PAOLO PELOSI, LAURA MARIA CHIERICHETTI, PAOLO SEVERGNINI

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1 MANAGEMENT OF WEANING EUROANESTHESIA 2005 Vienna, Austria May RC11 PAOLO PELOSI, LAURA MARIA CHIERICHETTI, PAOLO SEVERGNINI Dipartimento Ambiente, Salute e Sicurezza, Universita degli Studi di Varese Ospedale di Circolo e Fondazione Macchi, Varese, Italy Sunday May 29, :00-17:45 Room E2 INTRODUCTION Acute respiratory failure is usually caused by lung injury or impaired respiratory mechanics [1]. In lung injury, lung volume is reduced, and alveolar consolidation or atelectasis reduce compliance and impair oxygenation. [2,3]. Reduced lung volume and airway dimensions cause increased airway resistance. Reduced compliance and increased airways resistance increase the elastic and resistive work of breathing. Increased airway resistance can cause intrinsic positive end-expiratory pressure (PEEPi), which will also increase inspiratory work. Mechanical failure of the respiratory system commonly leads to ventilatory failure with hypercapnia. The causes are muscle fatigue, central ventilatory depression or mechanical impairemnt of the chest wall. If demand exceeds the power, muscle fatigue results, with a reduction in tidal volume, increase in respiratory rate, disturbed breathing pattern, and dyspnoea. Accessory muscles are recruited to maximize the muscular effort. Intubation and mechanical ventilation are often necessary to improve oxygenation and compliance by reducing atelectasis, reduce the load of the respiratory muscles, and prevent respiratory muscle fatigue until the lung conditions are improved. After intubation the goals of clinical management are: 1) to define the cause of the respiratory failure; 2) to treat the condition 3) to reduce the ventilatory support, as quickly as possible, to allow extubation. Weaning is the process of progressive reduction of mechanical support and extubation. This process is not just the late phase of the ventilatory support, it should startfrom the moment that the patient has been intubated. Weaning accounts for over 40 % of total ventilator time [5], so it is very relevant in the overall management of intensive care patients. In this chapter we will discuss: 1) differences between types of ventilation during weaning; 2) clinical and physiologic indicators of readiness for a trial of spontaneous breathing 3) the most effective spontaneous breathing trial; 4) treatment plans to optimize weaning; 5) the differences in weaning measurements in general medical and surgical patients compared with specific patients, such as in neurology. EARLY WEANING After intubation, strategies should be started to reduce intubation time as much as possible. The two methods are: 1) low tidal volumes and 2) assisted breathing. In the early phases of acute respiratory failure, the volume of lung that is aerated is markedly reduced. This is the concept of the baby lung, i.e. the lung is small like that of a baby, which should be gently ventilated with low tidal volumes and reduced plateau pressures to minimize transpulmonary pressure and ventilator associated lung injury. A recent large multicenter study [6] showed that a tidal volume of 6 ml/kg ideal body weight and a plateau pressure of less than 30 cmh 2 O reduced mortality by 25% and that after 28 days, these patients had a better outcome. In this study a strict weaning policy was applied to standardize weaning after acute respiratory failure. In contrast high values of PEEP and small tidal volumes have not given uniform results [7,8]. The prone position does not improve survival or increase the number of ventilator free days [9]. However in post hoc analysis of a subset of patients, it did improve mortality at the 10th day. The second method allows respiratory activity to continue during mechanical ventilation. Diaphragm activity is maintained, to reduce ventilation in the dependent parts of the lung, which are the most perfused. This would also prevent muscle atrophy and allow less use of sedative drugs. In a small prospective randomized trial, weaning time was less when a spontaneous breathing method (BiPAP) was compared with conventional mechanical ventilation [10]. However, this study had faults: more sedation was used in the standard treatment group and the tidal volumes used were large. At present, assisted breathing techniques in early ventilatory support cannot be recommended. However, assisted breathing could be used when lung function partially recovers and oxygenation is acceptable, e.g. PaO 2 between 55 and 80 mmhg, with inspiratory oxygen fraction of 0.4, PEEP less than 11 cmh 2 O. 289

