Hextend, a physiologically balanced plasma expander for large volume use in major surgery: a randomized phase III clinical trial. Hextend Study Group

Hextend (BioTime, Inc., Berkeley, CA) is a new plasma volume expander containing 6% hetastarch, balanced electrolytes, a lactate buffer, and physiological levels of glucose. In preclinical studies, its use in shock models was associated with an improvement in outcome compared with alternatives, such as albumin or 6% hetastarch in saline. In a prospective, randomized, two-center study (n = 120), we compared the efficacy and safety of Hextend versus 6% hetastarch in saline (HES) for the treatment of hypovolemia during major surgery. Patients at one center had a blood sample drawn at the beginning and the end of surgery for thromboelastographic (TEG) analysis. Hextend was as effective as HES for the treatment of hypovolemia. Patients received an average of 1596 mL of Hextend: 42% received >20 mL/kg up to a total of 5000 mL. No patient received albumin. Hextend-treated patients required less intraoperative calcium (4 vs 220 mg; P < 0.05). In a subset analysis of patients receiving red blood cell transfusions (n = 56; 47%), Hextend-treated patients had a lower mean estimated blood loss (956 mL less; P = 0.02) and were less likely to receive calcium supplementation (P = 0.04). Patients receiving HES demonstrated significant prolongation of time to onset of clot formation (based on TEG) not seen in the Hextend patients (P < 0.05). No Hextend patient experienced a related serious adverse event, and there was no difference in the total number of adverse events between the two groups. The results of this study demonstrate that Hextend, with its novel buffered, balanced electrolyte formulation, is as effective as 6% hetastarch in saline for the treatment of hypovolemia and may be a safe alternative even when used in volumes up to 5 L.

IMPLICATIONS

Hextend (BioTime, Inc., Berkeley, CA) is a new plasma volume expander containing 6% hetastarch, balanced electrolytes, a lactate buffer, and a physiological level of glucose. It is as effective as 6% hetastarch in saline for the treatment of hypovolemia but has a more favorable side effects profile in volumes of up to 5 L compared with 6% hetastarch in saline.

Effect of alpha(alpha)-cross-linked hemoglobin and pyridoxalated hemoglobin polyoxyethylene conjugate solutions on gastrointestinal regional perfusion in hemorrhagic shock

BACKGROUND

Hemoglobin-based blood substitutes may cause vasoconstriction, which could limit organ perfusion during trauma resuscitation. We investigated the effect of two hemoglobin solutions on regional blood flow and mucosal perfusion in the gastrointestinal tract in a hemorrhagic shock model.

METHODS

Twenty-four swine were bled 30% of blood volume over 1 hour. Six additional animals were anesthetized and monitored but did not undergo hemorrhage. Bled animals were resuscitated with alpha(alpha)-hemoglobin (alpha(alpha)Hb), pyridoxalated hemoglobin polyoxyethylene conjugate (PHP), shed blood, or lactated Ringer's solution. Regional blood flow was measured by radiolabeled microspheres. Gastric mucosal perfusion was estimated by measuring intramucosal pH (pHi) by tonometry.

RESULTS

PHP and shed blood restored small-bowel flows to sham values, whereas lactated Ringer's solution and alpha(alpha)Hb did not. Shed blood and PHP, but not alpha(alpha)Hb, restored cardiac index (CI) to baseline (p < 0.05). Mean pulmonary artery pressure was elevated over baseline with alpha(alpha)Hb and PHP and remained elevated with alpha(alpha)Hb (p < 0.05). pHi was significantly lower after resuscitation with PHP than with other fluids.

CONCLUSION

PHP was efficacious in restoring CI and small-bowel flow, but the pHi remained low, indicating possible continued mucosal ischemia. Alpha(alpha)Hb led to limited recovery of CI and small-bowel blood flow but restored pHi close to baseline. Shed blood was efficacious in restoration of pHi, gastrointestinal blood flows, and systemic hemodynamics.

