By Dr. Abdolghader Pakniyat, peer-reviewed by Dr. Sabrina Berouk.

The Central Problem: The Overwhelmed Right Ventricle

Think of the heart’s ventricles as two different types of athletes.

• The Left Ventricle (LV) is a powerlifter. It’s thick-walled and built to pump blood against high resistance (your systemic blood pressure) day in and day out.
• The Right Ventricle (RV) is a marathon runner. It’s thin-walled and designed for endurance, gently pushing a large volume of blood through the low-resistance, sponge-like pulmonary arteries.

Pulmonary Hypertension is when the marathon runner is suddenly forced to become a powerlifter. The pulmonary vasculature becomes stiff and high-resistance. The RV, which is not designed for this, is forced to generate immense pressure to move blood forward.

This leads to two catastrophic problems that define the crashing PH patient:

1. The RV Ischemia “Death Spiral”: The RV gets its blood supply from the right coronary artery (RCA). Unlike the LV, which is mostly perfused in diastole, the thin-walled RV is perfused during both systole and diastole. When the RV has to squeeze against massive pressure, the wall tension gets so high that it physically compresses its own coronary artery, cutting off its blood supply.
   • The Spiral: High RV pressure → Increased RV wall tension → Compression of the RCA → RV ischemia → Weaker RV contraction → RV dilation → Even higher wall tension → Worsening ischemia… and so on. Simultaneously, a weak RV leads to low systemic blood pressure (shock), which further lowers the perfusion pressure for the RCA, accelerating the spiral.
2. Interventricular Dependence: The RV and LV share a wall—the interventricular septum. When the pressure-overloaded RV dilates, it bows the septum into the LV. This physically flattens and shrinks the LV chamber.
   • The Consequence: The LV can’t fill properly. This is not a volume problem; it’s a space problem. Less LV filling (preload) means catastrophically low cardiac output, leading to systemic hypotension. This is the classic “D-sign” you see on a POCUS parasternal short-axis view.

Understanding these two concepts—the ischemic death spiral and septal bowing—is the key to everything that follows.

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Applying Physiology to Your Outline: The “Why” Behind the Actions

Let’s connect this physiology to the excellent points in your outline.

Airway: Why We Avoid Intubation

Intubation is a perfect storm for the failing RV:

• Induction Agents (e.g., propofol): Cause systemic vasodilation, dropping the MAP. This critically reduces the perfusion pressure to the already ischemic RCA, accelerating the death spiral.
• Positive Pressure Ventilation (PPV): Does two terrible things simultaneously. It increases intrathoracic pressure, which (1) reduces venous return (preload) to the RV, and (2) increases pulmonary vascular resistance (PVR), making the RV’s job even harder (increased afterload).

This is why the guideline says “avoid intubation if possible.” If you must, you have to preemptively fight this impending collapse:

• Why pre-intubation norepinephrine? To support the MAP and ensure the RV’s coronary arteries stay perfused during the hypotensive storm of induction.
• Why no push-dose phenylephrine? Phenylephrine is a pure alpha-agonist. It powerfully constricts systemic vessels (good) but also constricts pulmonary vessels (very bad). It directly increases the RV’s afterload, pouring gasoline on the fire. Norepinephrine is better because its beta-1 effects provide some inotropy (contractility support) and it has a more favorable SVR:PVR effect ratio.

Circulation: Managing Preload, Afterload, and Squeeze

This is about delicately balancing the RV’s needs.

