HFOV新生儿高频通气

reduction of MAP may result in significant improvement of carbon dioxide removal when lung hyperinflation is the cause of CO2 retention.
CO2 Removal

HIGH FREQUENCY VENTILATION
Background

High frequency was accidentally discovered by anesthetist P. Lunkenheimer in 1973. In 1980, Bohn also using HFOV discovered excellent gas exchange in normal dogs with the use of oscillatory ventilation.

High Frequency Positive Pressure ventilation
Mechanisms of gas transport in High Frequency Ventilation

Direct alveolar ventilation Pendelluft effect Convective streaming Augmented (Taylor) dispersion Cardiogenic mixing Molecular diffusion
Hertz Amplitude ( P)
Thus CO2 elimination is more strongly affected by changes in VT than in frequency. Due to the special characteristics of the HFV machine, the delivered tidal volume is inversely related to frequency.
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Lungs as a two compartment model

First compartment: AIRWAYS. – Do not participate in gas exchange – referred as anatomic dead space

Second compartment: ALVEOLAR UNITS – responsible for gas exchange
Ventilator Settings

Hertz = BPM Power (Amplitude P) Paw FiO2 Bias Flow Inspiratory time %
Delta P (amplitude/power)




Delta P is the pressure fluctuation relative to the MAP. These fluctuation are clinically seen as visible vibrations on the chest wall. If the vibrations on the chest wall are absent or minimal, one may need to increase the power/ Delta P. Hz determines the number of oscillation of Delta P per unit
HFOV

SensorMedics 3100A
Active inspiration and active expiration
The fluctuation in airway pressure higher than the MAP create an inspiratory force, and pressure less than the MAP create a relatively negative or expiratory force.
Bias Flow rate


Bias Flow rate: Select MAP value for patient and while the oscillator is running set the MAP limit and adjust control to max. Turn Bias flow rate until MAP is 10 cm H20 higher than starting MAP. Now adjust MAP limit to appropriate value and MAP back to original value for the patient.
HFOV vs CMV
lung volume is maintained at a relatively constant level during HFV. Better gas distribution, avoids the development of regional atelectasis in less compliant lung units.
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HFOV
SensorMedics 3100A
SensorMedics 3100A Oscillatory Ventilator




The 3100A is a true high frequency oscillator with a diaphragmatically sealed piston driver. It is theoretically capable of ventilating patients up to 30 kg. Tidal volume typically delivered ≈ 1.5-3.0 cc/kg (< dead space). it is not capable of delivering sigh breaths for alveolar recruitment.
Management Strategies : Rescue Vs. Early Intervention



Rescue: Placing patient on HFOV after conventional mechanical ventilation has failed to adequately oxygenate and or ventilate the patient. Lungs are already damaged by conventional ventilation so outcomes are variable. Hospitals need clear criteria for initiation of rescue HFOV in order to improve outcome.
OI = FiO2 x Paw PaO2

Predictor of mortality High value = bad outcome
Factors that affect ventilation in HFV

Amplitude pressure (power) Bias flow Frequency (Hz) Inspiratory time
Factors that affect oxygenation in HFV

Main factors: – Mean Airway Pressure (Paw) – FiO2

Circumstantial factors: – Inspiratory time – Frequency (Hz)
Oxygenation Index
Amplitude vs power?



Many HFOV centers have you order amplitude or delta P (ĢP) to regulate ventilation instead of power. We have decided that the Power setting is a more reliable way of adjusting this ventilator and thus we order changes in power in order to regulate ventilation. Start with the power setting dial at 2.0 for infants. Wiggle should extend to umbilicus. Change in 2-4 cm H20 increments.
Elements of HFV
ຫໍສະໝຸດ Baidu
Use of supraphysiologic ventilatory rates (high ventilation rate of at least 2 Hz) Use of tidal volume smaller than the anatomic dead space (1.5-3.0 cc/kg)

Types of HFV
High Frequency Oscillatory Ventilation High Frequency Jet Ventilation high frequency flow interrupter (HFFI)

sigh breathes can be used Draegar babylog 8000 infant start

Hazards of HFOV




Over distension Tension Pneumothorax Lung collapse Difficulty maintaining ET tube position Difficulty assessing breath sounds due to the loud noise from the HFOV
Neonatal Uses of HFOV



As primary treatment for RDS Persistent pulmonary hypertension Neonatal air leaks (Pulmonary interstitial emphysema) Sepsis / Pneumonia(As rescue therapy when CMV fails) Congenital diaphragmatic hernia Meconium aspiration syndrome
CO2 Removal


If PaCO2 more than 50-60mmHg, first increase power. Change power by 0.2-0.3 to change CO2 24mmHg. At lower Hz, the ventilator is able to achieve most of the delta P, thereby generating effective ventilator, increasing the size of breath and lowering the PaCO2.
CMV vs HFOV
Advantages of HFOV

it is believed that there is less barotrauma with this mode. By oscillating around the MAP, cyclic overdistention of the lungs can be avoided and lung recruitment is easier to achieve and thereby provide better saturation.
Management Strategies : Rescue Vs. Early Intervention

Early Intervention: Patient is placed on HFOV within 2 hours of birth. The goal is to achieve optimal lung inflation as quickly and as gently as possible.