Linezolid brain penetration in neurointensive care patients

BACKGROUND

Linezolid exposure in critically ill patients is associated with high inter-individual variability, potentially resulting in subtherapeutic antibiotic exposure. Linezolid exhibits good penetration into the CSF, but its penetration into cerebral interstitial fluid (ISF) is unknown.

OBJECTIVES

To determine linezolid penetration into CSF and cerebral ISF of neurointensive care patients.

PATIENTS AND METHODS

Five neurocritical care patients received 600 mg of linezolid IV twice daily for treatment of extracerebral infections. At steady state, blood and CSF samples were collected from arterial and ventricular catheters, and microdialysate was obtained from a cerebral intraparenchymal probe.

RESULTS

The median fAUC0-24 was 57.6 (24.9-365) mg·h/L in plasma, 64.1 (43.5-306.1) mg·h/L in CSF, and 27.0 (10.7-217.6) mg·h/L in cerebral ISF. The median penetration ratio (fAUCbrain_or_CSF/fAUCplasma) was 0.5 (0.25-0.81) for cerebral ISF and 0.92 (0.79-1) for CSF. Cerebral ISF concentrations correlated well with plasma (R = 0.93, P < 0.001) and CSF levels (R = 0.93, P < 0.001).The median fAUC0-24/MIC ratio was ≥100 in plasma and CSF for MICs of ≤0.5 mg/L, and in cerebral ISF for MICs of ≤0.25 mg/L. The median fT>MIC was ≥80% of the dosing interval in CSF for MICs of ≤0.5 mg/L, and in plasma and cerebral ISF for MICs of ≤0.25 mg/L.

CONCLUSIONS

Linezolid demonstrates a high degree of cerebral penetration, and brain concentrations correlate well with plasma and CSF levels. However, substantial variability in plasma levels, and thus cerebral concentrations, may result in subtherapeutic tissue concentrations in critically ill patients with standard dosing, necessitating therapeutic drug monitoring.

The Effect of Oral Nimodipine on Cerebral Metabolism and Hemodynamic Parameters in Patients Suffering Aneurysmal Subarachnoid Hemorrhage

INTRODUCTION

Nimodipine is routinely administered to aneurysmal subarachnoid hemorrhage patients to improve functional outcomes. Nimodipine can induce marked systemic hypotension, which might impair cerebral perfusion and brain metabolism.

METHODS

Twenty-seven aneurysmal subarachnoid hemorrhage patients having multimodality neuromonitoring and oral nimodipine treatment as standard of care were included in this retrospective study. Alterations in mean arterial blood pressure (MAP), cerebral perfusion pressure (CPP), brain tissue oxygen tension (pbtO2), and brain metabolism (cerebral microdialysis), were investigated up to 120 minutes after oral administration of nimodipine (60 mg or 30 mg), using mixed linear models.

RESULTS

Three thousand four hundred twenty-five oral nimodipine administrations were investigated (126±59 administrations/patient). After 60 mg of oral nimodipine, there was an immediate statistically significant (but clinically irrelevant) drop in MAP (relative change, 0.97; P<0.001) and CPP (relative change: 0.97; P<0.001) compared with baseline, which lasted for the whole 120 minutes observation period (P<0.001). Subsequently, pbtO2 significantly decreased 50 minutes after administration (P=0.04) for the rest of the observation period; the maximum decrease was -0.6 mmHg after 100 minutes (P<0.001). None of the investigated cerebral metabolites (glucose, lactate, pyruvate, lactate/pyruvate ratio, glutamate, glycerol) changed after 60 mg nimodipine. Compared with 60 mg nimodipine, 30 mg induced a lower reduction in MAP (relative change, 1.01; P=0.02) and CPP (relative change, 1.01; P=0.03) but had similar effects on pbtO2 and cerebral metabolism (P>0.05).

CONCLUSIONS

Oral nimodipine reduced MAP, which translated into a reduction in cerebral perfusion and oxygenation. However, these changes are unlikely to be clinically relevant, as the absolute changes were minimal and did not impact cerebral metabolism.

