Reduktion der Aggressivität der Beatmung nach Therapie eines Ölsäure-induzierten Lungenversagens durch Inhalation von Perfluorhexan

INTRODUCTION

The application of perfluorohexane (PFH) vapor led to an improvement of oxygenation and mechanical lung function in a model of oleic acid-induced ARDS in sheep. The aim of this study was to investigate the effects of PFH on gas exchange over an extended time period and to reduce the invasiveness of ventilation.

METHOD

ARDS was induced in sheep ( n=12) by injecting 0.1 ml/kg body weight oleic acid intravenously. Six sheep were treated for 30 min with 18 vol.% PFH (PFH-Tx) and followed up over a time period of 240 min while untreated sheep ( n=6) served as controls. Subsequently the F(I)O(2) was reduced to generate a p(a)O(2) between 100-140 mmHg. Gas exchange, respiratory and hemodynamic data were collected at regular intervals. Data were analysed using covariance analysis.

RESULTS

PFH treatment led to an improvement in oxygenation ( p<0.01) and in mechanical lung function ( p<0.01). Furthermore, mean pulmonary artery pressure ( p<0.01) and shunt ( p<0.01) were lower in PFH-Tx. F(I)O(2) could be reduced in all PFH-treated animals ( p<0.01).

CONCLUSION

Treatment of oleic acid-induced lung injury with PFH vapor improved oxygenation and mechanical lung function over a extended time period allowing a reduction in the invasiveness of ventilation.

Efficacy and Safety of the Platelet-Activating Factor Receptor Antagonist BN???52021 (Ginkgolide??B) in Patients with Severe Sepsis

OBJECTIVE

To evaluate the efficacy and safety of the natural platelet-activating factor receptor antagonist, BN 52021 (ginkgolide B) in the treatment of patients with severe sepsis related to Gram-negative and mixed bacterial infection.

DESIGN AND SETTING

Prospective, randomised, double-blind, placebo-controlled, multicentre study carried out in 13 academic medical intensive care centres in Germany with up to 14 patients per centre.

PATIENTS

88 patients with severe sepsis under standard medical and surgical care: nine patients with pure Gram-positive infection, 79 patients with Gram-negative or mixed bacterial infections (subgroup for which efficacy was to be established).

INTERVENTIONS

Patients were randomised to receive either placebo or BN 52021 1.25 mg/kg bodyweight intravenously every 12h over a 4-day period in addition to their standard medical and surgical care.

MAIN OUTCOME MEASURES AND RESULTS

The primary efficacy variable was the 28-day all-cause mortality rate. The treatment groups were similar with respect to demographic data and prognostic factors influencing the outcome except for bodyweight and adequacy of antibiotic therapy. Analysis of patients with Gram-negative or mixed bacterial infection, for which efficacy was to be established, resulted in a 28-day all-cause mortality of 42.5% in the placebo group (n = 40; 17 deaths) versus 38.5% in the BN 52021 group (n = 39; 15 deaths). Among all randomised patients, the 28-day all-cause mortality rate was 40.9% in the placebo group (n = 44; 18 deaths) and 38.6% in the BN 52021 group (n = 44; 17 deaths). There were no differences in frequency and severity of adverse events between the two treatment groups.

CONCLUSIONS

Four-day administration of BN 52021 failed to demonstrate a statistically significant reduction in mortality in patients with severe sepsis suspected or confirmed to be related to infections other than Gram-positive bacterial infection.

An approach to quality management in anaesthesia: a focus on perioperative care and outcome

Health care systems throughout the world are faced with continuously rising health care expenditure. In Germany, a fee per capita system will be introduced by 2003 to keep the budgets for hospital care within limits. As a result, numbers of hospital beds and hospitals will be cut in the coming years. On the other hand, more and more patients and health care providers are asking if they are really receiving an adequate value for their money in the treatment they receive. All this will have a strong impact on the anaesthesiologist's work and her/his perception of the different facets of quality. Quality has various aspects for the anaesthesiologist. The patient as a customer should not incur any detrimental effects after a surgical procedure, and is accompanied by the anaesthesiologist throughout the perioperative setting. The surgeon needs optimal conditions to perform a procedure. The hospital must balance equally costs and income; this requires optimal operating room utilization. Finally, health insurance companies and the government are responsible for covering the cost of treatment according to the quality of the care delivered. Quality assessment concerning structure, process and outcome has to take these demands into account. Continuous quality improvement in the spirit of Deming's 'plan-do-check-act cycle' has to be part of anaesthesiologist's everyday routine. In future, the traditional barriers between the specialities treating a patient will be disrupted when reimbursement for treatment is made according to quality and efficacy of treatment.

Relationship of comorbidity, age and perioperative complications in patients undergoing radical prostatectomy

OBJECTIVES

To investigate the prevalence and distribution of comorbidity and its association with perioperative complications in patients undergoing radical prostatectomy (RPE).

METHODS

In 431 unselected RPE patients, the American Society of Anesthesiologists Physical Status classification (ASA-PS), the New York Heart Association classification of cardiac insufficiency (NYHA), the classification of angina pectoris of the Canadian Cardiovascular Society (CCS), height, weight, the body mass index (BMI), and the number of concomitant diseases (NCD) were assessed and related to perioperative cardiovascular complications.

RESULTS

In RPE patients less than 70 years old, comorbidity rose nearly continuously with increasing age. However, after reaching an age of 70 years, the proportion of NYHA-0 patients increased (60-64 years, 86%; 65-69 years, 85%; >or=70 years, 87%). Furthermore, the severe comorbidities decreased in patients selected for RPE aged 70 or more years. There was a nonsignificant trend towards higher comorbidity in patients with perioperative cardiovascular complications.