2 DIFFERENT METHODS OF VENTILATION DURING LATE WEANING Different methods are suggested. 1) the method used for ventilatory assistance, 2) the spontaneous breathing trial. The most frequent modes used during weaning are: 1) Pressure support ventilation (PSV); 2) Assist control ventilation (ACV) in volume and pressure support associated with T tube trials; 3) Synchronized intermittent mandatory ventilation (SIMV). With PSV the patient makes an initial inspiratory effort, and the machine then supports this effort with a pre-selected pressure. All the breaths are triggered by the patient. The inspiratory time is regulated both by the patient and by the machine. The ventilator cycles into expiration when the inspiratory flow decreases to a preselected percentage ranging from 40 to 5 % of the peak inspiratory flow. The peak inspiratory flow will depend on the inspiratory effort of the patient and setting of pressure support. With pressure support, the ventilatory assistance given to the patient can be progressively adjusted and reduced. With assissted controlled ventilation, the physician can set the number of breaths to be delivered to the patients, but if the patient triggers a breath, inspiratory flow is delivered from the ventilator to the patient. The inspiratory time is determined by the delivered volume or can be preset. With ACV all breaths are supported by the machine, with either preset volume or pressure. For SIMV, assisted breaths (volume or pressure support )are given along with spontaneous unassisted breaths. For weaning, the numberof assisted breaths is progressively reduced so that the number of unassisted breaths increasesduring weaning. A spontaneous breathing trial is a short time when the patient is allowed to breathe, either from a T-tube ( with no ventilatory assistance or just positive end-expiratory pressure) or connected to the ventilator with minimal respiratory assistance. Several large prospective studiesof methods of weaning have been done. In one study, PSV was better than ACV or SIMV [11]. On the other hand, another study showed conflicting results, with ACV allowing earlier extubation than PSV or SIMV [12]. Other studies[13] found no difference between pressure support and ACV in the duration of mechanical ventilation and outcome. Although these studies were contradictory, they showed that: 1) weaning strategies influence the duration of mechanical ventilation; 2) the criteria used to initiate weaning may influence outcome; 3) the least effective approach was SIMV, a widely used strategy expecially in non- European countries [14]. CRITERIA TO START AND STOP SPONTANEOUS BREATHING TRIALS Clinical judgment has a low specificity, around 35% and a likelihood ratio of 1.5 to identify when to start a spontaneous breathing trial. Many complicated measures have been proposed to determine which patients are ready for spontaneous breathing trial or for extubation. Examples are P0.1, MIP (maximal inspiratory pressure ) and CROP ( compliance, rate, oxygenation and pressure index). Most are difficult to obtain at the bedside and inaccurate. In general, five simple measures can be made of patients each morning, even by the nurses in charge: 1) PaO 2 /FiO 2 > or equal to 200 mmhg. e.g., PaO 2 of 100/FiO 2 of 0.5; 2) Positive end expiratory pressure lower or equal to 5 cmh 2 O; 3) No infusions of vasopressor drugs or sedatives. Dopamine is acceptable at less than 5 microgram/kg/min, intermittent doses of sedatives are allowed; 4) The ratio between respiratory rate and tidal volume should be less than 105. A trial of spontaneous breathing trial fails if after half an hour, or in other studies two hours: 1) the respiratory rate is more than 35 breaths per minute for 5 consecutive minutes; 2) the SaO 2 is lower than 90% for more than 30 seconds of stable measurement; 3) the heart rate increases or decreases more than 20% from baseline for more than 5 minutes; 4) Systolic blood pressure is more than 180 mmhg or lower than 90 mmhg during at least one minute of continuous recording or repeated measurements; 5) Agitation, anxiety or diaphoresis, more than baseline, is present for more than 5 minutes. Successful extubation can be successfully achieved with spontaneous breathing trials lasting either30 minutes or 120 minutes [15]. Not only is passing a spontaneous breathing trial important clinically, but failing the trial has prognostic implications. Most of the patients who fail a trial of spontaneous breathing do so fairly early, after about 20 minutes. None of the weaning parameters described above consistently predicted time to failure [16]. 290

