Edmund Hey

Pulse oximetry, severe retinopathy, and outcome at one year in babies of less than 28 weeks gestation

AIM To determine whether differing policies with regard to the control of oxygen saturation have any impact on the number of babies who develop retinopathy of prematurity and the number surviving with or without signs of cerebral palsy at one year. METHODS An examination of the case notes of all the 295 babies who survived infancy after delivery before 28 weeks gestation in the north of England in 1990–1994. RESULTS Babies given enough supplemental oxygen to maintain an oxygen saturation of 88–98%, as measured by pulse oximetry, for at least the first 8 weeks of life developed retinopathy of prematurity severe enough to be treated with cryotherapy four times as often as babies only given enough oxygen to maintain an oxygen saturation of 70–90% (27.2%v 6.2%). Surviving babies were also ventilated longer (31.4 v 13.9 days), more likely to be in oxygen at a postmenstrual age of 36 weeks (46%v 18 %), and more likely to have a weight below the third centile at discharge (45% v17%). There was no difference in the proportion who survived infancy (53% v 52%) or who later developed cerebral palsy (17% v 15%). The lowest incidence of retinopathy in the study was associated with a policy that made little use of arterial lines. CONCLUSIONS Attempts to keep oxygen saturation at a normal “physiological” level may do more harm than good in babies of less than 28 weeks gestation.

Outcome of very preterm birth: children reviewed with ease at 2 years differ from those followed up with difficulty

AIM To determine whether those most easily reviewed in a population prevalence study differ from those followed up only with difficulty. METHODS All babies born before 32 weeks of gestation in the North of England in 1983, 1990, and 1991 were traced, and all the survivors assessed at two years by one of two independent clinicians. RESULTS 818 of the 1138 live born babies survived to discharge. There was some non-significant, excess disability in the 5% of long term survivors who were difficult to trace because of social mobility, but eight times as much severe disability in the 1% (9/796) in care and in the 5% (38/796) whose parents initially failed to keep a series of home or hospital appointments for interview, and five times as much emergent disability in the 2.7% (22/818) who died after discharge but before their second birthday. Had the babies who were seen without difficulty been considered representative of all the babies surviving to discharge, the reported disability rate would have been two thirds what it really was (6.9% instead of 11.0%). CONCLUSIONS Population prevalence studies that ignore those who seem reluctant to cooperate risk serious ascertainment bias. Key messages Children seen for review without difficulty in any study of community prevalence are seldom representative of those who are not assessed Failure to review those who prove difficult to trace introduces less bias than failure to review those who prove difficult to review once traced Studies where it is not possible to see some children for assessment might usefully include a calculation of what the total prevalence would be if there was a fivefold difference in the proportion with the condition in question among the children who were not seen Parental support for any such study can nearly always be obtained if an effort is made to make the family feel, from the outset, that they are partners in a collaborative exercise of genuine worth

Presentation of obstructive left heart malformations in infancy.

This study documents the presentation of acutely life threatening congenital heart disease in infancy in order to assess the performance of screening examinations soon after birth and at 6 weeks of age. All cases of obstructive left heart malformations presenting in infancy in one health region from 1987-91 were analysed retrospectively. Altogether, 120 infants presented with either hypoplastic left heart syndrome, interruption of the aortic arch, coarctation of the aorta, or aortic valve stenosis. Twelve became symptomatic or died within 24 hours. Thirty four had an abnormal neonatal examination, eight of whom were referred. Six more became symptomatic before discharge. Ninety four babies went home, 51 developed heart failure before 6 weeks, and another seven died without diagnosis. Twenty five of 36 (69%) reaching 6 weeks without diagnosis had a second examination which was abnormal in 17. Two babies died undiagnosed after 6 weeks and the other 18 presented at up to 11 months of age. The neonatal and 6 week examinations perform poorly as screening tests for congenital heart disease. A normal neonatal examination does not exclude life threatening congenital heart disease.

Haemodynamic features at presentation in persistent pulmonary hypertension of the newborn and outcome.

