“Respiratory equipments” Supply Delivery Piping Regulation
Mechanisms of Filters Interception Inertial impaction Gravitational settling - large particles Diffusion - small particles Electrostatic attraction - charged particles Most-penetrating-particle size = 0.05-0.5 um “bacteria” - 1μm; “virus” - 0.02 μm
Types of filters Mechanical (e.g. glass fibres) High fibre density High resistance to airflow Electrostatic (e.g. polypropylene) Lower fibre density Lower resistance to airflow
Filters Dead space inevitable Resistance increases as dead space decreases Occlusion can occur with excessive sputum/water
“Respiratory equipments” Supply Delivery Piping Regulation H2O Heat
The dilemma Upper airway Ventilator circuit/storage Warm Humid Filtered To allow mucociliary elevator functioning Room temperature Humid Free To protect cylinders, pipes and valves
Relationship between the humidity and temperature of inspired gas and the function of the airway mucosa, CCM 1996
Solutions Passive (Heat Moisture Exchanger) Active (Humidifier) Circle breathing system
HMEs Transparent housing Rely on chemical to trap heat and moisture in exhaled gas (e.g. Calcium chloride) Variable and unadjustable performance
Active humidification Bottle humidifier Active heat and moisture exchanger Heated humidifier Nebulizer
Bottle humidifier Driven by airflow Gas blown over water surface - inefficient Gas blown through water - more efficient but increased resistance, water-bound infections Maximal level of humidity limited by ambient temperature
Heated humidifier Vapor provided by heated water reservoir Heated tubing to prevent condensation Temperature of reservoir and tubing adjustable to control humidity and temperature of inspired gas
Active HME
Nebulizers Gas powered Ultrasonic May be used for medication delivery
Which one better? VAP risk AARC Evidence-Based Clinical Practice Guidelines - Care of the ventilation circuit and its relation to VAP. Respiratory Care 2003
Which one better? Mechanical effects of Heat-moisture exchangers in ventilated patients. Critical Care 1999
“Respiratory equipments” Supply Delivery Patient Exhaust Suction Piping Regulation H2O Heat
Suction - behind wall Pump Pump Vacuum Tank Filter
Suction - Patient end Catheters Narrowest point at tip Smooth surface to avoid trauma Maybe designed as close system Collecting system Cut off overflow valve Foam prevention
“Respiratory equipments” Supply Monitor Delivery Patient Exhaust Suction Piping Regulation H2O Heat
Pulse oximetry
Pulse Oximetry Motion Tissue perfusion Venous pulsation/engorgement Ambient Light Intravascular dye Abnormal hemoglobin
Waveform Jubran, Critical Care 1996
Oxygen Toxicity Retrolental fibroplasias in premature babies Acute lung injury, ?related to oxygen free radical production Absorption atelectasis high FiO2 may cause increased peripheral vascular resistance in congestive heart failure CO2 narcosis in chronic lung disease
Capnograph Graphical display of expired CO2 concentration (y) against time (x) IR spectrometry Affected by Pulmonary blood flow (cardiac output) pCO2 (metabolism) Alveolar ventilation
Clinical use Confirmation of artificial airway placement Early detection of disconnection/kinking within breathing circuit Estimate adequacy of ventilation Specific patterns in different pathologies
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