• Preload (Fluids): Why avoid big bolus fluids? Because in RV failure, the problem is almost never a lack of volume. The problem is a failure to pump forward against high pressure. The RV is already dilated and failing. Adding more fluid is like trying to cram more people into a subway car with a blocked exit. It only stretches the RV further, worsens the septal bowing, crushes the LV, and tanks the cardiac output.
  • The exception: True hypovolemia (e.g., from hemorrhage or severe dehydration). In this case, small, slow boluses (250 mL) with constant reassessment are key.
• Systemic Pressure & RV Perfusion (Vasopressors):
  • Why Norepinephrine first? It reliably increases MAP to protect RV perfusion with less direct PVR increase than phenylephrine. The primary goal is to keep the MAP ≥ 65 mmHg to feed the RCA.
  • Why Vasopressin second? Vasopressin is an excellent choice because it acts on V1 receptors to increase SVR with almost no effect on PVR. It’s a “PVR-sparing” pressor, making it ideal for supporting systemic pressure without punishing the RV.
• Contractility (Inotropes):
  • Why Dobutamine after MAP is stable? Once you’ve secured the RV’s blood supply with pressors, you may still have a stunned, ischemic RV that isn’t squeezing well. Dobutamine (a beta-1 agonist) directly increases RV contractility. However, it can also cause vasodilation, so you must have the blood pressure supported with a pressor first.
  • The sequence is crucial: 1. Secure Perfusion (Pressors) → 2. Improve Squeeze (Inotropes).

Breathing & Afterload Reduction

This is about making the RV’s job easier. The three biggest enemies that increase PVR are hypoxia, hypercapnia, and acidosis.

• Why HFNC/NIPPV? To correct hypoxia and hypercapnia, which are potent pulmonary vasoconstrictors. Fixing the blood gas can directly reduce the RV’s afterload.
• Why inhaled pulmonary vasodilators (iNO/iEpoprostenol)? This is the most elegant therapy. Because they are inhaled, they go directly to the well-ventilated alveoli and dilate the adjacent pulmonary arterioles. This selectively reduces PVR right where it’s needed, offloading the RV. Since they don’t enter the systemic circulation in significant amounts, they do not cause systemic hypotension. It’s a targeted weapon to reduce RV afterload.
• Why never interrupt a prostacyclin pump? These continuous infusions (epoprostenol, treprostinil) are potent pulmonary vasodilators with a very short half-life. Abruptly stopping them causes severe rebound pulmonary hypertension, which can be instantly fatal for a fragile patient. It is a true medical emergency.

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The Three Needs of the Failing RV

When you see a crashing patient with pulmonary hypertension, think of the RV as having three desperate needs:

1. It needs blood: Keep the MAP > 65 mmHg to perfuse its coronary artery. Use norepinephrine and vasopressin.
2. It needs an easier job: Decrease its afterload. Correct hypoxia and acidosis. Use inhaled vasodilators if you can. Avoid phenylephrine.
3. It needs space, not water: The RV is volume overloaded, not depleted. Do not give large fluid boluses. Diuresis is often the answer.

Do less — but do the right things

Recognize

• Known/suspected PH + shock/hypoxia/AMS ⇒ assume RV failure until proven otherwise.

Immediate priorities (in parallel)

1. Oxygen: HFNC; correct hypoxia/hypercapnia; avoid acidosis.
2. Pressure: Start norepinephrine now; target MAP ≥65 (think RV perfusion).
3. Probe: POCUS for RV size/function, septal D-sign, IVC; repeat to guide therapy.

Avoid harm

• No big fluid boluses. If clearly hypovolemic, use small test aliquots only; if congested, consider gentle diuresis.
• No phenylephrine.
• Avoid intubation if possible.

Early adds (as needed)

• Vasopressin as co-pressor if MAP marginal.
• Inhaled pulmonary vasodilator (iNO or inhaled epoprostenol) ASAP.
• Inotrope (e.g., low-dose dobutamine) after MAP secured if output remains low.

Medication safety (critical)

• Never interrupt continuous prostacyclin (epo/treprostinil); verify pump/line.
• Continue oral PAH meds if hemodynamically safe and no contraindications.

Treat triggers

• Hunt and treat PE, infection, arrhythmia, missed meds. Restore sinus rhythm if unstable.

Airway—only if you must

• Pressors running before induction; consider awake/DSI with etomidate/low-dose ketamine.
• Ventilate RV-protectively (low VT, lowest driving pressure; avoid severe hypercapnia; PEEP only as needed to prevent atelectasis).

Escalate early

• Call PH/ICU immediately; arrange transfer to PH/ECMO-capable center if refractory.

Mantra: Probe first. Pressors before pipes. Selective pulmonary vasodilator early. Don’t drown the RV.