Transcript RESP. 221
RESP. 221 WEEK 2 MECHANICS OF VENTILATION VENTILATION Chapter 3 & 4 Oxygenation vs. Ventilation • Alveoli-Capillary - Review • Oxygenation • Ventilation – Dead Space Ventilation – Minute Ventilation Oxygenation Estimating Pressure of O2 molecule (PO2) Equation = Atmosphere = PB x FIO2 (160) Oxygenation •Estimating PO2 once inhaled and travels down the trachea •Equation = Airway = PB-H20 x FIO2 (150) Oxygenation •Estimating PO2 once it’s in the alveoli ready for diffusion into the blood stream •Aka PAO2 •Equation – PAO2 • PA-aDO2 Oxygenation • Estimating PO2 once it’s in the blood stream (artery) • Aka PaO2 • Do NOT confuse PAO2 with PaO2 PAO2 & PA-aO2 • PAO2 Normal • 100mmHg (room air) • 663 mmHg (100% at sea level) • P(A-a)O2 Normal • 10-25 mmHg (R/A) • 30 -50 mmHg (100% O2) Examples What is the PAO2? pH 7.40 PaCO2 40mmHg PaO2 100mmHg HCO3 24mEq/L FIO2 40% (From Previous Slide) • Is lung function normal? • What is the patient having difficult with? Ventilation? Or Oxygenation? Example What is the PAO2? pH 7.40 PaCO2 40mmHg PaO2 300mmHg HCO3 24mEq/L FIO2 50% VENTILATION •PARTIAL PRESSURE OF CO2 •PaCO2 •Several Ways to measure Ventilation Capnometers – Capnography – ABG – VENTILATION 1. MINUTE VENTILATION 2. DEAD-SPACE VENTILATION 3. MINUTE ALVEOLAR VENTILATION 4. PHYSIOLOGIC DEADSPACE Ve • Minute Ventilation • Definition: • Expressed as: • Normal range of 6 L/min – 10L/min • What does the book say? • VT expressed in mL. • To convert to L, ÷ 1000 Calculate the minute ventilation in L/min: • RR: 8/min Vt: 400mL • RR: 16/min Vt: 550mL • RR: 20/min Vt: 600mL Drawback • Not useful in determining how much ventilation is taking place at the alveolar units • WHY NOT? _________________________________ _________________________________ Deadspace Ventilation (Vd) • 3 types • Anatomical • Alveolar • Physiological • “DEADSPACE” - Anatomical • 1/3 of Vt • Ex. 500ml • Estimated at 1 mL for every lbs. Alveolar- Anatomical = Physiological • ANATOMICAL DEAD SPACE------THE CONDUCTING AIRWAYS FROM MOUTH AND NOSE, ALL THE WAY AND INCLUDING THE TERMINAL BRONCIOLES CONSTITUTE ANATOMICAL DEAD SPACE. AIR MOVES THROUGH THEM TO GET TO THE ALVEOLI, BUT NO GAS EXCHANGE TAKES PLACE. WASTED VENTILATION, OR DEAD SPACE VENTILATION ARE SYNONIMOUS, AND REFER TO AS AIRWAYS THAT ARE VENTILATED (AIR PASING OVER THEM) BUT DO NOT RECEIVE BLOOD FLOW FROM THE PULMONARY CIRCULATION. • ALVEOLAR DEAD SPACE (Vda) - THE VOLUME CONTAINED IN NONPERFUSED ALVEOLI( ALVEOLI WITH NO BLOOD FLOW). ANY FACTOR DECREASING PULMONARY BLOOD FLOW, SUCH AS LOW CARDIAC OUTPUT OR PULMONARY EMBOLI, INCREASES ALVEOLAR DEAD SPACE. • PHYSIOLOGICAL DEAD (VD) SPACE IS THE SUM OF BOTH. SO VD CAN INCREASES IF THERE IS A DECREASE IN CARDIAC OUTPUT, AND ALSO INCREASES IF THERE IS AN INCREASE IN VT OVER THE ANATOMICAL DEAD SPACE AREA. • DEAD SPACE VENTILATION IS EQUAL TO APPX 1mL PER POUND OF IDEAL BODY WEIGHT. Physiologic Dead-space PaCO2 – PeCO2 / PaCO2 This equation tells you the TOTAL of inhaled volume that is dead spaced MINUTE ALVEOLAR VENTILATION • NOT ALL OF THE Ve REACHES THE ALVEOLI. ABOUT 1/3 OF TOTAL Vt STAYS IN THE CONDUCTING AIRWAYS, AND IS ELIMINATED WITH THE NEXT EXPIRATION. SO, APPX 1/3 OF THE FOLLOWING INHALATION IS REINSPIRED EXHALED AIR. • 1ml/lb (IBW) Example: Both patients have a deadspace of 150mL • Patient A • RR=30/min • VT= 200 • Patient B • RR=10/min • VT=600mL Which patient is ventilating better? RRT - Sample Which of the following would provide the largest alveolar ventilation for a 68-kg (150lb) patient? Tidal Volume (mL) A. 400 B. 500 C. 600 D. 750 Frequency (per min) 16 12 20 14 VENTILATION • If VA (alveolar) ventilation removes MORE CO2 per minute then is metabolically produced, alveolar and blood PCO2 decrease, and a state of hyperventilation occurs. •If VA removes LESS CO2 per minute then is metabolically produced, alveolar and blood PCO2 rise, and a state of hypoventilation occurs. •Hyper and Hypoventilation can only be accurately assessed through ARTERIAL BLOOD GAS ANALYSIS. (ABG’s). THINK about changing!!