Perioperative Fluids Flashcards
Define hematocrit
Percent VOLUME of blood that is RBCs
What percent of body weight is water?
60%
How is TBW divided between ECF and ICF?
1/3=ECF
2/3=ICF
How is ECF TBW divided between interstitial space and plasma?
Plasma= 1/4 of ECF
Interstitial space= 3/4 ECF
How is blood returned to intravascular space? And what is 3rd spacing?
Lymphatics
Loss of fluid to the interstitial space and inability of lymphatics to compensate
Goal of perioperative fluid management
Maintain homeostasis
-pH, euvolemia and oxygen carrying capacity
What are insensible losses?
Fever, sweating, hyperventilation
Impact of estimating deficit based on NPO status And rate of replacement
Overestimates due to ADH effect and conservation of water
During surgery replace half NPO deficit in 1st hour and remainder over next two hours
Intraoperative fluid requirement categories
Deficit
Maintenance
Insensible/3rd spacing
Blood loss (3:1)
What products are considered clear liquids and how long do you need to fast after receiving them?
Water
Juice without pulp
Carbonated beverages
Tea/coffee no milk
2 hours
Purpose for carbohydrate drinks 2 hours before surgery per ERAS
A fed, anabolic state preop reduces hyperglycemia postop which reduces surgical infection
Metabolic disturbance with vomitting
Low serum Na (ADH)
Metabolic alkalosis (loss of H+)
Metabolic disturbance with diarrhea
Low serum sodium (ADH)
NAGMA (loss of HCO3)
WTF is NAGMA
Normal anion gap metabolic acidosis
Metabolic disturbance with thiazide diuretics
Low serum sodium
Metabolic alkalosis (losss of K with aldosterone)
Metabolic disturbance with loop diuretics
High serum sodium
Metabolic alkalosis (losss of K with aldosterone)
Normal IV deficit after bowel prep in adults
500 ml crystalloid
What is considered adequate IV replacement with blood loss
Crystalloid vs colloid
3:1
1:1
Replacement of paracentesis in g of albumin
8g per 1L ascites removed
When do hemodynamic adverse events following paracentesis occur?
3 hours
How many g of albumin is in 25%? 5%?
25g/100ml
5g/100ml
Calculating NPO fluid deficit
Maintenance rate X hours NPO
Average volume of gastric secretions made by adult in 8 hours
500-1000 cc
4:2:1 rule
Maintenance requirements
First 10kg 4ml/kg/hr
Next 10kg 2 ml/kg/hr
Each kg above 20 kg add 1 ml/kg/hr
70 kg patient
40+20+ 50
Secondary calculation to get normal maintenance requirements
1.5 ml/kg/hr
-smaller numbers especially in children
IBW for men
50kg + 2.3 kg for every inch >5ft
IBW for women
45.5kg + 2.3kg for every inch over 5ft
Which weight should we use for fluid calculations?
Easier to die from Hypovolemia than pulmonary edema
Estimation of intraop blood loss
4x4s 10 ml
Laps soaked 100-150mls
Intraop hematocrit interpretation
Represents a minimum EBL, ie. Overestimates the true Hct
Blood loss is dynamic
Estimating allowable surgical blood loss based on crit
-Calculate EBV 65ml/kg (women) X weight in kg
-Calculate red blood cell volume current and anticipated
Starting crit 35%, anticipated 24%, blood volume 5525
(0.35x5525)
(0.24x5525)
Calculate the difference and multiply by three
Why do we multiply our red cell volume loss by 3 when calculating EBL
RBC are 1/3 of plasma volume
Why is our static goal for hematocrit > 21-24%?
Because less than this the CO has to greatly increase to maintain normal oxygen delivery
How much will a unit of PRBCs raise Hb/crit? In a sense of further bleeding
Adults- 1 g/dL Hb and 2-3% rise in Hct
Fluid requirements for minimal/moderate and severe tissue trauma due to third spacing/evaporative loss
Minimal 0-2 ml/kg/hr
Moderate 3-4 ml/kg/hr
Severe 5-8 ml/kg/hr
What is goal directed fluid therapy?
Fluid admin guided by direct or indirect measurements of an increase of SV >10% with infusion
Threshold for fluid administration with SVV
SVV >10-15% the patient would benefit from fluid
What will you always do to your fluids and why
Warm them!
