Improving Oxygen

In week one we discussed extrapulmonary effects of mechanical ventilation. Equally important however is understanding the pulmonary effects, the actual impacts of positive pressure ventilation on the lungs, and other respiratory structures. 

Competent respiratory therapists know how to ventilate patients in a way that achieves appropriate oxygenation levels and appropriate carbon dioxide levels, but in a way that also minimizes adverse effects on the pulmonary system. The concepts of barotrauma and volutrauma are especially important. The NBRC is very interested in assessing your knowledge in this area. The national board wants to credential therapists who know how to protect the patient’s lungs while effectively ventilating them. Another key topic this week involves weaning your patient from the mechanical ventilator. No patient wants to stay on a ventilator for life. We want to “liberate” the patient from the ventilator as soon as feasible, but it is so important to do that safely. We need to make sure that the problem that put the patient on the ventilator has been corrected, and we need to make certain that key parameters have reached safe levels before we give the patient a “spontaneous breathing trial” away from the ventilator. You will learn this week about essential monitoring to make sure that the patient is succeeding with that spontaneous breathing trial. Let us now take a closer look at weaning.

Weaning from Mechanical Ventilation

Ventilator management should be aimed at getting the patient off ventilator support as quickly and safely as possible after stabilization. Weaning (also known today as liberation) should be considered as soon as the underlying disease process that led to mechanical ventilation is under control. For example, if the patient was intubated and ventilated due to pulmonary edema, then weaning can commence as soon as the excess pulmonary fluid has been removed and the patient’s gas exchange improves. This will also be evident on the chest x-ray as the disappearance of the butterfly fluid pattern. If the patient was ventilated due to pneumonia, clearing of the chest x-ray infiltrates and improvement of sputum clearance would indicate that we could begin the weaning process.

Definitions Relating to Weaning from Mechanical Ventilation

First, sharing a few definitions to help us classify weaning:

  • Simple weaning: the ventilator is discontinued after the first weaning assessment
  • Difficult weaning: the ventilator is discontinued within one week after the first weaning assessment
  • Prolonged weaning: the ventilator is discontinued more than one week after the first weaning assessment
  • Weaning failure: this is failure to pass a spontaneous breathing trial (SBT) or the need for reintubation within 48 hours following extubation

Avoiding Reintubation

Obviously, we do not want to extubate our patients and then have to reintubate them. So predicting weaning success is very important for reducing the rate of reintubation. Careful attention to the criteria for weaning, and optimal patient management to increase weaning success can both help to avoid reintubation. Reintubation is a very bad prognosticator for the patient, but smart RRT’s can keep reintubation rates very low. Consider the following:

  • Reintubation is associated with a 7-10 fold increase in-hospital mortality
  • Reintubation rates of 10 to 15% are typical for most well run Respiratory Therapy weaning programs
  • A reintubation rate of 0% is not realistic, and it would mean that we are not being aggressive enough with our weaning efforts

Criteria to Begin Weaning

  • Lung disease is stable and resolving
  • Oxygen titration to FiO2 less than 0.5 and PEEP less than 5-8cmH2O
  • Hemodynamic stability, little or no pressure (blood pressure) agents
  • Neuromuscular ability to initiate spontaneous breathing

Approaches to Weaning from Mechanical Ventilation  

Weaning is typically a Two-step process leading up to ventilator liberation:

  • First, essential weaning parameters are assessed, sometimes called the “wean screen,” and the wean screen should be performed daily once the decision is made to begin weaning. Parameters to be measured here include Maximal Inspiratory Pressure, Spontaneous Tidal Volume, Spontaneous Vital Capacity, Spontaneous Minute Volume, and Spontaneous Respiratory Rate. The Rapid Shallow Breathing Index should also be calculated daily.
  • Next, we perform the first weaning trial

Patient Management to Avoid Weaning Delays:

Optimize Respiratory Muscle Power through:

  • Good nutrition
  • Discontinuing neuromuscular blocking drugs
  • Decreasing steroid use
  • Encourage spontaneous breathing but avoiding patient exhaustion
  • Stabilizing electrolytes
  • Physical Therapy for strength and range of motion

 Decrease Respiratory Work:

  • Patient should be sitting up

Decreasing Respiratory Demand:

  • Treat any pyrexia
  • Treat agitation
  • Minimize respiratory dead space
  • Decrease airway resistance
  • Decrease abdominal distension

Optimize Ventilatory Drive

  • Discontinue patient sedation
  • Consider any causes prior to the neuromuscular junction
  • Correct any metabolic acidosis

Increase Oxygen Carrying Capacity

  • Eliminate atelectasis
  • Correct anemia
  • Correct any shifts in the oxyhemoglobin dissociation curve

 Optimize Cardiac Function

  • Evaluate left ventricular function
  • Treat congestive heart failure
  • Treat ischemia

Optimize Sputum Clearance

  • Treat infection
  • Chest physiotherapy
  • Suction before trials
  • Therapeutic bronchoscopy if appropriate

Techniques of Weaning

  • Gradual reduction in mandatory rate during synchronized intermittent mandatory ventilation
  • Gradual reduction in pressure support ventilation
  • Spontaneous breathing through a T-piece
  • Spontaneous breathing via the ventilator on flow by with no pressure support and no PEEP

It is important to note that there is no evidence that gradual reduction of ventilation support speeds up the weaning process, so when patients meet Wean Screen criteria, the most rapid approach to weaning is to initiate spontaneous breathing trials, either by T-piece or by flow by.

Evidence-Based Protocols

Weaning protocols simply work, and this has been well demonstrated clinically over recent years. Protocol driven ventilator liberation procedures have clearly demonstrated that traditional care is often associated with significant delays in ventilator withdrawal. Respiratory Therapist (RT) run protocols consistently produce faster ventilator discontinuation times when compared to physician-run usual care in the ICU. Perhaps this is because physicians who are leading the weaning process do not adhere to evidence-based guidelines. Also, they simply not be available often enough to move the weaning process forward quickly. There are approved Respiratory Therapy weaning protocols in each facility that allow RT’s to be in charge of the weaning process.

Automated feedback systems

Several recent innovations are improving the weaning process, and automation of weaning is certainly a hot topic in critical care today. For example, Adaptive Support Ventilation (ASV) is the most studied closed-loop system in place today. It is an improvement over physician-led weaning. Automated systems use a closed-loop control to enable ventilators to perform basic and advanced functions while supporting respiration. These systems provide a unique automated weaning system that measures selected respiratory variables, adapts ventilator output to individual patient needs by operationalizing predetermined algorithms, and automatically conducts spontaneous breathing trials (SBTs) when predetermined thresholds are met. As a result, there is no delay in weaning when the patient is, in fact, ready. These systems are very new, and research is underway at this time to determine just how effective they really are.


In your own words, discuss the following relating mechanical ventilation:

Describe in detail four adverse effects of invasive positive pressure ventilation on ‘the pulmonary system’ specifically and offer proven strategies for minimizing or avoiding the negative effects entirely. Be specific about your recommended strategies.

Requirements (read these carefully):

Submit your responses, in your own words, as an essay form, complete sentences, in at least 500 words on a Word document (excluding the prompt, title, cover page, citations/references, quotations). Grammar and spelling count. You must cite at least three references in IWG format to defend and support your position.