Week 1 Mechanical ventilation.pdf - MECHANICAL VENTILATION...

This preview shows page 1 - 2 out of 5 pages.

MECHANICAL VENTILATION: BASIC REVIEW VERY BASIC RESPIRATORY PHYSIOLOGY What do the lungs do? Yes, the simple answer is gas exchange: Oxygenation: exactly that, the transfer of oxygen from the air we breathe to the blood. Ventilation: the transfer of CO2 from the blood to the alveoli and out of the body An important concept to remember: normal breathing is a negative-pressure phenomenon; mechanical ventilation is POSITIVE pressure ventilation. The end result is still airflow and gas exchange, but the mechanics are different. Some basic physiologic concepts to review (look in any good textbook or on the web): Air flow Compliance [Volume change per unit of pressure change across an elastic structure] Elastance [The reciprocal of compliance, a measure of the change in pressure per unit change in volume; i.e., stiffness] Resistance [Driving pressure divided by flow (P/V)] Dead Space [the portion of each breath that does not participate in gas exchange] Anatomic dead space: the volume of the conducting airways Physiologic dead space: also includes the contribution of alveoli that are well-ventilated but poorly perfused. Other important concepts to review: PO 2 (PaO 2 and PAO 2 ), SaO 2 (hemoglobin oxygen saturation), CaO 2 (oxygen content), the PCO 2 equation, the alveolar gas equation. IMPORTANT EQUATIONS TO KNOW A Change in pCO 2 of 10 torr = a change in pH of 0.08 The three steps to calculate the AaO 2 difference: P I O 2 = barometric pressure x FIO 2 P A O 2 = P I O 2 – (pCO 2 /R) AaO 2 difference = P A O 2 – pO 2 RESPIRATORY FAILURE Why intubate and mechanically ventilate your patient? 1. Airway protection (this is not ‘respiratory failure’: this implies no derangements in gas exchange, but a CNS or mechanical loss of airway protection/patency) 2. Hypoxic respiratory failure pO2 < 50 on 100% NRB Decreased ambient FiO2, Increased pCO 2 , Diffusion block, V/Q mismatch, Right-to-left shunt 3. Hypercarbic respiratory failure pH < 7.30. pCO2 > 50 Acute versus chronic; Won’t versus Can’t; CNS versus bellows MODES OF MECHANICAL VENTILATION - Some parameters are set, while others are variable. - There are two basic types of mechanical ventilation and all of the various modes fall into one of these two subsets. o Volume control o Pressure control There is a preset peak pressure limit which will therefore determine tidal volume. Note that pressure control only refers to the type of breath delivered, not the specific mode of ventilation (it is NOT synonymous with Pressure Support, which is a pressure control mode). - What can be set on modern mechanical ventilators? o FiO2: the percentage of inspired oxygen, recall that room air is 21% (0.21) at all altitudes. o Mode: see the more detailed discussion below and the graphics above. o Rate: how many mandatory breaths per minute your patient is given is your set rate. Your patient can ‘overbreathe’ at a higher rate, the level of support with these spontaneous breaths is also something that can be set (see discussion below).
Image of page 1

Subscribe to view the full document.

Image of page 2
  • Fall '18
  • airway pressure

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern