[Climatization of anesthetic gases using different breathing hose systems]

A novel, cassette-based nitric oxide delivery system with an advanced feedback control algorithm accurately delivers nitric oxide via the anesthesia machine independent of fresh gas flow rate and volatile anesthetic agent

Nitric oxide (NO), a selective pulmonary vasodilator, can be delivered via conventional ICU and anesthesia machine ventilators. Anesthesia machines are designed for rebreathing of circulating gases, reducing volatile anesthetic agent quantity used. Current cylinder- and ionizing-based NO delivery technologies use breathing circuit flow to determine NO delivery and do not account for recirculated gases; therefore, they cannot accurately dose NO at FGF below patient minute ventilation (MV). A novel, cassette-based NO delivery system (GENOSYL® DS, Vero Biotech Inc.) uses measured NO concentration in the breathing circuit as an input to an advanced feedback control algorithm, providing accurate NO delivery regardless of FGF and recirculation of gases. This study evaluated GENOSYL® DS accuracy with different anesthesia machines, ventilation parameters, FGFs, and volatile anesthetics. GENOSYL® DS was tested with GE Aisys and Dräger Fabius anesthesia machines to determine NO dose accuracy with FGF < patient MV, and with a Getinge Flow-i anesthesia machine to determine NO dose accuracy when delivering various volatile anesthetic agents. Neonatal and adult mechanical ventilation parameters and circuits were used. GENOSYL® DS maintained accurate NO delivery with all three anesthesia machines, at low FGF with recirculation of gases, and with all volatile anesthetic agents at different concentrations. Measured NO2 levels remained acceptable at ≤ 1 ppm with set NO dose ≤ 40 ppm. GENOSYL® DS, with its advanced feedback control algorithm, is the only NO delivery system capable of accurately dosing NO with anesthesia machines with rebreathing ventilation parameters (FGF < MV) regardless of anesthetic agent.

Minimal fixed flow anesthesia for off-pump coronary artery bypass surgery: A parallel randomized trail

Objectives

The aim of the present study was to test a safety of a fixed minimal (0.5 l/min) fresh gas flow (FGF) anesthesia as a method ensuring adequate oxygenation during off-pump coronary artery bypass grafting operations.

Design

A randomized, prospective study.

Setting

Single-center clinical hospital affiliated with a university.

Participants

208 patients underwent off-pump coronary artery bypass surgery.

Interventions

All patients received endotracheal inhalational anesthesia with fixed minimal FGF. Half of them were anesthetized by sevoflurane and another half by isoflurane. The fresh (carrier) gas was pure oxygen in the control groups and a mixture of medical air and oxygen (FiO2 0.8) in the trial groups.

Measurements and main results

In the control groups inhaled oxygen concentration changed minimally during the operation. In the trial groups in 28.8 % of cases inhaled oxygen concentration dropped below preliminary margin (0.4). Body surface area (BSA) (B = 38.7; p = 0.002) and patient's age (B = -0.47; p = 0.004) were retained into final logistic regression model as independent predictors. We divided BSA into subcategories and analyzed data by survival cox regression with Forward LR method. Patients with BSA>2.3 (Exp.B = 183) and BSA [2.2-2.3] (Exp.B = 59) had high chance to get less than 0.4 of inhaled oxygen concentration compared to the patients with BSA <2.0 (p < 0.001).Exp(B) or OR for the patients' age as independent predictor tested in multiple logistic regression was 0.628 In other words, for every year less the patient had 1/0.628 = 1.6 times more chance to reach the preliminary low margin (0.4) of oxygenation.

Conclusions

Fixed minimal FGF 0.5 l/min with FiO2 0.8 may not be sufficient for the younger patients with BSA >2.0 to maintain inhaled oxygen concentration above 0.4. Using pure oxygen as a carrier gas during fixed minimal flow long term anesthesia is much safer and more reliable.

