ABSTRACT
BACKGROUND: The relationship between hyperkalaemia and metabolic acidosis is well described in the critical care setting; however, the relationship between acute respiratory acidosis and plasma potassium concentration is less well understood. In a controlled model of increasing levels of hypercarbia, we tested the hypothesis of whether increasing levels of hypercarbia are associated with changes in plasma potassium concentrations. AIM: To determine whether increasing levels of hypercarbia are associated with changes in plasma potassium concentrations. METHODS: We performed a post-hoc study examining changes in serum potassium in 24 patients who received increased levels of hypercarbia during cardiac surgery. Arterial blood gases and plasma concentrations of potassium were measured at baseline, 3 min prior to, and then every 3 min for 15 min during the intervention of hypercarbia. The primary endpoint was the absolute change in serum K+ at 15 min compared to the baseline K+ value. The following secondary endpoints were evaluated: (1) The association between CO2 and serum K+ concentration; and (2) The correlation between plasma pH and serum K+ concentrations. RESULTS: During the intervention, PaCO2 increased from 43.6 mmHg (95%CI: 40.1 to 47.1) at pre-intervention to 83.9 mmHg (95%CI: 78.0 to 89.8) at 15 min after intervention; P < 0.0001. The mean (SD) serum potassium increased from 4.16 (0.35) mmol/L at baseline to 4.28 (0.33) mmol/L at 15 min (effect size 0.09 mol/L; P = 0.22). There was no significant correlation between PaCO2 and potassium (Pearson's coefficient 0.06; 95%CI: -0.09 to 0.21) or between pH and potassium (Pearson's coefficient -0.07; 95%CI: -0.22 to 0.09). CONCLUSION: Acute hypercarbia and subsequent respiratory acidaemia were not associated with hyperkalaemia in patients undergoing major surgery.
ABSTRACT
BACKGROUND: The setting of tidal volume (VT) during controlled mechanical ventilation (CMV) in critically ill patients without acute respiratory distress syndrome (ARDS) is likely important but currently unknown. We aimed to describe current CMV settings in intensive care units (ICUs) across Victoria. METHODS: We performed a multicentre, prospective, observational study. We collected clinical, ventilatory and arterial blood gas data twice daily for 7 days. We performed subgroup analysis by sex and assessment of arterial partial pressure of carbon dioxide (PaCO2) management where hypercapnia was potentially physiologically contraindicated. RESULTS: We recorded 453 observational sets in 123 patients across seven ICUs. The most commonly selected initial VT was 500 mL (33%), and this proportion did not differ according to sex (32% male, 34% female). Moreover, 38% of patients were exposed to initial VT per predicted body weight (VT-PBW) > 8.0 mL/kg. VT-PBW in this range were more likely to occur in females, those with a lower height, lower ideal body weight or in those for whom hypercapnia was potentially physiologically contraindicated. As a consequence, females were more frequently exposed to a lower PaCO2 and higher pH. CONCLUSIONS: In adults without ARDS undergoing CMV in Australian ICUs, the initial VT was a stereotypical 500 mL in one-third of participants, irrespective of sex. Moreover, around 40% of patients were exposed to an initial VT-PBW > 8.0 mL/kg. Finally, women were more likely to be exposed to a high VT and hyperventilation.
