Patients who have some form of asplenia have an increased susceptibility to these encapsulated bacterial infections mainly because they lack IgM memory B cells and their non-adherence to polysaccharide vaccines. Furthermore, there is a deficiency of other splenic cells e.g. splenic macrophages. This combined with the lack of B cells can provide an environment favourable for the development of bacterial infections. Partial splenectomy and preservation of splenic function
In an effort to preserve some of the spleens protective roles, attempts are now often made to preserve a small part of the spleen when performing either surgical subtotal (partial) splenectomy, or partial splenic embolization. This may be particularly important in poorer countries where protective measures for patients with asplenia are not available. However, it has been advised that preoperative vaccination is advisable until the remnant splenic tissue can reestablish its function. Risks
Asplenia is a form of immunodeficiency, increasing the risk of sepsis from polysaccharide encapsulated bacteria, and can result in overwhelming post splenectomy infection (OPSI), often fatal within a few hours. In particular, patients are at risk from Streptococcus pneumoniae, Haemophilus influenzae, and meningococcus. The risk is elevated as much as 350–fold.The increased risk of infection is due to inability to clear opsonised bacteria from circulating blood.
Even with a course of antibiotics and even with a history of relevant vaccination, persons without a functional spleen are at risk for Overwhelming post-splenectomy infection.In an emergency room or hospital setting, appropriate evaluation and treatment for an asplenic febrile patient should include a complete blood count with differential, blood culture with Gram stain, arterial blood gas analysis, chest x-ray, and consideration for lumbar puncture with CSF studies. None of these evaluations should delay the initiation of appropriate broad-spectrum intravenous antibiotics. The Surviving Sepsis Campaign guidelines state that antibiotics should be administered to a patient suspected of sepsis within 1 hour of presentation. Delay in starting antibiotics for any reason is associated with a poor outcome. Vaccinations
It is suggested that splenectomized persons receive the following vaccinations, and ideally prior to planned splenectomy surgery:

Pneumococcal polysaccharide vaccine (not before 2 years of age). Children may first need one or more boosters of  pneumococcal conjugate vaccine if they did not complete the full childhood series. Haemophilus influenzae type b vaccine, especially if not received in childhood. For adults who have not been previously vaccinated,  two doses given two months apart was advised in the new 2006 UK vaccination guidelines (in the UK may be given as a combined Hib/MenC vaccine). Meningococcal conjugate vaccine, especially if not received in adolescence. Previously vaccinated adults require a single booster and non-immunised adults advised, in UK since 2006, to have two doses given two months apart. Children too young for the conjugate vaccine should receive meningococcal polysaccharide vaccine in the interim.