Thursday, November 10, 2011

A Unique Way to Obtain the NIF

Using the trigger setting to quantify extubation readiness. Notice the measured PEEP value & set PEEP value, the patient is able to generate a NIF < -18 cmH2O.

There are multiple ways to obtain the Negative Inspiratory Force (NIF) NIP (negative inspiratory pressure), or MIP (maximal inspiratory pressure) measurement. The NIF “corresponds to the negative pressure generated by the inspiratory muscles during a maximal inspiratory effort, performed during temporary occlusion of the airway opening” [1]. This parameter is used to quantify that the respiratory drive is sufficient (paralytics, narcotics, sedation is worn off after general anesthesia) or that there is no respiratory muscle fatigue or exhaustion.

In previous postings [2 & 3] I mentioned techniques to obtain the NIF. Additionally, I mentioned potential hazards of performing the technique by airway occlusion in young, healthy, athletic patients. This novel technique in obtaining the NIF does not use an occlusion method, but uses the ventilators trigger setting.
 This simple technique was demonstrated to me by an anesthesiologist, which uses this technique on all of his patients that have general anesthesia.


1. Spontaneous breathing is initiated as soon as possible during the surgical procedure. The patients’ spontaneous efforts are augmented by either a PC-CMV or CSV-PS mode of ventilation.

2. Once the surgical procedure is over the trigger setting is titrated to make the trigger less sensitive (harder), while the EtCO2 waveform is assessed as well as the exhaled tidal volume.

3. The trigger is continued to be titrated until the trigger setting is at – 20 cmH2O.

4. If the patient is able to trigger a breath at -20 cmH2O, then the patient is extubated.

This technique can be reproduced in the ICU, if the ventilator has the capability of setting a trigger at -20 cmH2O.

Potential benefits over traditional techniques:

-No additional equipment necessary.

-One does not have to disconnect the patient from the ventilator.

-The patient is not trying to inhale against an occlusion.

-The patient can exhale anytime.

-The patient can receive all the flow they want after the trigger is initiated.

-There is only one setting that is changed.

-No issues with timing.

-Maybe safer & more comfortable to the patient.


Obtaining the MIP without a Manometer

The MIP: a Review of Obtaining Maximal Inspiratory Pressure

[1]. Lotti, G. & Braschi, A. (1999). Measurements of Respiratory Mechanics during Mechanical Ventilation. Rhazuns, Switzerland.

[2]. The MIP: a Review of Obtaining the Maximal Inspiratory Pressure.

[3]. Obtaining the MIP without a Manometer.