There is no easy recipe for fluid replacement in this situation. Most patients have elevated aldosterone and anti-diuretic hormone which reduce urinary output as part of the physiological response to the stress of injury. However, a pneumonectomy patient will have lost approximately one third of his "capacitance" vessels and his ability to tolerate excess fluid will be brittle.

Two patterns of iatrogenic injury to patients in the post lung resection setting are:

1. 1.Knee jerk prescription of diuretics producing renal injury both by reducing circulating volume and by a direct toxic effect on the kidneys causing renal failure or underperfusion of other vital organs.
   

2. 2.Pulmonary oedema produced by trying to induce a diuresis by infusing large volumes of intravenous fluid. A fluid challenge of about 250 mls (and no more than 500mls) of 5% Dextrose is a safe and reliable way of assessing fluid balance in the oliguric patient.
   

While the patient may produce gratifyingly increased urine outputs after diuretics or excess fluid boluses they may in fact lead to a more critical clinical situation as patients rarely survive either renal failure or pulmonary oedema following lung resection. Fluid challenges and diuretics should only be used judiciously after careful analysis of the clinical situation. Treat the patient, not the urinary output chart!

Note: that the combination of hypotension, hypoxia, fluid restriction, diuretics and NSAID’s is a potent recipe for renal failure.

The increased use of epidural analgesia has exacerbated this situation due to the vasodilatation and hypotension which accompany this form of analgesia. Inotropes may need to be considered rather than repeated boluses of fluid.

If there is any doubt as to the fluid balance a urinary catheter must be passed and hourly readings taken. Central pressure monitoring lines may be inaccurate due to a large pneumonectomy space which generally has a negative pressure. Daily U&E are mandatory. Daily weight is a good indicator of total body fluid changes.