Biomedical subjects

M F Hird

Publications and source records attributed to M F Hird.

17 recordsLinked to original sources

PubMed1992

Low cerebrospinal fluid concentration of free gamma-aminobutyric acid in startle disease.

The pathophysiology of startle disease (hyperekplexia) is unknown. Hyperactivity of the brainstem reticular formation has been suggested as a cause. We report a newborn infant with classic features of startle disease in whom cerebrospinal fluid (CSF) concentrations of gamma-aminobutyric acid (GABA) were substantially lower than normal during the first weeks of life. She improved greatly on clonazepam treatment. We suggest that the signs of this disorder may be due to a genetic defect or to delayed maturation resulting in low CSF GABA.

Clonazepam↗

PubMed1992

Nosocomial bacterial infections in very low birth weight infants.

The occurrence of congenital and nosocomial bacterial septicaemia has been documented by identifying the number of positive blood cultures by reviewing the laboratory and clinical records of 394 very low birth weight infants who were consecutively admitted to a neonatal intensive care unit over a 40-month period. The incidence of congenital septicaemia was 6% and of nosocomial septicaemia 17%. The commonest causes of congenital infection were Streptococcus agalactiae Staphylococcus epidermidis and Enterococcus faecalis (each in 18% of cases). The commonest cause of nosocomial infection was S. epidermidis (51% of cases), except in infants of birth weight less than 750 g. Risk factors for nosocomial infection were extremely low birth weight, very preterm birth and prolonged ventilation. Nosocomial infection was associated with significantly lengthened hospital admission.

Cross Infection↗

PubMed1992

Positive end expiratory pressure in acute and chronic respiratory distress.

The optimum level of positive end expiratory pressure (PEEP) was determined in 16 infants with respiratory distress syndrome (median gestational age 29 weeks, median postnatal age 1 day) and in 16 infants with chronic respiratory distress (median gestational age 25 weeks, median postnatal age 15 days). All infants were studied at a PEEP sequence of 3, 0, 3, 6, and 3 cm H2O, all other ventilator parameters being kept constant. Each PEEP level was maintained for 20 minutes and at the end of each period arterial blood gas was checked. During acute respiratory distress syndrome there were no significant changes in oxygenation but arterial carbon dioxide tension (PaCO2) significantly decreased from a mean of 4.93 kPa at 3 cm H2O to 4.40 kPa at 0 cm H2O and increased to a mean of 5.87 kPa at 6 cm H2O. In the infants with chronic respiratory distress, oxygenation fell from a mean of 8.66 kPa at 3 cm H2O to 6.40 kPa at 0 cm H2O and improved at 6 cm H2O to a mean of 10.50 kPa. There were no significant changes in PaCO2. We conclude that addition of PEEP, up to 6 cm H2O, may be useful even after the first week of life. High levels of PEEP, however, have previously been reported, in certain infants, to result in circulatory disturbance. It is therefore important to assess the use of 6 cm H2O PEEP in a controlled study of longer term clinical outcome.

Acute Disease↗

PubMed1992

Influence of increasing postnatal age on respiratory timing and reflex activity in preterm ventilated infants.

The influence of postnatal age on spontaneous respiratory time, measured both on and off continuous positive airways pressure (CPAP), and the occurrence of the Hering Breuer reflex has been investigated. Consecutive ventilated infants were recruited and only studied when making respiratory efforts during mechanical ventilation. Fifty-three infants were studied on 119 occasions, their median gestational age was 29 weeks and birthweight 1142 gms. All the infants were initially ventilated for the respiratory distress syndrome. Inspiratory and expiratory times were measured from simultaneous flow and oesophageal pressure recordings during a 20-second period of disconnection and during a similar period on 3 cmH2O CPAP. Prolongation of the inspiratory and expiratory time on CPAP compared to that measured during disconnection of more than 10% was evidence of the Hering Breuer reflex. No significant change in the inspiratory or expiratory time either on or off CPAP was noted either between days 1 to 5 or weeks 1 to 4. Both inspiratory and expiratory time tended to be longer on CPAP than during disconnection and these differences reached significance on days 1 and 2 and weeks 1 and 2. No influence of postnatal age was demonstrated on the proportion of infants in whom the Hering Breuer reflex was demonstrated. Our results suggest that, during the neonatal period, there is no influence of postnatal age on respiratory timings or reflex activity amongst ventilated infants who make spontaneous respiratory efforts during ventilation. These results have important implications regarding the optimum rate at which such infants should be ventilated.

Aging↗

PubMed1991

Importance of using lung function regression equations appropriate for ethnic origin.

