Inter-regional gas mixing between respiratory units with different time constants (Pendellu ft ventilation). Convective transportation from asymmetric inspiratory and expiratory veloc ity pro \201 les. Longitudinal dispersion via interaction between the axial velocity pro \201 le and the radial concentration gradient. During HFO, high frequencies (180 \200\223360bpm = 3 \200\2236Hz) generally maintain normal PaCO2 levels. At lower frequencies (3Hz), CO2 clearance usually improves because of the la rger VT generated. CO2 clearance can also be enhanced by higher proximal driving pressures (range 60 \200\22390cmH2O) and longer inspiratory times (range 30 \200\22350%) \200\224both have a similar effect on VT. Indications This technique is used as a rescue therapy for refractory hypoxaemia or ventila tory failure in ARDS. It is now being considered as an early strategy in patients with mild er forms of acute lung injury to prevent further deterioration. However, there are no contr olled data showing superiority over conventional techniques. Theoretically, low VT and high PEEP in HFO reduce the risk of cyclical alveolar collapse and over-distension, both import ant factors in ventilator-induced lung injury (VILI). The higher mean airway pressure, but lower cycling and plateau pressures, will also improve oxygenation and allow reduction in t he FIO2. Lung recruitment can often be achieved by temporarily increasing lung volumes by a stepwise increase in continuous distending pressure to an oxygenation or chest X-ray target. The incidence of pneumothorax is thought to be similar to conventional ventilation in adult s. HFO may reduce the size of an air leak and promote healing by reducing high peak airway pressures and the alveolar \200\223pleural pressure gradient. Reducing the diameter of the leak increases resistance to gas \202 ow and this facilitates lung healing. Changes in me an airway pres- sure will result in the greatest percentage change in the size of the air l eak. Potential problems with HFO \200 Inability to maintain spontaneous breathing such that the patient often requires heavy seda tion 9 paralysis. Novel technical developments incorporating a \202 ow-demand system to e nable \202 ow compensation may reduce the imposed work of breathing, increase patient com fort, and allow continued spontaneous breathing. Haemodynamic compromise that usually respo nds to volume loading. This is more common during recruitment maneuvers. HIGH FREQUENCY OSCILLATORY VENTILATION 65 See also: IPPV \200\224description of ventilators, p46; IPPV \200\224modes of ventilation, p48; High frequency jet ventila- tion, p62; Positive end expiratory pressure (1), p66; Posi tive end expiratory pressure (2), p68; Acute respiratory distress syndrome (1), p360; Acute respiratory distress syndrome (2), p362; Pneumothorax, p368. 66 CHAPTER 2 Respiratory therapy techniques Positive end expiratory pressure (1) Positive end expiratory pressure (PEEP) is a modality used in positive pressure ventilation to prevent the alveoli returning to atmospheric pres- sure during expiration. It is routinely set between 3 \200\2235cmH2O; however, in severe r espiratory failure, it will often need to exceed 10cmH2O to be above the lower in \202 exi on point of the pressure \200\223volume curve. This has been suggested as bene \201 cial i n patients with severe ARDS. It rarely needs to exceed 20cmH2O to avoid cardiorespiratory c omplications and alveolar over-distension (see below). It neither prevents nor attenuates A RDS, reduce capillary leak, or lung water. Respiratory effects PEEP improves oxygenation by recruiting collapsed alveoli, re-distribut ing lung water, decreasing A \200\223V mismatch, and increasing functional residual capacit y (FRC). Haemodynamics PEEP usually lowers both left and right ventricular preload, and increases RV afterload. Though PEEP may increase cardiac output in left heart failure and \202 uid ov erload states by preload reduction, in most other cases, cardiac output falls, even at rela tively low PEEP levels. PEEP may also compro- mise a poorly functioning right ventricle. Im proved PaO2 resulting from decreased venous admixture may sometimes arise solely from reduc tions in cardiac output. Physiological PEEP A small degree of PEEP (2 \200\2233cmH2O) is usually provided physiologi cally by a closed larynx. It is lost when the patient is intubated or tracheostomised and b reathing spontaneously on a T-piece with no CPAP valve (see CPAP). Intrinsic PEEP (auto-PEEP, air trapping, PEEPi) Increased level of PEEP due to insuf \201 cient time for expiration, leading to \200\230air trapping \200\231, CO2 retention, increa sed airway pressures, and increased FRC. Seen in pathological conditions of increased air \202 ow resistance (e.g. asthma, emphysema) and when insuf \201 cient expiratory time is s et on the ventilator. Used clinically in inverse ratio ventilation to