Lessons 5 & 6 Flashcards
Most important goal of fluid therapy
To maintain hemodynamic stability and protect vital organs from hypoperfusion
True/False: blood loss is better tolerated in a euvolemic patient
True
Total Body Water
Males vs Females
TBW is…
60% body weight in males
55% body weight in females
- Infants have up to 80%*
- Obese = less TBW (fat contains little water)*
Intracellular vs Extracellular Water
Intracellular = 2/3 of TBW
Extracellular = 1/3 TBW
*Note: the picture makes it look like extracellular takes up more space
How is extracellular water further subtyped?
Remember extracellular = 1/3 TBW
Extravascular water = 2/3 of Extracellular
Intravascular water = 1/3 of Extracellular
Define orthostatic hypotension
SBP decrease of >20 mmHg from supine to standing
Indicates fluid deficit of 6-8% body weight
Perioperative Fluid Requirement Factors to account for
- Maintenance Fluid
- Compensatory Fluid Bolus
- NPO and other deficits
- Third Space Losses
- Blood Loss
- Special additional losses
How to calculate maintenance fluid requirements?
4-2-1 Rule
4 ml/kg/hr for the 1st 10 kg of body weight
2 ml/kg/hr for the 2nd 10 kg of body weight
1 ml/kg/hr for every kg thereafter
OR
1.5 ml/kr/hr for adults
What is maintenance fluid replacement meant to account for?
Meant to replace insensible water losses from respiratory tract, sweat, feces, and urine
Why do we give a compensatory fluid bolus?
Potent inhalational agents decrease BP by vasodilation and, to a lesser extent, myocardial depression (propofol and barbiturates have similar action)
Fluid bolus (500 ml in a 70kg patient) early in anesthetic care is customary to mitigate severe decreases in BP
How to calculate NPO deficits
NPO = number of hours NPO x maintenance fluid replacement
Usually start in the am (healthy people do not wake up and drink their entire overnight fasting deficit)
Bowel prep may result in how much fluid loss?
up to 1 L
How do we replace “third space” losses?
Superficial surgical trauma: 1 ml/kg/hr
Minimal surgical trauma (hernia, knee surgery): 2 ml/kg/hr
Moderate surgical trauma (pelvic surgery): 3 ml/kg/hr
Major trauma (open abd surgery): 4 ml/kg/hr
Replacement of blood loss
The 4:1 rule
For every ml of isotonic cystalloid that stays intravascular, about 3-4 ml will be lost to extravascular space (replacement volume needs to be 4x blood loss)
Limitations of the 4:1 Rule
For patient’s with significant blood loss you are putting large volumes of fluid into their interstitial space intentionally…
…Edema disrupts normal function of extravascular space
When would you use colloids (6% hetastarch, 5% albumin) over crystalloids?
When blood loss exceeds 5 ml/kg
About 70% of colloid remains in intravascular space compared to 20% of crystalloid
Note, using colloids is controversial and some studies show increased mortality when used in trauma patients
Combination of water and electrolytes
Crystalloids
Balanced salt solutions = LR, Plasmalyte, Normosol
Hypotonic salt solution = D5W
Fluids containing molecules sufficiently large enough to prevent transfer across capillary membranes
Colloids
6% Hetastarch (Hespan) and 5% Albumin
Problems with D5W
Can result in hyperglycemia
Glucose is metabolized and taken up by cells…
…only 95% of pure water left behind remains in the intravascular space)
Large quantities of normal saline results in
a mild metabolic acidosis because the high levels of chloride ions exchange with bicarbonate ions, encouraging its elimination
“Problems” with LR
- Need to monitor sodium levels (identify declining sodium concentration)
- LR contains calcium and should not be mixed with banked blood (inactives the EDTA anticoagulant)*
- Hyperkalemia (especially in patients with renal failure)**
- *Unless 1 unit of packed red blood cells takes more than 2 hours to transfuse, this is not an issue*
- **In patients w/o RF, LR will typically on raise K levels if the person is below 4 (…which means they should have K replaced regardless)*
Does LR cause lactic acidosis?
NO
This has been proven by many studies…
BLUF: LR is replacing NS as the “go to” resuscitative fluid (exception = brain injuries requiring diuresis w/ hypertonic saline)
What is plasmalyte?
A product that tries to deliver the best aspects of LR and NS
It has no free water or calcium so it should not cause dilutional hyponatremia and can be mixed with blood. It does have potassium (dangerous with RF patients). It is rarely used in the OR since it is expensive and the real-life benefit is minimal.
