From the Guidelines
Morphine can cause hypotension primarily through vasodilation and decreased sympathetic tone, and its use should be carefully monitored, especially in patients with pre-existing hypotension, hypovolemia, or cardiovascular instability, as stated in the guidelines by 1 and 1. When administering morphine, it is crucial to monitor blood pressure closely. The hypotensive effect typically occurs within minutes of IV administration and may last for several hours. To manage morphine-induced hypotension, first ensure the patient is adequately hydrated with IV fluids such as normal saline.
Key Considerations
- Position the patient supine with legs elevated if appropriate.
- If hypotension persists despite these measures, consider reducing the morphine dose or administering it more slowly.
- For severe hypotension, vasopressors like norepinephrine (starting at 0.1-0.5 mcg/kg/min) or phenylephrine (100-500 mcg IV bolus followed by 0.5-2 mcg/kg/min infusion) may be necessary, as per the guidelines 1. The mechanism behind morphine-induced hypotension involves histamine release causing vasodilation, decreased peripheral vascular resistance, and reduced venous return. Additionally, morphine decreases sympathetic tone and can cause bradycardia, further contributing to hypotension.
Patient Susceptibility
- Elderly patients and those with compromised cardiovascular function are particularly susceptible to these effects.
- It is essential to weigh the benefits of morphine against the potential risks, especially considering the cautionary note raised by data from a large observational registry 1, which suggests a higher adjusted likelihood of death in patients receiving morphine.
From the FDA Drug Label
Morphine sulfate tablets may cause severe hypotension including orthostatic hypotension and syncope in ambulatory patients. There is increased risk in patients whose ability to maintain blood pressure has already been compromised by a reduced blood volume or concurrent administration of certain CNS depressant drugs (e.g., phenothiazines or general anesthetics) [see Drug Interactions (7)] .
Monitor these patients for signs of hypotension after initiating or titrating the dosage of morphine sulfate tablets. In patients with circulatory shock, morphine sulfate tablets may cause vasodilation that can further reduce cardiac output and blood pressure. Avoid the use of morphine sulfate tablets in patients with circulatory shock.
Morphine can cause severe hypotension, including orthostatic hypotension and syncope, especially in patients with compromised blood volume or those taking certain CNS depressant drugs. Key points to consider:
- Monitor patients for signs of hypotension after initiating or titrating morphine dosage.
- Avoid use in patients with circulatory shock, as morphine may worsen cardiac output and blood pressure.
- Inform patients about the risk of orthostatic hypotension and syncope, and instruct them on how to recognize symptoms of low blood pressure 2.
From the Research
Morphine Hypotension
- Morphine can cause hypotension, which can be a sign of significant underlying pathology 3
- Low-dose morphine has been shown to reduce tolerance to central hypovolemia in healthy adults, which can lead to hypotension 4
- The use of morphine in patients with hypotension should be carefully considered, as it can exacerbate the condition 4
Mechanisms of Morphine-Induced Hypotension
- Morphine can cause vasodilation, which can lead to a decrease in blood pressure 4
- Morphine can also affect the autonomic nervous system, leading to changes in heart rate and blood pressure 5
Treatment of Hypotension
- Treatment of hypotension is best targeted at the underlying etiology, although this can be difficult to discern early in a patient's disease course 3
- Vasopressors such as norepinephrine and phenylephrine can be used to treat hypotension, but the best choice of vasopressor is unknown 6, 7