Chapter 4: Critical Values

Question 1

Ventilation:

PH values

Answer 1

Normal: 7.35–7.45

Critical: <7.25

Question 2

Ventilation:

Arterial partial pressure of carbon dioxide (PaC02 in mmHg)

Answer 2

Normal:35-45 mmHg

Critical: >55 mmHg and rising

Question 3

Ventilation:

Dead space to tidal volume ratio

Answer 3

Normal: 0.3 - 0.4

Critical: > 0.6

Question 4

Oxygenation:

Arterial partial pressure of oxygen PaO2 MmHg

Answer 4

Normal: 80 - 100 mmHG

Critical: <70 mmHg (on O2 => 0.6)

Question 5

Oxygenation:

Alveolar-to-arterial oxygen difference P(A-a)O2 mmHg

Answer 5

Normal: room air = 5-20mmHg
100% 02 =25-65 mmHg

Critical: > 450 (on 02)

• • when Pa02 is Low and P(A-a)O2 is high, hypoxemia is due to:
    1) shunt
    2) diffusion defects
    3) VQ mismatch

This can also be found using a ratio

Question 6

Oxygenation:

Ratio of arterial to alveolar P02 (PaO2/PAO2)

Answer 6

Normal: 0.75-0.95 This indicated that 95% of the oxygen available in the alveoli is diffusing into the pulmonary capillaries

Critical: <0.15

Question 7

Oxygenation:

PaO2/FiO2

Answer 7

Normal: 475

Critical: <200

Example: using this ratio eliminates the need to calculate the PA02 (alveolar PO2).

90mmHg/0.21 = 428

40mmHg/1.00 = 40

Question 8

Maximum inspiratory pressure MIP or PImax:

Answer 8

Is the lowest pressure generated during a forceful inspiration effort against an included airway. it can usually be taken every 2 to 4 hours

Normal values equal -100 to -50 cm of H2O critical values equal -20 to 0 cm of H2O (A minimum of -20 is needed to produce a good cough)

Question 9

Vital capacity= biggest breath possible

The volume of air that can be maximally exhaled following a maximal inspiration

Answer 9

Normal: VC is typically 65 - 75 mL per kg of IBW but it may be as high as 100 mL per kilogram of ideal body weight

Critical Value: <10 -15ml/KG (IBW)

Question 10

Maximum expiration pressure or MEP

Answer 10

Normal value equals 100 cm of H2O

Critical value equals under 40 cm of H2O

Question 11

Tidal volume (Vt)

Answer 11

Normal adults equal 5 to 8 mL per kilogram of ideal body weight

Critical values equal under 5 mL per kilogram of ideal body weight

Question 12

Respiration frequency (f)

Answer 12

Normal range in breaths per minute is 12 to 20

Critical range in brass permanent is greater than 35

Question 13

Peak expiratory flow (PEF)

Answer 13

Peak expiratory flow is a good indicator of airway resistance in a patient’s ability to maintain airway patency

Normal ranges are from 350 to 600 L per minute

Critical ranges are from 75 to 100 L per minute

Question 14

Forced expiratory volume at one second (FEV1)

Answer 14

Forced expiratory volume at one second is another pulmonary function parameter that can be used to assess airway resistance. Normally around 80% of the vital capacity or 50 to 60 mL per kilogram of ideal body weight

Critical value is under 10 mL per kilogram of ideal body weight

Question 15

Minute ventilation (VE)

Answer 15

Minute ventilation is the product of title volume and respiratory rate

VE = Vt x F

Normal ranges are 5 to 6 L per minute and directly relates to the patient’s metabolic rate

Critical value equals a minute ventilation of greater than 10 L per minute

Question 16

Acute respiratory failure [ARFM]

Answer 16

ARF may be defined as the inability to maintain PA02, PAC02, and PH at acceptable levels

Question 17

What two values are used to assess respiratory muscle function?

Answer 17

Maximum inspiratory pressure and vital capacity

Question 18

What two assessments are used to assess airway resistance?

Answer 18

Forced expiratory volume at one second and peak expiratory flow