Tag Archives: spleen

Spleen Vaccines: So Confusing! – Part 1

November 8, 2019 The Trauma Pro Leave a comment

Earlier this year, there were a lot of television commercials for Prevnar 13, a 13-valent pneumococcal vaccine for immun-ocompromised or asplenic adults. And interestingly, I noticed that the CDC has added a recommendation that these patients receive this vaccination, followed by the original 23-valent vaccine (Pneumovax 23) 8 weeks later.

WTF? Patients with splenectomy (or significant angio-embolization) for trauma are considered functionally asplenic. And although the data for immunization in this group is weak, giving triple vaccinations with pneumcoccal, H. flu, and meningococcal vaccines has become a standard of care.

This was difficult enough already because there was debate around the best time to administer: during the hospital stay or several weeks later after the immune system depression from trauma had resolved. The unfortunate truth is that many trauma patients never come back for followup, and so don’t get any vaccines if they are not given during the hospital stay.

And then came the recommendation a few years ago to give a 5-year booster for the pneumococcal vaccine. I have a hard time remembering when my last tetanus vaccine was to schedule my own booster. How can I expect my trauma patients to remember and come back for their pneumococcal vaccine booster?

So what do we do with the CDC Prevnar 13 recommendation? If we add it, it means that we give Prevnar while the patient is in the hospital, and then hope they come back 8 weeks later for their Pneumovax. And then 5 years later for the booster dose. Huh?

Looking at the package insert, I read that Pneumovax 23 protects against 23 serotypes of S. Pneumo, which represent 85% of most commonly encountered strains out there. So it’s not perfect. Prevnar 13 protects against 13 serotypes, and there is no in-dication as to what percent of strains encountered are protected against.

So I decided to dig deeper and look at the serotypes included in each vaccine. They are shown in the chart below. The 23 bars with maroon in them (solid or striped) are Pneumococcal serotypes covered by Pneumovax 23. The 13 bars containing gray are ones covered by Prevnar 13. There is only one serotype in Prevnar 13 not covered by Pneumovax 23, serotype 6A. Unfortunately, it’s nearly impossible to find the prevalence of infections by serotype, and it varies geographically and over time anyway. So does cover-age of a single extra serotype by Prevnar 13 justify an additional vaccination and complicated administration schedule? Hmm.

It turns out that there is one significant difference between these two vaccines. Pneumovax 23 is a polysaccharide vaccine made up of fragments of polysaccharide from pneumococcus cell walls. Prevnar 13 is a “conjugated vaccine,” meaning that the polysaccharides are linked to a protein. This is thought to increase the immune system response to the vaccine.

(click for full-size graph)

The current CDC recommendations are listed below. In the old days, we just gave three vaccines before the patient left the hospital. Then the Pneumovax 23 booster was added at 5 years. Same for the meningococcal serogroup B booster at 4 weeks. Then the meningococcal conjugate vaccine (Menactra) came along and was added (with a booster at 8 weeks). Finally, Prevnar 13 was added with its own booster, and Pneumovax 23 was delayed for 8 weeks. Oh, and don’t forget the 5 year boosters for both Pneumovax 23 and the meningococcal conjugate vaccines. It has become very complicated.

(click for full-size chart)

In my next post, I’ll try to make sense of this mish-mash and offer some thoughts on how to decide what to do for your patients.

Abdomen

Early Mobilization In Solid Organ Injury

November 7, 2019 The Trauma Pro Leave a comment

Traditionally, most centers keep their solid organ injury patients in bed and NPO for a period of time. I suspect that they feel that walking may cause the organ to break and require operation. And if they need emergency surgery, shouldn’t they have an empty stomach?

Now let’s think about this. The success rate of nonoperative management for liver and spleen injuries in properly selected patients is somewhere between 93% and 97%. It’s been years since I’ve had a failure while the patient was in my hospital. And since we treat about 200 of these per year, I will be starving and restricting ambulation in a lot of patients just in case that one failure occurs.

The group at LA County – USC recently published a prospective, observational study of their 20-month experience comparing early ambulation vs delayed ambulation after liver, spleen, or kidney injury. They admitted 246 patients with these injuries, but excluded those who couldn’t walk, walked out against medical advice, died, or underwent operative intervention or angiography.

Here are the factoids:

There were 36 patients in the early ambulation group (<24 hours) and 43 late ambulators (>24 hours)
There were no complications in the early group, and three in the late group (one readmission, two developed pseudoaneurysm that required embolization)

Bottom line: This is a very small study, but it dove-tails with my personal experience. We removed activity restrictions and NPO status from our solid organ protocol two years ago and have not noted any complications while in the hospital.

Reference: Safety of early ambulation following blunt abdominal solid organ injury: A prospective observa-tional study. Am J Surg 214(3):402-406, 2017.

Complications

Overwhelming Post-Splenectomy Infection (OPSI)

November 6, 2019 The Trauma Pro Leave a comment

Most trauma professionals have heard of OPSI, but few have ever seen it. The condition was first described in splenectomized children in 1952. Soon after, it was recognized that this infection occurred in asplenic adults as well.

