Stress index

Stress index values 1, the curve presents an upward concavity, suggesting a continuous increase in elastance (decrease in compliance), and excessive PEEP may be present.

stress index value = 1, the curve is straight, suggesting the absence of tidal variations in elastance. Pao = airway pressure.

(Reprinted with permission from the American Thoracic Society.29)

Rapid shallow index

Yang and Tobin method 1991
After disconnect mechanical ventilator and brathing in room air for 1 minute
RR and TV is collect (via MV) to calculate RSBI

P0.1

About P0.1
The inspiratory depression of airways pressure, achieved after 100 ms of occlusion, is generally defined as the occlusion pressure or P0.1 and represents a valid indirect measurement of the activity of the respiratory centres. P0.1 is a reliable measurement of the intensity of the stimuli from the neurological centres to the peripheral respiratory muscles.
จาก studies ค่าP0.1ที่บ่งว่าผู้ป่วยสามารถ weaning สำเร็จ (+/-ไม่ต้องreintubate) อยู่ที่ 4.5-6cmH2O

จริงๆ จะเป็นค่า negative (represent pleural pressure) หาก drive น้อย occlusion pressure >-6 (เป็นลบน้อยกว่า)
หากมี drive occlusion pressure < -6 คืือดึง negative มากกว่าเดิม

Autopeep

Autopeep

End expire Palv > atmosphere

1.Dynamic hyperinflation + inhibit expire flow limitation
-COPD
2.Dynamic hyperinflation no expire flow limitation
-ventilator stting
High rate
High Vt
Inspire > expire
End expire pause
-tube resistant
3.No dynamic hyperinflation
-recruit of expiratory muscle

การสังเกตุว่ามี Dynamicheper inflation

Effect of autopeep
-Increase WOB
Lenght tension of inspire muscle loss
-decrease oxygen tension
inhomogenouse of lung unit
-hemodynamic compromise
Decrease venous return CO BP
Increase pul vascular resistance
Increase rt ventricular afterload
-effect CVP PCWP

-ตั้ง peep 50-80%of autopeep

-การตั้ง peep ไม่ได้ช่วยลด autopeep แค่ลดแรง trigger ต้องแก้สาเหตุด้วย

วิธีการวัด Autopeep
1. End expiratory occlusion technique
2. Zeep with peep titration
3. Esophageal balloon
4. Optoelectronic plethysmography (OEP)
5. จากสมการ End-inspiration volume

การวัด autopeep
1. Static = Occlusion
2. Dynamic = Esophageal pressure

-Dyanamic auto-peep represent lowest regional auto-PEEP and therefore underestimates static auto-PEEP in the presence of heterogenous mechanical properties
-Dynamic auto-PEEP considerably underestimates static auto-PEEP in patients with significant airway obstruction
-asynchony cause tensing of abdominal expiratory muscles at end-expiration may cause the measured auto-PEEP to greatly over estimate the end expiratory elastic recoil pressure
-airway occlusion be maintained for several seconds to avoid gross underestimation of average end expiratory alveolar pressure

Neuromuscular disease ใช้ vt>12ml/kg

1.Metabolic acidosis Kaussmall breathing
2.Spinal cord injury and probably other neuromuscular diseases too ja, to prevent atelectasis and its complication esp. pneumonia. Sometime, we set it as high as 20-25 ml/kg as long as the PPlat < 30, make sure the RR is not too high and it won't cause respi alkalosis because the extra large tidal volume will have some degree of dead space ventilation on its own. by aj atikun limsukon