Altered blood gas tensions of oxygen and carbon dioxide confound coronary reactivity to apnea

Abstract

PurposeArterial blood gases change frequently during anesthesia and intensive care. Apnea can occur during diagnostic exams and airway and surgical interventions. While the impact of blood gas levels on coronary blood flow is established, their confounding effect on coronary vasoreactivity in response to an apneic stimulus, especially in coronary artery disease, is not known.MethodsSix anesthetized control swine and eleven swine with coronary artery stenosis were examined. Nine different blood gas levels from a combination of arterial partial pressure of oxygen (70, 100, and 300 mmHg) and carbon dioxide (30, 40, and 50 mmHg) were targeted. Apnea was induced by halting controlled positive pressure ventilation for 3–30s, while the left descending coronary artery flow was measured and reported relative to apnea duration, and at the adjusted mean (12s).ResultsAt normoxemic-normocapnic blood gas levels, apnea increased coronary blood flow in proportion to the duration of apnea in the control (r = 0.533, p < 0.001) and stenosed groups (r = 0.566, p < 0.001). This culminated in a 42% (95% CI: 27–58) increase in controls (p < 0.001) and, to a lesser extent, 27% (15–40) in the presence of coronary artery stenosis (p < 0.001). Vasoreactivity was augmented by mild-hypoxemic levels [81% (65–97), and 66% (53–79) increase in flow respectively, p < 0.001 vs. normoxemia], but markedly reduced during hyperoxia (7.5% (−8.2–23) and 0.3% (−12–13), respectively, p < 0.001 vs. normoxemia).ConclusionAlterations of blood oxygen and carbon dioxide affect coronary vascular reactivity induced by apnea in swine, which was attenuated further in the presence of coronary stenosis. Especially hyperoxia significantly reduces coronary blood flow and blunts coronary vascular reactivity.

Hyperoxia-induced deterioration of diastolic function in anaesthetised patients with coronary artery disease – Randomised crossover trial

“…The consistent worsening of pre-existing diastolic dysfunction and deterioration of systolic function in select patients may be the sequential downstream functional sequalae of such an unfavourably shifted oxygenation balance. 14 , 23 , 24 On the other hand, our results also indicate that patients with quite poor baseline function may demonstrate an improved contractility with transition to hyperoxia ( Fig 4 ). With progressive coronary artery disease the probability of microvascular dysfunction in the coronary system also increases, and this could be a reason why patients with a higher ischaemic burden and lower systolic function at normoxaemia may benefit from hyperoxia.…”

Introducing a free-breathing MRI method to assess peri-operative myocardial oxygenation and function

“… 15 , 34 Future investigations need to assess whether the combination of hyperoxia and hypocapnia during such periods of preoxygenation will have incremental effects and whether supplementary oxygen blunts vasodilation during apnoea. 43 The peri-operative environment is quite complex for the heart because blood gas changes are not the only factors at play. Heart rate, for example, can rise not only during the deep breathing of preoxygenation, 18 , 44 but also during and after induction especially if anaesthesia is too shallow.…”

“…Oxygen itself is a coronary vasoconstrictor and has been shown to decrease myocardial oxygenation, as measured by OS-CMR in anaesthetised animal studies, in awake healthy controls and in chronic coronary syndrome patients 15,34 . Future investigations need to assess whether the combination of hyperoxia and hypocapnia during such periods of preoxygenation will have incremental effects and whether supplementary oxygen blunts vasodilation during apnoea 43 . The peri-operative environment is quite complex for the heart because blood gas changes are not the only factors at play.…”