Base excess (BE): reloaded.

The base excess value (BE, mmol/L), not standard base excess (SBE), correctly calculated including pH, pCO2 (mmHg), sO2 (%) and cHb (g/dl) is a diagnostic tool for several in vivo events, e.g., mortality after multiple trauma or shock, acidosis, bleeding, clotting, artificial ventilation. In everyday clinical practice a few microlitres of blood (arterial, mixed venous or venous) are sufficient for optimal diagnostics of any metabolic acidosis or alkalosis.The same applies to a therapeutic tool-then referred to as potential base excess (BEpot)-for several in vitro assessments, e.g., solutions for infusion, sodium bicarbonate, blood products, packed red blood cells, plasma. Thus, BE or BEpot has been a parameter with exceptional clinical significance since 2007.

The impact of modified fluid gelatin 4% in a balanced electrolyte solution on plasma osmolality in children-A noninterventional observational study.

BACKGROUND: Intravenous fluids for perioperative infusion therapy should be isotonic to maintain the body fluid homeostasis in children. Modified fluid gelatin 4% in a balanced electrolyte solution has a theoretical osmolarity of 284 mosmol L-1 , and a real osmolality of 264 mosmol kg H2 O-1 . Because both values are lower than those of 0.9% saline or plasma, gelatin would be expected to be hypotonic in-vitro and in-vivo. AIM: We thus hypothesized that the infusion of gelatin would be expected to decrease plasma osmolality. We performed an in-vitro experiment and an in-vivo study to evaluate the impact of gelatin on the osmolality in children. METHODS: In the in-vitro experiment, full blood samples were diluted with gelatin 4% or albumin (50 g L-1 ) from 0% (pure blood) to 100% (pure colloid), and the osmolality was measured by freezing-point depression. In the in-vivo study, blood gas analyses from children undergoing major pediatric surgery were collected before and after gelatin infusion, and the osmolality was calculated by a modified version of Zander's formula. RESULTS: In the in-vitro experiment, 65 gradually diluted blood samples from five volunteers (age 25-55 years) were analyzed. The dilution with gelatin caused no significant changes in osmolality between 0% and 100%. Compared with gelatin, the osmolality in the albumin group was significantly lower between 50% and 100% dilution (p < .05). In the in-vivo study, 221 children (age 21.4 ± 30 months) were included. After gelatin infusion, the osmolality increased significantly (mean change 4.3 ± 4.8 [95% CI 3.7-4.9] mosmol kg H2 O-1 ; p < .01) within a normal range. CONCLUSIONS: Gelatin in a balanced electrolyte solution has isotonic characteristics in-vitro and in-vivo, despite the low theoretical osmolarity, probably caused by the (unmeasured) negative charges in the gelatin molecules contributing to the plasma osmolality. For a better evaluation of the (real) tonicity of gelatin-containing solutions, we suggest to calculate the osmolality (mosmol kg H2 O-1 ) using Zander's formula. TRIAL REGISTRATION: ClinicalTrials.gov (ID: NCT02495285).

[Perioperative Infusion Therapy in Children]. / Perioperative Infusionstherapie bei Kindern.

The composition and type of intravenous fluids during paediatric anaesthesia have been subjects of debates for decades. Errors in perioperative infusion therapy in children may lead to serious complications and a negative outcome. Therefore, in this review historical and recent developments and recommendations for perioperative fluid management in children are presented, based on physiology and focused on safety and efficacy. Recent studies showed that optimized preoperative fasting times and liberal clear fluid intake until 1 h improve patient comfort and metabolic and haemodynamic condition after induction of anaesthesia. Physiologically composed balanced isotonic electrolyte solutions are safer than hypotonic electrolyte solutions or saline 0.9% to protect young children against the risks of hyponatraemia and hyperchloremic acidosis. For intraoperative maintenance infusion, addition of 1 - 2% glucose is sufficient to avoid hypoglycaemia, lipolysis or hyperglycaemia. Modified fluid gelatine or hydroxyethyl starch in balanced electrolyte solution can safely be used to quickly normalize blood volume in case of perioperative circulatory instability and blood loss. In conclusion, physiologically composed infusion solutions are beneficial for maintaining homeostasis, shifting the status more towards the normal range in children with pre-existing imbalances and have a wide safety margin in case of accidental hyperinfusion.

Perioperative fluid management in children: can we sum it all up now?

