Heme

Question 1

What lab values define anemia?

men

women

pregnancy

Answer 1

• men
  
  • Hgb <13 (nml = 13-17.5)
  • Hct <40% (nml = 42-52%)
• women
  
  • Hgb <12 (nml = 12-15.5)
  • Hct <36% (nml = 37-47%
• pregnancy hgb < 11
  
  • due to increase in plasma volume

Question 2

How do you calculate arterial oxygen content?

normal?

Answer 2

• CaO2 = (Hgb x 1.39)SaO2 + PaO2 (0.003)
  
  • 1.39 = O2 bound to hbg
  • SaO2 = satuation of hgb with O2
  • PaO2 = arterial pressure of O2
  • 0.003 = dissolved Oxygen
• Normal is 16-20

Question 3

How does the body compensate for anemia?

Answer 3

• Decreased blood viscoscity
• decreased SVR
• increased CO
  
  • increased SV and HR
  • chronic severe anemia can lead to high output heart failure
• Tissue redistribution of blood to organs with high extraction ratios
  
  • myocardium, brain, kidneys
  • causes pallor
• Kidneys secrete EPO
• Right shift on oxyhemoglobin curve
  
  • increased 2,3 DPG
  • fascilitates O2 release to tissues

Question 4

Basic anesthetic management for acute and chronic anemias

Answer 4

• Care must reflect underlying disease as well as anemia
• avoid disruption of compensatory mechanisms that are helping get O2 delivered to tissues
  
  • avoid decreasing CO (avoid high gas)
  • avoid left shift (alkalosis, hypothermia)
• Maximize O2 delivery
  
  • increase FiO2, transfuse PRBCs
• If you expect blood loss, dilute first with fluids

Question 5

What affects does anemia have on VA?

Answer 5

• VA are less soluble in anemic patients
  
  • results in accelerated uptake, but this is negated by increased CO
• no clinically detectable differences in the rate of induction
• the problem with VA and anemic pts is the myocardial depression

Question 6

How do you decide to transfuse an anemic patient?

Answer 6

• Hgb level
• risk of anemia vs risk of transfusion
• presence of co-existing disease
• magnitude of anticipated blood loss
• Clinical judgement that the O2 carrying capacity must be increased
• there is no longer a transfusion trigger–old “10/30” rule has no supportive evidence

Question 7

What are the goals of transfusing?

Answer 7

• to increase O2 carrying capacity
  
  • PRBCs
• correct a coagulation disorder
  
  • FFP, platelets, DDAVP, cryo

Question 8

How can the Hgb guide you in deciding to transfuse?

What specific co-ex disease process would you transfuse a little more aggressively?

Answer 8

• Hgb > 10, rarely indicated
• Hgb <6, almost always indicated
• Hgb 6-10, based on pts risk for complications and inadequate oxygenation
• Chronic anemia is generally well tolerated
• CAD- transfuse more agressively because Hgb <7 can lead to myocardial ischemia
  
  • or Hct 28-30%

Question 9

What are the risks of RBC transfusion?

Answer 9

• Hep B, C, HIV, and bacterial infections
• Longer ICU and hospital stays
• increased rates of ventilator associated PNA and transfusion related acute lung injury
• Hemolytic transfusion reactions
• higher mortality rates

Question 10

What are the guidelines for replacement of expected blood loss?

Answer 10

• <15% of total blood volume = no replacement needed
• 15-30% of total blood volume = replace with crystalloid
  
  • replace 3:1
• >30% generally requires RBC
  
  • replace 1:1
• >50% requires massive transfusion
  
  • RBC accompanied with FFP and platelets in ratio of 1:1:1

Question 11

How do you calculate ABL?

estimated blood volume for men?

women?

Answer 11

ABL = (EBV x (pts Hct - allowable Hct))/pts Hct

**can replact Hgb in this equation

Men = 75 ml/kg

women = 65 ml/kg

Question 12

1 unit PRBCs increases Hgb by ___ and Hct by ____.

1 unit PRBCs has a Hct of _____.

Answer 12

Hgb increased by 1 g/dl, Hct by 2-3%

70%

Question 13

What are S/S of actute blood loss?

20%?

40%?

Answer 13

• 20%
  
  • tachycardia
  • orthostatic hypotension
  • CVP change
• 40%
  
  • tachycardia
  • hypotension
  • tachypnea
  • oliguria
  • acidosis
  • restlessness
  • diaphoresis
  • ECG ischemia
  • CVP change

Question 14

How long does it take Hct to reach plateau after acute blood loss?

Decrease in Hct by 1% q24 hours can only mean ______

Answer 14

• Hct will take 3 days to reach plateau due to intravascular fluid shifts
• Decrease in Hct by 1% q 24 hours can only mean there is acute blood loss or intravascular hemolysis

Question 15

Management of anesthesia with acute blood loss:

monitoring

induction

maintenance

Answer 15

• Monitoring:
  
  • invasive? CVP, art, +/- PA
  • foley
• Induction
  
  • Ketamine
  • etomidate- need good volume
• Maintenance
  
  • may not tolerate VA
  • scopalomine, benzos, opioids all good choices
  • use vasopressors sparingly
  • keep warm
  • watch surgical field

Question 16

What labs would you want to monitor with acute blood loss?