Gastric mucosal tonometry: towards new methods and applications

Gastrointestinal tonometry is a minimally-invasive method of assessing splanchnic perfusion. The measurement of regional-CO2 (PrCO2) and calculation of intra-mucosal pH (pHi) using the gastro-intestinal tonometer has been shown to be predictive of outcome in critically ill patients. Furthermore, the use of tonometrically derived data as therapeutic indices have been associated with improved outcome. The original balloon-saline method of tonometry was laborious, cumbersome and prone to systematic errors. The Tonocap (Tonometrics Division Instrumentarium Corp., Datex, Finland) is an automated on-line air based system. We present here a detailed description of the Tonocap along with a summary of the results of some of the original in-vitro, animal in-vivo and human experiments. The Tonocap is a major advance in regional monitoring and its introduction into clinical practice should allow widespread assessment of the value of gastro--intestinal tonometry in the management of the critically ill.

epsilon-Aminocaproic acid plasma levels during cardiopulmonary bypass

epsilon-Aminocaproic acid (EACA) concentrations achieved during cardiopulmonary bypass (CPB) have not been previously reported. It is unknown whether plasma concentrations reported to inhibit fibrinolysis in vitro (130 microg/mL) are achieved or whether differences in these levels relate to variability in postoperative bleeding. EACA (total intraoperative dose 270 mg/kg) was administered to 27 patients undergoing cardiac reoperation. The plasma EACA concentration was measured by using high-pressure liquid chromatography: 1) 30 min after initiation of drug administration (baseline); 2) 30 min (CPB + 30) after initiation of CPB; 3) 90 min after initiation of CPB. (CPB + 90); and 4) at cardiopulmonary bypass termination (end CPB). Plasma EACA concentrations (microg/mL, min - max, mean +/- SD) were 276-998, 593 +/- 154 at baseline; 147-527, 302 +/- 95 at CPB + 30; 112-500, 314 +/- 100 at CPB + 90; and 84-537, 317 +/- 100 at end CPB. Twenty-four-hour postoperative thoracic drainage and allogeneic red blood cell transfusions were not associated with plasma levels at any time. Although plasma EACA concentrations greater than 130 microg/mL were consistently achieved, we observed a marked variability (more than sixfold) in plasma concentrations and bleeding outcomes despite the use of a weight-based dosing regimen. This variability in drug levels appears to have little relevance to bleeding outcomes, possibly since mean plasma levels exceeded 130 microg/mL during CPB, and nearly all patients (26 of 27) achieved that target level.

Measurement of gastrointestinal intramucosal pH is a poor guide to tolerable levels of anemia during isovolemic hemodilution in a canine model of coronary stenosis

OBJECTIVE

To determine the relationship between gastrointestinal intramucosal pH and myocardial oxygenation during isovolemic hemodilution in dogs with critical coronary artery stenoses.

DESIGN

Prospective sequential evaluation of ileal intramucosal pH and regional myocardial function of a critically perfused area of myocardial tissue in a canine model of normovolemic hemodilution.

SETTING

A research laboratory.

SUBJECTS

Fifteen dogs.

INTERVENTIONS

A micrometer snare was placed around a main coronary artery (8 left anterior descending artery, 7 right coronary artery). Three pairs of sonomicrometer crystals were placed in the heart to measure regional myocardial contraction. A gastrointestinal tonometer was placed in the ileum and used to measure luminal PCO2. This PCO2 value was used to calculate the ileal intramucosal pH. The animals underwent normovolemic hemodilution until myocardial ischemia occurred in the region supplied by the snared vessel. Measurements were continued for a further 40 minutes.