PURPOSE OF REVIEW: The composition and type of intravenous fluids during paediatric anaesthesia have been subjects of debates for decades. Errors in perioperative fluid management in children may lead to serious complications and a negative outcome. Therefore, in this review, historical and recent developments and recommendations for perioperative fluid management in children are presented, based on physiology and focused on safety and efficacy. RECENT FINDINGS: Optimized fasting times and liberal clear fluid intake until 1 h improve patient comfort and metabolic and haemodynamic condition after induction of anaesthesia. Physiologically composed balanced isotonic electrolyte solutions are safer than hypotonic electrolyte solutions or saline 0.9% to protect young children against the risks of hyponatraemia and hyperchloraemic acidosis. For intraoperative maintenance infusion, addition of 1-2% glucose is sufficient to avoid hypoglycaemia, lipolysis or hyperglycaemia. Modified fluid gelatine or hydroxyethyl starch in balanced electrolyte solution can safely be used to quickly normalize blood volume in case of perioperative circulatory instability and blood loss. SUMMARY: Physiologically composed balanced isotonic electrolyte solutions are beneficial for maintaining homeostasis, shifting the status more towards the normal range in patients with preexisting imbalances and have a wide margin of safety in case of accidental hyperinfusion.

Pure oxygen ventilation during general anaesthesia does not result in increased postoperative respiratory morbidity but decreases surgical site infection. An observational clinical study.

Background. Pure oxygen ventilation during anaesthesia is debatable, as it may lead to development of atelectasis. Rationale of the study was to demonstrate the harmlessness of ventilation with pure oxygen. Methods. This is a single-centre, one-department observational trial. Prospectively collected routine-data of 76,784 patients undergoing general, gynaecological, orthopaedic, and vascular surgery during 1995-2009 were retrospectively analysed. Postoperative hypoxia, unplanned ICU-admission, surgical site infection (SSI), postoperative nausea and vomiting (PONV), and hospital mortality were continuously recorded. During 1996 the anaesthetic ventilation for all patients was changed from 30% oxygen plus 70% nitrous oxide to 100% oxygen in low-flow mode. Therefore, in order to minimize the potential of confounding due to a variety of treatments being used, we directly compared years 1995 (30% oxygen) and 1997 (100%), whereas the period 1998 to 2009 is simply described. Results. Comparing 1995 to 1997 pure oxygen ventilation led to a decreased incidence of postoperative hypoxic events (4.3 to 3.0%; p < 0.0001) and hospital mortality (2.1 to 1.6%; p = 0.088) as well as SSI (8.0 to 5.0%; p < 0.0001) and PONV (21.6 to 17.5%; p < 0.0001). There was no effect on unplanned ICU-admission (1.1 to 0.9; p = 0.18). Conclusions. The observed effects may be partly due to pure oxygen ventilation, abandonment of nitrous oxide, and application of low-flow anesthesia. Pure oxygen ventilation during general anaesthesia is harmless, as long as certain standards are adhered to. It makes anaesthesia simpler and safer and may reduce clinical morbidity, such as postoperative hypoxia and surgical site infection.

Evaluation of 36 formulas for calculating plasma osmolality.

PURPOSE: Measuring or calculating plasma osmolality is of interest in critical care medicine. Moreover, the osmolal gap (i.e. the difference between the measured and calculated osmolality) helps in the differentiation of metabolic acidosis. A variety of formulas for calculating osmolality have been published, most of them relying on sodium, urea and glucose. A novel formula developed by Zander has recently been published, which also takes into account the effects of potassium, chloride, lactate and bicarbonate on osmolality. We evaluate the previously published formulas including the novel formula by comparing calculated and measured osmolality. METHODS: Arterial or venous blood samples from 41 outpatients and 195 acutely ill inpatients (total 236 subjects) were used to compare measured osmolality with calculated osmolality as obtained from 36 published formulas including the new formula. The performance of the formulas was statistically evaluated using the method of Bland and Altman. RESULTS: Mean differences up to 35 mosmol/kg H(2)O were observed between measured and calculated osmolality using the previously published formulas. In contrast, the novel formula had a negligible mean difference of 0.5 mosmol/kg H(2)O. The novel formula also had the closest 95 % limits of agreement ranging from -6.5 to 7.5 mosmol/kg H(2)O. CONCLUSION: Only 4 out of the 36 evaluated formulas gave mean differences between measured and calculated osmolality of less than 1 mosmol/kg H(2)O. Zander's novel formula showed excellent concordance with measured osmolality and facilitates a more precise diagnosis based on blood gas analysers. The new equation has the potential to replace separate measurements of osmolality in many cases.

Accurate and continuous measurement of oxygen deficit during haemorrhage in pigs.

