28. Pulmonary ventilation and blood gases, Use the information in table A below

Question

28. Pulmonary ventilation and blood gases, Use the information in table A below to calculate the missing values in Table B. Table A -Note: These gas concentrations were generated using breathing pattern A in Table B Parameter Paco: (arterial Pco.) Po2 (arterial Po) Peco, (PCO2 in expired air) Pco (PCO2 in inspired air) Po (Po2 in inspired air) Calculations Value 45 mm Hg 105 mm Hg 27 mm Hg 0 mm Hg 150 mm Hg Table B Change in Change in PacO2 MVR- minute VA -Alveolar Pa02 volume of ventilation compared to compared to Breathing Vr-tidalFrequency r Pattern volume (ml) (breaths/min) (ml/min) (mL/min)NC) , NC) respiration rate pattern A pattern A 500 12 A- Normal Pattern o 400 80 200 20o 500 600 900 15 30 30 9 12 5 00 O, 800 Which breathing pattern would lead to the largest increase in Pa0: (arterial Po)? Explain the basis for your answer Which breathing pattern in the table above would lead to rapid changes in blood gas concentrations that would quickly lead to life-threatening conditions if sustained for an extended period of time? Explain the basis for your answer.

Explanation / Answer

Depressed medullary respiratory centers causes respiratory problems.

When the subject was overbreathing (hyperventilating); the arterial PCO2 would be close to 25 mmHg; there must be a respiratory alkalosis

A rise in PCO2 40 mm Hg assists in offloading of oxygen in the tissues; a rise in PO2 assists in offloading of CO2 in the pulmonary capillaries. It forms carbonic acid more readily in plasma than in red blood cells; it readily diffuses in and out of red blood cells; more is taken up at any given PCO2 by desaturated than by fully oxygenated blood

Alveolar PO2 in the left lung will be approximately equal to the PO2 in inspired air

It refers to alveoli that are ventilated, but not perfused. No O2 or CO2 can be exchanged with air entering these alveoli because there is no blood flow to pick up O2 or to release CO2. In regions of the lung where there is dead space, alveolar PO2 and PCO2 approach their values in inspired air.

The ABG analysis is mainly used to evaluate gas exchange in the lungs. It is also used to assess integrity of the ventilatory control system and to determine the acid-bas level of the blood. The ABG analysis is also used for monitoring respiratory therapy (again by evaluating the gas exchange in the lungs).

PCO2 levels will directly affect the levels of acid in the blood.

PCO2 normal - 35 to 45 mm Hg

As you see, the conditions of respiratory acidosis or respiratory alkalosis can be determined by examining just the pH and the carbon dioxide levels in the blood.

This section is a guide to analysis of the ABG. Follow the steps as indicated in order to best interpret the results.

step 1 - examine pH

if low, indicates acidosis --
if high, indicates alkalosis --
if normal, check to see if borderline (may be compensation)

step 2 - examine CO2

if high, indicates respiratory acidosis (with low pH)
if low, indicates respiratory alkalosis (with high pH)
if normal, check for compensatory problem

step 3 - examine HCO3

if high, indicates metabolic alkalosis (with high pH)
if low, indicates metabolic acidosis (with low pH)
if normal, check for compensatory condition

step 4 - check PO2 levels

if low, indicates an interference with ventilation process (should evaluate the patient)
if normal, indicates patient is getting enough oxygen

step 5 - check signs/symptoms of patient

This analysis is for the patient whose respiratory status is fairly stable clinically, but acid/base balance is questionable. Following is a step-by-step account of how to analyze ABG if the prime concern is oxygenation.

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