Best Practice & Research Clinical Anaesthesiology

Editorial Board

2010-06-01

A physiologically oriented approach to the perioperative period: the role of the anaesthesiologist

Cesare Gregoretti, Paolo Pelosi — 2010-06-01

The current number of Best Practice & Research Clinical Anaesthesiology deals with the respiratory management of patients during the perioperative period. This is a very important and challenging topic because postoperative pulmonary complications contribute significantly to overall perioperative morbidity and mortality rates. The frequency rate of respiratory complications varies from 5% to 70% depending on variations among studies in the definition of postoperative pulmonary complications, as well as variability in patient-and procedure-related factors. Respiratory complications may prolong the hospital stay by an average of 1–2 weeks, and are likewise associated with increased morbidity and mortality. They account for up to 25% of deaths occurring within a few days of overt respiratory failure. Interestingly, the risk of postoperative complications varies with the type of surgery being performed. They occur much more often than cardiac complications in patients undergoing elective surgery to the thorax and upper abdomen. Conversely, operations at sites farther from the diaphragm are associated with a lower incidence of postoperative pulmonary complications. Postoperative pulmonary complications are also more common in patients with pre-existing lung disease, medical co-morbidities, poor nutritional status, overall poor health, and in those who smoke. Not all of these risk factors are modifiable, although strategies exist to reduce their risk even among high-risk patients.

Perioperative modifications of respiratory function

Michelle Duggan, Brian P. Kavanagh — 2010-06-01

Postoperative pulmonary complications contribute considerably to morbidity and mortality, especially after major thoracic or abdominal surgery. Clinically relevant pulmonary complications include the exacerbation of underlying chronic lung disease, bronchospasm, atelectasis, pneumonia and respiratory failure with prolonged mechanical ventilation. Risk factors for postoperative pulmonary complications include patient-related risk factors (e.g., chronic obstructive pulmonary disease (COPD), tobacco smoking and increasing age) as well as procedure-related risk factors (e.g., site of surgery, duration of surgery and general vs. regional anaesthesia). Careful history taking and a thorough physical examination may be the most sensitive ways to identify at-risk patients. Pulmonary function tests are not suitable as a general screen to assess risk of postoperative pulmonary complications. Strategies to reduce the risk of postoperative pulmonary complications include smoking cessation, inspiratory muscle training, optimising nutritional status and intra-operative strategies. Postoperative care should include lung expansion manoeuvres and adequate pain control.

Mechanisms of atelectasis in the perioperative period

Göran Hedenstierna, Lennart Edmark — 2010-06-01

Atelectasis appears in about 90% of all patients who are anaesthetised. Up to 15–20% of the lung is regularly collapsed at its base during uneventful anaesthesia prior to any surgery being carried out. Atelectasis can persist for several days in the postoperative period. It is likely to be a focus of infection and may contribute to pulmonary complications. A major cause of anaesthesia-induced lung collapse is the use of high oxygen concentration during induction and maintenance of anaesthesia together with the use of anaesthetics that cause loss of muscle tone and fall in functional residual capacity (a common action of almost all anaesthetics). This causes absorption atelectasis behind closed airways. Compression of lung tissue and loss of surfactant or surfactant function are additional potential causes of atelectasis. Ventilation of the lungs with pure oxygen after a vital capacity manoeuvre that had re-opened a previously collapsed lung tissue results in rapid reappearance of atelectasis. If 40% O2 in nitrogen is used for ventilation of the lungs, atelectasis reappears slowly. A post-oxygenation manoeuvre is regularly performed to reduce the risk of hypoxaemia during awakening. However, a combination of oxygenation and airway suctioning will most likely cause new atelectasis. Recruitment at the end of the anaesthesia followed by ventilation with 100% O2 causes new atelectasis before anaesthesia is terminated but not with ventilation with lower fraction of inspired oxygen (FIO2). Thus, recruitment must be followed by ventilation with moderate FIO2.

New insights into experimental evidence on atelectasis and causes of lung injury

Thomas Muders, Hermann Wrigge — 2010-06-01

Development of atelectasis is common in both patients with and without lung injury during mechanical ventilation. Atelectasis might contribute to or attenuate lung injury by different possible mechanisms. Possible direct effects of atelectasis include inflammatory activation or infection of the affected regional lung tissues. In addition, the loss of aerated lung volume due to atelectasis in mechanically ventilated patients indirectly results in increased mechanical strain of the reduced number of ventilated lung regions, if ventilation is not adequately decreased. This study discusses possible mechanisms and interactions between atelectasis formation in the lungs and the development or aggravation of acute lung injury.

