Authors: Fernando Cuadrado, MD - Cincinnati Children’s Hospital Medical Center, Cincinnati, OH and
Destiny F. Chau, MD - Arkansas Children’s Hospital/University of Arkansas for Medical Sciences, Little Rock, AR
A 7-year-old boy with a history of pulmonary arterial hypertension treated with sildenafil and ambrisentan presents for cardiac catheterization. After induction of anesthesia, the blood pressure decreases from 98/50 to 60/40 mmHg along with a decrease in oxygen saturation from 97% from 88%. Which of following medications is the MOST appropriate treatment for hypotension in this patient?
EXPLANATION
Pulmonary arterial hypertension (PAH) is defined as mean pulmonary artery pressure (mPAP) greater than 20 mmHg and a pulmonary vascular resistance (PVR) greater than 3 Woods units (WU) in adults and children older than three months of age. Chronically elevated PAP and PVR can significantly impair the right ventricle’s (RV) function over time due to long-standing pressure overload and RV hypertrophy with subsequent diastolic dysfunction and impaired ventricular filling. This may lead to downstream adverse effects on left ventricular (LV) filling and systemic cardiac output as RV function deteriorates. LV function and systemic cardiac output is further compromised with leftward shift or bowing of the interventricular septum into the LV cavity. Due to interventricular dependence, this leftward shift of the ventricular septum negatively affects LV geometry leading to further impaired function. Additionally, RV hypertrophy significantly increases wall tension of the myocardium resulting in increased myocardial oxygen demand and the mean arterial pressure required to maintain adequate coronary perfusion pressure.
Systemic hypotension and thus reduced coronary perfusion pressure can easily lead to myocardial ischemia and further reduced myocardial function, resulting in a vicious cycle if not treated expeditiously. A hypertrophied RV has very little reserve for coronary hypoperfusion and promptly fails. Rapid treatment of hypotension is essential to preserve coronary perfusion pressure (CPP) and maintain oxygen delivery to the RV at risk for acute decompensation. Pulmonary hypertensive (PH) crisis is a sudden increase in PVR leading to RV failure with subsequent decreased LV preload, cardiac output and coronary perfusion. Cardiac arrest will ensue very quickly if PH crisis is not treated aggressively and rapidly.
As mentioned previously, prompt treatment of hypotension is necessary to prevent further deterioration in RV function and RV failure in patients with PH. Several vasoactive medications can be used to increase SVR and maintain coronary perfusion pressure. Vasopressin is the optimal choice to increase SVR, spare PVR, and thereby raise MAP and CPP without increasing heart rate and myocardial oxygen consumption. At moderate to high doses, epinephrine increases SVR, MAP, heart rate and myocardial contractility, as well as PVR. Likewise, dopamine, when used at the higher end of its dosing range, increases SVR, heart rate, MAP, myocardial contractility, and PVR. In addition to their undesirable effects on PVR, both epinephrine and dopamine increase heart rate, thereby shortening diastolic filling time and increasing myocardial oxygen demand, which can be highly detrimental for an RV at high risk of failure. Phenylephrine is a more readily available and commonly used vasoactive medication that increases SVR and MAP leading to a reflex decrease in heart rate. It may be used in this clinical scenario as well. However, it is a less optimal choice compared to vasopressin due to an undesirable effect of increasing PVR.
Of the three answer choices in the stem, vasopressin is the ideal drug for treating hypotension in patients with pulmonary hypertension due to minimal effects on PVR. Although other vasoactive agents may be used, they may be associated with detrimental increases in PVR and undesired tachycardia with resultant increased myocardial oxygen demand and shortened diastolic filling time.
REFERENCES
Wadia RS, Bernier ML, Diaz-Rodriguez NM, Goswami DK, Nyhan SM, Steppan J. Update on perioperative pediatric pulmonary hypertension management. J Cardiothorac Vasc Anesth. 2022;36(3):667-676.
Triposkiadis F, Giamouzis G, Boudoulas KD, et al. Left ventricular geometry as a major determinant of left ventricular ejection fraction: physiological considerations and clinical implications. Eur J Heart Fail. 2018;20(3):436-444.
Kaestner M, Schranz D, Warnecke G, Apitz C, Hansmann G, Miera O. Pulmonary hypertension in the intensive care unit. Expert consensus statement on the diagnosis and treatment of paediatric pulmonary hypertension. The European Paediatric Pulmonary Vascular Disease Network, endorsed by ISHLT and DGPK. Heart. 2016;102 Suppl 2:ii57-ii66.