MEASUREMENTS AND MAIN RESULTS

Following instrumentation, stabilization, and critical constriction of a coronary vessel, percentage changes in systolic shortening of myocardial tissue in the region of critical perfusion were determined every 20 minutes. Ileal intramucosal pH and commonly measured cardiovascular variables were determined at the same time points. Myocardial ischemia occurred after 80 minutes of hemodilution, when the mean (+/- SD) hemoglobin concentration had fallen from a baseline level of 123 +/- 18 g/L to 82 +/- 14 g/L (P < .01). From the start of hemodilution to 40 minutes after myocardial ischemia occurred, there were no significant changes in heart rate, cardiac output, oxygen consumption, arterial acid-base balance, or arterial PCO2. Oxygen delivery decreased by approximately 45% (5.99 +/- 1.66 to 3.41 +/- 0.90 mL/kg per minute; P < .01) but there were no changes in ileal intramucosal pH (7.31 +/- 0.08 to 7.30 +/- 0.08; P = .90).

CONCLUSIONS

Myocardium compromised by coronary stenosis is more sensitive to normovolemic hemodilution-induced ischemia than the normally perfused gut mucosa. This limits the potential utilization of the measurement of gastrointestinal intramucosal pH as a guide to tolerable levels of anemia in critically ill patients.

The successful implementation of pharmaceutical practice guidelines. Analysis of associated outcomes and cost savings. SWiPE Group. Systematic Withdrawal of Perioperative Expenses

BACKGROUND

Although approximately 2,000 medical practice guidelines have been proposed, few have been successfully implemented and sustained. We hypothesized that we could develop and institute practice guidelines to promote more appropriate use of costly anesthetics, to generate and sustain widespread compliance from a large physician group, and to decrease costs without adversely affecting clinical outcomes.

METHODS

A prospective before and after comparison study was performed at a tertiary care medical center. Clinical outcomes data and times indicative of perioperative patient flow were collected on the first of two sets of patients 1 month before discussion of practice guidelines. Practice guidelines were developed by the physicians and their associated care team for the intraoperative use of anesthetic drugs. A drug distribution process was developed to aid compliance. Clinical outcomes data and times indicative of perioperative patient flow were collected on the second set of patients 1 month after institution of practice guidelines. Hospital drug costs and adherence to guidelines were noted throughout the study period and for each of the following 9 months by querying the database of an automated anesthesia record keeper.

RESULTS

A total of 1,744 patients were studied. Drug costs decreased from 56 dollars per case to 32 dollars per case as a result of adherence to practice guidelines. Perioperative patient flow was minimally affected. Time (mean +/- SD) from end of surgery to arrival in the post-anesthesia care unit (PACU) increased from 11 +/- 7 min before the authors instituted practice guidelines to 14 +/- 8 min after practice guidelines (P < 0.0001). Admission of inpatients to the PACU receiving monitored anesthesia care increased from 6.5 to 12.9% (P < 0.02). Perioperative patient flow and clinical outcomes were not otherwise adversely affected. Compliance and cost savings have been sustained.

CONCLUSIONS

This study is an example of a successful physician-directed program to promote more appropriate utilization of health care resources. Cost savings were obtained without any substantial changes in clinical outcomes. Institution of similar practice guidelines should result in pharmaceutical savings in the range of 50% at tertiary care centers around the country, with a slightly smaller degree of savings expected at institutions with more ambulatory surgery.

Comparison of commonly used clinical indicators of hypovolaemia with gastrointestinal tonometry

OBJECTIVE

The gastrointestinal tonometer, which allows measurement of gastrointestinal mucosal CO2 and subsequent derivation of gut intramucosal pH (pHi), has been demonstrated to be a sensitive predictor of outcome following major surgery. Current theory suggests that the origin of the low pH may be hypovolaemia. This study was designed to compare the temporal sequence of changes in tonometric readings with invasive blood pressure, stroke volume, heart rate, lactate and arterial blood gas measurements during progressive haemorrhage.

DESIGN

Observational healthy volunteer study.

SETTING

Intensive care unit at University College London Hospitals.

SUBJECTS

Six healthy, medically qualified volunteers.

INTERVENTIONS

After obtaining baseline measurements, the subjects were progressively bled 25% (range = 21-31%) of their blood volume over a period of 1 h in two approximately equal aliquots. Equilibration was allowed for 30 min following the bleed, after which further measurements were made and the blood was then retransfused over 30 min.

