Flashcards in sickle cell anemia Deck (37):
what is hydroxyurea and how does it work?
treats SCA by increasing HbF and decreasing sickling. it increases HbF production by NO activation which upregulates cGMP. this in turn increases gamma globin synthesis and HbF production from F cells.
decreases sickling by reduced sickle adhesion to endothelium, improved SC hydration, NO-mediated vasodilation, and reduced neutrophil activation (which decreases the amount of pro-inflammatory mediators released)
where is the classic SCA mutation?
chromosome 11 resulting in substitution of valine for glutamic acid on the beta chains of Hb
what is the pathophysiology of SCA?
HbS molecules can polymerize into a sickled shape. these sickled polymers can cause occlusion of capillaries and ischemic end-organ injury. they are hemolyzed much faster than RBCs with Hb (HbS RBC lifespan: 12-17 days, Hb RBC lifespan: 120 days)
what circumstances increase sickling?
what is 2,3-DPG?
a molecule that preferentially binds to the beta subunit of deoxygenated Hb (more space for it to bind than with oxygenated Hb). it decreases the affinity of Hb to O2, thereby promoting the release of the remaining O2 molecules
if hypoxia is related to sickling, why don't all HbS RBCs sickle in the presence of venous blood?
it is a time-dependent process. although some will start to sickle, only about 5% have sickled by the time they reach the lungs and then oxygenation results in a reversal of much of this.
what is aplastic crisis?
bone marrow suppression, usually secondary to infection (parvovirus B19) or folate deficiency. decrease in production coupled with decreased life span of HbS RBCs leads to profound anemia.
how is aplastic crisis treated?
correction of folate deficiency and blood transfusion until bone marrow suppression resolves (4-7 days)
what is the appropriate preop evaluation of this patient?
thorough history and physical.
given her history of SOB, i would be looking for history of aplastic crisis, acute chest syndrome, and any end-organ damage, such as cor pulmonale, CHF, MI, pulm fibrosis, or pulm HTN. on physical exam, i would specifically evaluate her airway for potential difficulty, IV sites for bleeding, recent BPs and also current volume status.
to aid in my evaluation of these problems i would order CXR, ECG, room air ABG, CBC (H/H and platelet count), and BMP (to check renal function). other tests might include ECHO and PFTs but these would be directed by her history and urgency of c-section.
given her severe anemia, preeclampsia, and her history of previous c-section x 3, a blood transfusion would be prudent and likely she may need IVF infusion (preeclampsia is associated with further hypovolemia).
is an exchange transfusion necessary?
likely no, a transfusion of leukocyte-reduced HbS-free RBCs to a Hct of 30% would be adequate. exchange transfusion is associated with many negative sequalae, such as electrolyte disturbances, thromboembolism, and thrombocytopenia.
would you do general or regional?
due to risk of difficult airway (edema secondary to preeclampsia) and increased risk of aspiration (secondary to pregnancy), i would prefer regional. i do recognize that she has thrombocytopenia and would need careful evaluation for possible decreased platelet function (IV site bleeding, easy bruising, etc)
epidural or spinal or cse?
i would prefer epidural. it can be slowly titrated to effect, which will give her more time to compensate for the sympathectomy than a spinal will. additionally, it is a repeat csection x 4 and the surgery may outlast the effect of the spinal. i would prefer to have an epidural to be able to give extra medication through the catheter if necessary. finally, with her chronic narcotic use, an epidural would be the best choice for controlling postop pain.
how can you reduce risk of sickling?
I would avoid hypotension and venostasis by ensuring adequate fluid administration to compensate for the sympathectomy from neuraxial anesthesia. I would avoid hypoxia by administering supplemental O2 and monitoring pulse-oximetry. I would ensure adequate oxygen-carrying capacity by preoperatively transfusing the patient to Hct of 30%. I would maintain normothermia (hyperthermia increases O2 consumption and hypothermia causes vasoconstriction). I would ensure adequate ventilation to avoid acidosis.
what is the diff dx of seizures immediately following delivery?
1. amniotic fluid embolus
3. vaso-occlusive crisis
4. local anesthetic toxicity
how will you manage this patient?
immediate cricoid pressure, supply 100% O2, stop all local anesthetics. call for help, difficult airway supplies, and lipid rescue kit. IV versed to treat seizure. perform careful laryngoscopy and secure airway.
once ett placement has been confirmed, i would reassess the patients vital signs, treating hemodynamic instability (with IVF and pressors) and ensuring adequate ventilation (elevated PCO2 lowers seizure threshold, increases sickling, prolongs LA toxicity) and oxygenation (hypoxia increases sickling, prolongs LA toxicity). ensure adequate IV access and place an intra-arterial catheter and check magnesium (as well as ensure t&c has been performed - may need blood products due to coagulopathy from AFE)).
signs and symptoms of amniotic fluid embolus?
phase 1: pulmonary htn (due to pulm vasospasm), hypotension (right heart failure), hypoxia (VQ mismatch), seizure, cardiac arrest
phase 2: LV failure, pulm edema, coagulopathy (secondary to circulating trophoblast)
signs and symptoms of LA toxicity?
