Disturbances in acid-base balance during hypophosphatemia and phosphate depletion

Clinical Outcomes in Patients with Phosphate Abnormalities After Cardiac Surgery: A Retrospective Cohort Study

BACKGROUND

The clinical significance and incidence of phosphate abnormalities in cardiac surgery have not been investigated extensively. We hypothesize that phosphate abnormalities are associated with a longer time to tracheal extubation.

METHODS

This was a single-center, retrospective cohort study in patients who underwent nontransplant cardiac surgery with cardiopulmonary bypass between August 2009 and December 2020. Serum phosphate levels were measured within 6 hours of arrival to the intensive care unit (ICU). Select clinical outcomes were extracted from an intramural database: time to tracheal extubation, hospital length of stay, and in-hospital mortality. The lactate level within 6 hours of arrival to the ICU was extracted as well.

RESULTS

A total of 2659 patients were included. There were 502 (18.9%) patients who were found to be hypophosphatemic (phosphate <2.5 mg/dL), 1905 (71.6%) had normal phosphate levels (phosphate 2.5-4.5 mg/dL), and 252 (9.5%) were hyperphosphatemic (phosphate >4.5 mg/dL). Hyperphosphatemia was associated with 26% longer time to tracheal extubation (incident rate ratio, 1.26, 95% confidence interval [CI], 10%, 44%, P = .001), 37% longer hospital length of stay (acceleration factor = 0.63, 95% CI, -43% to -30%); P < .001), and increased in-hospital mortality (odds ratio, 4.0; 95% CI, 2.3-7.1; P < .001) when compared to patients with normal phosphate levels. These associations were not found for hypophosphatemia.

CONCLUSIONS

Hyperphosphatemia in the immediate postoperative period after cardiac surgery is associated with adverse clinical outcomes. Future studies will need to investigate if actively correcting the phosphate level has an impact on clinical outcomes.

The Effects of Acid on Calcium and Phosphate Metabolism

A variety of changes in mineral metabolism aiming to restore acid-base balance occur in acid loading and metabolic acidosis. Phosphate plays a key role in defense against metabolic acidosis, both as an intracellular and extracellular buffer, as well as in the renal excretion of excess acid in the form of urinary titratable acid. The skeleton acts as an extracellular buffer in states of metabolic acidosis, as the bone matrix demineralizes, leading to bone apatite dissolution and the release of phosphate, calcium, carbonate, and citrate into the circulation. The renal handling of calcium, phosphate and citrate is also affected, with resultant hypercalciuria, hyperphosphaturia and hypocitraturia.

The Association Between Hypophosphatemia and Lactic Acidosis After Cardiac Surgery With Cardiopulmonary Bypass: A Retrospective Cohort Study

OBJECTIVES

The clinical significance of hypophosphatemia in cardiac surgery has not been investigated extensively. The aim of this study was to evaluate the association of postoperative hypophosphatemia and lactic acidosis in cardiac surgery patients at the time of intensive care unit (ICU) admission.

DESIGN

A retrospective cohort study.

SETTING

At a single academic center.

PARTICIPANTS

Patients who underwent nontransplant cardiac surgery with cardiopulmonary bypass between August 2009 and December 2020.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Serum phosphate and lactate levels were measured upon ICU admission in patients undergoing nontransplant cardiac surgery with cardiopulmonary bypass. There were 681 patients in the low-phosphate (<2.5 mg/dL) group and 2,579 patients in the normal phosphate group (2.5-4.5 mg/dL). A higher proportion of patients in the low phosphate group (26%; 179 of 681; 95% CI: 23-30) had severe lactic acidosis compared to patients in the normal phosphate group (16%; 417 of 2,579; 95% CI: 15-18). In an unadjusted logistic regression model, patients in the low phosphate group had 1.9-times the odds of having severe lactic acidosis (serum lactate ≥4.0 mmol/L) when compared to patients in the normal phosphate group (95% CI: 1.5-2.3), and still 1.4-times the odds (95% CI: 1.1-1.7) after adjusting for several possible confounders.

