Clinical prediction scores predicting weaning failure from invasive mechanical ventilation: Role and limitations

Table 1 Criteria for failure of spontaneous breathing trial

Objective criteria	Subjective criteria
Tachycardia; tachypnoea; hypertension or hypotension; hypoxemia; acidosis; arrhythmias	Agitation or distress; altered or depressed mental status; sweating; increased work of breathing

Table 2 Classification of patients on the basis of weaning process

Simple weaning	Initiation of weaning to successful extubation in the first attempt without encountering any difficulty
Difficult weaning	Failed initial weaning and requirement of up to 3 SBTs or as long as 7 days from the first SBT to achieve weaning success
Prolonged weaning	Failed at least 3 weaning attempts or require 7 days or more of weaning after the first SBT

SBT: Spontaneous breathing trial.

Table 3 Causes of weaning failure

Respiratory factors[29-32]	Increased airway resistance - bronchospasm, excessive secretions, ET block, kinks, blood in ET Decrease compliance - pulmonary edema, fibrosis, atelectasis, acute respiratory distress syndrome (ARDS) Ventilator induced lung injury - ventilator associated pneumonia, pneumothorax, hemothorax Increased work of breathing - dynamic hyperinflation, patient - ventilator dyssynchrony/asynchrony
Cardiac factors[33-35]	Pre-existing cardiovascular disorders – ischemic heart disease, valvular heart disease, pericardial diseases; stress cardiomyopathy; unresolved primary systemic disease
Neuromuscular factors[36-42]	Primary neuromuscular disorders
	Myasthenia gravis
	Guillain-Barre syndrome
	Myopathies
	Peripheral neuropathies
	Secondary causes
	Ongoing sedatives
	On neuromuscular paralyzing agents
	Critical illness neuromyopathies
	Ventilator induced diaphragmatic dysfunction
	Long term corticosteroid use
Neuropsychological[43-45]	ICU delirium; anxiety
Metabolic & endocrine[41]	Dyselectrolytemias; hypokalaemia, hypomagnesemia, hypophosphatemia; hypo/hypernatremias; hypo/hyperglycaemia; hypothyroidism; hypoadrenalism; long-term corticosteroid use
Nutrition[46,47]	Pre-existing malnutrition; underweight; Inadequate calorie intake; refeeding syndrome

ARDS: Acute respiratory distress syndrome; ET: Endotracheal tube; ICU: Intensive care unit.

Table 4 Criteria to assess for readiness to wean

Clinical criteria	Objective criteria
Primary disease for which patient needed IMV is improving; good cough reflex; absence of secretions	Respiratory; SaO2 > 90% with FiO2 < 0.4 (Pf > 150), PEEP < 8 cm H2O; RR < 35/min; MIP < 20-25 cm H2O; Vt > 5 mL/kg on SBT; VC > 10 mL/kg; No acidosis. Cardiovascular; HR < 140/min; SBP 90-160 mmHg with minimal to no vasopressors; neurological; conscious or adequate mental status with good airway reflexes

FiO₂: Fraction of inspired oxygen; IMV: Invasive mechanical ventilation; SBT: Spontaneous breathing trial; HR: Heart rate; MIP: Maximum inspiratory pressure; PEEP: Positive end-expiratory pressure; RR: Respiratory rate; SaO₂: Oxygen saturation of arterial blood; SBP: Systolic blood pressure; Vt: Tidal volume; VC: Vital capacity.

Table 5 Summary of various scores for predicting weaning failure in patients receiving invasive mechanical ventilation

Score	Components	Value	Advantages	Disadvantages
A: RSBI	Respiratory rate; Vt; RSBI = RR/Vt	< 105 – weaning success; > 105 – weaning failure	Simple; easy to calculate	Affected by multiple factors – fever, infection, anxiety, restrictive disorders, weaning technique and suctioning; not the best predictor for COPD/neuro-medical and neurosurgical pt.
B: CROP index	Compliance (thoracic); respiratory rate; oxygenation (Arterial); pressure (P1 Max)	> 13 mL/breath/min – successful weaning	Incorporates respiratory and ventilatory parameters	Complex calculations; not tested in neuro-medical/neurosurgical pt.
C: ExPres score	RSBI; dynamic lung compliance; days of IMV; GCS; muscle strength; haematocrit; creatinine; neurological comorbidity	Score; > 59 – extubate pt.; 45-58 with no risk factors – extubate pt.; 45-58 with risk factors – extubate to NIV; < 44 – extubation failure	More robust score; simple tool; shown to reduce extubation failure rates	Needs large scale studies for validation
D: HACOR	Heart rate; acidosis; consciousness; oxygenation; respiratory rate	Score > 5 – weaning failure	Simple bedside tool	Limited studies; large scale trials required to assess for validity
E: WEANS NOW	Weaning parameters; endotracheal tube; ABG; nutrition; secretions; neuromuscular blocking agents; obstructive airway disease; wakefulness	Score of 1 or more – weaning failure	Incorporates multiple parameters	Very complex score; widespread application may be difficult
F: BWAP	Pulmonary; physiological; psychological	Score > 50 – weaning success	Comprehensive weaning checklist	Limited literature; modified-BWAP may be more practical
G: Morganroth scale	Adverse factor score; ventilator score	Score < 55 – successful weaning; range – 27 variables max score 75	Can be applied to pt. requiring short-term and long-term IMV	Small study; multiple variables considered
H: Persian weaning tool	Respiratory; cardiovascular; general status of pt.	26 parameters; range 26-75; score > 50 –readiness to wean	Comparable to BWAP score	Limited literature regarding its utility
I: Gluck & Corgian score	RSBI; ratio of dead space/Vt; static lung compliance; airway resistance; CO2 pressure	Score < 3 – weaning success; score of 3 – not equivocal; > 3 failure to wean	Simple tool; easy bedside measurement	Small study; large trials warranted

BWAP: Burns wean assessment program; CO₂: Carbon dioxide; COPD: Chronic obstructive pulmonary disease; GCS: Glasgow coma scale; IMV: Invasive mechanical ventilation; NIV: Non-invasive ventilation; pt.: Patient; RR: Respiratory rate; RSBI: Rapid shallow breathing index; Vt: Tidal volume; ABG: Arterial blood gas.