Doctors knock out sheep to discover anaesthesia’s dark side

|      Jason Gale      |

BENEATH green surgical sheets and a tangle of tubes, a healthy young ewe is undergoing a heart-lung bypass procedure to help answer one of several urgent questions about a pillar of modern medicine: anaesthesia.

Almost two centuries after anaesthetics revolutionised surgery, a growing body of research is pointing to disturbing side effects that range from delirium to cancer-proliferating immune suppression. Researchers knocked out the sheep last month at the University of Melbourne to try to understand why common open-heart procedures lead to acute kidney injury in up to a third of patients – part of a broader effort to study the impact of anaesthesia on the immune system, brain and other major organs.

The findings are already undermining decades of soothing messages about the harmlessness of being put into a sleep-like state. “Anaesthetists are now trying to say actually it’s not that safe,” said Andrew Davidson, head of anaesthesia research at the Murdoch Children’s Research

Institute in Melbourne. “You don’t die on the table, but quite a lot of you don’t get home.”

Of the 200 million adults worldwide who undergo non-cardiac surgery annually, more than one million will die within 30 days. That risk jumps to one in 20 for patients 70 years and older.

A surgical team at the Florey Institute of Neuroscience and Mental Health in Melbourne, Australia, attends to a sheep undergoing open heart surgery during a clinical trial to understand the risk of acute kidney injury related to anaesthetics during surgical operations. – WP-BLOOM

Less than a mile from Davidson’s centre at the Royal Children’s Hospital in Melbourne, separate groups at the Florey Institute of Neuroscience and Mental Health and the Peter MacCallum Cancer Centre are working to understand whether inhaled volatile gases like isoflurane and sevoflurane – used by anaesthetists to render some 80 per cent of patients unconscious – may be more harmful than intravenous agents, such as propofol and fentanyl.

With 313 million operations undertaken each year, the findings may have significant global economic and social implications, and could herald a paradigm shift in surgical care, researchers say.

The science is conflicting and incomplete. A study by Davidson and colleagues, published late Thursday in the Lancet medical journal, found an hour of general anaesthesia in early infancy has no lasting impact on the developing human brain. But some surgery may last longer, and Mayo Clinic doctors found an association between anaesthesia and attention-deficit hyperactivity disorder (ADHD) in children.

The ADHD link is “scientifically plausible, but the evidence is not strong,” according to Davidson.

On the fourth floor of a University of Melbourne laboratory building, scientists at the Florey Institute are using fibre optic probes to measure blood flow and oxygen levels in different regions of the kidney of the two-year-old Merino undergoing open-heart surgery.

The research, conducted by a team of clinicians and scientists under human surgical conditions, is designed to track kidney changes before, during and after the procedure, as well as identify risks attributable to two kinds of anaesthetic agents, and find ways to protect the blood-filtering organ.

As many as 30 per cent of patients who undergo open-heart surgery develop an acute kidney injury that increases their risk of chronic kidney disease and death, according to Yugeesh Lankadeva, a researcher studying the interaction.