A patient could have died when a bypass machine failed just six minutes into major heart surgery, sending doctors into a scramble to replace the ageing pump.

The patient was unharmed thanks to the quick actions of a technician, but the failure sparked a fast-track request to the Waikato District Health Board for $1.5 million to replace its heart lung bypass machines.

Waikato Hospital interim chief operating officer Dr Grant Howard said the the pump failed on December 8 when a patient was undergoing coronary artery bypass surgery.

"One of the arterial pumps failed at around six minutes after bypass had begun."

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Howard said a perfusionist, who manages the patient's physiological status during surgery, used a hand crank as a manual pump while doctors grabbed a nearby pump already primed in case of emergency.

"We were able to replace the pump with one from another heart lung machine and the procedure continued.

"We are fortunate that there was no harm caused to the patient."

The patient came through the surgery well, Howard said, and he and his family were informed and understanding.

Howard admitted the patient could have died but said it was highly unlikely because doctors were always prepared for such emergencies.

The pump was only serviced the week before and now cannot be repaired because it is so old. It had only failed once before, during a test.

The request for the $1.5m funding, rubber-stamped by the board this week, includes replacement of all three of the DHB's heart lung bypass machines and four arterial pumps.

The equipment is used in 650 cardiac procedures done at Waikato Hospital's cardiothoracic surgical department each year. It pumps oxygen into the blood and pushes lood around the body by acting as the heart and lungs during surgery.

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But the pumps are 20 years old and supplier Medtronic told the DHB it can no longer source replacement parts for them.

The bypass machines were made in 2001 and 2006 and all three were now at the end of their life, worrying doctors who have elevated the risk of the equipment to "major".

"Usual practice is that when two cardiac theatres run concurrently it is safe practice for a third machine to be available in the event of equipment failure, as occurred recently, or should an emergency case arise or if an earlier case needs to return to theatre," Howard said.

"However there is increasing risk of equipment failure due to the ageing of the [machines] and the increased workload."

There was also concern the unreliable equipment could hamstring the hospital's elective surgery lists, though that hadn't happened yet.

"We cannot undertake cardiac surgery procedures without putting patients on cardiopulmonary bypass," Howard said.

"The risk impacts on patient safety and the potential for Waikato DHB to continue to deliver cardiac services."

Howard told board members the DHB sought new equipment in September last year but decided to join New Zealand Health Partnerships in its national procurement activity that was scheduled to begin early this year.

However, after the Waikato failure, DHB staff including clinicians agreed to fast-track buying the equipment individually.

Howard said the request would go to a regional capital committee for approval next month and after that it's expected to take 12 weeks to get the new machines, which are more compact, lighter and easier to manoeuvre.