increase oxygenation and decrease peak airway pressures. However, high levels of PEEPi can slow weaning by an in creased work of breathing; use of extrinsic PEEP may overcome this. PEEPi can be measured b y temporarily occluding the expiratory outlet of ventilator at end-expiration for a few sec onds to allow equilibration of pressure between upper and lower airway, and then reading th e ventilator pressure gauge (or print-out). \200\230Best \200\231 PEEP Initially described as the level of PEEP producing the lowest s hunt value. Now generally considered to be the lowest level of PEEP that achieves SaO2 \211 90% allowing, wherever possible, lowering of FIO2 (ideally \211 0.6), though not at t he expense of peak airway pressures >35 \200\22340cmH2O or signi \201 cant reductions in D O2. POSITIVE END EXPIRATORY PRESSURE (1) 67 See also: IPPV \200\224description of ventilators, p46; IPPV \200\224modes of ventilation, p48; IPPV \200\224adjusting the ventilator, p50; IPPV \200\224complications of ventilation, p56; Positive end expiratory pressure (2), p68; Continuous positive airway pressure, p70; Lung recruitment, p72; Atelectasis and pulmonary collapse, p352. 68 CHAPTER 2 Respiratory therapy techniques Positive end expiratory pressure (2) Adjusting PEEP 1. 2. 3. 4. Measure blood gasses and monitor haemodynamic variables. If indicated, alter level of PEEP by 3 \200\2235cmH2O increments. Re-measure gasses and haemodynamic variables after 15 \200 \22320min. Consider further changes as necessary (including additional changes in PEEP, \202 uid challenge, or vasoactive drugs) A number of clinical trials have adjusted PEEP levels according to FIO2 requirements (see t able below). Although unlikely to constitute \200\230optimal PEEP \200\231 for an individu al patient, this provides a useful approximation and starting point for further titration o f therapy. FIO2 PEEP (cmH2O) 0.3 0.4 0.4 0.5 0.5 0.6 0.7 0.7 0.7 0.8 0.9 0.9 0.9 1.0 18 \211 18 5 5 8 8 10 10 10 12 14 14 14 16 Indications \200 \200 \200 \200 \200 \200 Hypoxaemia requiring high FIO2. Optimizing the pressure \200\223volume curve in severe resp iratory failure. Hypoxaemia secondary to left heart failure. Improvement of cardiac output in left heart failure. Reduced work of breathing while weaning patients with high PEEPi. Ne urogenic pulmonary oedema (i.e. non-cardiogenic pulmonary oedema following relief of upper airway obstruction). Complications \200 Reduced cardiac output. May need additional \202 uid loading or even inotropes. This shou ld generally be avoided unless higher PEEP is necessary to maintain adequate arterial oxyge nation. Caution should be exercised in patients with myocardial ischaemia. Increased airway pressure (and potential risk of ventilator trauma). Overin \202 ation leading to air trap ping and raised PaCO2. Use with caution in patients with chronic air \202 ow limitation or asthma. In pressure-controlled ventilation, over-distension is suggested when an increase in PEEP produces a signi \201 cant fall in tidal volume. High levels will decrease venous return, raise intracranial pressure, and increase hepatic congestion. PEEP may change the a rea of lung in which a pulmonary artery catheter tip is positioned from West zone III to no n-zone III. This is suggested by a rise in wedge pressure of at least half the increase in PEEP and requires re-siting of the catheter. \200 POSITIVE END EXPIRATORY PRESSURE (2) 69 See also: IPPV \200\224description of ventilators, p46; IPPV \200\224modes of ventilation, p48; IPPV \200\224adjusting the ventilator, p50; IPPV \200\224complications of ventilation, p56; Positive end expiratory pressure (1), p66; Continuous positive airway pressure, p70; Lung recruitment, p72; Atelectasis and pulmonary collapse, p352. 70 CHAPTER 2 Respiratory therapy techniques Continuous positive airway pressure Continuous positive airway pressure (CPAP) is the addit ion of positive pressure to the expiratory side of the breathing circuit of a spontaneously ventilating patient who may or may not be intubated. This sets the base- line upper airway pressure above atmospheric pressure, prevents alveolar collapse, and may recruit already c ollapsed alveoli. It is usually adminis- tered in 2.5cmH2O increments to a maximum of 10cmH 2O. It is applied either via a tight- \201 tting face mask (face CPAP), nasal mask (nasal CPAP), a whole head helmet, or the expiratory limb of a T-piece breathing circuit. A high- \202 ow (i.e. above peak inspiratory \202 ow) inspired air \200\223oxygen supply or a la rge reservoir bag in the inspiratory circuit is necessary to keep the valve open. CPAP impr oves oxygenation and may reduce the work of breathing by reducing the alveolar-to-mouth pre ssure gradient in patients with high levels of intrinsic PEEP. Transient periods of high CP AP (e.g. 40cmH2O for 40s) may be a useful maneuver for recruiting collapsed alveoli and imp roving oxygenation