Evaluation of two methods to calculate p50 from a single blood sample.

BACKGROUND: The hemoglobin-oxygen affinity is conveniently described as the oxygen tension at which the hemoglobin is 50% saturated (p50). We compared two methods of single-point analysis for p50 calculation, using clinical data. METHODS: From patients submitted to anesthesia for major surgery, 114 arterial or venous blood samples were analyzed by using the Sigaard-Andersen oxygen status algorithm (p50OSA) and Doyle's method (p50Doyle) based on Hill's equation. RESULTS: The oxygen saturation and tension varied respectively between 0.64-0.96 and 3.8 kPa-11.0 kPa. A Bland-Altman analysis showed a mean difference of 0.04 kPa (SD 0.12 kPa). The limits of agreement were -0.20 kPa and +0.28 kPa. CONCLUSIONS: The Siggaard-Andersen oxygen status algorithm is presently the most clinically useful single-point method of p50 calculation.

Effect of acid-base management with or without carbon dioxide on plasma phosphate concentration during and after hypothermic cardiopulmonary bypass.

Variations of the phosphate concentration in plasma were studied in two groups of 12 patients undergoing cardiac surgery with hypothermic cardiopulmonary bypass (CPB). Management of the acid-base status differed between the groups, according to whether or not carbon dioxide was added to the anesthetic gas mixture during hypothermia ('pH-stat' vs. 'alpha-stat' mode) following correction vs. no correction of pCO2 and pH for body temperature. Phosphate variations throughout the study were mostly within normal limits. From the start to the end of CPB, the mean rise in phosphate levels was 70% in the pH-stat group and 37% in the alpha-stat group (p < 0.001). During 3 hours after CPB, the phosphate values continued to rise by a mean of 25% in the alpha-stat patients, but fell by a mean of 3% in the pH-stat patients (p < 0.001). Such different phosphate patterns during and immediately after CPB may reflect profound metabolic disturbances and may be related to the altering effects of CO2 addition and respiratory acidosis on intracellular metabolic activity and phosphate homeostasis.

Effects of erythrocytes, bicarbonate, temperature and albumin on in vitro ionized calcium variations with pH.

Using a heart lung machine as an in vitro model, the relation between ionized calcium (cCa2+) and pH has been shown to depend on several variables such as erythrocytes, temperature and albumin as well as the total calcium and bicarbonate concentrations. The respiratory acid-base disturbances were simulated by changing the gas flow between 1.0 and 2.41 min-1 by adding CO2, to the machine at a concentration of 0 to 17%. When pCO2 was used to alter pH, cCa2+ varied from 0.16 mmol l-1 per pH unit to 0.52 mmol l-1. The regression slope of cCa2+ on pH was made steeper by decreasing erythrocyte volume fraction and by increasing temperature and the concentrations of HCO3, calcium or albumin. The metabolic acid-base alterations were produced by HCl or NaHCO3 at a constant gas flow, cCA2+ changes per pH unit were 0.70 mmol l-1 in plasma and 1.04 mmol l-1 in whole blood. The different results found in plasma and in erythrocyte fluids may be explained by their different buffering capacity. Haemoglobin may buffer hydrogen ions, and the formation of HCO3- is catalysed by carbonic anhydrase from the red cells.

Calcium and other biochemical alterations induced by masseter spasm following suxamethonium.

Calcium and other biochemical disturbances are reported from the plasma of a child which presented masseter spasm following the administration of suxamethonium during the induction of halothane anesthesia. After masseter spasm, the ionized calcium concentration decreased whereas the total calcium level remained unchanged despite the occurrence of metabolic and respiratory acidosis. Throughout the rest of anesthesia, the total and ionized calcium concentrations continued to decrease. These variations may indicate that complex metabolic and biochemical events influenced the calcium binding to albumin and the calcium transfer into the muscle cells.

Effect of magnesium gradient concentration between plasma and dialysate on magnesium variations induced by hemodialysis.

The magnesium gradient concentration between plasma and dialysate was found to be the main factor responsible for the magnesium decrease induced by hemodialysis with a high-flux membrane using a dialysate magnesium concentration of 0.76 mmol.l-1. The changes in magnesium were negatively correlated to the predialysate magnesium concentration difference between plasma and dialysate. The magnesium changes tended to be less pronounced in the presence of an intradialysate protein increase greater than 9.6 g.l-1, reflecting loss of plasma water by ultrafiltration.

Calcium, magnesium and phosphate during and after hypothermic cardiopulmonary bypass without temperature correction of acid base status.

