🌬Weaning From Ventilator

A full echo study is indicated in any patient who has failed multiple extubations or is slowly weaning.

Echo when the patient is under weaning stress, e.g. a spontaneous breathing trial, is more likely to reveal any underlying cardiac abnormality e.g. RWMA, AS, MR, LVOT gradient or poor LV relaxation.

Additionally – other pathology e.g. large pleural effusions can precipitate diastolic dysfunction and should be sought and treated.

Below will consider various clinical findings and what must be considered during each.

Moderate or severe LVH:

Consider HOCM: LV wall thickness ratio of >1.5. Evidence of LVOT obstruction. SAM of MV. Will require expert help.

Functional LVOT obstruction can occur with mod/severe LVH +/- relative hypovolaemia – will improve with filling and rate control.

Prolonged deceleration time will suggest an underlying diastolic dysfunction which would benefit from rate control.

Moderate or severely impaired LV function:

Look for regionality. Lack of wall thinning suggests recent event. Look for complications of MI. May want to consider PCI or ACEI.

Global LV dysfunction may lead to episodes of LVF when PEEP is weaned or during SBTs. Need to control BP, establish on diuretics and consider ACEI.

Evidence of right heart dysfunction:

Look for underlying pulmonary hypertension – RVH, RV dilatation, reduced TAPSE, mild to moderate TR with high velocity jet. Expert help and consider pulmonary vasodilators.

Overventilation can cause acute right heart strain. Look for reduced TAPSE and low-velocity moderate/severe TR.

Unexpected right heart strain – consider PE.

Evidence of reduced LV compliance of raised LVEDP:

Examine two functional components of diastolic function during intercurrent illness:

Normal LV relaxation – septal/lat e’ <8/10cm/s. Look at LVEDP: E/e’ >13 suggests raised LVEDP. Slow relaxation may respond to rate control and AVRI. Raised LVEDP may respond to diuretics.

Remember diagnosing degrees of diastolic function should not be performed unless 6 weeks after acute illness.

Evidence suggests that an E/e’ ratio measured 10 min into SBT of >14.5 predicts weaning failure with sensitivity of 75% and specificity of 95.8%

Moderate to severe MR:

Functional MR most often due to LV systolic failure and dilatation. Maximise LV function and diurese.

Moderate to severe structural MR may not respond to diuretics and ACEI Seek cardiology opinion.

Moderate to severe AS or MS:

Establish structural cause and accompanying valvular regurgitation. Seek expert cardiology opinion.

Unexpected pericardial fluid >5mm in depth:

Pyopericardium may be an unexpected source of sepsis, particularly where pneumonia was the primary pathology. Obtain a fluid sample where clinically indicated.

Prolonged sepsis and underlying inflammatory conditions may lead to pericardial constriction. Look for fibrin strands wtihin the pericardium. Restrictive LV filling occurs late. Seek expert help.

Investigate for shunts:

ASD/PFO relatively common cause of fixed shunt in ventilated patients. Look for colour flow across atrial septum. Perform a shunt calculation: Qp/Qs (RVOT area x pulm VTI) / (LVOT area x aortic VTI). Seek expert help.