Unit 9 - Fluids & Electrolytes Flashcards
1
Q
what is the plasma volume of a 70 kg male
A
3 L
2
Q
total body water of 70 kg male
A
42 L
3
Q
body water distribution in 70 kg male
A
60/40/20 (15/5)
water = 60 % TBW
ICF = 40% TBW (28 L)
ECF = 20% TBW (14 L)
interstitial fluid = 15% (11L)
plasma fluid = 5% (3L)
4
Q
components of extracellular fluid
A
interstitial fluid (11L)
plasma (3 L)
5
Q
major ions of ICF
A
K+, Mg2+, PO42-
6
Q
major ions of ECF
A
Na+, Ca2+, Cl-, HCO3-
7
Q
volume of ICF vs ECF
A
ICF = 40% of TBW or 28 L
ECF = 20% of TBW or 14 L
8
Q
population differences in TBW
A
- Neonates have higher TBW % by weight
- Females, the obese, and the elderly have a lower TBW % by weight
9
Q
what is plasma volume
A
non-cellular fraction of circulating blood volume
10
Q
what determines net movement of fluid between intravascular & interstitial spaces
A
Starling forces & glycocalyx
11
Q
what are starling forces
A
dictate passive exchange of water between capillaries and interstitial fluid
forces that move from capillary to interstitial space and vice versa
12
Q
starling forces: Pc
A
Pc = capillary hydrostatic pressure (pushes fluid out of capillary)
13
Q
Starling forces: π if
A
π if = interstitial oncotic pressure (pulls fluid out of capillary)
14
Q
Starling forces: Pif
A
Pif = interstitial hydrostatic pressure (pushes fluid into capillary)
15
Q
Starling forces: π c
A
π c = capillary oncotic pressure (pulls fluid into capillary)
16
Q
how do fluids tend to be pulled back into the capillary
A
capillary oncotic pressure
17
Q
how is fluid pushed out as it enters the capillary
A
capillary hydrostatic pressure
18
Q
net filtration pressure =
A
(Pc - Pif) - (πc - πif)
19
Q
NFP > 0 =
NFP < 0 =
A
> 0 = filtration (fluid exits capillary)
< 0 = reabsorption (fluid pulled into capillary)
20
Q
Gatekeeper that determines what can pass from vessel into interstitial space
A
Glycocalyx
21
Q
Conditions that impair glycalyx integrity
A
sepsis
ischemia
DM
major vascular surgery
22
Q
function of glycocalyx
A
- forms a protective layer on the interior wall of blood vessel
- determines what can pass from vessel to interstitial space
23
Q
blood volume =
A
sum of plasma volume and blood cell volume (60% plasma & 40% blood)
24
Q
what is Hct
A
the fraction of blood volume occupied by erythrocytes
25
how is Hct increased
by increased # RBCs (polycythemia) or decreased plasma volume (hypovolemia)
26
how is Hct decreased
by decreased # RBCs (anemia) or increased plasma volume (hemodilution)
27
why are erythrocytes considered part of intracellular compartment
filled with fluid but considered part of intracellular compartment bc contained by a membrane
28
what is the interstitium
space between cells
29
what makes up nearly all of interstitial "fluid"
gel consisting of fluid & proteoglycan filaments
30
fluid movement in the interstitium is a function of:
diffusion
31
fluid scavenger that removes fluid, protein, bacteria, & debris that has entered the interstitium
Lymphatic System
32
how does the lymphatic system propel lymph
pumping mechanism
33
how does the lymphatic system affect pressure in interstitial space
Produces net negative pressure in interstitial space
34
what causes edema in regards to the lymphatic system
occurs when rate of interstitial fluid accumulation exceeds rate of removal by lymphatic system
35
how is lymph returned to venous circulation
via thoracic duct at juncture of IJ & subclavian
36
why is left IJ CVL insertion assoc. with greater risk of chylothorax
thoracic duct is larger on the left
37
how do most solutes get across semipermeable membranes separating the body's compartments
carrier proteins transport these solutes from one side to another
38
what is osmosis
net movement of water across a semipermeable membrane (only water, not solute, can pass through membrane)
39
what drives direction of water movement via osmosis
difference in solute concentration on either side of membrane
## Footnote
Water tends to move from areas of lower solute to areas of higher solute concentration
40
what is diffusion
net movement of a substance from area of **higher** concentration to area of **lower** concentration across fully permeable membrane