Prevention and reversal of lung collapse during the intra-operative period

Gerardo Tusman, Stephan H. Böhm — 2010-06-01

General anaesthesia induces ventilation/perfusion mismatch by lung collapse. Such lung collapse predisposes patients to preoperative complications since it can persist for several hours or days after surgery.Atelectasis can be partially prevented by using continuous positive airway pressure (CPAP) and/or by lowering FiO2 during anaesthesia induction. However, these manoeuvres are dangerous for patients presenting with challenging airway or ventilator conditions.Lung recruitment manoeuvres (RMs) are ventilatory strategies that aim to restore the aeration of normal lungs. They consist of a brief and controlled increment in airway pressure to open up collapsed areas of the lungs and sufficient positive end-expiratory pressure (PEEP) to keep them open afterward. The application of RMs during anaesthesia normalises lung function along the intra-operative period. There is physiological evidence that patients of all ages and any kind of surgery benefit from such an active intervention. The effect of RMs on patient outcome in the postoperative period is, however, not yet known.

Perioperative tidal volume and intra-operative open lung strategy in healthy lungs: where are we going?

Beatrice Beck-Schimmer, Ralph C. Schimmer — 2010-06-01

Tidal volumes have tremendously decreased over the last decades from <15mlkg−1 to ∼6mlkg−1 actual body weight. Guidelines, widely agreed and used, exist for patients with acute lung injury or acute respiratory distress syndrome (ARDS). However, it is questionable if data created in patients with acute lung injury or ARDS from ventilation on intensive care units can be transferred to healthy patients undergoing surgery. Consensus criteria regarding this topic are still missing because only a few randomised controlled trials have been performed to date, focussing on the use of the best intra-operative tidal volume. The same problem has been observed regarding the application of positive end-expiratory pressure (PEEP) and intra-operative lung recruitment.This article provides an overview of the current literature addressing the size of tidal volume, the use of PEEP and the application of the open-lung concept in patients without acute lung injury or ARDS. Pathophysiological aspects of mechanical ventilation are elucidated.

Perioperative management of obese patients

Paolo Pelosi, Cesare Gregoretti — 2010-06-01

Obesity is a metabolic disease that is on the increase all over the world. Up to 35% of the population in North America and 15–20% in Europe can be considered obese. Since these patients are characterised by several systemic physiopathological alterations, the perioperative management may present some problems, mainly related to their respiratory system. Body mass is an important determinant of respiratory function before and during anaesthesia not only in morbidly but also in moderately obese patients. These can manifest as (a) reduced lung volume with increased atelectasis; (b)derangements in respiratory system, lung and chest wall compliance and increased resistance; and (c) moderate to severe hypoxaemia. These physiological alterations are more marked in obese patients with hypercapnic syndrome or obstructive sleep apnoea syndrome. The suggested perioperative ventilation management includes (a) awake and/or facilitated endotracheal intubation by using a video-laryngoscope; (b) tidal volume of 6–10mlkg−1 ideal body weight, increasing respiratory rate to maintain physiological PaCO2, while avoiding intrinsic positive end-expiratory pressure (PEEPi); and (c) a recruitment manoeuvre (35–55 cmH2O for 6 s) followed by the application of an end-expiratory pressure (PEEP) of 10 cmH2O. The recruitment manoeuvre should always be performed only when a volemic and haemodynamic stabilisation is reached after induction of anaesthesia. In the postoperative period, beach chair position, aggressive physiotherapy, non-invasive respiratory support and short-term recovery in intermediate critical care units with care of fluid management and pain may be useful to reduce pulmonary complications.

Management of mechanical ventilation during laparoscopic surgery

2010-06-01

Laparoscopy is widely used in the surgical treatment of a number of diseases. Its advantages are generally believed to lie on its minimal invasiveness, better cosmetic outcome and shorter length of hospital stay based on surgical expertise and state-of-the-art equipment. Thousands of laparoscopic surgical procedures performed safely prove that mechanical ventilation during anaesthesia for laparoscopy is well tolerated by a vast majority of patients. However, the effects of pneumoperitoneum are particularly relevant to patients with underlying lung disease as well as to the increasing number of patients with higher-than-normal body mass index. Moreover, many surgical procedures are significantly longer in duration when performed with laparoscopic techniques. Taken together, these factors impose special care for the management of mechanical ventilation during laparoscopic surgery. The purpose of the review is to summarise the consequences of pneumoperitoneum on the standard monitoring of mechanical ventilation during anaesthesia and to discuss the rationale of using a protective ventilation strategy during laparoscopic surgery. The consequences of chest wall derangement occurring during pneumoperitoneum on airway pressure and central venous pressure, together with the role of end-tidal-CO2 monitoring are emphasised. Ventilatory and non-ventilatory strategies to protect the lung are discussed.

