Intensive Care Unit, Royal Albert Edward Infirmary, Wigan Lane, Wigan WNI 2NN, UK
* Corresponding author. E-mail: rsgsaad{at}hotmail.com
Accepted for publication February 2, 2004.
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Abstract |
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Keywords: complications, adult respiratory distress syndrome ; complications, air leaks ; complications, pneumothoraces ; ventilation, high frequency oscillatory
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Introduction |
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Case report |
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Over the next week, her ventilatory variables remained essentially the same. She developed bilateral spontaneous pneumothoraces and her was between 8 and 9 kPa with an
of 1. Her tidal volumes were reduced to 300350 ml, ventilatory rate increased to 25 bpm and she was started on hydrocortisone 800 mg daily, and diuretics to achieve a negative fluid balance. Her oxygenation failed to improve over the next 4 weeks and she developed two further pneumothoraces, such that she now had five chest drains in situ.
She was started on HFOV 40 days after admission to ITU. The initial settings were as follows: amplitude 55 cm H2O, mean airway pressure 22.5 cm H2O, frequency 5 Hz, and 0.95. Over the next 24 h, her oxygenation improved with a
of 10.5 kPa and within 1 week it was possible to reduce the
to 0.8. Her oxygen requirements continued to decrease as her oxygenation improved. She remained haemodynamically stable and did not develop any further pneumothoraces. The existing pneumothoraces resolved whilst on the oscillator. After 16 days on HFOV, she was changed back to conventional ventilation. She went back onto the Drager Evita 2 ventilator on BIPAP ASB (assisted spontaneous breathing) with an
of 0.6, pressures adjusted to give a tidal volume of 300350 ml, rate 22 bpm, I:E ratio 1:2 and PEEP 15 cm H2O. She remained on BIPAP for the next 30 days. During this time her oxygenation continued to improve.
By 86 days post-admission, she was able to tolerate CPAP. She was finally discharged to the ward 123 days after admission on oxygen 28% via facemask. She was discharged home 3 weeks later with no neurological deficit and no supplementary oxygen requirement.
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Discussion |
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This has led to the introduction of a more lung friendly form of ventilation with small tidal volumes, rapid rates, and high PEEP.10 The rationale of this is that in ARDS the normal lung is essentially small, hence the small tidal volumes and the use of a high PEEP serves to increase ventilated lung volume and prevent end-expiratory alveolar collapse. The rapid rates facilitate carbon dioxide clearance with the acceptance that carbon dioxide elimination is not the priority in ARDS.
HFOV may be regarded as the extreme end of this lung protective spectrum. The very small tidal volumes (13 ml kg1), allow use of a higher end-expiratory lung volume, achieving greater alveolar recruitment while avoiding damage as a result of excessive end-inspiratory lung volumes. The combination of a high continuous distending pressure with minimal pressure changes prevents the damage caused by cyclical alveolar collapse. HFOV also provides a rapid rate (up to 2400 bpm) and an active expiratory phase, both of which decrease air trapping and maintain normal or near normal carbon dioxide levels. It is for these reasons that HFOV has a well-established position in paediatric and neonatal practice, and is now emerging as a promising prospect in the treatment of ARDS. Recent studies25 show an association between early introduction of HFOV in ARDS and improved survival. Its use in adults is still, however, in its infancy and a trial of its effectiveness in comparison with the gold standard conventional ventilation recommended by the ARDS network10 is awaited.
When HFOV was first introduced, there was considerable concern that the benefits it provides in improved oxygenation and better alveolar stability might be outweighed by the possibility of increased risk of pneumothoraces and haemodynamic compromise as a result of the high mean airway pressures used. Recent studies2 4 indicate that haemodynamic instability is not a problem and that HFOV may both decrease the risk of and have a role in the treatment of air leaks.1115 Animal studies have supported the role of HFOV in the management of air leaks. Wang and colleagues14 ventilated surfactant depleted rabbits with bilateral pneumothoraces using high-frequency ventilation. The peak airway pressure was found to decrease significantly as the frequency setting was increased. There were no significant differences in mean airway pressure when high frequency was compared with conventional ventilation and during high-frequency ventilation; peak airway pressures measured at the mouth were actually decreased. An association between increasing frequency and decreasing chest tube flow was also noted in the treatment of experimental pneumothoraces in piglets.15 In this study, Ellsbury and colleagues suggest that the very short inspiratory time and small tidal volume of each HFOV breath minimize dilation of existing air leaks. The resultant decrease in diameter of the leak may then increase the resistance to gas flow and promote its closure. This is supported by their findings that increasing inspiratory time increased chest tube flow. There have also been reports of the successful use of high-frequency ventilation in children with air leaks,1113 and in neonatal pulmonary interstitial emphysema; however, we did not find any information regarding its use in adults with air leaks. It is also interesting to note that Derek and colleagues2 excluded patients with more than one chest tube per hemithorax and a persistent air leak for more than 120 h from their randomized controlled trial.
The case we present posed a difficult challenge to the success of HFOV not only because she had 40 days conventional ventilation before starting oscillation, but also because of the fact that she had multiple bilateral air leaks and had five chest drains in situ at the time of starting oscillation. Her oxygenation improved, she did not develop any further air leaks, and the existing pneumothoraces resolved while she was on the oscillator.
It may well be that this unconventional form of ventilation not only has a role in the management of ARDS but that its success in the treatment of air leaks in children,1113 and in animal studies,14 15 may also be applicable to adults.
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Footnotes |
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References |
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