The plasma concentration variations of calcium, magnesium and phosphate were studied in ten patients during and after hypothermic cardiopulmonary bypass (CPB) without temperature correction of acid base status. During the study, pH remained stable, but all the other studied components varied significantly (P less than 0.001). At the start of CPB, the mean ionized calcium concentration increased 25%, and magnesium and phosphate decreased 29% and 40%, respectively, from their control values. At the end of blood cooling, ionized calcium was still 11% above its initial value, magnesium 50% above, and phosphate 39% below. Before weaning from CPB, ionized calcium remained 10% above its initial level, magnesium 41% above, and phosphate 26% below. After CPB, the different divalent ions returned to their initial levels within 1 h for ionized calcium, 6 h for phosphate and 9 h for magnesium. One day post-CPB, ionized calcium was at its start level, magnesium 13% lower, and phosphate 36% higher. During cardiac surgery, the acid base regulation without temperature correction (so-called "alpha stat mode") avoided the appearance of carbon dioxide acidosis. There were widespread disturbances of the divalent ions concentrations, due principally to the different fluids used during CPB, pump priming fluids and cardioplegic solution.

Laryngospasm-induced pulmonary oedema.

A case of pulmonary oedema following laryngospasm in a healthy young woman is reported. Laryngospasm occurred following surgery and was treated with positive pressure oxygen ventilation by mask and by deepening of the level of anaesthesia. The rest of anaesthesia was uneventful. During the following hour, spontaneous respiration deteriorated progressively and ended in manifest pulmonary oedema which was treated by endotracheal intubation and mechanical ventilation with PEEP for some hours.

In vivo and in vitro ionized calcium variations induced by acute respiratory acid base disturbances.

The effects of acute respiratory acid base changes on the ionized calcium concentration were studied in mechanically ventilated patients and compared to the results which were found using an in vitro model. In both in vivo and in vitro studies, the ionized calcium changes correlated negatively with the pH variations. The good agreement between the in vivo and in vitro investigations showed a mean ionized calcium change of 0.40 mmol/l per pH unit. At the same time, the ionized calcium changes correlated positively with the changes of plasma bicarbonate. The mean ionized calcium change was 0.01 mmol/l per mmol/l bicarbonate variation. During respiratory acid base disturbances, the ionized calcium variations due to the competitive albumin binding between hydrogen and calcium ions are buffered and blunted by the bicarbonate ions.

Marked hypocalcemia in a fatal poisoning with chlorinated phenoxy acid derivatives.

A fatal poisoning with a herbicide which contains chlorinated phenoxy acid derivatives is reported with a special attention to the profound disturbances in calcium homeostasis related to an acute renal failure with hyperphosphatemia.

Ionized and total calcium variations induced by haemodialysis.

The variations of ionized and total calcium concentrations were studied during haemodialysis with high flux membrane using dialysate calcium concentrations of 1.63 and 1.76 mmol/l. The changes in ionized and total calcium were related to the predialytic calcium concentration difference between plasma and dialysate. The calcium changes were not influenced by the intradialytic pH variations. But the total calcium level increased more with the higher albumin concentration. Compared with previous studies, the calcium gradient concentration between plasma and dialysate was found to be the main factor responsible for the calcium variations observed during haemodialysis with high flux membrane.

Plasma ionized calcium during paediatric anaesthesia: effects of pH and succinylcholine.

Variations of plasma ionized calcium and pH were studied in 16 children anaesthetized with halothane and succinylcholine for minor surgery. During anaesthesia, a close negative correlation was noted between pH and ionized calcium. Intubation was followed by a fall of the ionized calcium concentration. A mean decrease of 0.04 mmol X L-1 was noted, without pH change. The acute elevation of carbon dioxide following extubation allowed the in vivo effects of pH on ionized calcium to be studied. For each pH unit decrease, a mean rise of 0.60 mmol X L-1 of ionized calcium was found. During the study, no significant variations of plasma total calcium concentration were observed. The variations in the hydrogen ion concentration and the administration of succinylcholine were accompanied by changes of the free calcium ion concentration, due probably to alterations in calcium binding to proteins, and perhaps to the formation of a calcium complex with anions. Our results emphasize the importance of knowledge of the pH for the interpretation of ionized calcium variations in the presence of acid-base disturbances.

The effects of plasma volume variations on the calcium concentration during epidural anaesthesia.