Functional residual capacity (FRC) can be assessed reliably in young children using a helium gas dilution technique. The aim of the present study was to determine if differences in lung volume are found in asthmatic children of different ethnic origins. Eighty-eight children were studied, 53 of Caucasian origin and 35 of Afro-Caribbean origin. Their median age was 6.1 years (range, 5.3-9.0 years). FRC measured by helium gas dilution is reported as a percentage of predicted for height, using a published regression equation as well as regression equations appropriate for the ethnic origin of the child. In the majority of both groups FRC was elevated above the ethnically appropriate regression equation for healthy children. The Caucasian children apparently had higher FRCs than the Afro-Caribbean children if comparing the absolute lung volume, and if lung volume was expressed as percent of predicted for height, by a regression equation uncorrected for ethnic origin (P less than 0.02). This difference disappeared when ethnically appropriate regression equations were used. We conclude that lung volumes are similar in asthmatic children of different ethnic origin and that it is important to use ethnically appropriate regression equations.

Asthma↗

PubMed1991

Hyperinflation in children with liver disease due to alpha-1-antitrypsin deficiency.

Fifty-nine patients (median age 6.0 years) with liver disease and ten healthy children without liver disease (median age 7.5 years) had serial measurements of functional residual capacity (FRC) over a period of at least 6 months. Twenty-eight children with alpha-1-antitrypsin deficiency (A1ATD) tended to have higher lung volumes than 26 with extrahepatic biliary atresia (EHBA). Fifteen children had persistent hyperinflation (FRC greater than 120% predicted for height; 2 SD above the mean of controls); in five children (four with A1ATD) this was unresponsive to bronchodilator therapy. Two of the children with A1ATD who had persistent unresponsive hyperinflation on three serial measurements were only 3 and 4 years of age. No healthy child without liver disease was hyperinflated. These results suggest that A1ATD may be associated with lung function abnormalities even in very young children.

Biliary Atresia↗

PubMed1991

Patient triggered ventilation in chronically ventilator-dependent infants.

Patient triggered ventilation (PTV) has been assessed as a method of respiratory support in infants remaining ventilator-dependent beyond the 1st week of life. Sixteen preterm infants were studied who had a median gestational age of 26 weeks and postnatal age of 22 days. PTV was delivered using a ventilator incorporating an airway pressure trigger. PTV was only successfully maintained until extubation in 3 infants, failing to provide a satisfactory method of respiratory support in the remaining 13 infants after a median of 1 h (range 1-10). One of the 13 infants was persistently asynchronous at 1 h despite manipulation of inflation time. The other 12 infants, at failure of PTV, were making respiratory efforts which were inadequate to consistently trigger the ventilator. Infants in whom PTV was successful were older, more mature and of greater birth weight; the trigger delay at 1 h was significantly shorter in this group (P less than 0.05). A predictor of failure of PTV was asynchrony in the 1st h after commencing PTV (P less than 0.02). We conclude PTV incorporating an airway pressure trigger infrequently provides a useful method of respiratory support in infants who are chronically ventilator-dependent.

Humans↗

PubMed1991

Home oxygen therapy following neonatal intensive care.

In a 12-month period 28 of 164 consecutive very low birthweight (VLBW) infants receiving intensive care within 48 h of birth at King's College Hospital developed chronic lung disease, (oxygen dependence beyond 28 days of age). Fifteen of the 28 infants were eligible for home oxygen therapy, but this was only practical, because of home circumstances, in 8 infants (4.9%). These 8 infants received home oxygen therapy. One further infant, born at term and suffering from pulmonary hypoplasia was also discharged home on oxygen therapy. Two infants subsequently required readmission due to a deterioration in their respiratory status and died. Three others required re-admissions (total duration 32 days) for respiratory problems. The median duration of home oxygen therapy was 17 weeks (range 4-486 days). We conclude that home oxygen therapy is needed by only a very small number of preterm infants and is appropriate for only a proportion of them. Parents need to be counselled carefully regarding the possibility that the need for oxygen might be protracted.

Home Nursing↗

PubMed1991

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 chest wall expansion was 22.8 cmH2O; no infant required a peak inflating pressure greater than 30 cmH2O. No further increase in inflation pressure was used during resuscitation and the median 5- and 10-min Apgar scores were 8 and 9, respectively.

Humans↗

PubMed1991

Comparison of different rates of artificial ventilation for preterm infants ventilated beyond the first week of life.

