ASV mode using the Hamilton G5 ventilator in NICU

ASV mode using the Hamilton G5 ventilator in NICU

By Heloisa Georgiev, RRT-NPS

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Our NICU, at Florida Hospital for Children in Orlando, trialed the Hamilton G5 ventilator in May 2009. Infants who weighed between 760 grams and 6.8 kg were placed on different modes such as APV/CMV, APV/SIMV and ASV. Out of all the patients who were placed on the G5, the one that definitely stood out the most was baby A who had been in our NICU for six months and weighed 6.8 kg.

At that time baby A was being ventilated on a in the Assist/Control mode with peak inspiratory pressures as high as 42 cm H20. Baby A was having multiple desaturation and bradycardia episodes and was asynchronous with the babylog. This asynchrony was delaying the weaning process.

Taking into consideration that the patient weighed over 3 kg, and his increased work of breathing in the assist/control mode, the decision was made to place him on the ASV mode (adaptive support ventilation) on the Hamilton G5. The staff had utilized this mode in the pediatric unit and felt very comfortable managing the patient.

Adaptive support ventilation (ASV) is a construct of closed loop ventilation. ASV designates programmed ventilator setpoints based on assessments of patient lung mechanics and breathing effort. Adaptive support ventilation provides for an optimal adaptation of ventilator settings in concert with the patients passive and active respiratory mechanics. [1]
Prior to making the switch, the patients minute volume on the assist/control mode was carefully noted and recorded. The goal was to set a target minute volume that was similar to what the patient was requiring before. Initial settings were: 1.7l target minute volume, 7cm PEEP and 21% O2.

Due to an initial increase in respiratory rate and patient actual minute volume, the minute volume setting was increased from 100% to 130% in order to match his actual minute volume need and provide the support required.

His respiratory rate decreased rapidly after this change and he appeared to be a lot more comfortable. Peak inspiratory pressures continued to be in the high 30s cm H20 range and tidal volume mid 30s to mid 40s mls.

A capillary blood gas was obtained an hour after placing him on the ASV mode. Results were: pH 7.56, PCO2 35, PO2 67, HCO3 31 and base excess +8. At that point the percent VE was weaned back to 100%, Baby A dictated how he wanted to be ventilated switching back and forth between breathing spontaneously with the aid of pressure support or receiving full controlled breaths from the ventilator. His respiratory rate remained stable in the mid 30s - 40s whenever breathing spontaneously. There was a remarkable decrease in his work of breathing due to improved patient synchrony in the ASV mode.

Another capillary blood gas was drawn 3 hours after being on the ASV mode at 100% VE setting which revealed pH 7.44, PCO2 44, PO2 48, HCO3 30 and base excess +5, the best capillary blood gas result the patient had had in days.

PIPs had decreased significantly to the mid 20s without compromising delivery of volumes.

Baby A continued on the ASV mode for over 36 hours. Every capillary blood gas obtained during that time was within normal limits. He appeared very comfortable on the ASV mode. No desaturation or bradycardic episodes were noted on ASV. When the trial time was over, it was a difficult task to take him off the ASV mode and place him back on his previous ventilator/settings.

The NICU staff was very pleased with the result they witnessed. Ventilating large infants in our NICU can be challenging at times. In utilizing the ASV mode, the infant was able to dictate how he wanted to be ventilated and it made weaning completely up to the patient. Pressure support was automatically adjusted as the patients lung compliance and resistance improved. Synchrony is a big issue in the neonatal population. ASV improved baby As clinical status by automatically tailoring settings to the needs of the patient.
ASV has several distinct advantages that aided in improving synchrony. The ability of the ventilator to adjust to the constantly changing status of our patients is critical. ASV has these desired effects:

  • the ability to automatically transition from full to partial to minimal support as the patients lung mechanics and respiratory drive/strength recover. Passive breaths are time cycled, however active breaths are flow-cycled to promote synchrony.
  • ASV automatically sets the optimal tidal volume and rate targets based on the patients pulmonary mechanics to minimize work of breathing.
  • ASV additionally employs a set of protective rules to prevent volutrauma,
    hypoventilation and autopeep.

These benefits translate into decreased ventilator days, decreased sedation, and decreased total hospital stay.

Literature:

  1. David Wheeler RRT, NPS. Ratiocinative Ventilator Control Algorithms. Focus Journal May/June 07 Page 24, 27