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You are in Home >> Exams >> Mitchell Anaesthetic Notes


Haematology

Created: 1/6/2006
Updated: 8/1/2007
 

Outline management of a sickle-cell patient for appendicectomy
 

Appendicectomy

  • Urgent operation, moderate risk

Patient factors

  • Sickle-cell anaemia
    • May be trait, sickle-cell disease or Hb SC or other variants
    • Severity of disease determined by Hb type
      • Hb SS
        - Anaemic Hb 70-80 g/L
        - Vaso-occlusive crises cause organ infarction
        - Especially spleen, renal papillae, skin (if cold), CNS
      • Complications
        - Poor spleen function, encapsulated organism susceptibility
        - Hepatomegaly
        - Impaired renal function
        - May cause “acute abdomen”, confused with appendicitis
  • Appendicitis
    • Causes fever, acidosis: increased risk of sickle crisis
    • Patient not fasted, commonly with an ileus: risk of aspiration

Preoperative

  • Assessment
    • Usual patient assessment: clinical, baseline investigations
    • Severity of sickle cell disease
      • FBE, history, abdominal and skin examination
    • Resuscitation status
      • Needs to be warm, well-filled, supplemental oxygen
  • Premedication
    • Usually avoided as may cause hypoventilation
    • Oxygen by face mask, prewarming with forced-air warmer


 

Intraoperative 

  • Objectives: normothermia, avoid hypoxaemia and acidosis to minimize risk of sickling
  • Monitoring
    • Usual monitoring
      • ECG, NIBP, SpO2, gas analysis, airway pressure, urinary catheter, temp
  • Anaesthetic technique
    • General anaesthesia: balanced technique with muscle relaxation
  • Induction
    • Rapid sequence induction
      • Check equipment, difficult airway equipment available
      • Preoxygenation, cricoid pressure
      • Thiopentone (3-4 mg/kg), suxamethonium (1-1.5 mg/kg)
        • Reduce thiopentone dose if underfilled to avoid hypotension
      • Secure airway with cuffed ETT
  • Maintenance
    • Ventilate with increased FiO2, normocapnia
    • Analgesia with local anaesthetic in wound plus narcotic as necessary
    • More likely to require transfusion if significant blood loss
    • Avoid hypothermia aggressively if necessary (often febrile)
  • Emergence
    • Extubation awake in lateral position
  • Postoperative
    • Maintain supplemental oxygen, keep warm 
    • Narcotic analgesia will be required, but hypoventilation is a risk 


Review of paediatric transfusion (RCH 1999)


Prompted by HIV transmission case

Transmission would have occurred once the infected unit had passed the screening
process. Directed transfusion would only have caused a different child to be infected.

Risks of transfusion


Causes of death associated with transfusion (FDA, 1990)

  • ABO incompatibility 50%
  • Pulmonary oedema 14%
  • Hepatitis C 12%
  • Hepatitis B 7%
  • Bacterial infection 7%
  • Delayed reaction, anaphylaxis, GVHD 9%
  • HIV 1%

Risk of viral transmission

  • Lowest in volunteer repeat donors
  • Minimized by screening questionnaire and serology
  • Estimate of risk of “window period” donation
    • HIV 1 in 1.2 million in Australia (twice as high in USA)
    • Hep B 1 in 370,000
    • Hep C 1 in 250,000
  • Risk in children
    • 5% of transfusions are given to children
    • 20% of paediatric transfusion is for elective surgery
    • Expected incidence of HIV transmission from elective paediatric surgical transfusion in Australia is 1 per 100 years.

Reducing risks

Transfuse only for specific clinical indications

  • Whole blood
    • Massive transfusion, exchange transfusion, CPB or ECMO
  • Packed cells
    • Under 4 months of age
      • Hb <130 g/L in neonates <24 h old or with severe pulmonary disease, cyanotic heart disease or heart failure
      • Acute loss of ≥10% of blood volume
      • Phlebotomy loss of 5-10% of blood volume
      • Hb <80 g/L with symptomatic anaemia
    • Over 4 months of age
      • Operative blood loss ≥15% of blood volume
      • Post-op Hb <80 g/L with symptoms
      • Hb <130 g/L with severe pulmonary disease requiring ventilation
      • Hb <80 g/L or symptomatic Hb <100 g/L without response to medical therapy
      • Suppression of endogenous erythropoiesis in some thalassaemia and sickle-cell patients
      • Prior to renal transplant

