Question

PRACTICE PROBLEMS

1. 7.41    

40

122

24

-1.2

What tidal will you recommend to the doctor using 5ml/kg: patient is a male, 5 foot 6 inches.

2. 7.22

88

82

26

+3.2

What tidal volume would you recommend to the doctor using 6ml/kg?  Patient is male, 6 foot 6 inches.

Answer 1

First question:

To calculate the tidal volume we need to first calculate the patient's predicted body weight.

The information provided is:

• Gender of the patient = Male
• Height - 5 foot, 6 inches

Formula for predicted body weight (Male) = 50 + [2.3 kgs (every inch above 5 feet)

predicted body weight (Female) = 45 + [ 2.3 kgs(every inch above 5 feet)]

• 50 + [ 2.3 (6 inchs) ]
• 50 + 13.8
• 63.8 kgs

recommended tidal volume = 5 ml / kg of predicted body weight

• 5 ml x 63.8 kgs
• 319 ml

The tidal volume for this patient should be 319 ml.

Second question:

To calculate the tidal volume we need to first calculate the patient's predicted body weight.

Information provided:

• Gender of the patient = Male
• Height - 6 foot, 6 inches

Height of the patient - 6 foot, 6 inchs

in other words:

5 feet + 1 foot and 6 inchs

(Conversion factor:1 foot = 12 inchs)

therefore, 12 inch + 6 inchs = 18 inch

Formula for predicted body weight: 50 + [2.3 kgs (every inch above 5 feet) --- male

• 50 + [2.3 kgs ( 18 inch)]
• 50 + 41.4
• 91.4 kgs

recommended tidal volume = 6 ml / kg of predicted body weight

• 6 ml x 91.4 kgs
• 548.4 ml

The tidal volume that should be recommended for this patient is 548 ml.

You will notice that the tidal volume recommendation of the patient in the second scenario is more compared to the first case scenario. This is because of:

• The arterial blood gas report of the first patient is normal
  • pH = 7.41 (Normal pH = 7.35 - 7.45)
  • pCO2 = 40 mmHg (Normal = 35 - 45 mmHg)
  • pO2 = 122 mmHg ( Normal = 80 - 100 mmHg)
  • HCO3- = 24 meq /L (Normal = 22 - 26 meq/L)
  • Base excess = -1.2 (Normal = +/- 2 meq/L)
• Therefore, a tidal volume of 319 ml is adequate.
• In the second case scenario, the arterial blood gas report is abnormal.
  • The pH is acidic (as it is less than 7.34)
  • The pCO2 is more than 45 mmHg.
  • The bicarbonate is normal
  • Therefore, this patient is suffering from respiratory acidosis.
• The pCO2 retention could be due to bronchospasm or hypoventilation.
• This can be corrected by increasing the minute ventilation
• Minute ventilation = respiratory rate x tidal volume
• By increasing the tidal volume, we will be able to increase the minute ventilation and therefore we'll be able to correct the acid-base disorder.