CONCLUSIONS

Hypophosphatemia is associated with lactic acidosis in the immediate postoperative period in cardiac surgery patients. Future studies will need to investigate it as a potential treatment target for lactic acidosis.

Genotype and phenotypic spectrum of vitamin D dependent rickets type 1A: our experience and systematic review

BACKGROUND

Vitamin D dependent rickets type 1 (VDDR1) is a rare disease due to pathogenic variants in 1-α hydroxylase gene. We describe our experience with systematic review of world literature to describe phenotype and genotype.

METHODS

Seven patients from six unrelated families with genetically proven VDDR1 from our cohort and 165 probands from systematic review were analyzed retrospectively. The clinical features, biochemistry, genetics, management, and long-term outcome were retrieved.

RESULTS

In our cohort, the median age at presentation and diagnosis was 11(4-18) and 40(30-240) months. The delayed diagnoses were due to misdiagnoses as renal tubular acidosis and hypophosphatemic rickets. Four had hypocalcemic seizures in infancy whereas all had rickets by 2 years. All patients had biochemical response to calcitriol, however two patients diagnosed post-puberty had persistent deformity. Genetic analysis revealed two novel (p.Met260Arg, p.Arg453Leu) and a recurring variant (p.Phe443Profs*24). Systematic review showed that seizures as most common presentation in infancy, whereas delayed motor milestones and deformities after infancy. Diagnosis was delayed in 27 patients. Patients with unsatisfactory response despite compliance were >12 years at treatment initiation. Inappropriately normal 1,25(OH)2D may be present, however suppressed ratio of 1,25(OH)2 D/25(OH)D may provide a clue to diagnosis. Various region specific and hot-spot recurrent variants are described. Patients with truncating variants had higher daily calcitriol requirement and greatly suppressed ratio of 1,25(OH)2D/25(OH)D.

CONCLUSION

Delayed diagnosis may lead to permanent short stature and deformities. Truncating variants tend to have severe disease as compared to non-truncating variants. Diagnostic accuracy of 1,25(OH)2 D/25(OH)D ratio needs further validation.

The clinical biochemistry of anorexia nervosa

In anorexia nervosa, under-nutrition and weight regulatory behaviours such as vomiting and laxative abuse can lead to a range of biochemical problems. Hypokalaemia is the most common electrolyte abnormality. Metabolic alkalosis occurs in patients who vomit or abuse diuretics and acidosis in those misusing laxatives. Hyponatraemia is often due to excessive water ingestion, but may also occur in chronic energy deprivation or diuretic misuse. Urea and creatinine are generally low and normal concentrations may mask dehydration or renal dysfunction. Abnormalities of liver enzymes are predominantly characterized by elevation of aminotransferases, which may occur before or during refeeding. The serum albumin is usually normal, even in severely malnourished patients. Amenorrhoea is due to hypogonadotrophic hypogonadism. Reduced concentrations of free T4 and free T3 are frequently reported and T4 is preferentially converted to reverse T3. Cortisol is elevated but the response to adrenocorticotrophic hormone is normal. Hypoglycaemia is common. Hypercholesterolaemia is a common finding but its significance for cardiovascular risk is uncertain. A number of micronutrient deficiencies can occur. Other abnormalities include hyperamylasaemia, hypercarotenaemia and elevated creatine kinase. There is an increased prevalence of eating disorders in type 1 diabetes and the intentional omission of insulin is associated with impaired metabolic control. Refeeding may produce electrolyte abnormalities, hyper- and hypoglycaemia, acute thiamin depletion and fluid balance disturbance; careful biochemical monitoring and thiamin replacement are therefore essential during refeeding. Future research should address the management of electrolyte problems, the role of leptin and micronutrients, and the possible use of biochemical markers in risk stratification.

The consequences of negative energy balance in anorexia syndrome

STUDY OBJECTIVE

Using four cases, this study describes common etiological factors and clinical sequelae in anorexia nervosa and athletic anorexia to present a biological explanation for interactions.

DESIGN

Four anorectic girls were interviewed regarding their training programs and dietary intake. Bone mineral content, hormonal status, and energy intake were assessed during follow-ups.

