"In my view, Registered Nurse A's failures in this case were individual clinical errors and cannot be attributed to the system within which she was working," he said.
The nurse, who had graduated less than a year before the incident, is now in a new job.
She has written a letter apologising to the man's family and told the commissioner: "My conscience reminds me of my huge error regularly, which saddens me and emotionally takes me to a place of remorse and wishing I could change that whole day."
She said that in her new job she had "completed additional training and worked with another registered nurse to implement an electronic medication system that ensures that medication is delivered in a safe and timely manner".
However Hill has also recommended that the Nursing Council consider undertaking a competence review of the nurse.
His report said the man was aged 73, had a history of heart problems, and had been taking a daily dose of 47.5mg (two tablets) of metoprolol, which reduces blood pressure.
He was admitted to hospital with shortness of breath, leg swelling, diarrhoea and vomiting. His blood pressure was 112/79mmHg, below the normal range of over 120/80mm/Hg.
On his second day in hospital, a doctor found that he had symptoms of heart failure, which was confirmed in an ultrasound scan on the third day. By then his blood pressure had dropped to 85/54.
He was given another medication which raised his blood pressure to 100/70 by the fourth day and his heart rhythm returned to normal. On the fifth day a doctor restarted his daily metoprolol, but at a low rate of 11.875mg (half a tablet).
On the seventh day the man came into the care of Registered Nurse A. She said she looked at his medication instructions at 9am that day.
"I looked at the dose (11.875mg) and questioned to myself whether it was the correct dose," she said.
"I had given metoprolol a number of times before, but never in a dose that small. I had previously given 118.75mg doses on several occasions."
She believed the doctor might have placed the decimal point in the wrong place and said: "I had intended to leave the medication room and contact the house officer about the dose, however prior to my leaving I was distracted by another nurse talking to me and so forgot about the need to check the dose with the house officer."
She realised something was wrong at 12pm when she took the man's blood pressure again and found it had dropped to 80/52.
The hospital procedures indicated that this was a high-level "Early Warning Score" which should have been reported to the ward nurse so that the patient could be reviewed by a doctor within 30 minutes.
However the nurse did not tell her ward co-ordinator. She told the commissioner she had approached the co-ordinator with questions before and "on some occasions I felt unsupported in my conversations and at times was made to feel bewildered, embarrassed, alone and confused".
Instead, she rang the house officer (doctor), who told her to give the man oral fluids, check his blood pressure again in 30 minutes, and then contact another doctor who was working in the ward if necessary.
She then contacted the second doctor and told her of the man's low blood pressure, but the doctor said the nurse did not mention the Early Warning Score. The doctor said she told the nurse to keep the man under close observation and to contact her again if he deteriorated.
At 2pm the man rang his call bell because he was having trouble breathing. The nurse called another doctor, who found that the man's blood pressure had dropped further to 70/58, and the nurse's medication error was discovered.
At 3.30pm two doctors told the man's wife and son about his heart failure and the medication error, and "explained that he may not pull through this".
The man was transferred to the critical care unit at 4pm and was given medication to increase his blood pressure, but he died at 11.55pm.
The man's daughter told the commissioner that the family found out only moments before his death that his file had been marked on the day he entered hospital, "Do not resuscitate."
The doctor who wrote that instruction did not record any conversation with the man or his family about it. The commissioner criticised this and said the doctor should have recorded his reasons for the instruction and his discussions with the patient about it.
