Patient breathing against closed system, so they must fully sedated with no respiratory effort.
A/C-vents at preset Vt and Rate, if pt initiates a breath, it is given at preset Vt.
In positive pressure, distribution is to non-dependant regions.
What you need to know for each mode is the trigger, the limit, and the cycle.
(ESICM 2008 in Lisbon Abstract 22 in Inten Care Med) (Final In-Press) High PEEP causes right ventricular problems mostly by increased right vent afterload, not decreased preload.
But you can still overcome this by fluid as shown by the PLR abolishment of the effects (CCM 2010;38(3):802-807) Higher PEEP associated with increased survival in ARDS patients in SR/MA (JAMA 2010;303(9):865) If you place a patient on 100% for 5-15 minutes, P (A-a) is entirely from shunt, divide by 20 to get shunt fraction Normal shunt fraction is 3% Always consider atelectasis as shunt fraction 40-50%, increasing Fi O2 will not change Sa O2 The total work of breathing can be partitioned between an elastic and resistive work.
This is examplified in obese patients, and explains their chronic respiratory failure.
Low chest wall compliance can be acquired in critical illness due to circumferential chest dressings, extensive edema, and, in particular, raised abdominal pressure.
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Best Textbook (Tobin MJ Principles and Practice of Mech Vent) Handout for Studs Review Article for Residents My Vent Lecture Handout Mech ventilated patients have a dead space to alveolar ratio of 1:1 as opposed to the 1:2 in a normal patient Va for a normal CO2 is 60 cc/kg/min, so we need to double that (120 cc/kg/min) If a 70kg man needs 8400 cc/minute either deadspace for production of CO2 is elevated. Patients were randomly allocated to mechanical ventilation with a tidal volume of 10 ml per kilogram of predicted body weight or a tidal volume of 6 ml per kilogram of predicted body weight. The trial was stopped after 150 patients were enrolled because development of lung injury was higher in the group treated with conventional tidal volumes as compared to the lower tidal volume group (13.5% vs. Analysis of the lavage ﬂuid cytokine proﬁles revealed no differences over time between the two ventilation groups.
Dividing the delivered tidal volume by this difference quantifies the respiratory system compliance.
Oxygen Physiology PAO2=PIO2((760-47)x0.21 or 150 on room air)-Pa CO2/R(0.8) Amount of O2 dissolved in the blood 1.34x Hbx(Sa O2/100) 0.003 x PO2=20.8 DO2=(1.39 x Hb x Sa O2 (0.003x Pa O2)) x Q Q=cardiac Output Predicted body weight (PBW) can be calculated by the following formula: in men, PBW (kg)=50 0.91 (centimeters of height152.4); in women, PBW (kg)=is 45.5 0.91 (centimeters of height152.4) each time we disconnect the vent, we cause derecruitment Hyperoxia screws up left ventricular function and filling pressures (Chest 2001;120(2):467) Doppler study of healthy volunteers shows that hyperoxia screws up heart function (Cardiovasc Ultrasound 2004;2(22): positive intrathoracic pressure decreases venous return but also decreases afterload In supine pts, spont breathing distributes air preferentially to dependant regions.
Moreover, the heart increases in size and weight and compresses the left lower lobe.