Splendid question. This is a big topic, and actually a somewhat specialized one, but I'll say what I can.
Pulmonary hypertension is a bit of a bogeyman. Sometimes we seem to ignore it, sometimes we get scared by its very mention. Truly understanding it is not easy, and you have to start by breaking it down by etiology.
You don't need to memorize the names of the
WHO groups, but you need to understand how they differ. In brief,
Group 1: Primary/idiopathic. This is Pulmonary
Arterial Hypertension, usually due to a not-well-understood degenerative condition that occurs in the unlucky. These people are often on chronic pulmonary vasodilators, in some cases via continuous drip by pump. Like a patient with an LVAD, they need this to live on a minute-by-minute basis (so don't trip over it). They need their vasodilators and should be managed by specialists.
Group 2: Cardiac cause. Pretty easy to understand, this is typical left heart failure stuff.
Group 3: Pulmonary cause. Your COPD or sleep apnea patients.
Group 4: Thrombotic cause. Your PEs.
Group 5: Other/mixed/miscellaneous junk.
You probably recognize that there are disease-specific treatments for many of these. For instance, one of the goals of therapy with lytics or clot retrieval in PE is to reduce the incidence of chronic PH (group 3, see?). But there are some general principles that can be useful:
Right heart strain leading to failure is what you fear. PH causes a lot of effects ranging from vascular remodeling to thrombogenesis, but the acute worry is that the right heart will suddenly poop out. Remember the RV is a
low pressure system. Unlike the burly LV, it is a thin-walled chamber accustomed to creating gentle forward pressures only. Normal pulmonary vascular pressures are below 20 or 30 mmHg, compared to the systemic pressures (>100) you know so well. The chunky LV not only has the hypertrophy to squeeze that hard, it also has reserves to go even harder; if systemic BP increases (or there are other obstacles creating afterload, such as outflow obstructions like aortic stenosis), it can push past that, too. Like Jordan at the buzzer, it's got grit.
Unlike Jordan, the RV is more likely to choke in the clutch. If you increase pulmonary arterial pressures sufficiently, it won't squeeze harder; it will simply fail. Cardiac output will drop, the RV will dilate further, and the cycle will worsen. The RV is also easily affected by malperfusion, and cardiogenic shock will hence tend to cause ischemia here, decreasing output and further feeding the cycle.
You may be thinking about right-sided STEMI here, and how we teach to flush with fluids, because you need to help preload the left heart. Implicit here is the idea that you don't really "need" the RV. But this is a very different situation, because in isolated right-sided STEMI, pulmonary vascular pressures are low, and you can passively push fluid through by increasing venous pressures. But in PH the
pulmonary vascular pressures are high. You need the RV to do its job in order to push blood against that resistance. If your pulmonary diastolic pressure is 40, and your CVP is 10, I guarantee that blood will not move forward unless the RV can help.
Now, like most things, chronic things are tolerated better than acute things. Over time, the RV can hypertrophy to better withstand the higher pressures. Thus, the COPDer may do better with their PH than the PE patient.
So, to boil this down to basic management:
- Follow the Goldilocks approach. These patients cannot withstand "permissive" anything. Hypoxia or hypercarbia will increase pulmonary vascular resistance (by pulmonary vasoconstriction); do not allow it. Hypotension will cause RV ischemia, but hypertension will increase afterload, so avoid both. Use cardiostable drugs, don't get laissez-faire, and keep these people in the box.
- Do not fluid overload. The Starling curve of the left heart flattens out eventually, yielding little increase in cardiac output for additional preload. But the Starling curve of the right heart peaks and then actually falls; it is U-shaped, and with overdilation you can suddenly cause the RV to suddenly drop its output. A little fluid is okay in most patients; stop after that.
- Beware perturbations in thoracic impedence. Too much PEEP on the ventilator will only add to the external squeeze upon the pulmonary vascular vessels. In fact, the mere switch from negative to positive pressure during intubation can easily cause arrest. The anesthesia gang (who can comment further if they wish) fears these people, and high-risk patients should probably not be going to the OR in a place without rescue bypass available. I once saw a routine post-op patient with undiagnosed PH get a bit hypercarbic in the PACU and suddenly code.
- Pressors as needed to maintain perfusion. Vasopressin may be good as it doesn't squeeze the pulm vessels. Norepi is fine. Milrinone may be your best inotrope, in theory. Multiple agents are often needed. Invasive monitoring is often appropriate, and PA catheters can have a role. Pulmonary vasodilators can have a role, although effects probably vary by the PH type.
Helpful?
