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The Winning Weaning Parameters

Parameter
Normal Range
Indications for Weaning
Definition









Respiratory Rate









10-20 breaths/min









<30 breaths/min*
The number of respiration per minute. This includes all control, IMV/SIMV and spontaneous respiration. An elevated respiratory rate is the compensating mechanism for a drop of tidal volume as a result of increased body exertion. This increase, outside the normal range, is a possible indicator of the onset of fatigue associated with the failure of the ventilatory pump to maintain adequate output in the face of the imposed workload. A low respiratory rate may result in hypoventilation and a respiratory acidosis.










Delta Esophageal Pressure











5-10 cmH2O











<15 cmH2O

Delta Esophageal Pressure is the pressure change in the esophagus due to ventilation. This measurement has been reported to accurately track changes in the pleural pressure. During any ventilation activity, airway pressures maybe transmitted across the pleural space to the esophagus. On patient initiated breaths, the true value of Delta Esophageal Pressure is the negative deflection of the esophageal pressure. On assisted breath during mechanical support  or during controlled mechanical ventilation, positive airway pressure may be transmitted across the potential space causing a rise in esophageal pressure above the normal end esophageal pressure point. Delta Esophageal Pressure is an excellent weaning indicator. Normal Range for non-ventilated patient is 2-10 cmH2O




Tidal Volume





7-10 ml/kg





>5 ml/kg*
Tidal Volume is the volume of inhaled (VTins) or exhaled (VTexp)gas per each breath. This is monitored during mechanical ventilation to determine if the level of mechanical support is adequate for the patient. It may also be an indicator of respiratory fatigue
Vital Capacity
>15 ml/kg
Yes, you should know this by now!
Minute Ventilation
5-10
 liters/minute
<10
liters/minute
This one too!










TI  / TTOT
Respiratory Time Fraction











.3-.4











Increase of >.1*
Respiratory Time Fraction (TI / TTOT) indicates endurance and is defined as the ratio of the inspired time to the total time of the respiratory cycle. This value is a ratio and there is no unit of measure. As the respiratory muscles fatigue, the fraction of the breathing cycle spent in inspiration tends to increase. When there is respiratory muscle fatigue and impending respiratory failure the ratio between inspiratory time and total time available for the breath may incrementally increase to a point in which the respiratory pump can no longer maintain itself and the (TI / TTOT) may decrease dramatically. Excessive work of breathing is the common cause of elevated
(TI / TTOT)
WOBp
.3-.6 joules/liter
<.75 joules/liter*



Pressure
Time
Index



.05-1.2



<.15*
Pressure Time Index (PTI) is a measure of strength and endurance combined into one value. It combines the strength measurement of esophageal pressure and the maximum inspiratory pressure with the endurance value of respiratory time fraction.








Airway Resistance








2-5
cmH2O/L/sec








<15
cmH2O/L/sec
There are two kinds: Mean Airway Resistance - the result of friction in the patient airways and endotracheal tube throughout the entire respiratory cycle. Expiratory Airway Resistance is the result of friction in the patient's airways, endotracheal tube and expiratory limb of the ventilator circuit during expiration only. Airway resistance normally varies inversely with lung volume and increases in obstructive and reactive airways disease. It increases rapidly with decreases in ET tube size as a result of Poiseulle's Law.


Lung Compliance


50-100
ml/cm H2O


>25
ml/cm H2O
Don't forget to subtract the PEEP:-)
If you don't know how to calculate this parameter yet, please drop me an e-mail and include your school  and your instructor.













Pressure Time Product













200-300
cm H2O/sec/min
Pressure Time Product (PTP) is an estimate of metabolic work (oxygen consumption) of the respiratory muscles. This maybe used to evaluate patient effort to overcome both mechanical and isometric force of respiration. PTP decreases with the application of optimal pressure support (PSV) and continuous positive airway pressure (CPAP). PTP varies directly with total lung resistance. This variable is an important indicator of the actual patient effort to breath. Any isometric muscle contraction by the patient  exerted to overcome Auto PEEP or to open the inspiratory demand system results in no tidal volume change and, therefore, accomplishes little or no  measurable work. In this case, PTP may reflect the patient's muscular effort more faithfully than work of breathing. Non- intubated patients should average between 60-80 cm H2O/sec/min.









Maximum Inspiratory Pressure









-30 cm H2O
 low effort

-140 cm H2O
high effort









>-20
 cm H2O*
low effort
Maximum Inspiratory Pressure (MIP) is the pressure change measured by esophageal balloon, that the patient can generate when the airway is occluded for several breaths. MIP is a reflection of diaphragmatic strength and may also be used to monitor respiratory muscle endurance when serial measurements are made. MIP differs slightly from the more commonly used negative inspiratory force (NIF), which is measured at the mouth but also reflects or measures diaphragmatic strength.







Auto PEEP







0







<3 cm H2O
Auto PEEP results when insufficient expiratory time is available between breath to reestablish resting equilibrium. A residual alveolar pressure remains at the end  exhalation which is undetected by the ventilators circuitry. Causes of Auto PEEP are: too large delivered tidal volume, too short expiratory time, increased circuit impedance, low peak inspiratory flows, high respiratory rate, expiratory airways obstruction or dynamic airways collapse.








P0.1 Respiratory Drive









2-4
cmH2O









<6
cmH2O
P0.1 Respiratory Drive actually measures the neural drive to stimulate the force of diaphragmatic contraction. It is defined at the airway occlusion pressure at the first 100 msec after airway closure prior to the patient's conscious recognition of occlusion. A heightened Respiratory Drive increases work expenditure during patient initiated ventilator breaths and may indicate a problem in the cardiopulmonary system. It plays an essential part during machine assisted breaths in determining the energy expenditure of the patient. A low value for P0.1 Respiratory Drive may indicate when respiratory drive is blunted. Problems with P0.1 Respiratory Drive therefore, are important indicators of the ability of the patient to wean from mechanical ventilation.




RSB Index
(RR/Vt)




60-90




<105*
The ratio of respiratory frequency to tidal volume is called the Rapid, Shallow Breathing Index (RSBI). The ratio has proven to be an accurate predictor of success when weaning patients from mechanical ventilation  
*Research indicates that these pulmonary parameters may aid qualified personnel in evaluating weaning potential. If measured values exceed acceptable range,
successful weaning may be less likely. Ranges from these parameters are not intended as a substitute for clinical assessment.