Temperature loss by ventilation in a calorimetric bench model

In intensive care medicine heat moisture exchangers are standard tools to warm and humidify ventilation gases in order to prevent temperature loss of patients or airway epithelia damage. Despite being at risk of hypothermia especially after trauma, intubated emergency medicine patients are often ventilated with dry and in winter probably cold ventilation gases. We tried to assess the amount of temperature-loss due to ventilation with cold, dry medical oxygen in comparison to ventilation with warm and humidified oxygen. We ventilated a 50-kg water-dummy representing the calorimetric capacity of a 60-kg patient over a period of 2 hours (tidal volume 6.6 mL/kg = 400 mL; respiratory rate 13/min). Our formal null-hypothesis was that there would be no differences in temperature loss in a 50 kg water-dummy between ventilation with dry oxygen at 10°C vs. ventilation with humidified oxygen at 43°C. After 2 hours the temperature in the water-dummy using cold and dry oxygen was 29.7 ± 0.1°C compared to 30.4 ± 0.1°C using warm and humidified oxygen. This difference in cooling rates between both ventilation attempts of 0.7 ± 0.1°C after 2 hours represents an increased cooling rate of ~0.35°C per hour. Ventilation with cool, dry oxygen using an automated transport ventilator resulted in a 0.35°C faster cooling rate per hour than ventilation with warm humidified oxygen in a bench model simulating calorimetric features of a 60-kg human body.

Brief review: theory and practice of minimal fresh gas flow anesthesia

PURPOSE

The aim of this brief review is to provide an update on the theory regarding minimal fresh gas flow techniques for inhaled general anesthesia. The article also includes an update and discussion of the practical aspects associated with minimal-flow anesthesia, including the advantages, potential limitations, and safety considerations of this important anesthetic technique.

PRINCIPAL FINDINGS

Reducing the fresh gas flow to < 1 L·min(-1) during maintenance of anesthesia is associated with several benefits. Enhanced preservation of temperature and humidity, cost savings through more efficient utilization of inhaled anesthetics, and environmental considerations are three key reasons to implement minimal-flow and closed-circuit anesthesia, although potential risks are hypoxic gas mixtures and inadequate depth of anesthesia. The basic elements of the related pharmacology need to be considered, especially pharmacokinetics of the inhaled anesthetics. The third-generation inhaled anesthetics, sevoflurane and desflurane, have low blood and low tissue solubility, which facilitates rapid equilibration between the alveolar and effect site (brain) concentrations and makes them ideally suited for low-flow techniques. The use of modern anesthetic machines designed for minimal-flow techniques, leak-free circle systems, highly efficient CO(2) absorbers, and the common practice of utilizing on-line real-time multi-gas monitor, including essential alarm systems, allow for safe and cost-effective minimal-flow techniques during maintenance of anesthesia. The introduction of new anesthetic machines with built-in closed-loop algorithms for the automatic control of inspired oxygen and end-tidal anesthetic concentration will further enhance the feasibility of minimal-flow techniques.

CONCLUSIONS

With our modern anesthesia machines, reducing the fresh gas flow of oxygen to 0.3-0.5 L·min(-1) and using third-generation inhaled anesthetics provide a reassuringly safe anesthetic technique. This environmentally friendly practice can easily be implemented for elective anesthesia; furthermore, it will facilitate cost savings and improve temperature homeostasis.

[Prevention of infections under anesthetic breathing with breathing filters: concerted recommendations of the Deutsche Gesellschaft für Krankenhaushygiene e.V. (DGKH) and the Deutsche Gesellschaft für Anästhesiologie und Intensivmedizin e.V. (DGAI)]

An interdisciplinary working group from the German Society of Hospital Hygiene (DGKH) and the German Society for Anesthesiology and Intensive Care (DGAI) worked out the following recommendations for infection prevention during anesthesia by using breathing system filters (BSF). The BSF shall be changed after each patient. The filter retention efficiency for airborne particles is recommended to be >99% (II). The retention performance of BSF for liquids is recommended to be at pressures of at least 60 hPa (=60 mbar) or 20 hPa above the selected maximum ventilation pressure in the anesthetic system.The anesthesia breathing system may be used for a period of up to 7 days provided that the functional requirements of the system remain unchanged and the manufacturer states this in the instructions for use. The breathing system and the manual ventilation bag are changed immediately after the respective anesthesia if the following situation has occurred or it is suspected to have occurred: Notifiable infectious disease involving the risk of transmission via the breathing system and the manual bag, e.g. tuberculosis, acute viral hepatitis, measles, influenza virus, infection and/or colonization with a multi-resistant pathogen or upper or lower respiratory tract infections. In case of visible contamination e.g. by blood or in case of defect, it is required that the BSF and also the anesthesia breathing system is changed and the breathing gas conducting parts of the anesthesia ventilator are hygienically reprocessed.Observing of the appropriate hand disinfection is very important. All surfaces of the anesthesia equipment exposed to hand contact must be disinfected after each case.

