiting for 2 days and
    has not eaten for 5 days.
  • Surgery is complicated. Open Right Hemi-Colectomy
    is necessary.
  • There is much Fecal Contamination and the need
    for an Ileostomy.
  • Why would you manage his IV fluids differently.

100
Electrolytes, Fluids and Shock
Mr. S. P SBO with Shock
  • A 47 yr old man is admitted with bowel
    obstruction. He has been Vomiting for 2 days and
    has not eaten for 5 days.
  • Surgery is complicated. Open Right Hemi-Colectomy
    is necessary.
  • There is much Fecal Contamination and the need
    for an Ileostomy.
  • Why would you manage his IV fluids differently.
  • He has a huge inflammatory process
  • His micro-circulation is very altered
  • His Capillaries are Leaky

101
Electrolytes, Fluids and Shock
Mr. S. P SBO with Shock
  • A 47 yr old man is admitted with bowel
    obstruction. He has been Vomiting for 2 days and
    has not eaten for 5 days.
  • Surgery is complicated. Open Right Hemi-Colectomy
    is necessary.
  • There is much Fecal Contamination and the need
    for an Ileostomy.
  • Why would you manage his IV fluids differently.
  • He has a huge inflammatory process
  • His micro-circulation is very altered
  • His Capillaries are Leaky
  • Would you admit him to ICU?
  • Would you leave him on the Ventilator?
  • Would you put in an Epidural Catheter?

102
Electrolytes, Fluids and Shock
Mr. S. P SBO with Shock
  • A 47 yr old man develops has evident bowel
    obstruction on the background of severe Crohns
    disease.
  • His Blood work shows
  • Hb 90G/L WBC 18,000
  • His Na is 150, Cl-110, K 3.2, HCO3 10.
    Creatinine 320
  • pH 7.2, pCO2 30, HCO3, 10 pO2 90 on nasal oxygen,
    Lactate 5

How are you going to resuscitate him?
103
Electrolytes, Fluids and Shock
What is the proportion of blood in the arterial
side of the circulation compared to the Venous
side?
ARTERIOLE
VENULE
Pressure 35 mmHg
Pressure 7 mmHg
X
X
104
Electrolytes, Fluids and Shock
Capillary system in Sepsis
VASOSPASM
THROMBUS
ARTERIOLE in Sepsis Pressure 30mmHg.
VENULE in Sepsis Pressure 20 mmHg.
X
VASODILATATION
105
Electrolytes, Fluids and Shock
Mr. S. P SBO with Shock
  • A 47 yr old man develops has evident bowel
    obstruction on the background of severe Crohns
    disease.
  • In intestinal obstruction, not only does
    absorbtion stop, fluid is secreted into the bowel
    lumen.
  • This can increase dilation/pressure enough to
    produce ischemia/translocation.
  • The shock state thus comprises
  • Fluid loss from vomiting and inanition
  • Fluid loss into the gut
  • Leaky capillaries from inflammation/sepsis

How are you going to resuscitate him?
106
Electrolytes, Fluids and Shock
Secretion type Volume Na K Cl HCO3
Stomach 1000-2000 60-90 10-30 100-130 0
Small Intestine 2000-3000 120-140 5-10 90-120 30-40
Colon Little 60 30 40 0
Pancreas 600-800 135-145 5-10 70-90 95-115
Bile 300-800 135-145 5-10 90-110 30-40
107
Electrolytes, Fluids and Shock
Mr. S. P SBO with Shock
  • A 47 yr old man develops has evident bowel
    obstruction on the background of severe Crohns
    disease.
  • There is thus, hypovolemia, Sodium and Chloride
    loss.
  • Intra-cellular cations (K, Mg) may be lost if
    this process has occurred over days.

How are you going to resuscitate him?
108
Can Your Patient Cope with the Inflammation of
Surgery?
But you are smart and the anesthetist is smart.
No shock will occur during the surgery.
Flow or Healing Phase
Flow
The ebb phase is really the inflammatory
stimulus induced by everything. The flow
needed to permit healing is determined by the Ebb.
Ebb or Shock Phase
Time
109
Can Your Patient Cope with the Inflammation of
Surgery?
110
Can Your Patient Cope with the Inflammation of
Surgery?
Flow or Healing Phase
Flow
The more severe and more prolonged the ebb, the
greater the flow must be to permit healing.
Ebb or Shock Phase
Time
Cuthbertson Quart.J.Med.19321233-38
111
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