Lessons 5 & 6

Question 1

Most important goal of fluid therapy

Answer 1

To maintain hemodynamic stability and protect vital organs from hypoperfusion

Question 2

True/False: blood loss is better tolerated in a euvolemic patient

Answer 2

True

Question 3

Total Body Water

Males vs Females

Answer 3

TBW is…

60% body weight in males

55% body weight in females

• Infants have up to 80%*
• Obese = less TBW (fat contains little water)*

Question 4

Intracellular vs Extracellular Water

Answer 4

Intracellular = 2/3 of TBW

Extracellular = 1/3 TBW

*Note: the picture makes it look like extracellular takes up more space

Question 5

How is extracellular water further subtyped?

Answer 5

Remember extracellular = 1/3 TBW

Extravascular water = 2/3 of Extracellular

Intravascular water = 1/3 of Extracellular

Question 6

Define orthostatic hypotension

Answer 6

SBP decrease of >20 mmHg from supine to standing

Indicates fluid deficit of 6-8% body weight

Question 7

Perioperative Fluid Requirement Factors to account for

Answer 7

1. Maintenance Fluid
2. Compensatory Fluid Bolus
3. NPO and other deficits
4. Third Space Losses
5. Blood Loss
6. Special additional losses

Question 8

How to calculate maintenance fluid requirements?

Answer 8

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

Question 9

What is maintenance fluid replacement meant to account for?

Answer 9

Meant to replace insensible water losses from respiratory tract, sweat, feces, and urine

Question 10

Why do we give a compensatory fluid bolus?

Answer 10

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

Question 11

How to calculate NPO deficits

Answer 11

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)

Question 12

Bowel prep may result in how much fluid loss?

Answer 12

up to 1 L

Question 13

How do we replace “third space” losses?

Answer 13

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

Question 14

Replacement of blood loss

Answer 14

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)

Question 15

Limitations of the 4:1 Rule

Answer 15

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

Question 16

When would you use colloids (6% hetastarch, 5% albumin) over crystalloids?

Answer 16

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

Question 17

Combination of water and electrolytes

Answer 17

Crystalloids

Balanced salt solutions = LR, Plasmalyte, Normosol

Hypotonic salt solution = D5W

Question 18

Fluids containing molecules sufficiently large enough to prevent transfer across capillary membranes

Answer 18

Colloids

6% Hetastarch (Hespan) and 5% Albumin

Question 19

Problems with D5W

Answer 19

Can result in hyperglycemia

Glucose is metabolized and taken up by cells…

…only 95% of pure water left behind remains in the intravascular space)

Question 20

Large quantities of normal saline results in

Answer 20

a mild metabolic acidosis because the high levels of chloride ions exchange with bicarbonate ions, encouraging its elimination

Question 21

“Problems” with LR

Answer 21

• 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)*

Question 22

Does LR cause lactic acidosis?

Answer 22

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)

Question 23

What is plasmalyte?

Answer 23

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.

Question 24

Clinical Evaluation of Fluid Replacement

Answer 24

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”

Question 25

What is the main purpose of blood

Answer 25

Delivery of oxygen to the tissues

Question 26

What is the main determinant of oxygen content in the blood

Answer 26

Hemoglobin

Question 27

How to calculate oxygen delivery (DO₂)?

Answer 27

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)

Question 28

When is transfusion necessary?

Answer 28

Think oxygen delivery (DO₂)

Transfusion threshold = Hgb < 7 (sooner if they are unstable/symptomatic)

Question 29

What blood type do you give if you must transfuse but have no time to ascertain the recipient’s blood type?

Answer 29

Type O Rh negative

(can use Rh positive for males)

Question 30

Fresh Frozen Plasma contains…

Answer 30

all clotting factors (except platelets)

used when PT and PTT are >1.5 normal

Question 31

Cryoprecipitate contains…

Answer 31

factors VIII and fibrinogen

used in Von Willebrand’s disease

Question 32

1 unit pRBCs raises Hgb by how much?

Answer 32

1 gm/dL

Question 33

When do you transfuse platelets?

Answer 33

Intraoperatively if platelet count drops below 50,000

1 unit of platelets increases platelet count 5,000-10,000

Question 34

Treatment of Acute Hemolytic Reactions

Answer 34

Immediate discontinuation of blood products

Support Hemodynamics

Maintenance of urine output with crystalloid infusions

Mannitol or Furosemide for diuretic effect

Question 35

What is most common agent transmitted through blood products?

Answer 35

CMV (only affects immunocompromised and neonates)

Question 36

Erythropoietin (alternative to blood products)

Answer 36

Can be used as an adjunct to autologous blood donation with iron, B12, and folate

Raises Hct for isovolemic hemodilution

Question 37

What is Isovolemic Hemodilution?

Answer 37

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

Question 38

Intra-op Blood Salvage

Answer 38

Commonly known as “cell-saver”

Allows collection of blood during surgery for re-transfusion (RBCs washed and centrifuged from plasma)

Question 39

Hyperbaric Oxygen Therapy

Answer 39

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

Question 40

During all anesthetics the following parameters will be continually monitored:

Answer 40

Oxygenation

Ventilation

Circulation

Temperature

Question 41

How do we monitor oxygenation?

Answer 41

Inspired oxygen gas analyzer

Pulse ox

Illumination/exposure

Question 42

How do we monitor ventilation?

Answer 42

Qualitative: chest excursion, observation of reservoir bags, auscultation

Quantitative: end tidal CO₂, volume of expired gas, continuous circuit disconnect monitor

Question 43

Hyperventilation does what to pCO₂

Answer 43

Lowers it = respiratory alkalosis

Question 44

How do we monitor circulation?

Answer 44

Continuous electrocardiogram monitoring

Arterial BP and HR q5

Palpation of pulses, auscultation, pulse ox, doppler peripheral pulse

Question 45

Traditional Auscultatory Cuff Pressure

Answer 45

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

Question 46

What do digital/automatic BP cuffs measure?

Answer 46

MAP

Unlike manual BPs, BP cuffs used during surgery will employ oscillometric measurements to determine BP based on the mean arterial pressure

Question 47

Too small BP cuff results in…

Answer 47

erroneously high measurements

also happens with cuffs that are too large

Question 48

4-5-6-7-8-9 rule

Answer 48

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)

Question 49

Which monitors should be attached first in the PACU?

Answer 49

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.