From the Guidelines
Lopressor (metoprolol) can potentially contribute to hypoxia in certain patients, particularly those with underlying respiratory conditions or heart failure, due to its effects on beta-1 receptors and potential for bronchospasm or reduced cardiac output. Metoprolol is a beta-blocker that works by blocking beta-1 receptors in the heart, reducing heart rate and blood pressure 1. In patients with underlying respiratory conditions such as asthma or COPD, metoprolol may cause bronchospasm by inadvertently affecting beta-2 receptors in the lungs, which can lead to airway constriction, reduced oxygen exchange, and subsequent hypoxia 1. This risk is higher with non-selective beta-blockers, but even selective agents like metoprolol can lose some selectivity at higher doses.
Some key points to consider when prescribing metoprolol include:
- Starting with lower doses (such as 25-50 mg twice daily) and gradually increasing as tolerated while watching for signs of respiratory distress or decreased oxygen saturation 1
- Monitoring patients with respiratory conditions closely when starting metoprolol 1
- Being cautious in patients with heart failure, as metoprolol could temporarily worsen cardiac output during initial treatment or dose increases, potentially reducing oxygen delivery to tissues 1
- Avoiding metoprolol in patients with marked first-degree AV block, any form of second- or third-degree AV block, or a history of asthma, severe LV dysfunction or HF, or at high risk for shock 1
The most recent guidelines suggest keeping the SaO2 above 90% for the majority of acutely ill patients, with a desirable target saturation range of 94–98% 1. Healthcare providers should be aware of the potential risks of hypoxia associated with metoprolol and take steps to minimize these risks, particularly in vulnerable patient populations. The key to minimizing the risk of hypoxia in patients taking metoprolol is careful patient selection, dose titration, and monitoring.
From the Research
Lopressor and Hypoxia
- Lopressor, also known as metoprolol, is a beta-blocker used to treat various cardiovascular conditions, including hypertension, angina, and heart failure.
- The relationship between Lopressor and hypoxia is complex and has been studied in various contexts.
Effects of Metoprolol on Hypoxia
- A study published in 2011 2 investigated the effects of metoprolol on hypoxia- and isoflurane-induced cardiac late-phase preconditioning.
- The study found that metoprolol abolished the protection of both isoflurane- and hypoxia-induced late-phase preconditioning in cardiomyocytes.
- Another study published in 1983 3 evaluated the effects of metoprolol on cardiac and pulmonary function in patients with chronic obstructive pulmonary disease (COPD) and found that metoprolol did not significantly affect forced expiratory volume in 1 second (FEV1) or forced vital capacity.
Hypoxia and Pulmonary Function
- A study published in 2016 4 investigated the effects of hypoxia-induced pulmonary arterial hypertension on lung injury and airway reactivity caused by ozone exposure.
- The study found that hypoxia-induced pulmonary arterial hypertension augmented lung injury and airway reactivity caused by ozone exposure.
- Another study published in 2003 5 evaluated respiratory and cerebrovascular responses to hypoxia and hypercapnia in patients with familial dysautonomia and found that patients with familial dysautonomia developed central depression in response to hypoxia, leading to hypotension, bradycardia, hypoventilation, and potentially respiratory arrest.
Metoprolol and Chronic Heart Failure
- A review published in 2000 6 discussed the use of metoprolol in chronic heart failure and found that metoprolol controlled-release/extended-release (CR/XL) was associated with a 34% reduction in relative risk of all-cause mortality in patients with chronic heart failure due to ischemic or dilated cardiomyopathy.
- However, the relationship between metoprolol and hypoxia in the context of chronic heart failure is not well established.