41
pressure of a solution against a semipermeable membrane, prevents water from diffusing across that membrane
Osmotic pressure
42
what is osmotic pressure a function of
the number of osmotically active particles in a solution
| NOT a function of molecular weights
43
number of osmoles per liter of solution
osmolarity
| mOsm/L of total solution
44
number of osmoles per liter of solution
osmolarity
| mOsm/L of total solution
45
number of osmoles per kg of solution
osmolarity
| mOsm/kg of H2O
46
number of osmoles per kg of solution
osmolarity
| mOsm/kg of H2O
47
number of osmotically active particles in a solution
osmole
48
normal plasma osmolarity
280-290 mOsm/L
49
Most important determinant of plasma osmolarity
Na+
50
how do hyperglycemia or uremia affect plasma osmolarity
can increase
51
helps us understand how different IV solutions impact volumes of ECF & ICF as well as plasma & cellular osmolarity
Dannow-Yannet Diagrams
52
what happens to cells in hypotonic solutions
water enters, cells swell
53
what happens to cells in hypertonic solutions
water exits, cells shrink
54
it is assumed that addition or loss of fluid occurs where?
in ECF
55
osmolarity of hypotonic solutions vs plasma
lower than plasma
56
how do hypotonic solutions affect ECF, ICF, and plasma osmolarity
↑ ECF & ICF volumes
↓ plasma osmolarity
57
why should a patient with increased ICP never receive a hypotonic solution
These fluids are akin to giving free water, which distributes throughout all body compartments
58
examples of hypotonic solutions
D5W
NaCl 0.45%
59
osmolarity of isotonic solutions vs plasma
Osmolarity approximates plasma (or cells)
60
how do isotonic solutions affect ECF, ICF, plasma volume, and plasma osmolarity
expand plasma volume & ECF (ICF and plasma osmolarity stay the same)
60
how do isotonic solutions affect ECF, ICF, plasma volume, and plasma osmolarity
expand plasma volume & ECF (ICF and plasma osmolarity stay the same)
61
how long do crystalloids tend to remain in intravascular space
~30 min
62
adverse effect of large amounts of NS
hyperchloremic metabolic acidosis
63
how does LR reduce risk of metabolic acidosis
Lactate in LR functions as a buffer
Lactate is converted to bicarb by liver & kidneys
Bicarb reduces risk of metabolic acidosis
64
what fluids can be used to dilute PRBcs
NS or Plasmaylte
(LR historically avoided but research shows that LR can be used safely when rapidly infusing PRBCs)
65
examples of isotonic solutions
* NaCl 0.9%
* Hespan 6%
* Plasmalyte A
* Albumin 5%
66
osmolarity of hypertonic solutions vs plasma
Osmolarity exceeds plasma (or cells)
67
how do hypertonic solutions affect intravascular volume, ECF, ICF, and plasma osmolarity
* expand intravascular volume by pulling fluid from ICF into ECF
* ECF & plasma osmolarity ↑
* ↓ ICF
68
consequence of increasing serum Na+ too quickly
central pontine myelinolysis
69
examples of hypertonic solutions
* 3% NS
* D5LR
* D5NS 0.9%
* D5NS 0.45%
* Dextran 10%
70
blood replacement volume with crystalloids
3:1
71
how long can crystalloids expand plasma volume
for 20-30 min
72
effects of dilution with crystalloids
dilutional coagulopathy
dilution of albumin = decreased capillary oncotic pressure
73
how long can colloids increase plasma volume
3-6 hours
74
effects of dextran 40
↓ blood viscosity
improves microcirculatory flow in vascular surgery
75
FDA black box warning on synthetic colloids
risk renal injury
76
coagulopathy with synthetic colloids
dextran > Hetastarch > Hextend
77
max volume of synthetic colloids
max 20 mL/kg
78
which colloid has the highest anaphylactic potential
dextran
79
synthetic colloid that does not have a problem with coagulopathy
Volvuven
80
only colloid that is derived from human blood products
albumin
81
Vd of albumin
approximates plasma volume
82
electrolyte imbalance possible with albumin
hypocalcemia (binds calcium)
83
normal serum potassium
3.5 - 5.5 mEq/L
84
plasma osmolarity calculation
85
conditions that increase osmolarity
hypernatremia
hyperglycemia
uremia
86
colloid that impairs ability to cross-match blood
dextran
87
which expands ECF - crystalloids or colloids?
