Gasometric gradients between blood obtained from the pulmonary artery wedge and pulmonary artery positions in pulmonary arterial hypertension

Abstract

IntroductionLittle is known on the pulmonary gradients of oxyhemoglobin, carboxyhemoglobin and methemoglobin in pulmonary arterial hypertension (PAH). We sought to determine these gradients in group 1 PAH and assess their association with disease severity and survival.MethodsDuring right heart catheterization (RHC) we obtained blood from pulmonary artery (PA) and pulmonary artery wedge (PAW) positions and used co-oximetry to test their gasometric differences.ResultsWe included a total of 130 patients, 65 had group 1 PAH, 40 had pulmonary hypertension (PH) from groups 2–5 and 25 had no PH during RHC. In all groups, PAW blood had higher pH, carboxyhemoglobin and lactate as well as lower pCO2 than PA blood. In group 1 PAH (age 58 ± 15 years, 72% females), methemoglobin in the PAW was lower than in the PA blood (0.83% ± 0.43 vs 0.95% ± 0.50, p = 0.03) and was directly associated with the degree of change in pulmonary vascular resistance (R = 0.35, p = 0.02) during inhaled nitric oxide test. Oxyhemoglobin in PA (HR (95%CI): 0.90 (0.82–0.99), p = 0.04) and PAW (HR (95%CI): 0.91 (0.84–0.98), p = 0.003) blood was associated with adjusted survival in PAH.ConclusionsMarked differences were observed in the gasometric determinations between PAW and PA blood. The pulmonary gradient of methemoglobin was lower in PAH patients compared to controls and a higher PAW blood methemoglobin was associated with a more pronounced pulmonary vascular response to inhaled nitric oxide. Pulmonary artery and PAW oxyhemoglobin tracked with disease severity and survival in PAH.

Reply: Will the Real Pulmonary Pressure Please Stand Up?

“… PAWP determination: We routinely seek to obtain blood from the distal port of the pulmonary artery catheter while in the wedge position. A blood oxygenation >90% ( 5 ) supports the PAWP determination ( 6 ). When we questioned the validity of the PAWP measurement, we reduced the amount of air in the pulmonary artery balloon or advanced the pulmonary artery catheter to a different branch or the contralateral pulmonary artery ( 5 ).…”

Significance of Hypocapnia in the Risk Assessment of Patients with Pulmonary Hypertension

“…Therefore, other pathophysiological explanations should be considered, which may be supported by our results. An analysis of postcapillary blood gases in a small retrospective study showed that patients with PAH had significantly lower PaCO 2 values in blood gases derived from the pulmonary artery than patients with PH in Groups 2-5, and this difference becomes much more pronounced in postcapillary gases (i.e., with more pulmonary passage of blood) [25]. This implies that hypocapnia is a very consistent feature of PH Group 1 (PAH) and could have other explanations, perhaps due to specific features and pathophysiological changes in the pulmonary artery that play a central role in PAH, such as endothelial dysfunction.…”