1 RSPT 2353 – Neonatal/Pediatric Cardiopulmonary Care High Frequency Ventilation in the Pediatric and Neonatal Patient Lecture Notes I. High-Frequency Jet Ventiliation (HFJV) – a. Used in tandem with a conventional ventilator b. Operate in 4 – 11 Hz; pulses of gas is delivered through adapter at ETT c. Conventional ventilator Allow sighs Provides PEEP Allows continuous flow of gas available at ETT d. Limitations HFJV allows passive exhalation More compliant lungs require lower rates II. High Frequency Oscillating Ventilation (HFOV) was designed to perform the following functions: a. To serve as a ventilation mode when conventional ventilation has failed. b. To provide a mode of ventilation that minimizes barotrauma, or damage to the delicate tissue in the lungs. III. Definition of HFOV: a rapid rate ventilation using low tidal volumes a. The oscillator uses a diaphragm piston unit to actively move gas in and out of the lungs and requires a special circuit (rigid or flexible) b. Differs from conventional ventilation in that it provides rate of 1201200 bpm with volumes of 0.1 – 1.5 cc/kg. Conventional ventilation provides rates of 1 – 120 bpm and 4 – 20 cc/kg. IV. Indications for HFOV – They are not clearly defined, but do include: a. Air leaks such as pneumothorax and pulmonary interstitial emphysema (PIE) b. To reduce barotrauma when conventional ventilator settings are getting very high c. When conventional ventilation is failing, particularly in meconium aspiration syndrome (MAS), pneumonia, persistent pulmonary hypertension of the newborn (PPHN), and pulmonary hemorrhage. d. Respiratory Failure – Defined as PaCO2 > 55 torr, PaO2 <50 torr V. Effects on lung tissue a. The lung parenchyma in children is especially delicate and the high peak pressure used in conventional ventilation can be harmful to the delicate lung tissue. 2 b. Barotrauma occurs when the lung tissue is damaged due to the excessive pressures. c. HFOV offer the advantage of improved CO2 removal at lower peak pressures. VI. Effects on cardiopulmonary status a. HFOV can cause hemodynamic changes b. This is due to the continuous pressures that are generated by HFOV which causes increased pressures in the thoracic cavity. c. The increased thoracic pressure can impede cardiac output. d. The decreased CO affects the blood pressure and a vicious cycle can ensue. e. To avoid this happening, the pt hemodynamic status must be monitored continuously. f. Arterial lines are necessary. VII. Settings a. Amplitude – also called ΔP HFOV is more dependent on amplitude than on rate. Similar to Vt on conventional ventilation Proper setting is determined by observing chest excursion/movement with oscillation. This setting should be enough to vibrate or “wiggle” the thorax from the nipple line to the umbilicus Settings are changed by 1-2 cmH2O Changes in amplitude require readjustment in the MAP. b. Frequency Similar to rate in conventional ventilation Measured in Hertz (Hz) Multiply the number of Hz X 60 to obtain the exact rate Initial Hz settings < 1000 gms 15 Hz 2 - 12 kg 10 Hz 13 - 20 kg 8 Hz 21 - 30 kg 7 Hz > 30 kg 6 Hz Setting depends on the size of the pt and the disease process Changes in frequency dramatically changes Amplitude and MAP c. MAP Similar to peak airway pressure in conventional ventilation For diffuse alveolar disease, the initial MAP should be set approx 2-4 cmH2O over the value of MAP on the conventional ventilator If compression of the heart is noted on CXR, and decrease in MAP is necessary. 3 Decrease by 0.5 to 1 cmH2O on the MAP dial. A spontaneous pneumothorax is a complication that can result from increased MAPs d. FiO2 VIII. Initial FiO2 is selected to optimize pulmonary vascular resistance while the ventilator is opening the lungs. Monitoring on HFOV a. Arterial access (UAC in neonates, peripheral in pediatric) is advantageous. b. Blood pressure is especially important because of the hemodynamic changes that can occur during HFOV High pressures lead to a decrease in CO – tissues and organ perfusion are affected Also includes monitoring of Urine output, kidney function c. CXR Obtain a CXR 30-60 minutes after initiation of HFOV Determines if MAP is compressing the heart Chest expansion of 8.5 to 9 ribs indicates proper inflation As lungs heal, they are more compliant and can become hyperinflated leading to pneumothorax. Regular chest films should be taken to monitor chest expansion. d. Paralytic agents May cause fluid retention and should be taken into consideration The pt may be paralyzed initially, but paralytics should not be used for extended periods of time. As soon as tolerated by pt, paralytic agents should be discontinued.