Which Humidifier for Longer-Term Mechanical Ventilation?
August 1, 1998 3 minutes read
Which Humidifier for Longer-Term Mechanical Ventilation?
ABSTRACT & COMMENTARY
Synopsis: In a prospective randomized comparison under extended use in mechanically ventilated patients, a hygroscopic condenser humidifier (HCH) performed as well as a heated-wire gas humidification system.
Source: Kollef MH, et al. Chest 1998;113:759-767.
Patients from all adult medical and surgical intensive care units at Barnes-Jewish Hospital in St. Louis (900 beds), except patients who were transferred, post-heart or -lung transplantation, or those with massive hemoplysis, were prospectively randomized to receive an HCH for up to seven days or a heated-wire circuit to maintain mechanical ventilator circuit humidification. After seven days, patients in the HCH group were crossed over to a heated-wire circuit as were patients with excessive secretions. On an every two hour basis the patient-ventilator system was evaluated and every eight hours the patency of the artificial airway was assessed. In both groups, an inline suction catheter was placed on the artificial airway, a metered-dose inhaler (MDI) inline delivery chamber on the catheter assembly, followed by the HCH or heated circuit. All patients could be suctioned and receive aerosol MDI therapy without breaking the ventilator circuit.
There were 163 patients randomized to the HCH group and 147 to the heated-wire system group. A total of nine patients were crossed over to heated wire prior to seven days because of excessive secretions. Nineteen patients in the HCH group required 27 changes of their HCHs due to soiling of the HCH before seven days; however, no HCH developed mechanical failure. Not a single artificial airway in either group obstructed during the study. In addition, ventilator-associated pneumonia rates, duration of mechanical ventilation, length of intensive care, length of hospital stay, and hospital mortality were the same in both groups. The cost of providing HCH in this study was $2605 (including the cost of heated wire circuits in those patients requiring them) as compared to $5625 in the heated wire circuit group.
COMMENT BY ROBERT M. KACMAREK, PhD, RRT
Again, Kollef's group has shattered one of the myths of ventilatory support-the need to change HCHs frequently and to cross over to heated humidification after a few days. Many of the problems inherent with the use of HCHs in this study were avoided by design and protocol. Frequent evaluation of the patient-ventilator system, with emphasis on ensuring that the artificial airway was patent by passing a suction catheter every eight hours, avoided the occurrence of airway obstruction. Frequent disruption of the ventilator circuit was avoided by placing an inline suction catheter and MDI inline chamber between the HCH or heated wire and the airway, greatly reducing the potential of cross contamination.
Of concern was the lack of data regarding the effect of the HCH system on work of breathing. The HCH used (Duration, Nellcor Puritan Bennett, Eden Prairie, MN) was specifically designed for long-term use and has a dead space of 90 mL. This plus the dead space of the inline suction catheter and the MDI adapter may have imposed a ventilatory load. In addition, Kollef and associates did not assess the resistance of the HCH after seven days of actual use when some cellular debris may have accumulated in the device. They indicated in a laboratory assessment that the resistance after seven days use was 1.6 cm H2O/L/sec at a flow of 60 L/min.
The results of this study provide us with a mechanism both for improving the quality of care and for decreasing hospital costs. Kollef et al indicated that extrapolating these cost savings in their institution to a whole year would result in saving $41,441 per year. This, coupled with the saving achieved by extending the use of ventilator circuits and inline suction catheters to one week, is a substantial amount to most hospitals. This group should be commended for again performing a much needed study that should result in more efficient, cost effective practice.
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