Case 50 - Sickle cell disease Flashcards
What is the difference between sickle cell trait and sickle cell disease?
Sickle cell trait
- asymptomatic heterozygous carrier
Sickle cell disease
- symptomatic homozygous for sickle cell gene
What is the underlying genetic abnormality responsible for sickle cell disease, and how does this lead to sickling?
Normal RBC
- Hemoblobin A (HbA) is composed of two alpha-globin and two beta-globin chains
HbS (hemoglobin S gene)
- disorder of the beta-hemoglobin chain
- one abnormal and one normal beta-globin gene = heterozygous carrier state
- two abnormal beta-globin gene = homozygous genotype = sickle cell disease
Sickling
- dexoygenation of HbS leads to hemoglobin instability and decrease molecular stability
- results in sickling (membrane distortion)
- consequences
- RBC clumping –> slugish movement of RBC (inc viscosity) –> decrease tissue blood flow
- hemolysis with resulting anemia
- reduced life span
- vascular obstruction / occlusion
Describe the presentation of sickle cell disease
Mechanism of action
- deoxygenated HbS –> molecular instability –> sickling –> RBC clumping and inc viscosity –> vascular obstruction/occlusion
- symptoms = multi-systemic disease
1) acute vasoocclusive (pain) crisis
- sickle cells occlude vessels –> inflammatory response results –> increased intramedullary pressure and nociceptor stimulation –> bone pain
- tx: rest, warmth, hydration, opioids, ABX
2) Acute Chest syndrome (ACS)
- medical emergecy
- occlusion of pulmonary vessels –> chest pain, hypoxemia, respiratory distress
- leading cause of death and hospitaliazation
- tx: O2, CPAP or mech vent, hydration, bronchodilators, ABX, steroids
What are tx goals for SCD that present to the hospital?
Goals
- avoid any states of dexoygenated HbS –> avoid right shift of O2-Hgb dissociation curve (facilitates O2 unloading to tissue with resultant deoxy Hgb form)
- avoid stressors on body (hypoxia/hypercarbia, pain, dehydration, poor perfusion, acidosis, anemia, etc…)
- hydration
- adequate pain medication
- supportive management
Describe hemolytic crisis and splenic sequestration crisis
Hemolytic crisis (aplastic crisis)
- rapid RBC death and massive suppression of normal erythopoieis
- Parvovirus B19, Epstein-Barr virus)
Splenic sequestration crisis
- due to sickling of cells, spleen sequesters damanged RBCs to destroy them.
- massive amounts of RBC lead to splenomegaly
other conditions
-
any where in the body can be affected secondary to vasc occlusion and ischemia
- coronary infarct, pulm infarct
- renal infarct
- stroke
- peripheral neuropathy
- chronic hemolysis –> elevated bili –> cholelithiasis
What are your perioperative goals to prevent sickling?
Major Goal - avoid stress on body, avoid conditions resulting in deoxygenated HbS, avoid right shift in O2-Hgb curve (facilitates o2 release, thus deoxy hgb)
1) oxygenation
* maintain SaO2 > 95%
2) tissue perfusion
- maintain normovolemia/hydration
- avoid prolonged fasting times
- aggressive replacement of fluid or blood losses
3) acid-base regulation
* avoid acidosis (causes right shift in O2-Hgb curve)
4) temperature control
* normothermia. Hyperthermia causes right shift, hypothermia causes sludging
5) hematologic
- transfusing to incresae Hgb to 10 g/dL (not more, not less)
- avoid high Hgb levels –> inc viscosity and sludging
6) infections
* Abx therapy
7) postop analgesia
* regional anesthesia and multimodal approach
why are patients with SCD typically placed on ABX?
- typically get splenic sequestration crisis secondary to spleen sequestering massive amount of damaged RBCs
- result in hyposplenic or asplenic (auto-infarction) infection
- organisms –> encapsultaed baceterial organism (strep pneumo, neisseria meningitidis, H. influenzae).
Also, patients have infarcts throughout the body –> necrosis –> nidus for bacteria to grow
How will you perform your pre-op assessment in SCD patients?
History
- past sickle cell manifestations
- hospitalizations for SCD
- review all organ system to see if they are damaged (CNS, CVS, Pulm, Renal, Heme)
- CNS - stroke, cranial nerve neuropathy, peripheral neuropathy
- CVS - coronary syndrome, cardiomyopathy (inc blood viscosity –> inc SVR –> inc afterload)
- pulm - pulm htn, infarcts, baseline SaO2, pneumonia
- renal - infarct, AKI
- Liver - liver infarct –> liver dysfunction
- Heme - hemolytic anemia, aplastic crisis
Meds
- pain meds, bronchodilators, ABX, steroids
- steroids –> dec inflammatory response assoc with vasc occlusion. helps with pain too.
Labs
- CBC + Plt
- type and screen (look for antibodies 2/2 previous transfusion hx)
Tests
- consider Echo (cardiac dysfuction), PFT, baseline ABG
Should every patient with SCD have a HgB of 10 g/dL in periop period?
Transfusion Pros
- correct anemia
- HbS red blood cell dilution
Cons
- alloimmunization (antibody development)
- transfusion rxn
- infection
- fluid overload
Recommend
- transfuse to a Hgb of 10 g/dL for moderate to high-risk procedures (CTS, neurosurg, laparotomy, ortho)
-
exchange transfusion
- decrease HbS to < 30%
- aggresive form of transfusion therapy
- consider for high-risk procedure and high-risk pts
What is exchange transfusion?
Define
- procedure involves slowly removing the patient’s blood and replacing it with fresh donor blood or plasma.
Post-op concerns for SCD patients
Same goals as periop goals - avoid right shift of O2-hgb dissociation curve, avoid stressors on body
- pain control
- tissue perfusoin via hydration
- avoid anemia - RBC transfusion as necessary
- avoid acidosis
- normothermia
- avoid hypoxia and hypercarbia
what causes right shift of o2-hgb curve
right shift of curve
- facilitates O2 unloading from Hgb to tissues
- inc temp
- inc 2-3 DPG
- decrease pH
- inc PaCO2
- CADET, face Right!” for CO2, Acid, 2,3-DPG, Exercise and Temperature
Is there a role for regional anesthesia in SCD patients?
yes there is a role
- SCD patients have opioid requirements, most are not opioid naive.
- improve pain -> less stress on body –> improve HbS molecular state
- Epidural –> dec resp splinting, dec pain, dec opioid- induced resp depression
