From: Use of ‘tidal volume challenge’ to improve the reliability of pulse pressure variation
Limitations | Mechanisms for failure | Type of error | |
---|---|---|---|
1 | Spontaneous breathing activity | Irregular variations in intrathoracic pressure and thus the variation in stroke volume cannot correlate with preload dependency | False positive (may occasionally be false negative depending on the type of breathing) |
2 | Cardiac arrhythmias | The variation in stroke volume is related more to the irregularity in diastole than to the heart‐lung interactions | False positive |
3 | Mechanical ventilation using low tidal volume (<8 ml/kg) | The small variations in intrathoracic pressure due to the low tidal volume are insufficient to produce significant changes in the intrathoracic pressure | False negative |
4 | Low lung compliance | The transmission of changes in alveolar pressure to the intrathoracic structures is attenuated | False negative |
5 | Open thorax | No change in intrathoracic pressure during the respiratory cycle | False negative |
6 | Increased intra‐abdominal pressure | Threshold values of PPV will be elevated | False positive |
7 | Low HR/RR ratio < 3.6 (severe bradycardia or high frequency ventilation) | If the RR is very high, the number of cardiac cycles per respiratory cycle may be too low to allow variation in stroke volume | False negative |