Cardiovascular effects of morphine during hypothermia

Area of Science:

• Anesthesiology
• Pharmacology
• Cardiovascular Physiology

Background:

• Morphine is commonly used for analgesia.
• Hypothermia can alter drug pharmacokinetics and pharmacodynamics.
• The cardiovascular effects of morphine under hypothermia are not fully understood.

Purpose of the Study:

• To investigate the cardiovascular effects of morphine in anesthetized dogs at normal and hypothermic temperatures.
• To determine the influence of route of administration (intravenous vs. intracisternal) on morphine's cardiovascular effects.
• To explore the role of opioid receptors and histamine release in morphine-induced cardiovascular changes during hypothermia.

Main Methods:

• Anesthetized dogs were subjected to two temperature conditions: 37°C and 30°C.
• Morphine was administered intravenously (1 mg/kg) or intracisternally (0.1 mg/kg).
• Cardiovascular parameters were monitored, and plasma/cerebrospinal fluid morphine levels and histamine release were measured. Naloxone was used as an antagonist.

Main Results:

• Intravenous morphine caused significant cardiovascular depression at 30°C but not at 37°C.
• Intracisternal morphine did not produce significant cardiovascular effects at either temperature.
• Hypothermia increased plasma and cerebrospinal fluid morphine levels and enhanced morphine-induced histamine release.
• Naloxone antagonized the cardiovascular effects, indicating a peripheral opioid mechanism.

Conclusions:

• Hypothermia potentiates the cardiovascular depressant effects of intravenous morphine.
• Peripheral opioid receptor activation and histamine release contribute to morphine's cardiovascular effects under hypothermia.
• Concomitant use of high-dose opioids and hypothermia may pose risks for patients with compromised cardiovascular reserve.