An Interactive Guide for Health Professionals
Mechanical Ventilation (MV) is a life support strategy which uses a machine (ventilator) to help a patient breathe or to breathe completely for them.
It is not a curative therapy, but a bridge which maintains respiratory function while the underlying cause of respiratory failure is treated and the body recovers.
The VM is a measure of medium, not a cure. Its purpose is to give the body time to heal. Is this fundamental concept clear?
The decision to start MV is based on the clinical evaluation of respiratory failure, which is the inability of the respiratory system to maintain adequate gas exchange. It is classified into:
Failure in oxygenation. PaO₂ < 60 mmHg with FiO₂ ≥ 60%.
Common causes: Pneumonia, ARDS, pulmonary edema.
Ventilation failure. PaCO₂ > 50 mmHg with pH < 7.35.
Common causes: Severe asthma, neuromuscular disease, CNS depression.
The decision to intubate is not based on a single number, but on the clinical trend and the evaluation of respiratory work. Do you identify signs of muscle exhaustion as a critical indication?
There are two main types of VM depending on access to the airway and multiple modes depending on how the ventilator delivers support.
Support through a mask (nasal, facial) or nasal cannulas. The patient must have his own respiratory drive.
Ideal for: Cardiogenic pulmonary edema, mild-moderate asthma attacks, exacerbated COPD.
Support through an endotracheal tube or tracheostomy. Allows total control of the airway and ventilation.
Indicated in: Severe respiratory failure, NIV failure, airway protection.
The ventilatory mode defines the relationship between the patient and the ventilator. The most common modes are:
| Mode | Control Variable | Description | Pediatric Advantages | Disadvantages |
|---|---|---|---|---|
| PCV (Pressure Controlled Vent) | Pressure | An inspiratory pressure is set. The volume delivered is variable and depends on lung mechanics. | Protects against barotrauma, better gas distribution in non-homogeneous lungs. Ideal for neonates and infants with leaks through the tube. | Tidal volume is not guaranteed, risk of hypoventilation if compliance worsens. |
| VCV (Volume Controlled Vent) | Volume | A tidal volume is set. The pressure is variable. | It guarantees a stable minute volume, useful in older children and in pathologies where CO₂ control is crucial (e.g. TBI). | Risk of barotrauma if compliance decreases or resistance increases. |
| PSV (Pressure Support Vent) | Flow | Spontaneous mode. The patient initiates breathing and the ventilator supports it with a fixed pressure until the patient's inspiratory flow declines. | Improves comfort, reduces respiratory work and facilitates weaning. | Requires a patient with reliable respiratory drive. It does not guarantee volume or frequency. |
| SIMV (Synchronized Intermittent Mandatory Ventilation) | Volume or Pressure | It combines mandatory (controlled) breaths with periods where the patient can breathe spontaneously. | Allows the patient to exercise the respiratory muscles between controlled cycles. Theoretically it makes weaning easier. | May increase work of breathing. Deprecated as a primary mode, surpassed by PCV/VCV + PSV combinations. |
In pediatrics, especially in infants, the mode is often preferred. pressure controlled (PCV). Can you explain why protection against excessive pressure (barotrauma) and leak management are key in this age group?
The initial programming of the ventilator must be safe and adapted to the age and pathology of the child. Here is a general guide. Always individualize!
| Parameter | Neonate (<1 month) | Infant (1m - 2a) | Child (2nd - 12th) | Adolescent (>12a) | Physiological Objective |
|---|---|---|---|---|---|
| Mode | PCV (+PSV if breathing) | PCV or VCV (+ PSV if breathing) | Protect lung, synchrony | ||
| FiO₂ | Start with 100%, lower rapidly to SatO₂ >92% (or 88-92% in some heart diseases) | Correct hypoxemia, avoid toxicity | |||
| VT (Tidal Volume) | If VCV is used: 6-8ml/kg ideal weight. In ARDS: 4-6ml/kg. | Adequate ventilation, avoid volutrauma | |||
| PIP / P. Control | 18-25 cmH₂O | 20-28 cmH₂O | 22-30 cmH₂O | 25-30 cmH₂O | Achieve desired VT, avoid barotrauma |
| PEEP | 4-6 cmH₂O | 5-8 cmH₂O (may be higher in ARDS) | Prevent alveolar collapse, improve oxygenation | ||
| FR (Response Frequency) | 30-50rpm | 25-40rpm | 20-30rpm | 12-20rpm | Maintain normal PaCO₂ for age |
| You (T. Insp.) | 0.3-0.5s | 0.5-0.8s | 0.8-1.0s | 1.0-1.2s | Allow alveolar filling and emptying |
Normal respiratory rate decreases dramatically with age. Observe the trend in this graph.
