Respiratory Weaning Case File
Eugene C. Toy, MD, Manuel Suarez, MD, FACCP, Terrence H. Liu, MD, MPH
Case 10
A 27-year-old woman with cystic fibrosis has a new bacterial pneumonia requiring intubation. On ICU day 3, her oxygen saturation is 93% with an F1O2 of 30% on MV and a pressure support of 10 cm H2O. She has a spontaneous breathing rate averaging 14 breaths/minute and a positive end expiratory pressure (PEEP) of 2.5 cm H2O. Weaning parameters (measurements of a patient's spontaneous respiratory efforts) show she is generating an average tidal volume of 400 ml and a negative inspiratory pressure of -35 cm H2O. An ABG shows a pH of 7.39, PACO2 37 mm Hg, and PAO2 of 100 mm Hg. She has been afebrile for the last 48 hours and her white cell count is now within normal limits. On physical examination, she is in no acute distress and answers questions by nodding or writing on a paper pad. Her temperature is 36.9°( (98.4°F}, blood pressure 132/66 mm Hg, heart rate 76 beats/minute, and respiration rate 14 breaths/minute. Auscultation of the chest reveals good air movement throughout. Chest radiographs indicate a clearance of a left sided pulmonary infiltrate present on the admission x-ray.
⯈What is the best next step in this patient's management?
⯈What other steps should be considered?
ANSWER TO CASE 10:
Respiratory Weaning
Summary: This 27-year-old woman has markedly improved from her pneumonia and respiratory failure. The weaning parameters all point to a successful extubation. MV is no longer needed and should be removed. After conducting a successful spontaneous breathing trial, the patient should be liberated from MV.
- Best next management step: A spontaneous breathing trial (SBT) should be performed since the weaning parameters are acceptable. If the SBT is successful, it would lead to extubation or liberation from MV.
- Other steps: Prepare the patient for the weaning and extubation process and observe her closely postextubation. Elevate the head of the bed to minimize the risk for aspiration. In the presence of cystic fibrosis, the clearance and control of secretions are essential.
ANALYSIS
Objectives
- To understand the clinical and the objective parameters that predict a successful liberation from mechanical ventilation.
- To understand the predictors of weaning failure.
- To understand a logical approach to weaning.
Considerations
This 27-year-old woman with cystic fibrosis required intubation for respiratory failure and pneumonia. She has been treated for 2 days in the ICU. The patient is generally alert and responsive. Weaning parameters are favorable, with a PAO2 of 60 or greater, an FIO2 <60%, and a PEEP <5 mm H20 present. When the MV patient reaches these criteria, it is safe to proceed to spontaneous breathing trials; if these trials are successful, then the next step is extubation and liberation from MV. Pressure support ventilation (PSV) or continuous positive airway pressure (CPAP) would be the best way to wean this patient.
Approach To:
Respiratory Weaning
INTRODUCTION
Weaning or liberation from invasive or noninvasive mechanical ventilation is the process of freeing the patient from positive pressure mechanical ventilation (see Case 11 for more information on NIV) . Because of the significant morbidity and
mortality associated with prolonged mechanical ventilation, it is generally accepted that all mechanically ventilated ICU patients should be assessed on a daily basis for their readiness to wean. This assessment should include the cessation of sedation and a reevaluation of its need. Weaning can be started after the first formal assessment of the patient's respiratory condition indicates that weaning could be successful. Nearly 50% of unexpected self-extubation during the weaning process do not require reintubation. It is important to be aware of the frequency of weaning failures and predictors of such failures.
APPROACH TO WEANING
Liberation from mechanical ventilation is a central component in the care of the critically ill patient. To start weaning a patient from MV, one must begin with a patient who is ready for the process and who has a good possibility of success (Table 10-1) .
Underlying disease should b e treated since its persistence can contribute to requiring continued MV. Successful weaning depends on many variables including adequate mental status, muscle strength required to maintain spontaneous breathing, and hemodynamic stability. Are the ABG values acceptable? Are electrolyte values normal including Mg+, K, Ca2+, and PO4? Adequate nutrition must be maintained, but overfeeding should be avoided, especially with carbohydrates; increased CO2 production may result and require increased minute ventilation (Ve). Fatty meals are advised, since fat produces more energy than carbohydrates (8 kcal for each gram of fat vs 4 kcal for every gram of carbohydrates) with much less CO2 production. Some basic weaning goals should be attained: PAO2 of 60 or more with an FIO2 <60% and a peep <5 cm H2O. When the MV patient reaches these criteria, it is safe to proceed to spontaneous breathing trials and if successful, then moving to extubation and liberation from MV.
