E. D. Bennett

The strong ion gap does not have prognostic value in critically ill patients in a mixed medical/surgical adult ICU

AbstractObjective. To examine whether the strong ion gap (SIG) or standard base excess corrected for abnormalities of serum chloride and albumin (BEUA) can predict outcome and to compare the prognostic abilities of these variables with standard base excess (SBE), anion gap (AG), pH, and lactate, the more traditional markers of acid-base disturbance. Design. Prospective, observational study. Setting. University teaching hospital, general adult ICU. Patients. One hundred consecutive patients on admission to the ICU. Measurements and results. The anion gap (AG) was calculated and corrected for abnormal serum albumin (AGcorrected). Serum lactate was measured and SBE, BEUA, SIG, and APACHE II scores calculated for each patient. 28-day survival was recorded. There was a significant difference between the mean APACHE II (P<0.001), SBE (P<0.001), lactate (P=0.008), AG (P=0.007), pH (P<0.001), and BEUA (P=0.009) of survivors and non-survivors. There was no significant difference between the mean SIG (P=0.088), SIDeff (P=0.025), and SID app (P=0.254) between survivors and non-survivors. The pH and SBE demonstrated the best ability of the acid-base variables to predict outcome (AUROC curves 0.72 and 0.71, respectively). Neither of these were as good as the APACHE II score (AUROC 0.76) Conclusion. Traditional indices of SBE, BEUA, lactate, pH, AG, and APACHE II all discriminated well between survivors and non-survivors. In this group of patients the SIG, SIDeff, and SIGapp appear to offer no advantage in prediction of outcome and their use as prognostic markers can therefore not be advocated.

Acid-base physiology: the 'traditional' and the 'modern' approaches

Summary The interpretation and understanding of acid–base dysfunction has recently been revisited. The ‘traditional’ approach developed from the pioneering work of Henderson and Hasselbalch and is still the most widely used in clinical practice. There are a number of problems identified with this approach, however. The ‘modern’ approach derives from Stewarts work in physical chemistry. In this review we describe the origins of the traditional approach and discusses related concepts. We then describe Stewarts approach, including how it is derived and how it may be used to classify acid–base derangements. The applications of Stewarts approach to clinical scenarios in intensive care is then discussed briefly before we examine some published clinical studies based on his work.

Isoflurane and propofol for long-term sedation in the intensive care unit. A crossover study.

Propofol and isoflurane have been reported recently to offer better sedation than alternative agents in patients who require long‐term ventilation in the Intensive Care Unit. This is the first report of a direct comparison between propofol and isoflurane. Twenty‐four patients predicted to require artificial ventilation for at least 48 h were entered into a randomised crossover study to monitor sedation quality and time to recovery from sedation. There were no significant differences between the two agents in either end‐point, with over 95% optimal sedation achieved by the use of each drug. Few adverse events were noted. Technological advances in the administration of volatile agents as long‐term sedatives in the Intensive Care Unit may facilitate their more widespread use.

A cost analysis of a treatment policy of a deliberate perioperative increase in oxygen delivery in high risk surgical patients

Objective:To investigate the cost implications of a treatment policy of a deliberate perioperative increase of oxygen delivery in high risk surgical patients.Design:A cost-effectiveness analysis comparing ‘protocol’ high risk surgical patients in whom oxygen delivery was specifically targeted towards 600 ml/min/m2 with ‘control’ patients.Interventions:In a randomised, controlled clinical trial we previously demonstrated a significant reduction in mortality (5.7% vs 22.2%, p=0.015) and morbidity (0.68±0.16 complications vs 1.35±0.20, p=0.008) in ‘protocol’ high risk surgical patients in whom oxygen delivery was specifically targeted towards 600 ml/min per m2 compared with ‘control’ patients. This current study retrospectively analysed the medical care and National Health Service resource use of each patient in the trial. Departmental purchasing records and business managers were consulted to identify M28.9nthe unit cost of these resources, and thereby the cost of treating each patient was calculated.Results:The median cost of treating a protocol patient was lower than for a control patient (£6,525 vs £7,784) and this reduction was due mainly to a decrease in the cost of treating postoperative complications (median £213 vs £668). The cost of obtaining a survivor was 31% lower in the protocol group.Conclusion:Perioperative increase of oxygen delivery in high risk surgical patients not only improves survival, but also provides an actual and relative cost saving. This may have important implications for the management of these patients and the funding of intensive care.