in ARDS. Indications \200 \200 \200 \200 Hypoxaemia requiring high respiratory rate, effort, and FIO2. Left heart failure to improve hypoxaemia and cardiac output. Weaning modality. Reduces work of breathing in patients wit h high PEEPi (e.g. asthma, chronic air \202 ow limitation). NB. Use with caution, monitor closely. Management 1. Measure blood gasses, monitor haemodynamic variables and respiratory rate. Prepare T-piece circuit with a 5cmH2O CPAP valve on the expiratory limb. Connect inspiratory limb to \202 ow generator/large volume reservoir bag. Adjust air \200\223oxygen mix to obtain desired F IO2 (measured by O2 analyzer in circuit). Use a heat-moisture exchanger to humidify the inh aled gas. If not intubated, consider nasal, face, or helmet CPAP. Attach mask to the patien t \200\231s face by an appropriate harness, attach a T-piece to the mask, and ensure no air leak is present. If using a nasal mask, encourage patient to keep their mouth closed. Repe at measurements after 15 \200\22320min. Consider further changes in CPAP (by 2.5cmH2O incre ments). Consider: (i) \202 uid challenge (or vasoactive drugs) if circulatory compromise, and (ii) nasogastric tube if gastric atony present. 2. 3. 4. 5. Complications \200 With mask CPAP, the risk of aspiration increases as gastric dilatation may occur from swall owed air. Insert a nasogastric tube, especially if consciousness is impaired or gastric mot ility is reduced. Reduced cardiac output due to reduced venous return (raised intrathoracic pressure). May need additional \202 uid or even inotropes. Overin \202 ation leading to air trapping and high PaCO2. Caution is urged in patients with chronic air \202 ow limita tion or asthma. May reduce venous return and increase intracranial pressure. Occasional poo r patient compliance with tight- \201 tting face mask due to feelings of claustrophobia an d discomfort on bridge of nose. Inspissated secretions due to high \202 ow, dry gas. \200 CONTINUOUS POSITIVE AIRWAY PRESSURE 71 See also: Positive end expiratory pressure (1), p66; Positive end expiratory pressure (2), p68; Lung recruit- ment, p72; Dyspnoea, p346; Airway obstruction, p348; Respiratory failure , p350; Atelectasis and pulmonary collapse, p352. 72 CHAPTER 2 Respiratory therapy techniques Lung recruitment There has been considerable interest in recent years in the concept of lun g recruitment. The rationale is that re-opening of collapsed alveoli results in improved ga s exchange, with resulting reductions in airway pressures and FIO2. Timing is crucial as co llapsed alveoli are more likely to be recruitable in the early stages of respiratory failur e. It appears that bene \201 t is more likely in extra-pulmonary causes of ARDS rather than i n cases of direct pulmonary pathology such as pneumonia. Some animal studies suggest that r ecruitment procedures may even be potentially injurious in the latter situation. Consideration should be given to lung recruitment soon after intuba- tion of patients with severe respiratory failure, and procedures causing de-recruitment, e.g. endotracheal suctio n, airway disconnection. Recruitment techniques \200 Several techniques are used to recruit collapsed alveoli, e.g. applying 40cmH2O PEEP for 40 s with no ventilator breaths; delivering a few large-volume, ventilator-delivered breaths; or by using a combination of varying levels of PEEP and increasing pressure-delivered breat hs to obtain optimal gas exchange. Although anecdotal successes are reported, with occasion ally dramatic improvements in lung compliance and gas exchange, no comparative trials have been performed and outcomes have not been assessed prospectively. Haemodynamic compromise m ay occur during the procedure though this usually recovers on cessation. LUNG RECRUITMENT 73 Key paper Brower RG, Morris A, MacIntyre N, et al. for the ARDS Clinical Trials Network.(20 03) Effects of recruitment maneuvers in patients with acute lung injury and acute respirato ry distress syndrome ventilated with high positive end-expiratory pressure. Crit Care Med 3 1: 2592 \200\2237. See also: IPPV \200\224modes of ventilation, p48; IPPV \200\224failure to deliver ventilati on, p54; High frequency oscillatory ventilation, p64; Positive end expiratory pressure (1), p66; Positive end expiratory pressure (2), p68; Continuous positive airway pressure, p70; Chest physiotherapy, p90; Atelectasis and pulmonary collapse, p352. 