The respiratory drive is the intensity of the neural stimulus that determines how much the respiratory muscles contract. Excessive or low respiratory drive can be encountered in different clinical scenarios in patients on mechanical ventilation. High respiratory drive potentially leads to an injurious effect on the diaphragm (myotrauma), and on the lung (patient-self-inflicted lung injury). The low respiratory drive may cause disuse atrophy which leads to difficulty in weaning off the ventilator. Occlusion pressure at 100 ms (P 0.1) is the negative pressure measured 100 ms after the initiation of an inspiratory effort performed against a closed respiratory circuit and has been used as an indirect measure of the respiratory drive. This blog will discuss what is P 0.1, how is it used to assess respiratory drive in patients on mechanical ventilation, and what is the reliability of the test.
Do you use P 0.1 to assess the respiratory drive of your patients on the ventilator?
- Yes
- No
- Never heard of it!
What is P 0.1?
P 0.1 is the negative pressure measured 100 ms after the initiation of an inspiratory effort with an occluded airway. Due to the brevity of the maneuver, the patient does not exert any effort due to the occluded airway. In addition, it is not affected by respiratory mechanics or influenced by respiratory muscle weakness (except in severe cases of respiratory muscle weakness), therefore, it assesses the respiratory drive indirectly and serves as a mechanical index of respiratory drive. This pressure is used to detect potentially excessive inspiratory efforts due to high inspiratory drive. Normal P 0.1 values range from 1.5 to 3.5 cm H2O and indicate an acceptable respiratory drive and high chance of weaning success in association with other predictive values.
How is it measured?
Compared to other measures of the respiratory drive such as the electrical activity of the diaphragm, esophageal pressure, or diaphragmatic ultrasound, P 0.1 is a noninvasive, simple, fast, and feasible measurement in ventilated patients. Most of the recent ventilators are equipped with the ability to measure P 0.1. It is assessed by measuring the inspiratory pressure generated against a closed respiratory circuit during the first 100 milliseconds of inspiration. This can be done through a whole breath occlusion maneuver or an occlusion for the first 100 ms of inspiration. In some new ventilators, such as Hamilton G5, where the inspiratory valve is always open for the patient's comfort, the pressure is measured with an extrapolated line from the steepest segment of the pressure drop to the vertical line at 100 ms of inspiration.
How reliable is the test?
The P 0. I has been found to be a reliable measure of respiratory drive with a high intra-class correlation coefficient (ICC). The ICC for P0.I between repeated measures have been reported to range from 0.88 to 0.96 in one study that included 11 healthy subjects. P 0. I is also a reliable measure of respiratory drive when compared to other measures of respiratory drive such as transdiaphragmatic pressure (TDP) or electrical activity of the diaphragm (EAdi), with ICCs ranging from 0.75 to 0.92 [1].
A recent study published in the American Journal of Respiratory and Critical Care Medicine looked at the use of P 0.1 as a measure of respiratory drive in patients on mechanical ventilation. The study found that P 0.1 was a valid and reliable predictor of respiratory drive and could be used to detect potentially injurious inspiratory efforts.
P 0.1 correlated well with the electrical activity of the diaphragm and the esophageal pressure–time product as a measure of the respiratory drive. A reference value of >3.5 cm H2O was 80% sensitive and 77% specific for detecting high effort. P 0.1 ≤1.0 cm H2O was 100% sensitive and 92% specific for low effort (≤50 cm H2O ⋅ s ⋅ min−1). The area under the receiver operating characteristics curve for P 0.1vent to detect potentially high and low effort was 0.81 and 0.92, respectively [2].
Based on the above study and multiple other studies in the intensive care unit, a P 0.1 value of 1.5-3.5 is representative of acceptable respiratory drive. Values higher than 3.5 can be used to detect potentially injurious high effort and values lower than 1.5 (1.1 in some references) are used as an indication of low effort. P 0.1 also predicts the success of ventilator weaning. In general, values higher than 5 or lower than 1 are associated with higher rate of weaning failure. A P 0.1 value of 0 means that there is no inspiratory effort against the closed airway, which can be due to severe muscle weakness, neuromuscular blockade, or apnea.
What does a P 0.1 value of -6.7 cm H2O indicate?
- Low respiratory drive
- May require sedation
- Weak inspiratory muscles
- High potential of weaning success
Conclusion
P 0.1 has been found to be a valid and reliable predictor of respiratory drive in patients on mechanical ventilation. It correlates well with the electrical activity of the diaphragm and the esophageal pressure-time product as a measure of the respiratory drive. P 0.1 is a reliable bedside tool to assess respiratory drive and detect injurious inspiratory effort. A P 0.1 value of 1.5-3.5 is representative of acceptable respiratory drive. Values higher than 3.5 can be used to detect potentially injurious high effort while values lower than 1.5 are indicative of low effort ventilations. Clinicians should use P 0.1 in addition to other weaning parameters such as RSBI and minute ventilation in prediction of weaning success.
References
Kera T, Aihara A, Inomata T. Reliability of airway occlusion pressure as an index of respiratory motor output. Respir Care. 2013 May;58(5):845-9. doi: 10.4187/respcare.01717. PMID: 23107621.
Telias I, Junhasavasdikul D, Rittayamai N, Piquilloud L, Chen L, Ferguson ND, Goligher EC, Brochard L. Airway Occlusion Pressure As an Estimate of Respiratory Drive and Inspiratory Effort during Assisted Ventilation. Am J Respir Crit Care Med. 2020 May 1;201(9):1086-1098. doi: 10.1164/rccm.201907-1425OC. PMID: 32097569.