Effects of acute hypercapnia and hypocapnia on plasma and red cell potassium, blood lactate and base excess in man during anesthesia

No change in plasma potassium concentration during 10 minutes of apnoea: An observational study on potential organ donors

BACKGROUND

Acute acidosis can increase the plasma potassium concentration. However, data on the effects of acute respiratory acidosis on plasma potassium concentration are conflicting. This study aimed to determine whether acute respiratory acidosis induces an immediate increase in plasma potassium concentration.

METHODS

This observational study was conducted on participants undergoing apnoea testing prior to final radiological examination, registered in an internal quality registry at Oslo University Hospital between 25 April 2013 and 1 May 2020. A total of 124 donors were assessed for inclusion. Sixteen donors with blood glucose concentrations exceeding 10 mmol L^-1 were excluded; finally, data from 108 donors were included in the study. The apnoea test, which is a standard neurological test performed in potential organ donors prior to radiological confirmation of ceased brain circulation, induces respiratory acidosis. The arterial plasma potassium concentration, pH and PaCO₂ before and after the apnoea test were compared. Statistical analysis was conducted using the paired t test.

RESULTS

The pre-apnoea and post-apnoea mean plasma potassium concentrations were 3.79 (95% confidence intervals [CI] 3.70-3.87) and 3.79 mmol L^-1 (95% CI 3.70-3.88), respectively. The mean difference was -0.002 mmol L^-1 (95% CI -0.04 to 0.04); the difference was not significant. The pre-apnoea and post-apnoea mean pH were 7.39 and 7.21, respectively, and the mean difference was 0.175 (P < .01). The pre-apnoea and post-apnoea mean PaCO₂ were 5.66 and 9.48 kPa, respectively, and the mean difference was -3.83 (P < .01).

CONCLUSIONS

Acute respiratory acidosis does not lead to rapid changes in plasma potassium concentration during apnoea testing in potential organ donors.

The association of acute hypercarbia and plasma potassium concentration during laparoscopic surgery: a retrospective observational study

BACKGROUND

It is uncertain whether increases in PaCO₂ during surgery lead to an increase in plasma potassium concentration and, if so, by how much. Hyperkalaemia may result in cardiac arrhythmias, muscle weakness or paralysis. The key objectives were to determine whether increases in PaCO₂ during laparoscopic surgery induce increases in plasma potassium concentrations and, if so, to determine the magnitude of such changes.

METHODS

A retrospective observational study of adult patients undergoing laparoscopic abdominal surgery was perfomed. The independent association between increases in PaCO₂ and changes in plasma potassium concentration was assessed by performing arterial blood gases within 15 min of induction of anaesthesia and within 15 min of completion of surgery.

RESULTS

289 patients were studied (mean age of 63.2 years; 176 [60.9%] male, and mean body mass index of 29.3 kg/m²). At the completion of the surgery, PaCO₂ had increased by 5.18 mmHg (95% CI 4.27 mmHg to 6.09 mmHg) compared to baseline values (P < 0.001) with an associated increase in potassium concentration of 0.25 mmol/L (95% CI 0.20 mmol/L to 0.31 mmol/L, P < 0.001). On multiple regression analysis, PaCO₂ changes significantly predicted immediate changes in plasma potassium concentration and could account for 33.1% of the variance (r² = 0.331, f(3,259) = 38.915, P < 0.001). For each 10 mmHg increment of PaCO₂ the plasma potassium concentration increased by 0.18 mmol/L.

CONCLUSION

In patients receiving laparoscopic abdominal surgery, there is an increase in PaCO₂ at the end of surgery, which is independently associated with an increase in plasma potassium concentration. However, this effect is small and is mostly influenced by intravenous fluid therapy (Plasma-Lyte 148 solution) and the presence of diabetes. Trial registration Retrospectively registered in the Australian New Zealand Clinical Trials Registry (Trial Number: ACTRN12619000716167).

Randomised controlled trial to investigate the relationship between mild hypercapnia and cerebral oxygen saturation in patients undergoing major surgery

OBJECTIVES

The effects of hypercapnia on regional cerebral oxygen saturation (rSO₂) during surgery are unclear. We conducted a randomised controlled trial to investigate the relationship between mild hypercapnia and rSO₂. We hypothesised that, compared with targeted normocapnia (TN), targeted mild hypercapnia (TMH) during major surgery would increase rSO₂.