CONCLUSIONS

These data suggest that documentation of the distribution of ASA-PS, CCS, NYHA and of concomitant diseases might be helpful to characterize the general health status and the degree of selection of prostate cancer treatment populations especially in series with a high portion of patients aged 70 or more years. Concerning perioperative complications, the individual predictive value of comorbidity seems to be poor in the radical prostatectomy setting.

Grand mal convulsion and plasma concentrations after intravascular injection of ropivacaine for axillary brachial plexus blockade

We report a patient to whom ropivacaine 1.1 mg kg(-1) was administered for brachial plexus blockade and who developed grand mal convulsions because of inadvertent i.v. injection. No symptoms of cardiovascular toxicity occurred. Venous blood samples were taken 15, 45, 75 and 155 min after the injection. The measured total plasma concentrations of ropivacaine were 3.3, 1.6, 1.2 and 1.0 mg litre(-1) respectively. Initial plasma concentration after the end of the injection period was estimated at 5.75 mg litre(-1) using a two-compartment pharmacokinetic model.

A comparison of five solutions of local anaesthetics and/or sufentanil for continuous, postoperative epidural analgesia after major urological surgery

BACKGROUND AND OBJECTIVE

The aim of the present study was to compare and assess the quality of analgesia, the safety and the side-effects after the use of a continuous, thoracic epidural infusion of sufentanil (5 microg h(-1)), 0.25% bupivacaine (10 mL h(-1)), 0.2% ropivacaine (10 mL h(-1)) alone or in combination in patients who had undergone major urological surgery. This prospective, randomized, double-blinded study investigated the efficacy of thoracic epidural infusions after major urological surgery.

METHODS

Patients received a 72-h continuous infusion (10 mL h(-1)) of 0.25% bupivacaine (B), 0.2% ropivacaine (R), 0.25% bupivacaine with 0.5 microg mL(-1) sufentanil (BS), 0.2% ropivacaine with 0.5 microg mL(-1) sufentanil (RS) or 0.5 microg mL(-1) sufentanil only (S). The analysis included 109 patients.

RESULTS

The mean visual analogue scale (VAS) scores for pain were highest in the groups R and S (P < 0.001). The PaCO2 values were significantly higher in the groups RS and S (P = 0.003). Motor block occurred more frequently in the groups B and BS than in the other groups (P < 0.001). Sedation, nausea and pruritus were more common in the groups that received sufentanil.

CONCLUSIONS

A continuous, epidural infusion with these drugs was safe and effective in our patients. The combination of 0.2% ropivacaine plus sufentanil appeared preferable because of the low incidence of motor block.

Perfluorohexane attenuates proinflammatory and procoagulatory response of activated monocytes and alveolar macrophages

BACKGROUND

A number of studies have demonstrated the effectiveness of liquid ventilation with perfluorocarbons in improving pulmonary function in acute respiratory distress syndrome. Although it is known that perfluorocarbon-associated gas exchange facilitates lung mechanics and oxygenation, the complete mechanism by which perfluorocarbons exert their beneficial effects in acute lung injury still remains unclear. Possibly, an influence of perfluorocarbons on proinflammatory and procoagulant features of monocytic cells present in the alveolar space, such as alveolar macrophages (AMs), may be involved. Therefore, we examined in an in vitro model the effects of perfluorocarbon on both activated mononuclear blood cells (MBCs) and AMs by monitoring the expression of interleukin (IL)-1 beta, tumor necrosis factor (TNF)alpha, and tissue factor (TF).

METHODS

Mononuclear blood cells, obtained from peripheral blood of healthy volunteers, or AMs from diagnostic bronchoalveolar lavage were stimulated by incubation with lipopolysaccharide in the presence of different amounts of perfluorohexane, which was devoid of cytotoxicity.

RESULTS

Using both video-enhanced contrast and electron microscopy, the authors observed that perfluorohexane droplets were phagocytosed by activated monocytes as well as by in vitro--cultured AMs within 1--3 h. After lipopolysaccharide stimulation of monocytes or AMs, we observed a down-regulation of TF mRNA and a significant inhibition (P < 0.05) of cellular TF antigen by perfluorohexane. In addition, the concentration of both IL-1 beta and TNF alpha in the supernatant of lipopolysaccharide-stimulated MBC was significantly decreased (P < 0.01) by perfluorohexane compared with controls without perfluorohexane. By preincubation of lipopolysaccharide-containing medium with perfluorohexane, the authors could exclude that the inhibitory effect of perfluorohexane was caused by binding or sequestering limited amounts of lipopolysaccharide.

CONCLUSION

Taken together, our results demonstrate an interference of perfluorohexane with the expression of the procoagulant protein TF on monocytes and AMs as well as with the release of proinflammatory cytokines by MBCs. These effects may contribute to the protective role of liquid ventilation with perfluorocarbons in injuries associated with local activation of inflammatory processes.