OPSI is principally due to infection by encapsulated organisms, those with a special polysaccharide layer outside of the bacterial wall. This layer is only weakly immunogenic, and confers protection from the normal immune mechanisms, particularly phagocytosis. However, these bacteria are more easily identified and removed in the spleen.

OPSI may be caused by a number of organisms, the most common being Strep. pneumonia, Haemophilus influenza, and meningococcus. For this reason, the standard of care has been to administer vaccines targeting the usual organisms to patients who have lost their spleen.

How common is OPSI? A recent paper from Gernany reviewed comprehensive data from 173 intensive care units over a 2-year period. Here are some of the more interesting factoids:

2,859 ICU beds were screened, but the number of unique patients was not given. This is very disappointing because incidence cannot be calculated!
52 cases of OPSI occurred
Only half of the patients had received vaccines
Pneumococcus was the most common bacterium (42%). There were no H. Flu or meningococcal infections.

Bottom line: Yes, OPSI exists and can occur in your asplenic patients. It is uncommon enough that you and your colleagues will probably never see a case. But proper vaccination remains important. Papers consistently show that we are collectively not very good at ensuring that our splenectomized patients receive all their vaccines, ranging from only 11-50%. We collectively need to make better efforts to provide them to our at-risk patients.

Reference: Overwhelming Postsplenectomy Infection: A Prospective Multicenter Cohort Study. Clin Infec Diseases 62:871-878, 2016.

Abdomen, Abstracts

AAST 2019 #3: Delayed Splenectomy In Pediatric Splenic Injury

September 9, 2019 The Trauma Pro Leave a comment

Nonoperative management of the blunt injured spleen is now routine in patients who are hemodynamically and have no evidence of other significant intra-abdominal injury. The trauma group at the University of Arizona – Tucson scrutinized the failure rate of this procedure in children because it is not yet well established.

They reviewed 5 years of data from the National Readmission Database. This is actually a collection of software and databases maintained by the federal government that seeks to provide information on a difficult to track patient group: those readmitted to hospitals after their initial event.

Patients who had sustained an isolated spleen injury who were less than 18 years old and who had either nonoperative management (NOM), angioembolization (AE), or splenectomy were analyzed. Outcome measures included readmission rate, blood transfusion, and delayed splenectomy. Common statistical techniques were used to analyze the data.

Here are the factoids:

About 9500 patients were included, with an average age of 14
Most (77%) underwent NOM, 16% had splenectomy, and 7% had AE (no combo therapies?)
Significantly more patients with high grade injury (4-5) had splenectomy or AE than did the NOM patients (as would be expected)
A total of 6% of patients were readmitted within 6 months of their initial injury: 12% of NOM *, 8% of AE *, and 5% of those with splenectomy (* = statistically significant)
The NOM and AE patients were also more likely to receive blood transfusions during their first admission
Delayed splenectomy occurred in 15% of cases (7% NOM and 5% AE) (these numbers don’t add up, see below)
Statistical analysis showed that delayed splenectomy was predicted by high grade injury (of course), blood transfusion (yes), and nonoperative management (huh?)
In patients who were readmitted and splenectomized, it occurred after an average of 14 days for the NOM group and 58 days for AE (huh?)

The authors concluded that “one in seven children had failure of conservative management and underwent delayed splenectomy within 6 months of discharge.” They stated that NOM and AE demonstrated only a temporary benefit and that we need to be better about selecting patients for nonoperative management.

Hmm, there are several loose ends here. First, what is the quality of the study group? Was it possible to determine if these patients had been treated in a trauma center? A pediatric vs adult trauma center? We know that there are outcome disparities in spleen trauma care at different types of trauma centers.

Next, are they really pediatric patients? Probably not, since age < 18 were included and the average age was 14. Injured spleens in pre-pubescent children behave much better than adolescents, which are more adult-like.

And what about the inherent bias in the “readmission data set?” You are looking only at patients who were readmitted! By definition, youare looking at a dataset of poorer outcomes. What if you had identified 9,500 initial patient admissions from trauma registries and then tried to find them in the readmission set. I know it’s not possible to do that, but if it were I would bet the readmission and delayed splenectomy numbers would be far, far lower.

And what about those delayed splenectomy numbers? I can’t get the percentages to match up. If 15% of the 7965 patients who didn’t have an initial splenectomy had it done later, how does 7.2% of the 7318 NOM patients and 5.3% of the 1541 AE patients add up?

Bottom line: The usual success rate tossed around for well-selected nonoperative management is around 93% when optional adjunctive AE is part of the algorithm. That’s a 1 in 14 failure rate, and it generally occurs during the initial hospitalization. In my experience, readmissions are very rare. And that’s for adults; children tend to behave even better!

I wouldn’t consider changing my practice yet based on these findings, but the devil will probably be in the details!

Here are some questions for the presenter and authors:

Please provide some detail on the data set. We really need to know an age breakdown and the types of centers they were treated at, if available.
Discuss the potential data set bias working backwards from a database that includes only readmitted patients.
Please clarify the delayed splenectomy statistics to help match up the numbers.

I’m anticipating a great presentation at the meeting!

Reference: Delayed splenectomy in pediatric splenic injuries: is conservative management overused? AAST 2019 Oral abstract #8.

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