Hypovolemia and Dopamine

Shock can be caused by a variety of pathologies, and can often be effectively treated with IV fluids and/or vasoactive/chronotropic/inotropic medications like dopamine. It is ideal to target the therapy to the suspected etiology of the shock. Depending on the cause of shock, the risk/benefit considerations will sometimes favour one treatment modality over the other, although often both modalities are indicated. When preload depletion is a contributor to shock then volume replacement can be helpful. When shock is due to vasodilation, bradycardia, or contractility issues, medications like dopamine can be helpful. This is because dopamine is a catecholamine that has both B1 adrenergic effects (heart rate and contractility), and alpha effects (vasoconstriction). Sometimes it is not clear to what extent one etiology is more of a factor than another, or the patient is so moribund/peri-arrest, that either or both treatments are indicated.

Breaking down the ALS PCS medical directives that delegate dopamine administration, we have symptomatic bradycardia, ROSC, and cardiogenic shock. For all of these conditions, IV fluids and dopamine can be helpful, but depending on what factors the paramedic assesses to be more or less causative of the shock, the risk/benefit analysis of these interventions will sometimes favour one treatment over the other.

If the paramedic judges that bradycardia is causing shock, it makes sense to treat this with a B1 agonist to increase the heart rate. If the patient is hypovolemic, IV fluids can help, but this will not likely increase the heart rate (at least not in adults), and therefore hypovolemia would not be a contraindication to treating bradycardia with dopamine.

In post-ROSC patients, shock can be caused by myocardial dysfunction related to the anoxic event of cardiac arrest, vasodilation from release of inflammatory mediators resulting from the global anoxia which also causes relative hypovolemia, and the underlying etiology of the cardiac arrest itself (MI, PE, hypoxemia from lung disease, to name a few). Importantly, post-ROSC patients with hypotension have worse outcomes than those with MAPs > 65 and SBP > 90, and re-arrest is so common, that the risk/benefit analysis favours support of hemodynamics with all tools available. Even if a post-ROSC patient is hypovolemic and will benefit from fluid resuscitation, the imperative to improve blood pressure quickly, combined with what we know about myocardial dysfunction and vasodilation post-ROSC, favours using dopamine in addition to IV fluids to support hemodynamics.

In patients with cardiogenic shock due to STEMI, we have dysfunctional myocardium due to a mismatch of supply/demand of oxygen from coronary artery occlusion. Because dopamine can increase the myocardial oxygen demand by increasing heart rate and contractility from the B1 effects, the risk with dopamine is that it worsens the mismatch, which could potentiate the myocardial dysfunction and trigger lethal arrhythmias. If the patient is in severe shock then this risk might be acceptable, as myocardial function needs to be supported or death will occur, but IF the patient is concurrently hypovolemic, IV fluids would be the much better option to improve hemodynamics, as the risk here is lower. To be clear, the risks and benefits of dopamine and IV fluids are assumed in all of these cases (bradycardia, post-ROSC, and STEMI with shock), it is simply that the risk/benefit equation in a hypovolemic STEMI patient strongly favours IV fluids as the first line treatment, for the reason explained above, and why dopamine would be contraindicated in this case, until hypovolemia is resolved.

This risk/benefit analysis should be performed by the paramedic before any treatment is provided. Clinical medicine is complex, and as the scope and skills of paramedics broadens, it is harder and harder to write directives for every clinical situation. As always, if a paramedic performs a risk/benefit analysis for a patient they are treating, and believes there is a treatment that is indicated despite the ALS PCS not authorizing it, a patch to OMC is always welcome.