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Blood pressure measurement 22/01/2019 (Arterial Blood Pressure…

- - - - If it is applied too tightly, the pressure measurements will be erroneously low since the cuff itself, acting as a tourniquet, will partially occlude the underlying artery.
      - If the cuff is too loose, the pressure measurements will be erroneously high since excessive cuff pressure will be required to occlude the underlying artery.
      - The cuff is inflated and the artery is occluded, the cuff is then lowered in pressure, the flow returns [intermittently. the cuff pressure is lowered slowly. Small positive deflections of the cuff pressure may be observed each time the pulse wave hits the cuff
      - The oscillometer analyzes the fluctuations of pressure within the cuff as it is slowly deflated.
      - Small vessel size (due either to small vessel size or to vasoconstriction) and motion can interfere with measurements.
  - - - The dorsal metatarsal, radial/carpal, coccygeal, lingual, femoral, and auricular arteries are commonly used in dogs and cats
      - , the facial and metatarsal arteries in horses,
      - auricular arteries in ruminants and swine.
      - Feline issues
        
        Cats have a few unique problems: (1) their arteries are small for percutaneous catheterization and some expertise is required; (2) arteries soon constrict with cut‐down manipulation; and (3) collateral circulation is sparse;
        
        Ischaemia is an issue and necrosis can occur
      - arterial catheter can also be attached to a
        commercial transducer and physiograph.
        
        Transducer needs to be zeroed periodically, placed at the level of the right atrium of the heart
        
        Tubing from the transducer to the arterial catheter must be rigid, non flexible
        
        Generally, smaller catheters, longer and more compliant tubing, and blood clots or air bubbles overdamp a signal.
        
        If over damping is occurring, systolic will be lower and diastolic will be higher. mean will be normal
        
        If over damping occurs, check for leaks, air in the tubes, kinks, clots, IF not fixed switch to shorter tubing and less compliant tubing
        
        under damping also occurs, the signal will be peaked and higher systolic than expected
        
        Transducers
        
        the liquid in the infusion tubing is in contact with a diaphragm that moves in response to the transmitted pressure wave form
        
        analogue movement is converted to an electrical signal by a transducer
        
        Strain gauges use the principle that resistance of a wire
        increases with increasing length and visa versa.
        
        The diaphragm of the transducer moves a small plate that is connected to four strain gauges.
        
        The transducer needs to be kept horizontally level with the
        patient; traditionally, the right atrium.
        
        A 10 cm change in height will alter the pressure reading by 7.5 mm Hg.
        
        resonance
        
        The specific cannulae and infusion tubing used in invasive
        arterial pressure monitoring are designed to keep its natural frequency above 40 Hz,
- - - - Primarily determined by stroke volume and arterial system complicane