Why can an inadequate anesthetic dose make a lethal injection especially painful?

In the context of capital punishment, a lethal injection procedure typically involves a three-drug protocol designed to induce death humanely. The first drug, sodium thiopental, is an anesthetic intended to render the prisoner deeply unconscious. The second drug, pancuronium bromide, is a powerful muscle relaxant that paralyzes all voluntary muscles, and the third, potassium chloride, induces cardiac arrest.1

If a prisoner receives an inadequate dose of the anesthetic, they may regain consciousness and sensation while the subsequent drugs are administered. Because the second drug causes total paralysis, the prisoner may experience excruciating pain from the final injection but be physically unable to signal their distress or show any outward signs of suffering. This potential for severe, hidden agony is a primary concern regarding the ethics of lethal injection protocols, as it contradicts the fundamental principle that state-sanctioned executions should avoid the unnecessary infliction of pain.12