CNS then heart.
usually CNS excitation (perioral numbness, shaking, seizures) then CNS depression (resp depression/arrest). then cardiac arrhythmias and arrest.
signs and symptoms of eclampsia?
htn, proteinuria. n/v/blindness, then seizure.
if AFE, would you pull the epidural catheter postop?
no, she is at high risk for coagulopathy and pulling the catheter during this time would place her at a higher risk for epidural hematoma and possible paralysis.
but what about increased risk of infection with prolonged neuraxial catheterization?
the catheter should have been placed sterilely and have a sterile occlusive dressing. i would monitor the patient for signs of infection, such as fever, headache, backache, erythema or tenderness at the catheter site. if i suspected infection at any time i would remove the catheter and order culture of the tip. furthermore if i suspected the patient had developed an abscess i would order a CT or MRI and consult a neurosurgeon.
could this patient have N2O?
no, i would want to continue administering 100% FiO2 to reduce the risk of sickling. additionally, it is unknown what was injected into her eye for her retinal detachment and due to the recent history of this procedure i would want to avoid N20. it is highly soluble and could expand the intra-vitreal bubble and cause an increase in intra-ocular pressure, retinal artery occlusion, and ischemia.
what would you do if the surgeon reported uterine atony?
i would reduce my VA to MAC
what if the optho used intravitreal air for retinal tamponade?
i would be less concerned to use N2O (the air is reabsorbed within 5 days), however i would still like to maintain high oxygen saturation to reduce sickling risk.
what are the different substances that can be injected to induce retinal tamponade and how long must you avoid N20 before and after their injection?
N2O should be d/c'ed 15 min prior to injection for all substances
air - avoid for 5 days
sulfur hexafluoride - avoid for 10 days
perfluoropropane - avoid for 30 days
the patient continues bleeding and you initiate massive transfusion protocol. after 5 pRBCs and 4 FFP bp drops to 78/44 and is refractory to phenylephrine. what's going on?
1. inadequate resuscitation
2. citrate toxicity and hypocalcemia
3. myocardial depression from anesthetic
4. mag toxicity
5. right heart failure from pulm htn (SCLD)
6. transfusion rxn
7. pulm embolism
after 2 gm of Ca her bp returns to low-normal. why?
likely citrate-induced hypocalcemia or hypermagnesemia was the culprit. since her hypotension developed after massive transfusion, it is likely due to citrate.
why does citrate-toxicity occur? what are the signs and symptoms?
occurs because FFP and blood contain citrate which chelates ionized calcium with subsequent myocardial depression.
s/s: increased CVP, narrow pulse pressure, QT prolongation, flattened T waves, widened QRS, increased intraventricular EDP.
how will you manage her postoperative pain?
i would continue her preoperative dose of narcotic. i would administer a combination of local anesthetic and narcotic running continuously with a patient-controlled bolus dose available.
a few hours later, she develops dyspnea, wheezing, and has an infiltrate on CXR. what is your ddx?
1. acute chest syndrome
6. Mag toxicity
what is the presentation of ACS?
fever, tachypnea, cough, hypoxemia, pulm infiltrate on CSR, chest pain
what is the presentation of TRALI?
noncardiogenic pulm edema within 6 hours of transfusion. pulm infiltrate on CXR, dyspnea, fever, chills and hyper/hypotension
what is the presentation of TACO?
cardiogenic (hydrostatic) pulmonary edema due to transient volume overload
what is the presentation of TAD?
resp distress within 24 hours of transfusion
lets assume it is acute chest syndrome. what is your course of action?
1. provide supplemental oxygen, bronchodilators, incentive spirometry, chest physiotherapy.
2. administer abx to cover atypical and encapsulated organisms.
3. adequate pain control
4. correct anemia with simple transfusion. depending on pt condition may consider exchange transfusion or even mech vent.
what if patient refuses pregnancy testing for carpal tunnel release?
surgery may proceed after risks and benefits have been explained to patient regarding teratogenesis and after a legal waiver has been signed.
your institution mandates pregnancy testing, what woudl you do?
i would not proceed.