The New Review of children's cardiac services at Bristol, commissioned by NHS England's medical director Professor Sir Bruce Keogh after an appeal from parents who lost a child at the unit, has published a further update parents are being kept in suspense about its methods or findings to date.

The latest update relates to what appear to be the later stages of the process, focusing on contact with the people who have been scrutinised during the investigation.

Warning letters to hospital staff

The review team has said that it will issue 'warning letters' to individuals who are due to be criticised in the review. These letters, formerly known as 'Salmon letters' (named after Lord Salmon, who held a public ethics review in the 1970s), allow the subjects of criticism by a review the opportunity to respond before the publication of a report. A recent example of Salmon letters being sent is the Chilcot Inquiry, the report of which is still awaited, where Tony Blair and Jack Straw were sent letters ahead of the report being published.

According to the Review update, there will be no 'significant or explicit' criticism of any individual who has not received a warning letter. It is unlikely that the contents of these letters, or the responses of the people due for criticism, will be made public. Although produced in the interests of fairness, these letters are always controversial – the fear is that a person facing criticism will inevitably resist the allegations and seek to change the minds of the inquiry panel – a process known as 'Maxwellisation' after the case involving Robert Maxwell in 1969.

However, the fact that the Salmon letters are being produced suggests, on the face of it, that this inquiry is the in-depth investigation that was promised.

It is hoped that the warning letter process will not delay the Review unduly – the Inquiry into the Mid Staffs scandal was, according to its Chair Sir Robert Francis QC, held up for six months while warning letters were responded to and challenged.

The 27 cases

The Review has commissioned experts to consider the cases of 27 children, producing reports into their treatment, and the Review will meet with those families whose children were considered after the final report has been published. The Review has offered counselling services to parents of children whose cases were reviewed.

What next for the Review?

The parents of children who died or were injured at Bristol still harbour anxieties about the Review. The apparent shortcomings at the cardiac unit, many of which have been revealed through Inquests and claims brought by individual families, appear to be systemic and long-standing, and the families are waiting apprehensively to see what is revealed about their children's treatment. Understandably, the Review panel has not divulged much information about its findings so far.

What is known is that there are a number of unresolved issues at Bristol that would seem to be relevant to the Review. One is that the Trust committed internally, in the investigation into the death of Luke Jenkins in April 2012, to conduct a review of the preceding 50 deaths of cardiac children at the unit, and the outcome of this review will be of significant interest. It is also known that the Care Quality Commission, following its inspection of the unit in late 2012, noted that there had been 10 internal expressions of concern in seven months leading up to it visit to the unit.

Bristol's history has, at times, been troubled, since the scandal of the1990s in which dozens of children were harmed. What all the families affected by the New Review want to see is that Bristol is being maintained as a safe unit. Those who have endured tragedies, in particular, want to see that the lessons of the past have been learned and that, if their children were harmed by inappropriate care, that these errors will also act as lessons and will never be repeated. It is not yet known what implications this New Review will have for the national child heart surgery reconfiguration programme, on which NHS England has recently made recommendations.