PURPOSEThis prospective observational study aims to evaluate the accuracy of dead-space fraction derived from the ventilator volumetric capnography (volumetric CO₂) or a prediction equation to predict the survival of mechanically ventilated patients with acute respiratory distress syndrome (ARDS).

METHODSConsecutive VD/VT measurements were obtained based upon a prediction equation validated by Frankenfield et al for dead-space ventilation fraction: VD/VT = 0.320 + 0.0106 (PaCO₂-ETCO₂)⁺ 0.003 (RR)⁺0.0015 (age) in adult patients who had infection-related severe pneumonia and were confirmed as having ARDS. Here PaCO₂ is the arterial partial pressure of carbon dioxide in mmHg; ETCO₂, the end- tidal carbon dioxide measurement in mmHg; RR, respiratory rate per minute; and age in years. Once the patient had intubation, positive end expiratory pressure was adjusted and after Phigh reached a steady state, VD/VT was measured and recorded as the data for the first day. VD/VT measurement was repeated on days 2, 3, 4, 5 and 6. Meanwhile we collected dead-space fraction directly from the ventilator volu- metric CO₂ and recorded it as Vd/Vt. We analyzed the changes in VD/VT and Vd/Vt over the 6-day period to determine their accuracy in predicting the survival of ARDS patients.

RESULTSOverall, 46 patients with ARDS met the inclusion criteria and 24 of them died. During the first 6 days of intubation, VD/VT was significantly higher in nonsurvivors on day 4 (0.70 ± 0.01 vs 0.57 ± 0.01), day 5 (0.73 ± 0.01 vs. 0.54 ± 0.01), and day 6 (0.73 ± 0.02 vs. 0.54 ± 0.01) (all p =0.000). Vd/Vt showed no significant difference on days 1e4 but it was much higher in nonsurvivors on day 5 (0.45 ± 0.04 vs. 0.41 ± 0.06) and day 6 (0.47 ± 0.05 vs. 0.40 ± 0.03) (both p=0.008). VD/VT on the fourth day was more accurate to predict survival than Vd/Vt. The area under the receiver-operating characteristic curve for VD/VT and Vd/Vt in evaluating ARDS patients survival was day 4 (0.974 ± 0.093 vs. 0.701 ± 0.023, p = 0.0024) with the 95% confidence interval being 0.857-0.999 vs. 0.525-0.841.

CONCLUSIONCompared with Vd/Vt derived from ventilator volumetric CO₂, VD/VT on day 4 calculated by Frankenfield et al's equation can more accurately predict the survival of ARDS patients.

Adult ; Capnography ; Female ; Humans ; Male ; Middle Aged ; Prospective Studies ; ROC Curve ; Respiration, Artificial ; Respiratory Dead Space ; physiology ; Respiratory Distress Syndrome, Adult ; mortality ; physiopathology

This study was performed to elucidate the mechanism of improved oxygenation after surfactant replacement therapy in respiratory distress syndrome (RDS) of the newborn infants. In 26 newborns with RDS, end tidal-CO2 tension (PetCO2), arterial blood gas analysis and pulmonary function tests were measured at baseline, 30 min, 2 hr and 6 hr after surfactant administration. The changes in dead space/tidal volume ratio (VD/VT ratio=(PaCO2-PetCO2)/PaCO2), oxygenation index and arterial-alveolar partial pressure difference for oxygen ((A-a)DO2) were elucidated and correlated with pulmonary mechanics. Oxygenation index and (A-a)DO2 improved, and VD/VT ratio decreased progressively after surfactant administration, becoming significantly different from the baseline at 30 min and thereafter with administration of surfactant. Pulmonary mechanics did not change significantly during the observation period. VD/VT ratio showed close correlation with OI and (A-a)DO2, but not with pulmonary mechanics. These results suggest that decreased physiologic dead space resulting from the recruitment of atelectatic alveoli rather than improvement in pulmonary mechanics is primarily responsible for the improved oxygenation after surfactant therapy in the RDS of newborn.
Airway Resistance ; Human ; Infant, Newborn ; Lung/physiopathology* ; Lung Compliance ; Pulmonary Gas Exchange ; Pulmonary Surfactants/therapeutic use* ; Respiratory Dead Space* ; Respiratory Distress Syndrome/physiopathology ; Respiratory Distress Syndrome/drug therapy* ; Tidal Volume*

PURPOSE: Examine the clinical utility of the alveolar dead space ventilation ratio (VdA/VT) as a predictor of acute respiratory distress syndrome (ARDS) in severe sepsis and septic shock patients. METHODS: A prospective observation study was done for 113 patients with severe sepsis and septic shock seen at the emergency department of a university hospital from January 2005 to June 2007. Therapies in the emergency department included central venous access, antibiotics, fluid resuscitation, mechanical ventilation, vasopressors and inotropes as required. The major outcome assessed was the development of ARDS within 3 days after admission. Hemodynamic variables, arterial blood gas values, serum lactate concentration, and estimated VdA/VT were evaluated at presentation (0 hour) and at 4 hours. Briefly the estimated VdA/VT was calculated by dividing the deference of the arterial CO2 and end-tidal CO2 by the PaCO2 value. Data were presented as median+/-SD. RESULTS: ARDS developed in twenty-two patients (<24 hours: 17 persons, 24~48 hour: 4 persons, 48~72 hour: 1 person). Patients who developed ARDS had significantly higher age, higher frequency of pneumonia, greater use of mechanical ventilation and dubutamine during ED therapy, and higher sepsis related organ failure assessment (SOFA) scores. The in-hospital mortality of patients with ARDS was significantly higher than that of patients without ARDS (54.5% vs. 15.4%, p<0.001). Pneumonia, use of dobutamine during ED therapy, and VdA/VT at 4 hours were independent predictive factors for the development of ARDS. The area under the receiving operating characteristic curve for predicting ARDS was 0.891 (95% CI; 0.808-0.980) with a value of VdA/VT at 4 hours. The cut off value of VdA/VT at 4 hours was 0.25 (sensitivity 81.8%, specificity 93.3%). At 4 hours, patients with VdA/VT equal to or greater than 0.25 under resuscitation showed a high rate of fluid and high inhospital mortality when compared with patients with VdA/VT <0.25 (CVP<10 cmH2O; 37.5% vs. 16.9%, p=0.047, mortality; 75.0% vs. 4.5%, p<0.001). In patients with VdA/VT equal to or greater than 0.25 at 0 hour, patients without ARDS showed significantly improvement of VdA/VT at 4 hours. CONCLUSION: VdA/VT was found to be an independent predictive variables for ARDS in the early in-hospital period. Improvement of VdA/VT through early goal directed therapy in emergency department may decrease the development of ARDS in severe sepsis and septic shock patients.
Anti-Bacterial Agents ; Carbon Dioxide ; Dobutamine ; Emergencies ; Hemodynamics ; Hospital Mortality ; Humans ; Lactic Acid ; Pneumonia ; Prognosis ; Prospective Studies ; Respiration, Artificial ; Respiratory Dead Space ; Respiratory Distress Syndrome, Adult ; Resuscitation ; Sensitivity and Specificity ; Sepsis ; Shock, Septic ; Ventilation