One of the more Sherlock Holmes-like stories of internal medicine that makes me love this specialty.

I arrive at work to see the admission documents of one of my new cases.

"Eighty-five year old male, past history of tracheostomy for laryngeal cancer and diabetes. Admitted with ?cardiac arrest. Daughter found patient unresponsive and commenced CPR for 30mins."

I glance at the patient in question, expecting an intubated, unconscious, almost-dying man. 30 minute CPRs usually mean the brain is mush because of the prolonged down time (period during which the heart isn't pumping by itself and therefore the brain is starved of oxygen). The chance of any significant neurological recovery is near zero. The chance of discharge is even lower.

Instead, I see a man sitting in bed staring idly out of the window. No tube down his throat or into the hole in his throat (the tracheostomy). Very alert. Definitely not someone who had cardiac arrest and received CPR for 30 minutes.

Other issues: high blood sugar, dehydration, acute kidney injury (suspect dehydration causing his kidney function to deteriorate suddenly). His cardiac enzymes (blood markers that indicate a heart injury, usually sky-high in someone who has had a heart attack or a cardiac arrest and definitely if someone has had effective CPR) are only marginally raised; this can be attributed to his acute kidney injury.

I call up the daughter. She says she was changing her dad's nappy when suddenly he stopped breathing and became unresponsive. She thought his heart had stopped and he'd died. So she started doing chest compressions.

I ask if she'd checked if he had a pulse. No, she didn't check.

I ask if she'd received any training in CPR (seeing as one of the first things taught in Basic Life Support is checking for a pulse, or lack thereof, before starting CPR). No, she hadn't. She only mimicked what people on TV did.

So the facts were: this man has a history of diabetes; he lost consciousness for whatever reason but definitely did not have a cardiac arrest; he came in with very high blood sugars and dehydration. Somehow, they all link together.

Then, it clicks. This is someone who has a history of diabetes, who probably has an infection somewhere (my bet is urine, because diabetics get a lot of UTIs), causing his blood sugar to skyrocket. Because his blood sugar is so high, he pees out large amounts of the sugar along with the water in his system and gets dehydrated. The dehydration is made worse because he has a concurrent infection. Because he's so dehydrated, he gets a vasovagal attack (i.e. he faints because he's too dry). Vasovagals can mimic cardiac arrests, including the sudden loss of facial colouring and a pause in breathing.

But vasovagal attacks have pulses. The daughter didn't check for a pulse.

He gets insulin in the short-term for his high blood sugar. He gets IV fluids for his dehydration. I start him on antibiotics whilst awaiting for his urine culture results to come back. He gets better within days.

His urine culture returns as ESBL Klebsiella, which is a relatively resistant type of bacteria. Et voila. He gets discharged a week later after some stronger IV antibiotics because of the resistant bacteria.

I also advise the daughter, without trying to shame her or embarrass her, to attend CPR courses. Whilst it was admirable she immediately jumped to CPR her apparently arrested dad, CPR done inappropriately and improperly can actually cause more harm than good, including causing rib fractures and heart arrhythmias. I hope there isn't a next time but at least I'd like her to be prepared should there be another unfortunate soul that loses consciousness in front of her.