Tasty Morsels of Critical Care 081 | Pulmonary Hypertension ICU management strategies

Welcome back to the tasty morsels of critical care podcast.

We’ve been talking about pulmonary hypertension, last time we had a pretty broad overview with a focus on group 1 or pulmonary arterial hypertension. This time we’re going to go through some management strategies that might keep you between the hedges on a night on call or a fellowship exam viva.

We briefly mentioned the PH specific drugs that someone might be on. The evidence base for these is almost exclusively in group 1 PH. But what should we do with these meds in someone with group 1 PH who has just arrived back from theater after a laparotomy and a hartmans and they’re on a bit of noradrenaline? The simple answer is continue them. The more complicated answer is you should usually continue them. For example there will be the very rare patient whose pulmonary vascular resistance is kept low in the community with a PICC line and an epoprostenol pump. They are critically dependent on this drug with a very short half life and it should be continued at all costs. Think about it like an adrenaline infusion running at 10mcg/min, not something you can tolerate a break in.

A recurring message from the review papers on critically ill patients with PH is to focus on treating PVR not PA pressures. This is a somewhat philosophical approach that reminds us that the PA pressures themselves don’t prognosticate especially well but a failure of flow from right to left will result in cardiogenic shock and death.

We have a lot of vasoactives to choose from in helping with this, most of which have varying impacts on the PVR. Vasopressin has some animal data suggesting it causes less rise in PVR than our beloved noradrenaline but take that with an appropriately loosely defined portion of salt given that animal data is not ICU patients. Milrinone seems like a great idea as an inotrope that is easy on the PVR but the often dramatic drop in SVR is often a disaster. Dobutamine has the benefit of at least having substantial clinical experience in PH patients even if the tachycardia and even worse the a fib is less than desirable.

The ventilator is a bit of a poisoned chalice. Not only do you have to tolerate a significant risk of peri-intubation cardiac arrest even once you get them on the vent you have to deal with the adverse effects of positive pressure on the RV. The only upside of the vent is that it might make them easier to oxygenate but only if the cause of the hypoxia was a big shunt physiology like a pnuemonia. Oxygen is a great tool for reducing PVR so if we can leverage that then that’s great. However, a lot of hypoxia in end stage PH is reduced mixed venous oxygenation due to low cardiac output and the vent does nothing good for this.

Once on the vent we want a goldilocks’s zone of lung unit recruitment. Too little PEEP we have atelectasis and shunt and hypoxia and vasoconstriction. Too much PEEP and we have overdistension which itself can raise PVR by squeezing the pulmonary vasculature. Finding that sweet spot for the PEEP is a whole post or 10 on its own.

While on the vent it’s a good opportunity to deliver some inhaled therapies. The original gangster here is of course nitric oxide which is one of our target molecules in PH. In a crisis and a failing RV, this might get you out of a tricky spot. But given its expense and not being widely available its worth considering other inhaled options, particularly intermittent nebs of iloprost or a continuously nebulised eporprostenol solution both of which i have seen implemented to good effect.

In terms of monitoring should we be reaching for a PAC? Well, take a step back to start with. We probably need the CVP more. The RV is the first downstream organ that suffers under the burden of worsening PH and if the RV is failing then the CVP will be rising. Like any monitoring tool, a PAC in itself is g