The effect on blood gases of different ventilator rates in preterm infants ventilated beyond the first week of life was assessed. Seventeen infants, median gestational age 25 weeks, were studied at median postnatal age of 11 days. The infants were ventilated through a set sequence of rates: 30, 60, 30, 100 and 30 breaths per min (bpm), each rate being maintained for 20 min. Peak and positive end expiratory pressure and I:E ratio (1:1) were unchanged at each rate and mean airway pressure was kept constant by altering flow as necessary. No significant change in oxygenation was demonstrated at either rates of 60 or 100 bpm compared to 30 bpm. PaCO2 levels were, however, significantly reduced at 60 bpm (P less than 0.001) compared to 30 bpm; but this improvement in PaCO2 was not seen at 100 bpm. These results suggest that increasing ventilator rate higher than 60 bpm in the majority of infants ventilated after the first week of life is not advantageous.

Bronchopulmonary Dysplasia↗

PubMed1991

Spontaneous respiratory effort during mechanical ventilation in infants with and without acute respiratory distress.

Respiratory interactions of 27 ventilated preterm infants were recorded daily during the first 14 days of life to assess the effect on respiratory efforts of recovery from acute respiratory distress syndrome (RDS). Active expiration and persistent asynchrony only occurred during acute RDS (P less than 0.01). Throughout the 14-day period, in the majority of infants making respiratory efforts, a ventilator rate could be found from a standard sequence 30, 60, 90, 120 breaths/min which provoked a synchronous interaction, but with increasing postnatal age apnoea became more common (P less than 0.01). We conclude that the preterm infants' spontaneous respiratory efforts are a less important influence on the outcome of mechanical ventilation following recovery from acute RDS.

Humans↗

PubMed1991

Patient triggered ventilation using a flow triggered system.

The role of patient triggered ventilation (PTV) for the newborn was assessed using a new patient triggered ventilator, the Draeger Bablylog 8000, which incorporates significant improvements in both ventilator performance and the triggering system. Thirty three infants, median gestational age 30 weeks and postnatal age 2.5 days, were entered into the study to compare blood gases obtained during conventional and patient triggered ventilation. Oxygenation did not improve with PTV in the group overall but increased significantly (median change 7%) in infants greater than 28 weeks' gestation. Arterial carbon dioxide tension (PaCO2) decreased during PTV in the majority of infants (median reduction 7%), this was not related to the gestational or postnatal age, but was greatest in infants previously on a low conventional ventilation rate. Blood gases (both PaO2 and PaCO2) deteriorated in infants requiring the highest inspired oxygen concentration. We conclude that patient triggered ventilation is most useful in infants with mild respiratory distress.

Carbon Dioxide↗

PubMed1991

Comparison of triggering systems for neonatal patient triggered ventilation.

The efficacy of two triggering systems was compared during neonatal patient triggered ventilation: the Graseby MR10 respiration monitor and airway pressure changes. Ten preterm infants were studied, median gestational age 33 weeks (range 28-35). Patient triggered ventilation was administered via the SLE ventilator at a series of inflation times (0.24, 0.3, and 0.4 seconds). Comparison was made between the trigger systems of the trigger delay, inflation volume delivered, and proportion of spontaneous respiratory efforts detected. The airway pressure trigger gave a superior performance: at the two lower inflation times the trigger delay was shorter and inflation volume delivered greater. At the longest inflation time a greater proportion of respiratory efforts were detected. We conclude the airway pressure trigger should be used in preference to the respiration monitor as the triggering system of choice for neonatal patient triggered ventilation.

Humans↗

PubMed1991

Randomised trial of patient triggered ventilation versus high frequency positive pressure ventilation in acute respiratory distress.

Synchronous respiration during mechanical ventilation of preterm neonates with acute respiratory distress is extremely beneficial as it improves oxygenation and is associated with a very low incidence of pneumothorax. We have assessed which form of ventilation: patient triggered ventilation (PTV) or high frequency positive pressure ventilation (HFPPV) is most successful in provoking this beneficial respiratory interaction, synchrony. Preterm infants of less than 4 hours of age and gestational age greater than or equal to 27 weeks were entered into a randomised controlled trial. Thirteen patients received PTV, median gestational age 30 weeks (range 27-36) and 36 HFPPV, median gestational age, 29 weeks (range 27-40). HFPPV was delivered by Sechrist ventilators at rates between 61 and 120 breaths/minute. Patient triggered ventilation was delivered by an SLE ventilator and an airway pressure trigger was used. Inflation times during PTV were between 0.2 and 0.45 seconds. HFPPV provoked synchrony which persisted until extubation in 25 patients, but PTV provoked persistent synchrony only in four patients (p less than 0.05). No infant developed a pneumothorax. Eleven of 36 patients became asynchronous on HFPPV and 5 of 13 on PTV. In addition, four patients on PTV developed recurrent apnoea with deteriorating blood gases. Thus, 11 of 36 patients on HFPPV and 9 of 13 on PTV required transfer to conventional ventilation (p less than 0.05). Transfer occurred at a median of 30 hours (range 6-84) on HFPPV and 1 hour (range 1-25) on PTV, p less than 0.01. Infants who required transfer from the randomised mode of ventilation required a longer period of intubation (median 174 hours, range 30-2928) compared to 38 hours (range 1.5-456) for successful cases, regardless of randomisation (p less than 0.01). This study demonstrates PTV is significantly less successful in promoting synchrony than HFPPV. We therefore conclude HFPPV is a more useful form of respiratory support than PTV for preterm infants with acute respiratory distress.