WEANING PREDICTORS
Weaning is the progressive reduction in the amount of support provided by a mechanical ventilator. The term weaning is frequently used to describe the transition from intubation and full mechanical support to spontaneous breathing by the patient with a protected airway. Weaning predictors act as guidelines to identify those patients that qualify for spontaneous breathing trials and liberation from MV with successful extubation. These predictors are based on measurements of the work of breathing, which help determine whether the patient's respiratory system can adjust to spontaneous unassisted respiration.
An NIF > -25 cm H20 is predictive of successful weaning from MV. This confirms the patient's respiratory muscle strength is suitable and that the patient's own respiratory system is conditioned to breathe without MV support. Stable vital signs with an improving clinical picture during the weaning process is critical. Stable vital signs can be used to predict the stability of the arterial blood gases (ABG) reducing the need for repetitive ABG analyses. ABG studies are costly, painful, and not free of possible complications, including distal arterial occlusion or dissection of the artery. Achievement of a spontaneous minute ventilation (Ve) <10 L/min (maintaining oxygenation without excessive work) is an excellent predictor of successful liberation from MV.
WEANING TECHNIQUES
A successful trial of spontaneous breathing has become the gold standard for weaning. Every intubated patient on MV should be evaluated daily with a trial of some form of spontaneous breathing. A sedation holiday should also be attempted; if sedation is still required, it can be restarted at half the previous dose. The patient should be on a minimal sedation dose to avoid depression of respiratory functions. Trials of spontaneous weaning can be performed with or without MV assistance. Weaning trials with MV assistance increase the safety of the procedure since respiratory parameters are more precisely monitored and patient deterioration can be diagnosed earlier. So-called traditional T-piece trial with FIO2% delivery only via plastic tubing without the aid of MV gives a realistic evaluation of the patient's breathing without MV help or the resistance of MV sensor valves. Surveys of respiratory departments have shown that SIMV with or without PS assistance was the most common method of MV weaning. This was closely followed by T-piece trials and by PS weaning. Use of the rapid shallow breathing index RR/Vt, of <105 as shown by Yang and Tobin has an excellent predictive value of extubation failure. Different weaning parameters are better predictors in specific diseases.
T-Piece Trials
T-piece trials are conducted in a spontaneously breathing patient via an ETT connected to an FIO2 source ( thus the T) with the open end of the FIO2 hose open to ambient air. This method is the oldest and still most effective method of ventilator weaning techniques. Sequentially increasing the amount of time the patient spends on the T-piece will enhance the prospect of complete liberation from MV. A single daily spontaneous breathing trial is as efficient and effective as multiple short trials and is less labor intensive. If needed, PEEP can always be added to the circuit by an expiratory valve or possibly be better accomplished with the patient breathing spontaneously on the MV with the desired PEEP level and a CPAP setting of 0 cm H2O. These measures are not needed if the patient is on PEEP <5 cm H2O. The FIO2 source should be humidified, creating a mist at the open end of the T-piece. If this fine aerosol disappears completely during inspiration, the patient's inspiratory flow is overcoming the inspiratory FIO2 flow and inhaling 21% room air via the open end of the tube. This circumstance causes a lower actual FIO2 versus the set FIO2 affecting the ABG values because of a decrease in FIO2 reflected in the lower PAO2 (Table 10-2 ).
Noninvasive Ventilation
Noninvasive ventilation (NIV) is a useful tool in the difficult-to-wean patient. It avoids the complications of intubation and sedation and reduces the total time of invasive mechanical ventilation. The goal of NIV in weaning can be separated into 2 parts: to prevent extubation failure, and to provide a rescue therapy for postextubation respiratory distress. NIV permits early extubation in patients who fail to meet standard extubation criteria.
Pressure Support Ventilation Weaning
Pressure support ventilation ( PSV) allows the patient to determine the most comfortable depth, length, flow, and rate of breathing. It is used as a weaning tool by gradually reducing pressure support by 2 to 4 cm H2O as long as the patient is successfully tolerating these decreases. This results in a progressive reduction in ventilatory support over hours or days. PSV is superior to SIMV in reducing the duration of mechanical ventilation in difficult-to-wean patients. PSV weaning compared to T-piece weaning revealed T-piece weaning to be superior. However, one small prospective trial has recently suggested that PSV weaning is superior to T-piece weaning in patients with chronic obstructive pulmonary disease (COPD ).
Intermittent Mandatory Volume Weaning
SIMV is a poor weaning mode (unless associated with PS ), and should not be used in isolation as a weaning tool. SIMV with PS weaning involves a progressive reduction of the respiratory rate in steps of 1 to 3 breaths/minute. SIMV may actually contribute to respiratory muscle fatigue, because of the increased work of breathing due to ventilator factors ( increased effort to activate the SIMV demand valve, inspiratory, and expiratory dyssynchrony). SIMV with T-piece spontaneous breathing resulted in a longer duration of MV compared to PSV. SIMV had higher rates of weaning failure. SIMV-based weaning strategies resulted in a longer duration of mechanical ventilation (5 days ) compared with a PSV-based strategy (4 days) and T-piece ventilation (3 days ).
