VENTILATION


CAPNOGRAPHY


CO2 identified in expired gas by spectrographic properties (using IR, Raman, or mass spectroscopy)



Hazards of Capnography:


•  Old in-line IR detectors can heat up, causing facial thermal injury


•  May fail to detect disconnection if machine disabled by secretions, or alarms disabled


CAPNOGRAPHS


Figure 8-2. Normal capnograph (normal expired CO2 waveform).




Figure 8-3. Normal and abnormal flow volume loops.



MECHANICAL VENTILATION: PROTECTIVE STRATEGIES


Current Strategies to Prevent Volutrauma, Barotrauma, Atelectrauma, Tracheal Ischemia & O2 Toxicity


•  Alveolar overdistention (volutrauma), rather than excessively ↑ airway pressure (barotrauma), may be more injurious to lung


•  Smaller tidal volumes (6 mL/kg) are recommended with greater respiratory rate


•  Higher PaCO2 levels allowed (permissive hypercapnia) in treating acute lung injury & ARDS


Specific Settings


•  TV 6 mL/kg (prevents volutrauma: trauma from overdistention of alveoli)


•  Plateau pressure <30 cm H2O (prevents barotrauma: trauma from excessive press.)


•  PEEP >6–10 cm H2O (prevents atelectatic trauma: repeated alveolar closure at end-expiration)


•  FiO2 <50% to prevent O2 toxicity






BIPAP VS. CPAP


•  CPAP = delivery of continuous positive air pressure throughout respiratory cycle


•  BiPAP = two levels of positive air pressure, inspiratory (triggered by insp effort) & expiratory (present throughout the rest of the respiratory cycle) (expiratory pressure is lower to facilitate exhalation)


DISCONTINUING MECHANICAL VENTILATION


SIMV Plus PS is a Common Weaning Mode in Many ICUs


•  Start with full support (IMV ≈ 10), plus PS 10–15 cm H2O, PEEP 5–10


•  Decrease by 1–2 breaths per minute till IMV = 0


•  Now wean PS 1–2 cm H2O at a time until PS/PEEP is 10/5 or 5/5 cm H2O or lower (for more deconditioned pts, you may need to go as low as PS/PEEP = 2/5)


•  At the same time gradually reduce FiO2 according to SaO2 or PaO2 (more sensitive to oxygenation changes)



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Aug 28, 2016 | Posted by in ANESTHESIA | Comments Off on VENTILATION

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