What does the spleen actually do?
The spleen performs a number of immune functions including:
- It performs like a large lymph gland because it is packed full of lymphoid tissue (about 25% of the body’s total lymphoid tissue)
- It filters particles from blood including bacteria through the monocyte-macrophage system; it particularly targets bacteria taken up by phagocytic cells and antibody labelled bacteria (especially those described as capsular bacteria e.g. Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis, Capnocytophaga canimorsus)
- It can react very quickly to infection by rapidly increasing it’s lymphoid and monocyte-macrophage components
Having a splenectomy or having a spleen that doesn’t work properly therefore leads to a poor immune response, especially where encapsulated bacteria are concerned. Studies have shown that post-splenectomy patients are twice as likely to get pneumonia, and twice as likely to die from their pneumonia, than other patients. They are two and a half times more likely to get meningitis, three and a half times more likely to have sepsis, and three times more likely to die from sepsis than other patients. These effects on infection continue for more than ten years following the splenectomy and are not related to age.
There are number of ways in which the risk of severe infection post-splenectomy can be reduced, although an increased infection risk can never be prevented completely.
Inform the patient of the risk of infection
Patients without a functioning spleen must be warned about the increased risk of infection. They don’t need to be reduced to panic or compelled to live in a bubble but they do need to have some knowledge. In particular they should advise anyone involved in their medical care that they have no spleen. It is also wise for them to carry a warning card or wear a medical alert bracelet in case they are unable to advise healthcare workers themselves.
Patients should also be specifically advised to avoid exposure to C. canimorsus which is part of the normal oral flora of dogs. It may seem strange but splenectomy patients are particularly vulnerable to this bacterium which they can acquire from dog bites, scratches or even exposure to dog saliva. In order to minimise the risk of exposure to C. canimorsus some patients may need to make a difficult decision about whether they should continue to keep a dog as a pet.
Immunisation reduces the risk of infection
Splenectomy patients should be immunised against:
- Streptococcus pneumoniae
- Haemophilus influenzae type b (Hib)
- Neisseria meningitidis
- Influenza virus
Immunisations should ideally be given at least 14 days before splenectomy, but in traumatic splenic injuries this is obviously not possible. In the case of an unplanned splenectomy the immunisations should be delayed until at least 14 days post-splenectomy. The reason for waiting at least 14 days after splenectomy is that the antibodies produced in response to immunisation before 14 days do not work as well and do not last as long, although it is not clear why. If immunisations are given before 14 days then a booster dose of the immunisations should be given eight weeks later.
Current guidance for adults and children over 5 years old advises that previous vaccination history does not matter. However for children less than 5 years old the advice is age specific and takes their vaccination history into account; advice needs to be considered on an individual basis following the guidance in the reference below. The current UK recommendations for adults and children over 5 years are:
The evidence for antibiotic prophylaxis post-splenectomy is based on studies in children which showed that they reduce the incidence of infection by about 50% and also the risk of death by about 90%. The aim of antibiotic prophylaxis is primarily to prevent S. pneumoniae sepsis. The commonly used agents are:
In the UK it is also recommended that lifelong prophylaxis is given for specific patients:
- The patient has had an inadequate serological response to pneumococcal immunisation
- The patient has a history of invasive S. pneumoniae infection
- The patient has a haematological malignancy, especially if on-going immunosuppression
Early treatment of infection
Irrespective of whether a patient is on antibiotic prophylaxis or not it is sensible for the patient to have a dose of antibiotics against S. pneumoniae which they can self-administer if they develop symptoms or signs of infection e.g. fever, sore throat, cough, shortness of breath, etc. The choice of antibiotic IS affected by antibiotic prophylaxis as it is not appropriate to try and treat a patient with the same antibiotic that has failed to prevent the infection from occurring; it is likely that the bacterium will be resistant to the prophylaxis.
The choices of antibiotics are:
So the lady who had to have an emergency splenectomy following her riding accident was started on antibiotic prophylaxis immediately after her operation. She was immunised at 2 weeks and given a dose of “emergency” antibiotics to take if she develops signs of infection. On discharge she also had a card to carry at all times explaining that she had had a splenectomy and was advised to consider getting a medical alert bracelet. Her discharge letter to her GP advised the schedule for booster immunisations.
The horse got nothing…not even a carrot!
Green Book Chapter 7: Immunisation of individuals with underlying medical conditions