Thirty four newborns presenting with persistent hypoxaemia in the first three days of life underwent detailed haemodynamic assessment using Doppler echocardiography, including measurements of pulmonary arterial pressure (PAP), left ventricular (LV) function, and left ventricular output (LVO). Results were compared with values from 51 healthy babies, and those of survivors were compared with non-survivors. Four of the 34 babies were excluded from this analysis because one was found to have transposed great arteries, one had a large left-to-right shunt with no evidence of persistent pulmonary hypertension, and two had diffuse skeletal myopathy. Tricuspid regurgitation was present in 70%, permitting systolic PAP estimation. The pulmonary:systemic arterial pressure ratio range was 0.7:1 to 1.83:1 (mean 1.02:1). A patent duct was present in 83%, and flow patterns indicated PAP approaching, or above, systemic pressure in all. Systolic time interval ratio TPV/RVET (time to peak velocity at the pulmonary valve/right ventricular ejection time) was mostly (65%) in the normal range, and did not correlate with other PAP measurements. LV function was below the 10th centile in only 11%, but values for LVO lay below the 10th centile in 41%, and for left ventricular stroke volume index (LSVI) in 66%. Results of 18 survivors were compared with 10 non-survivors (excluding two premature babies who died early with pulmonary interstitial emphysema). There were no significant differences for any parameter of PAP or LV function, but LVO and LSVI were significantly lower in non-survivors: LVO survivors (mean (SD)), 205 (57), non-survivors 138 (63) ml/kg/minute (P < 0.01); LSVI survivors, 1.29 (0.51), non-survivors 0.86 (0.31) ml/kg (P < 0.05). All four babies with LVO < 100 ml/kg/minute died, and 6/7 babies with LSVI < 1 ml/kg died. Detailed echocardiographic evaluation shows that the haemodynamic features of persistent pulmonary hypertension are diverse and that clinical diagnosis can be incorrect. Low LV output and stroke volume, usually with normal LV function, were the only Doppler echocardiographic parameters to predict subsequent death. This correlation with outcome requires further prospective evaluation.

Non-invasive assessment of pulmonary arterial pressure in healthy neonates.

Doppler echocardiograms were carried out on 51 healthy babies three times during the first 72 hours of life to estimate pulmonary arterial systolic pressure by measuring regurgitant tricuspid jet velocity and applying the Bernoulli equation. Tricuspid regurgitation was detected at some stage in all preterm babies and most of those born at full term. Pulmonary arterial pressure could be measured from peak regurgitant velocity in babies with pansystolic regurgitation. The incidence of pansystolic regurgitation among 34 term babies at 0-12, 13-36, and 32-72 hours of age was 22, 27, and 19%, and in 17 preterm babies (within the same age groups) was 53, 50, and 31%, respectively. Estimates of pulmonary artery pressure in the term babies were in accord with known catheter values. Pressure fell rapidly during the first day in all 51 babies. The ratio of pulmonary:systemic arterial pressure was comparable between the two groups throughout. Ductal flow patterns mirrored the fall in this ratio with age--bidirectional flow was associated with a ratio of between 0.88:1 and 1.22:1 and high velocity left to right flow with a ratio of between 0.49:1 and 0.66:1. Both these techniques are noninvasive ways of assessing neonatal pulmonary arterial pressure.

How effectively can clinical examination pick up congenital heart disease at birth

Aims: To assess what proportion of all cardiac abnormality can be suspected at birth when all clinical examination before discharge is undertaken by a small stable team of clinicians. Methods: A prospective audit of all the 14 572 births in a maternity unit only staffed by nurse practitioners between 1996 and 2003. Results: 1.2% of all babies born in the unit were found to have a structural defect (as confirmed by echocardiography) within a year of birth. The number not suspected before discharge declined over time, and only 6% were first suspected after discharge in the last four years of this eight year study. Four potentially life threatening conditions initially went unsuspected in 1996–8, but none after that. A policy of referring every term baby with a murmur at 1 day of age that was still present at 7–10 days resulted in 4.2% requiring cardiac referral; 54% of these babies still had a murmur when assessed one to two weeks later, and 33% had a structural defect. Parents said in independent, retrospectively conducted, interviews that they found it confidence building to have any possible heart defect identified early and the cause of any murmur clearly and authoritatively explained. Conclusions: Effective screening requires experience and a clear, structured, referral pathway, but can work much better than most previous reports suggest. Whether staff bring a medical or nursing background to the task may well be of less importance.

Creatinine and urea clearances compared to inulin clearance in preterm and mature babies

Simultaneous clearances of inulin, urea and creatinine were compared in 41 babies of 26-40 weeks gestation on 122 occasions during the first month of life. In each case creatinine was measured by a reaction rate method, and in thirty specimens it was also measured after adsorption onto resin. Urea clearance averaged only 62% of inulin clearance (P less than 0.001), and was a poor marker of glomerular filtration. Creatinine clearance measured by resin adsorption equalled inulin clearance, but the assay is manual and not suitable for routine clinical use. Creatinine clearance measured by reaction rate analysis underestimated inulin clearance by a quarter (P less than 0.01) because this automated method overestimated plasma creatinine by an average of 22 mumol/l. Urinary creatinine excretion was 72 +/- 17 nmol/kg per min (mean +/- S.D.) during the first week of life, and 66 +/- 13 nmol/kg per min in weeks two to four, and was not influenced by gestation or body size. Using these values, glomerular filtration rate, urine flow, and the urinary excretion rates of substances may be estimated from measurements made on plasma and untimed urines. Although these estimates are imprecise, with 9% confidence limits of 62-161%, they are useful in clinical practice because they avoid the need to make accurately timed collections of urine.