74 CHAPTER 2 Respiratory therapy techniques Prone positioning Prone positioning is used to treat patients with ARDS to improve gas exch ange. Various theories have been proposed to explain improvement, including: reduction in c ompression atelectasis of dependent lung regions (temporary), reduction in chest wall compl iance, increasing intratho- racic pressure and alveolar recruitment, better regional diaphr agmatic movement, better V/Q matching, improved secretion clearance, and less alveolar dist ension leading to better oxygenation. Indications Prone positioning may be considered when: PaO2 <8.5, FIO2 0.6, PEEP >10cmH2O de spite optimization of other ventilatory support. Technique Positioning the patient takes time and preparation. Four members of staff are req uired to turn a patient and one person to secure the head and ET tube. The turn itself is a two-stage procedure via the lateral position. The arm on which the patient is to be rolled is tucked under the hip with the other arm laid across the chest. Pillows are placed under the abdomen and chest prior to rotation to the lateral position. If stable, the turn may b e completed to prone. Pillows are placed under shoulders and pelvis. The head of bed is rai sed and one arm is extended at the patient \200\231s side while the other is \202 exed wi th head facing opposite way. Frequency of turns The response to prone ventilation is dif \201 cult to predict. Some pat ients may have no improvement in gas exchange; others may have a temporary bene \201 t, re quiring frequent turns; and others may have dif \201 culty returning to a supine position. For compression atelectasis, it is likely that bene \201 t will last up to 2h before resu mption of supine position is required. For other conditions, up to 18h prone position may b e required. The head and arms should be repositioned 2-hourly. Complications There are problems associated with positioning the patient prone, including; facial oedema, incorrect positioning of limbs leading to nerve palsy, and accidental remova l of drains and catheters, pressure necrosis, myositis ossi \201 cans. These problems are preventable so long as awareness of their potential is understood. Contraindications There are two absolute contraindications to prone position: severe head, spinal, or abdominal injury; and severe haemodynamic instability. Relative contraindication s include: \200 \200 \200 \200 Recent abdominal surgery. Large abdomen. Pregnancy. Spinal instability (though special beds are available for turning affected patients). Frequent seizures. Multiple trauma. Raised i ntracranial pressure. \200 \200 PRONE POSITIONING 75 Key paper Gattinoni L, Tognoni G, Pesenti A. et al. for the Prone-Supine Study Group. (2001 ) Effect of prone positioning on the survival of patients with acute respiratory failure. N Engl J Med 345: 568 \200\22373. See also: Acute respiratory distress syndrome (1), p360; Acute respiratory distress syndrom e (2), p362. 76 CHAPTER 2 Respiratory therapy techniques Non-invasive respiratory support Devices of varying sophistication are available to augment spontaneous breathing in the compliant patient by either assisting inspiration (inspirator y support) and/or providing CPAP. Non-invasive support is usually delivered by tight- \201 tting face or nasal mask, or via a helmet. Inspiratory support can also be delivered via a mouthpiece. Some devices allow connection to an endotracheal tube for the intubated but sp ontaneously breathing patient. Indications \200 \200 \200 \200 Hypoxaemia requiring high respiratory rate, effort, and FIO2. Hypercapnia in a fatiguing pa tient. Weaning modality. To avoid endotracheal intubation where desirable (e.g. severe chro nic air \202 ow limitation, immunosuppressed patients). Reduces work of breathing in patie nts with high PEEPi (e.g. asthma, chronic air \202 ow limitation). Use with caution and mo nitor closely. Physiotherapy technique for improving FRC. Sleep apnoea. \200 Inspiratory support (IS) A preset inspiratory pressure is given when triggered by the patie nt \200\231s breath. The trigger can be adjusted according to the degree of patient effort. Some devices deliver breaths automatically at adjustable rates. The I:E ratio may also be adjustable. The VT delivered for a given level of inspir- atory support varies according to the patient \200\231s respiratory compliance. An example of an IS device is the Bird venti lator, commonly used by physio- therapists to improve FRC and expand lung bases. BiPAP (Bilevel positive airways pressure) This device delivers adjustable levels of pressur e support and PEEP. Delivered breaths can be either patient-triggered and/or mandatory. Som e BiPAP devices are driven by air; to increase the FIO2, supplemental O2 can be given via a circuit connection or through a portal in the mask. Management 1. 2. 3. 4. Select type and delivery mode of ventilatory support. Connect patient as per device instruc tions. Use an appropriate-sized mask that is comfortable and leak-free. A delivered pressur e (IPAP) of 10 \200\22315cmH2O is a usual starting point which can be adjusted according to patient response (respiratory rate, degree of fatigue, comfort, blood gasses, etc.). Expir atory pressure support (EPAP) is usually in the 5 \200\22312cmH2O range. Patients in respir atory distress may have initial dif \201 culty in coping. Constant attention and encourage ment will help to accustom them to the device and/or mask while different levels of support , I:E ratios, etc. are tested to \201 nd optimal settings. Cautious administration of low dose opiate injections (e.g. diamorphine 2.5mg SC) may help to calm the patient without de pressing respiratory drive. The tight- \201 tting mask may become increasingly claustropho bic after a few days \200\231 use. Pre-empt if possible by allowing the patient regular bre aks. Protect pressure areas such as the bridge of the nose. 5. 