MEASUREMENTS AND MAIN RESULTS

There was no consistent change in any of the haemodynamic variables other than gastric intramucosal CO2:arterial CO2 gap (PiCO2-PaCO2) after removal of the first aliquot of blood, although five of the six subjects also demonstrated a fall in pHi. After removal of the second aliquot of blood, PiCO2-PaCO2 gap and pHi continued to indicate a worsening gastric intramucosal acidosis; stroke volume, as measured by suprasternal Doppler, demonstrated a marked fall, while all other variables measured had not altered consistently or to such a degree as to elicit a clinical response or cause suspicion of a hypovolaemic state. On retransfusion, all variables returned towards baseline.

CONCLUSIONS

This study demonstrates the value of tonometry as an early monitor of hypovolaemia and highlights the shortcomings of other more commonly measured clinical variables.

Relationship of preoperative antiendotoxin core antibodies and adverse outcomes following cardiac surgery

OBJECTIVE

To test the hypothesis that low serum antiendotoxin core antibody (EndoCAb) level is an independent predictor of adverse outcome following cardiac surgery.

DESIGN

Prospective, blinded, cohort study.

SETTING

Tertiary care medical center.

SUBJECTS

A total of 301 patients undergoing coronary artery bypass graft surgery and/or valvular heart surgery.

DESIGN

Preoperative serum was assayed for IgM EndoCAb, IgG EndoCAb, total IgM, and total IgG levels. Known preoperative risk factors were assessed, and patients were assigned a risk score using a validated method.

MAIN OUTCOME MEASURE

A major complication, defined as either in-hospital death or postoperative length of stay greater than 10 days.

RESULTS

Overall, a major complication occurred in 34 patients (11.3%). Lower IgM EndoCAb level independently predicted (P=.002) increased risk of major complication over and above the effects of preoperative risk score (P=.02), total IgG level (P=.07), and all other known perioperative risk factors. In contrast, IgG Endo-CAb and total IgM concentrations did not predict outcome. No association existed between risk score and level of IgM EndoCAb.

CONCLUSION

There is marked preoperative variability in humoral immunity against endotoxin core, which is not accounted for by differences in known preoperative risk factors. In this study, low levels of IgMEndoCAb were an important independent predictor of adverse postoperative outcome, which supports the theory that endotoxemia is a cause of postoperative morbidity.

Effect of temperature during cardiopulmonary bypass on gastric mucosal perfusion

The purpose of our study was to prospectively study the splanchnic response to hypothermic and tepid cardiopulmonary bypass (CPB) using alphastat management of arterial blood-gas tensions. Twenty-four patients for elective CABG surgery were allocated randomly to tepid (35-36 degrees C) or hypothermic (30 degrees C) bypass groups. Measurements were made at four times: (1) baseline, (2) stable during CPB (inflow temperature = nasopharyngeal temperature) 30 degrees C for hypothermic patients, bypass +20 min for tepid patients, (3) 10 min before the end of bypass, (4) after bypass, skin closure. Both groups demonstrated a significant reduction in gastric intramucosal pH (pHim) from time 1 to time 4 and there was no difference in the incidence of a low pHim between the tepid and cold groups (4/12 vs 3/12; ns) at time 4. pHim was significantly lower in the tepid groups at time 3 (P = 0.03) but this discrepancy may have been because of an artefactually high pHim in the cold group. There was a significantly higher incidence of postoperative non-cardiac complications in patients who had a low pHim at time 4 (P = 0.0008). Therefore, we conclude that although the temperature during CPB had a transient effect on pHim it is unlikely to be a major determinant in the pathogenesis of gut mucosal hypoperfusion after bypass.