The PREM score: a graphical tool for predicting survival in very preterm births

Objective: To develop a tool for predicting survival to term in babies born more than 8 weeks early using only information available at or before birth. Design: 1456 non-malformed very preterm babies of 22–31 weeks’ gestation born in 2000–3 in the north of England and 3382 births of 23–31 weeks born in 2000–4 in Trent. Outcome: Survival to term, predicted from information available at birth, and at the onset of labour or delivery. Method: Development of a logistic regression model (the prematurity risk evaluation measure or PREM score) based on gestation, birth weight for gestation and base deficit from umbilical cord blood. Results: Gestation was by far the most powerful predictor of survival to term, and as few as 5 extra days can double the chance of survival. Weight for gestation also had a powerful but non-linear effect on survival, with weight between the median and 85th centile predicting the highest survival. Using this information survival can be predicted almost as accurately before birth as after, although base deficit further improves the prediction. A simple graph is described that shows how the two main variables gestation and weight for gestation interact to predict the chance of survival. Conclusion: The PREM score can be used to predict the chance of survival at or before birth almost as accurately as existing measures influenced by post-delivery condition, to balance risk at entry into a controlled trial and to adjust for differences in “case mix” when assessing the quality of perinatal care.

Gestational assessment assessed

AIMS To review the accuracy with which obstetric information on gestation is recorded in the neonatal records; and the reliability of the methods used for assessing gestational age after birth. METHODS Service information on all babies born in 1989, and research information on all babies of <32 weeks gestation born in the Northern Region in 1990–91, were reviewed to determine the accuracy with which antenatally collected information had been recorded in the neonatal records after birth. A prospective study was also mounted to assess how reliably paediatric staff could assess the gestational age of babies born to mothers with certain obstetric dates under service conditions. Paediatric residents looked at 347 babies of > 32 weeks gestation, and senior staff looked at 105 babies of < 30 weeks gestation. RESULTS The best techniques for estimating gestation immediately after birth were only half as accurate (95% CI ± 17 days) as estimates based on antenatal ultrasound at 15–19 weeks gestation. Assessments that relied on the tone, posture, and appearance of the baby at birth in those of < 32 weeks gestation were less reliable than assessments based on a retrospective review of when various reflex responses first appeared. They also tended to overestimate true gestation. Antenatal information of high quality was ignored, and arithmetic and transcription errors were introduced during the transfer of antenatal information into over 10% of postnatal records. CONCLUSIONS Current ultrasound techniques for “dating” pregnancy antenatally are better than any of the methods of postnatal assessment. Given the reliability of the antenatal information now available, it is regrettable that so many inaccuracies have been allowed to creep into the routine computation and recording of gestation at birth. Key messages The best techniques for estimating gestation immediately after birth are only half as accurate (95% CI ± 17 days) as estimates based on antenatal ultrasound Such estimates are even less accurate than this in babies of less than 30 weeks gestation Documenting when various reflexes appear can provide a better retrospective estimate of gestation in the preterm baby than methods based on posture, tone and physical appearance The transfer of obstetric information relating to gestation into the neonatal record is frequently faulty; such records were in error by > one week in 15% of preterm babies entered into one recent multi-centre research study, and 92% of the errors involved an under recording of gestation More care should be taken over collecting obstetric information relating to gestation at birth, given its potential value

Six years' experience of prophylactic oral vitamin K

AIMS The ability of oral vitamin K to eliminate all risk of vitamin K deficiency bleeding during the first three months of life was studied. METHODS Babies (n=182 000) in the north of England judged well enough to be offered milk within 12 hours of birth were given 1 mg of phytomenadione (vitamin K1) suspended in a medium chain triglyceride oil by mouth at delivery between 1993 and 1998. The parents of those who were breastfed were given a further three doses to give to the baby once every two weeks after discharge. RESULTS Four breastfed babies developed late vitamin K deficiency bleeding. In two, staff failed to follow policy guidelines, and in two there was undiagnosed α1 antitrypsin deficiency. Audit suggested that 93% of breastfed babies had all four doses, as advised. CONCLUSIONS An oral product that parents can administer themselves would be popular if licensed, but the total dose offered may need to be more than in this study if babies with undiagnosed liver disease are to be protected.