6. NON-INVASIVE RESPIRATORY SUPPORT 77 Key papers Brochard L, Mancebo J, Wysocki M, et al. (1995) Non-invasive ventilation for acu te exacerbations of chronic obstructive pulmonary disease. N Engl J Med 333: 817 \200\22322 . Antonelli M, Conti G, Rocco M, et al. (1998) A comparison of non-invasive positive-pressure ventilation and conventional mechanical ventilation in patients with acute respiratory fai lure. N Engl J Med 339: 429 \200\22335. See also: Ventilatory support \200\224indications, p44; IPPV \200\224description of ventila tors, p46; IPPV \200\224modes of ventilation, p48; IPPV \200\224failure to tolerate ventila tion, p52; IPPV \200\224weaning techniques, p58; IPPV \200\224assessment of weaning, p60; C ontinuous positive airway pressure, p70. 78 CHAPTER 2 Respiratory therapy techniques Extracorporeal respiratory support These techniques have declined in popularity over recent years after several trials failed to demonstrate clear outcome bene \201 t in adults with very severe respiratory failure. Survival rates of 50 \200\22360% are reported, but clear superiority over conventional ventilation has not yet been demon- strated in controlled stu dies. A large, prospective, randomized study (the \200\230CESAR \200\231 trial) has recent ly been completed, but failed to show bene \201 t from extracorporeal support. Extracorporeal CO2 removal (ECCO2R) An extracorporeal veno-venous circulation allows CO2 cl earance via a gas exchange membrane. Blood \202 ows of 25 \200\22333% cardiac output are typically used, allowing only partial oxygenation support. Low frequency (4 \200\2235/min) positive pressure ventilation is usually used with ECCO2R, with continuous oxygenation thro ughout inspiration and expiration. The lungs are \200\230held open \200\231 with high PEEP (20 \200\22325cmH2O), limited peak airway pressures (35 \200\22340cmH2O), and a continuous fresh gas supply. Thus, oxygenation is pro- vided with lung rest to aid recovery. Anticoag ulation of the extracorporeal circuit can be reduced by using heparin-bonded tubing and mem branes. Extracorporeal membrane oxygenation (ECMO) An extracorporeal veno-arterial circulation with high blood \202 ows (approaching cardiac output) through a gas exchange membrane enables most if not all of the body \200\231s gas exchange requirements to be met. Main disadvanta ges compared to ECCO2R are the need for large bore arterial puncture with its consequent ri sks and high extracorporeal blood \202 ows with the potential for cell damage. Indications Failure of maximum intensive therapy and ventilatory support to sustain adequat e gas exchange as evidenced by the criteria opposite. Contraindications \200 Chronic systemic disease involving any major organ system (e.g. irreversible chronic CNS di sease, chronic lung disease with FEV1 <1L, FEV1/FVC <0.3 of predicted, chronic PaCO2 >6.0kP a, emphysema or previous admission for chronic respiratory insuf \201 ciency, incurable or rapidly fatal malignancy, chronic failure of heart, kidney or liver, HIV- related disease) . Lung failure for >7d (although treatment with extracorporeal respiratory support may pers ist for longer than 14d). Burns (>40% of body surface). More than three organ failures in a ddition to lung failure. \200 EXTRACORPOREAL RESPIRATORY SUPPORT 79 Criteria for ECCO2R/ECMO \200 Rapid failure of ventilatory support: immediate use of these techniques should be considere d in those meeting the following criteria for a period >2h despite maximum intensive care: \200 \200 \200 Slow failure of ventilatory support: consider use after 48h maximum in tensive care for those meeting the following gas exchange and mechanical pulmonary function criteria for a period >12h: \200 \200 \200 \200 \200 PaO2 <6.7kPa. FIO2 1.0. PEEP >5 \200\22310cmH2O. PaO2 <6.7kPa. PEEP >5 \200\22310cmH2O. Qs/Qt >30% on FIO2 of 1.0. PaO2/FIO2 <11.2kPa. TSLC <30mL/cmH2O at 10mL/kg in \202 ation. See also: Anticoagulants, p318; Prostaglandins, p330; Acute respiratory distress syndrome ( 1), p360; Acute respiratory distress syndrome (2), p362. 