[Combined anesthesia with epidural catheter. A retrospective analysis of the perioperative course in patients ungoing radical prostatectomy]

Patients requiring radical prostatectomy (rPE), including retroperitoneal lymphadenectomy are often aged and have coexisting cardiopulmonary diseases, increasing the risk of perioperative complications. The aim of the present study was to evaluate our perioperative anaesthesiologic regimen over the last five years, in terms of safety and patients comfort. Records of 433 patients who underwent rPE between 1994 and 1999 in our hospital were retrospectively reviewed. Patients were divided in those who received: 1. general anaesthesia (GA) alone, 2. a combination of lumbar epidural anaesthesia (LEA) + GA or, 3. thoracic epidural anaesthesia (TEA) + GA. General anaesthesia was performed as balanced anaesthesia, and epidural administered local anaesthetics were bupivacaine 0.25% or ropivacaine 0.2%, 8-12 ml/h. In terms of intra- and postoperative numbers of tachycardiac and hypertensive episodes, a reduced stress response was observed under epidural anaesthesia (EA). Moreover, the weaning duration was shorter under EA and onset of gastrointestinal motility was found earlier ([h] GA: 50.6 +/- 11.1/LEA: 39.3 +/- 13.6/TEA: 33.8 +/- 13.0). Furthermore, a trend to rarer phases of postoperative vomiting and a significant decrease of in hospital stay of about one day ([d] GA: 12.4 +/- 5.8/LEA: 11.1 +/- 3.1/TEA: 11.5 +/- 3.8) was observed. The duration of personnel binding in the OR did not differ significantly between GA and TEA ([min] GA: 222.9 +/- 43.5/LEA: 238.2 +/- 41.8/TEA: 227.0 +/- 46.2), but ICU stay was shortened under TEA. Besides this, TEA reduced the number of pathologic postoperative thorax-x-rays. Senso-motor blockades, decreases of SaO2 and cardiac complications were experienced more frequent under LEA as compared with TEA. Combination of GA and EA, especially TEA, appears to improve perioperative care of patients undergoing rPE, in terms of patients safety and comfort.

Hemodynamic effects of hypertonic hydroxyethyl starch 6% solution and isotonic hydroxyethyl starch 6% solution after declamping during abdominal aortic aneurysm repair

Fluid resuscitation with hypertonic hydroxyethyl starch solutions (HES) is effective in haemorrhagic shock due to the rapid mobilisation of fluids into the intravascular compartment. Declamping of the abdominal aorta with acute redistribution of blood into the vessels of the lower body half causes declamping-induced hypotension. Usually large amount of fluids or vasopressors are necessary to restore hemodynamic stability. Therefore, infusion of a hypertonic colloid solution may be an attractive option to achieve hemodynamic stability. This study was conducted to determine the amount of fluid of either hypertonic HES (HES 6%;7.2% NaCl) or isotonic HES (HES 6%;0.9% NaCl) needed to attain best wedge pressure (PCWP) cardiac index (CI) relation after declamping. Thirty-two high-risk patients undergoing elective abdominal aneurysm resection were enrolled in a prospective, randomised, double blinded study. The individual optimised PCWP/CI relation was determined after induction of anaesthesia. After declamping, both solutions were titrated in small boluses of 100 mL until the previously determined best wedge was reached. The amount of fluid after declamping was significantly reduced in the hypertonic HES- group 162 mL vs. 265 mL in the control group (P < 0.05). Resuscitation time was shortened, and cardiac index was slightly higher in the treatment group. The use of hypertonic HES-solution after aortic declamping led to a significant reduction of fluids necessary to attain optimised PCWP/CI relation. In this clinical trial with moderate blood loss in high-risk patients, hypertonic HES applied in a titrated fashion restored hemodynamic stability faster and without volume overload.

Combination of balanced and regional anaesthesia for minimally invasive surgery in a patient with myasthenia gravis

A 45-year-old man with cryptorchism, who was known to suffer from generalized myasthenia gravis, was admitted to hospital for surgical treatment using laparoscopy. Such minimally invasive surgery requires good muscle relaxation. However, the use of neuromuscular blocking agents in patients with myasthenia gravis may lead to prolonged apnoea after operation, thus necessitating mechanical ventilation of the lungs. We used a combination of general anaesthesia (with desflurane), and epidural anaesthesia (with the amide local anaesthetic ropivacaine) to obtain excellent abdominal relaxation during surgery. Tracheal extubation was possible immediately after the operation and no adverse effects were observed. The patient was discharged from hospital on the second day after operation. The combination of regional and general anaesthesia for minimally invasive surgery in this patient permitted safe anaesthetic management.

[From isoflurane to perfluorohexane? Perfluorocarbons--therapeutic strategies in acute lung failure]

The introduction of Perfluorochemicals into medicine and especially into the treatment of severe lung injury is a fascinating scientific task. Many recall the famous experiments from Clark et al. in 1966 when he demonstrated "liquidventilation with perfluorocarbons" in the mammal species for the first time. After this hallmark, perfluorocarbons were subsequently introduced in research of acute lung injury by the techniques of Total- and Partial-Liquid-Ventilation (TLV; PLV). Perfluorocarbons (saturated organofluorids) have unique chemical and physical properties which made them attractive substances for intraalveolar application. The strong C-F bindings in the perfluorocarbon molecules are responsible for their chemical stability, biochemical inertness, high capacity to dissolve respiratory gases, low surface tension and high vapor pressures. Furthermore, the high density of the PFC lead to radio-opacity and their distribution to dependent lung areas. The efficacy of PFC liquid, applied by TLV/PLV has been demonstrated in numerous animal studies using different models of acute lung injury. Currently, several mechanisms of action of perfluorocarbon fluids in acute lung injury are discussed: recruitment of atelectatic alveoli, prevention of endexpiratory collapse of alveoli ("liquid PEEP"), redistribution of perfusion, oxygen transport, surfactant like effects and decrease of inflammation. Since total liquid ventilation has been used only in experimental models of lung injury, partial liquid ventilation has been introduced successfully into clinical trials (phase I-II). However, the results of the first randomised, controlled study of PLV in 90 adult patients suffering from severe respiratory failure (ALI/ARDS) showed no differences between PLV and conventional treatment. Furthermore, the instillation of relatively large amounts of liquid into the lungs poses several technical challenges and may be associated with complications such as liquithoraces, pneumothoraces and hypoxia. Since mammal lungs are evolutionary specialised to gas exchange using atmospheric oxygen, the application of liquids, even if they transport respiratory gases very well is not physiologic. To overcome these unwanted side effects, we developed a technique of perfluorocarbon vaporisation in analogy to the application of inhalation anaesthetic agents. After resolving some technical issues, this application technique was used successfully in an animal model of acute lung injury. Vaporisation of perfluorohexane in a concentration of 18 Vol.% of inspired gas improved significantly oxygenation and lung compliance. Though these results are promising, mechanisms of action, dose-efficacy relation, surfactant-perfluorocarbon interaction or anti-inflammatory effects of vaporised perfluorohexane are still unclear. These questions need to be clarified before this technique can be applied clinically. However, the inhalation of vapor, a technique already familiar to anaesthesiologists should avoid risks of large amounts of fluids in the bronchoalveolar space. Furthermore, this technique can be administered by established anaesthetic equipment with the advantage of exact dosing, continuous monitoring, and demand application in a way near to clinical routine.

