Basic Terms and Concepts of Mechanical Ventilation Flashcards
-Normal Mechanics of Spontaneous Ventilation
-Ventilation and respiration
-Spontaneous Ventilation -The movement of air into and out of the lungs
-Respiration
-The exchange of oxygen and carbon dioxide between and organism and its environment
-Two components -External respiration- Involves the diffusion of oxygen and carbon dioxide between the alveoli the pulmonary capillaries -Internal respiration- involves the exchange of oxygen and carbon dioxide between the systemic capillaries and the cells of the body
-Gas flows and pressure gradient during ventilation
-Gas flow and pressure gradient
-For air to flow, a pressure gradient must exist -Lung volumes change as a result of gas flow into and out of the airways -This is caused by changes in the pressure gradient between the airways openings and the alveoli
-Spontaneous inspiration and expiration
-Inspiration
-Contraction of the inspiratory muscles
-Decrease ( more negative) in the intrapleural and alveolar pressure
-Alveolar pressure becomes less that the pressure at the airway opening and gas flows into the lungs
-Spontaneous inspiration and expiration
-Expiration
-Relaxation of the inspiratory muscles causes in the decrease in the thoracic volume
-Increase in the alveolar pressure -Gas flows out
-Key terms:
-Airway opening pressure
-Mouth pressure -Airway pressure -Upper-airway pressure -Mask Pressure -Proximal airway pressure
-Is zero or atmospheric pressure
-Unless pressure is applied at the airway opening
-Key terms:
pressures
-Intrapleural pressure- The pressure in the potential space between the parietal and visceral pleura
-Alveolar pressure- Is also called intrapulmonary pressure or lungs pressure -Transairway pressure- pressure between the airway opening and the alveolus -Transthoracic pressure- Pressure between the alveolar space or lung and the body's surface -Transpulmonary pressure- pressure difference between the alveolar space and the pleural space -transrespiratory pressure-pressure difference between the airway opening and the body surface
Types of Mechanical Ventilation
-In developing ways to mimic or replace the normal mechanism of breathing, three basic methods have been developed. These are:
-Negative pressure ventilation -Positive pressure ventilation -High frequency ventilation
Negative Pressure Ventilation
-Attempts to mimic the actual function of respiratory measles to allow breathing through normal physiological mechanisms
-Examples of a negative pressure ventilator is the iron lung -Individuals head is exposed to ambient pressure while their thoracic area or entire body in encased in a airtight chamber that is subjected to negative pressure -The negative pressure is generated throughout the thoracic area and transmitted across the chest wall into the intrapleural space and finally into the intra alveolar space
Negative Pressure Ventilation Iron Lung
-The intra-alveolar space becomes increasingly negative in relation to the pressure at the mouth
-This pressure gradient results in air moving into the lungs -In this way, the negative pressure ventilator resemble normal lung mechanics -Expiration occurs when the negative pressure around the chest wall is removed and the normal elastic coil of the lungs allow air to flow out passively -The negative pressure ventilator decline considerably during the 1970s and early 1980s and is rarely used to hospitals, current use is mostly for care of pts in the home
Positive Pressure Ventilation
-Occurs when the mechanical ventilator literally blow air into the patients lungs by way of an endotracheal tube or mask
-At any point during inspiration, the inflating pressure at the upper airway will equal the sum of the pressures requiring to overcome the elastic resistance of the lung and chest wall and the resistance of the airway -The pressure in the alveolus progressively builds and becomes more positive -The intrapleural space may become more positive at the end of inspiration -At the end of inspiration, the vent stops delivering positive pressure -Mouth pressure returns to ambient (zero) -This creates a gradient between the mouth and the alveolus, and air flows out
-High Frequency Ventilation
Is the use of high ventilating rates, which are above normal, with low ventilating volumes, which are below normal
-There are 3 basic modes of high-frequency ventilation
-High frequency positive pressure ventilation (HFPPV)
-HF jet Ventilation (HFJV)
-HF oscillation (HFO)
-HFPPV uses respiratory rates between about 60-100 bpm
-HFJV uses RR between about 100-400, up to 600 BPM
-HFO uses rates into the thousands, up to about 4000 breaths/ min
-High frequency ventilation has been used primarily in infants with respiratory distress and in adults or infants with open air leaks such as bronchopleural fistulas
-Reading of Pressures in positive Pressure Ventilation
-At any point in breath cycle during mechanical ventilation, the clinician can check the manometer, or pressure gauge of a ventilator for reading of the pressure present at that moment
-This reading is measured either very close to the mouth (proximal airway pressure) or on the inside of the ventilator, where to closely estimates pressure at the mouth -There are various pressure points used i the monitoring of patients -To describe modes of ventilation -To calculate a variety of parameters -To monitor PTs receiving mechanical ventilation
-Baseline Pressure
-Pressures are read from a baseline value
-The baseline pressure is usually zero (Or atmospheric) which indicates that no additional pressure is applied at the airway opening during expiration and before inspiration
Positive end-expiratory pressure, or PEEP
-Sometimes the baseline pressure is higher than zero, such as when the vent operator selects a higher pressure to be present during exhalation
-When PEEP is set, the vent prevents the PT from exhaling to zero, (atmospheric pressure)
-PEEP increases the volume of gas left in the lungs at the end of a normal exhalation, that is … PEEP increases the functional residual capacity (FRC) , it is an oxygenation tool that will be discussed in detail later
auto PEEP or intrinsic PEEP
-PEEP that is applied by the operator is called extrinsic PEEP
-Air that is accidentally trapped in the lung ( a complication of positive pressure ventilation) Is called auto PEEP or intrinsic PEEP -This usually occurs when a PT does not have enough time to exhale before the vent delivers another breath
Peak Pressure
-During Positive Pressure ventilation, the manometer rises progressively to a peak pressure
-This is the highest pressure recorded at the end of inspiration -Also called Ppeak or peak inspiratory pressure (PIP)
Plateau Pressure
effect of the elastic recoil
-However the relaxation of the respiratory muscles are elastic recoil of the lung tissues are exerting force on the inflated lungs
-This creates a positive pressure and reads on a manometer as a positive pressure -Because it occurs during a breath hold, or pause, the reading is stable it “plateaus” at a certain value -The Plateau pressure reflects the effect of the elastic recoil on the gas volume inside the alveoli