Infection prevention during anaesthesia ventilation by the use of breathing system filters (BSF): Joint recommendation by German Society of Hospital Hygiene (DGKH) and German Society for Anaesthesiology and Intensive Care (DGAI)

An interdisciplinary working group from the German Society of Hospital Hygiene (DGKH) and the German Society for Anaesthesiology and Intensive Care (DGAI) worked out the following recommendations for infection prevention during anaesthesia by using breathing system filters (BSF). The BSF shall be changed after each patient. The filter retention efficiency for airborne particles is recommended to be >99% (II). The retention performance of BSF for liquids is recommended to be at pressures of at least 60 hPa (=60 mbar) or 20 hPa above the selected maximum ventilation pressure in the anaesthetic system. The anaesthesia breathing system may be used for a period of up to 7 days provided that the functional requirements of the system remain unchanged and the manufacturer states this in the instructions for use.THE BREATHING SYSTEM AND THE MANUAL VENTILATION BAG ARE CHANGED IMMEDIATELY AFTER THE RESPECTIVE ANAESTHESIA IF THE FOLLOWING SITUATION HAS OCCURRED OR IT IS SUSPECTED TO HAVE OCCURRED: Notifiable infectious disease involving the risk of transmission via the breathing system and the manual bag, e.g. tuberculosis, acute viral hepatitis, measles, influenza virus, infection and/or colonisation with a multi-resistant pathogen or upper or lower respiratory tract infections. In case of visible contamination e.g. by blood or in case of defect, it is required that the BSF and also the anaesthesia breathing system is changed and the breathing gas conducting parts of the anaesthesia ventilator are hygienically reprocessed.Observing of the appropriate hand disinfection is very important. All surfaces of the anaesthesia equipment exposed to hand contact must be disinfected after each case.

The moisture-conserving performance of breathing system filters in use with simulated circle anaesthesia breathing systems*

Breathing system filters can be used to humidify gases delivered to patients. Performance can be determined by measuring the net moisture loss (the difference between expired and inspired levels of humidity) from a patient model. The net moisture loss should be decreased by increasing the level of humidity in the breathing system by, for example, using a circle breathing system. The effect of four different filters, three different levels of humidity in the breathing system (7, 13 and 19 g.m-3) and two tidal volumes (0.5 l and 1.0 l) on the net moisture loss from a patient model was measured. The net moisture loss decreased as the humidity in the breathing system increased and was less for the lower tidal volume. Adequate levels of humidity (>/= 20 g.m-3) will be delivered to patients by most filters provided they are used in conjunction with circle breathing systems and low fresh gas flows.

Minimal-flow anaesthesia with controlled ventilation: comparison between laryngeal mask airway and endotracheal tube

BACKGROUND AND OBJECTIVE

Minimal- and low-flow anaesthesia (fresh gas flow below 1 L min(-1)) provide many advantages, including reduced cost, conservation of body heat and airway humidity. An airtight seal is essential between the airway device and the airway of the patient. Therefore, we investigated whether the airtight seal created by a laryngeal mask airway allows controlled ventilation of the lungs when the fresh gas flow is reduced to 0.5 L min(-1) and compared this with an endotracheal tube.

METHODS

In a prospective clinical study, 207 patients were managed using a laryngeal mask or an endotracheal tube. After intravenous induction of anaesthesia and 15 min of high fresh gas flow, the flow was reduced to 0.5 L min(-1). The breathing system was monitored for airway leaks, and the patients were assessed for complications after airway removal and postoperative discomfort.

RESULTS

Both the laryngeal mask and endotracheal tube allowed fresh gas flow reduction to 0.5 L min(-1) in 84.7% and 98.3% of cases respectively (small leaks: 12% laryngeal mask, 1.7% endotracheal tube). Three patients with the laryngeal mask (3.3%) had airway leaks that were too large to permit any reduction in the fresh gas flow.

CONCLUSIONS

The use of the laryngeal mask airway was more likely to be associated with a gas leak than use of an endotracheal tube; however, if modern anaesthesia machines and monitors are used, in 96.7% of the patients managed with a laryngeal mask a reduction in the fresh gas flow to 0.5 L min(-1) was possible. The incidence of coughing and postoperative complaints (sore throat, swallowing problems) was higher after use of an endotracheal tube.