[Combined anesthesia procedures]

The additive properties of general and regional anesthetic techniques are brought together in combined anesthesia to minimise side effects of the individual techniques. Despite a wide experience with both used as single anesthetic techniques, no definite recommendations regarding indications, general contraindications and procedure exist for their combination. Beneficial effects on haemodynamics, respiratory function, intestinal motility and postoperative stress response have been demonstrated for a combination of general anesthesia and thoracic epidural anesthesia (TEA). In addition TEA is favourable in the management of postoperative pain, which has advantageous effects on convalescence especially in a high risk patient group. Nevertheless, until now no reduction of perioperative morbidity and mortality has been demonstrated. Since the combination of two anesthesia techniques theoretically increases the rate of complication, the expected benefit for the patient must predominate. To estimate the risks and benefits of combined anesthesia, the anesthesiologist must be familiar with each single method, as well as with the synergistic effects of both techniques in order to evaluate the individual indication.

Role of NO and endothelin in hemoglobin-induced pulmonary vasoconstriction

The underlying mechanisms of hemoglobin (Hb)-induced vasoconstriction are not yet well understood. The aim of this study was to elucidate the influence of nitric oxide (NO) and endothelin (ET) on Hb-induced pulmonary vasoconstriction. Therefore, an autologous Hb preparation was administered into isolated rabbit lungs, in which pulmonary artery pressure (PAP) and weight gain was monitored. Either glyceroltrinitrate (GTN; 10(-5) M; n=6), L-arginine (10(-2) M; n=6), L-NAME (10(-4)M; n=6), ET(A)- or ET(B)-receptor antagonists (BQ,23, 10 6M, n=6) or (BQ788, 10(-6) M, n=6) were added to the perfusion fluid and NOx and thromboxane A2 levels were measured.

RESULTS

In the control group the Hb-stimulation resulted in a pressure response up to 25.1+/-2.1 mmHg (p < .05), which was 136+/-6% of the reference value. The PAP increase was significantly (p < .05) blunted after GTN (71+/-5%), L-arginine (93+/-6%) and BQ788 (88+/-7%). Pretreatment with L-NAME (139+/-13%) or BQ123 (115+/-9%) did not show significant changes in PAP.

CONCLUSION

The reduction of the Hb-induced pulmonary hypertension by NO-donors points toward the inactivation of NO by free hemoglobin. Likewise, ET(B)-receptor mediated vasoconstrictive effects without changes in NOx concentrations seem to play a pathogenetic role in the Hb-induced pulmonary vasoconstriction.

White blood cell counts and plasma C3a have synergistic predictive value in patients at risk for acute respiratory distress syndrome

OBJECTIVE

To investigate and select nonassociated variables with predictive value for acute respiratory distress syndrome (ARDS) in patients at risk.

DESIGN

Prospective, observational study.

SETTING

A university hospital intensive care unit.

PATIENTS

Twenty-four critically ill patients with different risk factors for ARDS.

INTERVENTIONS

Arterial and mixed venous blood, as well as urine samples, were collected. Invasive hemodynamic measurements were performed.

MEASUREMENTS AND MAIN RESULTS

Fifty-nine variables pertaining to the cardiorespiratory, hepatic, immunologic, and renal systems and including plasma complement activation products C3a and SC5b-9 and polymorphonuclear elastase, were determined every 6 hrs for 3 days in patients at risk for ARDS. Associations among variables were investigated and the predictive value of nonassociated variables for ARDS was determined. Patients who developed ARDS (n=8) had lower white blood cell counts at the time they entered the study (p=.006) and during the first 24 hrs thereafter (p=.032). Also, plasma C3a concentrations were markedly higher during the first 24 hrs in patients who developed ARDS (p=.006). Plasma C3a had better predictive value than did white blood cell counts for cutoff points set by discriminant analysis at 1075 ng/mL (1.075 x 10(-3) g/L) and 5700 cells/mL, respectively. The combination of both variables in a discriminant function improved the predictive value for ARDS.

CONCLUSIONS

The most notable and nonassociated alterations observed in patients who developed ARDS were lower white blood cell counts and higher plasma C3a concentrations compared with counts and concentrations in patients who did not develop ARDS. Plasma C3a concentrations showed better predictive value than white blood cell counts. The combination of white blood cell counts with plasma C3a concentrations synergistically improved the predictive value for ARDS. This combination may prove useful for identifying subpopulations at highest risk for ARDS and may contribute to make treatment at an early stage of the syndrome possible.

