A simple method of mechanical power calculation: using mean airway pressure to replace plateau pressure

In this study, we evaluated the performance of a humidified nasal high-flow system (Optiflow™, Fisher and Paykel Healthcare) by measuring delivered FiO2 and airway pressures. Oxygraphy, capnography and measurement of airway pressures were performed through a hypopharyngeal catheter in healthy volunteers receiving Optiflow™ humidified nasal high flow therapy at rest and with exercise. The study was conducted in a non-clinical experimental setting. Ten healthy volunteers completed the study after giving informed written consent. Participants received a delivered oxygen fraction of 0.60 with gas flow rates of 10, 20, 30, 40 and 50 l/minute in random order. FiO2, FEO2, FECO2 and airway pressures were measured. Calculation of FiO2 from FEO2 and FECO2 was later performed. Calculated FiO2 approached 0.60 as gas flow rates increased above 30 l/minute during nose breathing at rest. High peak inspiratory flow rates with exercise were associated with increased air entrainment. Hypopharyngeal pressure increased with increasing delivered gas flow rate. At 50 l/minute the system delivered a mean airway pressure of up to 7.1 cmH2O. We believe that the high gas flow rates delivered by this system enable an accurate inspired oxygen fraction to be delivered. The positive mean airway pressure created by the high flow increases the efficacy of this system and may serve as a bridge to formal positive pressure systems.

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Dissociation of mean airway pressure and lung volume during high-frequency oscillatory ventilation

Critical Care Medicine ◽

10.1097/00003246-198805000-00012 ◽

1988 ◽

Vol 16 (5) ◽

pp. 531-535 ◽

Cited By ~ 9

Author(s):

DAVID W. SMITH ◽

LORRY R. FRANKEL ◽

RONALD L. ARIAGNO

Keyword(s):

Lung Volume ◽

High Frequency ◽

Airway Pressure ◽

High Frequency Oscillatory Ventilation ◽

Mean Airway Pressure ◽

Oscillatory Ventilation ◽

High Frequency Oscillatory

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The effect of frequency and mean airway pressure on volume delivery during high-frequency oscillation

Pediatric Pulmonology ◽

10.1002/ppul.1950150310 ◽

1993 ◽

Vol 15 (3) ◽

pp. 183-186 ◽

Cited By ~ 22

Author(s):

V. Chan ◽

A. Greenough ◽

A. D. Milner

Keyword(s):

High Frequency ◽

Airway Pressure ◽

High Frequency Oscillation ◽

Mean Airway Pressure ◽

Frequency Oscillation

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Estimation of Mortality Risk in Chronically Ventilated Infants With Bronchopulmonary Dysplasia

PEDIATRICS ◽

10.1542/peds.88.6.1153 ◽

1991 ◽

Vol 88 (6) ◽

pp. 1153-1160 ◽

Cited By ~ 1

Author(s):

Debora W. Overstreet ◽

J. Craig Jackson ◽

Gerald van Belle ◽

William E. Truog

Keyword(s):

Mechanical Ventilation ◽

Bronchopulmonary Dysplasia ◽

Airway Pressure ◽

Life Support ◽

Water Pressure ◽

Accurate Estimation ◽

Regression Equations ◽

Bacterial Sepsis ◽

Mean Airway Pressure ◽

Predictors Of Mortality

Bronchopulmonary dysplasia is a chronic, sometimes fatal lung disease, which primarily affects premature infants and often leads to a dependence on mechanical ventilation lasting many months. To identify prognostic factors of mortality at 1 and 2 months of age, the authors reviewed the medical records of the 144 neonates admitted to two neonatal intensive care units in Seattle from January 1, 1986, through December 31, 1988, who required mechanical ventilation throughout the first month of life. Likely predictors of mortality were tested by logistic regression analysis. The calculated mean airway pressure at 30 days of age (MAP30) and the diagnosis of bacterial sepsis at any time during the first month of life (Bact0-30) were statistically significant predictors of mortality (P < .001 and P = .018, respectively) and had the lowest deviance in the regression model. The probability of mortality was estimated by 1/(1 + e-x, where x = -6.510 + 0.4588 (MAP30) + 1.475 (Bact0-30), and where MAP30 is expressed as centimeters of water pressure (1 cm H2O = 0.0978 kPa) and the presence or absence of bacteremia is 1 and 0, respectively. The records of the 57 infants who still required mechanical ventilation at 60 days of age were reanalyzed with clinical data available during the first 2 months of life. Mean airway pressure (MAP60) and the fraction of inspired oxygen (F60) at 60 days of age combined to form the best predictors of mortality, where x = -7.668 + 0.2940 (MAP60) + 5.935 (F60). The occurrence of bacterial sepsis during the first 2 months of life, the degree of hypochloremia, and the duration of chronic sedative use were also significant predictors of survival, even controlling of MAP60 and F60. These regression equations allow more accurate estimation of the likelihood of survival for chronically ventilated infants and may facilitate decisions regarding withdrawal or continuation of life support.

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Effect of the Ti/Te ratio on mean intratracheal pressure in high-frequency oscillatory ventilation

Journal of Applied Physiology ◽

10.1152/jappl.1998.84.5.1520 ◽

1998 ◽

Vol 84 (5) ◽

pp. 1520-1527 ◽

Cited By ~ 16

Author(s):

Ulrich Thome ◽

Frank Pohlandt

Keyword(s):

High Frequency ◽

Airway Pressure ◽

High Frequency Oscillatory Ventilation ◽

Inspiratory Time ◽

Mean Airway Pressure ◽

Air Trapping ◽

Oscillatory Ventilation ◽

Mean Pressure ◽

Oscillation Frequencies ◽

High Frequency Oscillatory

In high-frequency oscillatory ventilation (HFOV), an adequate mean airway pressure is crucial for successful ventilation and optimal gas exchange, but air trapping cannot be detected by the usual measurement at the y piece. Intratracheal pressures produced by the high-frequency oscillators HFV-Infantstar (IS), Babylog 8000 (BL), and the SensorMedics 3100A (SM) [the latter with either 30% (SM30) or 50% (SM50) inspiratory time] were investigated in four anesthetized tracheotomized female piglets that were 1 day old and weighed 1.6–1.9 kg (mean 1.76 kg). The endotracheal tube was repeatedly clamped while the piglets were ventilated with an oscillation frequency of 10 Hz, and the airway pressure distal of the clamp was recorded as a measure of average intrapulmonary pressure during oscillation. Clamping resulted in a significant decrease of mean airway pressure when the piglets were ventilated with SM30(−0.86 cmH2O), BL (−0.66 cmH2O), and IS (−0.71 cmH2O), but airway pressure increased by a mean of 0.76 cmH2O with SM50. Intratracheal pressure, when measured by a catheter pressure transducer at various oscillation frequencies, was lower than at the y piece by 0.4–0.9 cmH2O (SM30), 0.3–3 cmH2O (BL), and 1–4.7 cmH2O (IS) but was 0.4–0.7 cmH2O higher with SM50. We conclude that the inspiratory-to-expiratory time (Ti/Te) ratio influences the intratracheal and intrapulmonary pressures in HFOV and may sustain a mean pressure gradient between the y piece and the trachea. A Ti/Te ratio < 1:1 may be useful to avoid air trapping when HFOV is used.

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