Emergency department haematology

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Chapter 43 Emergency department haematology

Anthony J. Dodds

COMMON HAEMATOLOGICAL EMERGENCIES

Neutropenic sepsis

(Also see Chapter 42, ‘The immunocompromised patient’.)

Severe neutropenia is defined as a neutrophil count less than 0.5 × 10⁹/L, but severe sepsis is unusual until the neutrophil count is less than 0.2 × 10⁹/L. Causes for severe neutropenia include cancer chemotherapy drugs, agranulocytosis (an idiosyncratic reaction to an otherwise non-marrow suppressive drug) and haematological disorders causing marrow failure (acute and chronic leukaemias, myeloma, lymphoma, aplastic anaemia etc).

Patients presenting with a fever above 38°C require urgent investigation and therapy.

Investigations

Investigations should be directed to possible sites of infection; however, local sites are detected in fewer than 50% of such patients. Suggested investigations include chest X-ray, blood cultures and urine culture. If there is a central line, cultures through this line are also important.

Management

Therapy with broad spectrum antibiotics should not be withheld while investigations are being performed. Gram negative infections usually arising from the gut are the commonest causes but, in the presence of a central venous catheter, treatment of possible gram positive skin organisms should also be considered.

Most institutions have an approved protocol to treat such patients. Usually a broad spectrum cephalosporin is combined with gentamicin until Pseudomonas has been excluded. If the fever does not respond to this after 48 hours or a central venous catheter is present, then additional antistaphylococcal therapy is added.

Severe thrombocytopenia and bleeding

Severe bleeding with thrombocytopenia is not usually a problem until the platelet count is less than 10 × 10⁹/L. When patients present with bleeding secondary to thrombocytopenia, an urgent assessment of the cause of the thrombocytopenia is necessary.

Differential diagnosis

1. Marrow failure, e.g. chemotherapy drugs, haematological malignancy etc. Such patients usually have a pancytopenia and a history of being given marrow suppressive therapy. Urgent platelet transfusion is indicated.

2. Peripheral destruction of platelets. This may be an autoimmune disorder (immune thrombocytopenic purpura or ITP) or less commonly an immune drug-related disorder. Heparin is a common drug cause for immune thrombocytopenia. Patients presenting with ITP may have no preceding history and have isolated thrombocytopenia. The disorder may be postviral and reversible in children but commonly chronic in adults. If there is any doubt about the diagnosis, a marrow biopsy is indicated. This will show a normal marrow with plentiful megakaryocytes. Urgent corticosteroids (prednisolone 1 mg/kg daily) are indicated for ITP with severe thrombocytopenia, especially with bleeding.

3. Disseminated intravascular coagulation (DIC). DIC can occur with malignancy or severe sepsis. Treatment is aimed at the underlying cause rather than treating by platelet transfusion alone.

THE ANAEMIC PATIENT

Anaemia is defined as a reduced haemoglobin (Hb) concentration in the blood. The red cell mass and the plasma volume can affect this value, so both these factors must be considered when interpreting a single value. Thus, severe dehydration can produce an elevated Hb and increased plasma volume, such as in pregnancy, can produce a falsely low Hb.

The symptoms and signs of anaemia (pallor, fainting, lethargy and anorexia) are unreliable. Anaemia may be asymptomatic and detected only on a routine blood count. The cause of anaemia can be ascertained by a logical sequence of investigations as follows. This is based on the mean corpuscular volume (MCV), which is part of an automated blood count.

Microcytic (normal MCV)

• Iron deficiency—serum ferritin low

• Thalassaemia trait—serum ferritin normal or raised

Macrocytic (raised MCV)

• Megaloblastosis—low serum B₁₂ or red cell folate levels

• Secondary macrocytic anaemia, e.g. alcohol, liver disease, hypothyroidism, some marrow disorders, marked reticulocytosis

Principles of therapy

1. Establish the cause and treat.

2. Blood transfusion only indicated for:

• acute anaemia with hypovolaemia

• refractory anaemias (Hb < 80 g/L)

• severe symptoms, e.g. angina.