Clinical Evaluation of Fluid Replacement
Urine Output: 0.5 ml/kg/hr
Vital Signs: BP and HR
MMM
Arm and Neck veins
Invasive monitoring (CVP, PCWP, echo)
Lab tests (Hct, BUN, pH, serum bicarb)
*Note: this is a very simplistic way to look at “volume responsiveness”
What is the main purpose of blood
Delivery of oxygen to the tissues
What is the main determinant of oxygen content in the blood
Hemoglobin
How to calculate oxygen delivery (DO2)?
DO2 = Oxygen Content (CaO2) x Cardiac Output (CO)
CaO2 (Hgb + Plasma) = Hgb x 1.34 x O2 sat + PaO2 x 0.003
CO = HR x SV
*This equation is important when trying to increase oxygen delivery in sick patients (i.e., you can give blood to increase Hgb, give O2 to improve their sats, and “theoretically” increase CO by increasing HR and/or SV…PaO2 is neglible in this equation)
When is transfusion necessary?
Think oxygen delivery (DO2)
Transfusion threshold = Hgb < 7 (sooner if they are unstable/symptomatic)
What blood type do you give if you must transfuse but have no time to ascertain the recipient’s blood type?
Type O Rh negative
(can use Rh positive for males)
Fresh Frozen Plasma contains…
all clotting factors (except platelets)
used when PT and PTT are >1.5 normal
Cryoprecipitate contains…
factors VIII and fibrinogen
used in Von Willebrand’s disease
1 unit pRBCs raises Hgb by how much?
1 gm/dL
When do you transfuse platelets?
Intraoperatively if platelet count drops below 50,000
1 unit of platelets increases platelet count 5,000-10,000
Treatment of Acute Hemolytic Reactions
Immediate discontinuation of blood products
Support Hemodynamics
Maintenance of urine output with crystalloid infusions
Mannitol or Furosemide for diuretic effect
What is most common agent transmitted through blood products?
CMV (only affects immunocompromised and neonates)
Erythropoietin (alternative to blood products)
Can be used as an adjunct to autologous blood donation with iron, B12, and folate
Raises Hct for isovolemic hemodilution
What is Isovolemic Hemodilution?
Blood is withdrawn in collection bags after induction to a Hct of 30%
Equal volume replaced with colloids
Blood kept at room temp
Infused in reverse order of collection
Rationale = loose low Hct blood intra-op then give high Hct blood & factors post-op
Intra-op Blood Salvage
Commonly known as “cell-saver”
Allows collection of blood during surgery for re-transfusion (RBCs washed and centrifuged from plasma)
Hyperbaric Oxygen Therapy
Used to increase plasma oxygen content (useful in Jehovah’s Witness)
100% O2 at sea level = 1.8 ml/dl blood of O2
100% O2 at 3 ATA = 5-6 ml/dl blood of O2
O2 consumption of the body = 5=6 ml/dl blood
During all anesthetics the following parameters will be continually monitored:
Oxygenation
Ventilation
Circulation
Temperature
How do we monitor oxygenation?
Inspired oxygen gas analyzer
Pulse ox
Illumination/exposure
How do we monitor ventilation?
Qualitative: chest excursion, observation of reservoir bags, auscultation
Quantitative: end tidal CO2, volume of expired gas, continuous circuit disconnect monitor
Hyperventilation does what to pCO2
Lowers it = respiratory alkalosis
How do we monitor circulation?
Continuous electrocardiogram monitoring
Arterial BP and HR q5
Palpation of pulses, auscultation, pulse ox, doppler peripheral pulse
Traditional Auscultatory Cuff Pressure
Phase 1 = first sound and corresponds to systolic pressure
Phase 2 = loudest sound
Phase 4 = muffling
Phase 5 = loss of audible sound and corresponds to diastolic pressure
What do digital/automatic BP cuffs measure?
MAP
Unlike manual BPs, BP cuffs used during surgery will employ oscillometric measurements to determine BP based on the mean arterial pressure
Too small BP cuff results in…
erroneously high measurements
also happens with cuffs that are too large
4-5-6-7-8-9 rule
allows you to use SpO2 to estimate PaO2
SpO2 70% = PO2 of 40 (supplemental oxygen is essential on any patient)
SpO2 80% = PO2 of 50 (some chronic lungers live here)
SpO2 90% = PO2 of 60 (This is what you want to maintain for most patients)
Which monitors should be attached first in the PACU?
Pulse ox
The pulse ox and capnograph detect the majority of mishaps
The ECG has relatively little objective value except in the cardiac patient or in other patients who are at risk of dysrrhythmia, such as patients with trauma and electrolyte disturbance. When we say the ECG has low value, we mean in the particular context of a pulse oximeter being used at the same time. The oximeter provides information that overlaps that of the ECG but is in many ways more valuable. In addition to telling us what the saturation is, it tells us that the heart is undergoing mechanical as well as electrical systole, what the heart rate is, and roughly its regularity.