Role of spontaneous and assisted ventilation during general anaesthesia

Lennart Magnusson — 2010-06-01

Spontaneous ventilation during general anaesthesia has been shown to favour atelectasis formation and decreased functional residual capacity. Therefore, general anaesthesia is commonly associated with endotracheal intubation and mechanical ventilation. Laryngeal lesions, residual curarisation, haemodynamics impairment, but most importantly, situation of cannot ventilate – cannot intubate may occur. Recently developed anaesthetic ventilators are able to detect spontaneous ventilation (triggering) and to give a pressure-limited flow cycled assisted breath (pressure support ventilation, PSV). Spontaneous ventilation assisted by PSV with laryngeal mask may avoid all the complications of endotracheal intubation and mechanical ventilation. Therefore, PSV should be a valid alternative for all patients having general anaesthesia with the exception of some contraindication. A close monitoring of tidal volume and minute ventilation is also needed.

Role of non-invasive ventilation (NIV) in the perioperative period

Samir Jaber, Pierre Michelet, Gerald Chanques — 2010-06-01

Anaesthesia, postoperative pain and surgery (more so if the site of the surgery approaches the diaphragm) will induce respiratory modifications: hypoxaemia, pulmonary volume decrease and atelectasis associated to a restrictive syndrome and a diaphragm dysfunction. These modifications of the respiratory function occur early after surgery and may induce acute respiratory failure (ARF). Maintenance of adequate oxygenation in the postoperative period is of major importance, especially when pulmonary complications such as ARF occur. Non-invasive ventilation (NIV) refers to techniques allowing respiratory support without the need of endotracheal intubation. Two types of NIV are commonly used: non-invasive continuous positive airway pressure (CPAP) and non-invasive positive pressure ventilation (NPPV) which delivers two levels of positive pressure (pressure support ventilation+positive end-expiratory pressure). NIV may be an important tool to prevent (prophylactic treatment) or to treat ARF avoiding intubation (curative treatment). The aims of NIV are: (1) to partially compensate for the affected respiratory function by reducing the work of breathing, (2) to improve alveolar recruitment with better gas exchange (oxygenation and ventilation) and (3) to reduce left ventricular after load increasing cardiac output and improving haemodynamics. Evidence suggests that NIV, as a prophylactic or curative treatment, has been proven to be an effective strategy to reduce intubation rates, nosocomial infections, intensive care unit and hospital lengths of stay, morbidity and mortality in postoperative patients. However, before initiating NIV, any surgical complication must be treated.The aims of this article are (1) to describe the rationale behind the application of NIV, (2) to report indications (including induction of anaesthesia) and contraindications and (3) to offer some algorithms for safe usage of NIV in high-risk surgery patients.

Influence of non-ventilatory options on postoperative outcome

Daniel Chappell, Matthias Jacob — 2010-06-01

Perioperative patient handling should urgently be updated according to current evidence and, if none is available, at least according to physiological knowledge. To prevent pulmonary aspiration, preoperative fasting for 2h (clear fluids) and 6h (solid food) and abdication of 20min for smoking is sufficient. Beta-blockage requires an indication. Bowel preparation should be abandoned and minimal invasive surgery as well as local and regional anaesthesia should be used where possible. Fluid therapy should be rational and requirement-adapted, and hypothermia, postoperative nausea and vomiting, unnecessary drains, tubes and catheters avoided. A multi-modal opioid-sparing pain therapy, sufficient oxygenation as well as early nutrition and mobilisation all play an important role for patient outcome.Recent studies have postulated that combining single-modality evidence-based care principles into a multi-modal effort to enhance postoperative recovery has improved patient outcome. Henrik Kehlet termed such a principle the ‘fast-track concept’, comprehending the entire perioperative phase starting with preoperative preparation, over atraumatic surgical and anaesthesiological techniques reducing the neuroendocrine stress response and also comprising the postoperative treatment. This strategy has been shown to positively influence organ function, homeostasis, morbidity, need for hospitalisation and convalescence and, therefore, to reduce costs. Despite these promising results, general implementation of evidence-based measures leaves a lot to be desired. Further development of surgical minimally invasive techniques and ongoing evaluation of procedure-specific strategies is urgently warranted.

Physiotherapy in the perioperative period

Nicolino Ambrosino, Luciano Gabbrielli — 2010-06-01

Surgery and general anaesthesia have direct effects on the respiratory system depending on the organ/system involved and modality of delivery, potentially leading to postoperative pulmonary complications that increase hospital morbidity, prolong hospital stay and add to health-care costs.Postoperative complications have been reported to be as high as 30% for thoracotomy and lung resection in patients with chronic obstructive pulmonary disease. Most of the complications are due to respiratory muscle dysfunction and surgery-related changes in chest wall mechanics. In general, preoperative optimisation of medical therapy combined with physiotherapy and early extubation and mobilisation may improve clinical outcomes in high-risk surgeries, including upper abdominal and thoracic surgery in patients with severe emphysema.Evidence from randomised controlled trials or meta-analyses is limited and most of the recommendations on perioperative physiotherapy come from either uncontrolled or non-randomised trials or from observational studies and expert opinion.

Keyword index

2010-06-01