Apnea or impending respiratory arrest.

Acute exacerbation of COPD or acute severe asthma with dyspnea, tachypnea, and acute respiratory acidosis (hypercapnia and decreased arterial pH) plus at least one of the following:

● Acute cardiovascular instability.

● Altered mental status or persistent uncooperativeness.

● Inability to protect the lower airway.

● Copious or unusually viscous secretions.

● Abnormalities of the face or upper airway that would prevent effective noninvasive positive pressure ventilation.

Acute ventilatory insufficiency in cases of neuromuscular disease accompanied by any of the following:

● Acute respiratory acidosis (hypercapnia and decreased arterial pH).

● Progressive decline in vital capacity to below 10 to15 mL/kg.

● Progressive decline in maximum inspiratory pressure to below −20 to −30 cm H₂O.

Acute hypoxemic respiratory failure with tachypnea, respiratory distress, and persistent hypoxemia despite administration of a high fraction of inspired oxygen (FiO₂) with high-flow oxygen devices or in the presence of any of the following:

● Acute cardiovascular instability.

● Altered mental status or persistent uncooperativeness.

● Inability to protect the lower airway.

Need for endotracheal intubation to maintain or protect the airway, like in patients with low GCS, or to manage secretions.

Assist/control mode is the preferred ventilator mode for most conditions. The name may vary depending on the type of ventilator (e.g., Draeger- IPPV assist, SCMV, Vol A/C).

Decision on whether to put pressure control ventilation (PCV) or volume control ventilation (VCV) depends on the operator and institutional preference. In Nepal. First preferred mode is Volume Assist Control.

V _T is commonly set at 6 ml/kg of predicted body weight (PBW).

In PCV, the pressure control should be adjusted to achieve the target V _T.

Respiratory rate (RR) is set to achieve the target minute ventilation (V_E). RR= V_E/ V _T

E.g., if target V _E is 6 L and target V _T is 300 ml then RR is set at 6000/300= 20 breaths/min.

For obstructive airway diseases (e.g., COPD), initial RR should be kept low at 8-12 breaths/min to avoid air trapping and generation of auto PEEP.

Start with FiO ₂ of 100%.

Once stable, titrate to the lowest FiO ₂ required to achieve adequate oxygenation. Targets may vary according to disease condition (e.g., ARDS: PaO₂≥55mmHg or SPO₂≥ 88%; TBI: SPO₂≥ 94%).

Start with a minimum PEEP of 5 cm H₂O.

Adjust to the lowest PEEP required to achieve adequate oxygenation.

Many methods of setting PEEP; most common technique is to use the PEEP- FiO ₂ table of ARDSnet trial.

Lower PEEP may be required in obstructive airway diseases without spontaneous breathing.

PEEP selection can be done from one of the following tables. In Nepal, we commonly use lower PEEP/higher FiO₂(Table 1).

FiO ₂

0.3

0.4

0.4

0.5

0.5

0.6

0.7

0.7

0.7

0.8

0.9

0.9

0.9

1.0

PEEP

(cmH₂0)

5

5

8

8

10

10

10

12

14

14

14

16

18

18-24

FiO ₂

0.3

0.3

0.3

0.3

0.3

0.4

0.4

0.5

0.5

0.5-0.8

0.8

0.9

1.0

1.0

PEEP

(cmH₂0)

5

8

10

12

14

14

16

16

18

20

22

22

22

18-24

I:E ratio is set at 1:2.

Higher ratio (1:1) may be required for better oxygenation and a lower ratio (1:3) may be required for carbon dioxide removal and for patients with obstructive airway disease (e.g., COPD).

I:E ratio can be set directly in some ventilators (e.g., Maquet Servo); in some, this will be determined by setting the inspiratory time and RR (e.g., Drager Evita XL).

Keep plateau pressures (measured during inspiratory pause) < 30 cm H₂O by decreasing Vt up to 4 ml/kg.

Keep driving pressure (Pplat- PEEP) <14 cm of H₂O by optimizing PEEP and V_T.

Adjust RR (maximum 35 breaths/min) as per the target CO₂. This can be achieved by using the formula:

Desired RR= Current RR x Current CO₂/ Desired CO ₂

Accept permissive hypercapnia while maintaining pH>7.2. Contraindication to permissive hypercapnia includes intracranial hypertension, acute coronary artery disease, arrhythmias, right heart failure and worsening pulmonary hypertension.

Clinical criteria

● Resolution of disease

● Adequate cough and less amount of secretions

Objective criteria

● Adequate oxygenation

▪ SpO₂≥ 90% or PaO ₂ > 60 mmHg with PEEP ≤ 8 cm H₂O and FiO₂≤ 0.4.

▪ PaO₂/FiO₂≥ 150.

● Adequate Ventilation

▪ RR ≤ 35 breaths/min, generated V_T>5 ml/kg, Vital capacity >10 ml/kg.

▪ No clinically significant respiratory acidosis.

● Stable Cardiovascular system

▪ HR < 140 bpm, stable blood pressure, or no to minimal pressors/ inotropes.

● Combined indices: Rapid shallow breathing index (RSBI) = RR/V_T<105, where V _T is in liter

● Adequate mentation: Arousable, GCS ≥13, no continuous sedative infusions.

Once a patient is assessed to be ready to wean, SBT should be performed daily using any of the methods- PSV, CPAP, T-piece, ATC (automatic tube compensation)

PSV of ≤ 8 for half an hour (maximum 2 hours) is the preferred method in most cases of first weaning trial.

Assess for tolerance as below

● SpO ₂ ≥ 90 and/or PaO ₂ ≥ 60 mmHg.

● Spontaneous V _T ≥ 4 ml/kg PBW.

● RR ≤ 35/min.

● pH ≥ 7.3

● No respiratory distress (Absence of 2 or more of following: HR > 120% of baseline; Marked accessory muscle use; Abdominal paradox; Diaphoresis; Marked dyspnea).

If the patient’s SBT is successful, extubation can be performed if there is strong cough.

Cuff leak is performed for patients with high risk of subglottic edema, which include

● Traumatic intubation.

● Intubation >6 days.

● Reintubation after unplanned Extubation.

● Females.

● Large endotracheal tube for size.

If extubation has to be postponed, reassessment for possible extubation should be done after 12 hours.

Obese patients.

Those with moderate to severe COPD.

Hypercapnia.

> 2 failed SBT.

Congestive heart failure.