Congenital heart surgery at high altitude – Should we re-analyze the data?

There is not a single definition of high altitude. In High-Altitude or Mountain Medicine, ‘high altitude’ is defined as 1500 to 3500m above sea level, with ‘very high altitude’ defined as that between 3500m and 5500m, and ‘extreme altitude’ as that above 5550m. But common practice has been to refer to ‘high altitude’ as any elevation above 2500m, probably because rarely do any of the altitude sickness syndromes (acute, subacute and chronic), related to hypoxemia and/or increased pulmonary vascular resistance, appear under this altitude.

Pulmonary vascular resistance (PVR) has been traditionally accepted to be elevated at “high altitude”. Therefore, centers located even at altitudes as low as 1500m usually consider themselves as having to deal with increased PVR in the management of patients with congenital heart disease. Interestingly, however, when reviewing the literature, most of the data obtained at high altitude have been obtained by observations performed above 3000m.^1,2 There are no data reported that allow us to assume any increase in PVR at levels between 1500 and 3000m, where most of the centers performing cardiac surgery at “high altitude” are located. In fact, there is some evidence obtained from clinical ³ and animal studies⁴ that suggests that PVR might begin to increase approximately around 3000m above sea level.

In 2019, we reported our results in patients undergoing the non-fenestrated Fontan procedure at our two centers in Mexico City, located at altitudes of 2312m and 2691m above sea level.⁵ Our data showed normal preoperative PVR, as well as normal pulmonary pressures in the Fontan circulation in the immediate postoperative period. We also achieved high early extubation rate, low mortality, and overall similar results as those previously reported in series from Fontan procedures performed at sea level. More recently, we also published our results of early extubation at 2691m, with an early extubation rate of 81% in our overall population, specifically 73% and 89% for the Glenn and Fontan patients respectively, and 85% for the group of patients with Down syndrome⁶.

These data suggest that the PVR is probably normal at altitudes where most centers doing cardiac surgery at “high altitude” are located. Some perioperative management strategies that might have been adopted for many years in these centers, based upon the unproven hypothesis that PVR is increased at 2500m (or even at 1500m) above sea level, may in fact not be essential for managing these patients successfully. Although fenestration has been routinely used in centers located at “high altitude”, its obligate right-to-left shunt might not have significant benefit but only worsen desaturation, particularly during the immediate post-operative period, when oxygenation is already compromised due to the inflammatory process in the lungs after cardiopulmonary bypass.

Based on these facts, we think it is necessary to analyze with more detail the data available and the real overall global effects of altitude in the physiology of patients undergoing cardiac surgery at centers located at “high altitude”, to optimize their pre- and post-operative management.

REFERENCES

1.- Allemann Y, Stuber T, de Marchi S. Pulmonary artery pressure and cardiac function in children and adolescents after rapid ascent to 3450 m. Am J Physiol Heart Circ Physiol 2012; 302: H2646-H2653.

2.-Peñaloza D, Sime F, Banchero N. Pulmonary hypertension in healthy men born and living at high altitude. American Journal of Caardiology  1963;11(2):150-157

3.- Peñaloza D, Arias-Stella J. The heart and pulmonary circulations at high altitude. Circulation. 2006;115:1132-1146.

4.- Ward JPT, Aaronson P. Mechanisms of hypoxic pulmonary vasoconstriction: can anybody be right? Resp Physiol 1999; 115(3):261-271

5.- Palacios-Macedo A, Díliz-Nava H, Tamariz-Cruz O. Outcomes of the non-fenestrated Fontan procedure at high altitude. WJPCHS. 2019; 10(5):590-596.

6.-Tamariz-Cruz O, García-Benítez L, Díliz-Nava H. Early extubation in a Pediatric Cardiac Surgery program located at high altitude. WJPCHS. 2021;4:473-479