Total intravenous anesthesia (TIVA) in pediatric cardiac anesthesia

Sequestration of Midazolam, Fentanyl, and Morphine by an Ex Vivo Cardiopulmonary Bypass Circuit

Cardiopulmonary bypass (CPB) circuits can significantly sequester intravenous anesthetics. Adsorption of medications by our institution's standard circuit (Terumo CAPIOX FX05 oxygenator; noncoated polyvinylchloride tubing) has not been described. We prepared ex vivo CPB circuits with and without oxygenators. Medication combinations studied included midazolam (0.5 mg), fentanyl (50 µg), midazolam (0.5 mg) with morphine (0.5 mg), and midazolam (0.5 mg) with fentanyl (50 µg). Medications were administered after obtaining baseline samples. Samples were drawn at 2, 5, 15, 30, 60, 120, and 180 minutes, and analyzed for concentration of injected medications. Midazolam demonstrated no sequestration after 180 minutes. Fentanyl concentration at 180 minutes was lower with an oxygenator (52.7 ± 12.5 vs. 110.9 ± 12.0 ng/ml, P = 0.00432). More fentanyl was found in solution after 180 minutes when given with midazolam compared to fentanyl given alone in the presence of an oxygenator (101 ± 22.3 vs. 52.7 ± 12.5 ng/ml, P = 0.044). Less midazolam was present after 180 minutes when given with morphine compared to midazolam given alone in the absence of an oxygenator (1264.9 ± 425.6 vs. 2124 ± 254 ng/ml, P = 0.037). We successfully characterized the adsorption of various combinations of midazolam, fentanyl, and morphine to our CPB circuit, showing that fentanyl and midazolam behave differently based on other medications present.

Remifentanil and propofol undergo separation and layering when mixed in the same syringe for total intravenous anesthesia

BACKGROUND

Propofol and remifentanil can be combined to deliver total intravenous anesthesia (TIVA). Propofol and remifentanil are sometimes mixed in the same syringe. Since remifentanil is a solution and propofol is an emulsion, we hypothesized that they would separate over time when mixed in the same syringe.

METHODS

Nine 60-ml polypropylene syringes were prepared as follows: Group A: 1.25 ml of remifentanil solution (1 mg·ml(-1) ) was added to 48.75 ml of propofol (10 mg·ml(-1) ) in three syringes. Group B: 2.5 ml of remifentanil (1 mg·ml(-1) ) was added to 47.5 ml of propofol (10 mg·ml(-1) ) in three syringes. Group C: 5 ml of remifentanil (1 mg·ml(-1) ) was added to 45 ml of propofol (10 mg·ml(-1) ) in three syringes. The remifentanil lyophilized powder was reconstituted with sterile water and added to the propofol by injection through the port on the bottom of the syringe. The syringe was then inverted five times in succession to mix the drugs. The syringes were mounted in an upright vertical position (plunger on top, port on bottom) with wire on a pegboard. Samples of the mixture were taken from the bottom port (via a 3-way stopcock) and from the top of the syringe (via a stopcock on an 18-gauge needle placed 5 mm through the plunger) at the following time intervals (min) from baseline: T0, T10, T30, T60, T120, T180, T240, T300. Remifentanil and propofol were quantified using specific and validated HPLC/MS/MS assays with automated online sample preparation.

RESULTS

Concentrations of remifentanil were significantly greater at the top than the bottom of the syringes in groups A and B. Concentrations of propofol were significantly greater at the bottom than the top of the syringes in all groups.

CONCLUSION

Our data indicate that remifentanil solution and propofol emulsion are immiscible: remifentanil separates from propofol and rises to the top. Thus, concentrations of remifentanil and propofol delivered to patients from the same syringe during TIVA are not those expected and cannot be reliable. Remifentanil and propofol should be administered in separate syringes when used in combination for TIVA.

