J. Pool

Plasma catecholamine levels in preterm infants. Effect of birth asphyxia and Apgar score.

ABSTRACT. Catecholamine levels were measured in cord arterial blood from preterm infants. Relatively lower catecholamine levels were found in the preterm infants than in term infants, although no significant correlation was found between noradrenaline and adrenaline levels and either gestational age or birthweight. Significantly higher catecholamine levels were found after labour. Preterm females had significantly higher catecholamine levels than boys after asphyxia and tended also to have higher catecholamine levels without asphyxia, although not significant. Catecholamine levels were also significantly elevated in those infants with a low Apgar score (<7 at 5 min) and those who were acidotic (cord arterial pH <7.25). A good correlation was found between a low Apgar score and the presence of acidosis.

Fighting the ventilator — are fast rates an effective alternative to paralysis?

We investigated the effect of increased ventilator rates on the respiratory activity of 17 infants, all actively expiring against the ventilator at conventional rates. Fast rate ventilation was rarely associated with apnoea (3 babies only) and the infants respiratory efforts even at rates of 120/min had an important effect on tidal exchange. Seven infants altered their respiratory response to breathe in synchrony with the ventilator at 60 breaths/min and 5 maintained this at 120 breaths/min. Nine of the 17 infants continued to actively expire against positive pressure inflation at 60 breaths/min and in two this persisted at 120/min, the remaining 7 infants showed incoordinated breathing at that rate. We conclude that fast rate ventilation appears to have only limited success in suppressing respiratory activity in infants actively expiring against the ventilator.

Comparison of Different Rates of Artificial Ventilation in Preterm Neonates with Respiratory Distress Syndrome

The effectiveness of three different ventilator rates of artificial ventilation (30, 60 and 120/min) was studied in 32 preterm infants, all of whom were suffering from the Respiratory Distress Syndrome (16 were paralysed). Ventilator pressures, I: E ratio and MAP were kept constant at each rate. Increase in rate from 30 to 60 and to 120/min was well tolerated and not associated with episodes of hypotension. The only significant improvement in oxygenation was amongst the non‐paralysed infants and at a rate of 120/min (p<0.01) this was associated with synchronous respiration. Two different ventilators were used in the study and a significant change in Paco2, (reduction) occurred only in non‐paralysed infants ventilated at a rate of 120/min by Sechrist ventilators (p<0.05). This difference may be a direct reflection of differences in ventilator performance at fast rates.

The therapeutic actions of theophylline in preterm ventilated infants

40 preterm, ventilated infants (gestational ages 24-33 weeks) were entered into a double-blind randomised trial to assess the effect of oral theophylline on lung function and ventilator dependence. Theophylline administration was associated with a significant improvement in compliance (P less than 0.05) and hastened weaning from ventilation (P less than 0.01).

Ethnic variation in respiratory function in young children

The effect of ethnic origin on respiratory function was assessed in 57 young children aged between 4.9 and 8 years. Functional residual capacity (FRC) and peak expiratory flow rate (PEFR) were measured and related to sitting and standing height in Caucasian and Afro-Caribbean children. No significant differences were found between the two groups in PEFR when related to either standing or sitting height. FRC, when related to standing but not sitting height, was greater in Caucasian children (P less than 0.01). Sitting height related to standing height was lower in children of Afro-Caribbean descent (P less than 0.01), suggesting that anthromorphic differences may explain the apparent influence of ethnic origin on respiratory function in young children.

Abnormalities of Functional Residual Capacity in Symptomatic and Asymptomatic Young Asthmatics

ABSTRACT. Functional residual capacity (FRC) was measured by helium gas dilution in 186 young asthmatics, aged between 2 and 9 years. The majority were hyperinflated, as evidenced by an increase in FRC, regardless of symptom status. Symptomatic children and those hospitalized with an acute asthma attack (15) had significantly elevated FRC when compared to asymptomatic children (p<0.01). Eight symptomatic children, following treatment modification, became asymptomatic. This was associated with a reduction in FRC. We suggest that an FRC result greater than one standard deviation from the mean of asymptomatic asthmatics could be used to predict inadequacy of treatment.