3 SPONTANEOUS BREATHING TRIAL: T-TUBE OR LOW PRESSURE SUPPORT Successful extubation can be predicted with equal efficacy by a spontaneous breathing trial with either a small amount of pressure support ventilation or a T-piece.[17]. This suggests that changing the ventilatory circuit is not necessary for the test, which can reduce workload. Morover, since the patient is connected to the ventilator a small amount of positive end expiratory pressure can be used. This is extremely useful because an endotracheal tube increases airways resistance and also prevents the action of the vocal cords during expiration which maintains an adequate end expiratory lung volume. WEANING BY PROTOCOL OR BY PHYSICIAN? In general, physicians do not wean patients efficiently. As many as half of those patients who extubate themselves prematurely do not need to be re-intubated within 24 hours [18]. Physicians inaccurately predict successful weaning, with specificity and sensitivity around 50-70% [19]. These studies did not include a non protocol group, so it was not known if protocols were superior to physician decision-making at the bedside. Systematic protocols for weaning were therfore compared with a physician directed strategy. In a two-step process, screening by respiratory care practitioners was followed by spontaneous breathing trials when the patient passed the daily screening [20]. Using a systematic protocol reduced the duration of weaning and ventilation, as well as the frequency of reintubation, the duration of mechanical ventilation for more than 21 days, and complications.the protocol was broadly applicable not only in experienced hospitals but also in community hospital settings. Intensive care units were recommened to adopt or adapt the methods of this study or establish their own protocols with similar goals. Applying this protocol to four patients would allow one patient to be weaned after 48 hours, who otherwise would not have been. In addition if the protocol were used in six patients, one less complication would be expected. In another study, protocol directed weaning was also found better than physician directed weaning [21]. These methods reduce the cost of intensive care. However, these studies used respiratory therapists and nurses in a way that differs from European practice. In Europe the physician is more involved in clinical management, and respiratory therapists and nurses are less used in this role. Protocol-directed weaning may be less needed in a closed ICU with generous physician staffing and structured rounds [22]. DIFFERENCES BETWEEN SUBGROUPS OF PATIENTS Different types of patients should be managed differently. Patients who might need different treatment include those with COPD, ischaemic heart disease, congestive heart failure, after neurosurgery and perhaps the elderly. With the development of non invasive ventilation, many have considered using PSV or pressure control ventilation (PCV) to assist weaning from mechanical ventilation, or to avoid re-intubation after unplanned extubation. A study of patients with COPD considered a weaning protocol using non invasive PSV ventilation after extubation [23]. At 48 hours after intubation, trial of spontaneous breathing from a T-piece was attempted. If this failed, two methods of weaning were compared: 1) extubation and non invasive ventilation by a face mask vs 2) further PSV via an endotracheal tube. The average PSV in the face mask group was 20 cmh2o while the endotracheal group received 17 cmh2o. Importantly, both groups of COPD patients received at least two spontaneous breathing trials per day. The criteria to pass the spontaneous breathing trial were those reported above, except that successful spontaneous breathing was required for 3 hours and a ph > or equal to 7.35 was required. In the patients managed by non ivasive ventilation, weaning time and intensive care unit stay were less, there was less nosocomial pneumonia and 60 day survival rate was better. These pioneering results were supported by similar studies performed in COPD patients [24,25], but not in patients without COPD[26]. Recent developments in the devices used for non invasive ventilation, such as helmets instead of masks, could markedly improve the applicability of this method. Studies show that non invasive ventilation can be delivered by helmet with similar success rates as with the mask. The helmet is better tolerated, can be used for a longer period of time and causes less complications than the mask [27,28,29]. Patients with neurological disturbance after trauma or surgery have different requirements. Early tracheostomy may be helpful in weaning and aid management of these patients [30,31]. Tracheostomy is better tolerated than intubation via the larynx, allows a better hygieneof the pharynx, makes sinusitis less likely, and reduces the work of breathing. With the development of percutaneous techniques, the manoeuvre appears to be easier and safer [32]. Daily evaluation of spontaneous or minimally assisted breathing during weaning is necessary in these patients to avoid delay in discharge and to reduce costs [33].However, the usual measures of weaning do not apply in these patients, and neurological clinical evaluation is very important [34]. 291