crystalloids only
88
Most common electrolyte disorder in clinical practice
hypokalemia
89
Most abundant intracellular cation
K+
90
electrolyte that regulates RMP in nervous tissue, skeletal muscle, and cardiac muscle
K+
91
responsible for maintaining intracellular distribution of K+
Na-K-ATPase
92
Most important ion during repolarization of neural tissue & muscle cells
K+
93
GI losses that can result in hypokalemia
* V/D
* NG suction
* Zollinger-Ellison syndrome
* jejunoileal bypass
* kayexalate
94
4 etiologies of hypokalemia
1. diet (poor K+ intake)
2. GI loss
3. renal loss
4. redistribution
95
causes of renal loss of K+
* diuretics
* metabolic alkalosis
* licorice (can cause pseudo-Conn’s syndrome)
96
causes of hypokalemia from redistribution
| (K+ shift intracellular)
* insulin + D50
* hyperventilation
* bicarb
* beta 2 agonists
* hypokalemic periodic paralysis
97
presentation of hypokalemia
skeletal muscle cramps
weakness
paralysis
98
EKG findings with hypokalemia
* long PR
* long QT
* flat T wave
* U wave
99
why is assessing total body K+ with a serum K+ often inaccurate
~98% of total body K+ is stored inside cells
100
why is it important to evaluate cause of hypokalemia before treating
If due to intracellular redistribution, supplemental K+ could lead to lethal hyperkalemia when cause of redistribution resolves
101
max rate of potassium infusion
PIV = 10 mEq/hr
CVL = 20 mEq/L
102
5 etiologies of hyperkalemia
1. increased intake
2. impaired excretion
3. redistribution
4. cellular injury
5. pseudohyperkalemia
103
causes of impaired K+ excretion that can lead to hyperkalemia
* acute oliguric renal failure
* hypoaldosteronism
* drugs that impair K+ excretion (NSAIDs, spironolactone, triamterene)
104
drugs that impair K+ excretion
NSAIDs, spironolactone, triamterene
105
causes of K+ redistribution that contribute to hyperkalemia
| K+ shifts extracellularly
* acidosis
* succinylcholine
* beta blockers
* hyperkalemic periodic paralysis
106
causes of cellular injury that contribute to hyperkalemia
* tumor lysis
* hemolysis
* burns
* crush injury
* rhabdo
107
EKG findings with hyperkalemia
* 5.5-6.5 = peaked T waves
* 6.5-7.5 = flat P wave, prolonged PR
* 7.0-8.0 = prolonged QRS
* > 8.5 = QRS - sine wave - V-fib
108
serum K level associated with sine wave
8.5 or greater
109
serum K+ assoc. with peaked T waves
5.5-6.5 mEq/L
110
treatment of hyperkalemia
* stabilize cardiac membrane with calcium
* shift K intracellularly (insulin + D50, hyperventilation, bicarb, beta 2 agonist)
* K+ elimination with K+ wasting diuretics, kayexelate, dialysis
111
normal serum Na+
135-145 mEq/L
112
Most abundant extracellular cation
Na+
113
Primary determinant of serum osmolarity
Na+
114
Plays important role in regulating ECF volume through osmotic forces
Na+
115
when is Na+ most important
during **depolarization** of neural tissues and muscle cells
116
how is Na+ homeostasis regulated
* GFR
* renin-angiotensin-aldosterone system
* ANP/BNP
117
consider delaying surgery if Na+ is <
130
118
the serum Na+ concentration should be corrected no faster than:
2 mEq/L/hr
119
consequence of treating hyponatremia too quickly
* causes fluid to shift from ICF to ECF
* can cause central pontine myelinolysis
120
consequence of treating hypernatremia too quickly