Answer 16

• coags (PT, PTT, INR)
• CBC
• fibrinogen
• Ca and K levels
• ABGs
  
  • metabolic acidosis reflects hypovolemia and inadequate O2 delivery to tissues
• *Watch surgical field for oozing

Question 17

What should you anticipate post op with acute blood loss?

Answer 17

• may require post-op ventilation due to anticipated fluid shifts from resuscitation
• Pulmonary edema
• ARDS

Question 18

What is definition of massive transfusion?

Answer 18

• transfusion > 10 units of RBC in 24 hour period
• replacement of at least one blood volume in 24 hr period
• replacement of 50% blood volume in 6 hr period

Question 19

What are complications associated with massive transfusion?

Answer 19

• Hypothermia- use fluid warmer
• volume overload
• dilutional coagulopathy- no clotting factors in PRBCs
• decreased 2,3 dpg- effects curve
• hyperkalemia due to K leak
• citrate toxicity- binds to Ca and causes hypocalcemia
• blood contains glucose which is converted to lactat and can cause acidosis

Question 20

What disease processes can cause anemia?

Answer 20

• renal disease
• cancer
• lupus
• RA
• DM

Question 21

What do you need to consider for anesthetic management of B12 deficiency?

Answer 21

• airway evaluation and plan
  
  • thick large tongue
• maintain adequate oxygenation
• avoid N2O- depresses bone marrow and decreases B12
• RBC transfusion for life-threatening anemia (usually unnecessary)
• may want to avoid regional if paresthesia is present

Question 22

What is the anesthetic management of a pt with hereditary spherocytosis?

Answer 22

• Depends on severity and if hemolysis is staple or in a period of exacerbation
• avoid infections- higher risk due to splenomegaly and fewer macrophages ?
  
  • also higher risk of arterial and venous thromboembolism with no spleen
• cardiac bypass and mechanical heart valves are especially disruptive, lead to excessive hemolysis
  
  • ask surgeon to do procedure off pump
    *

Question 23

Paroxysmal nocturnal hemoglobinuria anesthetic management

Answer 23

• avoid respiratory depressants
• avoid hypoxemia, hypo-perfusion and hypercarbia
  
  • use ETT, not LMA
• maintain hydration and DVT prophylaxis
• if transfusion required, use “washed” RBCs to decrease complement activation

Question 24

Anesthetic management of G6PD Deficiency

Many things you should avoid

Safe drugs?

Answer 24

• Try to avoid hemolysis
  
  • avoid oxidative drugs:
    
    • NSAIDS, quinolones, sulfa
• Avoid drugs that further depress G6PD deficiency
  
  • Iso, Sevo, diazepam, metroclopramide
• Avoid Methylene blue- life threatening if administered
• Avoid drugs that cause methemoglobinemia
  
  • lidocaine, prilocaine, benzocaine, silver nitrate
• Avoid and aggressively treat conditions that cause oxidative stress:
  
  • hypothermia, acidosis, hyperglycemia, infections
• Safe drugs:
  
  • codeine, midaz, propofol, fentanyl, ketamine, des

Question 25

What are the perioperative risks and concerns associataed with hemolytic anemias? (3) What are the treatments?

Answer 25

* Risks: * increased risk of tissue hypoxia * If previous splenectomy, increase risk of periop infection * increased risk of venous thrombosis d/t activation of coagulation cascade * Treatment: * erythropoietin is often prescribed for 3 days preoperatively * Acute drops below \<8 g/dl and cronic \<6 g/dl should be considered for transfusion * preop hydration and prohpylactic RBCs * Caution with methylene blue administration

Question 26

What sickle cell patients are at higher risk for perioperative complications? Pt risk factors surgical considerations

Answer 26

* Risk factors: * advanced age * frequent severe sickling epidsodes * evidence of end-organ damage (low O2 saturation, elevated Cr, cardiac dysfunction, stroke) * concurrent infection- postpone if infected * Surgical considerations: * Low risk surgeries- extremity and minor procedures * moderate risk- inraabdominal * high risk- intracranial, intrathoracic, and hip replacement

Question 27

When would you consider a preop transfusion of a sickle cell patient? What would your goals be?

Answer 27

* Pt may benefit from conservative transfusions with high risk surgeries * goal to increase HCT to 30% without regard to ratio of sickle Hgb to normal Hgb * For major noncardiac surgeries transfuse goal of HbS \<30% * Cardiopulmonary bipass surgeries goal of HbS \<5% (require exchange transfusion)

Question 28

What should you avoid during the peri-op management of a sickle cell patient?

Answer 28

* Hypoxemia/acidosis * hypovolemia * stasis * hypothermia

Question 29

How can you reduce the peri-op risks of Sickle cell disease? Besides a conservative blood transfusion....

Answer 29

* Supplemental O2- even when transporting * Pre0op hydration for 12 hrs before surgery (usually admitted night before) * Avoid resp dep with premeds * Regional is good for pain control * aggressive pain management * avoid infections * avoid tourniquets (but not contraindicated) * keep patient warm * maintain high CO * position to prevent stasis

Question 30

What are the perioperative risks and concerns for Thalassemia Major?

Answer 30

* CHF common with severe anemia (might want echo) * Cardiac arrhythmias d/t heart failure * pt may not tolerate cardiac depression caused by anesthetic agents * pts are very sensitive to digitalis * hepatosplenomegaly * hypersplenism can result in thrombocytopenia and increased risk of infection * Coagulopathy- may not be able to use regional * Complications associated with high Fe- see other card