3. Most patients with anaemia do not need blood transfusion unless the Hb < 80 g/L. Transfusion can be risky with severe compensated anaemia, especially in the elderly and those with cardiac disease.

THE PATIENT WITH ABNORMAL BLEEDING

Screening haemostasis tests are not warranted or cost effective in the absence of clinical signs or history to suggest a bleeding diathesis.

The following are suggestive:

• family history of bleeding disorder

• past history of excessive bleeding with minor haemostatic insults, e.g. tooth extraction, minor surgery, minor trauma, childbirth

• excessive local bleeding without an obvious cause

• generalised bleeding or bruising.

The usual screening tests are:

• vascular or platelet disorder—platelet count (PC), platelet function tests

• coagulation disorder—prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT).

The following is a guide to the interpretation of these tests.

Therapy

Specific therapy is usually only required if the patient is bleeding or an operative procedure is contemplated.

Components available include:

1. fresh frozen plasma (FFP)—DIC, massive transfusion, liver disease

2. platelet concentrates—thrombocytopenia due to marrow failure

3. factor concentrates—Prothrombinex-HT (freeze-dried concentrate of human blood coagulation factors II, IX and X) or specific factor concentrates.

ANTICOAGULANT THERAPY

Unfractionated heparin

Heparin inhibits coagulation at a number of sites, mainly via activation of antithrombin-III. Administration is usually via constant IV infusion.

• Monitoring: the APPT is the usual method. A baseline APPT should be established, repeated 4 hours after commencing heparin, then therapeutic interval checked with laboratory. A platelet count should be done every second day.

• Reversal: for overdose or serious bleeding, stop the heparin and give protamine sulfate slowly IV (1 mg/100 U heparin).

• Side effects: bleeding; thrombocytopenia—thrombosis (HITTS).

Low-molecular-weight heparins

These are often used for prophylaxis but are also commonly given for ambulatory full-dose therapy. They are usually given by subcutaneous injection. They have a much longer half-life than unfractionated heparin. They cannot be monitored by APTT testing and cannot be reversed by protamine sulfate. They may cause less bleeding and less thrombocytopenia.

Vitamin K antagonists/oral anticoagulants (e.g. coumadin)

These inhibit synthesis of vitamin K-dependent clotting factors (II, VII, IX, X plus protein C and protein S).

International normalised ratio (INR) is a standardised prothrombin ratio and is used to monitor side effects: bleeding; rash; teratogenesis.

Surgery in patients receiving vitamin K antagonists

What to do will depend on the type of surgery and the reason for administering anticoagulants. For minor procedures (e.g. tooth extraction), therapy may not need to be ceased (see institutional protocols). For major procedures, it may be necessary to change to heparin if continuing anticoagulation is required (e.g. artificial heart valve).

Changing from heparin to vitamin K antagonists

When commencing vitamin K antagonists, the INR will begin to fall within 36 hours, but this only reflects factor VII levels. It is necessary to continue heparin at lower doses for at least a 3-day overlap when commencing oral anticoagulants.

Reversal

Fresh frozen plasma (FFP) or Prothrombinex-HT will acutely reverse the effect in bleeding patients. Vitamin K will act more slowly and permanently reverse the effect, but in large doses may make it more difficult to anticoagulate the patient again.

A protocol for the management of an elevated INR is shown in Figure 43.1.

Figure 43.1 St Vincent’s Hospital guidelines for the management of an elevated international normalised ratio (INR) in adult patients with or without bleeding

Based on Baker RI, Coughlin PB, Gallus AS et al., the Warfarin Reversal Consensus Group. Position statement. Warfarin reversal: consensus guidelines, on behalf of the Australasian Society of Thrombosis and Haemostasis. MJA 2004; 181(9):492–497 Compiled: 11/05. Reviewed by: Dr. J. Joseph (Haematology). Endorsed by: St Vincent’s Hospital Drug Committee 2/06

BLOOD TRANSFUSION

Transfusion reactions

• Delayed (1–2 weeks after transfusion).This is due to a secondary antibody response and there is often no incompatibility at initial crossmatch. The following suggest a delayed haemolytic transfusion reaction:

• fall in haemoglobin or late jaundice

• positive Coombs’ test and antibody screen.