causes fluid to shift from ECF to ICV
can cause cerebral edema
121
serum Na+ that defines hyponatremia
< 135 mEq/L
122
causes of hyponatremia related to decreased total body Na+ content
* diuretics
* salt-wasting disease
* hypoaldosteronism
123
causes of hyponatremia with normal total body Na+ content
* SIADH
* hypothyroid
* water intoxication
* periop stress
124
causes of hyponatremia assoc with increased total body Na+ content
CHF
cirrhosis
125
presentation of hyponatremia
* 130-135 = no signs to mild signs
* 125-129 = N/V, malaise
* 115-124 = headache, lethargy, altered LOC
* < 115 (rapid onset) = seizures, coma, cerebral edema, respiratory arrest
126
s/s hyponatremia at 125-129 mEq/L
N/V
malaise
127
s/s hyponatremia at 125-129 mEq/L
HA
lethargy
altered LOC
128
Na+ level assoc with seizures and cerebral edema
< 115 mEq/L
129
hyponatremia treatment
goal is to restore Na+ balance by manipulating serum osmolality and fluid balance with **H2O restriction**, **IVF** selection based on tonicity, and **diuretics**
130
serum Na+ in hypernatremia
> 145
131
etiologies of hypernatremia assoc with decreased total body Na+ content
* osmotic diuresis
* N/V
* adrenal insufficiency
132
causes of hypernatremia assoc with normal total body Na+ content
diabetes insipidus
renal failure
diuretics
133
causes of hypernatremia assoc with increased total body Na+ content
hyperaldosteronism
↑ intake (3% saline)
134
what determines presentation of hypernatremia
serum osmolality
| serum Na+ concentration determines presentation with hyponatremia
135
what determines presentation of hypernatremia
serum osmolality
| serum Na+ concentration determines presentation with hyponatremia
136
presentation of hypernatremia
depends on serum osmolality
* 350-375 = headache, agitation, confusion
* 376-400 = weakness, tremors, ataxia
* 401-430 = hyperreflexia, muscle twitching
* > 431 = seizures, coma, death
137
normal **total** plasma calcium
8.5 - 10.5 mg/dL
4.5 - 5.5 mEq/L
or 2.12 - 2.62 mmol/dL
138
normal **ionized** plasma calcium
4.65-5.28 mg/dL
2.2-2.6 mEq/L
or 1.16-1.32 mmol/dL
139
Calcium:
____ % is ionized
____% is bound to albumin
____% is bound with an anion
50% is ionized
40% is bound to albumin
10% is bound with an anion
140
Most abundant electrolyte in the body
calcium
141
where is nearly all calcium stored
in bone
## Footnote
serves as a reservoir for maintaining plasma calcium level
142
where is nearly all calcium stored
in bone
## Footnote
serves as a reservoir for maintaining plasma calcium level
143
important functions of calcium
* 2nd messenger systems
* neurotransmitter release
* muscular contraction
* phase 2 of cardiac muscle cell AP
* factor 4 in coagulation pathway
144
Antagonizes effects of Mg2+ at NMJ
calcium
145
how does acidosis affect ionized calcium
increases
(albumin binds H+ and displaces Ca2+ into plasma)
146
how does alkalosis affect ionized calcium
decreases
(albumin binds Ca2+ and displaces H+ into the plasma)
147
how does parathyroid hormone affect serum calcium
increases
148
how does calcitonin affect serum calcium
decreases
149
osteoclast activity with increased serum calcium level
inhibited
150
what releases calcitonin in response to increased calcium level
thyroid
151
