Effects of atrial natriuretic peptide (99-126) in chronic renal disease in man.

Plasma concentrations of human atrial natriuretic peptide (99-126) are elevated in patients with end-stage chronic renal failure and on haemodialysis. Plasma atrial natriuretic peptide (ANP) concentrations change with extracellular fluid volume, suggesting that ANP continues to have a role in chronic renal failure. We have studied the effects of an infusion (5 pmol/kg per min) in subjects with chronic renal failure (CCr) less than 30 ml/min per 1.73 m2). Glomerular filtration rate and effective renal plasma flow increased by 23% (P less than 0.01) and 27% (P less than 0.01) respectively and sodium excretion more than doubled. Systolic and diastolic blood pressures decreased by 14 (SD 1.6) and 6 (SD 0.8) mmHg respectively (P less than 0.001), and plasma renin activity declined (P less than 0.01). Plasma ANP concentrations were elevated compared to normal subjects and reached a peak of 224 (SD 87) pmol/l at the end of the infusion. Plasma half-life was 4.8 (SD 2.7) min. Plasma concentrations are elevated in chronic renal failure and ANP may play a physiological role in controlling extracellular fluid volume and blood pressure.

Does intermittent mandatory ventilation correct respiratory alkalosis in patients receiving assisted mechanical ventilation?

One of the claimed advantages of intermittent mandatory ventilation (IMV) over assisted mechanical ventilation (AMV) (assist-control) is the avoidance or correction of acute respiratory alkalosis, ostensibly by allowing patients to achieve normal alveolar ventilation (VA) and PaCO2 through the function of an intact ventilatory drive. However, although respiratory alkalosis in patients being hyperventilated with controlled mechanical ventilation (CMV) can be corrected by a change to IMV, CMV is seldom appropriate for patients with acute respiratory failure, and whether IMV affects respiratory alkalosis in patients triggering the ventilator in the AMV mode has not previously been tested. We studied 26 patients with acute respiratory alkalosis (pH greater than or equal to 7.48) while receiving AMV. Measurements of arterial blood gases and CO2 production (VCO2), and calculation of VA, were performed after 30 min of AMV, repeated after 30 min of IMV at a mandatory rate one half the previous AMV rate, and then repeated again 30 min after a return to the original AMV settings. Mean arterial pH decreased slightly from 7.51 during AMV to 7.48 during IMV, and returned to 7.51 on resumption of AMV (p less than 0.05 for both changes); corresponding mean values for PaCO2 were 28.6, 29.7, and 27.5 mmHg, respectively. These changes were related to an increase in VCO2 during IMV as compared with AMV (p less than 0.05), without a significant alteration in VA. When the mandatory rate was further reduced during IMV from one half to one fourth the prior, triggered AMV rate in 10 patients, no additional reduction in pH occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

A practical procedure for measuring functional residual capacity during mechanical ventilation with or without PEEP.

The measurement of functional residual capacity (FRC) in patients receiving mechanical ventilation may provide valuable data in the assessment and management of acute respiratory failure. Previous descriptions of apparatus and techniques for FRC measurement have either been inapplicable to patients receiving positive end-expiratory pressure (PEEP), or insufficiently detailed to allow convenient duplication in the clinical setting. The authors describe a helium rebreathing method for bedside determination of FRC which can be performed during ventilation with PEEP and which is applicable in patients with prolonged equilibration times. The method is both reproducible in patients (variation from mean FRC: +/- 2.2%) and accurate (coefficient of variation from in vitro FRC of 3000 ml: +/- 1.7%). The apparatus and assembly are described in detail and require only components which are readily available commercially, so that they may be applicable to clinical use in a general hospital.