The physiological response to norepinephrine during hypothermia and rewarming.

Area of Science:

• Physiology
• Cardiovascular Research
• Thermoregulation

Background:

• Hypothermia can significantly alter cardiovascular function.
• Norepinephrine (NE) is a critical vasopressor used to manage hypotension.
• The impact of hypothermia on NE's physiological effects requires further elucidation.

Purpose of the Study:

• To investigate the influence of core hypothermia on physiological responses to norepinephrine (NE).
• To determine if rewarming reverses the observed effects of hypothermia on NE response.

Main Methods:

• Animals were instrumented to measure mean arterial pressure (MAP) and cardiac output (CO).
• Core temperature was manipulated through normothermia (37.5°C), hypothermia (30°C), and rewarming (37.5°C) using an external shunt.
• NE was infused at varying doses (0.2, 1.0, 5 µg/kg/h), with MAP, CO, and calculated systemic vascular resistance (SVR) measured at each temperature phase.

Main Results:

• During normothermia, NE significantly increased MAP and SVR at higher doses.
• Hypothermia significantly blunted the pressor response to NE, with significant MAP increases only at 1.0 and 5 µg/kg/h.
• Following rewarming, the pressor response to NE remained significantly blunted, with significant MAP increase only at the highest dose.

Conclusions:

• Core hypothermia significantly alters physiological responses to norepinephrine.
• The observed changes in NE response due to hypothermia are not fully reversed by rewarming.
• Hypothermia-induced alterations in NE cardiovascular effects may have clinical implications for managing hypotension in hypothermic patients.