The Effect of Pregabalin on the Minimum Alveolar Concentration of Sevoflurane: A Randomized, Placebo-Controlled, Double-Blind Clinical Trial

Background

Pregabalin is commonly used perioperatively to reduce post-operative pain and opioid consumption and to prevent the development of chronic pain. It has been shown to reduce anesthetic consumption in balanced anesthesia, but studies investigating its effect on the minimum alveolar concentration (MAC) of volatile anesthetics are lacking. The aim of this study was to investigate the effect of two different doses of pregabalin on the MAC of sevoflurane.

Methods

In a randomized, double-blinded, placebo controlled clinical study, 75 patients were assigned to receive placebo, 300 mg pregabalin, or 150 mg pregabalin, as a capsule 1 h before anesthesia induction with sevoflurane only. After equilibration, the response to skin incision (movement vs. non-movement) was monitored. The MAC was assessed using an up- and down-titration method.

Results

The MAC of sevoflurane was estimated as 2.16% (95% CI, 2.07–2.32%) in the placebo group, 1.44% (95% CI, 1.26–1.70%) in the 300 mg pregabalin group, and 1.81% (95% CI, 1.49–2.13%) in the 150 mg pregabalin group. We therefore report a 33% reduction in the MAC of sevoflurane in the 300 mg pregabalin group as compared to placebo. The MAC of the 150 mg pregabalin group was reduced by 16% as compared to placebo but was not statistically significant.

Conclusions

The administration of 300 mg pregabalin reduced the MAC of sevoflurane by 33%, while the administration of 150 mg pregabalin did not significantly reduce the MAC of sevoflurane. Pregabalin use led to a small reduction in post-operative pain levels but increased side effects in a dose-dependent manner.

Validation of bedside ultrasound to predict lumbar muscle area in the computed tomography in 200 non-critically ill patients: The USVALID prospective study

BACKGROUND & AIMS

Skeletal muscle area (SMA) in the computed tomography (CT) at the third lumbar vertebra (L3) level is a proxy for whole-body muscle mass but is only performed for clinical reasons. Ultrasound is a promising tool to determine muscle mass at the bedside. It is still unclear how well ultrasound and which ultrasound measuring points can predict CT L3 SMA.

METHODS

This prospective observational trial included 200 non-critically ill patients, who underwent an abdominal CT scan for any clinical reason within 48 h before the ultrasound examination. Ultrasound muscle thickness was evaluated at 3 measuring points on the thigh and 2 measuring points on the upper arm with minimal compression. On the CT scan, the entire L3 SMA was measured based on Hounsfield units. Using a model selection algorithm based on the Bayesian information criterion (BIC) and clinical considerations, a linear prediction model for CT L3 SMA based on the ultrasound muscle thickness and other independent variables was fitted and assessed with cross-validation.

RESULTS

67,5% and 32,5% of the patients were from surgical and medical wards, respectively. Mean ultrasound muscle thickness values were between 2,2 and 3,6 cm on the thigh and between 1,4 and 2,8 cm on the upper arm. All ultrasound muscle thickness values were higher in men than in women (P < 0,05). CT L3 SMA was 40 cm² higher in men than in women (P < 0,001). The final prediction model for CT L3 SMA included the following 4 independent variables: ultrasound muscle thickness at the ventral measuring point of the thigh in the short-axis plane, sex, weight, and height. It had a similar BIC (BIC of 1515) compared to larger models with 6-8 independent variables including multiple ultrasound measuring points (BIC of 1506-1519). Additional clinical considerations to choose the final model were less time consumption when measuring a single ultrasound measuring point and better anatomical overview at the short-axis plane. The final model predicted CT L3 SMA with a R² of 0,74 (P < 0,001) and a cross-validated R² of 0,65.

CONCLUSIONS

One single ultrasound measuring point at the thigh together with sex, height and weight very well predicts CT L3 SMA across different clinical populations. Ultrasound is a safe and bedside method to measure muscle thickness longitudinally to monitor the effects of nutrition and physical therapy.

