On his way to the hospital, 15-year-old Max McKenzie was gripped by fear, believing he might not survive the journey.

The teenager had unwittingly ingested nuts while visiting a family member, triggering severe breathing difficulties.

In response, Max administered his own Epipen and used an asthma inhaler while waiting for emergency services to arrive.

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Advanced life support paramedics reached Max shortly before 2 p.m. on August 6, 2021. They discovered he was struggling to breathe and provided him with adrenaline and an oxygen mask to stabilize his condition.

Within 10 minutes, his breathing became worse so a MICA intensive care ambulance was requested.

He was given a second adrenaline shot and placed on a nebuliser, which was initially not working and then corrected when he got into the ambulance.

"In the process of being removed from the house and settled in the ambulance, Max became increasingly agitated and restless," counsel assisting the coroner Rachel Ellyard said.

"He was pulling on equipment. He expressed a fear that he was going to die. He was visibly hypoxic and understandably very distressed."

An enlarged photo of Max sat on an easel inside Melbourne Coroners Court today as an inquest into his death began in front of his grieving parents.

Coroner David Ryan is investigating the circumstances around Max's death and the appropriateness of all medical care he received on August 6.

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Max suffered a seizure on his way to Box Hill Hospital, was given more adrenaline and ventilated with a bag valve mask.

He was unresponsive when he arrived at the hospital, and was taken to a resuscitation bay where a bag valve mask for oxygen was administered.

The coroner will investigate the "very live" question of whether he was given appropriate ventilation after arriving at hospital, Ellyard said.

Six minutes after arriving a code blue was called, Max's heart rate slowed and he was given CPR.

Drugs were administered to relax his vocal chords so a tube could be inserted to help him breathe.

Just after 3pm an emergency incision was made to create an airway, and the timeliness and appropriateness of this intervention is another question for the coroner.

Max was then transferred to The Alfred where scans revealed he had suffered a brain injury.

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"It's clear that that injury must have been caused, or at least the initial insult to the brain must have been suffered, sometime in the period between 2.30 and shortly after 3 o'clock," Ellyard said.

He was taken to the Royal Children's Hospital for management and investigation into his neurological injuries, where further scans found he had suffered a significant hypoxic ischemic brain injury.

On August 19, Max experienced a sudden cardiac arrest which he could not be resuscitated from.

Forensic pathologist Victoria Francis was called to give evidence today about Max's cause of death and she said his brain injury was the "most likely contributor" to the arrest he suffered before dying.

The inquest will continue tomorrow.