Medical Management and Therapy of Bronchopleural Fistulas in the Mechanically Ventilated Patient: DRAINAGE SYSTEMS

10 May
2011

DRAINAGE SYSTEMS

As with the chest tube, the resistance to flow of gases is an integral consideration in the choice of the drainage system connected with the chest tube in a patient with a BPF. The size of air leak and the flow that the drainage device can accommodate are necessary considerations when choosing the drainage system. Several drainage devices are commercially available, each with different capabilities (Table 2). A recent review experimentally assessed four of the more commonly used devices: the Sentinel Seal, Thora-Klex, Pleur-Evac, and Emerson Post-Operative Pump. The maximal air flow achievable in these devices ranged from 2.3 to 35.5 L/min with —20 cm H20 vacuum. The Emerson and Pleur-Evac systems have lower resistances and can manage air flows of 35.5 L/min and 34.0 L/min, respectively. The level of suction applied to these drainage devices is also important. A level of — 20 cm H20 suction provided optimal drainage with an increase to — 40 cm H20 not significantly altering flow through the chest tube.

Ventilator Management Conventional Ventilation (CV)

A BPF in a mechanically ventilated patient presents problems in achieving adequate ventilation and oxy­genation while allowing repair of the BPF to occur.The air flow escaping through a BPF theoretically delays healing of the fistula site, and reducing flow through the fistula has been a major goal in promoting repair. The BPF provides an area of low resistance to flow and acts as a conduit for the escape of a variable percentage of the delivered tidal volume during con­ventional positive pressure mechanical ventilation. However, CV may still be possible and in some institutions the only means available.
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Table 2—Drainage Systems

Maximal Flow

(L/min) with

System

-20 cm H20


Emerson pump

35.5


Pleur-Evac A4000

34.0


Thora-Klex

19.7


Sentinel seal

2.3

Certain maneuvers while using CV in patients with BPF may maintain adequate ventilation and oxygena­tion while reducing fistula flow (Table 3). These maneuvers may be conflicting in their effects and require careful consideration and close monitoring of the patient s response. Reduction of airway pressures can reduce fistula flow and loss of effective tidal volume. Included in these steps is utilization of the lowest possible: (1) tidal volume; (2) number of me­chanical breaths per minute; (3) PEEP; and (4) inspir­atory time. Avoidance of expiratory retard will also reduce airway pressures. Allowing the greatest number of spontaneous breaths per minute, thereby reducing use of positive pressure, may be helpful. Intermittent mandatory ventilation (IMV) theoretically meets these specifications and may have an advantage over assist control ventilation in the setting of BPF.
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Table 3—Conventional Ventilation in Bronchopleural Fistulas (BPF)

• Decrease fistula flow (reduce airway pressure)
• Lowest effective tidal volume
• Least number of mechanical breaths
• Lowest PEEP and avoid expiratory retard
• Shorten inspiratory time
• Other maneuvers
• Selective intubation of unaffected lung
• Differential lung ventilation
• Patient position

A retrospective review of 39 patients with BPF maintained on CV supports a role for CV in this setting. All patients were supported by CV with appropriate ventilator adjustments providing adequate ventilation, even in the face of significant fistula leaks, with only two of the 39 patients developing severe respiratory acidosis (pH <7.30). Fistula air leak vol­ume per breath affected patient mortality and was recorded in 38 of 39 patients. All eight patients with larger maximum air leaks (>500 ml per breath) died while those with smaller maximum air leaks (<500 ml per breath) had 43 percent survival (13 of 30 patients survived). It is noteworthy that 33 of the 39 patients were maintained on assist control ventilation and six were maintained on IMV.

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