Mechanical ventilation is a life support strategy that uses a machine (ventilator) to perform or assist breathing in a patient who cannot do so effectively on their own. In neonatology, it is a crucial intervention for newborns with respiratory failure.
Main Objectives:
- Improve gas exchange: Correct hypoxemia (low O₂) and hypercapnia (high CO₂).
- Reduce work of breathing: Reduce the effort the baby makes to breathe.
- Protect the lung: Use strategies that minimize ventilator-induced lung injury (VILI).
- Stabilize the chest wall.
VM is divided into two large groups, and within invasive, there are multiple modalities.
Non-Invasive VM (NIVM)
Support without the need for an endotracheal tube. A mask or nasal cannulas are used. The most common way is CPAP (Continuous Positive Airway Pressure).
Invasive VM (VMI)
Requires intubation of the patient. Allows much more precise control of ventilation.
Common VMI Modalities:
VCP/PCV
(Pressure Controlled Ventilation) An inspiratory pressure (PIP) is set. The volume delivered varies depending on the compliance and resistance of the lung. It is the most used in neonates.
SIMV
(Synchronized Intermittent Mandatory Ventilation) Combine mandatory ventilator breaths with the baby's spontaneous breaths. Useful for weaning.
PSV
(Pressure Support Ventilation) The baby initiates all breaths and the ventilator helps with fixed pressure support. Requires inspiratory effort from the patient.
HFOV / HFOV
(High Frequency Oscillatory Ventilation) Use very small volumes at very high frequencies. It is a lung protection strategy in cases of severe respiratory failure.
VG/Volume Guarantee
(Guaranteed Volume) Dual mode that operates in VCP but adjusts PIP to ensure a target tidal volume (VT). Reduces volutrauma.
The decision to start MV is based on clinical and blood gas criteria that indicate respiratory failure.
Respiratory Failure
PaO₂ < 50-60 mmHg with FiO₂ > 0.6.
Severe hypercapnia
PaCO₂ > 60-65 mmHg with acidosis (pH < 7.20-7.25).
Recurrent Apnea
Frequent or severe episodes causing bradycardia or desaturation.
CPAP failure
Inability to maintain adequate oxygenation/ventilation with NIV.
Postoperative
After major surgeries (cardiac, abdominal).
Shock or Instability
To reduce the oxygen consumption of the work of breathing.
The initial programming of the ventilator depends on the pathology, weight and condition of the neonate. Typical ranges for a preterm newborn with Respiratory Distress Syndrome (RDS) are shown here.
| Parameter | Starting Range (SDR) | Main Function |
|---|---|---|
| FiO₂ | 0.3 - 0.6 (or previous) | Control the oxygenation (PaO₂ / SpO₂) |
| PIP (Peak Pressure) | 15 - 20 cmH₂O | Control the ventilation (eliminates CO₂) and helps oxygenation. |
| PEEP (Positive End Expiratory Pressure) | 5 - 6 cmH₂O | Maintains alveolar recruitment, prevents collapse and improves oxygenation. |
| RR (Respiratory Rate) | 40 - 60 rpm | Control the ventilation (removes CO₂). |
| Ti (Inspiratory Time) | 0.3 - 0.4s | Control the duration of inspiration. It affects the volume delivered and oxygenation. |
Adjustments are made according to the arterial blood gas analysis and the patient's symptoms. The objective is to achieve adequate gas exchange with minimal pulmonary aggression.
Quick Guide to Gasometric Adjustments:
Improve OXYGENATION (low PaO₂)
Target: SpO₂ 90-95%
- Increase FiO₂: It is the fastest and most direct measure.
- Increase PEEP: Improves alveolar recruitment (being careful not to over-distend).
- Increase PIP: Increases mean airway pressure (MAP).
- Increase Ti: Prolongs gas exchange time.
Improve VENTILATION (high PaCO₂)
Target: PaCO₂ 45-55 mmHg
- Increase FR: More breaths per minute remove more CO₂.
- Increase PIP: Increases the tidal volume (VT) mobilized with each breath.
- Decrease PEEP (if it is very high): May improve the pressure gradient for expiration.
Careful! Always evaluate the impact of each change. For example, an excessive increase in PIP or PEEP can compromise venous return and cause hypotension in addition to barotrauma.
Weaning is the gradual process of removing ventilatory support so that the patient resumes spontaneous breathing. It should be started as soon as the cause of respiratory failure has resolved or significantly improved.
Criteria to Start Weaning:
- Hemodynamic stability (without vasoactive drugs or at low doses).
- Resolution of the underlying pathology.
- Low FiO₂ needs (< 0.3-0.4).
- "Low" ventilatory parameters (e.g. PIP < 15-18, RR < 20-30).
- Patient with spontaneous and effective respiratory effort.
- Acceptable blood gases.
Weaning Process (Example):
-
1. Reduce PIP/Pressure Support
Gradually decrease to minimum levels (e.g. 12-15 cmH₂O).
