Case 48 - blood replacement Flashcards
what is oxygen delivery (DO2) calculated? How is arterial oxygen content calculated?
Blood oxygen content
- CaO2 = (Hb x 1.34 x SaO2) + (PaO2 x .003)
Oxygen delivery =
- DO2 = CO x CaO2
Describe compensatory mechanisms for blood loss?
- blood loss = decrease intravasc volume and reduced oxygen carrying capacity 2/2 loss of Hgb
Compensation - increase delivery
- intravasc decreaes –> compensatory vasoconstrictoin and tachycardia to increase CO (and thereby maintain DO2)
- eventually CO will decrease with continued loss –> need fluids to normalize CO
Compensation - Oxygen extraction
- decrease DO2 to tissues will lead to increase O2 extraction
- normally venous saturation is 75%. This will decrease as more oxygen is extracted to hypoxic tissues
What is the minimum acceptable hemoglobin concentration (transfusion trigger)?
- controversial
- ASA - RBC usually administered with HgB <6 and…are usually unnecessary when level is > 10 g/dL
Consideratoins
- PRBC transfuion have adverse effects - viral transmission, TRALI, acute hemolytic anemia
- Risk vs benefit
Considerations:
- health of patient and comorbidities
- nature of surgery
- presence of coagulopathies
- likelihood of post-operative oozing/bleeding
- hemodynamic stability
- evidence of adequate or inadequate oxygen carrying capacity
- risk of transfusion reaction/infection, age of patient
What are consideration for PRBC transfusion in cardiac patients?
Cardiac patients
- maximal stress on DO2 occurs in heart
- although 25% of oxygen is extracted by tissues, the heart has the highest O2 extraction of 70%.
- In stress, the heart cannot extract anymore oxygen, therefore only compensation is increase coronary blood flow.
- this is compromised in CAD patients
- as such, critical HcT level - transfusion trigger - may be higher than general population
what are examples of autologus blood transfusion?
- autologous blood transfusion - using one’s own blood for transfusion
- Examples:
- preop autologous blood donation
- acute isovolemic hemodilution
- intraop cell savage
- post-op cell savage
what are advantages of acute isovolemic hemodilution, and how is it done?
acute isovolemic hemodilution
- whole blood removed perioperatively, while intravasc volume maintained by simultaneous infusion of crystalloid or colloid
- Whole blood –> contains rbc, clotting factors, plt
Advantages
- red blood cell loss reduced with each mL of surgical hemorrhage
- fresh whole blood (with all factors) available for transfusion
- tissue perfusion improved with dec viscosity
what is the physiologic response to acute isovolemic hemodilution?
1) CaO2 decreases as RBC is removed (dec Hgb)
2) DO2 remains constant or increases
- although CaO2 decrease (dec Hgb), DO2 increases
- hemodilution –> dec blood viscosity –> inc venous return –> inc SV and CO
3) CO increases
- dec blood viscositiy –> dec SVR and inc venous return –> inc SV
- HR is unchanged as long as intravasc vol maintained
4) homogenous distribution of capillary blood flow
how is acute isovolemic hemodilution accomplished?
Removal:
- two large-bore IV catheters
- may also use an arterial catheter
- simultaneous admin of crystalloid (3:1) or colloid (1:1)
- allowable blood loss formula
- EBV = weight (kg) * Average blood volume
Allowable Blood Loss = {(Hi-Hf)/Hi} x EBV
Monitoring - when to replace fluid
- +/i arterial line
- serial HcT measurement
- tachycardia (sign of hypovolemia)
- UOP
retransfusion
- retransfuse units in reverse order of collection
- first unit is least dilute & richest in blood components –> should be last unit transfused
*
- first unit is least dilute & richest in blood components –> should be last unit transfused
What are contraindications for acute isovolemic hemodilution?
- major compensatory mechanism for hemodilution is increased blood flow
-
contraindicated in patients whose ability to increase systemic or coronary blood flow is compromised:
- CAD
- renal disease
- carotid stenosis
- anemia
What are the characteristics of blood obtained by cell savage?
- colected blood is washed and contains no clotting factors or PLT
- HcT typically 50-60%
- large volumes of salvaged blood can lead to dilutional thrombocytopenia and low levels of clotting factors
cell salvage (vs blood bank)
- normal 2,3-DPG
- normal K+
- normal pH
- no microaggregate formation
indications for cell savage
indications
- EBL > 1L
- jehovah’s witness (not all will accept it)
- rare blood type or multiple Antibodies
- surgery where blood loss is confined to discrete area (cardiac, ortho, vascular)
Benefit
- has decreased average homologous blood requirements
Controversies and contraindcations involving intraop cell savage?
Controversy
1) tumor surgery
- debated about tumor cells collecting in salvage container and being transfused –> concern of dissemination of tumor
- homologous transfusion produce an immnosuppresive effect, resulting in earlier tumor recurrence and decreased survival time in some forms of cancer
2) abdominal trauma
* concern of contaminated intestinal contents (bacteria) entering salavage system, and then being transfused back to patient
Contraindications
- topical hemostatic agents
- iodine, bacitracin, topical ABX used with irrigant solution
- blood contaminated with amniotic fluid
