Commentary

David Ogilvie takes you through this paper and explains what it means

Imagine that you are a paramedic faced with a seriously injured casualty at the roadside. You have the necessary training and equipment to intubate the patient and secure the airway, which everyone knows is critical to staying alive. Surely it makes sense to get on and do it? The investigators in this study clearly had their reservations about the value of intubating casualties who are so deeply unconscious that they can be intubated without using drugs. So they set out to see what happens to these people once they reach hospital.

What is survival anyway?

You need to be very clear what you mean when you study the survival of patients. In this study, survival was very simply defined in terms of whether the patient was discharged from hospital alive or not. This is fine for short term situations, but if you want to study, say, the survival of people with cancer after different types of treatment, things get more complicated because some people move away and you lose track of them, some of them die of other diseases, and so on. You may come across various techniques of survival analysis for investigating these more complex problems.

What did they look at?

The important thing to note about this study is that, although the authors tell us that 492 casualties were intubated without drugs and the rest (988) were intubated with drugs, they only tell us what happened to the first group. They made no attempt to compare the two groups. This keeps things simple—but also limits what we can learn from the results.

What did they find?

The bottom line is that 486 patients were intubated without drugs outside hospital and followed up until discharge and only one of them left hospital alive. This leads very reasonably to the conclusion that the value of intubation without drugs is doubtful. Should we do it at all? The authors point out that:

• Patients who can be easily intubated without drugs are extremely unwell and are likely to die anyway.
• Attempted intubation can be hazardous.
• Time and money have been spent teaching paramedics to intubate without drugs.
• Simple airway manoeuvres might be just as good.
• There is very little evidence about what is the best thing to do. In other words, a call for more research and discussion.

What else could you do?

It is useful to consider what other information might have been obtained in a study of this group of patients. If you read the prepublication history of the paper on bmj.com you can see some of the suggestions made by the reviewers. The most obvious question is, “What happened to all the patients who were intubated with drugs?” It would be interesting to compare the chances of survival between the two groups. We assume that the 988 who were given drugs did better, but should we? The problem is that if we simply compared the proportion of each group who survived, and found that they were different, we would not really know why. The authors tell us that patients who can be intubated without drugs have a poor prognosis. Is that because they have more severe injuries, in which case they are less likely to survive whatever we do for them, or is it because intubation without drugs is a bad idea, and we would be better off managing the airway differently? We do not know what happened to patients whose airway was secured with other devices. Any fair comparison of survival between groups would require more information about the confound­ ing factors which might affect the result. The chance of a patient surviving major trauma depends, among other things, on the patient's age and the type and severity of the injuries. If these are not similar in both groups then we would need to allow for the differences in our analysis. There are various statistical techniques for doing this.

So what?

The issue of confounding illustrates why researching this issue further is not straightforward. The authors say that there have been no controlled trials comparing different ways of managing the airway, and you can see that such trials would be difficult. Many of the things we do in health care are not justified by evidence of the highest quality, but we still have to try to do the best for our patients. So how much evidence either way is enough to prompt a change in practice?

David Ogilvie, specialist registrar in public health medicine, Hamilton, Lanarkshire
Email: david.ogilvie@lanarkshirehb.scot.nhs.uk


studentBMJ 2001;09:305-356 September ISSN 0966-6494