A NARROW RANGE, MEDIUM MOLECULAR-WEIGHT PENTASTARCH REDUCES STRUCTURAL ORGAN DAMAGE IN A HYPERDYNAMIC PORCINE MODEL OF SEPSIS

Objective: to compare diafiltered 6% pentastarch (Pentafraction-PDP, MWn 120000 and MWw 280000) and native pentastarch (Pentaspan-PSP, MWn 63000 and MWw 264000 dalton) in a porcine model of faecal peritonitis.Design: Randomised prospective study in 12 adolescent pigs.Interventions: Prior to infection the study solution was infused to increase Qt by 25%. Thereafter adjustments in infusion rate were made (up to 1 l/h) in an attempt to maintain Qt at 25% above baseline values.Measurements and results: Animals were sacrificed at 8h. Tissue was excised from the right lobe of liver and from the right lung and fixed for later electron microscopy and digital morphometric analysis. Patent sinusoidal lumen was significantly greater in group PDP compared to PSP (11.3%±2.3% of liver tissue versus 4.8%±1.1%,p<0.05) and this was accounted for by a significantly lower proportion of sinusoidal lumen occluded with white cells (2.1%±0.6% versus 6.6%±1.9%,p<0.05). Similarly, patent capillary represented a significantly higher proportion of lung tissue for group PDP versus PSP (26.2%±1.9% versus 18.5%±2.7%,p<0.05). The arithmetic mean alveolar capillary barrier thickness was significantly greater in group PSP than in group PDP (4.3±03 μm versus 2.5±03 μm,p<0.01).Conclusions: The molecular weight profile of Pentafraction was associated with less structural organ damage including less tissue oedema and less white cell occlusion.

External high frequency oscillation in normal subjects and in patients with acute respiratory failure

External high frequency oscillation was performed on 20 healthy volunteers using a cuirass‐based system, the Hayek Oscillator. Five‐min periods of oscillation were carried out on each subject at frequencies of 1, 2, 3, 4 and 5 Hz. Effective ventilation was measured in terms of the fall in alveolar partial pressure of carbon dioxide immediately after oscillation. The optimum frequency for oscillation was 1–3 Hz but most of the subjects were adequately ventilated over a wide range of frequencies. Thus, the Hayek Oscillator is capable of adequately ventilating normal subjects by means of chest wall oscillation. We also compared external high frequency oscillation with intermittent positive pressure ventilation in five patients with respiratory failure. Using the same inspired oxygen fraction, the external high frequency oscillation replaced intermittent positive pressure ventilation for a 30‐min period. External high frequency oscillation improved oxygenation by 16% and reduced the arterial carbon dioxide by 6%. These preliminary findings suggest that normal subjects and intensive care unit patients can be adequately ventilated by means of external high frequency oscillation.

Tracheal dilatation complicating prolonged tracheal intubation

A patient with severe acute respiratory distress syndrome requiring prolonged tracheal intubation and mechanical ventilation is described. Tracheal dilatation was noted to have occurred following an elective surgical tracheostomy. Eventually, the patient was successfully weaned from mechanical ventilation and the tracheostomy tube removed.

Prognostic factors in intensive care

Predicting the outcome of critical illness remains an evolving art despite many recent advances. This review article describes the tools currently employed, appraising each in turn. The subject is viewed from the perspective that physiological reserve and inflammatory response are the essential elements in assessing prognosis in patients with multi-organ dysfunction/failure, the most commonly encountered syndrome in intensive care practice.

State of the art: critical care

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