Anaesthesia essentials: Overview

Regional Anesthesia & Pain Medicine, the official publication of the American Society of Regional Anesthesia and Pain Medicine (ASRA Pain Medicine), is a monthly journal that publishes peer-reviewed scientific and clinical studies to advance the understanding and clinical application of regional techniques for surgical anesthesia and postoperative analgesia. Coverage includes intraoperative regional techniques, perioperative pain, chronic pain, obstetric anesthesia, paediatric anesthesia, outcome studies, and complications.

Abstract
Background: Whether volatile anesthetic solubility affects postanesthesia recovery time in clinical practice is unclear. We investigated the association among 3 volatile agents and 2 clinically relevant outcomes-postanesthesia care unit (PACU) recovery time (time from PACU admission to fulfillment of discharge criteria) and oversedation (Richmond Agitation-Sedation Scale score ≤-3)-as a potential contributor to delaying PACU discharge. The volatile agents studied were isoflurane, desflurane, and sevoflurane. We hypothesized that increased solubility of the volatile agent (isoflurane versus desflurane or sevoflurane) would be associated with longer PACU recovery time and higher rates of oversedation.

Methods: This retrospective observational study included adults (≥18 years) who underwent surgical procedures under general anesthesia with a volatile agent and were admitted to the PACU from May 5, 2018, to December 31, 2020. The primary outcome was PACU recovery time, and the secondary outcome was oversedation. PACU recovery time was log-transformed and analyzed with linear regression. Oversedation was analyzed by using logistic regression. To account for potential confounding, inverse probability of treatment weighting (IPTW) was used. Pairwise comparisons of the 3 agents were performed, with P < .017 (Bonferroni-adjusted) considered significant.

Results: Of 47,847 patients included, 11,817 (24.7%) received isoflurane, 11,286 (23.6%) received desflurane, and 24,744 (51.7%) received sevoflurane. Sevoflurane had an estimated 4% shorter PACU recovery time (IPTW-adjusted median [interquartile range {IQR}], 61 [42-89] minutes) than isoflurane (64 [44-92] minutes) (ratio of geometric means [98.3% confidence interval {CI}], 0.96 [0.95-0.98]; P < .001). Differences in PACU recovery time between desflurane and the other agents were not significant. The IPTW-adjusted frequency of oversedation was 8.8% for desflurane, 12.2% for sevoflurane, and 16.7% for isoflurane; all pairwise comparisons were observed to be significant (odds ratio [98.3% CI], 0.70 [0.62-0.79] for desflurane versus sevoflurane, 0.48 [0.42-0.55] for desflurane vs isoflurane, and 0.69 [0.63-0.76] for sevoflurane versus isoflurane; all P < .001). Although oversedated patients had longer PACU recovery time, differences in the oversedation rate across agents did not result in meaningful differences in time to PACU recovery.

Conclusions: In clinical practice, only small, clinically unimportant differences in PACU recovery time were observed between the volatile anesthetics. Although oversedation was associated with increased PACU recovery time, differences in the rate of oversedation among agents were insufficient to produce meaningful differences in overall PACU recovery time across the 3 volatile agents. Practical attempts to decrease PACU recovery time should address factors other than volatile agent selection.

Abstract
Background: Sevoflurane and desflurane are halogenated hydrocarbons with global warming potential. We examined the maximum potential benefit assuming 100% efficiency of waste gas capture technology used in operating rooms and recovery locations.

Methods: We performed computer simulations of adult patients using the default settings of the Gas Man software program, including the desflurane vaporizer setting of 9% and the sevoflurane vaporizer setting of 3.7%. We performed 21 simulations with desflurane and 21 simulations with sevoflurane, the count of 21 = 1 simulation with 0-hour maintenance + (1, 2, 3, 4, or 5 hours of maintenance) × (0.5, 1, 2, or 4 L per minute fresh gas flow during maintenance).