Maintenance of therapeutic plasma aprotinin levels during prolonged cardiopulmonary bypass using a large-dose regimen

Aprotinin concentrations in the range of 127-191 kallikrein inactivator units (KIU)/mL at the end of cardiopulmonary bypass (CPB) (< 2 h duration) reduce transfusion requirements. It has been suggested that prolonged CPB may require higher infusion rates which significantly increase cost. We tested the hypothesis that large-dose aprotinin maintains therapeutic plasma levels during prolonged periods of CPB (< 2 h). Aprotinin was administered as follows: 2 x 10(6) KIU upon skin incision; 0.5 x 10(6) KIU/h x 4-h infusion on initiation of CPB; and 2 x 10(6) KIU added to the CPB prime solution. Aprotinin activity was measured 1) 30 min after initiation of drug administration (Pre-CPB); 2) 30 min after initiation of CPB (CPB + 30); 3) 90 min after initiation of CPB (CPB + 90); and 4) at CPB termination (End CPB). CPB duration (mean +/- SD) was 158 +/- 51 min. Plasma aprotinin concentrations (KIU/mL, mean +/- SD) were: 234 +/- 30 at Pre-CPB; 229 +/- 35 at CPB + 30; 184 +/- 27 at CPB + 90; and 179 +/- 22 at End CPB. In all patients, aprotinin levels at the completion of CPB were in the range previously reported to be effective. The authors conclude that large-dose regimen limited to 6 x 10(6) KIU maintained therapeutic plasma aprotinin concentrations during prolonged CPB.

Perioperative plasma volume expansion reduces the incidence of gut mucosal hypoperfusion during cardiac surgery

OBJECTIVE

To test the hypothesis that perioperative plasma volume expansion would preserve gut mucosal perfusion during elective cardiac surgery.

DESIGN

Prospective randomized open study.

SETTING

Teaching hospital.

PATIENTS

Sixty American Society of Anesthesiology grade III patients with a preoperative left ventricular ejection fraction of 50% or greater undergoing elective cardiac surgery.

INTERVENTIONS

Patients were allocated randomly to a control or protocol group. The control group was treated according to standard practices. After induction of general anesthesia, the protocol group received, in addition, 200-mL boluses of a 6% hydroxyethyl starch solution to obtain a maximum stroke volume. This procedure was repeated every 15 minutes until the end of surgery, except when the patient underwent cardiopulmonary bypass.

MEASUREMENTS AND RESULTS

Cardiac stroke volume was estimated by an esophageal Doppler system, and gastric mucosal perfusion was measured by tonometric assessment of gastric intramucosal pH in all patients. Patients were followed up postoperatively until discharge from the hospital or death. The incidence of gut mucosal hypoperfusion (gastric intramucosal pH < 7.32) at the end of surgery was reduced in the protocol group (7% vs 56%) (P < .001), as were the number of patients in whom major complications developed (0 vs 6) (P = .01), mean number of days spent in the hospital (6.4 [range, 5 to 9] vs 10.1 [range, 5 to 48]) (P = .011), and mean number of days spent in the intensive care unit (1 [range, 1 to 1] vs 1.7 [range 1 to 11] days) (P = .023).

CONCLUSIONS

Perioperative plasma volume expansion with colloid during cardiac surgery, guided by esophageal Doppler measurement of cardiac stroke volume, reduced the incidence of gut mucosal hypoperfusion. This group of patients also had an improved outcome when compared with controls.

Maintaining blood flow in the extracorporeal circuit: haemostasis and anticoagulation

OBJECTIVES

To review the methods and developments in maintaining extracorporeal circuits in critically ill patients.

DESIGN

The review includes details of the pathophysiological processes of haemostasis and coagulation in critically ill patients, methods of maintaining blood flow in the extracorporeal circuit and methods of monitoring anticoagulation agents used.

SETTING

Information is relevant to the management of critically ill patients requiring extracorporeal renal and respiratory support and cardiopulmonary bypass.

CONCLUSIONS

Heparin is the mainstay of anticoagulation for the extracorporeal circuit although the complex abnormalities of the coagulation system in critically ill patients are associated with a considerable risk of bleeding. Alternative therapeutic agents and physical strategies (prostacyclin, low molecular weight heparin, sodium citrate, regional anticoagulation, heparin bonding and attention to circuit design) may reduce the risk of bleeding but expense and difficulty in monitoring are disadvantages.