Blood compatible polymers in intensive care units: state of the art and current aspects of biomaterials research

The use of artificial organs in cases of acute renal failure, acute respiratory distress syndrome (ARDS) and multiorgan dysfunction syndrome (MODS) has lead to a significant reduction of mortality. However, the interaction between body and biomaterials results in the activation of the coagulation system and in the induction of systemic inflammatory response syndrome. The necessary anticoagulation may be contraindicated and may even further increase the risk for the patient. This article evaluates the currently applied polymeric materials used in intensive care units (ICU) and gives a possible outlook into future developments. It is emphasized that systematic interdisciplinary research of physicians and biomaterial scientists is essential for the successful development of new polymers with improved biocompatibility. For this purpose a brief overview of analytical techniques for surface characterization is given, and future developments to a fully biocompatible polymer are described.

Reduced cerebral vasomotor reactivity as an indicator of postoperative confusion

Surgical intervention in elderly patients carries a high risk. A frequent problem with surgery in these patients is the occurrence of a temporary confusional state, which increases both the risk of postoperative complications and the need for intensive care. We hypothesised that, in part, temporary confusional state results from cerebral hypoxia occurring in response to blood pressure fluctuations during surgery. To assess whether disruption of autoregulation of cerebral blood vessels plays a role in temporary confusional state, we studied 31 patients over 55 years of age, using the Doppler-carbon dioxide test. We determined whether vasomotor reactivity could be used diagnostically to identify those patients most likely to experience temporary confusional state. Blood flow velocity in the middle cerebral artery was detected using Doppler ultrasound, and hypercapnia was induced by breathing carbon dioxide until an end-tidal concentration of 8.0% by volume was reached. Vasomotor reactivity was calculated on the basis of the changes in blood flow velocity in response to the increase in carbon dioxide. Temporary confusional state was assessed using the Syndrome Short Test (Syndrom-Kurztest). We found that resting blood flow velocity was inversely related to age (p < 0.05). In addition, there was a significant inverse correlation between vasomotor reactivity and temporary confusional state (p < 0.05). These data indicate that vasomotor reactivity, as measured by the Doppler-carbon dioxide test, is a reliable tool to identify patients at risk for postoperative psychological disturbances.

Partial carbon dioxide rebreathing: a reliable technique for noninvasive measurement of nonshunted pulmonary capillary blood flow

OBJECTIVE

To determine the validity and clinical utility of the partial CO2 rebreathing technique for measurement of nonshunted pulmonary capillary blood flow and cardiac output.

DESIGN

Prospective, controlled animal laboratory investigation and clinical trial.

SETTINGS

Animal research facility and intensive care unit of a university hospital.

SUBJECTS

Fifteen adult sheep, weighting 58 to 78 kg.

PATIENTS

Mechanically ventilated patients with different underlying diseases (n = 12) and with adult respiratory distress syndrome (ARDS) (n = 8).

INTERVENTIONS

CO2 elimination rate (VCO2) was measured breath-by-breath with a system developed for the study and also by gas collection (validation procedure in patients with different underlying diseases). Partial CO2 rebreathing maneuvers, cardiac output by thermodilution, and blood gas analysis were performed in sheep with lung atelectasis and in patients with ARDS.

MEASUREMENTS AND MAIN RESULTS

The degree of correlation between VCO2 measured with the system developed and gas collection was very good (r2 = .95, p < .0001), and bias and precision calculations (1 +/- 9 mL/min) showed close agreement between methods. The overall degree of correlation between partial CO2 rebreathing measurements and cardiac output was moderate (r2 = .54, p < .0001), the noninvasive method tending to underestimate cardiac output, as shown by bias and precision calculations (-1.69 +/- 1.90 L/min). In contrast, the overall degree of correlation between partial CO2 rebreathing measurements and nonshunted pulmonary capillary blood flow was good (r2 = .73, p < .0001). Bias and precision calculations (0.25 +/- 0.83 L/min) showed a tendency for the partial CO2 rebreathing technique to slightly overestimate pulmonary capillary blood flow. Variance differences between partial CO2 rebreathing measurements and cardiac output could be mostly explained by intrapulmonary right-to-left shunt fraction (r2 = .51, p < .0001).

CONCLUSIONS

Our results support the use of the system developed for breath-by-breath VCO2 measurements. The lack of agreement between partial CO2 rebreathing measurements and cardiac output was mostly explained by intrapulmonary right-to-left shunt, suggesting that this technique may not be appropriate for monitoring cardiac output in patients with increased venous admixture. In contrast, our results demonstrate that the partial CO2 rebreathing technique is reliable for measurement of the effective nonshunted pulmonary capillary blood flow. This technique may prove useful to guide ventilatory therapy adjustments in an attempt to optimize nonshunted pulmonary capillary blood flow.

Regional heterogeneity of cerebral blood flow response to graded volume-controlled hemorrhage

OBJECTIVE

Of the animal models of human hemorrhagic shock, the volume-controlled hemorrhage model appears to come closer to the clinical situation than the commonly used pressure-controlled model, since the volume-controlled model allows regulatory adjustment of blood pressure. The effects of volume-controlled hemorrhage on local cerebral blood flow (LCBF) of conscious animals are not known. The present study investigates specific reaction patterns of LCBF in comparison to mean cerebral blood flow (CBF) during graded volume-controlled hemorrhagic shock in conscious rats.

METHODS

Conscious, spontaneously breathing, and minimally restrained rats were subjected to different degrees of volume-controlled hemorrhage (taking either 25, 30, 35, or 40 ml arterial blood/kg body weight (b.w.). Thirty minutes after the completion of blood taking, LCBF was determined during hemorrhagic hypovolemia using the autoradiographic iodo (14C) antipyrine method. A group of untreated rats (no hemorrhage) served as controls. LCBF was determined in 34 defined brain structures and mean CBF was calculated.

