Hemodynamic measurements with a pulmonary artery catheter are likely to be useful for excluding nonseptic causes of shock. Unlike in hypovolemic shock, cardiac output during septic shock is more likely to be normal or increased and peripheral resistance decreased. The ECG may show nonspecific ST-T wave abnormalities and supraventricular and ventricular arrhythmias, in part related to hypotension. Urinalysis may disclose that the urinary tract is the source of infection, particularly in patients who have indwelling catheters. Respiratory alkalosis, with a low PCO 2 and increased arterial pH, is present early and compensates for lactic acidemia.
Serum bicarbonate is usually low, and serum and blood lactate are increased.
As shock progresses, metabolic acidosis supervenes. The ECG may show depressed ST segments with T-wave inversions and occasionally atrial and ventricular arrhythmias. The BUN and creatinine concentrations usually increase progressively as a result of renal failure with decreased creatinine clearance. Poor results often follow failure to institute therapy soon enough. Once severe lactic acidosis with decompensated metabolic acidosis becomes established, especially in conjunction with multiorgan failure, septic shock is likely to be irreversible despite therapy.