Ethanol reduces the minimum alveolar concentration of sevoflurane in rats

A high number of trauma patients are under the influence of alcohol. Since many of them need immediate surgical procedures, it is imperative to be aware of the interaction of alcohol with general anesthesia. To counter challenges that arise from clinical studies, we designed an animal experiment in which 48 adult Wistar rats either received 1 g · kg-1 ethanol, 2 g · kg-1 ethanol or placebo via intraperitoneal application. Subsequently, they were anesthetized with an individual concentration of sevoflurane. The minimum alveolar concentration (MAC) of the different groups was assessed using Dixon's up-and-down design and isotonic regression methods. The bootstrap estimate of the MAC of sevoflurane in the placebo group was 2.24 vol% (95% CI 1.97-2.94 vol%). In the low dose ethanol group, the bootstrap estimate was 1.65 vol% (95% CI 1.40-1.98 vol%), and in the high dose ethanol group, it was 1.08 vol% (95% CI 0.73-1.42 vol%). We therefore report that intraperitoneal application of 1 g · kg-1 or 2 g · kg-1 ethanol both resulted in a significant reduction of the MAC of sevoflurane in adult Wistar rats: by 26.3% and 51.8% respectively as compared to placebo.

Meropenem concentrations in brain tissue of neurointensive care patients exceed CSF levels

BACKGROUND

Inadequate antibiotic exposure in cerebral infections might have detrimental effects on clinical outcome. Commonly, antibiotic concentrations within the CSF were used to estimate cerebral target levels. However, the actual pharmacological active unbound drug concentration beyond the blood-brain barrier is unknown.

OBJECTIVES

To compare meropenem concentrations in blood, CSF and cerebral microdialysate of neurointensive care patients.

PATIENTS AND METHODS

In 12 patients suffering subarachnoid haemorrhage, 2000 mg of meropenem was administered every 8 h due to an extracerebral infection. Meropenem concentrations were determined in blood, CSF and cerebral microdialysate at steady state (n = 11) and following single-dose administration (n = 5).

RESULTS

At steady state, the free AUC0-8 was 233.2 ± 42.7 mg·h/L in plasma, 7.8 ± 1.9 mg·h/L in CSF and 26.6 ± 14.0 mg·h/L in brain tissue. The brain tissue penetration ratio (AUCbrain/AUCplasma) was 0.11 ± 0.06, which was more than 3 times higher than in CSF (0.03 ± 0.01), resulting in an AUCCSF/AUCbrain ratio of 0.41 ± 0.16 at steady state. After single-dose administration similar proportions were achieved (AUCbrain/AUCplasma = 0.09 ± 0.08; AUCCSF/AUCplasma = 0.02 ± 0.00). Brain tissue concentrations correlated well with CSF concentrations (R = 0.74, P < 0.001), but only moderately with plasma concentrations (R = 0.51, P < 0.001). Bactericidal thresholds were achieved in both plasma and brain tissue for MIC values ≤16 mg/L. In CSF, bactericidal effects were only reached for MIC values ≤1 mg/L.

CONCLUSIONS

Meropenem achieves sufficient bactericidal concentrations for the most common bacterial strains of cerebral infections in both plasma and brain tissue, even in non-inflamed brain tissue. CSF concentrations would highly underestimate the target site activity of meropenem beyond the blood-brain barrier.

Detrimental effects of intrahospital transport on cerebral metabolism in patients suffering severe aneurysmal subarachnoid hemorrhage

OBJECTIVE

Intrahospital transport for CT scans is routinely performed for neurosurgical patients. Particularly in the sedated and mechanically ventilated patient, intracranial hypertension and blood pressure fluctuations that might impair cerebral perfusion are frequently observed during these interventions. This study quantifies the impact of intrahospital patient transport on multimodality monitoring measurements, with a particular focus on cerebral metabolism.

