Pulmonology 6

zwinthrop's version from 2015-04-16 02:56

Vent Lab

Question Answer
Complaincea measure of the eleasticity or stretchability of the lung tissue→ the higher the compliance, the more easily the lung is streched
Functional Residual Capacity (FRC)The volume of air left in the lungs at the end of a normal exhalation→ the residual air prevents alveolar collapse. This residual air is caused by negative pressure in the pleural cavity, thus preventing the lungs from collapsing completely on exhalation The FRC is large (2-2.5 L) compared to a normal tidal volume (0.5 L).
Peak PressureThe maximum pressure generated by inhalation→ 2 factors determine peak pressure: (1) resistance of the airways and (2) complianc of the lungs.
Plateau Pressurethe pressure generated during an artifical pause in mechanical ventilatory cycle After a tidal volume has been delivered, the ventilator pauses, closing the valves and forcing the patient to “hold their breath” for a short time before allowing exhalation→ it is measured as the air in the lungs stands still→ nullifying any resistance the airways may provide. Generated solely by the compliance of the lung tissue as it tires to recoil after being inflated→ this is an artifact seen in mechanical ventilation but not spontaneous respiration.
GradientThe peak pressure minus the plateau pressure→ by observing the difference between the plateau pressure (due to lung compliance) and the peak pressure (a mizture of airway resistance and lung compliance) the gradient gives an idea of the airway pressure. A small gradient always signifies a small (low) airway resistance
Minute VentilationThe volume of air (in liters) inhaled in one minute→ directly connected to CO2 exchanged in the lungs in an inverse fashion. The higher the minute ventilation the lower the CO2. Thus, the minute ventilation directly influences the blood CO2 levels and pH balance → it is measured based on the patient’s blood O2 and CO2 levels. Can change the respiratory rate or the tidal volume to deliver the appropriate breath ventilation
Positive End-Expiratory Pressure (PEEP)During spontaneous breathing, end-expiratory pressure returns to a baseline of 0, relative to atmospheric pressure. In certain diseases there is a tendency for the alveoli to collapse (ex: ARDS, surfactant disrupions). In order to prevent alveolar collapse, the ventilator is set so that exhalation is ended while there is still a small residual (positive) pressure in the lungs. PEEP can range from 2-5 (mild) to 15 for more severe problems.
Resistancethe pressure generated by the airway as the air attempts to flow through it.
Increased resistanceex: anaphylaxis, the peak pressure is higher sue to increased resistance but plataue pressure is normal→ increased gradient
Decreased complianceex; fibrosis, pulm edema (ARDs, pulm HTN), resist all stages of inhalation, will have the same overall shape because all phases of inhalation are affected similarly→ but the peak and plataue pressures will increase as seen in the diagram
Increased compliance ex:emphysema, Normal gradient because both peak and plautaue pressures are reduced by similar amounts→ can lead to rise in FRC
**physiological ventilation patterns are altered during machine ventilation, causing a V/Q mismatch and necessitating a higher minute ventilationDue to gravity there is a gradient of blood flow through the zones of the lung, with the bottom zone having more perfusion. During spontaneous breathing there is a gradient of air flow through the zones, with more ventilation occurring in the lower zone. This creates an ideal ventilation / perfusion match. When on a ventilator all zones of the lungs receive equal ventilation, even though the perfusion gradient is unchanged. This causes a mismatch and necessitates a higher minute ventilation in order to provide sufficient air to the perfused zones at the bottom. “Top” and “bottom” do not correlate to “cranial” and “caudal”. This mechanism is based on gravity and is unrelated to whether the patient is standing or lying down.
**Narrowing down the location of the problemUse oxygen saturation to help to determine where the problem lies. If the saturation falls, then parenchymal problems should be at the top of the problem list. If there is no drop in saturation, then the parenchyma is working fine, and the problem is most likely in the airway itself

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