Dr Ingo Hille was giving evidence on the second day of the hearing into the death of retired farmer Peter Saint, of The Bank, in Somersham, who died on June 28, 2016. Mr Saint underwent a routine knee operation at Hinchingbrooke Hospital on June 23, which had to be halted when complications arose and he went into cardiac arrest. It was later discovered that a breathing tube had been inserted into his oesophagus instead of his trachea. The 71-year-old suffered brain damage after he was deprived of oxygen for more than 20 minutes. Dr Hille told the inquest, at Huntingdon Town Hall, that he suffered extreme shock after Mr Saints death, and after completing his evidence, he turned to Mr Saints family and said: I offer my sincere condolences for this tragic death and I am deeply sorry. The inquest heard that Mr Saints Co2 oxygen levels became dangerously low during his surgery and a decision was made to change his anaesthetic mask. Mr Saint was described as obese and suffered from occasional reflux and it was suggested to Dr Hille, who has worked at Hinchingbrooke for 13 years, that he should have used a different mask from the outset. He told the coroner there was body of evidence to support his choice and he felt Mr Saint posed a low to moderate risk as he was otherwise fit and healthy. When the mask was removed, Mr Saint regurgitated a large amount of brown liquid. Dr Hille and his senior operating department practitioner, Alison Glass-Parker, noticed Mr Saints Co2 levels were low and Dr Hille made the decision to insert the breathing tube. Mrs Glass-Parker said this was a difficult procedure due to Mr Saints size. Dr Hille had already halted the surgery which was being carried out by consultant orthopaedic surgeon, Mr Mairwann El-Kaubaisy. Dr Hille remained convinced that the new mask had improved the oxygen levels, but it transpired he had misread the machinery and believed the O2 level was the Co2 reading. A read-out of the data later showed that Mr Saint had not received any oxygen from 3.48 pm to 4.25pm. During this time, Dr Hille said he believed he had seen the Co2 trace on the machine and was shocked to be shown the data. I mistook the O2 curve for the Co2 curve, he said. The levels began to rise and I thought thank God, but I accept now I was looking at the wrong curve. The situation was compounded when two other doctors arrived to help but did not realise the tube had been inserted incorrectly. The mistake was picked up by operating department technician Mick Collins who told Dr Hille several times he suspected the tube was wrongly placed. Mr Horstead asked Dr Hille: Why did it take someone else to point this out to you? Dr Hille replied: I cant logically answer that question. I was baffled. It was a crucial error. Mr Saint subsequently went into cardiac arrest and although attempts to revive him and replace the tube were successful he never recovered and died five days later. His brother Bruce told the inquest several of Mr Saints organs had been donated as well as some skin and his eyes. He told the inquest he was angry and saddened by his brothers death. We want to take steps to make sure this does not happen again, he said in his statement. The inquest heard the machinery used to measure oxygen levels has been updated as a result of the incident. The hearing continues.