LARRY’S GUIDE TO WEANING

 

 

1.   BASIC PRINCIPLES

 

a.   Most patients do not require “weaning,” that is, the gradual withdrawl of mechanical ventilatory support and can be summarily extubated when the process that required intubation has been reversed.

b.            “Weaning” should be directed at identifying when a patient is ready to be liberated from mechanical support, and if not, WHY not.

 

1.      IDENTIFYING READINESS FOR LIBERATION

 

a.   PaO2 > 60mmHg on FiO2 < 0.5

b.   PEEP < 5.0cmH2O

c.   Not in shock

d.   No excessive respiratory load (Ra < 20 cmH2O)

e.            Parameters:

 

Parameter

Normal

Cutoff value

PPV

NPV

MIP/PImax/NIP

-120cmH2O (M)

-90cmH2O (F)

< -20cmH2O

60%

100%

VC

65-75mL/kg

> 10ml/kg

 

 

VE

5-7L/min

< 10L/min

50%

40%

Compliance, Rate, Oxygenation, Pressure (CROP): dynCrs x PImax x (PaO2/PAO2)/frequency

 

> 13

71%

70%

Index of Rapid Shallow Breathing (RVR): RR/TV

< 50/min/L

< 105/min/L

78%

95%

 

1.      IDENTIFYING REASONS FOR FAILURE

 

Respiratory pump insufficiency

 

CNS

narcotics, sedatives, hypothyroidism

 

PNS

AML, polio, phrenic nerve injury, Guillain-Barre, myasthenia gravis, aminoglycoside toxicity, botulism

 

Muscle

respiratory muscle fatigue, electrolyte abnormalities (K+, Mg++, PO4+), sepsis, shock, malnutrition(check pre-albumin), critical illness myopathy or polyneuropathy, steroid myopathy

 

Increased respiratory load

 

Pulmonary

asthma, COPD, autoPEEP, pneumonia, interstitial fibrosis

 

Structural

kyphoscoliosis, obesity, edema, pleural effusions, abdominal distension

 

Systemic

fever, sepsis, metabolic acidosis, pulmonary embolism, hypovolemia

 

Other

ETT obstruction, over-feeding

 

 

 

COMPLIANCE:  normal- 70-160

 

     TV(cc) / (Plateau-PEEP)(cmH2O)

 

RESISTANCE:  normal- 5

 

     (PIP-Plateau)(cm/H2O) X 60 / IFR(L/min)

 

 

2.      WEANING ALGORITHM