Ventilators Overview

1. General Ventilation

Noninvasive

• CPAP
  • Analogous to PEEP on ventilator
  • keeps from exhaling all the way out, to a certain pressure BiPAP
  • Bi-level: set TWO levels of airway pressure
  • Inhalation (pushes extra amount in) and Exhalation (keeps from collapse)
• Indications:
  • COPD or Neurmuscular Dz pt’s who need ICU but not intubation right this minute
  • PNA in bone marrow transplant unit; 99% mortaility when intunated
  • Significant pulmonary edema

Invasive

• ET Intubation; Indications:
  • #1 – “THE LOOK”
  • “VOPS” mnemonic
    • Ventilation, Oxygenation, Protection [of airway], Secretions

2. Modes of Ventilation

Volume Control (*Preferred Type)

• Assist Control/Volume Control (“AC/VC”)
  • Set RR and TV; pt gets breath by dropping airway pressure ~2cmH20 -> triggers machine and gives breath of set volume
  • Good default start setting because it accomplishes goal of RESTING PT

• Intermittent Mandatory Ventilation (“SIMV”)
  • Set RR and TV; pt can take extra breath and machine does nothing (you see big IMV breaths and little pt breaths)
  • Not ideal deafult because might not achieve goal of resting pt’s respiratory muscles

Pressure Control

• Assist Control/Pressure Control (“AC/PC”)
  • Set RR, PIP, Insp Time; every set amount of time (RR) it will push set amount of pressure in (PIP) and then holds it in (Insp Time)
  • Good for ARDS, refractory hypoxemia (hold it in to try to help gas exchange), refractory hypoxemia, pt comfort (more physiologic). Can switch to this setting

• Pressure Support (“PS”)
  • ONLY set a pressure (PIP = Peak Insp Press); machine does nothing until pt wants a breath and drops airway pressure (2mmHg). More physiologic
  • Comfortable and no barotrauma BUT no back up rate

3. ONCE INTUBATED

Check CXR

• Ensure ET tube location
  • Want the tip just above carina
  • Right mainstem -> barotrauma

Check Blood Pressure

• Hypertensive: inadequate sedation; Fentanyl and then Propofol drip if needed
• Hypotensive: Intubation creates positive intrathoracic pressure -> impedes venous return
• SOME hypotension expected post-intubation -> give 500cc fluid -> if not work consider pressors

Establish Settings

• MODE: AC/VC, RR: 12, TV: 6cc/kg of ideal BW, PEEP: 5cm H20, Fi02: 100%
• Try to get FiO2 <60% ASAP using pulse ox as guide; drop Fi02 q5min O2 stays OK, then check ABG once adequately titrated down

Monitor Resistance and Compliance

• Resistance: Peak Pr – Plateau/Flow
  • Secretions, biting tube, bronchospasm, kink
  • Check kink, suction, biting block, bronchodilators
• Compliance: Vol/Pr = TV[cc]/(P[plateau]-PEEP)
  • Right mainstem, tension PNTX, hemothorax, abdominal pathology (perforation)

4. WEANING

Ask 5 Questions every day

1. Is the cause resolved or gone?
2. No pressor requirement?
3. Require >40% FiO2 + 5 PEEP
4. CNS function OK?
5. No impending doom – does nurse say “are you crazy?!” when you bring up idea of extubating pt?

Check Weaning Parameters

• Rapid Shallow Breathing Index (RSBI)
  • freq (RR)/TV (L) < 104 = weaning success
  • Best predictor of weaning success
• Negative Inspiratory Force (NIF)
  • nml = -60cmH20; weak = 0 to -20cmH20
  • Best predictor of weaning failure

Weaning Trial

• Keep intubated but turn down ventilator support
  • SIMV (5d to extubation)
    • Gradually decreasing RR or “backup rate”
  • Pressure Support (4d to extubation)
    • Switch from whatever they were on to Press Support
    • Gradually decrease PIP
  • *Spontaneous Breathing Trial/”T-Piece” (3d)
    • Vent off, T-piece allows oxygenation to be delivered but no other support (30min=Extbt)

5. SCENARIO: ARDS

ARDS Criteria:

1. Acute (<1wk)
2. p/F ratio <300 (PaO2/FiO2)… <200 = mod, <100 = severe
3. CXR with diffuse opacities (“bilateral”, “3/4 quadrants”)
4. NOT 2/2 heart failure or fluid overload = CLINICAL assessment

TREATMENT OPTIONS for Hypoxia of ARDS:

1. Tx the cause of the ARDS (#1 = Sepsis; #2 = PNA; #3 = Aspiration)
2. Increase FiO2 (Shunt pathology will not respond to FiO2)
   • PvO2 = 40mmHg, PaO2 = 100mmHg -> leaky capillaries -> O2 leaks out
   • “v” and “a” even out
   • Don’t leave at toxic FiO2 levels if it’s not helping!
3. Diurese the pt: less fluid leaking into alveoli if less fluid in capillaries
4. Increase PEEP: pushes edema out into interstitium -> better gas exchange
   • Go down on PEEP very slowly
5. Optimize mixed venous PO2… AKA decrease VO2 (consumed O2)
   1. Sedate to decrease skeletal o2 consumption;
   2. Tx fevers;
   3. Consider paralytics;
   4. Increase O2 Delivery (Dobutamine to increase forward flow or transfuse)
6. Consider PRONE positioning
   • Mortality benefit!
   • Gravity will send blood flow to less involved lung areas
7. Consider ECMO
   • Re-oxygenate blood outside of body

6. SCENARIO: COVID-19

Still evolving, but preliminary evidence is showing two main scenarios:

1. COVID-19 infection leading to ARDS or superimposed bacterial infection – 30-40%
   • Use standard ventilator indications and protocols
   • Treat like ARDS
2. COVID-19 infection with low O2 saturation but no significant respiratory distress -
   • Pt’s do not have the typical air hunger/respiratory distress/”the look”
   • CT and XR imaging shows fairly healthy lung without consolidation/atelectasis/edema
   • Theorize that the virus disrupts hypoxic pulmonary vasoconstriction mechanism -> unable to divert de-oxygenated blood away from lung tissue not providing any gas exchange -> blood flows to damaged lung tissue

TREATMENT OPTIONS

Follow physiology; the “art of medicine”, not just protocols

• 1st consider JUST high flow O2
• 2nd consider high FiO2 on low pressure Vent setting
  • Barotrauma has become large problem with these pt’s
  • Track resistance and compliance closely
• Pressure control may have a larger role here