Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content ++ Involves intermittent administration of positive pressure:Expiratory phase is passive:Flow out of patient is determined by airway resistance and lung elastance (1/compliance)In general, ventilators in anesthesia machines are simpler than ventilators seen in an ICU setting; however, the distinction between the two is increasingly blurred ++ Controlled mechanical ventilation:Designed for anesthetized, and often paralyzed, patientsVolume controlled and pressure controlled:Volume controlled (Figure 49-1):A tidal volume and a respiratory rate are programmedTidal volumes are constant, but airway pressures vary with airway resistance and lung and chest wall compliancesPressure controlled (Figure 49-2):Inspiratory pressure, inspiratory time, and respiratory rate are programmedThe ventilator delivers a constant pressure during inspirationThe inspired pressure with each breath is constant, but tidal volumes may change with any changes in airway resistance and lung and chest wall compliances (i.e., abdomen insufflation, bronchospasm, ETT kinking, secretions in ETT)Need to closely monitor actually delivered VtMay be useful in conditions under which high peak pressures are generated under volume-controlled ventilation, for example, ALI/ARDS, morbidly obese patients, laparoscopic surgery in patients in steep Trendelenburg positionNo evidence that “protective ventilation” used for ARDS patients improves outcome in patients with healthy lungsPartially controlled mechanical ventilation:Designed for spontaneously breathing patients. Not all OR ventilators have these modesModes:Synchronized intermittent mandatory ventilation (SIMV; Figure 49-3):A tidal volume and a respiratory rate are programmedThe patient may spontaneously breathe at a rate higher than that which is programmedThe ventilator will allow this, but will not assist the patient’s spontaneous breathsPressure support ventilation (PSV; Figure 49-4):The patient breathes spontaneouslyWith each breath, the ventilator adds a programmed amount of pressure to assist the patientTypically 5 cm H2O will eliminate the extra work of breathing due to the resistance of the circuit and the ETT. Beyond that, the machine assists the patient’s breathingSIMV + PSV combines the two previous modes:Mechanical breaths are deliveredSpontaneous breaths are assisted ++Figure 49-1. Volume-Targeted Square Wave Flow Controlled-Mode VentilationGraphic Jump LocationView Full Size||Download Slide (.ppt)Note that inspiratory flow is constant while pressure increases until the start of expiration. Also, there is no negative deflection before each breath, as the breaths are not initiated by the patient. Vt 700 mL, RR 15, I:E 1:2, PEEP 5 cm H2O. Reproduced with permission from Hess DR, MacIntyre NR, Mishoe SC, et al, eds. Respiratory Care: Principles and Practice. Philadelphia: WB Saunders; 2002:786–791. © Elsevier.++Figure 49-2. Pressure-Targeted Controlled-Mode Ventilation (PCV)Graphic Jump LocationView Full Size||Download Slide (.ppt)Note that inspiratory flow increases to achieve the target pressure, and then decreases as the lungs fill. Pinspired 25 cm H2O, RR 15, I:E 1:1, PEEP 5 cm H2O. Reproduced with permission from Hess DR, MacIntyre NR, Mishoe SC, et al, eds. ... Your MyAccess profile is currently affiliated with '[InstitutionA]' and is in the process of switching affiliations to '[InstitutionB]'. Please click ‘Continue’ to continue the affiliation switch, otherwise click ‘Cancel’ to cancel signing in. Get Free Access Through Your Institution Learn how to see if your library subscribes to McGraw Hill Medical products. Subscribe: Institutional or Individual Sign In Username Error: Please enter User Name Password Error: Please enter Password Forgot Username? Forgot Password? Sign in via OpenAthens Sign in via Shibboleth