HLTH 407 ‑ Formulas and Normal Values Review

Question-and-answer flashcards covering normal respiratory values, pressure conversions, ventilatory settings, physiologic measurements, and key formulas required for HLTH 407.

What is the normal adult inspiratory time (TI)?

0.8–1.2 seconds

What is the normal I:E ratio in adults at rest?

1:2 to 1:3

What is the normal resting respiratory rate (RR) for adults?

12–20 breaths per minute

How many cmH₂O equal 1 mmHg?

1 mmHg = 1.36 cmH₂O

How many mmHg equal 1 kPa?

1 kPa = 7.5 mmHg

How many mmHg equal 1 Torr?

1 Torr = 1 mmHg

How many mmHg and cmH₂O equal 1 atmosphere (atm)?

1 atm = 760 mmHg ≈ 1034 cmH₂O

What is the ideal peak inspiratory pressure (PIP) limit and absolute maximum if necessary?

Ideal < 30 cmH₂O; absolute maximum < 40 cmH₂O

What plateau pressure (Pplat) should be maintained to avoid lung injury?

< 28–30 cmH₂O

What is the recommended driving pressure (Pplat − PEEP)?

< 15 cmH₂O (some sources allow up to 18 cmH₂O)

What is normal static lung compliance in a spontaneously breathing adult?

0.05–0.17 L/cmH₂O (50–170 mL/cmH₂O)

What is normal static compliance in intubated adult males?

0.04–0.10 L/cmH₂O (40–100 mL/cmH₂O)

What is normal static compliance in intubated adult females?

0.035–0.10 L/cmH₂O (35–100 mL/cmH₂O)

What is normal airway resistance for a spontaneously breathing adult?

0.6–2.4 cmH₂O/L/s

What airway resistance is typical in non-intubated patients with asthma or emphysema?

≈ 6 cmH₂O/L/s

What airway resistance range is typical in intubated patients?

13–18 cmH₂O/L/s

What tidal-volume range (mL/kg IBW) is used for patients with normal lung pathology?

6–8 mL/kg of predicted body weight

What tidal-volume range (mL/kg IBW) is used for restrictive disease or lung-protective ventilation?

4–6 mL/kg of predicted body weight

What is the typical pressure trigger sensitivity for a mechanical ventilator?

1–2 cmH₂O below baseline

What is the typical flow trigger sensitivity for a mechanical ventilator?

2–3 L/min

What are normal arterial blood gas (ABG) values for pH, PaCO₂, PaO₂, and HCO₃⁻?

pH 7.35–7.45; PaCO₂ 35–45 mmHg; PaO₂ 75–100 mmHg; HCO₃⁻ 22–26 mEq/L

What is the normal maximal inspiratory pressure (MIP) and its critical value?

Normal −50 to −100 cmH₂O; critical value > −20 cmH₂O (i.e., less negative than −20)

What is the normal maximal expiratory pressure (MEP) and its critical value?

Normal ≈ 100 cmH₂O; critical value < 40 cmH₂O

What is the normal vital capacity (VC) expressed in mL/kg IBW and its critical value?

Normal 65–75 mL/kg; critical < 10–15 mL/kg

What is the normal FEV₁ in mL/kg IBW and its critical value?

Normal 50–60 mL/kg; critical < 10 mL/kg

What is the normal peak expiratory flow rate (PEFR) in adults and its critical value?

Normal 350–600 L/min; critical < 75–100 L/min

Approximately how much work of breathing (WOB) is required per liter of ventilation?

≈ 0.5 Joules per liter

How do you calculate total cycle time (TCT) from respiratory rate?

TCT = 60 s ÷ RR

How is static compliance (Cstat) calculated?

Cstat = VT ÷ (Pplat − PEEP)

How is dynamic compliance (Cdyn) calculated?

Cdyn = VT ÷ (PIP − PEEP)

What formula is used to calculate airway resistance (Raw) on the ventilator?

Raw = (PIP − Pplat) ÷ Flow (in L/s)

How is driving pressure defined in mechanical ventilation?

Driving Pressure = Pplat − PEEP

What is the imperial (inches) formula for predicted body weight (PBW) in adult males?

PBW (lb) = 106 + 6 × (height in inches − 60)

What is the imperial (inches) formula for predicted body weight (PBW) in adult females?

PBW (lb) = 105 + 5 × (height in inches − 60)

What is the metric (cm) formula for predicted body weight (PBW) in adult males?

PBW (kg) = 50 + 0.91 × (height in cm − 154.2)

What is the metric (cm) formula for predicted body weight (PBW) in adult females?

PBW (kg) = 45 + 0.91 × (height in cm − 154.2)

How many centimeters are in one inch?

1 inch = 2.54 cm

How many pounds are in one kilogram?

1 kg = 2.2 lb

What is the basic formula for minute ventilation (VE)?

VE = VT × RR

What is the approximate normal resting VE in adults?

≈ 5–6 L/min

Give two quick estimation methods for required minute ventilation.

• 100 mL/kg IBW • 3.5 × BSA for females or 4 × BSA for males

How do you calculate inspiratory time (TI) if tidal volume and flow rate are known?

TI = VT ÷ Flow (convert flow to L/s first)

What is the formula for tubing compliance (CT)?

CT = Volume ÷ Pressure (mL/cmH₂O)

How do you compute a desired FiO₂ based on an ABG?

Desired FiO₂ = (Desired PaO₂ × Current FiO₂) ÷ Current PaO₂

How do you compute a desired minute ventilation (VE) to reach a target PaCO₂?

Desired VE = (Current VE × Current PaCO₂) ÷ Desired PaCO₂