Capnography & Ventilation Waveforms PDF

Capnography & Ventilation Waveforms Kathleen Minott, DNAP, CRNA Carbon dioxide analysis Capnometry – measurement of CO2 in a gas mixture Monitor correct placement of ETT or LMA and until airway is removed with a monitor It is standard of care for every patient receiving anesthesia, or moderate to de...

Capnography & Ventilation Waveforms Kathleen Minott, DNAP, CRNA Carbon dioxide analysis Capnometry – measurement of CO2 in a gas mixture Monitor correct placement of ETT or LMA and until airway is removed with a monitor It is standard of care for every patient receiving anesthesia, or moderate to deep sedation Used during MAC & sedation Can assess metabolism, circulation, ventilation Can detect airway obstruction, apnea, extubation, incompetent valves ETCO2 is usually 2-5 torr < PaCO2 Resistance Resistance – ratio of change in driving pressure to change in flow rate cm H2O/L/s Raw = (PIP-Pplat)/Flow Total airway resistance - peak – plateau pressure, normally 2-5 cm H2O May differ between inspiration & expiration Tube diameter, secretions, bronchoconstriction Spirometry Loops Graphic representation of the dynamic relationship of 2 variables during inspiration & exhalation Pressure & volume, flow & volume Kinked tubes, disconnects, migration of tube Lung disease ventilation problems PressureVolume Loop Volume on vertical axis, pressure on horizontal Slope = compliance More horizontal the loop, less compliant Flow-Volume Loop Volume on horizontal axis & flow on vertical axis TV is point where flow returns to zero Expiration is passive & reflects elastic recoil of lung, chest wall & resistance of bronchial tree & airway Volume Control Ventilation (VCV) Most common Preset TV delivered CRNA controls TV, RR, MV independent of patient Flow rate is constant during inspiration If too low, TV decreases If too high, TV reached before end of inspiration Inspiratory phase can be terminated before set TV delivered if peak airway pressure reaches high airway pressure limit 11 12 Pressure Control Ventilation (PCV) Pressure Control Ventilation (PCV) Used whenever goal is to avoid high airway pressure Provides ventilation at lower pressures than VCV E.g., obese patients, lung injuries, single-lung ventilation, presence of airway leak (e.g., uncuffed tube, SGA) Fixed I:E ratio ↑RR shortens inspiratory time and ↓Vt If machine allows adjustment of inspiratory flow: Good lung compliance = inspiratory flow should be high to ensure inspiratory pressure is rapidly attained Bad lung compliance = maximum inspiratory flow should be limited to avoid overshooting target pressure 14 15 Synchronized Intermittent Mandatory Ventilation (SIMV) Synchronizes ventilator-delivered breaths with patient’s spontaneous respirations When detecting inspiratory activity, ventilator adjusts mandatory breaths to achieve set RR In between mandatory breaths = spontaneous breathing/trigger time Trigger time – ventilator detects whether airway pressure has dropped a minimum amount (trigger limit) below the pressure measured at end of expiratory phase 16 Synchronized Intermittent Mandatory Ventilation (SIMV) Provider sets RR and Vt I:E ratio not required Helps transition from controlled to spontaneous ventilation Ensures minimum amount of ventilation without requiring manual ventilation ↓Incidence of patientventilator disharmony 17 Mandatory Minute Ventilation Method of mechanical ventilation Amount of ventilatory support automatically adjusted to reach set MV Ventilator monitors exhaled volume 18 Pressure Support Ventilation (PSV) 20 Pressure Support Ventilation (PSV) Because the pressure is reached early in inspiration and is maintained throughout inspiratory phase, pressure waveform has a square shape In pure PSV mode, patient can become apneic Usually have backup or apneic SIMV rate Provider sets trigger sensitivity and inspiratory pressure (usually from 5 to 10 cm H2O). Trigger sensitivity should be set so that it will respond to inspiratory effort without auto-cycling in response to artifactual changes in airway pressure 22 Pressure Support Ventilation (PSV) Vt determined by pressure support level, lung characteristics, and patient effort Desired Vt should be calculated and pressure support level adjusted so that the desired volume is delivered If exhaled volume is inadequate, the inspiratory pressure should be increased Useful in obese patients (↑ FRC), SGAs, Improves gas exchange and ventilation and lowers work of breathing during spontaneous breathing Can be used with MAC, inhalation induction, and ventilation for fiber-optic intubation 23 Pressure Support Ventilation (PSV) Advantages: synchrony between patient and ventilator Patient controls rate, volume, and inspiratory time Can compensate for leaks (to an extent) Peak/mean airway pressures are lower than VCV Asynchrony can occur with airflow obstruction (e.g., COPD) Disadvantages High inspiratory flow can cause patient discomfort Delivers variable MV – dangerous in patients with changing respiratory drive Inappropriately triggered by leak, patient movement, or cardiac contractions 24