The plasma variations of the ionized and total calcium concentration in relation to protein concentration and plasma volume were studied in 12 patients during epidural anaesthesia for transurethral prostatectomy. The most significant changes were noted during the onset of anaesthesia. From arrival in the operating theatre to start of operation, the plasma concentration of ionized calcium decreased from 1.28 (s.d. = 0.05) mmol/l to 1.22 (s.d. = 0.04) mmol/l and total calcium decreased from 2.39 (s.d. = 0.11) mmol/l to 2.17 (s.d. = 0.10) mmol/l. At the same time, however, the decrease in ionized calcium concentration and the increase in plasma volume were associated with a rise of 10.3% in the pool of free calcium ion in plasma. After the start of surgery, the plasma ionized calcium concentration remained almost unaffected throughout the rest of the study period. The total plasma calcium concentration as well as the total protein concentration remained stable during operation, only increasing after the end of surgery. The preoperative changes in the plasma calcium concentration may have been the result of both haemodilution and mobilization of calcium ions from its bone stores. Postoperatively, an increased urinary loss of calcium must have followed the administration of furosemide at the end of surgery.

[Carpopedal spasm during anesthesia with halothane: malignant hyperthermia or tetany?]. / Spasme carpopédal au cours d'une anesthésie à l'halothane: hyperthermie maligne ou tétanie?

A case of probable crisis of malignant hyperthermia triggered by halothane is reported. The diagnosis was rapidly suspected; it evolved rapidly after the start of the specific treatment of malignant hyperthermia and the injection of calcium and thiopentone. The diagnosis and the role of calcium and thiopentone are discussed.

Plasma magnesium during epidural anaesthesia. A study in patients undergoing transurethral prostatectomy.

The variations of plasma magnesium concentration in relation to protein concentration and plasma volume were studied in 12 patients during epidural anaesthesia for transurethral prostatectomy. The most significant changes in plasma magnesium concentration were observed during the onset of anaesthesia. From the arrival in the operating theatre to the start of operation, the concentration of plasma magnesium decreased from 0.88 (SD 0.10) mmol/l to 0.82 (SD 0.10) mmol/l. At the same time, the increase of 16 per cent in plasma volume was associated with a rise of 8.4 per cent in the total amount of magnesium in plasma. After commencement of surgery, the plasma magnesium concentration was unchanged throughout the remainder of the study period. The total plasma protein concentration and the erythrocyte volume fraction decreased during the onset of anaesthesia, remained stable during surgery and returned to initial values one hour postoperatively. The pre-operative changes in the plasma magnesium concentration may have been the result of haemodilution and mobilisation of magnesium ion from its bone stores. Postoperatively, an increased urinary loss of magnesium must have followed the injection of frusemide at the end of surgery. The consequences of these variations in plasma magnesium concentration are unlikely to be of clinical significance, except in patients with pre-existing subclinical magnesium deficiency.

Patterns of ionized and total calcium in serum of children following suxamethonium.

Serum ionized and total calcium levels of forty children, aged 3 to 18 years, were studied before and after the administration of suxamethonium during halothane inhalation in 20 children under the age of 10 (group I) and 10 children over the age of 10 (group II), and during intravenous induction of anesthesia with pancuronium and thiopentone in 10 children over the age of 10 (group III). In all groups suxamethonium was followed by a small but significant (p less than 0.02) decrease in the serum ionized calcium concentration. The fall was greater in group I. The serum total calcium concentration was lowered in groups II and III. But the decrease was only significant (p less than 0.001) in group III. In group I, there was a great discrepancy in the changes in serum total calcium concentration ranging from a fall of 0.535 mmol.l-1 to a rise of 0.680 mmol.l-1. The decrease in the total calcium concentration may have been caused by the depolarizing action of suxamethonium leading to the migration of the calcium ions into the muscle cells. But the changes in the ionized calcium concentration are more complex and may involve the movements of this ion in the cells, its binding to the proteins and its complexion to anions.

[Changes in temperature during transurethral resection of the prostate under peridural anesthesia]. / Variations des températures au cours de la résection transurétrale de la prostate sous anesthésie péridurale.

Superficial and central body temperatures were measured during anaesthesia and recovery in eleven elderly patients undergoing transurethral resection under epidural anaesthesia. A significant decrease in central body temperature as measured on the tympanic membrane was found during surgery. After a significant increase during induction of anaesthesia, mean skin temperature remained stable throughout surgery. Mean body temperature calculated from central body temperature and mean skin temperature decreased significantly during surgery. During recovery, all temperatures increased significantly. But mean body temperature returned to normal faster than central body temperature. Routine monitoring of core temperature and the use of warmed irrigation fluids are recommended during transurethral resections in elderly patients.