What are the effects of Morphine (opioid analgesic) on blood pressure, specifically regarding hypotension?

From the Guidelines

Morphine can cause a significant decrease in blood pressure, leading to hypotension, especially in patients who are volume-depleted or have pre-existing cardiovascular conditions, and its use should be carefully monitored and managed to prevent adverse outcomes. When considering the effects of morphine on blood pressure, it is essential to understand the mechanisms by which it acts. Morphine causes venodilation, which can produce modest reductions in heart rate and systolic blood pressure, further reducing myocardial oxygen demand 1. This effect is potentially beneficial in certain clinical contexts, such as unstable angina or non-ST-elevation myocardial infarction (UA/NSTEMI), where reducing myocardial oxygen demand is crucial. However, the major adverse reaction to morphine is an exaggeration of its therapeutic effect, causing hypotension, especially in the presence of volume depletion and/or vasodilator therapy 1.

Key considerations for the use of morphine in relation to its effects on blood pressure include:

• The potential for hypotension, which can be exacerbated by volume depletion or the use of vasodilators
• The need for careful monitoring of blood pressure, especially during initial administration or dose increases
• The importance of considering alternative analgesics in patients with certain comorbidities or those at high risk of hypotension
• The availability of interventions to manage hypotension, such as supine or Trendelenburg positioning, intravenous saline boluses, and atropine for bradycardia, or pressors and naloxone in more severe cases 1.

In clinical practice, the decision to use morphine must be balanced against the potential risks, including the risk of hypotension, and careful consideration should be given to the patient's volume status, cardiovascular health, and the potential for adverse interactions with other medications. Given the potential for morphine to cause significant hypotension, its use should be approached with caution, and patients should be closely monitored for signs of hypotension, with prompt intervention if necessary.

From the FDA Drug Label

1. 8 Hypotensive Effect Morphine sulfate injection may cause severe hypotension in an individual whose ability to maintain their blood pressure has been compromised by depleted blood volume, shock, impaired myocardial function or concurrent administration of sympatholytic drugs, and drugs such as phenothiazines or general anesthetics Orthostatic hypotension is a frequent complication in single-dose parenteral morphine analgesia in ambulatory patients. The vasodilation produced by morphine sulfate injection may further reduce cardiac output and blood pressure in patients in circulatory shock.

Cardiovascular – Tachycardia, bradycardia, palpitation, faintness, syncope, and orthostatic hypotension.

Morphine can cause hypotension, particularly in individuals with compromised blood volume, shock, or impaired myocardial function. Orthostatic hypotension is a common complication in ambulatory patients receiving single-dose parenteral morphine analgesia. Key factors that contribute to hypotension include:

• Depleted blood volume
• Shock
• Impaired myocardial function
• Concurrent administration of certain drugs, such as sympatholytic drugs, phenothiazines, or general anesthetics
• Vasodilation produced by morphine sulfate injection, which can further reduce cardiac output and blood pressure in patients with circulatory shock 2

From the Research

Effects of Morphine on Blood Pressure

• Morphine can have varying effects on blood pressure, including hypotension, which is a decrease in blood pressure 3, 4, 5, 6.
• In some studies, morphine has been shown to reverse hypotension associated with severe hemorrhage in anesthetized rats 3, 4.
• The mechanism of morphine's effect on blood pressure is complex and may involve vasodilation, histamine release, and changes in sympathetic tone 5, 6.
• In human subjects, morphine has been shown to induce peripheral venous and arteriolar dilation, leading to a decrease in blood pressure 6.
• However, some studies have also reported an initial, transient increase in blood pressure and heart rate after morphine administration, possibly due to cardiovascular stimulation 7.

Mechanisms of Morphine's Effects on Blood Pressure

• Morphine's effects on blood pressure may be mediated by its action on central nervous system opioid receptors, which can influence sympathetic tone and vasodilation 3, 4.
• Histamine release is also thought to play a role in morphine-induced hypotension, although the exact mechanism is not fully understood 5, 6.
• The effects of morphine on blood pressure can be influenced by the dose and route of administration, as well as individual factors such as age and health status 5, 6, 7.

Clinical Implications

• The effects of morphine on blood pressure should be carefully considered in clinical settings, particularly in patients with cardiovascular disease or those who are at risk of hypotension 3, 4, 5, 6.
• Monitoring of blood pressure and other cardiovascular parameters is recommended when administering morphine, especially in high doses or in patients with underlying medical conditions 5, 6, 7.