On June 27, 2019, the Supreme Court of the United States released a decision in Mitchell v. Wisconsin, a case where the question was raised whether or not law enforcement can execute warrantless blood draws on unconscious motorists under the exigency exception. In a plurality opinion authored by Justice Alito, the Court ruled that when a driver is unconscious and cannot be given a breath test, the exigent-circumstances doctrine generally permits a blood test without a warrant.
The Court heavily relies on a previous decision Schmerber v. California, which established that exigency exists in regards to OUI cases. When BAC evidence is dissipating and when some other factor creates pressing health, safety, or law enforcement needs that would take priority over a warrant application. According to Justice Alito and the Court, being unconscious in and of itself represents a medical emergency, thus satisfying the second prong.
It is worth noting that the Supreme Court isn’t making a decision on all cases where a citizen is unconscious. The Court doesn’t rule out circumstances where defendants are able to show that their blood would not have been drawn if law enforcement had not been seeking BAC information, or where law enforcement could have reasonably obtained warrant interfering with other pressing needs or duties.