Chapter 55

• Open mechanical ventilation system that may improve gas exchange at lower peak and mean airway pressures than conventional ventilation
• Pulsed cycles of small tidal volumes (2–5 mL/kg) at high frequencies (50–150 breaths/min)
• Inspiration: via a small cannula that delivers a jet stream of pulsed breaths to the lungs. The jet stream cannula should be small enough to avoid “sealing” the airway. Typically the cannula is placed through the vocal cords in the trachea, but in an emergency setting, a cannula or a large-bore Angiocath can be introduced through the cricothyroid membrane
• Expiration: passive around jet nozzle
• High-frequency jet ventilation (HFJV) parameters and settings:
• Driving pressure: major determinant of tidal volume. Driving pressure settings are usually 20–25 psi in adults, with a maximum of 50 psi
• Inspiration time and respiratory frequency: the major determinants of “auto-PEEP” (air trapping). Inspiration time is usually set at 30–40% and respiratory frequency is between 50 and 150 bpm. By increasing either value, auto-PEEP is increased, which allows recruitment of alveoli, optimization of V/Q matching, and improvement in oxygenation. Auto-PEEP may also be beneficial when a “still” surgical field is desired because chest wall excursions are reduced
• FiO2: always set at 100%. It is the oxygen concentration at the jet nozzle. However, the actual FiO2 in the alveoli is significantly lower due to the Venturi effect (negative pressure around gas flow that drags air from the environment into the airway) and the use of an open system
• Humidification: used when prolonged jet ventilation anticipated in order to avoid mucus membrane damage or formation of mucus clot leading to airway obstruction
• The mechanism of gas exchange is unlike that in conventional ventilation: CO2 elimination is possible because of a combination of bulk convection, molecular diffusion, and turbulence of convective flow
• Due to the lower peak and mean airway pressures in HFJV, intrathoracic pressures are decreased leading to increased venous return and improved cardiac function

• Certain procedures requiring a shared or still operative field:
• Bronchosopy
• Laryngoscopy
• Tracheal reconstruction
• Laryngeal resection
• One-lung ventilation
• Respiratory failure in patients with:
• Bronchopleural and tracheoesophageal fistulas
• Laryngeal neoplasms
• Barotrauma
• Pulmonary fibrosis
• Severe ARDS
• Pulmonary hemorrhage
• Persistent fetal circulation in the neonate to enhance CO2 elimination
• Infants with congenital diaphragmatic herniation
• Difficult airways: the “cannot ventilate, cannot intubate” patient (through cricothyrotomy)

• Barotrauma (high pressure buildup in a closed tissue pocket):
• May lead to pneumothorax, pneumomediastinum, and subcutaneous emphysema
• Avoid by allowing adequate expiratory time and keeping the airway system open (avoid use in upper airway obstruction; if needed, place oral/nasal airway to maintain patency)
• Assure automatic shutoff mechanisms are properly functioning to allow termination of ventilation in overpressure situations
• Tracheal injury:
• Excessive auto-PEEP and dynamic hyperinflation:
• Usually occurs at frequencies above 150 bpm
• Avoid malposition of the jet ventilator catheter tip in the proximal conducting airways—should be at level of carina
• Auto-PEEP is usually a desired feature but can result in worsening ventilation and compromise systemic ...

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