Effects of analgesic doses of opioids on cardiorespiratory responses and survival to hemorrhage and trauma in rats

Opioids are used for analgesia, but questions persist about their safety after traumatic hemorrhage. We investigated analgesic doses of three opioids (morphine, fentanyl, and sufentanil) on cardiorespiratory responses and survival to moderate or severe (37% or 50% blood volume) hemorrhage after trauma. A conscious hemorrhage model with extremity trauma (fibular fracture + soft tissue injury) was used; mean arterial pressure (MAP) and heart rate (HR) were measured by telemetry, whereas minute volume (MV) was determined by whole body plethysmography. Male rats (<i>n</i> = 10/group) received saline, morphine (2 mg/kg), fentanyl (10 µg/kg), or sufentanil (1 µg/kg) after traumatic hemorrhage. Neither survival times (for 37% hemorrhage: <i>P</i> = 0.209; for 50% hemorrhage: <i>P</i> = 0.88) nor survival percentages (for 37% hemorrhage: <i>P</i> = 0.357; for 50% hemorrhage: <i>P</i> = 1.0) differed among groups. For 37% hemorrhage, MAP of all opioid groups was higher than that in the saline-treated group 10 min post injection. By 75 min post injection, MAP after sufentanil was higher than saline; MAP for other opioids did not differ from saline. HR did not differ across treatments. Opioid injection decreased MV within 10 min but did not vary by treatment subsequently. For 50% hemorrhage, opioid injection did not immediately alter MAP but morphine and sufentanil were lower than saline at ≥75 min post injection, with no treatment effects on HR. Fentanyl produced an immediate (5 min) decrease in MV with no treatment effects thereafter. Opioid effects on cardiorespiratory function were therefore modest and did not alter survival during a 4-h observation period, supporting the judicious use of analgesic doses after traumatic hemorrhage.<b>NEW & NOTEWORTHY</b> Administration of an analgesic dose of either morphine, fentanyl, or sufentanil produced only modest and transient effects on cardiorespiratory function after either moderate (37% blood volume) or severe (50%) hemorrhage in conscious rats with extremity trauma. Under the conditions of these experiments, analgesic doses of these commonly used opioids also did not alter survival after traumatic hemorrhage.