Autologous transfusion

  • Available at RCH from 40 kg up
    • 20-30 cases per year
    • 90% of elective surgery requiring transfusion is in ineligible children
  • Toronto HSC from 18 kg up
    • 100 cases per year, >50% discarded

Directed transfusion

 
Specific indications

  • Kidney transplant recipient preparation
  • Bone marrow transplant
  • Rare phenotype red cells
  • HLA-compatible platelet transfusion
  • Parent to neonate transfusion for alloimmune thrombocytopenia, neutropenia or haemolytic disease of the newborn

Other countries

  • UK: prohibited
  • Canada: available if parents insist
  • USA: some states prohibited, some mandate offering directed transfusion
  • California: 2-3% of donations are directed. Early 1980s HIV risk from donor blood in CA was 1/200-1/300

Practice

  • 88% chance of compatibility if both parents available, 72% for one parent (84% and 50% if identical group required for cardiac surgery)
  • 5 days notice requried
  • 31% of donations are used
  • More expensive than random donor transfusions

Safety

  • Viral markers may be slightly more prevalent in directed donations
  • 22% of donors might modify answers to screening questions to allow donation
  • No studies of long-term outcomes in children
    • 50% of blood is transfused to patients who are dead within 1 year
  • GVHD
    • Near HLA match allows lymphocyte engraftment in immune competent recipient
    • Risk 1 in 17-39,000 in Caucasians for random donor, 20 times higher if parent to child donation
  • TRALI
    • Donor neutrophil or HLA antibodies cause acute respiratory distress
    • May be more common in maternal plasma in the first few months after childbirth
  • HLA isoimmunization
    • Increased risk of rejection of subsequent marrow transplant

Ethical complications

  • Coercion of an unwilling donor, false screening declarations
    • 3% of donors feel forced to donate
  • Potentially worse therapy used based on parental desire
    • No conclusive evidence that directed donation is less safe
  • Potential for discovering a different biological parent
  • False positive viral screening tests
    • Positive theshold is set low for donor units
    • High false positive rate, donor counselling required
  • Impact on volunteer donor pool
  • Use of finite resources
  • Parental desire to help their children

Cost-effectiveness recommendations (Health Ministers, 1999)

  • Minimize blood loss
  • Autologous donation should be available but should not be promoted
  • Acute normovolaemic haemodilution should not be encouraged
  • Erythropoietin and desmopressin use should not be encouraged
  • Cell salvage should be evaluated
  • Aprotinin use should be actively supported

Conclusions

  • No evidence to ban directed donation
  • Should not be encouraged because of increased cost and possible increased risk
  • Should be permitted in defined circumstances 

 

Deep vein thrombosis


Pathogenesis

  • Venous stasis
    • No activity of muscle pump mechanism
    • Decreased venous return with IPPV or pneumoperitoneum
    • Patient position can affect venous return
  • Vascular injury
    • Direct trauma
    • Endothelial activation due to cytokines released in surgery
      • Increased tissue factor and PAI-1
      • Reduced thrombomodulin
  • Activation of coagulation
    • Local activation with vessel trauma
    • Systemic increase in coagulability with surgery or stress
  • Known risk factors
    • Age >60 years
    • Previous DVT
    • Major surgery
      • Surgical duration
      • Orthopaedic surgery to the hip or knee
      • Fractured pelvis, femur or tibia
      • Surgery for malignant disease
      • Immobility in the perioperative period
    • Medical conditions
      • Cardiac failure
      • Sepsis
      • Inflammatory bowel disease
      • Myocardial infarction
      • Varicose veins
      • Obesity

