2001 OPEN FORUM Abstracts
CASE SERIES: THREE DIFFERENT PATIENT RESPONSES TO VOLUME SUPPORT MODE
Jeff Lantz BS,RRT, Louisiana State University Health Sciences Center, Shreveport, LA
Introduction: VolumeSupport is a support mode of ventilation available on the SiemensServo 300 ventilator. The patient triggers each breath and the ventilator adjuststhe pressure support level, breath by breath, in an effort to match the deliveredvolume with the preset target volume. Reports on patient response to this modeare limited. In this case series we describe three typical scenarios that wehave experienced with its use.
Case #1: An 85y/o, 54 Kg male with a history of COPD was placed in Volume Support mode followinghip surgery. With initial parameters of .30 FiO2, 5 cmH2OPEEP, and 500 mL target tidal volume, the peak inspiratory pressure was 15 cmH2O,indicating that delivered pressure support was 10 cmH2O. The patientinitially displayed 2 brief periods of apnea and occasional wheezing. Theseventilator parameters were maintained overnight while bronchodilator therapywas delivered. The following morning, breath sounds were clear and the patientappeared more alert. Target tidal volume was decreased to 400 mL and peak inspiratorypressure subsequently dropped to 6 cmH2O indicating a delivered pressuresupport of 1 cmH20. The patient maintained a comfortable respiratorypattern with this level of support and was successfully removed from the ventilator.
Case #2: A 48y/o, 80 Kg male with history of hepatic disease was mechanically ventilatedfollowing respiratory failure. On day #2 he was placed in Volume Support mode,.30 FiO2, 5 cmH2O PEEP, and 600 mL target tidal volume.These parameters were maintained for the next 48 hours with peak inspiratorypressure ranging from 18 to 24 cmH2O indicating that delivered pressuresupport varied from 13 to 19 cmH2O with a delivered tidal volumeof approximately 600 mL.
Case #3: A 52y/o, 152 Kg male with respiratory failure and acute renal failure was beingventilated in the Volume Support mode. On day #6, with ventilator parametersof .40 FiO2, 6 cmH2O PEEP, and 500 mL target tidal volume,he was noted to display signs of increased work of breathing. Peak inspiratorypressure was 12 cmH2O, indicating that delivered pressure supportwas 6 cmH2O. The ventilator was changed to Pressure Support modewith .40 FiO2, 6 cmH2O PEEP, and 15 cmH2O pressuresupport. This patient displayed a more comfortable respiratory pattern withoutsigns of distress on these parameters.
Discussion: VolumeSupport uses the input of the delivered volume as a feedback to the ventilator?salgorithm for adjusting delivered pressure support on the next breath. As inCase #1, the delivered pressure support may be internally weaned to minimumas the patient?s respiratory drive returns to normal following sedation or followingimprovement in lung mechanics. Case #2 represents appropriate maintenance of?maximum pressure support? as the patient?s respiratory drive and/or lung mechanicsremain depressed. Case #3 represents our experience with Volume Support in apatient with an increased respiratory drive as often seen in anxiety, neuralinjury, and respiratory distress. If the patient?s efforts generate a deliveredvolume greater than the preset target volume, the ventilator will subsequentlydecrease the delivered support pressure. This may leave the patient with respiratorydistress in a situation of minimal ventilatory support.
Conclusion: Withclose observation from the clinician and an appropriate preset target volume,Volume Support can be an excellent support mode. However, relying on a singleinput, delivered volume, to titrate the amount of support is not adequate inall patients.