The key concept is lung protective ventilation: Use the lowest possible volume/pressure and FiO₂ to achieve acceptable goals (SatO₂ >92%, normal or permissive PaCO₂). Do you understand that "normalizing" gases at all costs can damage the lung?
Once the VM is started, the key is to monitor and tune. The goal is to find the "sweet spot" where support is effective and damage minimal.
1. Increase FiO₂: It is the fastest measure. Objective: use the lowest FiO₂ possible (<60%) to maintain SatO₂ >92%.
2. Increase PEEP (Mean Airway Pressure): The most important step to improve oxygenation in diseased lungs. Recruits collapsed alveoli, improving the V/Q ratio. Increase in steps of 1-2 cmH₂O. Monitor hypotension!
Reminder: Minute Volume (MV) = Respiratory Rate (RR) x Tidal Volume (VT). To "wash" CO₂, you have to increase the VM.
1. Increase Respiratory Rate (RR): It is the simplest way. Be careful not to generate auto-PEEP by shortening the expiratory time too much.
2. Increase Tidal Volume (VT): In VCV mode, increase ml/kg (without exceeding 8 ml/kg). In PCV mode, increase the inspiratory pressure (PIP or P. Control). Monitor baro/volutrauma!
Indicates overventilation. It is corrected by doing the opposite:
1. Decrease Respiratory Rate (RR).
2. Decrease Tidal Volume (VT) or Inspiratory Pressure.
It is vital to differentiate: FiO₂ and PEEP they manage the oxygenation. FR and VT they manage the ventilation (CO₂). If a patient has low SatO₂ but normal CO₂, which parameter would you adjust first?
The goal is to release the patient from the ventilator as soon as possible to avoid complications. Weaning must be an active and protocolized process.
It is the method of choice to evaluate whether the patient is ready for extubation. It consists of simulating post-extubation breathing conditions while still intubated.
The ventilatory mode is changed to minimal support for 30-120 minutes:
If the PRE is successful, we proceed to extubation.
The PRE is the "final examination" of the patient before extubation. A failure is not an error, it is valuable information that indicates that the patient needs more support time. Do you understand that the goal is safe extubation, not rapid extubation?
Clinic: Infant with severe tachypnea (RR 80 rpm), universal indrawing, nasal flaring and apnea pauses. SatO₂ 85% with high flow cannula. Gasometry: pH 7.25, pCO₂ 65, pO₂ 55.
Decision: Intubation due to respiratory exhaustion and mixed respiratory failure.
Initial parameters (Weight 5 kg):
Reasoning: PCV is chosen due to the high resistance of the airway (typical of bronchiolitis) and to limit pressure. PEEP is crucial. The RR is high, according to his age.
Clinic: Child with severe bronchospasm, silent, drowsy chest. Gasometry: pH 7.18, pCO₂ 80. Despite intensive treatment, there is no improvement.
Decision: Intubation due to severe hypercapnia and altered level of consciousness.
Initial parameters (Weight 25 kg):
Reasoning: The key in asthma is to avoid air trapping (auto-PEEP). This is achieved with a low RR and a long expiratory time. A high pCO₂ is tolerated (permissive hypercapnia) as long as the pH > 7.20-7.25 so as not to increase barotrauma.
Clinic: Patient with septic shock, bilateral pulmonary infiltrates. PaO₂/FiO₂ (PAFI) < 150. Refractory hypoxemia.
Decision: VM for moderate-severe ARDS.
Initial parameters (Ideal weight 60 kg):
Reasoning: The management of ARDS is based on minimizing ventilator-induced lung injury (VILI). This implies low VT (protection against volutrauma) and optimal PEEP (protection against atelectrauma), tolerating moderate hypercapnia.
Clinic: 5-year-old boy stable after correction of a VSD. He is transferred to the ICU intubated.
Decision: Maintain VM for a smooth transition and postoperative control.
Initial parameters (Weight 18 kg):
Reasoning: The lung is usually healthy. The goal is gentle support that allows the child to wake up and begin breathing on his or her own. SIMV or PCV+PS mode allows this transition. Weaning is usually quick if there are no complications.
Clinic: Patient with Duchenne Muscular Dystrophy admitted for pneumonia. He presents a weak cough, accumulation of secretions and progressive hypercapnia (pCO₂ 68) with good oxygenation.
Decision: Initiate ventilatory support due to muscle pump failure (Responsive Insufficiency Type II).
Choice: Non-Invasive Ventilation (NIV) with a face mask is tried first.
NIV parameters:
Reasoning: The lung is healthy, the problem is the weakness of the respiratory muscles. NIV can be very effective in "resting" these muscles, improving ventilation, and helping to remove secretions. If NIV fails or the patient does not tolerate it, intubation would proceed.
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