Critical care - self assessment quiz

ARTICLE IN PRESS Current Orthopaedics (2003) 17, 475-- 477 doi:10.1016/j.cuor.2003.09.002

CRITICAL CARE

Self Assessment Quiz M. Bellamy Consultant Aneasthetist and Critical Care Consultant, St. James’s Hospital, Beckett Street, Leeds LS9 7TF UK

QUESTIONS

ANSWERS

Question 1

Answer 1

What proportion of chest injuries can be treated conservatively? What are the general principles of conservative management of blunt chest trauma?

In the UK and Europe, around15% of chest injuries require surgical intervention, the remainder requiring medical management. History, examination and chest X-ray are useful to determine rib fractures/pneumothorax/haemothorax. Chest X-ray and CT are useful to exclude major disruptions of the aortic arch or bronchi (e.g. associated with first rib fracture). Immediate drainage of 41500 ml blood or hourly drainage 4200 ml necessitate surgical intervention.The presence of a flail segment usually does not. The principles of supportive management include adequate analgesia (including techniques such as thoracic epidural analgesia, intrapleural catheterisation and instillation, subcostal blockade, patient-controlled analgesia), physiotherapy and clearance of secretions, supplemental oxygen and careful fluid balance to avoid over-hydration. A minority require intubation and artificial ventilation.

Question 2 What are the arguments for and against drainage of pneumothoraces/haemothoraces in the conservatively managed patient with chest trauma? Question 3 What are the indications for artificial ventilation in this patient group? Question 4 When is it feasible to avoid intubation and ventilation: what are the available alternatives? Question 5 What are the implications of lung contusion? Question 6 Comment on the clinical (as opposed to pathological) lesions seen in ARDS. How may this syndrome be managed? Question 7 What prophylactic antibiotics/steroids are most appropriate in the treatment of ARDS? Question 8 Major injury is often followed by a systemic inflammatory response. Describe its key features. Question 9 How does SIRS differ from sepsis? Question 10 Should a Swan Ganz catheter be routinely used in a critically ill or septic patient?

Answer 2 Small pneumothoraces (o30%) or haemothoraces may be managed conservatively in patients who are able to continue breathing spontaneously. Larger lesions require drainage, as do all pneumothoraces in patients who are artificially ventilated.This is because of the risk of unpredictable rapid progression to a tension pneumothorax. Haemothoraces are generally drained because of the immediate risk of respiratory and haemodynamic embarrassment, and the late risks of sepsis and organisation. Answer 3 Indications for artificial ventilation include the need for systemic support, airway protection (e.g. maxillo-facial injury, altered conscious level with a Glasgow Coma Score below 8), or severe abnormalities of gas exchange. Many patients tolerate a PaO2 as low as 7-- 8 kPa, or an SpO2 of 85--90%, but trends rather than snapshot values are important. The presence of a rising PaCO2 or an inadequate respiratory pattern (paradox, accessory

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muscle breathing) is often a better indicator of the impending need for ventilatory support than are measurements of oxygenation. Answer 4 There are no hard-and-fast rules for embarking on artificial ventilation in this situation. Acidosis is a more significant feature than hypoxia and hypercarbia, and the clinical picture (conscious level, respiratory pattern, etc.) is more important than blood gas results. Intermittent positive pressure ventilation as conventionally delivered requires intubation of the trachea or tracheostomy. While this remains the technique of choice in the sickest patients, it has disadvantages in marginal cases. Endotracheal tubes may be a portal for infection and often require sedative drugs to render them tolerable.Most currently used sedative regimens induce further immune compromise, increase the risk of aspiration and nosocomial pneumonias, require additional venous access and cause cardiovascular depression.There are considerable advantages in avoiding intubation in the less sick patient. Non-invasive ventilation by using a tightly fitted facemask is often feasible. Commonly used systems include‘NIPPY’, a simple system applying intermittent breaths of air or oxygen-enriched air via the facemask. An alternative is bilevel positive airway pressure (BiPAP) where periods of high and low added airway pressure are applied.This promotes airway recruitment and helps maintain an adequate functional residual capacity, as well as augmenting the patient’s spontaneous minute volume. Continuous positive airway pressure (CPAP) is applied by a similar facemask but there is no mechanical ventilator and hence no augmentation of the minute volume. However, the functional residual capacity is maintained/increased, which results in improved oxygenation.Further, the patient may experience increased mechanical efficiency as a result of tidal volume breathing being shifted to a more compliant part of the respiratory pressure/volume curve. This reduces the work of breathing and may prevent tiring. Answer 5 Minor degrees of lung contusion may be self-limiting but give rise to an increasing degree of impaired gas exchange and predispose to secondary chest infection. Radiological evidence of lung contusion may not be immediately apparent. Impaired oxygenation and chest Xray infiltrates appear over 24 h. Secondary infection very frequently occurs in regions of contused lung. Microbiological diagnosis may be difficult and require directed broncho-alveolar lavage in some cases. Significant lung contusion is associated with the development of acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS).These conditions are part of a continuum characterised by a clear precipitating cause (local, e.g. smoke inhalation, chest injury, or distant, e.g. systemic sepsis, multi-organ failure), ‘normal’ cardiac function