Persistent lung hyperinflation in apparently asymptomatic asthmatic children

Serial measurements of functional residual capacity (FRC) by helium gas dilution were made in young asthmatic children over a 3 month period. Eight children were recruited during hospitalization for an acute asthma attack and eleven during routine outpatient attendances. Both groups of children had FRCs greater than 120% of that predicted for height at recruitment. Although the children denied symptoms throughout the three month follow-up period the majority remained hyperinflated. These results demonstrate a striking difference between objective and subjective assessment of respiratory function in young children. The significance of this persistent abnormality and its relationship to other lung function indices needs urgent investigation.

A 2-year longitudinal study of lung hyperinflation in young asthmatics

Functional residual capacity (FRC) was measured at 6-monthly intervals for at least 2 years in 42 young asthmatic children. Over the 2-year period FRC decreased in the 42 children from a median of 136% to 117% of that predicted for height (P less than 0.05). These changes in FRC were associated with a reduction in the number of children receiving no regular treatment (ten at recruitment, 0 at 2 years), P less than 0.05, and an increase in the number of children receiving inhaled steroids (ten at recruitment and 29 at 2 years), P less than 0.01. Twenty-five children were hyperinflated at recruitment (FRC greater than 120% of that predicted for height) with median FRC 152% compared to only 16 children at 2 years median FRC 117%, P less than 0.01. We conclude that FRC decreases as asthmatic children get older but some children, worryingly and despite increased use of prophylactic therapy, remain chronically overdistended which may put them at serious risk of chronic obstructive airways disease in later life.

ARE FAST RATES AN EFFECTIVE ALTERNATIVE TO PARALYSIS

We have previously demonstrated that infants who actively expire against positive pressure inflation at “conventional” ventilator rates develop pneumothoraces and amongst such infants pancuronium significantly reduces the incidence of air leaks (1) However pancuronium is not without side-effects, therefore this study investigated if fast rates could, as effectively, suppress spontaneous respiration and so possibly prevent pneumothoraces. 17 infants were demonstrated as actively expiring at ventilator rates of 30-40/minute by recording oesphageal pressure, tidal flow and volume simultaneously with ventilator pressure changes. The respiratory response of these infants to ventilator rates of 60 and 120/minute was then studied for 20 minute periods. The results are shown in the table.The 9 infants who remained actively expiring or had incoordinated respiration at fast rates were subsequently paralysed,only one developed a pneumothorax during ventilation.The 8 infants who breathed in synchrony or were apnoeic at fast rates were not paralysed and remained on increased rates, 4 later developed air leaks.We conclude that fast rate ventilation appears to have only limited success(18%)in suppressing respiratory activity in infants actively expiring against the ventilator. (1) Greenough et al Lancet 1984,i,1-4

PREVENTION OF HYPOXIA AND CETECHOLAMINE SURGE ASSOCIATED WITH INITIATION OF PARALYSIS BY PANCURONIUM IN PRETERM VENTILATED INFANTS

Although selective paralysis significantly reduces the incidence of pneumothoraces, initiation of paralysis with pancuronium has been associated with transient hypoxia and catecholamine surge, both of which could hazardously affect cerebral blood flow. This study investigated the effectiveness of increasing ventilator settings 1 immediately prior to paralysis to try and prevent transient hypoxia and consequent rise in catecholamine levels resulting from hypo- ventilation (associated with the first dose of pancuronium). 18 infants GA 30 wks (range 26-34), <48 hrs old and ventilated for RDS were entered into the study. Peak inspiratory pressure (PIP) was increased from mean 23 cms H2O (range 14-40) to 27 cms H2O (range 20-43) immediately before paralysis. Comparison of arterial blood gases immediately before and 20 mins after paralysis did not detect a change in PH or PCO2. In all infants arterial oxygenation rose post-paralysis but not significantly. Adrenaline was detected in 8 infants only with no consistent changes following pancuronium. The mean pre-paralysis noradrenaline level was 21.5nmol/l (range 3.3-78.9). Levels were significantly reduced post-paralysis 10.2nmol/l (range 1.7-29.9)p<0.05. These results suggest increasing PIP immediately prior to paralysis can effectively prevent the initial and transient disturbance of oxygenation and catecholamine surge previously associated with this otherwise beneficial treatment.