Hypothermia induces:
Coagulopathy
L shift oxy hemoglobin curve
Pulm hypertension
Shivering
Delayed awakening/drug metabolism
Half-life of crystalloid vs colloid
Crystalloid- 20-30 min
Colloid- 3-6 hours
What’s the physiologic difference between crystalloid and colloids?
Colloids maintain plasma oncotic pressure longer
What is the difference between crystalloid and colloids?
Crystalloids = water + electrolytes with or without glucose
Colloids = water + high molecular-weight substances such as proteins
[albumin and ”plasma protein fraction”] or large glucose polymers
What is dextran and why to use it
Complex polysaccharide colloid, name based on molecular weight
-reduces blood viscosity
-anticoagulant- impairs platelet adhesion
Dextran 70 vs 40
70- volume expansion
40- flow improving effects
Both have similar anticoagulant effects
First vs third generation hetastarch
Third gen has minimal effect on coagulation and renal function! G2G
● Minimal effect on coagulation
● No AE on renal function
● Minimal pruritis
● Hyperbilirubinemia with [potato-derived] HES 130/0.42
What are the advantages/disadvantages of colloid administration?
Rapid correction if IV deficit
Less tissue edema
Cost
Adverse effect of the Michelin man syndrome
Compression/restriction in micro vasculature that leads to poor wound healing
Na concentration in Nacl
154
Concentration Na in LR
130
Difference between osmolarity and osmolality
Number of osmoles (osmotically active particles) in solution
Osmolality- Osm/kg
Osmolarity Osm/L
What is tonicity
Measure of relative osmotic potential across membrane
NO UNITS
Only considers solutes that do NOT cross cell membrane- therefore predicts flow of water across membrane
Hypotonic fluids (water direction)
Water into cell
Hypertonic fluids (water direction)
Water out of cell
What is normal plasma osmolality
285-295 mOsm/L
How do we calculate plasma osmolality
2(Na) + (glucose/18) + (BUN/2.8)
Glucose and BUN in mg/dL
Osmolarity gap
Difference between measured and calculated osmolarity gap
Normal<10 mOsm/L
What does an elevated gap mean?
Presence of osmotically active compounds in plasma other than Na, Cl, glucose, and urea.
For example, ethanol, methanol,
ethylene glycol, or isopropyl alcohol.
What is the value of isotonic bicarbonate in uremic acidosis?
Correct acidosis while correcting volume status
Treat Hyperkalemia
How much does 150 mEq/L of NaHCO3 raise serum Na?
And amp of bicarbonate raises Na by 1-1.5 mEq/L-beware hypernatremia
Impact of LR on patients with hyperkalemia
Additional K at 4 mEq/L will not impact serum K
Can LR be given with blood?
Barry says yes
Calcium amount is insufficient to bind citrate
Relative contraindications to LR
Hepatic failure (lactate accumulation)
Elevated ICP- slightly hypotonic
Severe hyponatremia
Metformin induced lactic acidosis
Hypercalcemia
What happens to lactate in LR?
Converted in the liver to bicarbonate- eliminated via CO2 in the lungs
3 ways to choose between crystalloids for a given patient
Tonicity
Patients pH
Need for glucose or electrolytes
Tonicity of D5, LR and saline
D5W- hypotonic
LR- isotonic
NS (.9 or 3) hypertonic
3 regulators of serum sodium
Thirst (hypothalamus)
ADH (posterior pituitary)
Aldosterone (related to renal cation excretion ie. H+ & K+)- secondary
Describe non-linear mortality associated with hyponatremia
Moderate hyponatremia has highest mortality and is associated with life threatening diseases
Extreme hyponatremia has lower mortality and probably drug related
What is the horse animation in Barry’s lecture? And why is it in there
Quick straw magraw- highlights important points
Why do we keep patients slightly positive instead of the restrictive method?
Hypovolemic patients get acidotic and die faster than slightly positive patients if they get pulm edema
What’s the perfusion pressure of the skin?
Forward pressure - backward pressure = perfusion pressure??
Arterial-venous?
How many grams of albumin in 100 ml of 25%?
25g
Explain differential diagnoses of hyponatremia
Tonicity!!!
