Paediatric Intensive Care Unit, Guys Hospital, St Thomas Street, London SE1 9RT, UK*Corresponding author
Accepted for publication: December 21, 2001
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Abstract |
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Methods. We present data from three adolescents with severe acute respiratory distress syndrome (ARDS) who received HFO with the Sensormedics 3100B oscillator after failure of conventional mechanical ventilation. A manual recruitment manoeuvre was used in all patients prior to mechanical ventilation (conventional or HFO) and following tracheal suctioning or disconnection from the ventilator. Changes in oxygenation index were used to assess therapy.
Results. All patients showed at least a 25% reduction in oxygenation index within 2 h of HFO, with return to conventional ventilation after 27--65 h.
Conclusions. We found HFO, in conjunction with manual recruitment and prone positioning, to be a well-tolerated mode of ventilation in adolescents with ARDS and who were unresponsive to conventional ventilation. Given this success we hope to renew interest in this method for adults with ARDS, together with concurrent use of manual recruitment.
Br J Anaesth 2002; 88: 70811
Keywords: lung, acute respiratory distress syndrome; ventilation, high frequency
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Introduction |
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High-frequency oscillation (HFO) is an effective low tidal volume ventilatory strategy widely used in paediatric and neonatal acute lung injury.2 3 Until recently, its use in adult practice has been limited by the lack of an adequately powered oscillator. There are now some studies demonstrating its safe and effective application in adult acute lung injury.46 Successful use of HFO has also been hindered by failure to adequately recruit the lung during oscillation.7 8 Current practice is to use HFO to achieve, then maintain recruitment.4 5 Our practice is to use a high-pressure, rapid manual recruitment manoeuvre initially, and subsequently to use HFO with lower recruitment pressures. The use of lower pressures on HFO may be associated with less haemodynamic compromise and barotrauma. Manual recruitment manoeuvres in humans have only been described previously in conjunction with conventional ventilation.9
In this report we demonstrate the successful management of ARDS in three adolescents using a combination of rapid manual recruitment manoeuvres and HFO with the Sensormedics 3100B oscillator (Yorba Linda, CA). Given the size of our patients, this method could be used generally for adults.
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Methods and results |
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Changes in oxygenation index (mean airway pressure (mm Hg) x FIO2 x 100/[PaO2 (kPa) x 7.5]), were used to assess response to therapy. Failure of conventional ventilation was defined as PaO2 less than 8 kPa with an FIO2 greater than 0.7, peak inspiratory pressure greater than 30 cm H2O and PEEP greater than 10 cm H2O for at least 1 h despite placing prone, neuromuscular block and manual recruitment (see below).
Manual recruitment manoeuvre
A manual recruitment manoeuvre was done before mechanical ventilation (conventional or HFO) and following tracheal suctioning or disconnection from the ventilator. This involved sustained manual inflation of the lungs with an FIO2 of 1.0 using a Mapleson C circuit (Intersurgical, Berkshire), with the inflating pressure measured with a manometer connected by a sidearm between the tracheal tube and reservoir bag. The inflating pressure was increased to a maximum of 50 cm H2O until oxygen saturations increased to a stable value; this recruiting pressure was then maintained for 30 s after which the tracheal tube was clamped to prevent derecruitment whilst connecting the patient to the ventilator. The process took 12 min. The initial mean airway pressure on HFO was set 5 cm H2O below the recruiting pressure (Fig. 1A). Patients were treated with a 10 ml kg1 bolus of i.v. crystalloid if hypotension prevented a full recruitment manoeuvre; thereafter, the manoeuvre was re-attempted.
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Conventional ventilation was started again when the FIO2 was below 0.5 and mean airway pressure approximately 1820 cm H2O.
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Results |
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Discussion |
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With the Sensormedics 3100B oscillator, HFO can be applied to adults. This model has several modifications from its predecessor used in paediatrics (Sensormedics 3100A); it can achieve greater bias flow of up to 100 litre min1, has a greater amplitude, and possesses a more powerful electromagnet allowing faster acceleration to the required amplitude.
Three groups have reported recently the successful use of HFO in adults with ARDS.46
The patients in Fort and colleagues4 and Mehta and colleagues5 studies showed significant improvement in oxygenation indices only after 12 and 48 h of HFO, respectively. Our patients showed a sustained improvement in oxygenation index following initiation of HFO with a 25% decrease within the first 2 h. Our ventilatory strategy differed from the other reports in three respects.
First, we used a manual recruitment manoeuvre to rapidly (12 min) recruit the lungs at initiation of HFO, setting the initial mean airway pressure at 5 cm H2O less than the recruiting pressure. This was then reduced progressively maintaining oxygen saturations between 88 and 92% at an FIO2 less than 0.6. In Fort and colleagues4 and Mehta and colleagues5 studies, HFO was used for both achievement and maintenance of recruitment. With Forts patients, the initial mean airway pressure was set at 23 cm H2O above that of conventional ventilation and increased over a 3-h period, whilst on HFO, aiming for similar oxygen saturations. In Mehtas study, the initial mean airway pressure was set at 5 cm H2O above that of conventional ventilation after which the mean airway pressure was increased in increments of 12 cm H2O if an FIO2 more than 0.6 was required to maintain similar oxygen saturations. The recruiting pressures we used were greater than the initial mean airway pressures used during HFO in these two studies. We suggest this allowed us to rapidly and safely open the lung, and then apply lower mean airway pressures that could be rapidly reduced resulting in the dramatic decrease in the oxygenation index described (Fig. 1).
Secondly, we repeated recruitment after circuit disconnection, tracheal suctioning, or arterial desaturation to restore airway opening.
Thirdly, we used greater oscillatory frequencies than that reported by both Fort and colleagues4 and Mehta and colleagues5 (68 vs 35 Hz) without experiencing severe hypercarbia (all PCO2 values were below 9 kPa throughout HFO). The rationale for this was that lower frequencies during HFO result in higher alveolar tidal volumes, which may potentiate lung injury.10
Our criteria for failed conventional ventilation included peak pressures that were less than that described by Fort and co-workers4 (32 and 40 vs 65 cm H2O), with a similar range of oxygenation indices. This would result in earlier institution of HFO in some patients, using HFO to protect the lung rather than as salvage therapy. Indeed Patient 1 in our report who had the longest period of conventional ventilation pre-HFO (50 h) was treated for twice as long as the other two patients, whilst a significant discriminating feature between the survivors and non-survivors in both Fort and colleagues4 and Mehta and colleagues5 studies was the duration of conventional ventilation before HFO. Furthermore, we used the prone position for all our patients.
In conclusion, we found HFO in conjunction with manual recruitment to be a well-tolerated mode of ventilation in adolescents with ARDS who did not respond to conventional ventilation. Ventilator strategy may be important in achieving success with HFO. Given the success of HFO we hope to renew interest in this method for adults with ARDS with concurrent use of manual recruitment.
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References |
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10
Krishnan JA, Brower RG. High-frequency ventilation for acute lung injury and ARDS. Chest 2000; 118: 795807