Final answer:
The first sign of Mg toxicity often includes early neuromuscular symptoms like muscle twitching or fasciculations and changes in mental status such as confusion. Loss of deep tendon reflexes is a subtler initial change to monitor for in the assessment of Mg toxicity.
Step-by-step explanation:
The first sign of Mg toxicity can vary, but early symptoms often include changes in mental status such as confusion, as well as other neuromuscular signs such as muscle twitching or fasciculations, which can eventually lead to more serious conditions. When considering assessment of Mg toxicity, one must note the initial subtle changes like loss of deep tendon reflexes ahead of more severe and life-threatening symptoms like respiratory paralysis, cardiac arrest, and profound hypotension. It is important for healthcare providers to monitor patients receiving magnesium therapy closely for these early signs to prevent the progression of toxicity.