Thursday, February 26, 2009

Clinical Application of P0.1

  • Click on the picture for a larger image. 
Notice in the above pictured graph the dramatic increase in both p0.1 (blue) and work of breathing (yellow) after switching the patient to a low tidal volume strategy.

Maintaining this strategy in this referenced patient would put them at risk for:
  •  muscle fatigue
  • ventilator asynchronies
  •  higher sedation use
  • prolonged mechanical ventilation. 

"Forcing a tidal volume of 6 ml/kg on every patient can result in marked cardiovascular instability, as a result of the patient fighting the ventilator for a larger tidal volume. This increases the patients effort, discomfort, oxygen consumption, carbon dioxide production, and increases the complexity of managing the patient" (Kacmarek, R 2007). 

If the p0.1 is too high
  • Decrease the trigger sensitivity.
  • Shorten rise time (faster).
  • Increase Flow rate.
  • Change to a pressure mode.
  • Increase the Driving pressure.
  • Consider Proportional Assist Ventilation or Adaptive Support Ventilation. 
Grooms, D. (2006). P0.1 Trending to Evaluate Target Vt Settings. Excel Graph. Norfolk General Hospital. Norfolk, VA. 

Tuesday, February 24, 2009

What the heck is P0.1?

Airway Occlusion Pressure at 0.1 Second (P0.1)

P0.1 demonstrated, however it must be quantified due to the rapid occlusion (100 milliseconds).

P0.1 is the maximal slope of the airway pressure drop during the first 0.1 second when the airway is occluded.
Known as a mechanical index of respiratory drive it correlates with the patient workload of inspiration.

May be useful in appropriately setting:
  • Trigger sensitivity.
  • Flow.
  • Rise time.
  • Drive pressure.
  • Amount of pressure support.
P0.1 is measured in cmH2O:
  • -1 to -2 cmH2O, low range, normal
  • -4 to -5 cmH2O, large effort
  • < -6 cmH2O, excessive workload and/or high central drive. 
Low P0.1
Associated with a low level of muscular inspiratory activity, which is good in patients with no respiratory disease or damage in the central nervous system in relation to the respiratory muscles. 
A low P0.1 may also due to respiratory center depression:
  • Sedation.
  • Drug overdose.
  • Sleep cycles.
  • Brain trauma.
note- Evaluate additional parameters to assess if P0.1 shows comfort versus respiratory system depression or muscle dysfunction (e.g. sedation scales). 
Elevated P0.1 Values
May indicate inadequate trigger sensitivity and/or ventilator support.
Associated with a higher risk of fatigue or failure during spontaneous breathing trials.

Monday, February 23, 2009

Medical Device Companies names for APRV

There are various ventilators which a practitioner can utilize APRV.
Yes, APRV is a trade name for airway pressure release ventilation on Draeger brand ventilators. However, one must think of airway pressure release ventilation as a specific application of biphasic breath delivery and not solely focus on the name of a modality.

Below are photos of various ventilator modes which one can simulate airway pressure release ventilation.

APRV- trade name for Evita series ventilators. 

Bilevel- mode on the PB 840 used to mimic APRV

Bi-Vent- Servo-i ventilators, used to simulate APRV

DuoPAP+, this mode most resembles APRV in regards to initial settings. Hamilton ventilators. 

Waveform of the week: Auto-triggering

Auto-triggering is a condition in which the ventilator repeatedly triggers itself because the trigger threshold is set too sensitive. 

Auto-triggering is caused by flow distortions:
  • Water in the ventilator circuit.
  • Circuit leaks.
  • Chest tubes.
  • Endo-tracheal tube cuff leaks.
  • Cardiac oscillations (high cardiac output, or balloon pump). 

The above image demonstrates auto-triggering caused by a leak, by evidence of the volume waveform (highlighted) never returning to baseline. When no leaks are present the volume waveform will return to baseline. 

To determine if the auto-triggering is due to cardiac oscillations: 
  • Evaluate the ECG or SPO2 waveform, does the triggering match the waveforms?
  • Evaluate the Airway Occlusion Pressure @ 0.1 second (P.01) if the P.01 is zero & the measured frequency is greater than the set frequency the ventilator is auto-triggering. 
To prevent Auto-triggering
  • Minimize leaks.
  • Make the trigger threshold less sensitive. 

Friday, February 20, 2009

All exhalation valves are not created equal.

The new design of ventilator exhalation valves (e.g. active, floating) allows for unhindered spontaneous breathing during APRV. The valve prevents the ventilator from terminating the inspiratory phase and losing mean airway pressure during coughing or exhalation.
  • Can the exhalation valve design influence patient comfort and interaction? 

Each manufacturers exhalation design is different.

Draeger and Maquet uses a type of "pressure threshold resister".
  •  During inspiration a preset degree of force (pressure) against the exhalation valve keeps it seated proportional to the operator desired set pressure.
  • Should the patient want to exhale or cough prior to the inspiratory time being reached, the valve releases any excess pressure. 
Hamilton Medical and Puritan Bennet uses a type of electromagnetic valve for its exhalation valve design.
  • Uses known electrical current (force) relationships, expiratory pressure, flow monitoring, and algorithms to determine when to release excessive pressure. 
Is one design superior than the other in regards to ease of pressure release, expiratory resistance, and pressure over-shoot? 
Some medical device vendors (e.g. Draeger) argue that their product is superior and state that it is more responsive due to that it does not require a feedback loop to determine if excessive pressure should be released. 
  • Researchers reveled no statistical differences when comparing the Evita XL, PB 840, and Servo-I in regards to ease of pressure release and pressure over-shoot. 
  • There are differences when evaluating expiratory resistance. In one bench study (1) researchers discovered that the Evita XL had the highest exhalation resistance. 
  • There are no studies in regards to patient interaction and comfort, at this time. 
Exhalation valve actions are similar when comparing ease of pressure release and pressure over-shoot. There are differences in design and expiratory resistance, however there are no studies identifying if these differences influence patient interaction or comfort. 

  1. Jiao, G-Y. and Newhart, J. (2008). Bench Study of Active Exhalation Valve Performance. Respiratory Care. 53 (12): 1697-1702. 

Thursday, February 19, 2009

Do I need a Draeger ventilator to utilize Airway Pressure Release Ventilation?

The utilization of Airway Pressure Release Ventilation (APRV) for patients with Acute Respiratory Distress Syndrome (ARDS) has been safely practiced for over twenty years. APRV has been applied in adult, pediatric, and neonatal populations as an alternative to traditional mechanical ventilation strategies.

Some medical practitioners argue that APRV is superior to standard ventilation strategies (e.g. ARDS low tidal volume strategy) for patients with ARDS, however, no clinical trial to date have shown any meaningful clinical outcome benefit over conventional strategies. 

Additionally, few practitioners claim that APRV can only be applied with Draeger ventilators. 
Is this true? 
Is it going to harm my patient if I use another manufactures machine? 
What are my limitations? 

Well there is no clinical evidence to support this claim. Further more, I and several other practitioners have utilized various ventilators from different manufactures to safely & successfully simulate APRV.

More to come.