RESULTS

During less severe hemorrhage (25 and 30 ml/kg b.w.) mean CBF was significantly higher than in the control group (+19% and +25%). During severe hemorrhage (35 and 40 ml/kg b.w.) mean CBF remained unchanged compared to the control values, although significant increases in LCBF could be detected in many of the brain structures analyzed (maximum +44%). The mean coefficient of variation of CBF was increased, indicating a larger heterogeneity of LCBF values at shed blood volumes of 35 and 40 ml/kg b.w.

CONCLUSIONS

A comprehensive and novel description of the local distribution of CBF during graded volume-controlled hemorrhage in conscious rats shows unexpected increases in LCBF and mean CBF. This "hypovolemic cerebral hyperemia" might be caused by endogenous hemodilution, thus maintaining the blood supply to the brain during hypovolemic shock.

Coupling between local cerebral blood flow and metabolism after hypertonic/hyperoncotic fluid resuscitation from hemorrhage in conscious rats

The effects of small volume hypertonic/hyperoncotic fluid resuscitation from hemorrhage on brain metabolism and blood flow were evaluated by autoradiographic techniques with high spatial resolution. The data were compared to fluid resuscitation with a volume equal to shed blood of isotonic 6% hydroxyethyl starch solution (HES) and a control group without hemorrhage and fluid resuscitation (n = 6 in each group). In conscious rats, volume-controlled hemorrhage for 30 min (30 mL/kg body weight, resulting in a blood loss of approximately 50% of the circulating blood volume) was followed by intravenous infusion of a hypertonic/hyperoncotic saline hydroxyethyl starch solution (HTHO; 7.5% saline/10% hydroxyethyl starch, 4.0 mL/kg body weight). Local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCGU) were measured in 34 brain structures 2 h after fluid resuscitation by means of the quantitative autoradiographic iodo [14C]antipyrine and 2-[14C]-deoxy-D-glucose methods. Compared to the untreated control group, LCBF increased significantly in all brain regions analyzed after fluid resuscitation with HTHO (mean, +63%) or HES (mean, +56%). The increases in LCBF after fluid resuscitation were sufficient to restore cerebral oxygen delivery to the level calculated for the untreated control group. LCGU was unchanged after fluid resuscitation. The close relationship between LCGU and LCBF observed in the control group (r = 0.95) was preserved after hemorrhage and fluid resuscitation with HTHO (r = 0.97) and HES (r = 0.96), although the LCBF-to-LCGU ratio was reset to a higher level (1.5 mL/mumol in the control group and 2.7 mL/mumol after fluid resuscitation with HTHO and HES, P < 0.05). We conclude that the increase in LCBF compensates for the reduction of arterial oxygen content to maintain cerebral oxygen delivery. Therefore, "small volume resuscitation" appears to be as effective as resuscitation with large volumes of isotonic HES in meeting the circulatory and metabolic demands of the brain tissue within the first 2 h after fluid resuscitation from hemorrhage.

Effect of cyclooxygenase inhibition in a canine model of unilateral pulmonary occlusion and reperfusion

OBJECTIVE

To assess the effects of the cyclooxygenase inhibitor diclofenac in a canine model of pulmonary occlusion and reperfusion of the left lower lobe (LLL).

DESIGN

Twelve adult beagle dogs (13-17 kg) were randomly assigned to a control group (n = 6) and a diclofenac-treated group (n = 6). Animals in the treatment group received 20 mg diclofenac sodium/kg as a single dose both before the experiment and at the end of surgical preparation; six animals served as controls.

INTERVENTIONS

In the anesthetized animals, the left upper and middle lobes were resected. Circulation and ventilation of the LLL were selectively blocked by clamping. Complete occlusion of the LLL (30 min) was followed by periods of selective reperfusion (10 min, RP) and combined reperfusion and reventilation (120 min, RP/RV).

MEASUREMENTS AND RESULTS

Reperfusion of the LLL resulted in a significant increase in pulmonary arterial pressure (Ppa) in the early RP/RV period as compared to baseline values (25.3 +/- 4.7 vs 15.8 +/- 1.9 mmHg, p < 0.05, paired t-test). This increase was significantly inhibited in the diclofenac-treated animals (17.0 +/- 2.0 mmHg, p < 0.01 vs controls, ANOVA). Gravimetrically determined extravascular lung water (EVLW) showed no significant difference in the continuously ventilated lobes of the right lung between diclofenac-treated animals (3.8 ml/g dry weight) and controls (3.9 +/- 0.9 ml/g dry weight) at the end of the experiment. EVLW, however, increased significantly in the LLL of control animals after 2 h of combined reperfusion and reventilation, whereas this increase was significantly inhibited in the diclofenac-treated animals (4.5 +/- 0.7 ml/g dry weight in the diclofenac group vs 6.5 +/- 1.3 ml/g dry weight in the control group, p < 0.05).

CONCLUSIONS

Diclofenac inhibits the increase in both pulmonary arterial pressure and EVLW during reperfusion and reventilation of LLL. Thus, these changes appear to be mediated by cyclooxygenase metabolites.