Low intramucosal pH is associated with failure to acidify the gastric lumen in response to pentagastrin

OBJECTIVE

To determine if low gastric intramucosal pH is associated with impaired secretion of gastric acid after pentagastrin stimulation.

DESIGN

Prospective study.

SETTING

Intensive care unit of a university teaching hospital.

PATIENTS

20 patients requiring mechanical ventilation.

INTERVENTIONS

All patients with a gastric luminal pH > 4 were given pentagastrin 6 micrograms/kg s.c. to stimulate gastric acid secretion and the response assessed by further measurements of gastric luminal pH.

MEASUREMENTS AND RESULTS

Gastric intramucosal pH (pHi) and luminal pH (pHL) were measured. Patients were divided into two groups on the basis of a low or normal pHi (A value of 7.35 was taken as the lower limit of normal). Patients (n = 6) with normal pHi (7.40 +/- 0.05 [mean +/- SD]) and a luminal pH > 4 (5.65 +/- 1.25) all had a decrease in pHL in response to pentagastrin (decrease in pHL 4.02 +/- 1.52). Of the patients (n = 7) with low pHi (7.2 +/- 0.13) and a pHL > 4 (6.51 +/- 0.48) only one responded to pentagastrin (decrease in pHL for this group 0.93 +/- 1.86). Patients with a pHL < 4 (2.4 +/- 0.71) were not given pentagastrin (n = 7).

CONCLUSION

Some critically ill patients with low gastric intramucosal pH appear to have an impaired ability to acidify the gastric lumen in response to pentagastrin.

Intra-operative gut mucosal hypoperfusion is associated with increased post-operative complications and cost

OBJECTIVES

To determine CO and gastric mucosal perfusion in patients during elective major surgery; to seek a relationship with subsequent outcome.

DESIGN

Prospective descriptive study.

SETTING

University hospital.

PATIENTS

51 patients undergoing elective major surgery of an anticipated duration of greater than 2 h who were at risk of developing gut mucosal hypoperfusion and postoperative organ failure.

MEASUREMENTS AND RESULTS

CO was determined by oesophageal Doppler measurement of aortic blood flow. Gastric mucosal perfusion was determined by tonometric assessment of gastric mucosal pH (pHi). Blood pressure and urine flow were measured. At the end of surgery no patients were oliguric or hypotensive. Post-operatively morbidity, mortality, duration and cost of stay in the ITU and hospital were assessed. There were 32 patients with evidence of gastric mucosal ischaemia at the end of surgery (pHi < 7.32) despite maintenance of CO. This group of patients spent a mean of 4.7 (range 0-33) days in the ITU, 14 developed major complications (7 with multiple organ failure [MOF] and 6 died. In 19 patients gut mucosal perfusion was maintained during surgery (pHi > or = 7.32); these patients demonstrated an increase in CO of 48.4% (95% confidence interval 21.3 -75.6) and spent a mean of 1.0 (range 0-4) days in the ITU. Only one developed a major complication and none died. The total cost of post-operative care for the 51 patients was estimated at pounds 356650. Mean cost per patient in the low pHi group was significantly greater at pounds 8845 (range pounds 600--pounds 42,700) compared to pounds 3874 (range pounds 2,600--pounds 9,600) in the normal pHi group. The total.cost of post-operative care for the 7 patients who developed MOF was pounds 171,450 i.e. 48% of the total cost.

CONCLUSION

A low gastric pHi measured during the intraoperative period in a group of patients undergoing major (mainly cardiovascular) surgery is associated with increased post-operative complications and cost.

The rational administration of colloids

The safe administration of i.v. fluids is one of the most significant advances in the care of critically ill patients this century. However, despite advances in the monitoring of cardiovascular variables, the questions of what? when? and how much? remain areas of enormous controversy. Ironically as the choice of i.v. fluids becomes greater and the monitoring more sophisticated the controversy grows. This article will concentrate on the diagnosis of hypovolaemia, the consequences of hypovolaemia and the rational use of i.v. fluids, particularly colloids, to treat it.

