Question

Jane was a preterm neonate born at 28 weeks’ gestation, weighing 1.3 kg at birth. She was born by spontaneous vaginal delivery. Her mother received a course of antenatal steroids on admission to hospital to enhance surfactant maturation and to reduce the severity of respiratory distress syndrome (RDS). The neonate was rigorous at birth, spontaneously breathing, and required no resuscitation efforts except for some stimulation and prevention of heat loss. She was placed on nasal CPAP with a pressure of 5 cm H2O and 35% FiO2 to maintain an oxygen saturation between 89% and 93%. Her initial arterial blood gas (ABG) revealed the following: pH 7.32, PaO2 62 mm Hg, CO2 45 mm Hg, bicarbonate 23 mEq, and base excess mEq/L. However, 6 hours later, the neonate started to have increased work of breathing with tachypnea, chest retractions, and nasal flaring and an increasing oxygen requirement. The ABG showed a respiratory acidosis pH 7.24, PaO2 57 mm Hg, CO2 63 mm Hg, bicarbonate 21 mEq/L, and base excess 3. Therefore, the noninvasive ventilation was initiated at a PIP of 12 cm H2O and a PEEP of 7 cm H2O. With minimal improvement after an hour and worsening respiratory status, the patient was intubated. Mechanical ventilation was initiated on the following settings: SIMV PIP 24 cm H2O, PEEP 6 cm H2O, I-time 0.35 seconds, and a rate of 60 breaths per minute. She remained stable on this mode through the night. Weaning was initiated on day 2 of invasive ventilatory support. On day 4 the ventilator settings were weaned to SIMV PIP 18 cm H2O, PEEP 4 cm H2O, I-time 0.35 seconds, and a rate of 20 breaths per minute. The measured VT was 4 to 6 mL/kg; spontaneous breathing rate was 50 to 60 breaths per minute and synchronized with the mechanical breath delivery. She was weaned to CPAP and extubated on day 6.

1. What ventilator changes would you recommend if the ABG post intubation was pH 7.50, PaO2 80 mm Hg, CO2 32 mm Hg, and bicarbonate 19 mEq/b and base excess –3, L?

Answer 1

Normal ABG value at 28-40weeks of Gestation

pH- 7.25-7.45

PaO2- 50-70 mm/hg  

CO2-45-55 mm/hg

Bicarbonate : 18-20mEq/b

The ABG values provided

pH- 7.50 (Higher pH suggesting Alkalosis)

PaO2- 80 mm/hg (higher suggesting of hyperventillation)

CO2-32mm/hg (reduced suggesting of Alkalosis)

Bicarbonate : 19mEq/b (Normal range)

Conclusion drawn from the above mentioned values :- The above mentioned ABG values shows sign of Respiratoray Alkalosis because  pH is above 7.45 and CO2 value is below 45mm of Hg.

Definition:- Respiratory alkalosis occurs when the pCO2 level is lower than normal as a result of pulmonary hyperventilation.

Cause:

1. In neonatal ICU the commenest cause of respiratory Alkalosis is over-ventilation of the intubated child.
2. The ventilator is providing too many breaths or too longer breath leading to reduction in CO2 level and increases in Oxygen.

Ventilator changes recommend:-

The treatment of a respiratory alkalosis is to wean the mechanical ventilation by first reducing PIP or tidal volume followed by reducing the respiratory rate.

Necessary ventilatory changes needed:

• Wean the mechanical ventilation by first reducing PIP or tidal volume hence reducing the amount of oxygen given to baby ,
• Followed by reducing then respiratory rate thereby reducing the number of breath per minutes.