Calculation for arterial O2 content
CaO2 = SaO2(Hgb x 1.39) + PaO2(0.003) 1.39 = O2 bound to hemoglobin SaO2= saturation of hemoglobin with O2 PaO2= arterial partial pressure of oxygen 0.003 = dissolved oxygen ml/mmHg/dl Normal O2 capacity is 16-20 mL/dL
Normal value for O2 content / capacity
16-20mL/dL
O2 carrying capacity is defined by the presence of
hemoglobin More hemoglobin = more O2 carrying capacity
Causes of anemia
- Acute • Acute blood loss 2. Chronic • Nutritional deficiency • Hemolytic anemia • Aplastic anemia • Manifestation of another disease • Abnormal structure of RBC • Sickle cell, thalassemias
Compensatory mechanisms involved in anemia
– Increased cardiac output – Increased red blood cell 2,3-diphoshoglycerate (DPG) – Increased P-50 (partial pressure of O2 at which Hgb is 50% saturated with O2) – Increased plasma volume – Decreased blood viscosity – Decreased SVR (larger BV diameter allows more blood to flow through it) – RIGHTWARD shift of Oxygen-Hemoglobin dissociation curve – Redistribution of blood flow to organs with higher extraction ratio (ER) –> cardiac and brain cells
A shift to the right in the Hgb dissociation curve is associated with
- Facilitates release of O2 from Hgb to tissues - Hgb variants with O2 affinity - Due to Acidosis - Exercise - Hypermetabolism and fever - Increased 2,3 diphosphoglycerate (2,3-DPG)
A shift to the left in the Hgb dissociation curve is associated with
- Inhibits release of oxygen from HGB to tissues - Alkalosis - Hbg variants that increase O2 affinity (carbon monoxide) - Hypothermia - Decreased 2,3 diphosphoglycerate (2,3-DPG)
Anemia is suspected in these values for men and women
–
What is the most effective treatment of anemia?
Treat the cause! Remember that anemia is almost always the manifestation of another disease process
General anesthesia management for chronic anemia
- Maximize O2 delivery – Consider ↑ FiO2 – Transfuse If necessary 2. Avoid drug-induced ↓ in C.O. – Selection of induction agent (etomidate) – Anesthetic technique (↑ opioid) – Hydrate, if tolerated; avoid hypovolemia 3. Avoid conditions that favor a leftward shift of the oxyhemoglobin dissociation curve – Avoid respiratory alkalosis, hypothermia, etc. 4. Consider your volatile anesthetics – May be less soluble in plasma of anemic patient (b/c volatile anesthetics cling to the lipid layer of RBCs) • This is more theoretical than actual, but may need to decrease your IA dose – Consider that this decrease in solubility may be offset by the impact of increased cardiac output
Causes of iron deficiency anemia
o Disorder of hemoglobin resulting in reduced or ineffective erythropoiesis and microcytic RBCs o Most common form of nutritional deficiency in children and infants o In adults- reflects depletion of iron stores from chronic blood loss, which may be from: • Gastrointestinal tract • Menorrhagia • Cancer
S/S of Pernicious Anemia and Anesthetic Considerations
S/S: • Bilateral peripheral neuropathy (assess for this pre-op!) • Loss of proprioceptive and vibratory sensations in lower extremities • Decreased deep tendon reflexes • Unsteady gait • Memory impairment and mental depression Anesthesia: • Avoid regional blocks due to neuropathies • Avoid nitrous oxide (b/c it inhibits methionine synthase –> necessary for mylin formation) • Maintain oxygenation • Emergency correction for imminent surgery is with red cell blood transfusions
S/S of Folic Acid (B9) Deficiency anemia and anesthetic considerations
S/S • Smooth tongue • Hyperpigmentation • Mental depression • Peripheral edema • Liver dysfunction • Severely ill patients Anesthesia • Note thorough airway exam →Oral manifestations may make airway management challenging due to changes in tongue texture, etc. • Have an alternate airway management plan!
These are the 4 hereditary hemolytic anemias
• Hereditary spherocytosis • Paroxysmal nocturnal hemoglobinuria • Glucose-6-Phosphate Dehydrogenase Deficiency • Pyruvate Kinase Deficiency
Hereditary spherocytosis
o Hereditary disorder affecting red cell membrane skeletal structure o Lifelong hemolytic anemia o Most common red cell membrane defect-disorder of membrane skeletal proteins -> cell more rounded, fragile, shortened circulation half-life (destroyed in spleen) o Splenomegaly, fatigability, risk of episodes of hemolytic crisis, often precipitated by infections; risk of gallstones/ jaundice
Paroxysmal nocturnal hemoglobinuria (description and anesthetic considerations)
o Hereditary disorder of RBC structure o Clonal disorder that arises in hemotopoietic cells with a reduction in membrane protein in RBCs o Poor prognosis once diagnosed (8-10 years) • Preoperative hydration and prophylactic administration of RBCs have been advocated
Glucose-6 Dehydrogenase Deficiency (description and anesthetic considerations)
o Disorder affecting red cell metabolism o Most common enzymopathy- African Americans, Asians, Mediterranean populations-> G6PD activity decreases-> susceptible to damage by oxidation o ↑ rigidity of membrane & accelerates clearance • Affects approximately 10% of black males in U.S. • Acute and chronic episodes of anemia Anesthesia: • Need to avoid exposure to oxidative drugs (methylene blue, IAs, benzos, etc) • Avoid hypothermia, acidosis, hyperglycemia, infection
Pyruvate Kinase Deficiency
o Disorder affecting red cell metabolism o Deficiency of glycolic enzyme which converts glucose to lactate & is primary pathway for ATP production->results in K+ leak-> ↑ rigidity & accelerates destruction o Accumulations of 2.3-DPG in the RBCs cause right shift oxy-Hbg curve
Anesthetic Considerations for Hemolytic Anemias*******
o ↑ risk of tissue hypoxia o If previous splenectomy may have ↑ risk of perioperative infection o Increased risk venous thrombosis due to activation of coagulation o Erythopoietin is often prescribed for 3 days preoperatively o Preop hydration and prophylactic administration of RBCs have been advocated o Acute drops in Hb below
Patho of sickle cell disease
Mutant hemoglobin (S) due to valine substitution for glutamic acid on B-globulin chain-> Hgb aggregates & forms a polymer when exposed to low O2 concentrations This can cause small vessels to be occluded
Lifespan of a RBC is sickle cell disease
12-17 days
Is sickle cell TRAIT, the patient is heterozygous for the gene, and __% of their Hgb is S, and __ % is normal Hgb A
40% = S 60% = Normal Most patients are asymptomatic and does not pose risk for surgery or anesthesia.
In sickle cell DISEASE, the patient is homozygous for the gene and __% of their Hgb is Hgb (S) form
70-98%
Sickle Cell patients are at high risk for these complications peri-operatively d/t hemolysis and vasoocclusion
– Stroke – Heart failure – MI – Hepatic or splenic sequestration – Renal failure