METHODS

Forty intrahospital transports in 20 consecutive patients suffering severe aneurysmal subarachnoid hemorrhage (SAH) under continuous intracranial pressure (ICP), brain tissue oxygen tension (pbtO2), and cerebral microdialysis monitoring were prospectively included. Changes in multimodality neuromonitoring data during intrahospital transport to the CT scanner and the subsequent 10 hours were evaluated using linear mixed models. Furthermore, the impact of risk factors at transportation, such as cerebral vasospasm, cerebral hypoxia (pbtO2 < 15 mm Hg), metabolic crisis (lactate-pyruvate ratio [LPR] > 40), and transport duration on cerebral metabolism, was analyzed.

RESULTS

During the transport, the mean ICP significantly increased from 7.1 ± 3.9 mm Hg to 13.5 ± 6.0 mm Hg (p < 0.001). The ICP exceeded 20 mm Hg in 92.5% of patients; pbtO2 showed a parallel rise from 23.1 ± 13.3 mm Hg to 28.5 ± 23.6 mm Hg (p = 0.02) due to an increase in the fraction of inspired oxygen during the transport. Both ICP and pbtO2 returned to baseline values thereafter. Cerebral glycerol significantly increased from 71.0 ± 54.9 µmol/L to 75.3 ± 56.0 µmol/L during the transport (p = 0.01) and remained elevated for the following 9 hours. In contrast, cerebral pyruvate and lactate levels were stable during the transport but showed a significant secondary increase 1-8 hours and 2-9 hours, respectively, thereafter (p < 0.05). However, the LPR remained stable over the entire observation period. Patients with extended transport duration (more than 25 minutes) were found to have significantly higher levels of cerebral pyruvate and lactate as well as lower glutamate concentrations in the posttransport period.

CONCLUSIONS

Intrahospital transport and horizontal positioning during CT scans induce immediate intracranial hypertension and an increase in cerebral glycerol, suggesting neuronal injury. Afterward, sustained impairment of neuronal metabolism for several hours could be observed, which might increase the risk of secondary ischemic events. Therefore, intrahospital transport for neuroradiological imaging should be strongly reconsidered and only indicated if the expected benefit of imaging results outweighs the risks of transportation.

The Impact of Intra-Arterial Papaverine-Hydrochloride on Cerebral Metabolism and Oxygenation for Treatment of Delayed-Onset Post-Subarachnoid Hemorrhage Vasospasm

BACKGROUND

Delayed posthemorrhagic vasospasm remains among the major complications after aneurysmal subarachnoid hemorrhage (SAH) and can result in devastating ischemic strokes. As rescue therapy, neurointerventional procedures are used for selective vasodilatation.

OBJECTIVE

To investigate the effects of intra-arterial papaverine-hydrochloride on cerebral metabolism and oxygenation.

METHODS

A total of 10 consecutive patients, suffering from severe aneurysmal SAH were prospectively included. Patients were under continuous multimodality neuromonitoring and required intra-arterial papaverine-hydrochloride for vasospasm unresponsive to hypertensive therapy. Cerebral metabolism (microdialysis), brain tissue oxygen tension (ptiO2), intracranial pressure (ICP), and cerebral perfusion pressure (CPP) were analyzed for a period of 12 h following intervention.

RESULTS

A median dose of 125 mg papaverine-hydrochloride was administered ipsilateral to the multimodality probe. Angiographic improvement of cerebral vasospasm was observed in 80% of patients. During intervention, a significant elevation of ICP (13.7 ± 5.2 mmHg) and the lactate-pyruvate ratio (LPR) (54.2 ± 15.5) was observed, whereas a decrease in cerebral glucose (0.9 ± 0.5 mmol/L) occurred. Within an hour, an increase of cerebral lactate (5.0 ± 2.0 mmol/L) and glycerol (104.4 ± 89.8 μmol/L) as well as a decrease of glucose (0.9 ± 0.4 mmol/L) were measured. In 2 to 5 h after treatment, the LPR significantly decreased (pretreatment: 39.3 ± 15.3, to lowest 30.5 ± 6.7). Cerebral pyruvate levels increased in 1 to 10 h (pretreatment: 100.1 ± 33.1 μmol/L, to highest 141.4 ± 33.7 μmol/L) after intervention. No significant changes in ptiO2 or CPP occurred.