Results: (1) A completely efficient gas capture system could recover a substantive amount of agent even when the case is managed with low flows. All simulations had at least 22 mL agent recovered per case, considerably greater than the 12 mL that we considered the minimum volume of economic and environmental importance. (2) All 42 simulations had at least 73% recovery of the total agent administered, considerably greater than the median 52% recovery measured during an experimental study with one gas capture technology and desflurane. (3) The maximum percentage desflurane (or sevoflurane) that could be captured decreased substantively with progressively longer duration anesthetics for low-flow anesthetics but not for higher-flow anesthetics. However, for all 8 combinations of drug and liters per minute simulated, there was a substantively greater recovery in milliliters of agent for longer duration anesthetics. In other words, if gas capture could be near perfectly efficient, it would have greater utility per case for longer duration anesthetics. (4) Even using a 100% efficient gas capture process, at most 6 mL liquid desflurane or 3 mL sevoflurane per case would be exhaled during the patient's stay in the postanesthesia care unit. Therefore, the volume of agent exhaled during the first 1 hour postoperatively is not a substantial amount from an environmental and economic perspective to warrant consideration of agent capture by having all these patients in the postanesthesia care unit, or equivalent locations, using the specialized anesthetic gas scavenging masks with access to the hospital scavenging system at each bed.

Conclusions: Simulations with Gas Man show a strong rationale based on agent uptake and distribution for using volatile anesthetic agent capture in operating rooms if the technology can be highly efficient at volatile agent recovery.

Abstract
Jet injection is a drug delivery system without a needle. A compressed liquid drug formulation pierces the skin, depositing the drug into the subcutaneous or intramuscular tissues. We investigated the pharmacokinetics and patient experience of dexmedetomidine administered using jet injection in six healthy adult study participants. This needleless jet injection device was used to administer dexmedetomidine 0.5 μg/kg to the subcutaneous tissues overlying the deltoid muscle. Serum concentrations of dexmedetomidine were assayed at approximately 5 minutes, 15 minutes, 30 minutes, 1 hour and 4 hours after administration. Pharmacokinetic interrogation of concentration time profiles estimated an absorption half time for jet-injected dexmedetomidine of 21 minutes (coefficient of variation 69.4%) with a relative bioavailability assumed unity. In our samples the measured median peak (range) concentration was 0.164 μg/l (0.011-0.325 μg/l), observed in the sample taken at a median (range) of 13.5 minutes (11-30 minutes). The Richmond agitation sedation scale was used to assess the sedative effect, and scored 0 (alert and calm) or -1 (drowsy) in all participants. Five of the six participants stated they would prefer jet injection to needle injection in the future and one had no preference. The findings suggest that the use of a larger dose (>2 μg/kg) would be required to achieve the clinically relevant target concentration of 1 μg/l necessary to achieve deeper sedation (Richmond agitation sedation scale ≤3).

Abstract
Purpose: Memsorb™ is a novel device for carbon dioxide (CO2) removal from anesthesia circuits via a semipermeable polymeric membrane. We evaluated the performance of the memsorb device for the removal of CO2 in an Aisys™ CS2 machine and compared it with a standard chemical granulate absorber (CGA) using a high-fidelity lung simulator.

Methods: We used an in vitro lung simulator (DUCt) to control CO2 release by imitating alveolar gas exchange. The ventilator settings were identical for all measurements. The fresh gas flow (FGF) was randomized to either 0.5 L·min-1 or 2 L·min-1, completing three trials for each FGF for either memsorb or CGA. The EtCO2 and FICO2 levels were recorded for 30 min in each setting.

Results: EtCO2 was comparable between the groups with 2 L·min-1 FGF over the observation period. FICO2 was significantly higher in the memsorb group during the trial (2 L·min-1; 3.9 mm Hg; 95% CI, 4.4 to 3.3; P < 0.001). EtCO2 with 0.5 L·min-1 FGF was higher with memsorb than with CGA over the observation period (3.7 mm Hg; 95% CI, 2.7 to 4.7; P = 0.004). With 0.5 L·min-1 FGF, FICO2 was significantly higher in the memsorb group compared with CGA over the whole observation period (6 mm Hg; 95% CI, 6.4 to 5.5; P < 0.001).

Discussion: CO2 was successfully removed from the anesthesia circuit. FICO2 was significantly higher with memsorb throughout the observation period. Nevertheless, the clinical impact of these observations remains unclear. Further clinical trials are required to determine the utility of the novel device.

Keywords: anesthetics; carbon dioxide absorbent; intubation; mechanical ventilation; tidal volume.