-
2. Reduce Respiratory Rate
Lower the RR so that the baby assumes more work of breathing (e.g. up to 10-15 rpm).
-
3. Spontaneous Breathing Test
Switch to CPAP mode through the tube for a short period (30-60 min) to assess tolerance.
Extubation: If the patient tolerates the spontaneous breathing test (maintains good saturation, no increase in respiratory work, no apnea), he or she is considered ready for extubation, generally to NIMV (CPAP or high-flow cannulas).
Case 1: Preterm RN of 28 weeks with SDR
Clinic: Groaning, retractions, increasing need for O₂. Rx: Diffuse reticulogranular infiltrate.
Initial Parameters (VCP): FiO₂ 0.4, PIP 18, PEEP 6, FR 50, Ti 0.35s.
Evolution: After administration of surfactant, compliance improves. Greater thoracic excursion is observed. PIP is lowered to 15 to avoid volutrauma. FiO₂ reduces to 0.25 in 12h.
Weaning: It starts on the 3rd day, progressively lowering PIP and FR. Extubation to nasal CPAP on the 5th day.
Case 2: Term NB with Meconium Aspiration Syndrome (MAS)
Clinic: Cyanosis, severe hypoxemia despite FiO₂ 1.0. Suspected Persistent Pulmonary Hypertension (PPHN).
Management: HFOV is chosen for lung protection. Inhaled Nitric Oxide begins.
HFOV parameters: MAP 14, Amplitude 28, Frequency 10 Hz, FiO₂ 1.0.
Evolution: Slow improvement in oxygenation in 48 hours. FiO₂ is reduced and ON is removed. Transition to conventional VCP on the 4th day to begin weaning.
Case 3: NB with Apnea of Prematurity
Clinic: Preterm of 31 weeks. with recurrent and severe apneas that do not respond to caffeine or CPAP.
Management: Intubation was decided to ensure an airway and provide minimal support.
Initial Parameters (SIMV): FiO₂ 0.21, PIP 14, PEEP 5, backup RR 15, PS 8.
Evolution: Minimal support prevents desaturations. It is maintained for 72 hours until the respiratory center matures. He is extubated directly to nasal CPAP once the apneas cease.
Case 4: Postoperative Cardiac Surgery (CIA)
Clinic: 4kg NB in the immediate postoperative period. Sedated and paralyzed.
Management: He remains intubated for pain control, sedation and hemodynamic stability.
Initial Parameters (VCP): FiO₂ 0.3, PIP 20 (higher weight), PEEP 5, FR 30, Ti 0.5s.
Evolution: At 12 noon, sedoanalgesia is removed. The patient wakes up and begins to have respiratory effort. It changes to SIMV+PS mode. At 24 hours, he meets the criteria and is successfully extubated.
Case 5: Volume Guaranteed Ventilation (VG)
Clinic: 1kg NB with RDS and very labile lungs.
Management: VCP+VG mode is chosen to protect against volutrauma.
Initial Parameters: Target VT 4.5 ml/kg (4.5 ml). FiO₂ 0.5, PEEP 6, FR 55, Ti 0.32s. Maximum PIP is limited to 22.
Evolution: By improving compliance, the ventilator automatically lowers the PIP from 19 to 16 to deliver the same VT. This reduces the risk of baro/volutrauma. Weaning is more stable by controlling the minute volume.
1. If a neonate on IMV has a PaCO₂ of 70 mmHg and a pH of 7.18, what is the most appropriate adjustment to correct this respiratory acidosis?
Correct. Elevated PaCO₂ indicates hypoventilation. Increasing RR increases minute ventilation, which facilitates CO₂ elimination and corrects respiratory acidosis.
A is incorrect: PEEP primarily affects oxygenation (PaO₂) by keeping the alveoli open. Increasing it is not the main measure to lower PaCO₂.
C is incorrect: FiO₂ controls oxygenation. Lowering it would worsen hypoxia if it existed, but it does not directly affect PaCO₂.
D is incorrect: Increasing Ti can improve oxygenation and tidal volume, but can also trap air if RR is not adjusted, worsening hypercapnia. The most direct and safe adjustment is the FR.
2. What is the main function of PEEP (Positive End Expiratory Pressure)?
Correct. PEEP maintains a constant pressure in the airway during expiration, which prevents the alveoli from collapsing (atelectasis). This increases the Functional Residual Capacity (FRC) and improves the surface area for oxygen exchange.
B is incorrect: CO₂ removal (ventilation) is primarily controlled by RR and tidal volume (affected by PIP).
C is incorrect: An excessively high PEEP can, in fact, increase right ventricular afterload and decrease cardiac output by hindering venous return.
D is incorrect: Inspiration is initiated by the patient (in assisted modes) or by the ventilator according to the programmed RR, not by PEEP.
3. A premature newborn with RDS receives surfactant. What change would you expect in lung mechanics and what ventilatory adjustment would be necessary?
