Observational Study to Assess pH and Hypoxia During Haemodialysis

Alkalosis may explain multiple complications of HD treatment, most notably hypoxemia. Despite a strong rationale for these mechanisms, current consensus suggests ischaemia as the predominant catalyst for hypoxia with HD. However, few studies have characterised pH changes during HD with many using serum bicarbonate as a proxy of pH status. Nevertheless, these studies predominantly indicate acute alkalosis occurrence with HD. Despite these findings, few HD units individualise their bicarbonate prescription or assess pH prior to treatment. Of 554 dialysis facilities worldwide, 49% did not individualise bicarbonate prescriptions. Non-individualised bicarbonate prescription risks sub-therapeutic serum bicarbonate levels and sub-clinical hypoxemia during HD. Assumption of acidosis and consistent baseline pH prior to each HD session may further risk acute alkalosis with HD. Indeed, a normal pH was identified in 26 ESRD patients on commencing HD whilst prescribed dialysate bicarbonate of 32 mmol/L (7.38 ± 0.06) or 26 mmol/L (7.35 ± 0.06). However, pH increased throughout HD with acute alkalosis within the 32 mmol/L group (7.48 ± 0.05). These data, suggest individualised assessment of pH prior to HD could mitigate alkalosis and subsequent hypoxemia. However, small cohorts, limited studies of pH changes over consecutive HD treatments, and few studies of links between hypoxemia and pH limit current understanding. This study therefore aims to explore pH changes and occurrence of hypoxia with HD.

Adult patients (18+) will be recruited irrespective of age, gender, or ethnicity. Due to the observational nature of the study, no personal benefits will be expressed to the patient. Signed consent will be attained from a patient after a minimum of 24hrs has been provided on receipt of the participation information sheet. Any questions will be clearly answered prior to obtaining consent from the patient. Only patients who have full capacity to give consent and full understanding of the purpose and procedures of the study will be recruited.

There is no foreseen risk to the patient from the study. All blood samples are attained via arterial-venous catheter which is inserted prior to treatment as part of the patient's routine haemodialysis. In the small subset of patients who have their cardiac output assessed, the use of four small non-invasive sensors poses no additional discomfort, risk or restriction throughout routine haemodialysis treatment. In a previous project using the noninvasive cardiac output monitor (NICOM), no patient expressed any discomfort whilst using the device during haemodialysis.

All patients involved in the project will be anonymised with a study number for data collection purposes. No identifiable information will be used during post-hoc analysis. Signed consent forms or any other identifiable data will be securely logged within the study site file and secured within the renal research office. Only the chief investigator and renal research nurses will be aware of patient involvement in the study. Access to identifiable data will be strictly limited to the chief investigator.

There is no conflict of interest from the chief investigator or other members of the research team that may influence the study. After completion of the study, data will be compiled and drafted for scientific publication with all data securely archived within the study site file at the renal research department. Any patient expressing interest in the study findings will be provided with the appropriate information verbally or by a written summary of findings.