![]() ![]() This parameter is usefully monitored during the recruitment process – see section 2.4) ( NB – such rapid falls in CO 2 may be predicted by a significant rise in the tidal volume measurement (VThf). MAP has very little effect in CO 2 clearance in an infant with adequate lung inflation, but may cause rapid drops in PaCO 2 during lung recruitment. It is easy to cause hypocarbia with HFOV. Recheck a blood gas 20 minutes after making a change.You have now performed a “recruitment manoeuvre” and for the same MAP have achieved a greater lung volume and improved gas exchange. MAP should then be reduced back to 2-4cmH 2O below this critical opening pressure. Beyond the point of over-inflation (critical opening pressure) oxygenation will no longer improve (and may deteriorate).Usually the MAP would be incremented every 5-10 minutes, but more rapid increments in MAP, every 1-2 minutes, might be required depending on the clinical condition, (for example, in a baby with severe oxygenation problem with a collapsed lung volume). a stepwise increase in MAP of 1-2cmH 2O whilst monitoring response (oxygenation, CO 2 clearance, BP). Practically, this may involve a “recruitment manoeuvre”: i.e.Both under-inflation and over-inflation of the lungs will give sub optimal oxygenation. MAP is used to achieve and maintain the maximal recruitment of alveoli. On commencement of HFOV it is useful to ensure that optimal lung volume has been achieved (as discussed earlier). X-ray should show around 8 rib spacesĮxpect to stay with the baby and make adjustments to the MAP and ΔP (amplitude) in the first minutes of the initial hour of starting HFOV, based on oxygenation, CO 2 clearance, hemodynamic (BP) and chest x-ray. Obtain a chest x-ray after commencing HFOV to determine lung expansion, ideally within one hour.Obtain a blood gas within 20-30 minutes and adjust settings as appropriate.Set appropriate FiO 2 and titrate according to patient response and desired oxygen saturation range.I:E Ratio: I:E ratio is usually 1:1 and not changed except in special circumstances (e.g.Lower frequencies may be used in severe lung disease, with poor CO 2 clearance, especially in term infants. Frequency/ Hertz: Set appropriate frequency / hertz (determined by lung pathology and clinical condition): Usually frequency is set at 10 Hz.Higher ΔP (amplitude) should only be used with caution only in severe lung disease. Typical operating ranges for ΔP (amplitude) will between 20 to 30Hz.The starting amplitude required to achieve adequate “wiggle”, may in due course be reduced after initial lung recruitment, to avoid hypocarbia. Amplitude (ΔP): Set the amplitude ( ΔP) to approximately double the value of the MAP, sufficient to see a chest “wiggle” from the level of the nipple to the umbilicus.In situations of severe gas trapping, or air leak, a lower MAP may be selected If Higher MAPs are required, for example in in severe lung disease with very poorly compliant lungs, then they should be used with caution and careful monitoring to avoid over distension and air leak. ![]() Typical operating range for MAP will be between 10 to 16 cmH2O.However, to achieve optimal lung recruitment the operator should be prepared to start a recruitment manoeuvre – see section 2.3. Mean Airway Pressure (MAP): Generally the starting MAP is set 2-3cm above the current CMV mean airway pressure.Initial settings will be prescribed by medical staff, however the following is a guide: Consider invasive BP monitoring if possible.If BP not improving after volume expansion, consider starting inotropic support. ![]() Consider volume expansion to avoid a sharp fall in cardiac output.
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