4 Vigorous chest physiotherapy, careful positioning and fiberoptic bronchoscopy can remove deep secretions, and reduce the risk of ventilator associated pneumonia, although evidence is limited. Stopping sedative infusions each day decreased the length of time on the ventilator in a general population of critically ill patients [35]. However, in brain injured patients, the optimal level of sedation is controversial. Although sedation is necessary to limit intracranial pressure, it can delay weaning and prolong mechanical ventilation. CONCLUSIONS In conclusion, early identificication of patients who are ready to be extubated is vital. Prolonged intubation increases patients complications, worsens outcome, and increases costs. Simple bedside daily measures such as the PaO 2 /FiO 2 ratio, respiratory rate and tidal volume can identify patients for a spontaneous breathing trial. Different methods of ventilation such as PSV or ACV are equally effective for weaning, whereas SIMV should be abandoned. Finally for different types of patients, different weaning criteria and modalities should be adopted. In COPD patients, non invasive ventilation appears to be promising, and can also be used for problems after unplanned extubation. In patients with neurological problems, the usual criteria for weaning criteria are not applicable, and neurological evaluation has a major role. Regular assessment of sedation is also necessary to improve the weaning process. REFERENCES 1. Roussos C, Macklem PT. The respiratory muscles. N Engl J Med 1982; 310: Gattinoni L, Pelosi P, Caironi P, Goodman LC. What has computed tomography taught us about the acute respiratory distress syndrome? Am J Respir Crit Care Med 2001; 164: Rouby JJ, Puybasset L, Nieszkowska A, Lu Q. Acute respiratory distress syndrome: lessons from computer tomography of the whole lung. Crit Care Med 2003; 31: S285-S Pelosi P, Cereda M, Foti G, Giacobini M, Pesenti A. Alterations of lung and chest wall mechanics in patients with acute lung injury: effects of positive end expiratory pressure. Am J Respir Crit Care Med 1995; 152: Esteban A, Alia I, Ibanez J, Benito S, Tobin MJ. The Spanish Lung Failure Collaborative Group. Modes of mechanical ventilation and weaning. Chest 1994; 106: The Acute Respiratory Di stress Syndrome network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and acute respiratory distress syndrome. N Engl J Med 2000; 342: Amato MB, Barbas CS, Medeiros DM et al. Effect of a protective ventilation strategy on mortality in the acute respiratory di stress syndrome. N Engl J Med 1998; 338: Brower RG, Lanken PN, MacIntyre N et al. Higher versus lower positive end-expiratory pressures in patients with the acute respiratory distress syndrome. N Engl J Med 2004; 351: Gattinoni L, Tognoni G, Pesenti A et al Effect of prone positioning on the survival of patients with acute lung respiratory di stress failure. N Engl J Med 2001; 345: Putensen C, Zech S, Frigge H et al. Long term effects of spontaneous breathing during ventilatory support in patients with acute lung injury. Am J Respir Crit Care Med 2001; 164: Brochard L, Rauss Benito S et al. Comparison of three methods of gradual withdrawal from ventilatory support during weaning from mechanical ventilation. Am J Respir Crit Care Med 1994; 150: Esteban A, Frutos F, Tobin MJ et al. A comparison of four methods of weaning patients from mechanical ventilation. N Engl J Med 1995; 332: Confalonieri M, Potenza A, Carbone G, Porta RD, Tolley ED, Meduri UG. Acute respiratory failure in patients with severe community pneumonia. A prospective randomized evaluation of non invasive ventilation. Am J Respir Crit Care Med 1999; 160: Esteban A, Anzueto A, Alia I et al. How is mechanical ventilation employed in the intensive care unit? An international utilization review. Am J Respir Crit Care Med 2000; 161: Esteban A, Alia I, Tobin MJ et al. Effect of spontaneous breathing trial duration on outcome of attempts to discontinue mechanical ventilation. Am J Respir Crit Care Med 1999; 159: Vallverdu I, Calf N, Subirana M, Net A, Benito S, Mancebo J. Clinical characteristics, respiratory functional parameters, and outcome of a 2 hour T piece trial of patients weaning from mechanical ventilation. Am J Respir Crit Care Med 1999; 158: Esteban A, Alia I, Gordo F et al. Extubation outcome after spontaneous breathing trials with T-tube or pressure support ventilation. Am J Respir Crit Care Med 1997; 156: Listello D, Sessler C. Unplanned extubation: clinical predictors for reintubation. Chest 1994; 105: Stroetz RW, Hubmayr RD. Tidal volume maintenance during weaning with pressure support. Am J Respir Crit Care Med 1995; 152: Ely EW, Baker AM, Dunagan DP et al. Effect on the duration of mechanical ventilation of identifying patients capable of breathing spontaneously. N Engl J Med 1996; 335:

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