Natural history

  • Site
    • Most commonly superficial veins and deep veins of the calf
    • Proximal spread to involve popliteal, femoral and iliac veins
    • Other sites are uncommon
  • Symptoms and signs
    • Calf vein DVT is usually asymptomatic
    • Proximal DVT causes impaired venous drainage, perivascular inflammation, symptomatic PE
    • Post-thrombotic syndrome may occur in the long term
  • Prognosis
    • Untreated
      • 30% of small calf DVTs will spread proximally if untreated
      • Proximal spread is associated with 40-50% risk of PE
      • Historical mortality from PE was 20%
    • Treated
      • Proximal DVT associated with 5% incidence of significant events
      • Recurrent DVT after treatment
        • 5-10% at 1 year (4% for post-surgical DVT)
        • 30% at 8 years
        • Risk of recurrence is greatest in DVT associated with a non-reversible cause (i.e. malignancy or coagulation disorder)
    • Post-thrombotic syndrome
      • Incidence 25% after treated DVT 
      • Caused by increased venous pressure
        • Incompetent valves
        • Outflow obstruction
      • Oedema, pain, venous ulceration
    • “Thromboneurosis”

Prophylaxis

  • Proven cost-effective for high-risk patients
  • Prevent venous stasis
    • Pneumatic calf compression
      • Calf compression is as effective as low-dose heparin in abdominal surgery
    • TEDS stockings
      • Effective adjunct in the postoperative period
  • Modulate coagulation
    • Low-dose heparin
      • Cost-effective for general surgery
      • Reduces DVT risk by 50-70%
    • Warfarin, adjusted dose heparin, LMWH
      • LMWH is most effective in major orthopaedic surgery
  • Low risk
    • Age <40 years, uncomplicated surgery, mobile postoperative risks
      • Calf DVT 2%, proximal DVT 0.4%, fatal PE <0.02%
    • Prophylaxis
      • Early mobilization
  • Moderate risk
    • Age >40 years, medical risk factors, immobility (e.g. leg fracture)
    • Risks
      • Calf DVT 10-20%, proximal DVT 2-4%, fatal PE 0.2-0.5%
    • Prophylaxis
      • Low-dose heparin or pneumatic calf compression
  • High-risk
    • High-risk surgery, previous DVT
    • Risks
      • Calf DVT 40-70%, proximal DVT 10-20%, fatal PE 1-5%
    • Prophylaxis
      • LMWH or warfarin or adjusted dose heparin
  • Neurosurgery, ophthalmic surgery
    • If anticoagulation is contraindicated, pneumatic compression and stockings are safe

Diagnosis

  • Venography
    • Gold standard for diagnosis
    • Operator dependent
    • May be misleading in recurrent DVT
  • Venous ultrasound
    • Operator dependent
    • Inadequate resolution for calf veins
  • Impedance plethysmography
    • Fails to detect calf thrombi
  • Predictive value of tests is greatly influenced by clinical probability 

Ultrasound result Clinical probability Likelihood of DVT Management
Positive High 100% Treat
Positive Intermediate 96% Treat
Positive Low 63% Venography
Negative High 24% Venography or retest
Negative Intermediate 5% Retest
Negative Low <1% No treatment

    

  • Diagnosis of pulmonary embolism
    • Clinical features are non-specific
      • Shortness of breath (increased dead space)
      • Pain, haemoptysis, sudden death
    • Diagnostic tests
      • Pulmonary angiography
        • Gold-standard test
        • Highly invasive
      • Ventilation/perfusion scan
        • Interpreted in combination with clinical impression
        • “High probability” scan result means
          • PE in 96% of patients with high clinical suspicion
          • PE in 85% with intermediate clinical suspicion
          • PE in 50% with low clinical suspicion
        • “Low probability” scan means
          • PE in <6% with low clinical suspicion
      • Testing for the presence of a DVT may determine management
      • ECG
        • Significant negative predictive value if other pathology (e.g. pericarditis, infarction)
        • May show right heart strain
      • CXR
        • Useful positive diagnostic signs are uncommon
        • May show effusion, infarction, regional oligaemia, prominent pulmonary vessels at the hilum
      • ABG
        • Non-specific
        • May show hypoxaemia, hypocarbia in large PE in an awake patient

