Teaching, asking and assessing pneumonia severity.

I remember a senior colleague complaining once, when I was working in London, about how difficult it can be to teach junior doctors and medical students. His complaint was that they often ask questions which don't make sense.  For all of us as we learn, a fair amount of knowledge needs to be acquired prior to the point at which we begin to ask informed and sensible questions.  Until then our questions are often uninformed, or 'silly' – and for the super-smart professor, having to spend time addressing nonsense questions was laborious.


But it is so important that doctors in training – and indeed all people learning – are given permission to ask those ‘stupid questions’. I was never very good at that, and to the extent that I was not good at asking the dumb questions my learning was impeded.

 Which is a long-winded preamble to the fact that I have to take some student doctors for a tute tomorrow. We’re going to be talking about respiratory infections. Some of the discussion is going to be about community acquired pneumonia – so I’ve been looking over some of the pneumonia severity scales. These are tools that can be used by doctors (often junior) at the coal face – ie in emergency departments – to help evaluate whether hospital admission will be required.

I don’t use them very much, because I’m not often seeing the patient at the point of diagnosis of a community acquired pneumonia. But, in the interests of not looking stupid when I get asked a good question tomorrow about these tools I’ve been refreshing my mind.

 The two Australian indices most used, and detailed in our “Antibiotic guidelines” are the CORB and SMART-COP indices. The following summary of CORB – which is much simpler to use but a little less precise – was lifted from antibiotic guidelines:

CORB uses the following patient parameters, based on the most abnormal results obtained during the initial 24 hours of inpatient stay:
 C = acute confusion
 O = oxygen saturation 90% or less
 R = respiratory rate 30 breaths or more per minute
 B = systolic blood pressure less than 90 mm Hg or diastolic blood pressure 60 mm Hg or less

Interpretation of CORB score:
 'Severe CAP' = the presence of at least two of these features.

In the Australian study cohort, the accuracy of CORB for predicting need for IRVS using presence of at least two features was:
 sensitivity = 81%
 specificity = 68%
 positive predictive value (PPV) = 18%
 negative predictive value (NPV) = 98%
 area under the receiver operating characteristic (ROC) curve = 0.74.

A copy of the 'SMART-COP' index can be found by following this link.

 Now, I don’t intend to suggest to these student doctors that they memorise SMART –COP (although they should be able to memorise CORB). Perhaps the best thing about these indices is that they draw our attention again to important clinical parameters – to the sorts of things that we should all be paying attention to when we assess patients with pneumonia.

All of the guidelines go to some lengths to remind us that we cannot rely on the severity indices. We need to exercise clinical judgement when deciding which patients should be admitted to hospital. And there are particular ‘red flags’, any one of which necessitates inpatient care. To quote the antibiotic guidelines:

The presence of any one of the following key features indicates a high likelihood of the patient having severe  disease and these patients require inpatient care:


Clinical
 respiratory rate greater than 30 breaths/min
 systolic blood pressure less than 90 mm Hg
 oxygen saturation less than 92%
 acute onset confusion.


Investigations
 arterial (or venous) pH less than 7.35
 partial pressure of oxygen (PaO2) less than 60 mm Hg
 multilobar involvement on chest X-ray.