Positive pressure mechanical ventilation mechanics

Modern positive-pressure mechanical ventilators have been quite successful in treating patients with pulmonary disorders. Two major categories of breath dehvery modes for these ventilators are mandatory and spontaneous. The volume- and pressure-controlled mandatory breath delivery and the governing control equations for these modes are presented in this chapter. Similarly, CPAP and support pressure modes of spontaneous breath dehvery are described. Recent development of dual control modes that allow simultaneous monitoring and control of airway pressure and minute volume are also presented. 

Positive pressure mechanical systems can be used to force air into an area diluting and venting any potential build-up of flammable vapours. Any area provided with a positive pressure mechanical system will also need to be provided with sufficient openings to release the atmosphere created. LEV systems are designed to capture airborne contaminants such as flammable vapours, filter them and ventilate outside a building to a place of safety in the open air. 

Positive pressure mechanical ventilation (PPMV) uses positive pressure tidal breaths to either totally or partially affect O2 and CO2 transport between the environment and the alveolar spaces. Positive pressure is also used to maintain alveolar patency during expiration. The desired effect of PPMV is to maintain appropriate levels of P02 and PCO2 in arterial blood while properly unloading the ventilatory muscles. Although a life-support technology, PPMV can also be harmful if used inappropriately. The discussion that follows, describes the principles of PPMV, its physiologic effects, the complications that can occur, and recent innovations. 

II. Positive Pressure Mechanical Ventilator Design Features... 

Discharge from the intensive care unit requires maintenance of the preceding parameters in the absence of ongoing IV infusion therapy, mechanical circulatory support, or positive-pressure ventilation. 

Noninvasive positive-pressure ventilation (NPPV) provides ventilatory support with oxygen and pressurized airflow using a face or nasal mask with a tight seal but without endotracheal intubation. In patients with acute respiratory failure due to COPD exacerbations, NPPV was associated with lower mortality, lower intubation rates, shorter hospital stays, and greater improvements in serum pH in 1 hour compared with usual care. Use of NPPV reduces the complications that often arise with invasive mechanical ventilation. NPPV is not appropriate for patients with altered mental status, severe acidosis, respiratory arrest, or cardiovascular instability. 

This graph can be used to explain a number of different aspects of compliance. The axes as shown are for spontaneous ventilation as the pressure is negative. The curve for compliance during mechanical ventilation looks the same but the x axis should be labelled with positive pressures. The largest curve should be drawn first to represent a vital capacity breath. 

Stack effect Flow of air resulting from warm air rising, creating a positive pressure area at the top of a building and a negative pressure area at the bottom. This effect can overpower the mechanical system and disrupt building ventilation and air circulation. 

How should hospitals increase their capacity to provide mechanical ventilation for a surge of patients with acute respiratory failure during a mass casualty event or influenza pandemic Rubinson and colleagues address this issue in a recently published article (Rubinson, Branson, Pesik, Talmor, 2006). Their report is based on an evaluation and assessment of a wide range of positive pressure ventilation (PPV) equipment, with the goal of determining the suitability of each device for mass casualty care. The article provides information useful for determining which types of PPV equipment would be the best choice for hospitals in need of a serviceable alternative to full feature ventilators, which will be in short supply and are too expensive for hospitals to stockpile. 

HFPPV High-frequency positive-pressure ventilation conventional mechanical ventilation at faster-than-usual rates. 

Positive-pressure ventilation (PPV) provides vital support to maintain adequate ventilation and oxygenation during the acute phase of RDS. Effective PPV is accomplished by generating a pressure that exceeds the closing pressure of the lung. Ventilation modes delivering this positive pressure are conventional mechanical ventilation (CV), high-frequency ventilation (HFV), patient proportional... 

Cazzolli PA, Oppenheimer EA. Home mechanical ventilation for amyotrophic lateral sclerosis nasal compared to tracheostomy-intermittent positive pressure ventilation. J Neurol Sci 1996 139(suppl) 123-128. 

Abbreviations-. Sp02, saturation of oxygen in arterial blood NIPPV, noninvasive intermittent positive pressure ventilation MAC, mechanically assisted cough CO2, carbon dioxide IPAP, inspiratory positive airway pressure BiPAP, bi-level positive airway pressure. 

Elliott MW, Mulvey DA, Moxham J, et al. Domiciliary nocturnal nasal intermittent positive pressure ventilation in COPD mechanisms underlying changes in arterial blood gas tensions. Eur Respir J 1991 4(9) 1044-1052. 

Cazzolli PA, Oppenheimer EA. Home mechanical ventilation for motor neuron disease (MND/ ALS) nasal compared to tracheostomy intermittent positive pressure ventilation (IPPV). Abstracts of Papers, 6th Intemational Symposium on ALS/MND, Dublin, Ireland, November 17-19, 1995. Moss AH, Oppenheimer EA, Casey P, et al. Patients with amyotrophic lateral sclerosis receiving long-term mechanical ventilation advance care planning and outcomes. Chest 1996 110 249-255. 

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