July 2005 - The Hong Kong College of Anaesthesiologists

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Bull HK Coll Anaesthesiol Volume 14, Number 2 July 2005Table 1. Arterial blood gas, hemodynamic and ventilator parameters before and after double lumen tubeinsertion. SaO2 = Oxygen saturation, PaO2 = Arterial oxygen tension, PaCO2 = Arterial carbon dioxide tension, PEEP =positive end expiratory pressure, fiO2 = inspired oxygen fraction, PC = pressure control mode, PRVC = pressure regulated volumecontrol modeBlood GasBefore DLTAfter DLTpH 6.98 7.31SaO2 (%) 83.8 92PaO2 (kPa) 8.5 7.2PaCO2 (kPa) 22.3 8.8VentilatorMode/fiO2 PC/1.0 PRVC/1.0Airway Pressure (cmH2O) 41 28Pressure Support (cmH2O) 28 20PEEP(cmH2O) 10 6HemodynamicsAverage mean arterial68 110pressure (mmHg)Average heart rate (min ‐1 ) 110 90oxygenation, hemodynamic and ventilatorparameters before and after DLT insertion.Unfortunately, he eventually succumbed 48hours later as a result of sepsis induced multiorganfailure.DiscussionLung bullae are thin walled, air filled spacesresulting from destruction of alveolar tissue.They can be classified according to theiraetiologic origins i.e. bronchogenic, postinfective,infantile and emphysematous. The walls oflung bullae usually comprise visceral pleura,connective tissue septa and compressedparenchyma.Lung bullae have a tendency to increase insize with age, which may be a result of a oneway valve effect. They represent areas ofincreased compliance, which then form the pathof least resistance during positive pressureventilation. Since they do not take part ingaseous exchange, there is a resultant increase inalveolar dead space. The gradual increase in sizeof bullae during positive pressure ventilationmay lead to compression of adjacent normallung tissue resulting in further worsening of103ventilation/perfusion mismatching and hencegreater hypoxemia.A variety of complications, including gradualdecrease in effort tolerance of the patient,recurrent infections and pneumothoraces canoccur when bullae enlarge. Giant lung bullaeconstitute one of those thoracic diseases thatusually results in an improvement in lungfunction following resection, although oftenpreceded by exceedingly poor lung function inthe preoperative period.Some of the accepted indications forbullectomy include incapacitating dyspnea,giant size at presentation, repeated pneumothoraxand compression of a significant volumeof otherwise normal lung tissue. The complexityof the management of lung bullae for volumereduction surgery or in the immediate postoperativeperiod is dependent on whether thedisease is unilateral or bilateral. The latter mayrequire resorting to extra‐corporeal oxygenationduring the procedure itself and carries with itthe added risks of anticoagulation.The main principles of anesthetic andintensive care management of patients with
Bull HK Coll Anaesthesiol Volume 14, Number 2 July 2005unilateral bullous disease include avoidance ofnitrous oxide and positive pressure ventilation,wherever possible. If positive pressureventilation cannot be avoided, it isrecommended that small tidal volumes andrapid ventilatory rates be used, so as to maintainadequate minute ventilation. The aim is to keepthe airway pressures at or below 10 cmH2O. Insome cases, high frequency jet ventilation hasbeen used. Since there are no randomizedcontrolled studies to compare the outcomesusing different ventilatory strategies in bullousdisease, it is difficult to postulate which are thesuperior methods.In patients with unilateral bullous disease,endobronchial intubation is a treatment option.The primary objective of which is to isolate andselectively eliminate ventilation to the affectedlung or lobe.The choice of technique used for lungisolation depends on factors including thenature of the pre‐existing pathology, urgency ofthe situation, anatomical considerations and theknowledge and expertise of the user. Isolationtechniques are associated with complicationssuch as trauma to the airway, malpositioningand hypoxemia. To minimize the risks ofmalpositioning, several methods are availablefor checking the positioning of the tube. Theseinclude the use of fibreoptic bronchoscopy andchest auscultation. In general, the consensus isthat for left‐sided tubes, bronchoscopy is notalways necessary. On the other hand, whenusing right sided tubes, it is recommended thatpositioning be routinely checked with the helpof a fibreoptic bronchoscope.The main problems of this patient includedthe presence of a giant bulla resulting indisparity in lung compliance between the bullaand the remaining lung tissue resulting in ‘steal’of inspired lung volumes. The consequence wasa progressive increase in minute ventilationrequirements in order to maintain arterialcarbon dioxide tensions. Ventilation of the bullanot only represented ‘wasted’ ventilation, butposed a big risk for barotrauma and suddenpneumothorax. The occurrence of this wouldsurely have further compromised his alreadyprecarious clinical status. Other factors thataffected this patient’s treatment optionsincluded: a potential difficult airway from hisprevious radiotherapy and the necessity tomaintain uninterrupted ventilation whilstsubstituting tracheal tubes.The ventilatory aims for this patient were toisolate and occlude the right upper lobe, whileallowing continued ventilation of the remainderof his right lung. Previous reports have found animprovement in ventilation/perfusion mismatch2‐3 and hence oxygenation when severelydiseased lung is isolated from ventilation, orindeed when the lungs are subjected todifferential ventilation.Besides DLT’s, other methods available toachieve lung isolation include bronchial blockerssuch as the ‘Univent’ system, Foley 4 or Fogartycatheters and simultaneous intubation with twoDLT’s. All of these methods are of courserendered more reliable by means of fiberopticendoscopic visualization and guidance 5 . This isparticularly so with the right main bronchus dueFigure 3. Close‐up of bulla 24 hours afterDouble lumen tube insertion. Noted that there isno worsening of bulla (lower limit arrowed).104
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July 2005 - The Hong Kong College of Anaesthesiologists

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