The role of endotoxin immunity, neutrophil degranulation and contact activation in the pathogenesis of post-operative organ dysfunction

Gut mucosal hypoperfusion is associated with a poor outcome following major surgery but the pathogenetic mechanisms remain poorly understood. We have examined the relationship between gut mucosal hypoperfusion, endotoxin core antibodies (EndoCAb), neutrophil elastase alpha-1 antitrypsin complexes (NE) and components of the contact system during elective major surgery. Of the 26 patients studied 16 developed gut mucosal hypoperfusion (pHi < 7.32) by the end of surgery; of these four developed multiple organ failure (MOF) and three subsequently died. In this group there was a significant rise in NE (P < 0.005) and significant reductions in components of the contact system (factor XII, antithrombin III, prekallikrein and C1-inhibitor; P < 0.001) from immediately before surgery to 24 h later. Ten patients maintained gut mucosal perfusion (pHi > or = 7.32); none of these developed life threatening complications. In this group there was no significant increase in NE and, although there were significant reductions in some components of the contact system (P < 0.01), levels of C1-INH were not reduced. All patients demonstrated a significant reduction in both IgG and IgM EndoCAbs (P < or = 0.005) indicating exposure to endotoxin. However, the group that maintained gut mucosal perfusion had significantly higher IgG EndoCAb levels at baseline and 24 h (P < or = 0.005). These data suggest that all patients were exposed to endotoxin and that high levels of anti-endotoxin antibodies may contribute to the prevention of endotoxin-induced contact activation, neutrophil degranulation and gut mucosal hypoperfusion occurring during major surgery and thus reduce the likelihood of the development of post-operative MOF.

Postoperative multiple organ dysfunction syndrome associated with gut mucosal hypoperfusion, increased neutrophil degranulation and C1-esterase inhibitor depletion

We have examined the relationship between gut mucosal perfusion, as determined by gastric intramucosal pH (pHi), changes in plasma neutrophil elastase concentrations and components of the contact system during elective major surgery and related these findings to patient outcome. Of the 26 patients studied, 16 developed gut mucosal hypoperfusion (pHi < 7.32) by the end of surgery; four of these developed multiple organ dysfunction syndrome; three of these died. In this group there was a significant increase in neutrophil elastase (P < 0.005) and significant reductions in plasma components of the contact system from immediately before surgery to 24 h later. Ten patients maintained gut mucosal perfusion (pHi > or = 7.32); none of these developed life threatening complications. In this group there was no significant increase in neutrophil elastase and, although there were significant reductions in some plasma components of the contact system, concentrations of C1-esterase inhibitor (the main inhibitor of the contact system) were not significantly reduced. We conclude that gut mucosal hypoperfusion, neutrophil degranulation and activation of the contact system to the extent that C1-esterase inhibitor becomes depleted are associated with a poor outcome after major surgery.

Pharmacology and physiology of colloids

The importance of an adequate circulating volume in the critically ill is well established. Plasma, albumin, synthetic colloids and crystalloids may all be used for volume expansion but the first two are expensive and crystalloids have to be given in much larger volumes than colloids to achieve the same effect. Synthetic colloids provide a cheaper, safe, effective alternative. There are three classes of synthetic colloid; dextrans, gelatins and hydroxyethyl starches; each is available in several formulations with different properties which affect their initial plasma expanding effects, retention in the circulation and side-effects. There is no ideal colloid but those with low molecular weights such as gelatins are more suitable for rapid, short term volume expansion whilst in states of capillary leak where longer term effects are required hydroxyethyl starches are more effective. Dextrans are as effective as the alternatives but produce more side-effects and the need to pre-treat with hapten-dextran renders them unwieldy in use. Albumin is as persistent as hydroxyethyl starch in the healthy circulation but is retained less well in states of capillary leak. It has no significant advantages over starches and is much more expensive.

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 120,000 and MWw 280,000) and native pentastarch (Pentaspan--PSP, MWn 63,000 and MWw 264,000 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 8 h. 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 +/- 0.3 microns versus 2.5 +/- 0.3 microns, 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.