DESIGN

A prospective, randomised, controlled trial in adult participants undergoing elective major surgery.

SETTING

A single tertiary centre in Heidelberg, Victoria, Australia.

PARTICIPANTS

40 participants were randomised to either a TMH or TN group (20 to each).

INTERVENTIONS

TMH (partial pressure of carbon dioxide in arterial blood, PaCO₂, 45-55 mm Hg) or TN (PaCO₂ 35-40 mm Hg) was delivered via controlled ventilation throughout surgery.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary endpoint was the absolute difference between the two groups in percentage change in rSO₂ from baseline to completion of surgery. Secondary endpoints included intraoperative pH, bicarbonate concentration, base excess, serum potassium concentration, incidence of postoperative delirium and length of stay (LOS) in hospital.

RESULTS

The absolute difference between the two groups in percentage change in rSO₂ from the baseline to the completion of surgery was 19.0% higher in both hemispheres with TMH (p<0.001). On both sides, the percentage change in rSO₂ was greater in the TMH group than the TN group throughout the duration of surgery. The difference between the groups became more noticeable over time. Furthermore, postoperative delirium was higher in the TN group (risk difference 0.3, 95% CI 0.1 to 0.5, p=0.02). LOS was similar between groups (5 days vs 5 days; p=0.99).

CONCLUSION

TMH was associated with a stable increase in rSO₂ from the baseline, while TN was associated with a decrease in rSO₂ in both hemispheres in patients undergoing major surgery. This resulted in a clear separation of percentage change in rSO₂ from the baseline between TMH and TN over time. Our findings provide the rationale for larger studies on TMH during surgery.

TRIAL REGISTRATION NUMBER

The Australian New Zealand Clinical Trials Registry (ACTRN12616000320459).

Relationship between acute hypercarbia and hyperkalaemia during surgery

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.

Plasma potassium response to acute respiratory alkalosis

Acute respiratory alkalosis (hyperventilation) occurs in clinical settings associated with electrolyte-induced complications such as cardiac arrhythmias (such as myocardial infarction, sepsis, hypoxemia, cocaine abuse). To evaluate the direction, magnitude and mechanisms of plasma potassium changes, acute respiratory alkalosis was induced by voluntary hyperventilation for 20 (18 and 36 liter/min) and 35 minutes (18 liter/min). The plasma potassium response to acute respiratory alkalosis was compared to time control, isocapnic and isobicarbonatemic (hypocapnic) hyperventilation as well as beta- and alpha-adrenergic receptor blockade by timolol and phentolamine. Hypocapnic hypobicarbonatemic hyperventilation (standard acute respiratory alkalosis) at 18 or 36 liter/min (delta PCO2-16 and -22.5 mm Hg, respectively) resulted in significant increases in plasma potassium (ca + 0.3 mmol/liter) and catecholamine concentrations. During recovery (post-hyperventilation), a ventilation-rate-dependent hypokalemic overshoot was observed. Alpha-adrenoreceptor blockade obliterated, and beta-adrenoreceptor blockade enhanced the hyperkalemic response. The hyperkalemic response was prevented under isocapnic and isobicarbonatemic hypocapnic hyperventilation. During these conditions, plasma catecholamine concentrations did not change. In conclusion, acute respiratory alkalosis results in a clinically significant increase in plasma potassium. The hyperkalemic response is mediated by enhanced alpha-adrenergic activity and counterregulated partly by beta-adrenergic stimulation. The increased catecholamine concentrations are accounted for by the decrease in plasma bicarbonate.

Potassium and anaesthesia

Potassium is the principle intracellular ion, and its concentration and gradients greatly influence the electrical activity of excitable membranes. Because anaesthesia is so intimately involved with electrically active cells, potassium concentrations in surgical patients have received considerable attention in diagnostic and therapeutic applications. With the ongoing evolution in the indications for potassium, it is important to review the role of potassium in cellular activity, in storage and regulation, in diseases that alter potassium homeostasis, and in the therapeutic implications of perioperative alterations of potassium concentration. A rational approach to abnormal potassium values and the use of potassium in the operating room is sought, based on a physiological understanding of risks and benefits.