Early Human Development, 26 (1991) 69-12 Elsevier Scientific

Publishers

Ireland

69

Ltd.

EHD 01160

Inflating

pressures for effective preterm infants

Michael

F. Hird, Anne Greenough

resuscitation

and Harold

of

R. Gamsu.

Department of Child Health. King k College Hospital, London SE5 9RS (U.K.) (Received

20 July 1990; revision

received

23 November

1990; accepted

23 May 1991)

Summary The magnitude of inflating pressure necessary for effective resuscitation was examined in 70 preterm infants. The median pressure to cause adequate chest wall expansion was 22.8 cmHzO; no infant required a peak inflating pressure greater than 30 cmH,O. No further increase in inflation pressure was used during resuscitation and the median 5- and IO-min Apgar scores were 8 and 9, respectively. resuscitation;

preterm;

inflating

pressure;

Apgar

scores

Introduction Resuscitation by endotracheal intubation and mechanical ventilation is frequently required in preterm infants [3]. The inflating pressure recommended is one that will be sufficient to achieve adequate chest movement [2,5]. The magnitude of the peak pressure used, however, remains controversial: Lissauer and Harvey suggested a pressure rarely greater than 30 cmHzO [2], but Hoskyns et al. used 30 cmHzO as standard initial pressure [l]. The aim of this study was to assess the magnitude of inflating pressure which resulted in adequate chest wall expansion during resuscitation of preterm infants. Methods and Patients

Data was collected from all VLBW infants (birthweight Correspondence U.K.

to: Dr A. Greenough.

0378-3782/91/%3.50 Published

and Printed

0

Dept of Child Health.

1991 Elsevier Scientific in Ireland

Publishers

c

1500 g) born in a six

King’s College Hospital.

Ireland

Ltd.

London.

SE5 9RS.

70

month period and those with a birthweight between 1500 and 2000 g who were ventilated in the neonatal period. Resuscitation utilising endotracheal intubation and positive pressure ventilation was performed if standard criteria were fulfilled: failure to establish adequate respiration by 2 min or a heart rate falling below 100 with inadequate respiration prior to that time [4]. Infants were intubated with Coles’ shouldered endotracheal tubes which have a side-arm through which oxygen may be delivered. Inflation pressure is applied by occluding the end of the endotracheal tube with a linger. An initial pressure of 16 cmH*O was used regardless of the size of the baby. The paediatric staff were instructed to increase (by 2 cmHzO increments) the inflating pressure over serial inflations as necessary until observable chest wall expansion was achieved. This inflating pressure was then recorded from the pressure gauge on the resuscitation trolley (Vickers). After the initial inflation (length 2-3 s) the inflation pressures were applied at a frequency of 30/min with an inspiratory/expiratory ratio of 1:1. Resuscitation was continued until adequate regular respiration was established and the babies were then subsequently managed on usual clinical criteria. Infants failing to establish regular respiration by 20 min remained intubated and ventilated for transfer from the labour suite to the neonatal intensive care unit (NICU). The time to establish regular respiration and the 5- and IO-min Apgar scores were recorded. The accuracy of the pressure gauges on each of the four resuscitation trolleys used in the study was checked weekly against a water manometer from pressure between 10 and 32 cmHz0 using the standard gas flow of 6 l/min. The pressure gauges recorded a median of 101% of the applied pressure (range 95-l 15%). Patients Seventy infants, mean gestational age 28.8 weeks (range 24-36 weeks) and birthweight 1154 g (range 5161980 g), consecutively admitted to the neonatal intensive care unit were studied. This study was approved by the King’s College Hospital Ethics Committee. Statistical analysis To assess if differences were significant, the Wilcoxon Rank Sum Test was used and Spearman’s correlation coefficients were calculated to assess the relationship between the magnitude of inflating pressure used during resuscitation and the infant’s birthweight or gestational age. Results Fifty-nine of the 70 infants required intubation for resuscitation (median gestational age 28 weeks, range 23-36). The median inflating pressure used was 22.8 cmHz0 (range 14-30 cmH20). There was no correlation between the magnitude of inflating pressure and either the birthweight (r = -0.048) or the gestational age (r = -0.065) (Fig. 1). Fifteen infants made only irregular respiratory efforts by 20 min and were transferred ventilated to the NICU. These infants were of similar gestational age (median 28 weeks, range 23-32) to those who were extubated in the labour ward

