It is the debtor's obligation to assert all exemptions at the time a garnishment or execution is levied.
The most that can be garnished under federal law is 25 percent of disposable income.
Since there is a head of household exemption, you would assert that at the time any garnishment of wages is sought.
Click on "Find a Lawyer" above and locate a debt collection defense attorney in your area. If you have a significant amount of unsecured debt then it might do you well to consider bankruptcy instead.
There is no specific "Head of Household" exemption in Nevada per se. For a list of exemptions, see NRS 21.090 - Property exempt from execution. There is a specific exemption for 75% of your disposable income through a wage garnishment. Also, to be garnished, you need to gross in excess of 50x the federal minimum wage, which equates to $362.50 per week. If you make less than this, you can claim a complete exemption from garnishment.
You best bet is to talk to the creditor or their attorney about a more reasonable payment plan, if they are willing.