Those of you who read Sepsis I may have been amused by my attempt to compare lactate to a Pap smear – OK, it is a long bow (?in the running for the Agincourt Award). But my point is, we just don’t do enough lactates in the typical ED to try and catch all the subtle / early, hypoperfused septic / SIRS patients. So I have another analogy that I hope will be familiar to all the GPs and ED folk out there…
You are working in a medium-sized ED and have just seen a 15 yo boy with 12 hour history of (R) lower quadrant pain, nausea and not much else. His obs are pretty normal, mum thinks he might have had a fever earlier. There is no other diagnosis likely on exam – however when you feel his belly it is not convincing for peritonism – no guarding, rebound or mass, just a bit tender to deep palpation. You know he might have an early appendicitis, but you also know that a good number of these fizzle out to nothing overnight. So what to do?
- Send him home with mum and get another look at his abdo in the AM, “return if worse”
- Admit under the Surgeons for essentially the same management, the Surgeon will review in he AM
- Consider investigations: FBP, CRP, or even the nebulous ?appendix USS
- Find a keen surgeon who will just whip out his appendix and ask questions later
Appendicitis can be subtle, hard to diagnose in some. In others it is screamingly obvious – fever, rebound, localising RIF tenderness. My point is this – we are good at the obvious ones, easy to diagnose and satisfyingly pus-ridden appendixes are removed. However most surgeons will tell you that if every appendix they remove is purulent / perforated – then they are probably not doing enough(early) appendectomies! You have to remove some normal appendixes to ensure you are “catching” enough of the nasty ones (this is controversial, but the principle applies – see review).
OK, now back to sepsis screening in ED. You identify the population of patients who meet the criteria listed in Sepsis I. These are the people in whom the probability of sepsis is high enough for you to justify the minor cost / inconvenience of a panel of bloods (including a lactate). The lactate result then allows you to further stratify the risk with some objectivity. See review of its uses. So stratification might look something like this
- Lactate normal (<2): can be managed as per usual, ID source of sxs, outpatient management
- Lactate 2 – 4 : at risk, needs close observation, micro samples and empirical Abs, repeat lactate after initial intervention
- Lactate high (>4): needs urgent resuscitation, micro, empirical ABs. This group has a high 28-day mortality independent of the presence of shock. see Mikkelsen et al
The goal here is to identify the subtle ones – the ones that you might have otherwise sent home. If every ABG / lactate you order comes back positive – you likely have sent home somebody in early septic shock! You need to drop your threshold for ordering a VBG to the point where you have a decent ‘negative rate’ so you are not missing the early sepsis. So doing a lactate is a bit like asking the Surgeons to review the ?appendix – the smart surgeon stratifies the risk of perforation / complications against the risk of removing a “normal appendix”. However, doing a lactate is infinitely easier, cheaper and less invasive than an appendectomy. BUT, missing an occult sepsis is very bad. So you have not much to lose and all to gain. Oh, and the surgeon might use time as a “diagnostic tool” BUT this may not be such a great idea when it comes to ?Sepsis as we shall see as we progress through this series.