CURRENT ORTHOPAEDICS

(arbitrarily defined as a pulmonary capillary wedge pressure below 18 mmHg), tachypnoea, hypoxia, reduced lung compliance and bilateral infiltrates on chest X-ray. A PaO2/FiO2 ratio of 200 --300 mmHg implies ALI, and below 200 mmHg ARDS. Answer 6 ARDS is an inflammatory condition featuring local as well as distant pro-inflammatory mediators, neutrophil margination and diapedesis, altered vascular permeability, exudates and hyaline deposition. Clinically this gives rise to a ventilation-perfusion mismatch in which the shunt fraction is generally 20 --50% but in severe cases may be higher.This is exacerbated by areas of atelectasis and consolidation. The subsequent course frequently includes nosocomial pneumonia. The treatment of ARDS includes systemic support (addressing the underlying cause, nutrition, etc.) as well as specific measures.There is good evidence for a ‘dry lung’ approach, as increased extra-vascular lung water has been shown to impair oxygenation and is amenable to clinical manipulation. Ventilatory management is based around the ‘open lung’ philosophyFsheer stresses in the lung are minimised by the prevention of airway collapse and reopening, with consequent inhomogeneity of airway geometry. Airway recruitment manoeuvres may be applied, and airway opening and functional residual capacity subsequently maintained by the application of positive end-expiratory pressure (PEEP). In the spontaneously breathing patient, this is provided by application of continuous positive airway pressure (CPAP). Tidal volumes should be limited to 6 ml/kg and peak inflation pressures to 35 mmHg to prevent airway over-distension and volutrauma. There is good outcome evidence to support this approach. A consequence of this ventilator strategy is the need to accept incomplete correction of blood gasesF‘permissive hypercapnia’ and ‘permissive hypoxaemia’. Answer 7 There is no role for prophylactic use of antibiotics in ARDS, but close microbiological surveillance is mandatory. In ventilator-dependent patients, some authorities have advocated daily broncho-alveolar lavage. There is no evidence for the use of high-dose steroids in early ARDS, but some evidence suggests faster weaning from artificial ventilation and less late fibroproliferative change when steroids are used in established ARDS (410 days). Patients tend to die of associated multi-organ failure rather than specifically of ARDS. Of those who survive, up to 50% make a good functional recovery, the remainder developing long-term pulmonary changes (fibrosis, restrictive change, reduced gas transfer capacity). Answer 8 The systemic inflammatory response syndrome (SIRS) is common after major injury (including surgery). It is

ARTICLE IN PRESS SELF ASSESSMENT QUIZ

part of a continuum which includes multiple organ failure and septic shock.The exact mechanisms underlying SIRS are unclear but activation of the immuno-inflammatory cascade plays an important part. SIRS is said to be present when two or more of the following are present in the absence of direct cause: * * * * *

*

Temperature outside the range 36 --381C. Heart rate 490/min. Tachypnoea 420/min. Hyperventilation: PaCO2 o4.3 kPa. White blood cell count outside the range 4000 -12000 cells/mm3. Presence of 410% immature (band) neutrophils. Answer 9

SIRS with a positive culture becomes sepsis. The presence of end organ failure makes sepsis ‘severe sepsis’. This becomes septic shock when the systolic blood pressure is less than 90 mmHg or more than 40 mmHg below the patient’s habitual blood pressure. In up to 50% of cases, no causative organism is found. Septic shock may be characterised by hypotension, cold clammy peripheries , hypovolaemia and a low cardiac output (‘cold’ septic shock). After volume resuscitation the picture changes dramatically to one of warm well-perfused peripheries, a (very) high cardiac output and dramatic vasodilatation, but with the patient remaining relatively hypotensive (‘warm’ septic shock). The circulation at this stage may be so hyperdynamic that visible cardiac oscillation may be seen by observing the patient’s bed. Despite an apparently high cardiac output, this may still be inappropriately low for the degree of vasodilatation. Inadequate tissue oxygen delivery and utilisation as well as myocardial impairment may be

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features of microcirculatory failure. Patients who are this sick generally require intubation, ventilation and inotropic (vasopressor) support. At presentation, patients may have ‘warm’ or ‘cold’ septic shock. Consequently, whatever the initial clinical picture, sepsis must be considered as part of the differential diagnosis of shock. Answer 10 Traditional techniques for monitoring adequacy of the circulation include central venous pressure monitoring and the use of the pulmonary artery (Swann Ganz) catheter to measure pulmonary artery occlusion pressure (wedge pressure) and cardiac output.Wedge pressure is a surrogate for left atrial pressure and hence left ventricular end-diastolic volume. Recent work suggests that, paradoxically, optimising tissue oxygenation and blood flow improves outcome in critical illness or perioperatively, but that use of the pulmonary artery catheter does not (and may be harmful).There is much current interest in newer less invasive methods of assessing the adequacy of resuscitation and cardiac output. The best validated methods include gastric tonometry, mixed venous/central venous saturation monitoring (these assess tissue perfusion), and oesophageal Doppler cardiac output monitoring. Other techniques of great current interest include pulse-contour cardiac output analysis (e.g. as used in the PiCCO and LiDCO systems). These give a beat-by-beat measure of cardiac output based on analysis of the arterial waveform. The waveform has to be periodically calibrated against a true measure of flow. This can be done by thermodilution or indocyanine green dilution (PiCCO, LiMon) or by lithium dilution (LiDCO).