Hypotonic- ie true hyponatremia is 85% of cases <280 mosm/kg
Isotonic- pseudocholinesterase-hyponatremia 280-295
Hypertonic- translational hyponatremia >295
Causes of hypertonic! hyponatremia (translational)
Osmotically active solutes pull water into ECF
Hyperglycemia
Mannitol/sorbitol/glycine or irrigation solutions
Assessment of volume status in hypovolemic? hyponatremia
What does psychogenic polydipsia produce?
Euvolemic hyponatremia
SIADH
Most common cause of hyponatremia (30%)
Diagnosis of exclusion- can’t make diagnosis in presence of anything else
Euvolemic hypotonic hyponatremia and U Na>20
Diuretics that excrete sodium
Thiazide
Treatment of hyponatremia
Rapidity depends on acuteness
Fluid restriction/hypertonic/vaptan
Risk associated with rapid sodium correction in chronic setting
Osmotic demyelination syndrome
Osmotically demyelination syndrome
Central pontine myelinolysis
Slow over correction of sodium with DDAVP
Biphasic clinical picture- initial reduction in symptoms followed by new neurological findings (quadraparesis)
What are vaptans?
ADH receptor antagonists
What are ADH receptors?
=vasopressin receptors (V1, V2)
Rate of sodium correction based on duration of hyponatremia
● Duration of Hyponatremia = Hours
Rapid correction ok [4-6 mmol/l in 1st 6 hours if necessary]
● Duration of Hyponatremia = 1-2 Days
< 10 mmol/L/day
● Duration of Hyponatremia Unknown or > 2 Days
< 8 mmol/L/day or lower if at high risk for
DDx of hypernatremia depends on
Volume status
Conditions associated with hypervolemic hypernatremia
Cushing; primary hyperaldosertonism
NaHCO3
0.9% saline
Tonicity difference between hyper and hyponatremia
Hypernatremia always reflects a condition of hyper tonicity whereas hyponatremia can be iso/hypo/hyper
Clinical presentation of hypernatremia
Acute:
Rupture of bridging veins (ICH)
ODS
Lethargy/ weakness
Chronic:
Often asymptomatic
Treatment of hypernatremia
Always with D5W
Acute rapid
Chronic- slow to prevent cerebral edema
How does bowel prep factor into preop deficit?
500 ML IV CRYSTALLOID
Adjusted body weight
IBW + 0.4(actual-IBW)
Describe anticoagulant effect of dextrans
Direct thrombin inhibition and plasminogen activator
Reduces [VIII-vWF] resulting in impaired platelet adhesion
Describe hydroxyethyl starch’s- solvent, concentrations and tonicity
solvent- NS!!
6% isotonic
10% hypertonic
Colloid with macromolecules made from corn/potato
Osmolarity and osmolality both consider:
all particles in solution, not just those particles able or unable to cross a semipermeable membrane
Hypo-osmo vs iso-osmo lol
All hypo-osmolar solutions are hypotonic.
● But all iso-osmolar solutions are NOT isotonic
-due to the fact that osmo is in reference to freely flowing particles and tonicity is not
What do we give to correct or not exacerbate NAGMA?
D5W with some bicarbonate
What do we give to correct or not exacerbate uremic HAGMA
D5W and bicarbonate
What do we give to correct or not exacerbate
Metabolic alkalosis
0.9 NaCl
When might you see isotonic hyponatremia? -and what’s another name for it
Pseudo-hyponatremia
-Lab artifact in presence of hyperlipidemia and hypertriglycyeridemia
-Obstructive jaundice
States with high urine K
Cushing and hyperaldo
-uptick in cortisol forces excretion of K
Findings in SIADH hyponatremia
Diagnosis of exclusion but:
-euvolemic hypotonic hyponatremia
-(U)Na>20 mEq/L, or very high >40meq
-low BUN and Uric acid
Symptoms of hyponatremia
Severe: decreased LOC, seizures, muscle rigidity
Other: N/V, headache, bloating, weakness
When to use a vaptan
CHF
Pure fluid overload, antagonize vasopressin in the kidneys leading to increased UOP
Conivaptan
VA1
And V2
(VSM and platelets)
Tolvaptan
V2 inhibition PO
