7.2 Advanced Ventilatory Strategies: HFOV, APRV, Prone Positioning & ECMO Indications

Advanced support for severe pediatric respiratory failure

When gas exchange remains inadequate despite lung-protective ventilation, reassess the cause, airway, circuit, mechanics and circulation. Discuss rescue options and extracorporeal assessment early if the child continues to deteriorate.

High-frequency oscillatory ventilation

HFOV applies rapid pressure oscillations around a mean airway pressure. Piston oscillators actively move gas in both directions. Small oscillatory tidal volumes may be below anatomical dead space. Proximal bulk flow, mixing from oscillation and unequal regional time constants, and distal molecular diffusion can all contribute to gas transport. Trapping can still occur during active expiration. Experimental HFOV mechanics

PALICC-2 makes no recommendation for HFOV over conventional ventilation. HFOV can be considered when a lung-protective conventional strategy cannot achieve ventilation goals. If using HFOV for PARDS, explore lung recruitment with stepwise mean airway pressure increases and decreases while monitoring oxygenation, carbon dioxide and hemodynamics. Mean airway pressure and inspired oxygen are major determinants of oxygenation. Changes in lung volume can also alter ventilation. Check for air leak, asymmetry and overdistension. Radiography can help assess the airway, lung inflation and complications. A fixed posterior rib count does not establish optimal recruitment. PALICC-2 recommendations 3.8.1–3.8.2 · Pediatric HFOV cohort

Interpreting carbon dioxide during HFOV

The gas transport coefficient $DCO_2=f\times V_{T,osc}^2$ uses frequency in Hz and measured oscillatory tidal volume. Use the index to compare changes in transport capacity and use blood gases to assess ventilation. One Hz is one cycle per second, or 60 cycles/min. The set power and measured oscillatory pressure amplitude are distinct. Delivered oscillatory volume depends on the oscillator, amplitude, frequency, tube, leak and lung mechanics. Increasing amplitude often increases oscillatory volume. On some oscillators without volume targeting, decreasing frequency can increase oscillatory volume enough to improve carbon dioxide clearance. With volume held constant, lowering frequency instead lowers the calculated coefficient. Check measured volume when available, airway patency and blood gases when titrating. 3100A operator's manual · Pediatric oscillator bench study · Neonatal volume-targeted HFOV study

Worked example: At 10 Hz and 20 mL, $DCO_2=10\times20^2=4000$ mL²/s. If a trial at 7 Hz raises oscillatory volume to 26 mL, $DCO_2=7\times26^2=4732$ mL²/s, about 18% higher. If volume stayed 20 mL at 7 Hz, the index would fall to 2800 mL²/s. Recheck the arterial carbon dioxide and perfusion to determine the response.

Airway pressure release ventilation

APRV alternates time at a higher airway pressure with a brief release to a lower pressure. Spontaneous breaths are possible at both levels on devices that implement the mode that way. The high pressure and time influence mean airway pressure. The release allows expiration, and ending the release while expiratory flow persists can retain end-expiratory lung volume. The size of the release and the patient's spontaneous effort affect tidal volume and ventilation.

Use device and program expertise to interpret high and low pressures, time at each pressure and the release flow tracing. For example, a flow magnitude of 30 L/min at release termination after a peak of 40 L/min is 75% of peak. This is a description of the waveform. Animal work studied that target; it does not establish a universal pediatric endpoint. Check delivered volumes, spontaneous effort, blood gases and hemodynamics. Obstructive mechanics with air trapping, a significant air leak, intracranial hypertension or unreliable respiratory drive can complicate use. Several such groups were excluded from the pediatric trial, so its results cannot establish safety for them.

A small randomized crossover study in mild to moderate pediatric lung disease evaluated short-term physiology. In a separate pediatric ARDS randomized trial, early APRV showed no improvement in ventilator-free days and a concerning mortality signal at interim review, after which the trial stopped. Improved oxygenation alone does not establish benefit. Conventional lung-protective ventilation remains the starting strategy. Pediatric crossover trial · Pediatric ARDS randomized trial · Experimental release-time study

Prone positioning

Consider a monitored prone trial when hypoxemia persists despite other measures. PALICC-2 finds insufficient pediatric evidence for routine proning and gives no fixed session duration. The pediatric randomized trial did not improve ventilator-free days. When trying it, secure the airway and lines, protect pressure points and reassess oxygenation, hemodynamics and tolerance. PALICC-2 · Pediatric prone trial

Extracorporeal membrane oxygenation

Consult an ECMO team for severe, potentially reversible respiratory failure with inadequate gas exchange despite lung-protective strategies. Follow the trajectory, assess both ventricles and perfusion, and consider reversibility and bleeding risk. PALICC-2 supplies no universal cannulation threshold.

A pump moves blood through a membrane oxygenator and a heat exchanger controls temperature. Sweep gas flow is a major control of extracorporeal carbon dioxide removal. Effective blood flow relative to native output, hemoglobin, oxygenator performance and recirculation affect systemic oxygenation on VV. If support deteriorates, reassess the child and call the ECMO team. Review circuit flow, pressure trends, gas supply, pre- and post-oxygenator gases when appropriate, and cannula position and clot or hemolysis indicators. ELSO pediatric respiratory guideline · ELSO circuit guideline

Use the pediatric program's anticoagulation regimen and follow bleeding, thrombosis and circuit performance. If using unfractionated heparin, PEACE suggests considering anti-Xa together with one or more clot-based assays where available. Investigate discordance and ask which tests are affected by hemolysis, bilirubin or lipemia. PEACE finds insufficient evidence for routine antithrombin monitoring or replacement and for universal first-line bivalirudin. A subsequent 30-patient randomized pilot demonstrated feasibility of comparing bivalirudin with heparin. It was too small to establish comparative clinical benefit. Pediatric ECMO anticoagulation consensus · Pediatric ECMO pilot trial