| Effects of Mutual Changes of Tidal Volume and Respiratory Rates on Peak Airway Pressure, Compliance and Resistance during Positive-pressure Mechanical Ventilation. |
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Jung Won Hwang, Jae Hyon Bahk, Yong Seok Oh |
1Department of Anesthesiology, College of Medicine, Seoul National University, Seoul, Korea.
2Department of Anesthesiology, Samsung Medical Center Seoul, Korea. |
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| Abstract |
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Since the advent of positive-pressure mechanical ventilator in respiratory support, barotrauma has become a feared complication. Elevated peak airway pressure is one of the risk factors of barotrauma, so it has been tried how to change ventilator setting to minimize airway pressure. One method is to decrease tidal volume and increase respiratory rates. Therefore we studied changes of airway pressure, compliance and resistance of the total respiratory system according to change tidal volume and respiratory rates. We selected 23 patients over the age of 15 and with no respiratory problem. And we excluded patients received thoracic and abdomen surgery because airway pressure might be changed by surgical manipulation. The patients without premedication were ventilated during 5 minutes with 50% oxygen, N2O and isoflurane(1.0 vo1%) by closed circuit ventilator(Physio-Flex(TM)) after slow intravenous injection of thiopental sodium, fentanyl and vecuronium. Then we intubated with I.D. 8 mm sized endotracheal tube for men and with I.D. 7 mm for women. Minute ventilation(100 ml/kg), concentration of isoflurane(1.0 vo1%), gas flow rate and I:E ratio(1:2) were maintained constantly during controlled ventilation and we increased respiratory rates stepwise by 2 bpm from 8 to 24 bpm and decreased tidal volume to maintain minute ventilation. At 10 minutes after change of ventilator setting, we checked peak airway pressure, plateau airway pressure, arterial and end-tidal CO2 tension. And then we calculated compliance and resistance of the total respiratory system. Peak airway pressure and compliance decreased according to decreasing tidal volume and increasing respiratory rates, but arterial CO2 tension and resistance were not changed. We concluded that METHOD of decreasing tidal volume and increasing respiratory rates decrease peak airway pressure and keep minute ventilation to prevent hypercarbia. |
| Key Words:
Ventilation; Mechanical; Ttidal volume; Rate; Airway pressure; Lung; Resistance; Compliance |
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