1. Ventilator Management James Eakins, MD FACS Director, Trauma and Surgical Critical Care Hahnemann University Hospital

2. Overview Ventilation vs. Oxygenation Arterial blood gas analysis Modes of ventilation Methods of weaning Airway pressures ARDS Exotic ventilator modes

3. Ventilation / Oxygenation Ventilation is the process by which air enters the lungs Oxygenation is the process by which oxygen diffuses from inspired air into the blood Ventilation and Oxygenation occur, and should be looked at, independently

4. Ventilation Minute ventilation, abbreviated Ve, is the volume of air that is moved in and out of the lungs in one minute Ve = Respiratory Rate x Tidal Volume (Vt) Assessed by looking at the pCO2 on an arterial blood gas Normal pCO2 is 40

5. Oxygenation Assessed by looking at the pO2 and the oxygen saturation Most oxygen is carried bound to hemoglobin, so the saturation is more important (though they are related via the oxygen-hemoglobin dissociation curve) FiO2 and PEEP contribute to oxygenation

6. Blood gas analysis Blood gas components –pH – Normal 7.40 –pCO2 – Normal 40 –pO2 –Bicarbonate (calculated) – Normal 24 More accurate from Chem-7 –Base excess – Normal +3 to -3 –Oxygen saturation (usually calculated) pH and pCO2 important for assessing ventilation pO2 and saturation (measured or pulse-ox) important for evaluation of oxygenation

7. Blood Gas analysis pH of blood is a balance of acids and bases –Hydrogen ion –Bicarbonate –CO2 –Other acids –Assorted buffers Acidosis vs. Alkalosis is determined by the pH

8. Metabolic acidosis Excess accumulation of any acid pH less than 7.4 Patient will try to compensate by blowing off extra CO2, so pCO2 on ABG will be decreased Example: 7.31 / 27 / 105 Compensation is never complete Need to find and correct the cause of the acidosis

9. Metabolic alkalosis pH greater than 7.4 Accumulation of some base in the blood Body will attempt to compensate by allowing the pCO2 to rise above 40 Example: 7.50 / 48 / 109

10. Respiratory Acidosis pH less than 7.4 Accumulation of CO2 due to inadequate ventilation For some reason patient is not breathing enough Need more minute ventilation –Respiratory rate –Tidal Volume

11. Respiratory alkalosis pH greater than 7.4 Patient with too much minute ventilation, therefore pCO2 is below normal Why? –Pain –Anxiety –Hypoxia –Head injured –Iatrogenic Example: 7.52 / 25 / 99

12. Practice 7.25 / 60 / 105 Respiratory acidosis 7.49 / 48 / 99 Metabolic alkalosis 7.22 / 27 / 88 Metabolic acidosis 7.52 / 51 / 101 Metabolic alkalosis 7.55 / 25 / 99 Respiratory alkalosis

13. Ventilator Terms Tidal Volume Respiratory Rate –Set –Spontaneous FiO2 PEEP: Positive end expiratory pressure Minute Ventilation (Ve) Pressure Support

14. Ventilator Modes Volume Control (aka assist control) SIMV Pressure Control Pressure Regulated Volume Control (aka VC+, aka autoflow)

15. Volume Control Set rate, tidal volume, FiO2, and PEEP Machine will deliver the tidal volume you set at the rate you set If the patient attempts to take additional breaths, machine will sense it and deliver a full tidal volume

16. SIMV Synchronized intermittent mandatory ventilation Set the same parameters as VC Difference is that if patient initiates a breath the machine does not help them The machine will give pressure support on spontaneous breaths to offset resistance to flow through ventilator circuit Synchronized because vent will not deliver a full breath while patient is taking a spontaneous breath

17. Pressure Control Developed to limit airway pressures in patients with stiff lungs Set FiO2, PEEP, rate, and peak inspiratory pressure With each breath the ventilator will deliver as much tidal volume as it can without exceeding peak pressure

18. Pressure regulated volume control Similar to volume control Only difference is that ventilator automatically adjusts flow rate to keep peak airway pressure as low as possible

19. Plateau Pressure The airway pressure after the entire tidal volume is in the lungs –No flow –Before exhalation A function of the tidal volume and the stiffness of the lung, aka static compliance

20. Peak inspiratory pressure Occurs during inspiration Dependent on the factors that determine plateau pressure Also dependent of flow rate and resistance to flow in the airway (dynamic compliance)

22. 42 year old male, multiple rib fractures Settings: –VC –Rate 18 –Vt 400 cc –FiO2 60% –Peep 10 ABG: pH 7.25, pCO2 60, pO2 122, Sat 99% Vent Changes?

23. 75 year old female, stuck on vent after total abdominal colectomy for LGI bleed Settings –VC rate 14 –Vt 350 cc –FiO2 80% –Peep 12 ABG: pH 7.50, pCO2 28, pO2 55, Sat 87% Vent Changes?

24. ARDS Originally named shock lung, or “DaNang” lung Multiple definitions Multiple causitive factors Heterogeneous disease process Alveolar wall thickens and becomes fibrotic –Decreased gas exchange –Stiff lung (poor compliance)

25. ARDS Generally need PEEP to keep alveoli open ARDSnet study showed better survival using higher peeps and lower tidal volumes or 4 – 6 cc/kg

26. Morbidity of mechanical ventilation Barotrauma Volutrauma Oxygen toxicity Opening and closing of alveoli

27. Methods of weaning First, make sure oxygenation is adequate Three main approaches –Daily spontaneous breathing trial –SIMV plus pressure support –Pressure support wean Generally equivalent if applied aggressively

28. Fancy modes Airway pressure release ventilation (APRV), also known as bi-level High frequency oscillatory ventilation Both are forms of “open lung ventilation,”