Doxapram hastens the recovery following total intravenous anesthesia with dexmedetomidine, propofol and remifentanil

Dexmedetomidine is a suitable sedative for awake fiberoptic intubation in patients with obstructive sleep apnea (OSA). However, previous studies have shown that dexmedetomidine delays recovery from propofol-remifentanil anesthesia. This study aimed to determine whether doxapram may hasten the recovery following dexmedotomidine-propofol-remifentanil anesthesia. Sixty patients scheduled for uvulopalatopharyngoplasty with total intravenous anesthesia were randomized to two groups according to the medicine given at the end of surgery. These were the doxapram (1 mg/kg) and control (normal saline) groups (n=30 per group). The primary outcome was the time to eye opening on verbal command. The time to return to spontaneous breathing, to hand squeezing in response to verbal command, to extubation of the trachea, and the heart rate (HR), bispectral index (BIS) values, respiratory rate (RR) and pulse oximetry values were also recorded and compared. The time to return to spontaneous breathing (5.2±2.9 vs. 11.7±3.4 min, P<0.001), eye opening (9.3±4.7 vs. 15.9±6.3 min, P<0.001), hand squeeze to command (11.8±6.5 vs. 17.6±7.7 min, P=0.0026) and extubation (14.2±7.8 vs. 19.2±9.6 min, P=0.0308) were significantly shorter in the doxapram group compared with the control group. BIS scores (at 3–14 min), RR (at 4–10 min) and HR (at 2–13 min) were significantly higher in the doxapram group compared with those in the control group (P<0.05). Doxapram hastens the recovery from dexmedetomidine-propofol-remifentanil anesthesia in patients undergoing uvulopalatopharyngoplasty, and may benefit patients with OSA.

Evaluation of closed-loop anesthesia delivery for propofol anesthesia in pediatric cardiac surgery

OBJECTIVE

The objective of this study was to compare the feasibility of closed-loop anesthesia delivery with manual control of propofol in pediatric patients during cardiac surgery.

METHODS

Forty ASA II-III children, undergoing elective cardiac surgery under cardiopulmonary bypass (CPB) in a tertiary care hospital, were randomized to receive propofol either through a closed-loop anesthesia delivery system (CL group) or through traditional manual control (manual group) to achieve a target BIS of 50. Patients were induced and subsequently maintained with a propofol infusion. The propofol usage and the efficacy of closed-loop system in controlling BIS within ±10 of the target were compared with that of manual control.

RESULTS

The maintenance of BIS within ±10 of target and intraoperative hemodynamic stability were similar between the two groups. However, induction dose of propofol was less in the CL group (2.06 ± 0.79 mg·kg(-1) ) than the manual group (2.95 ± 1.03 mg·kg(-1) ) (P = 0.006) with less overshoot of BIS during induction in the closed-loop group (P = 0.007). Total propofol used in the off-CPB period was less in the CL group (6.29 ± 2.48 mg·kg(-1) h(-1) vs 7.82 ± 2.1 mg·kg(-1) h(-1) ) (P = 0.037). Phenylephrine use in the pre-CPB period was more in the manual group (16.92 ± 10.92 μg·kg(-1) vs 5.79 ± 5.98 μg·kg(-1) ) (P = 0.014). Manual group required a median of 18 (range 8-29) dose adjustments per hour, while the CL group required none.

CONCLUSION

This study demonstrated the feasibility of closed-loop controlled propofol anesthesia in children, even in challenging procedures such as cardiac surgery. Closed-loop system needs further and larger evaluation to establish its safety and efficacy.

Recent advances in paediatric cardiac anaesthesia

Paediatric cardiac anaesthesia involves anaesthetizing very small children with complex congenital heart disease for major surgical procedures. The unique nature of this patient population requires considerable expertise and in-depth knowledge of the altered physiology. There have been several developments in the last decade in this subspecialty that has contributed to better care and improved outcome in this vulnerable group of patients. The purpose of this review is to present some of the recent advances in the anesthetic management of these children from preoperative evaluation to postoperative care. This article reviews the role of magnetic resonance imaging and contrast-enhanced magnetic resonance angiography in preoperative evaluation, the use of ultrasound to secure vascular access, the use of cuffed endotracheal tubes, the optimal haematocrit and the role of blood products, including the use of recombinant factor VIIa. It also deals with the advances in technology that have led to improved monitoring, the newer developments in cardiopulmonary bypass, the use of centrifugal pumps and extracorporeal membrane oxygenation and the role of DHCA. The role of new drugs, especially the α-2 agonists in paediatric cardiac anesthetic practice, fast tracking and effective postoperative pain management have also been reviewed.