Problem 1: High Airway Pressures
When in the commonly used volume controlled ventilation setting, the tidal volume is set but the pressure varies. This is because positive pressure is applied until the goal tidal volume is reached. The amount of pressure that is needed to deliver a breath through the entire airway system (ETT, trachea, bronchi, etc) is known as the Peak Airway Pressure (Pap). There are two things that can affect this. One, there could be resistance in the system. This would cause the ventilator to work harder against this resistance and therefore require a higher pressure, which would trigger the ventilator to alarm this is happening. It could also mean that the lungs are becoming less complaint. What this basically means is that the lungs/chest wall have a restriction that does not allow them to inflate/expand. Similarly, a higher pressure is required to inflate the lungs, which again triggers the vent. So, high peak airway pressures could be due to a lung problem or an airway problem.
To figure this out, you need to determine if there is high resistance (airway problem), or decreased compliance (lung problem). To do this, you first make note of the Pap. The next step is to determine a Plateau pressure (Pplat). Recall that the plateau pressure represents the peak pressure in the alveoli. If this number is > 30 mmHg it puts the alveoli at risk for barotrauma. To measure this, you need to perform an “inspiratory hold” at the end of inspiration. The pressure will then plateau and leaves you this important value.
From there you can look at the difference between these two values. At baseline, the difference should be < 5 mmHg. If there is an increase in the Pap without a corresponding increase in Pplat, then the problem is due to increased resistance in the system. This is important because it does not mean you have to worry about the potential for barotrauma, but instead have to focus on decreasing the resistance. Common problems that may cause this could be:
- Kinked or obstructed ETT
- Mucous plugging
- Too narrow of an ETT
All of these problems have a potential fix:
- Pass a suction catheter and clear secretions. Unkink the tube at the tube holder.
- Again suction the ETT and/or trachea. Obtain a CXR to evaluate for an opacified lung indicating mucous plugging which requires aggressive pulmonary toilet or bronchoscopy.
- Administer inhaled bronchodilators
- Exchange the ETT, or accept a higher Pap
If when you perform an inspiratory hold and the Pplat is also elevated, it indicates there is decreased compliance and the problem is in the lungs. Common problems may be:
- Mainstem bronchus intubation
- Cardiogenic pulmonary edema
- Developing or worsening pneumonia
Again, all of these have a potential solution:
- Pull the ETT back
- Aggressive pulmonary toilet or bronchoscopy
- Administer diuretics or inotropes as necessary
- Use a lung protective strategy (lower tidal volumes of 4-6 mL/kg)
- Insert a chest tube
- Maximize antibiotic therapy
If none of these problems are present and the Pplat is still elevated, then decrease the tidal volume until this value is < 30 mmHg.
Problem 2: Hypoxia
Another problem that can be encountered is hypoxia. This can be caused by multiple reasons. A commonly used mnemonic used to ensure a systematic approach is DOPES and DOTTS. DOPES is for the differential and DOTTS includes what actions to take.
Differential for the Alarming Ventilator: DOPE(S)
D – Dislodged tube
O – Obstructed tube (mucous plug, blood, kink)
P – Pneumothorax
E – Equipment failure (ventilator, tubing, etc)
S – Breath Stacking [breath] (Auto-PEEP)
This is certainly helpful for diagnosing an alarming ventilator, but it does not provide an approach to dealing with these problems. While it’s still a mnemonic that I am going to keep in the back of my mind, I really liked the DOTTS mnemonic that he (referring to the EM:RAP post linked to below in references) offered to outline the things that you should do. While it could certainly be argued that if you know what you’re doing, DOPES will result in a similar approach, I liked the order and direction of DOTTS.
Approach to the Alarming Ventilator: DOTTS
D – Disconnect the patient from the ventilator , listen for a hiss to imply release of trapped air, +/- provide gentle pressure to the chest (assess for and treat breath Stacking and Equipment failure)
O – Oxygen (100%) and manual ventilation with a bag (check compliance by squeezing the bag: difficult bagging suggests Pneumothorax or Obstructed tube, very easy bagging suggests Dislodged tube or Equipment failure due to a deflated cuff)
T – Tube position/function (see if the tube has migrated to assess for Dislodged tube; pass a bougie or suction catheter through to see if the tube is Obstructed)
T – Tweak the vent (prevents breath Stacking by decreasing respiratory rate, decreasing tidal volume or decreasing inspiratory time)
S – Sonography (assess for pneumothorax, mainstem intubation, plugging)
This was borrowed from the blog “Boring EM” (its OK in the interest of FOAM). This is a great blog that I encourage you to take a gander at to see if you like what it has to offer.
Additionally you may need to apply additional PEEP to increase the functional residual capacity and “recruit” more alveoli to participate in gas exchange. Also, always consider PE as a potential diagnosis.
Problem 3: Dynamic Hyperinflation
This problem occurs when there is inadequate time for exhalation, and can be exacerbated by high airway resistance. When this happens, residual air is trapped in the lungs and leads to autoPEEP/breath stacking. This increases the alveolar and intrathroacic pressure and can cause pneumothorax or decreased venous return. These both can lead to hypotension and circulatory collapse. Aside from that, this also will create more dead space ventilation and lead to worsening hypoxia and/or hypercapnea. This can be measured by performing an expiratory hold (measuring the pressure present at the end of expiration). This value would normally be equal to the PEEP setting, but in the case of autoPEEP, the value will be much higher. Subtract the preset PEEP from the pressure value obtained at the end expiratory hold to calculate the autoPEEP.
The management goes back to the DOPES/DOTTS mnemonic. However specific management steps are:
- Disconnect the patient from the ventilator and allow the trapped air to escape.
- Allow for a longer expiratory time by decreasing the respiratory rate
- Shorten the inspiratory time to allow for an inspiration:expiration (I:E) ratio of 1:3-1:5 (ask RT)
- Decrease the tidal volume
- Increase the inspiratory flow from the standard 60 L/min to 80 L/min
- Treat bronchospasm to reduce airway resistance
· Disconnect the patient from the ventilator and allow the trapped air to escape.
· Allow for a longer expiratory time by decreasing the respiratory rate
· Shorten the inspiratory time to allow for an inspiration: expiration (I:E) ratio of 1:3 – 1:5 (ask RT)
· Decrease the tidal volume
· Increase the inspiratory flow from the standard 60 L/min to 80 L/min
· Treat bronchospasm to reduce airway resistance.
Well that was a quick review to add a little more on how to troubleshoot the ventilator. I hope it helps you understand how to approach this situation better. I encourage you to seek out other sources for further reading and understanding on this important topic.
Thanks for reading.
1. Boring EM
2. EM:RAP Episode 147 (Near minute 16)
3. Marino, Paul L. Chapter 25: Positive Pressure Ventilation. In: Marino’s ICU Book. 4th ed. Philadelphia: Lippincot Williams & Wilkin – a Wolters Kluwer Business; 2014: 487 – 503
4. Owens, William. Ventilator Management and Troubleshooting in the Emergency Department. EB Medicine: EM Critical Care. Volume 4, Number 5. September/October 2014.