Having kids has given me an acquaintance with health care that I virtually would have never thought possible. My boys are not the unhealthiest of children, but their conditions (severe autism and apraxia for my elder son, slightly less severe autism and mild hypotonia for my younger) have required some further investigation.
We had one of these investigative moments this past year with my younger son, specifically regarding the possibility of a metabolic disorder causing his hypotonia (and perhaps contributing to his autism and global delays as well). To get more clues, blood work was needed to test for the level of certain amino acids and other chemical markers. One of these markers was lactic acid: elevated levels might indicate a metabolic disorder and provide something for a geneticist to work with.
There was a problem with this, however: lactic acid levels tend to rise with muscle exertion, so the blood needed to be drawn from my 18-month-old son without causing him to exert himself while we were trying to get blood.