The Endotracheal Tube
The largest endotracheal tube (ETT) that can be safely be inserted should be used (>8 mm) . A larger caliber facilitates the removal of secretions by suction catheter and decreases in airflow resistance. Reducing high plateau pressures t o <30 cm H2O with Vt, volumes of 6 to 8 mL/kg will avoid barotrauma. The mere presence of an ETT in the trachea can induce significant bronchospasm. This is often noticed in the operative room postintubation. The presence of the ETT may cause bronchospasm or "rock bag" ventilation as it is sometimes described when this occurs during the anesthetic period. The administration of IV Lidocaine prior to intubation may prevent EET-associated bronchospasm. Intravenous corticosteroids may be used even though most volatile anesthetics are excellent bronchodilators. The addition of aerosolized β2 agonists may also be used and is easily delivered to the patient.
Role of Tracheostomy in Weaning
Tracheostomies can be important in weaning difficult patients. A tracheostomy is usually far less irritating to the patient than an endotracheal tube, and the reduced need for sedation usually facilitates weaning. Tracheostomy provides a secure airway, which reduces the work of breathing and minimizes the risk of pneumonia associated with MV (ventilator-associated pneumonia [YAP] ). Studies have not determined whether early or late tracheostomy is superior.
MANAGEMENT OF THE DIFFICULT TO WEAN PATIENT
The difficult-to-wean patient is defined as one who has already failed at least 1 spontaneous
breathing trial or has required reintubation within 48 hours of extubation. The failure of a spontaneous breathing trial may be accompanied by a significantly increased inspiratory effort with respiratory muscle fatigue. This may induce shortlasting, high-frequency fatigue. Failure of either a spontaneous breathing trial or extubation demands an identification of the exacerbating factors that caused the failure. Adjustments must be made that will increase the success of weaning and provide adequate ventilatory support. The clinician should conduct a careful physical examination and review the patient's diagnostic tests to uncover and treat any reversible contributory factors leading to weaning failure.
The most widely used modes of ventilation are (volume) assist control ventilation (ACV), synchronized intermittent mechanical ventilation (SIMV), and PSV. One classification system divides ICU patients into those simple to wean, those difficult to wean ( also called prolonged weaning) groups.
- Simple-to-wean patients are those who are successfully extubated on the first attempt. This group consists of patients in the intensive care unit (ICU) ( about 69% ) which have a low mortality rate (about 5 %).
- The difficult-to-wean or prolonged-weaning patients (requiring up to 3 attempts or up to 7 days from the onset of weaning efforts) require greater efforts to successfully liberate them from mechanical ventilation.
These difficult-to-wean and prolonged-weaning patients have a mortality rate of 25%. Longer duration of MV is associated with an increased mortality and expense (mechanical ventilation costs more than $2000/d), and it has been estimated that the 6% of patients who require prolonged MV consume 37% of ICU resources.
More severely ill patients usually require longer periods of mechanical ventilation. Overall, 40% to 50% of the time spent on mechanical ventilation occurs after the weaning process has started. Most critically ill patients require a period of rest after intubation. The weaning process should begin very soon after intubation.
WEANING PROTOCOLS
A lack of attention to the screening process to determine the ability of a patient to pass through the weaning process or unnecessary delays in progression through the weaning steps are associated with increased patient morbidity and mortality. The proper use of weaning protocols has reduced ventilator-associated pneumonia, lowered self-extubation rates, lowered tracheostomy rates, and minimized hospital costs. To be effective, these weaning protocols should include an interdisciplinary team approach with nursing and respiratory therapy personnel in association with physicians all of whom are experienced in the use of MV and weaning procedures.
CLINICAL CASE CORRELATION
- See also Case 8 (Airway Management/Respiratory Failure ), Case 9 (Ventilator Management), Case 11 (Asthmatic Management), and Case 12 (Non,invasive Methods of Ventilatory Support).
COMPREHENSION QUESTIONS
10.1 You are called to continue mechanical ventilator weaning on a 42-year-old man who is now on day 4 post admission. He has been intubated for adult respiratory distress syndrome (ARDS) secondary to smoke inhalation suffered
during his work as a fire fighter. The morning arterial blood gas (ABG) values with the patient awake and alert, sitting up in bed are: pH 7.38, PACO2 39 mm and PAO2 99 mm on CPAP mode of 5 cm H2O, +5 of positive end expiratory pressure (PEEP) , spontaneous tidal volume (Vt) of 400 mL, fraction of inspired oxygen (FIO2) of 28%. His spontaneous weaning parameters reveal a negative inspiratory force (NIF) of -30 cm H2O, respiratory rate (RR) of 20 breaths/ minute, Vt, 450 mL, FVC 1.5 L. He is afebrile and breathing comfortably on these settings. Which if the following is the next step in weaning this patient from the ventilator?