80 CHAPTER 2 Respiratory therapy techniques Tracheotomy The technique of creating a hole (the tracheostomy) in the trachea. Indications To provide an arti \201 cial airway in place of orotracheal or nasotracheal in tu- bation. This may be to provide better patient comfort, avoid vocal cord, mouth or nasal trauma or, in an emergency, bypass acute upper airway obstruction. The optimal time to per form a tracheotomy in an intubated patient is not known; a prospective randomized study (th e \200\230TracMan \200\231 trial) is underway in the UK. Reduced need for sedation, the po tential to eat, drink and speak, and facilitation of mouth care are all advantages. Percutaneous tracheotomy Percutaneous tracheotomy can be performed in the ICU. Coagulopathy should be excluded or treated \201 rst. Subcutaneous tissues are in \201 ltrated with 1 % lidocaine and epinephrine (adrenaline). After a 1 \200\2231.5cm midline skin crease incis ion, the subcutaneous tissue is blunt-dissected to the anterior tracheal wall. The ET tube tip is withdrawn to the level of the vocal cords. The trachea is then punctured in the midl ine with a 14G needle between the 1st and 2nd tracheal cartilages (or lower), allowing guid e wire insertion. The stoma is created by dilatation to 32 \200\22336Fr (Ciaglia technique) or by a guided forceps dilating tool (Schachner \200\223Ovill tech- nique). In the former case, the tracheostomy tube is introduced over an appropriate-sized dilator, and in the lat ter, through the open dilating tool. End-tidal CO2 monitoring con \201 rms adequate ventil ation during the procedure. Fibreoptic bronchoscopy may be used to con \201 rm correct tra cheal placement and no trauma to the posterior tracheal wall. Complications The main early complication is hemorrhage from vessels anterior to the trache a. This is usually controlled with direct pressure or, occasion- ally, sutures. Bleeding in to the trachea may result in clot obstruction of the airway; endotracheal suction is usuall y effective. Paratracheal place- ment should be rare, but promptly recognized by the inabil ity to ventilate the lungs. Later complications include tracheostomy tube displacement, sto mal infection, and tracheal stenosis. Stenosis is often related to low- grade infection and is claimed to be more common with open trache- otomy. Rare complications include tracheo-o esophageal \201 stula due to trauma or pressure necrosis of the posterior tracheal wall, or erosion through the lateral tracheal wall into a blood vessel. Maintenance of a tracheostomy Since the upper air passages have been bypassed, arti \201 c ial humidi \201 cation is required. Cough is less effective without a functioning larynx s o regular tracheal suction will be necessary. Natural laryngeal PEEP is lost with a tracheo stomy. The risk of basal atelectasis can be overcome with CPAP or attention to respiratory exercises that promote deep breathing. After 3 \200\2235d, the tracheostomy tube can be saf ely replaced. Tracheostomy tube removal Before removing the tube, ensure the upper airway is patent, eith er by allowing the patient to exhale passed an occluded tube or by visualization. TRACHEOTOMY 81 Tracheotomy tubes Standard high volume, low pressure cuff Fenestrated, with or without cuff Useful where airway protection is not a primary concern. May be closed during normal breat hing while providing intermittent suction access. Fenestrated, with inner tube As above, but with an inner tube to facilitate closure of the fenestration during intermittent mechanical ventilation. Fenestrated, with speaking valve Inspiration allowed through the tracheostomy to reduce dea d space and inspiratory resistance. Expiration through the larynx via the fenestration, all owing speech and the advantages of laryngeal PEEP. Adjustable \202 ange Accommodates extreme variations in skin to trachea depth while ensur ing the cuff remains central in the trachea. Pitt speaking tube A non-fenestrated, cuffed tube for continuous mechanical ventilation and airway protection with a port to direct air \202 ow above the cuff to the larynx. When ai r \202 ow is directed through the larynx, some patients are able to vocalize. Passy \200\223Muir speaking valve This expiratory occlusive valve is placed onto the trache ostomy tube to permit inspiration through the tracheostomy and expiration through the glott is. The tracheostomy tube cuff must be \201 rst de \202 ated. The valve allows phonation , facilitates swallowing, and may reduce aspiration. Small studies have suggested that it m ay reduce the work of breathing. The potential tidal volume drop through cuff de \202 atio n makes this valve only suitable in those patients requiring no (or relatively low level) i nvasive ventilatory support. Silver tube An uncuffed tube used occasionally in ENT practice to maintain a trache- ostomy \201 stula. See also: Endrotracheal intubation, p42; Ventilatory support-indications, p44; Minitracheot omy, p82; Airway obstruction, p348; Respiratory failure, p350. 