Out of various bits of data and a dollop of professional judgment the plaintiff's expert in a Texas medical malpractice case created a causal narrative that has survived on appeal. See Constancio v. Shannon Medical Center. Here's how.

Plaintiff was admitted to the hospital with a serious MRSA infection resulting in sepsis and eventually died following a depressive respiratory event that produced ultimately fatal brain damage. Plaintiff's theory was that a combination of drugs had precipitated the decedent's respiratory distress and that a failure to monitor his oxygen saturation level via pulse oximetry caused the staff to miss the resulting hypoxia which quickly progressed to devastating brain damage. Drawing from pieces of the medical records, analyses of the potential interactions among the implicated drugs in the medical literature and the his  experience treating similar patients, plaintiff's expert came up with the following:

"[I]f you intervene early, you can prevent deaths from sepsis."

If you give Phenergan it "can potentiate the effects of all the drugs."

It "can also increase the effects of sedation."

When this happens "you can have low blood pressure"; and

"the heart can stop";

and when that happens, if pulse oximetry is being used,

"the health care provider can increase the oxygen or have other medical interventions."

Please remember the product rule! Each of those cans is just begging to be explored with a "What are the odds of ...?" line of questioning. Assuming just 4 "cans" out of the 5 above the expert would have to opine that the odds of each individual event happening was 85% or greater if the chain of can-cans is to produce a more likely than not conclusion. Throw in two more "cans" for "increased oxygen can prevent hypoxia in such cases" and "such patients can go on to survive sepsis" and the expert would need to be over 90% on each link of his/her causal chain or it wouldn't reach the level of "more likely than not."

It ought not be up to Plaintiff to test her causal chain once she's created a plausible narrative.  That's Defendant's job.