West Midlands Ambulance chiefs moved the service to the highest risk rating this week, warning serious harm or death is 'almost certain'.
The transition to the extraordinary 'level 25' (out of 25) means the service expects patients to suffer 'catastrophic consequences' - with repeated serious harm or death 'almost certain'.
This is the first time the service has reached this risk level in its history.
The move comes after ambulances with critically ill patients on board have been routinely held up outside A&E departments across the region - sometimes for waits in excess of 10 hours.
Handovers are meant to take 15 minutes.
Earlier this month a patient died after waiting for five hours in the back of an ambulance at Worcestershire Royal Hospital.
An investigation has been launched by Worcestershire Acute Hospitals Trust and West Midlands Ambulance Trust into what happened.
A report to the West Midlands Ambulance Service board on October 4 showed the average waiting time for an ambulance arriving at Worcestershire Royal Hospital was two hours.
And there are growing fears that backlogs will have a catastrophic effect on patients who are both waiting to be transferred to A&E departments, or waiting for an ambulance to arrive.
A predicted 15,600 ambulance hours are set to be lost this month as a result of the delayed handovers.
Despite hospital staff's best efforts to reduce waiting times, they are continually being crippled by bed shortages and a lack of staff.
The situation is also said to be taking a significant toll on paramedics, who are calling the crisis "the worst pressure we've ever experienced".
GMB Union - a general trade union with over 600,00 UK members - has now urged the West Midlands Ambulance Service to declare a major incident over the 'catastrophic' crisis.
Stuart Richards, GMB Senior Organiser, has said that waiting times are a delayed consequence of "a decade of ruinous cuts".
"This is another sobering mid-pandemic example of the understaffing crisis in our NHS," he said.
"The pressure is unbearable after a decade of ruinous cuts.
"Significant delays are catastrophic for patients and staff working in the ambulance service.
"GMB members are left to support patients for hours on end, even scrabbling around trying to find food for patients while they wait in the cold outside hospitals.
"West Midlands Ambulance Service must declare a major incident so incident centres can be set up and specialist doctors brought in to prevent disaster."
A maximum rating of 25 means that every one of the service's risk categories is at the maximum.
In the report released by the West Midlands Ambulance Service board on Tuesday, October 26, the head of risk warned: "We believe that the consequence of prolonged handover delays is one of the biggest risks that our organisation (and therefore patients) faces."
The report goes on to state that the delays mean patients are not given the "optimum patient care or experience".
It adds: "Unfortunately, there have been several cases where severe patient harm has occurred due to the hospital delay resulting in several serious incidents.
"Although significant delays and harm to patients awaiting handover at hospital has, and continues to occur, there is perhaps a greater risk to patients in the community who cannot receive a timely and appropriate ambulance response, because of ambulances being held at hospital."
"Patients waiting for assistance are on the increase and it is not unusual to see over 200 incidents outstanding, many of which can be for several hours."
The board says that efforts are being made to divert '999' callers elsewhere if they don't requires emergency care.
Ambulances are also trying, where possible, to treat patients on the scene to avoid bringing them to hospital.
And the board has also recognised a significant impact on staff in its report.
"The impact on patients is distressing and unsafe but this also impacts our staff in various ways," it added.
"These situations are stressful and they are effectively undertaking a care assistant role, rather than utilising their actual Paramedic skills in the pre-hospital environment.
"They are encountering continued stress and frustration due to an inability to respond to other patients, and greater exposure to stressful and upsetting patient conditions, feeling helpless in some cases.
"Not only are frontline and patient facing staff affected, but (calls) staff are experiencing a relentless and unforeseen level of call demand.
"The hours lost during September, for example, equates to losing approximately 1,300 12-hour ambulance shifts over the month and subsequently, the ability of those crews to respond to patients waiting."
We have contacted the West Midlands Ambulance Service for comment, but they have yet to respond.
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