In Mitchell v. Wisconsin, the US Supreme Court considered the case where a blood draw is performed on an intoxicated driver who is so impaired he cannot do field tests, gives a PBT of .24, then passes out before a breath test can be given.  Under these circumstances, the court reasoned "exigency exists when (1) BAC evidence is dissipating and (2) some other factor creates pressing health, safety, or law enforcement needs that would take priority over a warrant application. Both conditions are met when a drunk-driving suspect is unconscious, so Schmerber controls: With such suspects, too, a warrantless blood draw is lawful."  

The court did not automatically affirm the Wisconsin supreme court's conviction.  The court explained that under the circumstances of the case, "[police] may almost always order a warrantless blood test to measure the driver’s BAC without offending the Fourth Amendment."  But because Mitchell had not been given an opportunity to challenge exigency, a remand was needed. 

As the dissent points out, that lack of showing was purposeful.  Wisconsin's primary argument was that their implied consent law justified the blood draw.   In its opinion, the Mitchell plurality (4-1-3) did not rely on the Implied Consent argument, instead they resurrected the exigency theory.  As the dissent points out, Wisconsin had earlier conceded exigency did not support the blood draw in this case, the theory was not argued below, and no evidence was offered to justify it.  This type of reasoning is not unprecedented.  An appellate court is not bound by concessions of the parties and they can consider any legal theory supported by the evidence that affirms the lower court.  

Because this is a 4th Amendment case, and not an implied consent case, the reasoning in Mitchell should also apply to exigency circumstances in Washington.   The test for "the unusual case" that is not an exigency circumstance in Mitchell is unclear and will require additional litigation.  The remand to Wisconsin should provide some insight into how the courts will construe the defendant's burden.

The full case is Mitchell v Wisconsin US Supreme Court Exigency 2019.pdf

National Public Radio Story: June 27, 2019