Optimal preoperative titrated dosage of hypertonic-hyperoncotic solutions in cardiac risk patients

Hypertonic-iso/hyperoncotic solutions have been the subject of numerous studies, mostly used in a fixed dosage (4 mL/kg bw or 250 mL). Nearly no study exists to prove whether this is the appropriate dosage especially in cardiac risk patients with accompanying diseases. We have compared preoperative volume loading with either 10% hydroxyethyl-starch/7.5% NaCl (HHT-HES) or 10% hydroxyethyl-starch/.9% NaCl (HES) in 50 mL bolus infusions. Volume loading was done with either HES or HHT-HES in 2 x 20 patients before aortic aneurysmectomy. The endpoint of stepwise infusion represented the highest cardiac index (CI) at the lowest possible wedge pressure (PCWP) (turning point of each individual Frank Starling relation). 167.5 mL (+/- 45.5 mL = 2.41 mL/kg bw) of HHT-HES and 440 mL (+/- 26.15 mL = 6.33 mL/kg bw) of HES were necessary. We observed a significant higher increase of the CI in the HHT-HES group. Significant increases of PCWP, pulmonary artery pressure, and central venous pressure occurred within the groups without any significant differences between the groups (p < .05). Results of the study showed: 1) The commonly used fixed dosage of 4 mL/kg bw of HHT-HES is too high in cardiac risk patients with slight hypovolemia. 2) HHT-HES should be given in an individual titration. 3) In the HHT-HES group we observed a positive inotropic effect (higher CI). 4) With the individual titration of HHT-HES no negative side effects occurred (especially no hypotension).

Effects of a perfluorocarbon emulsion on regional cerebral blood flow and metabolism after fluid resuscitation from hemorrhage in conscious rats

Regional cerebral blood flow and metabolism were investigated after addition of a small volume of perfluorocarbon (PFC) emulsion to the resuscitation fluid after hemorrhage. Severe volume-controlled hemorrhage (40 mL/kg body weight (bw) withdrawn over 30 min followed by hypovolemia of 30 min duration) was induced in conscious rats. While breathing 100% oxygen, the intravascular volume was repleted by the infusion of either 6% hydroxyethyl starch (mean mol wt 200,000/0.5; HES) or 6% hydroxyethyl starch plus perflubron (90% wt/vol emulsion of perfluoroctylbromide, 3 mL/kg bw; HES-PFOB). Two hours after fluid resuscitation either iodo[14C]antipyrine or 2[14C]deoxy-D-glucose were infused. Local cerebral blood flow (LCBF) or local cerebral glucose utilization (LCGU) were determined in 34 brain structures using quantitative autoradiography. Local cerebral metabolism was not disturbed in the HES and the HES-PFOB groups after fluid resuscitation, although slight reductions (mean -14%) were measured (HES-PFOB vs HES; P < 0.05). The HES-PFOB group showed LCBF values that were higher in the different brain structures than those of the HES group (mean +30%). A close correlation was found between LCGU and LCBF of the 34 brain structures in both groups (HES: r = 0.96, P < 0.01; HES-PFOB: r = 0.98, P < 0.01), whereas the LCBF-to-LCGU ratio was reset from 2.2 mL/mumol in the HES group to 3.4 mL/mumol in the HES-PFOB group (P < 0.05). The higher blood flows in the HES-PFOB group were sufficient to restore cerebral oxygen delivery to normal levels at a reduced arterial oxygen content.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoradiographic determination of regional cerebral blood flow and metabolism in conscious rats after fluid resuscitation from haemorrhage with a haemoglobin-based oxygen carrier

The effects of resuscitation fluids on the brain have been investigated in previous studies by global measurements of cerebral blood flow and metabolism. In this study we have examined the effects of a novel haemoglobin-based oxygen carrier on local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCGU) after resuscitation from a volume-controlled haemorrhage of 30 min (3.0 ml/100 g body weight) with ultrapurified, polymerized, bovine haemoglobin (UPBHB). LCBF and LCGU were measured in 34 brain structures of conscious rats 2 h after resuscitation using quantitative iodo(14C)antipyrine and 2-(14C)-deoxy-D-glucose methods. The data were compared with a control group without haemorrhage and fluid resuscitation. In the haemorrhage group, LCBF increased after resuscitation by 12-56% in the different brain structures (mean 36%). LCGU changed less (0 to +18%, mean +9%). In the control group there was a close relationship between LCGU and LCBF (r = 0.95). After fluid resuscitation the relationship was preserved (r = 0.95), although it was reset at a higher ratio of LCBF to LCGU (P < 0.05). We conclude that fluid resuscitation of a 30 min volume-controlled haemorrhage using the haemoglobin-based oxygen carrier, UPBHB, induced a moderate degree of heterogeneity in the resulting changes of LCGU and LCBF. Local disturbances of cerebral blood flow or metabolism were not observed.

Lack of dependence of cerebral blood flow on blood viscosity after blood exchange with a Newtonian O2 carrier

Whether the increase in cerebral blood flow measured after hemodilution is mediated by a decrease in blood viscosity or in oxygen delivery to the brain is debated. In the present study, blood was replaced by an oxygen-carrying blood substitute, ultrapurified, polymerized, bovine hemoglobin (UPBHB). In contrast to normal blood, UPBHB yields a constant and defined viscosity in the brain circulation, since its viscosity is not dependent on the shear rate. CBF was determined after blood exchange with UPBHB in one group of conscious rats (UPBHB group) and in another group of blood-exchanged conscious rats in which viscosity was increased fourfold by the addition of 2% polyvinylpyrrolidone (PVP), mw 750,000 (UPBHB-PVP group). Local CBF (LCBF) was measured in 34 brain structures by means of the quantitative iodo(14C)antipyrine method. After blood replacement, systemic parameters such as cardiac index, arterial blood pressure, blood gases, and acid-base status were not different between the UPBHB and the UPBHB-PVP groups. In particular, arterial oxygen content was similar in both groups. Compared with a control group without blood exchange, LCBF was increased after blood exchange in the different brain structures by 60-102% (UPBHB group) and by 33-101% (UPBHB-PVP group). Mean CBF was increased by 77% in the UPBHB group and by 69% in the UPBHB-PVP group. No significant differences were observed in the values of LCBF or mean CBF between the UPBHB group and the UPBHB-PVP group. The results show that a fourfold variation in the viscosity of a Newtonian blood substitute does not result in differences in CBF values.(ABSTRACT TRUNCATED AT 250 WORDS)

