Christa Pike's execution failed. Here's how lethal injection works

Lethal injections are under scrutiny after Christa Pike survived two rounds of drugs during Tennessee's failed attempt to execute her.Why it matters: Lethal injection has been the dominant U.S. execution method for decades, accounting for roughly 89% of the 1,683 executions carried out since 1976, per the Death Penalty Information Center.Driving the news: Pike, convicted of killing a classmate three decades ago, survived two rounds of lethal injection drugs Wednesday in what would have been the state's first execution of a woman in 200 years.In response, Gov. Bill Lee halted executions and ordered a "comprehensive, third-party review" of the failed attempt.Pike's execution attempt followed hours of legal whiplash in which courts first stayed the execution before reversing course.Pike is still alive as of Thursday afternoon, her attorney said at a news conference, according to the AP. She is receiving "lifesaving care" after a failed attempt Wednesday night that her attorney said amounted to "torture."The big picture: Execution protocols vary by state, but lethal injections generally follow the same basic process.Here's what to know.Why states adopted lethal injectionFlashback: Lethal injections emerged after the Supreme Court allowed capital punishment to return in the 1970s.Oklahoma became the first state to authorize the practice in 1977. Texas carried out its first five years later.Before lethal injections, states commonly used methods like electrocution, gas, hanging and firing squads. Lawmakers considered injections to be less violent and cheaper.Lethal injections are now used in all death penalty states.The Supreme Court requires states to reserve the death penalty only for the most heinous murders.Several states — Idaho, Mississippi, Oklahoma, South Carolina and Utah — allow firing squads.Idaho made firing squad its primary execution method in July.How lethal injections are administeredThere isn't one standard procedure. States use different protocols, but the basic process is similar.A fatal dose of drugs is delivered through an IV while the prisoner is restrained, often to a gurney.Arizona, for example, requires two IV catheters, one as a backup in case the first line fails.Physicians often don't administer lethal injections because the American Medical Association's Code of Medical Ethics says doctors should not participate in executions.States instead sometimes rely on execution teams that can include prison guards, corrections employees and other personnel trained to administer the drugs.What drugs are used in lethal injectionsHow it works: There are two main ways these drugs are administered. One drug path — The state administers a sedative or barbiturate, commonly pentobarbital, to cause death.Three drug path — Another method includes giving a sedative or anesthetic, then a paralytic before a final drug stops the heart.Yes, but: Pentobarbital itself is controversial, with critics questioning whether it really causes a painless death