A. Decrease ventilatory parameters and continue the weaning process.
B. Stop mechanical ventilation, extubate the patient, and start O2 via nasal cannula.
C. Change to assist control ventilation.
D. Increase pressure support to 10 cm H2O.
E. Give a 2-hour spontaneous breathing trial.
10.2 A 35-year-old white male has been o n a mechanical ventilator for 7 days. He suffers from ascending paralysis. He has an NIF of -5 cm H2O and cannot tolerate any spontaneous breathing trials for more than a few minutes without distress. He has copious secretions. The best option for mechanical ventilation (MV) is
A. Trial of pressure support (PSV) weaning.
B. Consider tracheostomy and plan on long-term MV and its needs.
C. Change to assist control ventilation.
D. Perform a spontaneous breathing trial.
E. Trial of noninvasive ventilation (NIV).
ANSWERS TO QUESTIONS
10.1 B. The patient has obviously recovered his control and ability to ventilate and oxygenate on his own without MV support. The improving respiratory status is seen clinically and fulfills objective measures of weaning parameters. Weaning parameters are positive predictors of successful extubation. In particular, the NIF of -30 cm H2O and >300 PAO2/FIO2 ratio is informatory. The next best step is to liberate the patient from MV by extubation of the patient and to start the patient on O2 via nasal cannula with a target O2 saturation of 92% to 95% O2 via pulse oxymetry (O2sat). An aerosol treatment with a β2 agonist and ipratropium bromide is usually given after the extubation since mild aspiration occurs and the manipulation of the ETT itself during extubation induces bronchospasm and cough.
10.2 B. The patient has ascending respiratory paralysis, otherwise known as Guillain- Barre syndrome. The severe respiratory muscle weakness will persists for a significant amount of time and will require long-term ventilator care. Since extubation is not likely in the near future, a tracheostomy for long-term care is indicated. The tracheostomy will allow better management of the copious secretions by frequent suctioning and decrease dead space ventilation, simultaneously improving patient comfort. The performance of a tracheostomy is an important tool in the difficult-to-wean patient. A tracheostomy is usually far less irritating to the patient than an endotracheal tube, and helps to decrease the requirement for sedation, enabling weaning strategies that would otherwise not be possible. Tracheostomy also provides a more secure airway, reduces the work of breathing by decreasing dead space, and carries a reduced rate of ventilator-associated pneumonia. Tracheostomy tubes with fenestrations or by presenting the balloon cuff in a down position may also allow the patient to speak. A one-way valve such as the Passy-Muir valve may be used to aid speech. This valve lets air enter during inhalation and closes during expiration, forcing the expired air to pass through the vocal cords thus allowing the patient to speak. This valve can be used with or without the ventilator. Studies have not determined which is a superior strategy, early <7 days or late tracheostomy >7 days.
CLINICAL PEARLS
⯈ Pressure support ventilation (PSV) is the simplest and most effective method of weaning patients from MV.
⯈ Weaning increases the patient's respiratory effort and increases myocardial oxygen (O2) demand, making it a cardiopulmonary stress test.
⯈ Assessment of the readiness to wean and reductions in sedative infusions should be considered early and frequently in critically ill patients receiving mechanical ventilation.
⯈ After the acute insult has improved or resolved, clinicians should have a low threshold for conducting a spontaneous breathing trial in all critically ill patients.
⯈ A Vd/Vt ratio of > 105 is an excellent predictor of weaning success especially when combined with an NIF exceeding -25 cm H2O and a stable clinical picture.
⯈ Weaning protocols are not a replacement for expert clinical opinion and management.
⯈ Application of NIV after extubation may assist post extubation from mechanical ventilation.
References
Brochard L. Pressure support is the preferred weaning method. Paper presented at the 5 th International Consensus Conference in Intensive Care Medicine: Weaning from Mechanical Ventilation. 2005 April 28-29.
Loscalzo J . Harrison's Pulmonary and Critical Care Medicine. New York, NY: McGraw-Hill; 201 1 .
Slutsky AS. Mechanical ventilation. American College o f Chest Physicians' Consensus Conference. Chest 1 993 ; 1 04 : 1 83 3 - 1 85 9 .
Toy E C , Simon B, Takenaka K, L i u T, Rosh A. Case Files Emergency Medicine. 2nd e d . N e w York: McGraw-Hill; 2009.
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