Local cerebral blood flow and glucose utilization after blood exchange with a hemoglobin-based O2 carrier in conscious rats

The effects of a blood exchange on cerebral blood flow and glucose utilization were studied. A near to total blood exchange (hematocrit < 3%) was achieved in conscious rats by isovolemic hemodilution. Ultrapurified, polymerized, bovine hemoglobin (UPBHB) served as a blood substitute. Local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCGU) were measured in 34 brain structures of conscious rats by means of the ido[14C]antipyrine and the 2-[14C]-deoxy-D-glucose methods. A group of rats without blood exchange served as control. After blood exchange LCBF increased from 36 to 126% in the different brain structures resulting in a nearly doubled mean cerebral blood flow (+82%). LCGU increased only moderately by 0-24%. Significant increases in LCGU were observed in 16 brain structures. Mean cerebral glucose utilization slightly increased (+14%). The relationship between LCGU and LCBF was found to be tight both in the control group (r = 0.95) as well as after blood replacement (r = 0.94), although it was reset to a higher overall LCBF-to-LCGU ratio. The profound increases in LCBF observed after blood exchange, which were not paralleled by comparable increases in LCGU, might be explained by a reduction of blood viscosity after blood exchange. Additional effects of blood exchange observed in the present study were an increase of mean arterial blood pressure and a decline of heart rate. The results indicate that replacement of blood with the hemoglobin-based oxygen carrier UPBHB appears to meet the cerebral circulatory and metabolic demands of the brain tissue.

[Myxedema coma as a rare postoperative complication]

Myxedema coma is characterized by severe lack of thyroid hormones, unconsciousness and serious restriction of vital functions. The mortality rate still ranges between 50 and 80%. In patients with inapparent hypothyroidism myxedema coma occasionally follows surgery, anesthesia or severe infection. A case of myxedema coma following surgery is reported. CASE REPORT. A 46-year-old woman was anesthesized for hip replacement. The intraoperative cardiovascular situation was characterized by hypotension and tachycardia. On the first postoperative day, unexpectedly a cardiac arrest occurred. Resuscitation with high doses of epinephrine was successful. There was no evidence of myocardial infarction, hypoxia and pulmonary embolism as causative factors for cardiac arrest. A pulmonary artery catheter was inserted and showed low cardiac output. Catecholamines and intravascular fluids were administered without hemodynamic improvement. In the next 5 days pneumonia was followed by ARDS and acute renal failure. After successful treatment of these complications the patient remained in deep coma. An intracerebral disease could be excluded by computerized tomography. Evaluation showed low thyroid hormones (T3; T4) and elevated TSH. The diagnosis of a myxedema coma was assumed. After failure of oral therapy with L-thyroxine (0.025-0.05 mg/day) for 10 days, intravenous therapy with 0.5 mg L-thyroxine was performed. Thirty-six hours later the patient regained consciousness, without cardiac complications. The patient progressed uneventfully under oral therapy with 0.1 mg L-thyroxine and was discharged from the hospital 6 weeks later. DISCUSSION. Pathophysiology and symptomatology of a case of postoperative myxedema coma are described (Tables 1-4). In this patient, the following symptoms occurred: low thyroid hormones (T3; T4), elevated TSH, deep coma, decreased ventilatory response to CO2, diminished myocardial contractility under catecholamine stimulation, impaired renal water excretion. After failure of oral substitution of L-thyroxine, intravenous therapy had to be performed in spite of the high risk of further cardiac complications in this patient. This led to complete recovery with normal neuropsychological and cardiopulmonary parameters. CONCLUSION. Myxedema coma is a rare complication in postoperative care, but in cases of inexplicable unconsciousness thyroid failure should be excluded. If myxedema coma is evident, intravenous therapy with L-thyroxine should be performed under the conditions of extended monitoring.

[Modified hemoglobin as a blood substitute in a rat model]

The use of modified haemoglobin solutions as blood substitutes has been investigated extensively during the past decades. Ultrapurified, polymerised bovine haemoglobin (upbHb) is a promising new substance in this respect. It was the aim of the present investigation to study the cardiovascular and respiratory effects of massive blood replacement with upbHb in a new model of conscious rats with continuous haemodynamic monitoring. METHODS. The right femoral artery and vein of 13 male Sprague-Dawley rats were catheterised during halothane-N2O-O2 anaesthesia. A thermistor catheter was placed in the descending aorta via the left femoral artery for measuring cardiac output by the thermodilution method. After recovery from anaesthesia blood replacement was achieved by arterial blood withdrawal and simultaneous venous infusion of upbHb in equal amounts. The haematocrit was lowered to < 3% and the animals were then left undisturbed in a rat restrainer while breathing room air. RESULTS. The animals showed no signs of disturbed behaviour patterns, distress, or adverse reactions. There were no significant changes in cardiac index and oxygen delivery during the investigation period of 4 h. A marked increase in mean arterial pressure (MABP) and systemic vascular resistance (SVR) of 30% was observed while stroke volume remained unchanged. Blood gases, acid-base status, and plasma glucose showed no major changes. Plasma oncotic pressure increased during the investigation period. CONCLUSIONS. The results indicate that there is adequate oxygenation and sufficient systemic oxygen delivery in conscious and drug-free rats after isovolaemic haemodilution with upbHb to a final haematocrit of < 3%. In contrast to previous haemodilution studies, which have tested non-oxygen-carrying solutions, no changes in cardiac index were observed. The cause of the increase in MAP and SVR remains to be established.