Ventilator circuit

Avoid unnecessary ventilator circuit changes/manipulation... 

Respiratory alkalosis associated with mechanical ventilation can often be corrected by decreasing the number of mechanical breaths per minute, using a capnograph and spirometer to adjust ventilator settings more precisely, or increasing dead space in the ventilator circuit. 

Everard, M.L., Stammers, J., Elardy, J.G., and Milner, A.D., New aerosol delivery system from neonatal ventilator circuits, Dis. Childhood, 67 826-830 (1992). 

The exact method of delivery and monitoring of inhaled nitric oxide therapy varies with the clinical indication and duration of treatment. " A number of descriptions have appeared, including the Douglas bag, the titration of nitric oxide continuously into the inspiratory limb of the ventilator circuit, and the use of a ventilator nebulizer to deliver nitric oxide during inspiration only or double-blender techniques adaptable to a variety of circumstances. We reviewed our initial experience with delivery and monitoring techniques in a variety of clinical settings in 123 patients and subsequently adapted a system to simplify the delivery in continuous-flow circuits suitable for paralyzed infants, as many others have done before us. ... 

Figure 20 Sketch of ventilator circuit incorporating jet nebulization. The lower panel describes method for measuring inhaled mass in vitro, the upper panel, in vivo gamma camera scanning. (From Ref. 35.)...

Nebulizers can be tested in a given ventilator circuit and, as shown in Fig. 22, the choice of nebulizer can have a significant impact on drug delivery. Inhaled mass versus time is shown for a number of common nebulizers, including the devices first tested in Fig. 5. Devices shown to be efficient for spontaneously breathing patients are often even more efficient on the ventilator provided that the ventila-... 

Ventilator circuits are often humidified and heated. Hygroscopic effects are complex in that there is considerable condensation and rainout of water in the connecting tubing between the nebulizer and the patient. This liquid is not recycled and aerosol lost is not recovered. The conditions in ventilator tubing are likely to be supersaturated and the aerosol particles serve as nuclei. Approximately 40-50% of drug can be lost when the circuit is humidified (for aerosols produced via nebulizer or MDl (27,33). 

A low-flow cascade impactor can be inserted into the ventilator circuit between the distal tip of the endotracheal (or tracheostomy) tube and the inhaled mass filter. Impaction experiments have repeatedly shown that the aerosols leaving the tube and entering the patient are similar to those produced by small-particle nebulizers such as the AeroTech n. Often the MMADs are about 1.0 pm (27). 

Figure 24 Diagram of neonatal ventilator circuit incorporating a nebulizer. This example illustrates an ultrasonic device. Cascade impaction can be performed at the distal tip of the endotracheal tube. (From Ref. 36.)...

Wildhaber JH, Hayden MJ, Dore ND, Devadason SG, LeSouef PN. Salbutamol delivery from a HFA pMDI in paediatric ventilator circuits. An in vitro study. Chest 1998 113 186-191. 

Everard ML, Stammers J, Hardy JG, Milner AD. New aerosol delivery system for neonatal ventilator circuits. Arch Dis Child 1992 67 826-830. 

Arnon S, Grigg J, Nikander K, Silverman M. Delivery of micronized budesonide suspension by metered dose inhaler and jet nebulizer into a neonatal ventilator circuit. Pediatr Puhnonol 1992 13 172-175. 

In order to improve the protection against sodium fire the following works are in progress and should be archived in 1998 partial isolation of each loop from the others, isolation of the sodium fiom the steam circuits, thermal protection of some structures (particularly the supports of the sodium pipes, the main parts of the structural steel network, the steam generator vessels), the construction of sodium recuperation tanks in case of leaks, the construction of a protection gallery for the command equipment, modification of the ventilation circuits, etc. 

At Zaporozhe NPP, the main control room and emergency control room has a common ventilation circuit for Units 1 to 4 while they are separated for Units 5 and 6. This disposition cannot ensure habitability in case of fire in locations ventilated by this circuit because of the smoke spreading. 

There are three main types of ventilator circuits used for HMV Single circuits with a leak, single circuits with a valve, and double circuits with a valve. When used with NIV, it is important that the appropriate mask be used. Table 5 summarizes the important points associated with each type of circuit. Circuits with a leak are used for bi-level devices. The intentional leak and CO2 washout for a given pressure vary significantly depending on the manufacturer and the type of mask. There are many choices of masks for the leak circuit as these masks are also used for CPAP. We have already reviewed the issue of CO2 washout and concluded that this is not a major concern when using a nasal mask (20). The only type of mask where this might be of clinical concern is with a full-face mask. A fiill-face mask is... 

Empty contaminated condensation from ventilator circuits ql2 hr or p.r.n. 

Ventilator circuit changes at intervals of less than 48 hours V... 

Ventilator circuit Do not change more often than every 48 hours lA A... 

The effect of changing ventilator tubing in the prevention of VAP has been explored. There appears to be no advantage in changing ventilator circuits more frequently than every 48 hours. Furthermore, we support the current data suggesting that they may not need to be changed at all (2,152-154). 

Small volume in-line medication nebuUzers, which are inserted into the mechanical ventilator circuit, are readily colonized from contaminated condensate and allow bacterial aerosols direct access to the lower airway, bypassing the normal host defenses (1,156,157). Both hand-held and in-line should be sterilized between patients and their use limited to clear indications. 

Craven DE, Goularte TA, Make BJ. Contaminated condensate in mechanical ventilator circuits a risk factor for nosocomial pneumonia. Am Rev Respir Dis 1984 129 625-628. 

Hartstein AI, Rashad AL, Liebler JM, et al. Multiple intensive care unit outbreak of Acinetobacter calcoaceticus subspecies anitratus respiratory infection and colonization associated with contaminated, reusable ventilator circuits and resuscitation bags. Am J Med 1988 85 624-631. 

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