BACKGROUND

The impedance threshold device (ITD) is designed to enhance venous return and cardiac output during cardiopulmonary resuscitation (CPR) by increasing the degree of negative intrathoracic pressure. Previous studies have suggested that the use of an ITD during CPR may improve survival rates after cardiac arrest.

METHODS

We compared the use of an active ITD with that of a sham ITD in patients with out-of-hospital cardiac arrest who underwent standard CPR at 10 sites in the United States and Canada. Patients, investigators, study coordinators, and all care providers were unaware of the treatment assignments. The primary outcome was survival to hospital discharge with satisfactory function (i.e., a score of ≤3 on the modified Rankin scale, which ranges from 0 to 6, with higher scores indicating greater disability).

RESULTS

Of 8718 patients included in the analysis, 4345 were randomly assigned to treatment with a sham ITD and 4373 to treatment with an active device. A total of 260 patients (6.0%) in the sham-ITD group and 254 patients (5.8%) in the active-ITD group met the primary outcome (risk difference adjusted for sequential monitoring, −0.1 percentage points; 95% confidence interval, −1.1 to 0.8; P=0.71). There were also no significant differences in the secondary outcomes, including rates of return of spontaneous circulation on arrival at the emergency department, survival to hospital admission, and survival to hospital discharge.

DISCUSSION

Physiological studies in animals and humans have suggested that interventions capable of decreasing mean intrathoracic pressure can augment the return of venous blood to the heart and improve hemodynamics during CPR.3-5,7 Despite such findings, this large effectiveness trial did not confirm a survival advantage with the use of an active ITD during standard CPR in patients with nontraumatic, out-of-hospital cardiac arrest.

One possible explanation for the neutral results is that, despite the evidence cited, the ITD may not generate the physiological effects that have been proposed. Two studies in animals that were published after the present trial began enrollment showed no improvement in hemodynamics or survival with application of the ITD during standard CPR.17,18

A second possible explanation is that use of the active ITD by the participating EMS systems did not recreate the physiological effects seen in some of the experimental studies.3-5,7 Delayed application of the ITD, failure to prevent airway leaks, and suboptimal performance of CPR can interfere with the hemodynamic improvements that are associated with ITD use.19-22 For these reasons, the ROC investigators implemented comprehensive training, retraining, electronic monitoring of the CPR process, and follow-up quality-assurance monitoring. The quality of the CPR provided was associated with outcomes in the sham-ITD group that were better than expected. Therefore, it is not likely that EMS systems would apply the ITD in a more operationally efficacious way than they were applied in this study.

Another possible explanation is that application of the active ITD produced the physiological effects seen in experimental studies but did not improve clinical outcomes. It is possible that failure to remove the ITD immediately after successful resuscitation, with the resulting increased work of breathing, increases interstitial lung fluid and left-sided pressures and worsens heart failure, or that such failure increases venous pressure, decreasing cerebral perfusion pressure in the resuscitated state. Other interventions (e.g., the administration of epinephrine) might exacerbate these potential complications.

Several limitations of the trial should be noted. The investigators did not directly measure hemodynamics, intrathoracic pressure, ventilation rate and duration, or the effects of ITD use during gasping and spontaneous ventilation. CPR process measures were not recorded in all cases. Although use of the modified Rankin scale has been validated for assessing the effects of stroke, it lacks validation for cardiac arrest. In only 61.5% of patients who received the active ITD was it placed within 5 minutes after the arrival of EMS personnel.

Another factor of potential importance that was not measured in this study is chest recoil.22 Loss of elastic recoil of the chest can occur over time during standard CPR.23 Since the purpose of the ITD is to enhance negative intrathoracic pressure by preventing passive air inflow during chest recoil, loss of such recoil is a potential limitation in achieving the desired physiological result. A recent study showed that combining the use of an ITD and active compression–decompression CPR significantly increases survival to hospital discharge with satisfactory function, as compared with standard CPR.24

In conclusion, we compared use of an active ITD with use of a sham ITD during standard CPR in patients with nontraumatic, out-of-hospital cardiac arrest. Use of the active ITD did not significantly improve survival with satisfactory function.

Characteristics before Randomization in the Modified Intention-to-Treat Population.pngPatient Characteristics and Treatments Received after Randomization in the Modified Intention-to-Treat Population..pngPatient Characteristics and Treatments Received after Randomization in the Modified Intention-to-Treat Population2.png  

Outcomes in the Modified Intention-to-Treat (ITT) and Safety Populations.png

arrow
arrow

    快樂小藥師 發表在 痞客邦 留言(0) 人氣()