parathyroid response to decreased calcium level
releases PTH
152
how does the body respond to decreased calcium levels
* parathyroid glands release PTH
* osteoclasts release calcium from bone
* calcium reabsorbed by kidneys
* increased calcium absorption in small intestine (via vitamin D synthesis)
153
etiologies of hypocalcemia
* hypoparathyroidism
* vitamin D deficiency
* renal osteodystrophy
* pancreatitis
* sepsis
154
presentation of hypocalcemia
* skeletal muscle cramps
* nerve irritability (paresthesia & tetany)
* laryngospasm
* AMS
* seizures
* Chvostek sign
* Trousseau sign
155
what phase of cardiac AP is calcium responsible for
phase 2 (plateau)
156
which factor is calcium in the coagulation pathway
factor 4
157
EKG findings of hypocalcemia
long QT
158
serum calcium in hypocalcemia
< 8.5 mg/dL
159
serum calcium in hypercalcemia
> 10.5 mg/dL
160
etiologies of hypercalcemia
hyperparathyroidism, cancer, thyrotoxicosis, thiazide diuretics, immobilization
161
presentation of hypercalcemia
* nausea
* abd pain
* HTN
* psychosis
* AMS - seizures
162
Chvostek sign
tapping on jaw of facial n./masseter muscle causes ipsilateral facial contraction
163
trousseau sign
upper extremity BP cuff inflated above SBP for 3 minutes = decreased blood flow accentuates neuromuscular irritability = muscle spasms of hand and forearm
164
electrolyte imbalance assoc with short QT
hypercalcemia
165
hypercalcemia treatment
0.9% NaCl, Lasix
166
normal **total** plasma magnesium level
1.7-2.4 mg/dL or 1.5-3 mEq/L
167
where is Mg contained
Only 1% of total body Mg resides in ECF (0.3% in plasma)
The rest is contained intracellularly (mostly muscle and bone)
| serum Mg may not correlate with total body Mg
168
where is Mg contained
Only 1% of total body Mg resides in ECF (0.3% in plasma)
The rest is contained intracellularly (mostly muscle and bone)
| serum Mg may not correlate with total body Mg
169
antagonizes effects of calcium
Mg
170
Required for DNA synthesis, essential cofactor in many enzymatic functions
magnesium
171
where is most Mg reabsorbed
renal tubules
172
what hormone raises serum calcium
parathyroid hormone
173
what hormone decreases serum calcium
calcitonin
174
serum Mg level assoc with loss of DTRs
7-12 mg/dL or 5.8-10 mEq/L
175
dose of mag for preeclampsia
4g IV load over 10-15 minutes then 1 g/hr for 24 hours
176
clinical uses of mag
* Opioid-sparing techniques (NMDA receptor antagonism)
* Acute bronchospasm
* Cardiac rhythm disturbances: symptomatic PVCs or torsades de pointes
177
neonatal risks of magnesium infusion
Mg crosses placenta
admin > 48h increases risk of neonatal respiratory depression, hypotension, & lethargy
178
how does magnesium affect NMB
Hypermagnesemia can potentiate NMB with succs and nondepolarizers
179
what should you assess in an OB patient receiving mag for preeclampsia
loss of DTRs
180
etiologies of hypomagnesemia
* poor intake
* alcohol abuse
* diuretics
* critical illness
* common with hypokalemia
181
serum Mg that defines hypomagnesemia
< 1.8 mg/dL or < 1.5 mEq/L
182
presentation of Mg < 1.2 mg/dL (or < 1 mEq/L)
* tetany
* sz
* dysrhythmias
183
s/s Mg 1.2-1.8 mg/dL or 1-1.5 mEq/L
* neuromuscular irritability
* ↓ K+
* ↓ Ca2+
184
EKG findings with hypomagnesemia
not significant unless very low (long QT)
185