Reactions to white cell antibodies—occur after previous transfusion or pregnancy (‘febrile reactions’)

• Are delayed from 0.5–3 hours after start of transfusion.

• Brisk rise in temperature to 38–40°C with chills and headache.

• Diagnosis by presence of white cell antibodies.

• Give paracetamol orally or antihistamine IV and slow rate of transfusion.

• Leucocyte-poor blood may be used by employing a leucocyte blood filter.

• Leucodepletion of all blood products by central blood banks is being introduced and should eliminate many of these reactions.

Urticarial and anaphylactic reactions

• Anaphylaxis (rare—due to allergy to donor plasma)

• Occasionally occurs in IgA-deficient individuals.

• Shock—bronchospasm, laryngeal oedema, severe urticaria.

• Stop blood, treat with adrenaline, antihistamines and occasionally corticosteroids.

Table 43.2 Commonly used blood products in emergency medicine

Product	Emergency indications
Fresh whole blood	Massive blood loss
Red cell concentrate	Severe or refractory anaemia Moderate blood loss
Platelet concentrate	Thrombocytopenia with bleeding Platelet dysfunctional bleeding
Fresh frozen plasma	Massive transfusion Severe liver disease with bleeding Reversal of coumarin therapy
Prothrombinex-HT	Reversal of coumarin therapy

• Urticarial reaction (occasionally accompanied by asthma)

• Response to antihistamines usually.

• Washed red cells may be used.

Reactions to bacterial pyrogens and bacteria

• Pyrogenic reaction:

• Extremely rare.

• Clinical picture resembles leucocyte and platelet antibody reaction.

• Infected blood. Causes shock, fever, coma, convulsions, sudden death. Beware blood removed prematurely from blood bank or heavily haemolysed supernatant or previously punctured top.

• Take blood for cultures.

• Treat shock and give large doses of appropriate antibiotics.

It is recognised that platelet transfusions carry an increased risk of bacterial infection because platelet donations are stored at room temperature. Central blood banks are introducing screening of platelet concentrates for infection.

Circulatory overload

• Slow or stop transfusion, treat as for cardiac or pulmonary oedema.

• May need venesection.

Air embolism

• Raised jugular veinous pulse (JVP), cyanosis, hypotension, praecordial murmur.

• Treat with head down, feet up and patient on left side.

• Administer 100% oxygen.

Citrate intoxication

• Usually only in neonates, impaired liver function and massive blood transfusion.

• Muscles twitching, hypotension, ECG changes, bleeding.

• Give calcium gluconate, 10 mL of 10% by IV injection.

Massive transfusion. Hypothermia (use blood warmer).

• Deficiency of coagulation factors. Check coagulation profile (use fresh frozen plasma).

• Thrombocytopenia (use platelet transfusion).

• Hypocalcaemia.

Infectious complications—possible risk with nucleic acid testing (NAT)

• HIV (< 1:920,000).

• Hepatitis B (< 1:100,000).

• Hepatitis C (< 1:10,000).

• HTLV-I (< 1:100,000).

• Others, e.g. syphilis, malaria, cytomegalovirus (CMV). CMV has the highest incidence but lowest risk to the patient unless they are immunocompromised.

Inappropriate use of blood components

• There is considerable evidence of inappropriate use of blood components. Various strategies have been developed to reduce this, including guidelines, consensus conferences, monitoring, education and self-audit by clinicians. Informed consent, including the potential risks and benefits of transfusion, is a vital part of any transfusion.

EDITOR’s COMMENT

The precise clinical place of newer drugs (e.g. factor VII, in profound haemorrhage), newer transfusion strategies (e.g. ratio of 1 unit blood:1 unit FFP, in massive bleeding) and synthetic components are not yet clear.

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