The essential equipment for anaesthesiologists is not a long list. Strip away everything that is nice to have, and three monitors remain, because each one answers a question the other two cannot. Is the patient ventilating? Is the patient oxygenated?

Capnography myths survive because they all sound sensible. Each one is a small, plausible shortcut, and each one has led someone to act on a number they should have questioned, or to ignore one they should have acted on. Here

EtCO2 in pregnancy breaks two rules that hold almost everywhere else in medicine. The normal range shifts down, so a reading of 31 mmHg in a pregnant woman is not hypocapnia, it is her physiology working correctly. And the gap

EtCO2 in sepsis behaves in a way that surprises people the first time they see it. The patient is infected, feverish and breathing hard, and the carbon dioxide reading is low. That low number is the point. It is the

EtCO2 in trauma tells you two very different things, and getting them confused can harm the patient. In a bleeding patient, a falling EtCO2 is a circulation alarm. It means blood is not reaching the lungs, and it can flag

Capnography in asthma and COPD is the one situation where the shape of the trace matters more than the number on it. In obstructive disease, the EtCO2 value can look almost normal while the patient is in serious trouble. But

Drugs that affect EtCO2 fall into two very different groups, and confusing them is how clinicians get misled. Some medications genuinely change the patient’s carbon dioxide, by slowing their breathing, speeding up their metabolism, or releasing CO2 into the blood.

Capnograph cost of ownership is the number that should drive a purchase decision, and it is almost never the number people compare. They compare the quote. Then they buy the cheapest device and pay for it every year afterwards. A

Capnograph maintenance is simpler than most people fear, and more important than most people realise. A capnograph is a measuring instrument. If it drifts, it does not stop working. It keeps giving you numbers, and they are quietly wrong. The

Capnography sensor placement is one of those tasks that looks trivial and quietly is not. Put the sensor in the wrong place, or skip the zeroing step, and the monitor will still show you a number. It will just be