Total Intravenous Anesthesia

Although TIVA does not necessarily require an opioid component, especially in minimally stimulating procedures, the fentanyl congeners most often are an important part of TIVA. Numerous advantages exist when drugs are administered by infusion.^[389]

Many different intravenous compounds can be employed in a number of combinations to provide TIVA. Most commonly, an opioid is combined with another drug more likely to provide hypnosis and amnesia. For example, the combination of alfentanil and propofol produces excellent TIVA. Alfentanil provides analgesia and hemodynamic stability while blunting responses to noxious stimuli. On the other hand, propofol provides hypnosis and amnesia and is antiemetic. Profound synergism also exists when more than two agents, such as propofol-alfentanil-midazolam, are combined.^{[390] [391]} Anesthetic induction with alfentanil (25–50 µg/kg) and propofol (0.5–1.5 mg/kg) followed by infusions of 0.5–1.5 µg/kg/min of alfentanil and 80–120 µg/kg/minute of propofol will produce complete anesthesia in patients ventilated with air and O₂ with or without N₂ O for a variety of procedures. It is proposed that alfentanil concentrations as low as 85 ng/mL, when combined with a blood propofol concentration of 3.5 µg/mL, can produce both optimal anesthetic conditions and speed of recovery.^[391] Stanski and Shafer suggested that bolus doses and initial infusion rates would be 30 µg/kg and 0.35 µg/kg/minute, respectively, for alfentanil and 0.7 mg/kg and 180 µg/kg/minute, respectively, for propofol.^[392] Recognizing that these calculations were

TABLE 11-9 -- Approximate opioid loading (bolus) doses, maintenance infusion rates, and additional maintenance doses for total intravenous anesthesia

	Loading Dose (µg/kg)	Maintenance Infusion Rate	Additional Boluses
Alfentanil	25–100	0.5–2 µg/kg/min	5–10 µg/kg
Sufentanil	0.25–2	0.5–1.5 µg/kg/hr	2.5–10 µg
Fentanyl	4–20	2–10 µg/kg/hr	25–100 µg
Remifentanil	1–2	0.1–1.0 µg/kg/min	0.1–1.0 µg/kg
From Bailey PL, Egan TD, Stanley TH: Intravenous opioid anesthetics. In Miller RD (ed): Anesthesia, 5th ed. New York, Churchill Livingstone, 2000, p 335.

based on EC₅₀ data in patients undergoing only moderately painful procedures, anesthesiologists should adjust these doses accordingly. Premedication prior to alfentanil-propofol anesthesia can prolong postoperative recovery and should be avoided if appropriate.^[393] In patients undergoing ear-nose-throat surgery, TIVA with remifentanil and propofol provided a more rapid respiratory recovery after brief surgical procedures, compared with TIVA with alfentanil and propofol. ^[394]

The optimal propofol-opioid concentrations that ensure adequate anesthesia and rapid emergence were determined by computer modeling.^[327] The optimal propofol concentration decreases in the order of fentanyl > alfentanil > sufentanil ≫ remifentanil. A shorter context-sensitive half-time allows the administration of greater amounts of opioid (and less propofol) during anesthesia without creating prolonged opioid effects.

Maintenance infusions vary according to patient condition and surgical stimuli. Propofol (75–125 µg/kg/minute) and alfentanil (1.0–2.0 µg/kg/minute) are initially recommended. Drug infusions should be terminated 10 to 20 minutes prior to end of anesthesia if N₂ O is employed. Otherwise, propofol infusions should be terminated 5 to 10 minutes before anticipated patient awakening. Alfentanil infusion rates do not need to be less than 0.25–0.5 µg/kg/minute until surgery is terminated. A multicenter evaluation demonstrated that in patients during elective surgery, remifentanil (1 µg/kg IV followed by 1.0 µg/kg/minute) when combined with propofol (75 µg/kg/minute) effectively controlled responses to tracheal intubation.^[381] Remifentanil infusion rate of 0.25 µg/kg/minute after tracheal intubation was also recommended.

Midazolam-opioid combinations can also provide complete anesthesia. However, midazolam-alfentanil TIVA has not been found to compare favorably to propofol-alfentanil TIVA even with flumazenil reversal of benzodiazepine actions.^[395] However, TIVA for major (cardiac) and/or long operations may be effectively achieved with the combination of midazolam and sufentanil.^[396]

TIVA techniques are especially useful when delivery of inhaled agents is compromised. By keeping the goals of balanced anesthesia in mind, combining modern opioids and other drugs, utilizing infusion pumps, and employing an increased understanding of pharmacokinetics, clinicians can successfully perform a wide variety of TIVA techniques. Approximate opioid doses and infusion rates for TIVA are listed in Table 11-9 .