Correct. The surfactant reduces the surface tension in the alveoli, making them easier to open and expand. This results in an increase in lung compliance (distensibility). If PIP is not reduced, the same level of pressure will deliver a much greater tidal volume, risking volutrauma. Therefore, it is crucial to decrease PIP.
A is incorrect: The opposite occurs. Compliance increases, not decreases.
B is incorrect: Surfactant has a drastic and immediate effect on lung mechanics, so adjustments are always required.
C is incorrect: Surfactant does not increase airway resistance; improves compliance of the lung parenchyma.
4. Which of the following ventilatory modalities requires the patient to have their own effective respiratory drive?
Correct. In PSV, the ventilator only delivers pressure support when it detects an inspiratory effort from the patient. If the patient apneas, they will not receive any breaths (unless there is a backup RR set, which would make it a mixed mode).
A is incorrect: VCP is a controlled mode. The ventilator will deliver breaths at the set rate, regardless of whether the patient is breathing or not.
B is incorrect: HFOV is a rescue mode where the ventilator takes full control of ventilation through oscillations. The patient is usually deeply sedated.
D is incorrect: Only PSV depends fundamentally on the patient's effort.
5. What is the main risk of using a high and prolonged FiO₂ in a premature newborn?
Correct. Hyperoxia (excess oxygen) is toxic to the immature tissues of the premature baby. It generates oxidative stress that damages the developing blood vessels of the retina (causing ROP) and the lung epithelium (contributing to BPD).
A and C are incorrect: Barotrauma (pressure damage) and its consequence, pneumothorax, are caused by excessive ventilatory pressures (PIP, PEEP), not directly by FiO₂.
D is incorrect: Hypotension may be caused by elevated intrathoracic pressures that compromise venous return, not by FiO₂.
6. During weaning of a neonate, a spontaneous breathing test is performed by transferring him to CPAP through the tube. What would a failure in the test indicate?
Correct. The appearance or increase of signs of respiratory distress (drawing, fluttering, moaning) indicates that the patient cannot sustain the work of breathing on his or her own and is failing the test.
A, B and C are incorrect: An SpO₂ of 94%, HR of 140 bpm, and RR of 50 bpm may be completely normal for a neonate during exertion. The key indicator of failure is increased visible work of breathing.
7. The Guaranteed Volume (VG) modality is a lung protection strategy because:
Correct. The main benefit of VG is to prevent volutrauma (excessive volume damage). When lung compliance improves, VG mode automatically reduces PIP to deliver the same preset volume, thus protecting the lung from accidental overdistention.
B is incorrect: That is the description of HFOV (High Frequency Ventilation).
C is incorrect: VG does not control FiO₂; that is a separate parameter that is adjusted manually.
D is incorrect: VG is an invasive ventilation modality that requires intubation.
8. A neonate on IMV has a PaO₂ of 45 mmHg (hypoxemia) with a FiO₂ of 0.6. What would be the first measure to improve oxygenation, assuming that the PEEP is 5?
Correct. The quickest and most direct measure to correct acute hypoxemia is to increase the fraction of inspired oxygen (FiO₂). Subsequently, other parameters such as PEEP can be optimized to recruit more alveoli and allow FiO₂ to be lowered to less toxic levels.
A and B are incorrect: Decreasing RR or PIP would worsen both ventilation and oxygenation.
D is incorrect: A patient with severe hypoxemia and high oxygen requirements does not meet the criteria to begin weaning; in fact, it needs more support.
9. In which neonatal pathology is High Frequency Oscillatory Ventilation (HOVFO) especially useful as a rescue strategy?
Correct. HFOV is an excellent lung protection strategy. In severe MAS, often associated with PPHN, the lungs are heterogeneous and fragile. HFOV allows maintaining an open lung (with a high and stable MAP) and ventilating with very small volumes (minimizing baro/volutrauma), which is ideal for this pathology.
A and C are incorrect: These are mild pathologies that are usually managed with non-invasive support (CPAP) or minimal, if any, conventional ventilation.
D is incorrect: Laryngomalacia is an obstruction of the upper airway and not a disease of the lung parenchyma; HFOV is not the indicated treatment.
10. What does "gentle ventilation" or lung protection strategy mean in neonatology?
Correct. Gentle ventilation focuses on minimizing Ventilator Induced Lung Injury (VILI). This involves using the lowest tidal volume (VT) and lowest pressure (PIP) that allow reasonable gas exchange. This often means accepting a slightly elevated PaCO₂ (permissive hypercapnia) and a saturation in the low range of normal, as long as the pH remains above 7.20-7.25.
B is incorrect: The idea is not to avoid ventilation if it is indicated, but to apply it in the least harmful way possible.
C is incorrect: HFOV is a powerful tool but is not the first line for all patients. Conventional ventilation can be "gentle."
D is incorrect: This is the opposite approach. Aggressively trying to normalize blood gases with high parameters is precisely what causes VILI.
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