RESULTS

All the girls began training before puberty and had a low energy intake for age and height. Amenorrhea, low bone mineral content with stress fractures in three cases, and growth retardation in one case, were present at the follow-up after 6 years. Low amount of body fat and high serum cortisol is indicated and included in the discussion. The etiology is presented in an integrated model in addition to a biological explanation based on a negative energy balance, an acidic condition.

CONCLUSION

Energy deficits during puberty can result in the clinical sequela of the anorexia syndrome.

The significance of routine laboratory analyses in the assessment of teenage girls with eating disorders and weight loss

Routine laboratory investigations that had been performed at disease assessment on 327 teenage girls with eating disorders and weight loss were analyzed. The laboratory investigations included erythrocyte sedimentation rate (ESR), blood haemoglobin concentration (Hb), white blood cell count (WBC), platelet count, serum alkaline phosphatase (ALP) activity, serum aspartate aminotransferase (ASAT) activity, serum alanine aminotransferase (ALAT) activity, serum albumin concentration, glycated haemoglobin (HbA1c) and serum concentrations of sodium, potassium, magnesium, calcium (corrected for albumin), inorganic phosphate, creatinine and urea. The results were for ESR, Hb, WBC, platelet count, ALP, ASAT, ALAT, inorganic phosphate, creatinine, urea and HBA1C related to weight and (ongoing) weight loss. The variations of the biochemical measurements were, however, largely within reference ranges, weight and weight changes predicted the biochemical measurements only to a small degree and in individual patients the results of the analyses often suggested normality. These analyses may therefore not be suited to assess the degree of weight loss and starvation in eating disorders. They may, however, be useful for the exclusion of other diseases which could show weight loss and biochemical abnormalities.

Role of alcohol in clinical nephrology

Different nephrological derangements are observed in severe alcoholics. Until now the direct toxicity of ethanol is only shown in the fetal alcohol syndrome with various malformations of the genitourinary tract. In the adult the kidney is often involved in the development, maintenance and counterregulation of complex electrolyte disturbances like phosphate and potassium hypoglycemia etc. The alcohol associated retention of urate, induced by hyperlactatemia and/or increased beta-hydroxybutyrate concentration is only rarely complicated by urate nephropathy. Alcohol intoxication (acute and chronic) predisposes to rhabdomyolysis with the risk of acute renal failure. There are some hints that chronic alcoholism with myopathy increases the vulnerability of the kidney for further toxic agents. In rats glycerol induced renal failure is enhanced by alcohol pretreatment. Finally, regular alcohol consumption raises the blood pressure, which per se is a risk factor for renal damage.

[Phosphate-depletion (author's transl)]

The essential and critical role of inorganic phosphate has been known in veterinary medicine and experimental research on animals for decades. However, only recently has the phosphate depletion syndrome found widespread attention by clinicians. Hypophosphatemia is usually observed in the following clinical situations:chronic alcoholism, recovery phase of diabetic ketoacidosis, administration of phosphate-free solutions in parenteral nutrition, severe respiratory alkalosis, and infusion of fructose. Disturbed organ function in hypophosphatemia is the result of a depletion of inorganic phosphate in the cytoplasm of somatic cells. Such phosphate depletion may be due to either of the following mechanisms or a combination of both. (1) Negative external phosphate balance resulting from phosphate loss in urine or feces or (2) translocation of phosphate from the extracellular into the intracellular space with or without concomitant negative external phosphate balance. In principle, phosphate depletion interferes with the function of all somatic cells. In acute phosphate depletion, the clinically most important disturbances are observed in striated muscle (rhabdomyolysis with myoglobinuric acute renal failure), heart muscle (acute heart failure), and hematological systems (hemolysis, disturbed leukocyte and thrombocyte functions). In contrast, in chronic phosphate depletion skeletal abnormalities (osteomalacia) predominate. Organ disturbances are thought to result from diminished synthesis of ATP and other organic phosphate esters and/or from hypoxia secondary to changes in erythrocyte 2,3-DPG.