Patients at a major Auckland hospital were so obese they couldn't fit inside MRI machines.

Anaesthetists are also struggling to guide needles through layers of body fat, ultrasounds can be clouded by excess weight, and staff risk injury trying to move patients, with up to six people sometimes needed.

A report by Middlemore Hospital's radiology department has detailed the effects of obesity rates.

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About 36,000 people living in Counties Manukau are morbidly obese, nearly twice the number of any other DHB. Dr Stuart Barnard, clinical director of radiology at the hospital, has reported on how that's changing his team's work.

Radiology includes x-rays, ultrasound, CT and MRI scans - used to diagnose conditions from stroke to cancer, check trauma injuries and guide other procedures.

Some patients had exceeded table weight limits, or couldn't fit into MRI machines, Barnard wrote in the report: "Occasionally, such patients simply cannot be scanned".

New MRI scanners were bought last year, one of which can take up to 220kg and has an internal diameter of 70cm. A DHB spokeswoman said that let all patients be scanned. Before that, about two to three patients couldn't fit the machine, over a six-month period.

Barnard's report noted how obesity had increased the numbers of patients deemed unsuitable for surgery or a general anaesthetic, and therefore need image-guided procedures like biopsy.

"If the patient is obese it can be very difficult to identify the target and the needle. This leads to longer procedures and a greater risk of complications such as bleeding or damage to adjacent structures."

Scans like ultrasounds rely on the detection of energy, and too much fat makes it hard or impossible to get a clear image. Quality also suffers when patients touch the sides of CT and MRI scanners.

Up to six staff can be needed to move a patient from bed to an examination table, and the weight of patients means injuries can be sustained.

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"Ultrasonographers are at risk of wrist and shoulder injuries and this is increased when scanning obese patients as sound waves are absorbed and scattered by fat," Barnard wrote.

"Sonographers will often push hard with their probes in the struggle to get diagnostic images."

Bigger patients have more problems like osteoarthritis, liver problems, injuries to tendons and ligaments and respiratory issues including sleep apnoea and hypertension. Obesity increases the risks of many cancers, heart and kidney disease and strokes.

About 36,000 people living in Counties Manukau are morbidly obese. Photo / 123RF
About 36,000 people living in Counties Manukau are morbidly obese. Photo / 123RF

This has greatly increased radiology workload to about 230,000 procedures a year.

Radiology nurses use ultrasound to help ward staff find patients' veins, Barnard reported, and "we are occasionally asked to do lumbar punctures ("spinal taps") in patients who are so obese that the medical and anaesthetic teams do not have needles long enough to reach the spine".

A lumbar puncture involves a needle being inserted between vertebrae to get a sample of fluid, which can be used to diagnose serious infection, cancers or nervous system disorders. They're also sometimes used to inject anaesthetics or chemotherapy drugs.

Asked about the needle length comment, a DHB spokeswoman said the main reason lumbar punctures were done under x-ray imaging was to help the specialist find the correct place to insert the needle.

Counties Manukau DHB chief executive Margie Apa has told her board she will put obesity on the agenda for a meeting with Ministry of Health officials, in order to "keep the issues clearly front and centre".

Other departments are feeling the strain. Obesity and diabetes have led to a surge in the number of pregnancies needing more monitoring and care, for example. Sixty per cent of joint replacement patients are overweight, and the DHB has just signed-off $1.4m to expand dialysis wards.

Associate Health Minister Peeni Henare talks about the diabetes problem in New Zealand. Video / Jason Oxenham

The DHB wants action from central government.

"We would love to see a stronger position on healthy food and drinks in schools for example, as well as on the advertising of fast food and drinks that target children," said Dr Gary Jackson, the DHB's director of population and health.

"Better child-targeted food and a sugar levy on manufacturers to encourage them to do more to counter the risk in obesity would certainly assist in addressing the issue."

Nationally, obesity rates have trebled since the 1970s. Almost one in three adults are obese, and a further third overweight.

Wellington region DHBs have previously written to the Health Minister urging a tax on sugary drinks and warning that "for the first time in history, NZ children could live shorter lives than their parents as a result of excess weight and obesity".

Associate Health Minister Peeni Henare last month said he believes measures like warnings on packaging and a sugar tax should be considered.

In response, the NZ Food & Grocery Council said taxes to artificially raise the price of energy-dense foods hadn't worked anywhere in the world, and its members were already making thousands of products healthier.

Health Minister David Clark has said he wants to work with the food industry itself in the first instance, to reduce sugar levels in processed food and drink. A new food labelling system is close to being announced.