An investigation into a number of patient deaths at West Herts hospitals has highlighted failings in the way they were assessed.

A report said the patients died after suffering blockages in arteries to their lungs and related the incidents to risk assessments not being completed correctly or followed up.

West Hertfordshire Hospitals NHS Trust has opened a serious incident investigation for 17 patients after failures were identified with examinations given to them to judge their susceptibility for blood clots (venous thromboembolism examination or VTE).

Concerns were initially raised in March by a nurse specialist after patients suffered pulmonary embolism, a clot in the artery to the lung, and deep vein thrombosis, a clot in one of the deep veins of the body, while still in hospital or during the 90 observation period after discharge.

In a report to the trust's board, Mel Withero, serious incidents investigations lead, said: "This prompted a thematic review Serious Incident to be declared for 17 patients who had suffered a pulmonary embolism, in some cases this event was fatal.

"The incidents relate to generally either: a) A failure to complete the VTE risk assessment correctly or completely or b) A failure to implement the outcomes of the risk assessment."

The serious incident report also noted two patients affected by VTE issues in January this year.

Dr Mike van der Watt, the trust's medical director, said: "When patients are admitted to hospital, and relatively immobile, it is important that a proper assessment is done to determine if they are at risk of developing a blood clot, otherwise known as a deep vein thrombosis (DVT).

"The safety of our patients is our top priority and we have consistently performed above the national target (95 per cent) for carrying out these assessments.

"However, through our routine auditing process we have picked up that a small number of patients who had developed DVTs either in hospital, or within 90 days of discharge, may not have been given the assessment and appropriate treatment.

"It is appropriate for us to launch an investigation to find out if this is the case, in order to reassure ourselves that the proper processes are being followed.

"The investigation is due to report back by June 15, when we will be in a position to know what action, if any, we need to take."