The Vent

Conference Lecture
10/7/2015
The Vent

Synopsis: A hands on, informal lecture given on vents and their alarms by Dr. Tom Perera

• You have to know the two types of ventilation out there used in the ER:
  • Volume A/C
  • Pressure A/C
    • This is wonderful theoretically, but as an emergency medicine physician you rarely use pressure A/C in the ER; these are “extreme” patients:
      • Failed volume A/C
      • Peak pressures are too high
      • Difficult asthmatics who are not doing well on volume A/C

• Volume Assist Control
  • Volume based ventilation where you set a baseline breath volume
  • If the patient wants to take a bigger breath, the ventilator will not let them; keep patients on this setting more sedated than not
  • Basic settings for airway protection (i.e. no underlying lung disease)
    • Respiratory rate: Calculate the minute ventilation you want the patient to get
      • The great thing: The vents can be set to do all the calculations for you (i.e. no math)
      • You’ll likely start at 12-14 bpm
    • Volume: Most patients start at 450mL-500mL
      • 6-7mL/kg of ideal body weight (calculated based on height)
    • FiO2: Start at 100% — “crank it all the way up”
      • As an ER doc, you’re not going to affect a patient’s COPD by giving them 100% oxygen on a vent, because they’re on a vent
      • Intubating somebody is a traumatic procedure and leads to hypoxia
      • Start at 100%, titrate down
      • If no lung damage, no trouble intubating; you can start at 40%
    • PEEP: Start at 5, which is about physiologic
      • What is PEEP? For most cases, PEEP is a good thing
      • PEEP keeps a non-compliant lung more open, helping alveolar ventilation and decreasing V/Q mismatch
    • With all of these settings: Wait 5 minutes and look at the different alarms going off, and titrate

• Making changes to vent settings: Special clinical scenarios
  • Let’s say the first ABG shows a low pO2. What changes can you make?
    • Obvious: Increase FiO2
    • Not as obvious: Increase PEEP
    • What you should do: Incrementally increase oxygen and PEEP together
  • Let’s say the patient is a bad asthmatic/COPD. What changes do you make?
    • Change the inspiratory/expiratory ratio. How?
    • The best way to do this is decrease the respiratory rate and to change the inspiratory peak flow rate
      • Most people start at an inspiratory peak flow rate of 60. If you increase this to 80, the inspiratory time decreases and the time spent on expiration increases
      • NB: If you do significantly decrease respiratory rate, make sure to have an adequate tidal volume
    • Decrease PEEP
      • These patients generally have so much auto-PEEP on board, that the thorax is kept in an “out-position” rather than fully collapsed
      • If you’re still fighting oxygenation with no PEEP, you can add a small amount of PEEP to see if that helps
    • Let’s say the patient has ARDS. What changes do you make?
      • Lung-protective ventilation: higher respiratory rate, smaller tidal volume
      • Large lung expansions worsen ARDS
      • Tidal volume: 4-6 ml/kg of ideal body weight
        • NB: This creates a higher percentage of dead space
      • Start RR at 18 and increase as needed
      • Wait 5 minutes, get an ABG and change settings as needed

• Vent alarms
  • When an alarm starts to sounds: Think DOPE
    • Disconnect the vent:
      • Start bagging the patient every time you are confused, you think there’s a problem, or the patient is not getting ventilated
      • Make sure the bag is attached to oxygen
    • Obstruction
      • Check for obstruction in tube, plugging in lung, kinking in the line
      • Suction the tube
    • Pneumothorax
      • First, listen to the lungs
      • Next: E-FAST. It used to be get a chest X-ray, but ultrasound is faster and might be more accurate
    • Equipment failure
  • High pressure limit alarm
    • What do you do? Disconnect and bag
    • By bagging them, you’ll know if the problem is in the lung (i.e. if it is difficult bagging them, you know the high pressure is caused by the lung)
    • Look through the tube and find out where air flow is obstructed
    • This might indicate that you need a larger diameter ET tube
    • Coughing and gagging can also cause a high pressure alarm. You should be able to figure this out by watching the patient. They might need more sedation
  • Low pressure alarm
    • What do you do? Disconnect the bag
    • What causes low pressure?
      • ET tube leak/rupture or a disconnect of the system
    • Apnea alarm
      • This occurs when you haven’t set a baseline rate and the patient is not initiating enough breaths
    • Loss of O2
      • The vent is not connected to the wall O2
      • “Some of these alarms are really simple…”
    • High tidal volume/high minute ventilation/high respiratory rate
      • The patient is freaking out (i.e. not sedated enough air)
      • Increase sedation
    • Low tidal volume/low minute ventilation
      • Causes: Loose connection or a leak, disconnected from vent, ET tube leak
    • Ventilator inoperative or low battery
      • “Some of these alarms are really simple…”

Cases

• Case 1: Recently intubated patient on SIMV with tidal volume = 500, FiO2 = 100%, respiratory rate = 12, PEEP = 5. The patient looks very uncomfortable, O2 = 93%, EtCO2 = 35. What do you do?
  • a) paralyze the patient
  • b) increase PEEP
  • c) increase ventilation
  • d) sedate the patient

• Case 2: Recently intubated patient on volume AC, RR = 18, PEEP = 5, FiO2 = 100%, tidal volume = 6cc/kg. Currently overbreathing the vent at 28 breaths/minute. The ABG shows pH = 7.65. What do you do?
  • a) increase PEEP
  • b) increase tidal volume
  • c) give NaHCO3
  • d) decrease tidal volume

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Answers:

Case 1 Answer: D (sedate the patient)

• Do not paralyze without sedating, you lose a lot of information when you paralyze somebody
• O2 = 93% is acceptable, FiO2 is already 100%
• EtCO2 can’t be used as a substitute for PCO2, but it gives you an idea of what’s going on. In this case, EtCO2 is acceptable, and increasing ventilation will decrease the EtCO2 even more

Case 2 Answer: D (decrease tidal volume)

• pH = 7.65 means the patient is very alkalotic and likely hyperventilating (blowing off their CO2). Decreasing the tidal volume will decrease their minute ventilation which will prevent hyperventilation
• Another option would be sedation which would decrease the overbreathing of the vent