82 CHAPTER 2 Respiratory therapy techniques Mini-tracheotomy The technique of placing a small diameter, uncuffed plastic tube through t he cricothyroid membrane under local anesthetic. Indications \200 \200 Removal of retained secretions, usually if patient \200\231s cough is weak. Emergency acces s to lower airway if upper airway obstructed. Contraindications/cautions \200 \200 Coagulopathy. Non-compliant, agitated patient (unless sedated). Technique Some commercial kits rely on blind insertion of a blunt introducer; others use a Seldinger technique where a guidewire is inserted via the crico- thyroid membrane into the trachea. An introducer passed over the wire dilates the track, allowing easy passage of the tube. 1. Use an aseptic technique. Cleanse site with antiseptic. Locate cricothyroid membrane (midli ne, \200\230spongy \200\231 area between cricoid and thyroid cartilages). In \201 ltrate local skin and subcutaneous tissues with 1% lidocaine 9 epinephrine (adrenaline). Advance n eedle into deeper tissues, aspirating to con \201 rm absence of blood, then in \201 ltrat e with lidocaine until cricothyroid membrane is pierced and air is easily aspirated. If usi ng Seldinger technique, insert the guidewire through the membrane into the trachea. Tether thyroid cartilage with one hand, incise skin and tissues vertically in midline (alongside w ire) using a short-bladed guarded scalpel provided with pack. Insert scalpel to blade guard level to make adequate hole through cricothyroid membrane. Remove scalpel. Insert introduc er through incision site into trachea (or over guidewire). Angle caudally. Relatively light resistance is felt during correct passage; do not force introducer if resistance is excess ive. Lubricate plastic tube and slide it over introducer into trachea. Remove introducer (+ wire), leaving plastic tube in situ. Con \201 rm correct position by placing own hand ove r tube and feeling air \202 ow during breathing. Suction down tube to aspirate intratrache al contents (check pH if in doubt). Cap opening of tube. Suture to skin. Perform CXR (unles s very smooth insertion and no change in cardiorespiratory variables). O2 can be entrained through the tube, or a catheter mount placed to allow bagging, the use of intermittent posi tive pressure breathing and/ or short-term assisted ventilation. 2. 3. 4. 5. 6. 7. 8. 9. Complications \200 Puncture of blood vessel at cricothyroid membrane may cause signi \201 cant intratracheal or external bleeding. Apply local pressure if this occurs after blade incision. If bleeding continues, insert mini-tracheotomy tube for a tamponading effect. If bleeding persists, in sert deep sutures either side of mini-tracheotomy; if this fails, contact surgeon for assis tance. Perforation of esophagus. Mediastinitis (rare). Pneumothorax. \200 \200 MINI-TRACHEOTOMY 83 See also: Tracheotomy, p80; Chest physiotherapy, p90; Atelectasis and pulmonary collapse, p 352. 84 CHAPTER 2 Respiratory therapy techniques Chest drain insertion Indications include drainage of air (pneumothorax), \202 uid (effus ion), blood (haemothorax), or pus (empyema) from the pleural space. Insertion technique 1. Use 28Fr drain (or larger) for haemothorax or empyema; 20Fr will suf \201 ce for a pure pn eumothorax. Seldinger-type drains with an integral guidewire are now available. The drain i s usually inserted through the 5th intercostal space in the mid-axillary line, \201 rst a nesthetizing skin and pleura with 1% lidocaine. Ensure that air/ \202 uid is aspirated. Ma ke a 1 \200\2231.5cm skin crease incision, create a track with gloved \201 nger (or force ps) to separate muscle \201 bres and open pleura. Insert drain through open pleura withou t trochar. Angle and insert drain to correct position (toward lung apex for pneumothorax an d lung base for haemothorax/effusion). CT scan or ultrasound is useful for directing placem ent for small collections. Connect to the underwater seal and keep bottle below level of he art. Secure drain to chest wall by properly placed sutures. Perform chest X-ray to ensure c orrect siting and lung rein \202 ation. Place on 5 \200\22310cmH2O (0.5 \200\2231.3kPa) ne gative pressure (low pressure wall suction) if lung has not fully expanded. 2. 3. 4. 5. 6. 7. 8. Subsequent management \200 \200 Do not clamp drains prior to removal or during transportation of patient. Drains may be rem oved when lung has re-expanded and no air leak is present (no respiratory swing in \202 u id level nor air leak on coughing). Unless long-term ventilation is necessary, a drain inse rted for a pneumothorax should usually be left in situ during IPPV. Remove drain at end-exp iration. Cover hole with thick gauze and Elastoplast ; a purse-string suture is not usuall y necessary. Repeat chest X-ray if indicated by deteriorating clinical signs or blood gas a nalysis. Complications \200 \200 Morbidity associated with chest drainage may be up to 10%. Puncture of an intercostal vesse l may cause signi \201 cant bleeding. Consider: (i) correcting any coagulopathy, (ii) plac ing deep tension sutures around drain, or (iii) removing drain, inserting a Foley catheter, in \202 ating the balloon, and