treatment of hypomagnesemia
mag sulfate supplementation
186
serum Mg in hypermagnesemia
> 2.5 mg/dL or > 2.1 mEq/L
187
etiologies of hypermagnesemia
* excessive admin
* renal failure
* adrenal insufficiency
188
s/s hypermagnesemia:
5-7 mg/dL
decreased DTRs
lethargy/drowsiness
flushing
N/V
189
s/s hypermagnesemia:
7-12 mg/dL
* loss of DTRs
* ↓ BP
* EKG changes
* somnolent
190
s/s hypermagnesemia:
> 12 mg/dL
* resp depression - apnea
* complete heart block
* cardiac arrest
* coma
* paralysis
191
magnesium levels assoc with dysrhythmias
< 1.2 mg/dL or > 7 mg/dL
192
treatment of hypermagnesemia
CaCl or CaGluconate
193
4-2-1 rule for calculating fluid maintenance
* 4 mL/kg/hr for first 10 kg body weight
* 2 mL/kg/hr for second 10 kg body weight
* 1 mL/kg/hr for each subsequent kg of body weight
| For an adult, can use body weight in kg + 40 mL
194
4-2-1 rule for calculating fluid maintenance
* 4 mL/kg/hr for first 10 kg body weight
* 2 mL/kg/hr for second 10 kg body weight
* 1 mL/kg/hr for each subsequent kg of body weight
| For an adult, can use body weight in kg + 40 mL
195
calculating fluid deficit
#fasting hours x calculated hourly IVF rate
196
third space replacement
* Very minimal surgical trauma (ex. orofacial surgery): replace 1-2 mL/kg/hr
* Minimal surgical trauma (ex. inguinal hernia): replace 2-4 mL/kg/hr
* Moderate surgical trauma (ex. major nonabdominal surgery): replace 4-6 mL/kg/hr
* Severe surgical trauma (ex. major abdominal surgery): replace 6-8 mL/kg/hr
| existence of third space is controversial
197
why is UOP an unreliable measure of fluid status
ADH reduces the kidney's ability to eliminate fluid
198
fundamental objective of goal directed fluid therapy
optimizing O2 delivery
199
how does inadequate or excessive fluid affect O2 delivery
* Inadequate circulating volume reduces CO and O2 delivery
* Excessive circulating volume promotes microvascular congestion (also impairs O2 delivery)
200
which area of the starling curve best correlates with preload dependence
slope (ascending limb)
201
key principle of goal directed fluid therapy
admin. of small quantities of fluid (~200-250 mL) to determine the difference between preload dependence and preload interdependence
202
what does plateau of Starling curve suggest
* Suggests an optimal balance between circulating volume and myocardial performance
* Additional fluid would not be expected to improve hemodynamics or O2 delivery and might cause harm by pushing the patient further right on the curve
203
risks of overshooting the Starling curve
CHF
pulmonary edema
204
ERAS was originally designed for what types of surgeries
colon
205
3 most important determinants of plasma osmolarity
1. Na+
2. BUN
3. glucose
206
consequence of correcting hyponatremia too quickly
osmotic demyelination syndrome
| more common when hyponatremia persisted > 48 hrs
207
consequence of correcting hyponatremia too quickly
osmotic demyelination syndrome
| more common when hyponatremia persisted > 48 hrs
208
sodium concentration of solutions containing 0.9% NaCl
| includes 5% albumin, NS, D5NS
154 mEq/L
209
sodium concentration of 5% albumin
154 mEq/L
210
which IVF is most physiologic
plasmalyte (Na+ 140)
211
Na+ concentration of LR-containing solutions
130 mEq/L
| includes LR and D5LR