CONCLUSION

The initial detrimental effects of the endovascular procedure itself were outweighed by an improved cerebral metabolism within 10 h thereafter. As the effect was very limited, repeated interventions or continuous application should be considered.

Duration of safe apnea in patients with morbid obesity during passive oxygenation using high-flow nasal insufflation versus regular flow nasal insufflation, a randomized trial

BACKGROUND

Obese patients are at risk for rapid oxygen desaturation during anesthesia induction. Apneic oxygenation with regular flow oxygen insufflation has successfully been used to prolong the duration of safe apnea without desaturation (DAWD) in morbidly obese patients. Using high-flown nasal insufflation of oxygen (HFNI) for apneic oxygenation might further increase the DAWD.

OBJECTIVES

To compare the duration of safe apnea using high-flown nasal insufflation of oxygen or standard flow oxygen insufflation for apneic oxygenation in a simulated difficult intubation scenario in patients with morbid obesity.

SETTING

Operating room, University Hospital, Austria.

METHODS

In a prospective, randomized, clinical trial, patients received standardized preoxygenation and anesthesia induction. Apneic oxygenation was performed using standard nasal prongs (10 L/min) or HFNI (120 L/min) during laryngoscopy. A Cormack-Lehane 3° view was maintained until the oxygen saturation on pulse oximetry (SpO₂) dropped ≤95% or for a maximum of 15 minutes. The primary outcome of this study was to compare the duration of safe apnea using HFNI or standard flow oxygen insufflation for apneic oxygenation. In addition, arterial blood gas results, and airway pressures were investigated.

RESULTS

In 40 patients with morbid obesity (body mass index [BMI] >40 kg/m²) and the American Society of Anesthesiologists physical classification ≤3 who underwent bariatric surgery, the median duration of safe apnea was 601 (268-900) seconds in the standard group and 537 (399-808) seconds in the HFNI group (P = .698). No differences in arterial blood gas results were observed between the groups. The median airway pressure was 0 (0-0) cm H₂O in the standard group and 1 (0-2) cm H₂O in the HFNI group (P = .005).

CONCLUSION

Compared with standard nasal apneic oxygenation, HFNI did not increase the duration of safe apnea in patients with morbid obesity. A significant but clinically negligible higher airway pressure was observed when using HFNI.

Urinary [TIMP-2] × [IGFBP-7] for predicting acute kidney injury in patients undergoing orthotopic liver transplantation

BACKGROUND

The product of the concentrations of urinary tissue inhibitor of metalloproteinases-2 and insulin-like growth factor binding protein-7 (urinary [TIMP-2] × [IGFBP-7]) has been suggested as biomarker for early detection of acute kidney injury (AKI) in various clinical settings. However, the performance of urinary [TIMP-2] × [IGFBP-7] to predict AKI has never been assessed in patients undergoing orthotopic liver transplantation (OLT). Thus, the aim of this study was to assess the early predictive value of urinary [TIMP-2] × [IGFBP-7] for the development of AKI after OLT.

METHODS

In this observational study, urinary [TIMP-2] × [IGFBP-7] was measured in samples from adult OLT patients. AKI was diagnosed and classified according to KDIGO criteria. Areas under the receiver operating curves (AUC) were calculated to assess predictive values of urinary [TIMP-2] × [IGFBP-7] for the development of AKI.

RESULTS

Forty patients (mean age 55 ± 8 years) were included. Twenty-eight patients (70%) developed AKI stage 1, 2, or 3 within 48 h after OLT. Urinary [TIMP-2] × [IGFBP-7] was not predictive for AKI at the end of OLT (AUC: 0.54, CI [0.32-0.75], P = 0.72), at day 1 (AUC: 0.60, CI [0.41-0.79], P = 0.31), or day 2 after OLT (AUC: 0.63, CI [0.46-0.8], P = 0.18).

CONCLUSION

Based on our results, routine clinical use of urinary [TIMP-2] × [IGFBP-7] cannot be recommended for risk assessment of AKI in patients undergoing OLT.