applying traction to tamponade bleeding vessel. If these m easures fail, contact (thoracic) surgeon. Puncture of lung tissue may cause a bronchopleura l \201 stula. Consider suction (up to 15 \200\22320cmH2O), pleurodesis, high frequency ve ntilation, a double-lumen endobronchial tube or surgery. Extubate if feasible. Perforation of major vessel (often fatal); clamp but do not remove drain, resuscitate, contact surgeon, consider double-lumen ET tube. Infection: take cultures; antibiotics (staphylococcal 9 ana erobic cover); consider removing/resiting drain. Local discomfort/pain from pleural irritat ion may impair cough. Consider simple analgesia, subcutaneous lidocaine, instilling local a nesthetic, local or regional anesthesia, etc. Drain dislodgement; if needed, replace/resite new drain, depending on cleanliness of site. Don \200\231t advance old drain (infection ri sk). Lung entrapment/infarction: avoid milking drain in pneumothorax. CHEST DRAIN INSERTION 85 See also: Pleurla aspiration, p86; Basic resuscitation, p338; Pneumothorax, p368; Haemothor ax, p370. 86 CHAPTER 2 Respiratory therapy techniques Pleural aspiration Drainage of \202 uid from the pleural space using needle, cannula, or \202 exible small-bore drain. Increasingly being performed under ultrasound guidance. Blo od/pus often requires large-bore drain insertion. Indications \200 \200 \200 Improvement of blood gasses. Symptomatic improvement of dyspnoea. Diagnostic \200\230tap \200\231. Contraindications/cautions \200 Coagulopathy. Technique 1. 2. Con \201 rm presence of effusion by CXR or ultrasound. Select drainage site either by maxi mum area of stony dullness under percussion or under ultrasound guidance. Use aseptic techn ique. Clean area with antiseptic and in \201 ltrate local skin and subcutaneous tissues wi th 1% lidocaine. Advance into deeper tissues, aspirating to con \201 rm absence of blood, then in \201 ltrate with local anesthetic until pleura is pierced and \202 uid can be as pirated. Advance drainage needle/cannula/drain slowly through chest wall and intercostal sp ace (above upper border of rib to avoid neurovascular bundle). Apply gentle suction until \202 uid is aspirated. Withdraw 50mL for microbiological (M, C & S, TB stain, etc.), bioch emical (protein, glucose, etc.) and histological/cytological (pneumocystis, malignant cells , etc.) analysis, as indicated. Either leave drain in situ connected to a drainage bag or c onnect needle/cannula by a three-way tap to a drainage apparatus. Continue aspiration/drain age until no further \202 uid can be withdrawn or if patient becomes symptomatic (pain/dy spnoea). Dyspnoea or haemodynamic changes may occur due to removal of large volumes of \202 uid (>1 \200\2232L) and subsequent \202 uid shifts; if this is considered to be a po ssibility, remove no more than 1L at a time, either by clamping/ declamping drain or repeat ing needle aspiration after an equilibration interval (e.g. 4 \200\2236h). Remove needle/dr ain. Cover puncture site with \201 rmly applied gauze dressing. 3. 4. 5. 6. 7. 8. Complications \200 \200 Puncture of lung or subdiaphragmatic viscera. Bleeding. Fluid protein level \200 Protein >30g/L (NB. This should be viewed in the context of the plasma protein level) is an exudates; caused by: in \202 ammatory, e.g. pneumonia, pulmonary embolus, neoplasm, colla gen vascular diseases. Protein <30g/L is a transudate caused by: (i) raised venous pressure (e.g. heart failure, \202 uid overload), (ii) decreased colloid osmotic pressure (e.g. c ritical illness leading to reduced [plasma protein] from capillary leak and hepatic dysfunc tion, hepatic failure, nephrotic syndrome). PLEURAL ASPIRATION 87 See also: Chest drain insertion, p84; Basic resuscitation, p338; Pneumothorax, p368; Haemot horax, p370. 88 CHAPTER 2 Respiratory therapy techniques Fibreoptic bronchoscopy Indications Diagnostic \200 Collection of microbiological 9 cytological specimens (by bronchoalveolar lavage, protected brush specimen, biopsy). Cause of bronchial obstruction (e.g. clot, foreign body, neoplasm ). Extent of inhalation injury. Diagnosis of ruptured trachea/bronchus. \200 \200 Therapeutic \200 \200 Clearance of secretions, inhaled vomitus, etc. Removal of obstructing matter (e.g. mucus pl ug, blood clot, food, tooth). Proximal obstruction rather than consolidation is suggested b y the X-ray appearance of a collapsed lung/lobe and no air bronchogram. Cleansing/removing soot or other toxic materials, irrigation with saline. Directed physiotherapy 9 saline to l oosen secretions. Directed placement of balloon catheter to arrest pulmonary bleeding. To a id dif \201 cult endotracheal intubation. \200 \200 \200 Contraindications/cautions \200 \200 Coagulopathy. Severe hypoxaemia. Procedure It is dif \201 cult to perform bronchoscopy in a nasally intubated patient. A na rrow lumen scope can be used but suction is limited. 1. 2. 3. 4. 5. 6.