Heme Flashcards
What lab values define anemia?
men
women
pregnancy
- 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
How do you calculate arterial oxygen content?
normal?
- 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
How does the body compensate for anemia?
- 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
Basic anesthetic management for acute and chronic anemias
- 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
What affects does anemia have on VA?
- 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
How do you decide to transfuse an anemic patient?
- 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
What are the goals of transfusing?
- to increase O2 carrying capacity
- PRBCs
- correct a coagulation disorder
- FFP, platelets, DDAVP, cryo
How can the Hgb guide you in deciding to transfuse?
What specific co-ex disease process would you transfuse a little more aggressively?
- 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%
What are the risks of RBC transfusion?
- 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
What are the guidelines for replacement of expected blood loss?
- <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
How do you calculate ABL?
estimated blood volume for men?
women?
ABL = (EBV x (pts Hct - allowable Hct))/pts Hct
**can replact Hgb in this equation
Men = 75 ml/kg
women = 65 ml/kg
1 unit PRBCs increases Hgb by ___ and Hct by ____.
1 unit PRBCs has a Hct of _____.
Hgb increased by 1 g/dl, Hct by 2-3%
70%
What are S/S of actute blood loss?
20%?
40%?
- 20%
- tachycardia
- orthostatic hypotension
- CVP change
- 40%
- tachycardia
- hypotension
- tachypnea
- oliguria
- acidosis
- restlessness
- diaphoresis
- ECG ischemia
- CVP change
How long does it take Hct to reach plateau after acute blood loss?
Decrease in Hct by 1% q24 hours can only mean ______
- 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
Management of anesthesia with acute blood loss:
monitoring
induction
maintenance
- 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
What labs would you want to monitor with acute blood loss?
- 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
What should you anticipate post op with acute blood loss?
- may require post-op ventilation due to anticipated fluid shifts from resuscitation
- Pulmonary edema
- ARDS
What is definition of massive transfusion?
- 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
What are complications associated with massive transfusion?
- 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
What disease processes can cause anemia?
- renal disease
- cancer
- lupus
- RA
- DM
What do you need to consider for anesthetic management of B12 deficiency?
- 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
What is the anesthetic management of a pt with hereditary spherocytosis?
- 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
*
- ask surgeon to do procedure off pump
Paroxysmal nocturnal hemoglobinuria anesthetic management
- 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
Anesthetic management of G6PD Deficiency
Many things you should avoid
Safe drugs?
- Try to avoid hemolysis
- avoid oxidative drugs:
- NSAIDS, quinolones, sulfa
- avoid oxidative drugs:
- 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
What are the perioperative risks and concerns associataed with hemolytic anemias? (3)
What are the treatments?
- 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
What sickle cell patients are at higher risk for perioperative complications?
Pt risk factors
surgical considerations
- 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
When would you consider a preop transfusion of a sickle cell patient?
What would your goals be?
- 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)
What should you avoid during the peri-op management of a sickle cell patient?
- Hypoxemia/acidosis
- hypovolemia
- stasis
- hypothermia
How can you reduce the peri-op risks of Sickle cell disease?
Besides a conservative blood transfusion….
- 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
What are the perioperative risks and concerns for Thalassemia Major?
- 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