OBJECTIVE: Haemorrhagic shock can cause organ failure and high mortality. Uncontrolled bleeding, a predetermined bleeding volume or blood pressure controlled bleeding are traditionally used to study haemorrhagic shock. These models are influenced by compensatory mechanisms preventing accurate knowledge about the severity of cellular insult. We describe the use of a method for continuous measurement of oxygen deficit during haemorrhage in pigs. METHODS: We defined a cumulative oxygen deficit of approximately 100mL/kg as the primary endpoint for severe haemorrhage. For continuous assessment of oxygen deficit a metabolic monitor (Deltatrac II, Datex-Ohmeda Instrumentation Corp., Helsinki, Finland) was used. Data are presented as mean+/-SD; (*)P<0.05 was considered to be significant. RESULTS: 17 out of 22 anaesthetised male pigs achieved a mean cumulative oxygen deficit of 106+/-3 mL/kg (range: 95-117 mL/kg) by withdrawing an average blood volume of 47+/-6 mL/kg over 1h. Mean arterial blood pressure (MAP) fell from 83+/-19 to 22+/-7mmHg (baseline versus shock), heart rate increased from 83+/-7 to 147+/-37min(-1). Venous base excess changed from 4.8+/-2.4 to -12.5+/-3.4 mmol/L and venous lactate increased from 1.5+/-0.4 to 13.3+/-2.4 mmol/L after haemorrhage. Two pigs (11%) died during the haemorrhagic shock phase. The traditional method of assessing haemorrhage (measuring blood volume lost) showed only a poor correlation with heart rate (r=0.3872; P=0.1540), MAP (r=0.3901; P=0.1505), mixed venous oxygen saturation (svO(2); r=0.0944; P=0.7379) or cardiac index (CI; r=0.2101; P=0.4523). Cumulative oxygen deficit correlated significantly better with heart rate (r=0.7175; P=0.0026), MAP (r=0.5039; P=0.0556), svO(2) (r=0.7084; P=0.0031) or CI (r=0.6260; P=0.0125). CONCLUSION: We describe a model to study haemorrhagic shock based on the cumulative oxygen deficit. We believe that the use of a metabolic monitor to measure oxygen deficit in our model represents an improvement on the current available methods to study the effects of haemorrhagic shock.

Use of an inspiratory impedance threshold valve during chest compressions without assisted ventilation may result in hypoxaemia.

INTRODUCTION: Although the concept of intermittent airway occlusion with the inspiratory impedance threshold valve (ITV) is a well-recognised strategy for improving efficiency of cardiopulmonary resuscitation (CPR), little is known about possible pulmonary side effects. METHODS: After a baseline chest CT-scan, 24 pigs with beating hearts undergoing apnoeic oxygenation received an injection of a contrast medium and were then assigned randomly to either active compression-decompression CPR with ITV (ACD ITV CPR), ACD CPR alone, or standard-CPR with ITV (standard-ITV CPR), or standard-CPR alone. After a maximum of 5 min of chest compressions or if oxygen saturation dropped below 70%, the experiment was stopped, haemodynamic variables and blood gas values were measured, and another CT-scan was performed; all animals underwent a 30 min recovery-period and a third subsequent CT-scan. RESULTS: At baseline arterial oxygen saturation by pulse oxymetry was 99% in all four groups; in both the ACD ITV CPR and the standard-ITV CPR groups, arterial oxygen saturation dropped below 70% within 126+/-9s, whereas chest compressions in all ACD CPR and standard-CPR pigs were performed over 5 min (P<0.001). Before stopping chest compressions arterial oxygen pressure decreased in the ACD ITV CPR group from 426+/-96 to 42+/-8 mmHg while it decreased in the ACD CPR group only from 415+/-116 to 197+/-127 mmHg (P<0.001 between groups); in the standard-ITV CPR group arterial oxygen partial pressure decreased from 427+/-109 to 34+/-5 mmHg while oxygen partial pressure decreased only from 467+/-44 to 144+/-98 mmHg in the standard-CPR group (P<0.004 between groups). After the second CT scan arterial oxygen partial pressure decreased further to 19+/-2 mmHg in the ACD ITV CPR versus 210+/-41 mmHg in the ACD CPR group; to 20+/-2 mmHg in the standard-ITV CPR versus 148+/-33 mmHg in the standard-CPR group. Lung-density values (Hounsfield units) were significantly higher in the ACD ITV CPR versus ACD CPR group (-134+/-54 versus -330+/-77) and standard-ITV CPR versus standard-CPR group (-98+/-50 versus -387+/-42). After a 30 min recovery-period, there were no significant differences in arterial oxygen partial pressure (ACD ITV CPR 275+/-110 mmHg versus ACD CPR 379+/-111 mmHg and standard-ITV CPR 265+/-138 mmHg versus standard CPR 367+/-55 mmHg). Furthermore, there were no differences in lung density values between groups after 30 min of recovery. CONCLUSION: In this animal model with a beating heart, intermittent airway obstruction through an ITV combined with apnoeic oxygenation and without active ventilation resulted in hypoxaemia due to transiently impaired lung function.

