**Marcelo Alcantara Holanda +
**

Click here to see the data below in table form

Ideal Body Weight (IBW)

**Gender: Male**

Equations: 50 + 0.91 * (Height - 152.4 cm).

Comments/Recommendations:

VT: 6 to 8 ml/kg - Start of MV.

**Gender: Female**

Equations: 45.5 + 0.91 * (Height - 152.4 cm).

Comments/Recommendations:

VT < 6 ml/kg - ARDS.

Respiratory Mechanics

**Airway Resistance (Raw)**

Equations: Peak p. – plateau p. (cmH_{2}O)/Flow (L/s).

Requires square flow type in VCV mode for accurate calculation.

Comments/Recommendations:

- Normal value: 4 to 10 cmH_{2}O/L.s .

- Keep Raw < 20 cmH_{2}O/L.s in obstructive airway diseases..

**Static Compliance (Cst)**

Equations: Tidal volume (ml) / (Plateau p. - PEEP) (cmH_{2}O).

Comments/Recommendations:

- Normal: 50 to 80 ml/cmH_{2}O.

- High - Emphysema.

- Low - ARDS, pulmonary edema, abdominal distention, pneumothorax, atelectasis.

**Peak airway pressure**

Definition: Maximum airway pressure.

Equations: None

Comments/Recommendations:

- Keep < 35 to 45 cmH_{2}O.

**Plateau pressure**

Definition: Alveolar pressure measured at the end of inspiration by pause of 0.5s.

Equations: None

Comments/Recommendations:

- Keep < 28 to 30cmH_{2}O or as low as possible.

**Auto-PEEP or intrinsic PEEP**

Definition: Alveolar pressure measured at the end of expiration by pause of 3s.

Comments/Recommendations:

- Normal value: zero.

- Keep < 10 cmH_{2}O in obstructive airway diseases..

**Driving pressure **

Equations: Plateau pressure - PEEP (cmH_{2}O).

Comments/Recommendations:

- Keep < 15 cmH_{2}O in ARDS and in patients at risk for VILI.

Gas Exchange

**PaO _{2}
**

Equations: None

Comments/Recommendations:

- Keep between 65 and 80 mmHg with the lowest FIO

_{2}possible.

**FIO _{2} to target PaO_{2}
**

Equations: Target PaO

_{2}(mmHg) * (Current FIO

_{2}/ Target PaO

_{2}(mmHg)).

**PaCO _{2}
**

Equations: None

Comments/recommendations:

- Set according to the pH.

- Permissive hypercapnia (PaCO

_{2}> 50mmHg) in ARDS, COPD or status asthmaticus.

- Keep between 35 to 38 mmHg in acute traumatic brain injury.

**pH**

Equations: None

Comments/recommendations:

- Keep between 7.34-7.44

- Permissive hypercapnia (PaCO_{2} > 50mmHg with pH > 7,20).

**PaO _{2}/FIO_{2}ratio**

Equations: PaO

_{2}(mmHg) /FIO

_{2}(absolute value, not in %)

Comments/Recommendations:

- Normal > 400 a 500mmHg - nível do mar

- It may estimate the amount of pulmonary shunt:

- 200 to 300, 10 to 20% shunt;

- 100 to 199, 20 to 40% shunt;

- < 100, > 40% shunt.

**SaO _{2} or SpO_{2}
**

Equations: None.

Comments/Recommendations:

- Keep between 92-96% (Check pulse oximetry plethysmographic waveform).

**FIO _{2} setting**

Equations: FIO

_{2}target = PaO

_{2}target (mmHg) * (FIO

_{2}current / PaO

_{2}current (mmHg)).

Comments/Recommendations:

- Set the lowest possible FIO

_{2}.

**Respiratory rate (RR) setting**

Equations: RR target = RR current * PaCO_{2} current / PaCO_{2} desired.

Comments/recommendations:

- Choose a PaCO_{2} target according to the patient’s condition and the pH.

Predictors of successful weaning

**Tobin Index or Rapid shallow breathing (RR/VT) ratio**

Equations: RR bpm / VT Mean (L)

Comments/Recommendations:

- Values > 105 bpm/L are associated with weaning failure.