Treatment

  • Anticoagulation
    • Heparin
      • Promotes inhibition of thrombin and factor Xa via AT-III
      • High concentrations required to affect clot-bound thrombin
    • Warfarin
      • Inhibits synthesis of factors requiring γ-carboxylation
        • Thrombin, VII, IX, X
    • Usual regimen
      • Therapeutic heparin, followed by warfarin to INR 2-3 for 3-6 months
        • Shorter duration is more appropriate if there is no ongoing predisposing factor
        • Patients with a thrombotic condition (e.g. antiphospholipid antibody) may require lifetime therapy
      • Overlap period should be about 4 days as INR rises as factor VII level falls (t1/2 7 h) but full anticoagulant effect requires a fall in factor II (t1/2 60 h)
      • Subcutaneous LMWH may be an alternative to IV heparin
    • Thrombolysis
      • Usually contraindicated in the postoperative period
    • Surgery
      • Caval interruption
      • Intracaval devices
      • Thrombectomy

Pregnancy

  • Diagnosis
    • Leg pain and swelling are frequent without DVT
    • Venography, V/Q scanning are relatively contraindicated
  • Management
    • Heparin is safe in pregnancy
    • Warfarin is teratogenic at 6-12 weeks and contraindicated at term
    • Women on prophylactic warfarin are changed to heparin or LMWH before 6 weeks' gestation (or before conception)
    • Heparin is ceased at the onset of labour

Children 

  • DVT is relatively rare
  • Highest risk surgery has <1% incidence of clinical DVT
  • 80% of neonatal and 40% of childhood DVTs are associated with CVCs

Perioperative management of anticoagulants 

  • “Low” risk patients on warfarin
    • Risk of thromboembolism from AF or prosthetic valves without anticoagulation is about 10% per year
    • Ceasing warfarin 4-5 days before surgery should carry <0.1% risk of thromboembolism
  • “high” risk patients on warfarin (e.g. recurrent thromboembolism)
    • Reduction in INR to 1.5 for surgery
    • Replacement of warfarin with heparin
      • Ceased 4-6 hours before surgery
      • Recommenced 12 hours after surgery 

Systemic mastocytosis 

  • Epidemiology
    • Prevalence 1 to 10 per 10,000
  • Pathology and clinical findings
    • 90% of mastocytosis is cutaneous, 10% systemic
    • Classified according to presence of associated haematological malignancy
    • Diffuse mast cell proliferation in skin and organs
    • Elevated baseline histamine
    • Diagnosed by skin biopsy, spleen or liver biopsy or bone marrow
    • Clinical signs
      • Brown macular discolouration
      • Dermographism: wheal and flare after mild contact
    • Triggered episodes of generalized degranulation
      • Release of histamine, PGD2, heparin, other inflammatory mediators
      • Flushing, itch, bronchospasm, diarrhoea, gastritis, circulatory collapse
      • Triggers include
        • Temperature change, physical stress
        • Alcohol
        • Drugs known to release histamine
        • Many other drugs
  • Treatment
    • Treatment of any associated haematological malignancy
    • H1 and H2 blockers ameliorate most symptoms
    • Aspirin or NSAID may be added to block PGD2 synthesis
      • Aspirin may also trigger degranulation
    • Ketotifen and cromoglycate also used in some patients
  • Anaesthetic considerations
    • Often undiagnosed for years after onset of symptoms
      • Difficult to diagnose clinically
    • May present for splenectomy or with pathological fractures
  • Anaesthetic management
    • Investigation
      • Skin testing of drugs may predict which are safe
    • Preoperative
      • Premedication with H1 and H2 blockers ± aspirin
      • Warming
    • Monitoring
      • Placement of arterial line and large IV before parenteral drug administration
    • Induction
      • Adrenaline drawn-up and available
      • Minimize or exclude drugs likely to cause histamine release
        • Relaxants, morphine, thiopentone
      • Propofol plus alfentanil probably safe
      • Sevoflurane plus remifentanil described as safe
    • Regional
      • Bier’s block described as unsafe
      • Ester local anaesthetics probably best avoided
      • Otherwise regional probably safe provided psychological stress is avoided
  • Surgery
  • Cautious handling of infiltrated organs
  • Postoperative
  • Close observation at times of drug administration
  • Management of degranulation
  • Normal resuscitative measures: 100% O2, IV fluid, adrenaline bolus or infusion
  • ICU availability

Kindly provided by Dr James Mitchell from his pharmacodynamics series


ArticleDate:20060601
SiteSection: Article
 
   
    
                                            
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