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Fig. I. The relationship -0.06, not significant).

of peak inflating

pressure

used during

resuscitation

to gestational

age (r =

(median 28 weeks, range 24-36). The inflating pressure used was significantly higher in those infants who failed to establish regular respiration by 20 min (median 25 cmH*O, range 16-30) compared to a median of 22 cmHzO (range 1630) in those infants extubated in the labour suite (P < O.Ot). The latter 44 infants who were extubated in the labour suite established regular respiration by 3.7 min (range 0.5-l 5). The median 5- and IO-min Apgar scores of the 70 infants were 8 (range 4-10) and 9 (7-10) respectively. The I-min Apgar score was significantly lower in infants requiring intubation for resuscitation (median 5, range l-9) compared to a median of 9 (range 4-10) of the non-intubated infants (P < 0.01) and lower in the infants who failed to establish regular respiration by 20 min (median 3, range l-8) compared to the other intubated infants (median 5, range 2-10). Although the 5-min Apgar was not lower in the infants failing to establish adequate respiration by 20 min (median 8, range 4-9) compared to the other intubated infants (median 8, range S-lo), the IO-min Apgar score was significantly lower (median 9, range 6-9) compared to a median of 10 (range 7-10) P < 0.05. Discussion

In the present population of preterm infants, inflation pressures of 30 cmHzO or less always resulted in adequate chest wall expansion. We did not make pulmonary measurements but Hoskyns et al. have reported that only 33% of preterm infants achieved adequate tidal volume exchange after three inflations, yet all were effectively resuscitated [l], thus tidal volume exchange is not a useful indicator of effective resuscitation. Other ways to assess the effectiveness of resuscitation are to note the proportion of infants who were extubated and the time taken to establish regular re-

72

spiratory efforts. More than two-thirds of the present population were extubated in the labour ward and established regular respirations by a median of 3.7 min. The 15 infants who remained intubated had significantly lower Apgar scores at 1 min and required significantly higher peak inflation pressures during resuscitation, suggesting they had more severe respiratory disease and thus a continuing need of mechanical ventilation. We recorded the Apgar score which, although may not accurately reflect acidosis, can reflect clinical status [ 11.All infants included in the study had an Apgar score of 7 or greater by 10 min, suggesting use of a peak inflating pressure of 30 cmH,O or less was not associated with ineffective resuscitation. The magnitude of peak inflating pressure used during resuscitation was not related to either the gestational age or the birthweight. It was, however, significantly higher in those who remained intubated and in those with the lowest I-min Apgdr scores. This suggests that the peak inflating pressure is related to the severity of lung disease and reflects the compliance of the respiratory system. In the present population of preterm infants we did not find evidence that inflation pressures less than 30 cmH,O during resuscitation were ineffective. We did not, however, compare the relative effectiveness of high and low pressure inflations or their associated side-effects; such a definitive study is now required. Acknowledgements

Dr M. Hird (Research Fellow) is supported by Children Nationwide Medical Research Fund. We are grateful to the staff of the neonatal intensive care unit, without whose cooperation this study would not have been possible. We thank MS Sue Williams for secretarial assistance. References Hoskyns, E.W.. Milner, A.D., Boon. A.W., Vyas, H.. Hopkin and I.E. (1987): Endotracheal resuscitation of preterm infants at birth. Arch. Dis. Child., 62, 663-666. Lissauer, T. and Harvey, D. (1989): Low birthweight babies and their problems. In: Obstetrics. Editors: A. Turnbull and G. Chamberlain. Churchill Livingstone, London. MacDonald, H.M., Mulligan, J.C., Allen, A.C. and Taylor, P.M. (1980): Neonatal asphyxia I. Relationship of obstetric and neonatal complications to neonatal mortality in 38.405 consecutive deliveries. J. Pediatr., 96, 898-902. Milner,A.D.and Vyas, H. (1985): Resuscitation ofthe newborn. In: Neonatal and Paediatric Respiratory Medicine, pp. l-17. Editors: A.D. Milner and R.J. Martin. Butterworths. London Royal College of Obstetricians and Gynaecologists (1989): Resuscitation of the Newborn. Part 2 Advanced Resuscitation. Butterworths, pp. 12-13. 21.

Inflating pressures for effective resuscitation of preterm infants.

The magnitude of inflating pressure necessary for effective resuscitation was examined in 70 preterm infants. The median pressure to cause adequate ch...
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