Australasian Anaesthesia 2011 - Australian and New Zealand ...

152 Australasian Anaesthesia 2011Sickle Cell Disease in Australia – a phantom menace? 153Sickle cell solubility testing relies on the relative insolubility of Hb S in high concentration phosphate bufferscompared with Hb A and other variant Hb. Hb S precipitates in this solution to form a cloudy, turbid solution.Figure 6. The Itano sickle solubility test. Images reproduced with permission from Dr Donald J.Innes,Jr.,MD,: University of Virginia School of MedicineSickle cell solubility testMost commercially available kits will reliably detect HbS levels down to 20%. An HbS level below this would beunlikely to cause significant clinical sequelae, so a sickle cell solubility test would be useful for rapid, emergencypre-anaesthetic screening. It does not exclude the presence of HbS concentrations lower than 20% and resultsshould state this. At the earliest opportunity, further Hb screening tests should be utilised e.g. Hb electrophoresis,HPLC to confirm the results.In terms of which patients should undergo pre-anaesthetic screening, the National Institute for Clinical Excellence(NICE) guidelines of 2003 in the UK recommend:• “It is important to offer to test all patients in these ethnic groups (North African, West African, South / subSaharan African, Afro-Caribbean) and people of other ethnic groups considered to be at risk”• “It is important to offer to test patients before they have an anaesthetic if there is any uncertainty aboutwhether they have the sickle cell gene”The British Committee for Standards in Haematology (BCSH) recommendations 24 for pre-operative/ pre-anaesthesiatesting are:• “All patients from groups with a high prevalence of HbS (listed below) should be offered testing as somecases of milder disease may be unrecognized and the presence of HbS heterozygosity may also influenceperi-operative techniques”• “For routine operations, FBC and Hb analysis using HPLC or a suitable alternative diagnostic method shouldbe performed at the pre-assessment visit”• “In an emergency, an FBC and sickle solubility test should be performed. Results in this situation should beevaluated clinically and must be followed by definitive testing.”ETHNIC GROUPS WITH A CLINICALLY SIGNIFICANT PREVALENCE OF HAEMOGLOBIN Ѕ AND βTHALASSAEMIAHaemoglobin S African including North Africans, African-Caribbeans, African- Americans, Black British andany other African ethnicity (e.g. Central and South Americans of partly African ethnicity), Greeks,Southern Italians including Sicilians, Turks, Arabs, Indiansβ thalassaemia All ethnic groups other than Northern EuropeansEmergency sickle testing availability in a telephone survey of eight metropolitan hospitals in Australia revealedonly half had the laboratory and/or manpower availability to carry this out.MANAGEMENTAs with any chronic illness, a multidisciplinary team approach is ideal to manage these patients, with close liaisonbetween primary care, haematologists, chronic pain services and specialist nurses.In general, chronic management has seven elements:1. Management of vaso-occlusive crises2. Management of chronic pain syndromes3. Management of haemolytic anaemia4. Prevention and treatment of infections5. Management of end organ damage and complications6. Stroke prevention7. Detection and treatment of pulmonary hypertensionVaso-occlusive crises are often managed by the patient at home with rest, increased fluid intake and simpleanalgesics. Severe crises warrant admission, investigation for an infective trigger, intravenous fluid therapy, oxygenand often parenteral opioids.Chronic, haemolytic anaemia requires folic acid supplementation and exclusion of concurrent iron deficiencyanaemia. Red cell transfusion is typically reserved for acute chest syndrome or stroke management, children withabnormal transcranial dopplers who are at risk of stroke, major surgery and pregnancy. 25Penicillin V prophylaxis is administered lifelong from infancy with regular vaccination against Pneumococcus,Haemophilus influenza type B, Meningococcus group C and influenza virus. Suspected infections should be treatedpromptly, initially with broad spectrum agents until causative organisms are identified and targeted agents used. 26Acute chest syndrome requires treatment with oxygen and appropriate respiratory support, incentive spirometry 27 ,intravenous broad spectrum antibiotics, analgesia, bronchodilators if airway hyperreactivity is present and inrefractory cases, exchange transfusion.All children with SCD require transcranial doppler studies annually. Those with abnormal studies are placed on28 29a blood transfusion regime to prevent stroke.All adult patients require regular echocardiography to assess their tricuspid regurgitation velocities as a markerof pulmonary hypertension. 30Hydroxyurea is currently the only agent shown to modify disease expression in SCD. It increases fetal Hb levelsand decreases the frequency and severity of vaso-occlusive crises. 31Trials of inhaled nitric oxide for pain crises and ACS treatment are ongoing.Bone marrow transplantation is currently the only curative option in SCD, but remains a high risk intervention,reserved at present for children with severe disease. 32 Trials of gene therapy via stem cell transfusion continue. 33PERI-OPERATIVE MANAGEMENTAs discussed earlier, the peri-operative period poses significant risks to SCD patients.Predictors of higher morbidity include: major surgery, increased patient age, more frequent complications andhospitalisations, abnormalities on chest x-ray, pregnancy, intercurrent infection and the patient’s haplotype (CentralAfrican Republic > Benin > Senegal). 34Pre-operative assessment should focus on establishing the frequency and severity of disease exacerbations,existence of end organ damage and whether the patient has predictors of high risk as listed above.Optimisation of the patient should involve haematology input for guidance on the need for prophylactic red celltransfusion (to achieve a haematocrit of >30%) or exchange transfusion (to achieve an Hb S % of