High-Frequency Ventilation↗

PubMed1991

Airway pressure triggered ventilation for preterm neonates.

The usefulness of airway pressure triggered ventilation for the preterm newborn has been assessed using a new patient triggered valveless ventilator, the SLE 2000 infant ventilator (SLE 2000). This ventilator performs well at fast rates with no inadvertent positive end expiratory pressure (PEEP) even at rates of 150 breaths per minute (bpm). The ventilator is triggered by a change in airway pressure equal to or exceeding 0.5 cmH2O. If the infant fails to achieve the change in airway pressure which will trigger the ventilator the infant is ventilated at the back-up rate which is predetermined in conventional mode prior to commencing PTV. Infants were ventilated for one hour on a conventional neonatal ventilator, then for one hour on the SLE 2000 in conventional mode without changing the ventilator settings and finally for one hour on the SLE 2000 in patient triggered mode. Arterial blood gases were checked at the end of each hour. During patient triggered ventilation (PTV) the peak pressure, inspiratory time and inspired oxygen concentration were the same as those used during conventional mode. Simultaneous recordings were made of flow, volume, ventilator and oesophageal pressure change, from this recording the trigger delay during PTV was calculated. The trigger delay, being the time lag from the start of spontaneous inspiration, indicated by the negative deflection in the oesophageal pressure trace, and the onset of the ventilator breath. Thirteen infants were included in the study, median gestational age 32 weeks (range 25-35) and birthweight 1640 g (range 838-3038). All were being ventilated for respiratory distress syndrome (RDS) and were 4 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation Studies as Topic↗

PubMed1990

Causes of failure of neonatal patient triggered ventilation.

Causes of failure of patient triggered ventilation (PTV) in neonates have been determined. In particular we have investigated the importance of the timing of ventilator inflation in the spontaneous respiratory cycle and hence the respiratory interaction provoked during PTV. Fifty-six infants (median gestational age 29 weeks) were studied on 63 occasions using two different trigger systems, changes in airway pressure and airflow. After one hour of PTV, only 26 infants were synchronous (inflation coinciding with and occurring only in inspiration), 8 were apnoeic. In the remaining 29 infants, inflation extended into expiration, five of whom were actively expiring. The timing of inflation in the spontaneous respiratory cycle and the interaction provoked was significantly related to the trigger delay, but not the inflation time or type of trigger used. Oxygenation after one hour of PTV improved in infants in whom inflation occurred in inspiration only and in some when it extended beyond. Failure of long term PTV was more common, however, in infants in whom inflation extended beyond inspiration (i.e. asynchronous), but this did not relate to the type of trigger used. Failure was also associated with a long trigger delay (P less than 0.01), a very short inflation time (P less than 0.01) and commencement of PTV early in the infant's illness (P less than 0.05). We conclude that synchrony is the most beneficial respiratory interaction during PTV. Our data suggest that this interaction would be more consistently provoked by the use of a sensitive triggering system which ensured a short trigger delay.

Apnea↗

PubMed1990

Gestational age: an important influence on the success of patient triggered ventilation.

We have evaluated a new patient triggered (PT) ventilator which has been produced as suitable for neonatal use. This ventilator, the Draeger Babylog 8000, is triggered by airflow changes detected by a hot wire anemometer. Laboratory assessment demonstrated maintenance of tidal volume and absence of inadvertent PEEP at flow rates up to 20 l min-1 and rates of 120 breaths min-1. The ventilator was then used in both conventional and trigger mode in 14 pre-term infants. The results were compared with PT ventilation delivered by the SLE ventilator. At all inflation times studied, using the Draeger ventilator 100% of respiratory efforts were detected in the majority of infants. The trigger delay varied from a median of 80-100 ms and was significantly shorter than the trigger delay of the SLE system (P less than 0.05). Oxygenation improved on Draeger PT compared with conventional ventilation, however, only in infants more mature than 27 weeks gestation. We conclude the Draeger Babylog 8000 is an important advance in patient triggered ventilation, particularly at fast frequencies, but PT ventilation should still be restricted to relatively mature infants.

Gestational Age↗