The Science Journal of the American Association for Respiratory Care

2001 OPEN FORUM Abstracts

Characteristics of acute lung injury (ALI) patients exhibiting respiratory distress or dyssynchrony during low VT ventilation

RH Kallet, MS RRT, JA Alonso RRT, L Martin RRT, M Eisner MD, JM Luce MD. NHLBI ARDS Clinical Trials Networkat San Francisco General Hospital (SFGH)

Background: Theincidence of respiratory distress and/or patient-ventilator dyssynchrony duringlow VT ventilation is unknown. We gathered preliminary informationby reviewing the medical records of all 21 patients enrolled into the ARDS Networklow VT study at SFGH and randomized to low VT (6mL/kg)ventilation.

Methods: Protocol-directedventilator adjustments were made with the intention of minimizing inspiratoryflow rate yI and inspiratory-phase dyssynchrony. The ventilator flowsheets and nursing notes were reviewed retrospectively for all documented incidencesof distress/dyssynchrony during the first 24 h of protocol management. Datawas expressed as mean (± standard deviation) and comparisons were made usingMann-Whitney tests. The relative risk for distress/ dyssynchrony was assessedby two-sided Fisher?s Exact test. Alpha was set at 0.05.

Results: Distress/dyssynchrony was documented in 67% (14/21) of the patients in the low VTgroup. Patients exhibiting signs of distress/dyssynchrony had a trend towarda lower pH, base excess (BE), and tended to require a higher VT despiteequivalent settings for peak yI, set f and trigger sensitivity (Psens).The relative risk of developing distress/dyssynchrony when the BE > -5 mEq/dLwas 2.05, but failed to achieve statistical significance (p = 0.08).


VariableDistress/Dyssynchrony ApparentSynchronyp
VT7.0 ± 0.99 mL/kg6.5± 0.6 mL/kg 0.076
yE16.4 ± 3.2L/min15.5 ± 3.6L/min0.55
yI88.8 ± 19.6mL/kg81.7 ± 21.6mL/kg 0.49
Set f29.7 ± 5.328.3 ± 29.70.75
Total f 31.3 ± 5.728.8 ± 5.20.34
Psens-1.0 ± 0.3cmH2O-1.4 ± 0.6cmH2O0.49
pH7.34 ± .08 7.38 ± .06 0.27
PaCO234.8 ± 8.4mm Hg 38.4 ± 5.0mm Hg 0.27
PaO282.7 ± 14.9mm Hg75.3 ± 10.0mm Hg0.47
BE-6.3 ± 6.5mEq/dL -2.7 ± 4.4mEq/dL0.18

Discussion/Conclusion:Setting a high peak yI, f and low Psens may notbe sufficient to prevent distress/dyssynchrony during low VT ventilation.Chronic metabolic acidosis increases ventilatory drive.1 Therefore,our data suggests an intriguing research question: will correcting metabolicacidosis improve patient tolerance of low VT ventilation? This maybe clinically relevant when high levels of sedation or paralytic agents arerequired to treat distress/ dyssynchrony, or a desired target VTcannot be achieved. (NIH R01-HL51856)

1. Berger AJ, et al.Regulation of respiration. N Engl J Med. 1977; 297(4):194-201.


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