You and your partner walk into the ER to find a 55-year-old patient intubated, on levophed and heparin, and with vital signs whispering, "get ready." This is the extreme (BAD) side of the pulmonary embolism spectrum, and you need a plan.
In this episode, Brian King & Shane O'Donnel,l from the FOAMfrat team join me to discuss several decision points you may encounter.
Risk Stratification & Preparation
Blood Pressure management
Fibrinolytics & Heparin
Ventilator Considerations
Inhaled Pulmonary Vasodilators
Risk Stratification & Prep
The terms massive & submassive actually have clinical definitions.
I personally use the acronym DELTA whenever I am preparing for transport. In this population, I think it is important to consider whether they have the ability to perform ECMO at the receiving facility. Being clear about your expectations is essential to assure everyone on the team has the same mental model.
"I expect this patient will likely deteriorate into cardiac arrest, and we need to be prepared for that."
Blood Pressure Management
Fight your initial response to give fluid; this will likely worsen things and increase right ventricular end-diastolic pressure.
There seems to be more anecdotal evidence suggesting epinephrine as a first-line pressor for the crashing PE patient. The epi can cause some pulmonary artery vasodilation while also increasing right ventricular inotropy to pump against the resistance of the clot burden within the pulmonary artery.
Fibrinolytics & Heparin
The MOPETT study looked at the role of "safe dose" thrombolysis in reducing pulmonary artery pressure in moderate PE, compared with anticoagulation alone. The dose of tPA used was 50 mg given as a 10mg bolus and 40 mg over two hours. Notice they did not stop the heparin during the tPA infusion.
The results showed a significant decrease in pulmonary artery pressure when a safe dose of tPA was administered.
Ventilator Considerations
We obviously are not going to "fix" this patient with ventilator settings, but a solid understanding of pulmonary vascular resistance in response to hypoxia, as well as changes with positive pressure ventilation, can help dial in settings that will not work against you. The chart below shows how the pulmonary vascular resistance makes a "U" shape with increased resistance on either side. This is because there is atelectasis and hypoxic vasoconstriction at very low lung volumes, and with large breaths, there is increased pressure on the capillaries surrounding the alveoli. This means moderate tidal volumes while maintaining a functional residual capacity above the minimal opening pressure is probably ideal. Patients with small BMI and low transalveolar pressure may benefit from zero PEEP when hemodynamics are severely compromised.
Inhaled Pulmonary Vasodilators
There was a super good talk by Dr. Oren Friedman at one of the EMCRIT conferences a while back discussing the role of pulmonary vasodilators within his pulmonary embolism response team (PERT). Here is the link to the episode https://emcrit.org/emcrit/pulmonary-embolism-treatment-team/
Essentially, Friedman stated that a lot of pulmonary vascular resistance and RV dilation come from inflammatory mediators following the events of a pulmonary embolism. This prevents other lung areas from dilating and compensating for the increased pulmonary artery pressures. There may be a role for inhaled pulmonary vasodilators in reducing secondary increases in PVR.
Dr. Josh Farkas did an excellent post on this here https://emcrit.org/pulmcrit/ntg/.
The main takeaways were:
Traditional inhaled pulmonary vasodilators (nitric oxide and epoprostenol) take a long time to set up and aren’t universally available. Therefore, they often aren’t feasible for immediate application in the crashing PE patient.
Nitroglycerin is metabolized into nitric oxide. Therefore, nebulized nitroglycerin can be used to deliver nitric oxide to the pulmonary vasculature selectively.
The above studies support that nebulized nitroglycerin is a safe and effective pulmonary vasodilator for both non-intubated and intubated patients.
Currently, nebulized nitroglycerin seems to be a reasonable intervention for the crashing PE patient. Unfortunately, given how rare and emergent this situation is, it’s unlikely that a large, multi-center RCT could ever be performed to prove this.
Now check out the episode!
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