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