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Editor—I read the descriptive study of Tinet al 1 with considerable interest. In essence it challenges two sacred cows of neonatal intensive care, whether intra-arterial monitoring is necessary, and what is the appropriate PaO2 at which to nurse critically ill babies.
They do not give us accurate details of arterial catheter use. There is a hint that they are used for the first few days before resorting to SpO2 and capillary measurements. Nor do they tell us what analgesia is used for multiple capillary samples.
A fundamental principle of neonatal intensive care is minimal handling, and indwelling arterial catheters allow all samples to be taken with no or minimal disturbance, and if the catheters are umbilical, they can also be used safely for virtually all infusions including TPN. Furthermore, as opposed to oscillometric techniques, they allow accurate blood pressure recordings.
Surprisingly, the literature, and my own clinical experience is that the serious complications of UAC are much more common in term infants, and within 48–72 hours of insertion, so that 28/52 babies leaving UAC in situ for many days is unlikely to have a major impact on the putative complication rate of this procedure that induces anxiety in neonatologists.
Local analgesia for heel pricks is surprisingly ineffective even if applied for (impractically) long periods prior to puncture. If general analgesia with, say, morphine is being used the manipulation involved in capillary sampling is still likely to result in the changes in oxygenation (and thus intracerebral haemodynamics with potentially damaging sequelae), that were so graphically illustrated in many papers in the 1970s and 1980s when continuos PaO2 and tcPO2 monitoring became available.
To inflict frequent painful capillary sampling procedures on an unstable 25/52 800 G neonate in the first week of life where blood gas sampling may be necessary at least 2–3 hourly could at best be described as ill judged, at worst negligent.
As they rightly say, running babies at SpO2 levels of 70–90 (PaO2 approximately 25–45mmHg, 3.3–6 kPa) is an old idea, and I remember spirited arguments about it with the late great Sir Peter Tizzard during my training in the mid 1960s.
It is interesting, but not new, that if you keep babies cyanosed, ROP is rare. Many anecdotal papers from the late 1950s during the panic over oxygen therapy showed that rigid restriction of oxygen dramatically reduced ROP, but probably increased mortality.2 Although the validity of papers reporting on an association between oxygen restriction in the late 1950s and 1960s and mortality have been challenged, it remains an anxiety.
It remains in this study with an overall mortality of 52%. We do not know the proportion of babies off 23/24 weeks in the study, but it is likely to be relatively small. Contemporary studies reported by Lorenz from the USA3 give an overall mortality of 38% in babies of compatible gestation and year of birth, falling to 26% in those of 25, 26, and 27 weeks. The figures for Cambridge were virtually identical. Therefore, unless the Newcastle units are overloaded with 23/24 week babies the overall mortality rate with “physiological” oxygenation (has Blairite spin even penetrated neonatology?) is worryingly high.
Reporting their cerebral palsy rate is irrelevant. Improved neonatal care has in general (depressingly) little effect on cerebral palsy rates; what changes is the number of survivors and the numbers dying.
Importantly, cerebral palsy is only one part of the problem of surviving ELBW. Equally worrying is their under performance at school in childhood and adolescence. In the past, when children with cyanotic congenital heart disease were either inoperable or operated on only in early childhood, prolonged early hypoxaemia of the level used by Tinet al was associated with subsequent cognitive defects.4 The Newcastle group has a distinguished track record of long term follow up studies, and hopefully the babies in this study will be followed until adolescence. However, until such data show that babies kept at 3.3–6.0kPa for days and weeks during a vulnerable period for brain development do as well as those kept adequately oxygenated, I would regard the practice as described by Tin et al as of unproven benefit and possibly dangerous.
Finally, the marked restriction of oxygen therapy was, at best, experimental. Was a protocol for this study presented to the local research ethics committee? If not, why not?
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