We know that the reduction of tidal volume during mechanical ventilation in adults with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) affects outcome.1 Although, the optimal tidal volume, airway pressures and ventilator modalities are still controversial, it is clear that 12 ml/kg tidal volume increases mortality in ALI and ARDS patients compared to 6 ml/kg tidal volume.
The optimal management of ALI and ARDS in children is even less clear. The incidence of ALI and ARDS is less in pediatrics and the associated mortality is 22% to 27%. There is a lack of primary data in children and most ALI and ARDS management is extrapolated from adult studies. Children are not merely small adults, recent laboratory studies suggest than infants2 and neonates3 are less susceptible to high tidal volume injury. We know that in adults, very low tidal volume ventilation increases the tendency to develop atelectasis and infants and children there might be a greater risk for atelectasis because of their lower FRC and more compliant chest wall. So it becomes important to verify the appropriateness of applying adult ventilator strategies in pediatric populations.
Albuali et al.4 from London Ontario, performed a retrospective study comparing ventilatory strategies of patients from 1988-1992, when protective lung strategies were less likely to be used, and from 2000-2004, when protective strategies were more likely to be used in ALI patients. The primary outcome of the study was mortality and the secondary outcome was ventilator free days. Ideally they would have preformed a prospective randomized controlled trial comparing ventilator strategies but could not because of the ethics of studying a ventilator strategy that has been found to be harmful in adults.
This retrospective study included 164 children with ALI, 79 children from 1988-1992 and 85 children from 2000-2004. In the recent group (2000-2004) 53% of the patients received a mean tidal volume of < 8 ml/kg actual body weight (ABW) and 23.5% of patients received < 7 ml/kg ABW. Patients in the past group (1988-1992) only 5.6% received a tidal volume of < 8ml/kg ABW and 1.4% received a tidal volume < 7 ml/kg ABW.
The mortality rate in the recent group was significantly lower than in the past group, 21% for the recent group vs. 35% for the past group. Despite the fact that the recent group had a lower mortality rate, they had a significantly higher oxygenation index (OI) and lower baseline PaO2/FiO2 than the past group of children. There were also more ventilator free days in the recent group compared with the past group. When further analysis of the data was performed it was found that PRISM III scores (Pediatric Risk of Mortality score), immunodeficiency, and tidal volume were all independently associated with increased mortality.
There were two main findings in this study:
1. the approach to ventilation in children with ALI was changed over the past 15 years and has followed adult recommendations
2. mortality decreased by 40% in this population over those years and that a higher tidal volume was associated with increased mortality and a decreased number of ventilator free days
For a number of years we know that tidal volume reduction in adults with ARDS decreases mortality but a definitive study has not been done on children. Some times clinical findings in adults are accepted for use in children without further study in children. While it would be wonderful to do a prospective randomized controlled trial it is not always possible. Albuali and his group4 from London, Ontario and their 15 year retrospective study on ventilation in children with ALI found that decreasing tidal volume was the only therapeutic intervention found to be associated with mortality. While more work needs to be done studying ALI interventions in children, this helps us to know that we are heading in the right direction when adopting certain adult recommendations for children.
1. ARDSnet. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. The Acute Respiratory Distress Syndrome Network. N Engl J Med 2000;342(18):1301-8.
2. Kornecki A, Tsuchida S, Ondiveeran HK, et al. Lung development and susceptibility to ventilator-induced lung injury. Am J Respir Crit Care Med 2005;171(7):743-52.
3. Copland IB, Martinez F, Kavanagh BP, et al. High tidal volume ventilation causes different inflammatory responses in newborn versus adult lung. Am J Respir Crit Care Med 2004;169(6):739-48.
4. Albuali WH, Singh RN, Fraser DD, et al. Have changes in ventilation practice improved outcome in children with acute lung injury? Pediatric critical care medicine 2007;8(4):324-30.