- Using the ventilometer, identify the minute volume and respiratory rate of the patient in spontaneous breathing, that is, disconnected from the ventilator.

- Apply the minute volume (VE) values to the equation: VE = VT/RR to find the tidal volume.

- VT (mean) = VE/RR

- After that, apply the values of VT and RR in the Tobin index equation: RR bpm / VT Mean (L).

**Maximum Inspiratory Pressure (MIP)**

Equations: None

Comments/Recommendations:

- MIP > (less negative) than - 20 to -30cmH_{2}O is associated with respiratory muscle weakness and extubation/weaning failure.

**P0.1**

Equations: None

Definition: Airway pressure measured at 100ms or 0.1s from the start of inspiration.

Comments/Recommendations:

- Normal: 1.5 – 3.5 cmH_{2}O (normal ventilatory drive / normal ventilatory assistance)

- Low respiratory drive: < 1.0cmH_{2}O (hypostimulated ventilatory drive / Overassistance / weaning failure)

- High respiratory drive: >4.0cmH_{2}O (hyperstimulated ventilatory drive / under - ventilatory assistance / weaning failure)

- Some ventilators can measure P0.1 with the help of specific software.

- Clinical application: assessment of the level of ventilatory support and muscle effort, estimation of neural command or respiratory drive.

Others

**Time constant**

Definition: time required for lung emptying.

Equation: Time constant = Rva (cmH_{2}O/L.s) * Cst (L/cmH_{2}O)

Ex.: Rva of 10 cmH_{2}O/L.s * Cst of 0,06 L/cmH_{2}O (Cst) = 0,6s.

Comments/Recommendations:

- It takes 4 to 5 time constants for adequate or near complete exhalation.

**Pmus (cmH _{2}O)**

Equation: Pmus = -3/4 * ∆ Pocc (occlusion pressure) or -0.75 * ∆ Pocc.

Comments/Recommendations:

- Clinical application: Estimates Pmus during MV, without the need for an esophageal catheter.

- For this, it is necessary to find ∆ Pocc (occlusion pressure).

- To identify the ∆ Pocc: Perform an expiratory pause (a drop in pressure is observed) and observe the pressure variation in the airway.

- (Delta Pocc = PEEP - lowest pressure achieved)

- Normal values Pocc: 5 - 10 cmH

_{2}O.

**Step by step**

**Step 1:** Performs an expiratory pause (occlusion maneuver).

**Step 2:** Freezes the MV screen.

**Step 3:** With the MV cursor, identify the value of ∆Pocc
(∆ Pocc = pressure drop + PEEP)

**Step 4:** Apply it to the formula (Pmus = -3/4 x ∆Pocc or -0.75 *∆Pocc)

- Pmus < 5cmH_{2}O (Overassistance, low drive - e.g. sedation, muscle weakness)

- Pmus ≤ 10cmH_{2}O (diaphragmatic protection)

- Pmus > 13-15 cmH_{2}O (excessive muscle exertion)

**ROX index**

Equation: ROX = (SpO_{2}/FIO_{2})*100/respiratory rate.

Comments/Recommendations:

- ROX index ≥4.88 measured 2, 6 or 12 h after initiation of HFNC is associated with a lower risk of intubation.

- ROX index <3.85 = high risk of HFNC failure.

- If ROX from 3.85 to < 4.88, score can.

**Asynchrony Index (%)**

Equation: AI = number of asynchronous events / total RR (cycles triggered or not)

Comments/Recommendations:

- AI > 10% considered severe.

**Mechanical Power (J/min)**

Definition: Energy transferred to the lungs by the mechanical ventilator.

Equation: MP = 0.098 x (VC/1000) x driving pressure x *f*

Comments/Recommendations:

- MP < 12 J/min – normal;

- MP 13 - 17 J/min - Lung injury;

- MP 18 - 22 J/min - mild ARDS;

- MP 23 - 24 J/min - moderate ARDS;

- MP 25 - 27 J/min - severe ARDS;

- MP > 27 J/min - ECMO indication.

**References**