Peter A. Dargaville

Electrical impedance tomography: a method for monitoring regional lung aeration and tidal volume distribution?

ObjectiveTo demonstrate the monitoring capacity of modern electrical impedance tomography (EIT) as an indicator of regional lung aeration and tidal volume distribution.Design and settingShort-term ventilation experiment in an animal research laboratory.Patients and participantsOne newborn piglet (body weight: 2 kg).InterventionsSurfactant depletion by repeated bronchoalveolar lavage, surfactant administration.Measurements and resultsEIT scanning was performed at an acquisition rate of 13 images/s during two ventilatory manoeuvres performed before and after surfactant administration. During the scanning periods of 120 s the piglet was ventilated with a tidal volume of 10 ml/kg at positive end-expiratory pressures (PEEP) in the range of 0–30 cmH2O, increasing and decreasing in 5 cmH2O steps. Local changes in aeration and ventilation with PEEP were visualised by EIT scans showing the regional shifts in end-expiratory lung volume and distribution of tidal volume, respectively. In selected regions of interest EIT clearly identified the changes in local aeration and tidal volume distribution over time and after surfactant treatment as well as the differences between stepwise inflation and deflation.ConclusionsOur data indicate that modern EIT devices provide an assessment of regional lung aeration and tidal volume and allow evaluation of immediate effects of a change in ventilation or other therapeutic intervention. Future use of EIT in a clinical setting is expected to optimise the selection of appropriate ventilation strategies.

Surfactant abnormalities in infants with severe viral bronchiolitis.

To determine whether abnormalities of pulmonary surfactant occur in infants with acute viral bronchiolitis, surfactant indices were measured in lung lavage fluid from 12 infants with severe bronchiolitis and eight infants without lung disease. Compared with controls, the bronchiolitis group showed deficiency of surfactant protein A (1.02 v 14.4 micrograms/ml) and disaturated phosphatidylcholine (35 v 1060 micrograms/ml) which resolved as the disease improved. Surfactant functional activity was also impaired (minimum surface tension 22 v 17 mN/m). These findings indicate that surfactant abnormalities occur in bronchiolitis, and may represent one of the pathophysiological mechanisms causing airway obstruction.

Effects of tidal volume and positive end-expiratory pressure during resuscitation of very premature lambs

BACKGROUND Guidelines recommend neonatal resuscitation without controlling tidal volume or positive end-expiratory pressure (PEEP). However, these may improve gas exchange, lung volume and outcome. AIM To investigate resuscitation of very premature lambs with a Laerdal bag without PEEP versus volume guarantee ventilation with PEEP. METHODS Anaesthetized lambs (n=20) delivered at 125 d gestation were randomized to three groups receiving 15 min resuscitation: (1) Laerdal bag and no PEEP; (2) ventilation with a tidal volume of 5 ml/kg and 8 cm H(2)O PEEP; (3) ventilation with 10 ml/kg and 8 cm H(2)O PEEP. They were then all ventilated for 2 h with tidal volumes of 5 or 10 ml/kg, and 8 cm H(2)O PEEP. Ventilation parameters and blood gases were recorded. RESULTS Different tidal volumes affected PaCO(2) within minutes, with 10 ml/kg causing severe hypocarbia. PEEP had little effect on PaCO(2). Oxygenation improved significantly with PEEP of 8 cm H(2)O, irrespective of tidal volume. CONCLUSION Very premature lambs can be resuscitated effectively using volume-guarantee ventilation and PEEP. Tidal volumes affected PaCO(2) within minutes but had little effect on oxygenation. PEEP halved the oxygen requirement compared with no PEEP. Resuscitating premature babies with controlled tidal volumes and PEEP might improve their outcome.

A new sensor for monitoring chest wall motion during high-frequency oscillatory ventilation.

The recently developed technique of fibre optic respiratory plethysmography (FORP) has been modified to monitor the rapid, small amplitude movements of the chest wall during high-frequency oscillatory ventilation (HFOV). The FORP sensor is an expandable belt encircling the chest, in which is housed a fibre optic loop that alters its radius of curvature as a function of chest perimeter. These curvature changes cause variations in macrobending losses of light transmitted through the fibre, which are proportional to the chest perimeter. Dynamic measurement of transmitted light intensity can hence be used to monitor chest wall motion (CWM). For application to HFOV, the design of the FORP belt was altered to increase sensitivity and the materials were chosen to maximise macrobending effects induced by the CWM. FORP was tested in four piglets ventilated with HFOV, both in the normal and surfactant-deficient lung. Measurement of CWM was possible over the full range of tidal volumes and ventilation frequencies used during HFOV. In all cases, the measured frequency of the CWM fell within 3% of the applied ventilation frequency. In addition, the technique was sufficiently sensitive to detect changes in the amplitude of CWM in response to changes in applied tidal volume. It is anticipated that application of this new non-invasive measurement device will lead to an increased understanding of the dynamics of chest and abdominal wall motion during HFOV.

Overdose of ergometrine in the newborn infant: Acute symptomatology and long‐term outcome

To document the short‐ and long‐term effects of accidental administration of ergometrine in adult dosage to the newborn infant.

Pulmonary surfactant concentration during transition from high frequency oscillation to conventional mechanical ventilation

Objective: To test the hypothesis that conventional mechanical ventilation (CV) provides a greater stimulus to secretion of pulmonary surfactant than high frequency oscillatory ventilation (HFO).

190 The Effect of Tidal Volume and Peep on Co2 and Oxygenation During Resuscitation of Very Premature Lambs

Background: Over-ventilation causing low arterial carbon dioxide levels (PaCO2) has been associated with the development of neonatal chronic lung disease and adverse outcomes. This may occur very soon after birth.Aim: To investigate the effect on PaCO2 and oxygenation of very premature lambs resuscitated with different tidal volumes and PEEP.Methods: Anaesthetised lambs delivered at 126 days gestation were randomised to 15 min resuscitation with 3 regimes: (1) Laerdal resuscitation bag (B) with 100% oxygen and no PEEP, (2) fixed tidal volume (VT) of 5 mL/kg, or (3) VT of 10 mL/kg, both delivered with a Babylog 8000 ventilator in volume guarantee mode with 8 cm H2O PEEP and variable FiO2. Frequent blood gases were measured and VT, mean airway pressure (Paw), minute volume (MV), ventilation rate (VR), respiratory system compliance (Crs) and alveolar/arterial oxygen difference (AaDO2) were recorded.Results: Twenty lambs were studied. B (1) was associated with more variable VT and peak inspiratory pressures (PIP) compared to fixed tidal volumes (2 and 3). The lambs ventilated with 10 mL/kg were over-ventilated, those ventilated with 5 mL/kg were slightly under-ventilated. Those ventilated with the Laerdal bag had a mean VT of 7.5 mL/kg and were normocarbic. The different tidal volumes had little effect on oxygenation. PEEP improved oxygenation. The table shows the values at 15 minutes expressed as mean and SEM.Conclusion: Very premature lambs can be effectively resuscitated from birth using volume guarantee ventilation. Within minutes of birth different tidal volumes had a large effect on PaCO2 and no effect on oxygenation. Studies are needed to determine the appropriate tidal volume for resuscitating very premature infants to maintain acceptable levels of PaCO2.