Final answer:
Perform CPR is the critical intervention that must be provided to an unresponsive patient with no palpable carotid pulse.
Step-by-step explanation:
The critical intervention that must be provided to a patient who suddenly goes unresponsive and has no palpable carotid pulse during the secondary assessment is perform CPR. CPR, or cardiopulmonary resuscitation, is necessary to manually compress the heart and push blood into the pulmonary and systemic circuits. It is crucial to perform high-quality chest compressions until the patient regains spontaneous contraction or is declared dead by a healthcare professional.