Monday, September 19, 2011

Transfusion triggers

Quick note today, just wanted to talk about the hemoglobin level at which we should consider transfusion.

There's a lot of bad data out there, much of it retrospective, heterogeneous populations, and so on. When I was a MICU resident, often the team would prefer to get the Hgb up above 10 to "help with the oxygen delivery." Marino, OTOH, in his The ICU Book, makes a persuasive case that the reduced viscosity in anemia facilitates oxygen delivery, and you mess with this compensatory mechanism (with pRBCs) at your peril. Incidently, Marino provides a review of some more recent transfusion-related papers from his website. Worth reading.

Let me review the single best, and most-oft cited, paper on this topic, which was done by Hêbert et al, published in the NEJM in 1999. The paper (pdf) can be downloaded free from NEJM, I think, but here's a copy.
Real interesting stuff.

They prospectively studied the effect of two different transfusion thresholds, either 7 g/dL (restrictive strategy) or 10 g/dL (liberal strategy), in ICU patients. The ICUs were mixed, both surgical and medical, and both community and academic. They excluded patients with, amongst other issues,  active hemorrhage or s/p cardiac surgery.
They found that 30-day mortality was the same in the two groups, but the hospitalization mortality was significantly lower in the restrictive-strategy group (22.3 percent vs. 28.1 percent, P=0.05).

Let me emphasize that a bit more:
28.1 - 22.3 = 5.8,  or an Absolute Rate Reduction of 5.8%
That gives us a Number Needed to Harm of a little over 17. In other words:

For every 17 patients that were transfused to stay above 10 g/dL, instead of above 7 g/dL, 1 died.


Closer look at the breakdown on adverse effects:
Hey, that's funny. Many folks feel that a chief reason to transfuse is to avoid exacerbating any cardiac ischemia. What they found here, however, was that bad cardiac events were more common with the liberal transfusion threshold!

Okay, that was in 1999 - what's changed since then? Not much. In fact, the evidence has become stronger with regard to the risks of transfusion, and the benefits of a restrictive strategy, across a spectrum of medical and surgical contexts.

Let me give the latest transfusion guidelines, published in 2009, written jointly by the Society for Critical Care Medicine,and the Eastern Association for Surgery on Trauma. This document is kinda unique, addressing both the medical and surgical perspectives regarding the literature. The salient recommendations are copied here. I just want to highlight a few of them:

1. Transfuse patients with active, ongoing hemorrhage. Be proactive!
2. If they're not bleeding out, don't transfuse until the Hgb drops below 7 g/dL.
3. At that point, only transfuse single units.

    A. Recommendations Regarding Indications for RBC Transfusion in the General Critically Ill Patient
      1.    RBC transfusion is indicated for patients with evidence of hemorrhagic shock. (Level 1)  
      2.    RBC transfusion may be indicated for patients with evidence of acute hemorrhage and hemodynamic instability or inadequate oxygen delivery. (Level 1)  
      3.    A “restrictive” strategy of RBC transfusion (transfuse when Hb < 7 g/dL) is as effective as a “liberal” transfusion strategy (transfusion when Hb < 10 g/dL) in critically ill patients with hemodynamically stable anemia, except possibly in patients with acute myocardial ischemia. (Level 1)  
      4.    The use of only Hb level as a “trigger” for transfusion should be avoided. Decision for RBC transfusion should be based on an individual patient's intravascular volume status, evidence of shock, duration and extent of anemia, and cardiopulmonary physiologic parameters. (Level 2) 
      5.    In the absence of acute hemorrhage RBC, transfusion should be given as single units. (Level 2)  
      6.    Consider transfusion if Hb < 7 g/dL in critically ill patients requiring mechanical ventilation (MV). There is no benefit of a “liberal” transfusion strategy (transfusion when Hb < 10 g/dL) in critically ill patients requiring MV. (Level 2)  
      7.    Consider transfusion if Hb < 7 g/dL in resuscitated critically ill trauma patients. There is no benefit of a “liberal” transfusion strategy (transfusion when Hb < 10 g/dL) in resuscitated critically ill trauma patients. (Level 2)  
      8.    Consider transfusion if Hb < 7 g/dL in critically ill patients with stable cardiac disease. There is no benefit of a “liberal” transfusion strategy (transfusion when Hb < 10 g/dL) in critically ill patients with stable cardiac disease. (Level 2) 
      9.    RBC transfusion should not be considered as an absolute method to improve tissue oxygen consumption in critically ill patients. (Level 2) 
      10.  RBC transfusion may be beneficial in patients with acute coronary syndromes (ACS) who are anemic (Hb ≤ 8 g/dL) on hospital admission. (Level 3)
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