Effects of Three Types of Mechanical Ventilations

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Name: Janet Pierce

Rank: LCDR, USNR

Organization: University of Kansas Medical Center

Performance Site: University of Kansas Medical Center, Kansas City, KS

Year Published: 1995

Abstract Status: Final

Abstract

This study was designed to provide information on the physiological effects of three control modes of mechanical ventilation. A miniaturized ultrasound sensor was used to determine the effects of different ventilation modes on diaphragm contractility in rats. To date there has been no direct means of measuring diaphragm contractility in patients experiencing respiratory failure and requiring mechanical ventilation. The ability to make such a direct measurement would help caregivers determine if the patient's respiratory muscles can meet the ventilatory demand. The specific aims of this study were to (1) investigate the differences in diaphragm shortening using three different types of mechanical ventilation: pressure regulated volume control (PRVC), volume control (VC), and pressure control (PC); and (2) examine the differences in cardiovascular and respiratory parameters during and following PRVC, VC, and PC modes of mechanical ventilation. The study sample consisted of 16 Sprague-Dawley rats with normal lung function, randomly assigned to receive PRVC, VC, or PC. Each rat was sequentially ventilated with PRVC, VC, or PC, the sequence based on a pre-randomized table. Each mode of ventilation was applied to the rat for approximately 14 minutes. Within each mode, the tidal volume was increased from 3 ml to 12 ml in increments of 3 ml. Waveform measurements of blood pressure (BP), central venous pressure (CVP), diaphragm thickening (DT), intrathoracic pressure (ITP), endtidal C02 and peak inspiratory pressure (PIP) were taken throughout the experiment via the CODAS computer data acquisition software package. The difference between EIP and EEP defined as delta intrathoracic pressure (ITP), is directly proportional to the extent of diaphragm shortening (DS) plus shortening of other inspiratory muscles.As the tidal volumes in all three control modes of mechanical ventilation were increased by 3 ml, the delta ITP increased. However, there were no significant differences in delta ITPs observed among PC, VC, or PRV, implying that in a normal lung all three modes exert the same amount of pressure in the thoracic cavity. There were no differences observed in PIP among the modes at all tidal volumes which suggests that compliances and airway resistances are the same for the three modes. However, it was observed that DS for PRVC at tidal volumes of 9 and 12 ml was significantly less than that for VC and P at the same tidal volumes. It was suggested that these significant differences in DS may be related to the differences in the resting length of the diaphragm. The values for MAP, CVP, CO, SVR and PetCO2 were found to be comparable for each control mode of mechanical ventilation. Although delta ITPs were not significantly different, at 3 ml and 12 ml EEP for PRVC was higher than that for VC and PC and at 12 ml DS was significantly lower during PRVC as compared with PC.The investigators suggest that the observation that passive DS was less during PRVC than VC or PC ventilation merits further study. Positive and expiratory pressure (PEEP) could be used to compare the magnitude of DS for the three modes at equal EEPs and tidal volumes. This would enable one to determine if the difference in DS among the VC, PC, and PRVC ventilation were due to differences in resting (end expiratory) diaphragm music length. If this was not found to be the case, it would suggest that PRVC affects the expansion of the chest differently than VC or PC. In the future, the investigators also plan to test a Percutaneous procedure for placement of the ultrasonic sensor device to avoid the abdominal incision currently in use for attachment of the device to the anterior surface of the diaphragm.This study provides valuable data on three control modes of ventilation that could be used in combat zone hospitals as well as stateside military facilities. The data can serve to alert clinicians to the cardiopulmonary effects of control modes and their effect on a diaphragm performance. Since diaphragm fatigue can result in ventilatory heart failure, early detection of diaphragm fatigue is essential to improving nursing care. All three control modes are available on the new Siemens Servo Ventilator 300. With its compact design and advanced technology, this ventilator may prove to be the ventilator of choice for the military and in particular for trauma patients. This study provides clinicians with a better understanding of the benefits and complications that may be associated with the three modes of ventilation and provides new information on PRVC, the newest mode of ventilation.

 

Final report is available on NTRL at: https://ntrl.ntis.gov/NTRL/dashboard/searchResults/titleDetail/PB2009107904.xhtml