Failure to wean from mechanical ventilation (failure to get the patients off the breathing
machine) is associated with prolonged stay in the intensive care unit and increased risk of
death. Some patients have difficulty successfully getting off the ventilator and breathing
on their own. Usually this difficulty is due to lung problems. But sometimes it is due to
heart problems, or heart failure. To improve a patient's chances of successfully getting
off the ventilator early, it is helpful to the doctors to know if patient has heart failure
and to measure how severe. With the new monitoring system being studied here, doctors may
be able to detect and measure heart failure more easily.
A new monitor (Vigileo TM) that is connected with a specific cable (Flo-TracTM) to a
catheter that is inside the patient's artery (arterial line) has lately been developed.
This monitor can estimate the amount of blood that the heart is pumping per minute, known as
cardiac output. The heart is supposed to pump blood harder when a patient is being weaned
from the breathing machine. With the above mentioned monitor, we hope to detect those
patients whose hearts are weak and are not pumping as hard as they should.
In the process of liberation or discontinuation from mechanical ventilation (also commonly
referred as "weaning") the goal is to achieve spontaneous breathing and ultimately
extubation. Weaning failure occurs in up to 25% of patients who meet criteria for weaning,
especially in those with underlying COPD or heart failure (1). Weaning failure is well
known to prolong intensive care unit (ICU) stay, and to increase morbidity and mortality in
critically ill patients. Early identification and treatment of causes of weaning failure is
of paramount importance to improve outcome in difficult to wean patients.
Although respiratory system failure is the most common cause of weaning failure, occult
cardiovascular insufficiency occurs very often in critically ill patients, and it can
contribute to, or be the only cause of weaning failure in many patients (2). Recognition of
cardiovascular origin of weaning failure is crucial since the use of vasodilators and/or
diuretics may result in successful weaning (1).
Cardiovascular instability during liberation from mechanical ventilation was first described
more than 30 years ago by Beach et al (3) in post-operative cardiac surgery patients.
Since then, a few other studies have described the hemodynamic changes both in patients who
underwent successful and unsuccessful weaning form mechanical ventilation (1,4,5,6,7).
Lemaire et al. (4) emphasized the use of a pulmonary artery catheter as the "gold standard"
to detect left ventricular dysfunction during spontaneous breathing trial (SBT). They
reported a markedly increased in pulmonary artery occlusion pressure (PAOP) in patients who
were suffering from COPD or heart failure who failed to wean from mechanical wentilation.
Jubran et al. (5) reported an increase in PAOP, decreased mixed venous oxygen saturation
(SvO2) and an increase in the oxygen extraction ratio in a group of patients who failed to
wean from mechanical ventilation. In contrast, De Backer et al. (6) described an increase
in cardiac index in a group of patients who were successfully weaned after cardiac surgery.
A recently published study by Frazier et al. (7) corroborated previous data by comparing the
hemodynamic changes between a group of patients who were successfully weaned and a group of
patients who failed to wean from mechanical ventilation. The cardiac output and stroke
volume were estimated by the differential Fick partial rebreathing technique, with carbon
dioxide as the indicator substance. The group of patients who were successfully weaned had
a statistical significant increase in both stroke volume and cardiac index, unlike the group
that failed weaning.
The physiologic changes that explain the above mentioned findings in hemodynamic parameters
during weaning are complex and not fully understood (1). It is well known that weaning can
place an excessive burden on the heart and it can be considered a form of "exercise" (2).
As studied by exercise physiologists, the increase in oxygen consumption during exercise in
healthy individuals is matched both by an increase in cardiac output and oxygen extraction.
In patients with overt heart failure, the increase in cardiac output is inadequate, and the
predominant response constitutes and increase in oxygen extraction. Return to spontaneous
breathing induces alteration in intrathoracic pressures that influence cardiovascular
function, producing, among other changes, an increase in venous return. Other postulated
physiologic changes include increase sympathetic tone, weaning-induced myocardial ischemia
and increased ventricular interdependence (2).
The recognition of cardiac origin of weaning failure is of vital importance. Unfortunately,
the clinical signs of patients who fail weaning because of acute heart failure (tachypnea,
tachycardia, anxiety, etc) are often difficult to distinguish from signs of respiratory
failure. Reliable bedside minimally invasive monitoring tools and tests need to be
developed to help the clinician in identifying these patients and help titrate
cardiovascular therapies during weaning trials. Currently, the list of such tools is short
and the validity of each technique in different situations is unknown (2).
Cardiovascular dysfunction may be the missing piece in predicting weaning success.
Cardiovascular monitoring can be useful in identifying and managing patients who fail to
wean due to lack of cardiac reserve.
We propose the use of Flo-Trac/VigileoTM, a semi-invasive technique that estimates cardiac
output from the arterial pressure waveform, as a tool for cardiac monitoring during the
process of weaning from mechanical ventilation.
1. Richard C and Teboul JL. Weaning failure from cardiovascular origin. Intensive Care
2. Pinsky MR. Breathing as exercise. Intensive care Med 2000;26:1164-1166
3. Beach T, Millen E, Grenvik A. Hemodynamic response to discontinuation from mechanical
ventilation. Crit Care med 1973;1:85-90
4. Lemaire F, Teboul JL, Cinotti L, Giotto G, Abrouk F, Steg G, Macquin-Mavier I and Zapol
W. Acute left ventricular dysfunction during unsuccessful weaning from mechanical
ventilation. Anesthesiology 1998;69:171-179
5. Jubran A, Mathru M, dries D and Tobin MJ. Continuous recordings from Mixed Venous
Oxygen Saturation during Weaning from Mechanical Ventilation and the Ramifications
Thereof. Am J Respir Crit Care Med 1998:158:1763-1769
6. De Backer D, El Haddad P, Preiser JC and Vincent JL. Hemodynamic responses to
successful weaning from mechanical ventilation after cardiovascular surgery. Intensive
Care Med 2000;26:1201-1206
7. Frazier SK et al. Hemodynamic changes during discontinuation of mechanical ventilation
in medical intensive care unit patients. Am J Crit Care 2006;15:580-593
- Age 18 years or older
- Arterial line in place
- Normal sinus rhythm by electrocardiographic monitoring
- Mechanical ventilation for at least 24 hours
- Ventilation via oral or nasal endotracheal tube
- Patient meets the following weaning criteria before starting weaning protocol:
- PaO2/FiO2 ratio >200
- FiO2 equal or less than 50%
- Positive end-expiratory pressure (PEEP) 5cm H20 or less
- Respiratory frequency/Tidal volume ratio less 105
- Respiratory rate < 30 breaths/min
- Presence of cough and gag reflex
- 12 hours free from sedation (opioids/benzodiazepine)
- 2 hours free from sedation in case patient is on Propofol
- Systolic blood pressure above 90 mmHg and below 180 mmHg
- Heart rate below 130 beats/min
- Known neurological disorder that might impair ventilatory drive
- Known neuromuscular disease
- Inotropic or vasopressor infusion
- Cardiac pacemaker
- Terminal condition