log timeouts to access log

[Richard Kearsley]

Hi
I would like to log an indication of weather a request ended because of 
a client timeout - in the access.log

e.g.

log_format normal '$remote_addr - $remote_user [$time_local] ' 
'"$request" $status $bytes_sent ' '"$http_referer" "$http_user_agent" 
"$client_send_timed_out"';
where $client_send_timed_out would be a true/false or an 0/1 etc

Is there anything in there that would allow me to log that?

Many thanks
Richard