Hemodynamics During Induction of General Anesthesia With Medium or Low Remifentanil Doses.

Typically, one or more adjuvant medications is administered during induction of general anesthesia. When anesthetic drugs are combined, the hypnotic effects are often synergistic. Propofol is associated with hypotension and bradycardia and used together with remifentanil or sedative agents it may give synergistic or additive sedative and hemodynamic effects.

Remifentanil is infused at 0.05-0.3 microg/kg/min during induction of anesthesia. Some use a loading dose of 0.5-1.0 microg/kg before starting the continuous infusion. The onset of action of remifentanil is within one to two minutes and it reaches rapidly a steady state effect site concentration after a bolus dose.

Kazmaier (2000) showed that a high-dose remifentanil anesthesia (2 microg/kg/min) reduced cardiac index (-25%), stroke volume (-14%) and mean arterial blood pressure (-39%) in a similar manner as propofol/remifentanil (propofol target 2 microg/ml and remifentanil 0.5 microg/kg/min), but systemic vascular resistance index decreased (-14%) in propofol/remifentanil combination. Fairfield et al have earlier (1991) showed that propofol 2.5 mg/kg induction without opioid reduces cardiac output (-15%) stroke volume (-5 %), mean arterial pressure (-33%) and systemic vascular resistance (-11%) and a slight reduction i heart rate. Guarracino (2003) suggests the reduction in cardiac index during induction with propofol/remifentanil with a low propofol target (1.2 microg/ml) may be due to decreased heart rate. Zaballos (2009) have shown that remifentanil depresses sinus node and atrioventricular (AV) -nodal function in comparison with propofol alone in a closed chest porcine model. Hayashi (2016) states that even in a low remifentanil effect site concentration (3.5 nanog/ml) it may reduce heart rate significantly when combined with propofol bolus 30-50 mg.

Inclusion criteria

• Gynecological procedure
• Age 18-50 years
• General anesthesia planned
• Systolic blood pressure < 150 mmHg, HR < 100 beats/min

Exclusion criteria

• Pre-existing hypertension
• Diabetes
• Ischemic heart disease or cerebrovascular disease
• Heart valve disease
• Verified cardiac arrhythmia other than extrasystoles
• Verified anaemia with hemoglobin level below 9.0 gr/dl.
• Kidney or hepatic disease
• Hypersensitivity for propofol, soya, eggs or peanuts
• Pregnancy
• Poor health state
• Illicit substance use
• BMI <20 or >35 kg/m2