Prediction of dilutional acidosis based on the revised classical dilution concept for bicarbonate.

Due to the controversy surrounding the term dilutional acidosis, the classical dilution concept for bicarbonate has been rigorously revised for the prediction of pH, actual bicarbonate concentration, and base excess. In the algorithms derived for buffer solutions, blood, and whole body (1-, 2-, and 3-fluid compartment), only bicarbonate is considered. On dilution at constant Pco(2), the final concentration of bicarbonate is the sum in terms of pH, due to the following processes: dilution, formation from chemical reaction with the nonbicarbonate buffers phosphate, hemoglobin, and plasma proteins, and transfer from erythrocytes and interstitial fluid to plasma. At constant Pco(2), the level of carbonic acid is held constant, whereas those of the buffer bases are reduced by dilution, resulting in acidosis. In mixed bicarbonate/phosphate buffer, the final concentration of HCO(3)(-) exceeds the diluted value due to additional buffering of H(2)CO(3) by HPO(4)(2-). For whole blood in vitro, pH, and actual bicarbonate concentration are predicted from dilution with 0.9% saline from initial Hb (100%) to infinite dilution (pure saline). The acidosis from dilution of plasma bicarbonate is mitigated by contributions from plasma proteins (<1 mmol/l) and from the erythrocytes ( approximately 5 mmol/l). Similarly, for whole body, the main contributions to combat primary dilutional acidosis in the range of hemodilution (relative Hb: 100-50%) are from the erythrocytes (1.2-2.2 mmol/l) and from the interstitial fluid (3.3-7.2 mmol/l). Perioperatively measured nonrespiratory acidosis is predictable if caused by hemodilution with fluids containing neither bicarbonate nor its precursors, irrespective of other electrolytes.

The accuracy of calculated base excess in blood.

Most equations used for calculation of the base excess (BE, mmol/l) in human blood are based on the fundamental equation derived by Siggaard-Andersen and called the Van Slyke equation: BE = Z x [[cHCO3-(P) - C7.4 HCO3-(P)] + beta x (pH -7.4)]. In simple approximation, where Z is a constant which depends only on total hemoglobin concentration (cHb, g/dl) in blood, three equations were tested: the ones proposed by Siggaard-Andersen (SA), the National Committee for Clinical Laboratory Standards (NCCLS) or Zander (ZA). They differ only slightly in the solubility factor for carbon dioxide (alphaCO2, mmol/l x mmHg) and in the apparent pK(pK'), but more significantly in the plasma bicarbonate concentration at reference pH (C7.4HCO3-(P), mmol/l) and in beta, the slope of the CO2-buffer line (mmol/l) for whole blood. Furthermore, the approximation was improved either by variation in Z (r(c)), or in the apparent pK (pK) with changing pH. Thus, from a total of seven equations and from a reference set for pH, pCO2 and BE taken from the literature (n=148), the base excess was calculated. Over the whole range of base excess (-30 to +30 mmol/l) and PCO2 (12 to 96 mmHg), mean accuracy (deltaBE, mmol/l) was greatest in the simple equation according to Zander and decreased in the following order: +/-0.86 (ZA); +/-0.94 (ZA, r(c)); +/-0.96 (SA, r(c)); +/-1.03 (NCCLS, r(c)); +/-1.40 (NCCLS); +/-1.48 (SA); and +/-1.50 (pK'). For all clinical purposes, the Van Slyke equation according to Zander is the best choice and can be recommended in the following form: BE= (1 -0.0143 x cHb) x [[0.0304 x PCO2 x 10pH-6.1-24.26] + (9.5+1.63 x cHb) x (pH -7.4)] - 0.2 x cHb x (1-sO2), where the last term is a correction for oxygen saturation (sO2). Hence, base excess can be obtained with high accuracy (<1 mmol/l) from the measured quantities of pH, pCO2, cHb, and SO2 in any sample, irrespective of whether venous or arterial blood is used.