The Use of the Novel Calcium Sensitizer Levosimendan in Critically Ill Patients

Levosimendan, a novel calcium sensitizer, enhances cardiac contractility by increasing myocyte sensitivity to calcium, and induces vasodilation. In this prospective observational study the haemodynamic effects of levosimendan in postoperative critically ill patients are reported. Twelve patients with the need for inotropic support were studied. One dose of levosimendan (12.5 mg) was administered at a rate of 0.1-0.2 μg.kg−1.min−1, either alone or in addition to pre-existing inotropic therapy. Haemodynamic measurements were obtained at baseline, and at 3 h, 6 h, 12 h, and 24 h after the start of the levosimendan infusion.

Levosimendan significantly increased cardiac output from (mean±SD) 4.3±0.9 l.min−1 to 5.2±1.5 l.min−1 after 24 h (P=0.013), by increases in stroke volume (baseline 47±15 ml, after 24 h 57±25 ml, P=0.05), as heart rate remained unchanged. Systemic vascular resistance decreased from 1239±430 dyn.sec.cm−5 at baseline to 963± 322 dyn.sec.cm−5 at 24 h (P<0.001). Pre-existing inotropic therapy present in ten patients remained unchanged or was reduced.

In postoperative critically ill patients, infusion of levosimendan exerted favourable haemodynamic responses. Levosimendan increased cardiac output by increasing stroke volume, which might be attributed primarily to its inotropic properties. Due to its cyclic adenosine monophosphate independent positive inotropic effects, levosimendan may be of value as adjunctive therapy to other inotropic drugs in critically ill patients.

Graft-derived macrophage migration inhibitory factor correlates with hepatocellular injury in patients undergoing liver transplantation

Experimental studies suggest that macrophage migration inhibitory factor (MIF) mediates ischemia/reperfusion injury during liver transplantation. This study assessed whether human liver grafts release MIF during preservation, and whether the release of MIF is proportional to the extent of hepatocellular injury. Additionally, the association between MIF and early allograft dysfunction (EAD) after liver transplantation was evaluated. Concentrations of MIF, aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), and creatine kinase (CK) were measured in effluents of 38 liver grafts, and in serum of recipients. Concentrations of MIF in the effluent were greater than those in the recipients' serum before and after reperfusion (58 [interquartile range, IQR:23-79] μg/mL vs 0.06 [IQR:0.03-0.07] μg/mL and 1.3 [IQR:0.7-1.8] μg/mL, respectively; both P<.001). Effluent MIF concentrations correlated with effluent concentrations of the cell injury markers ALT (R=.51, P<.01), AST (R=.51, P<.01), CK (R=.45, P=.01), and LDH (R=.56, P<.01). Patients who developed EAD had greater MIF concentrations in effluent and serum 10 minutes after reperfusion than patients without EAD (Effluent: 80 [IQR:63-118] μg/mL vs 36 [IQR:20-70] μg/mL, P=.02; Serum: 1.7 [IQR:1.2-2.5] μg/mL vs 1.1 [IQR:0.6-1.7] μg/mL, P<.001).

CONCLUSION

Human liver grafts release MIF in proportion to hepatocellular injury. Greater MIF concentrations in effluent and recipient's serum are associated with EAD after liver transplantation.

Feasibility of a 'reversed' isolated forearm technique by regional antagonization of rocuronium-induced neuromuscular block: a pilot study

BACKGROUND

The isolated forearm technique is used to monitor intraoperative awareness. However, this technique cannot be applied to patients who must be kept deeply paralysed for >1h, because the tourniquet preventing the neuromuscular blocking agent from paralysing the forearm must be deflated from time to time. To overcome this problem, we tested the feasibility of a 'reversed' isolated forearm technique.

METHODS

Patients received rocuronium 0.6 mg kg(-1) i.v. to achieve muscle paralysis. A tourniquet was then inflated around one upper arm to prevent further blood supply to the forearm. Sugammadex was injected into a vein of this isolated forearm to antagonize muscle paralysis regionally. A dose titration of sugammadex to antagonize muscle paralysis in the isolated forearm was performed in 10 patients, and the effects of the selected dose were observed in 10 additional patients.

RESULTS

The sugammadex dose required to antagonize muscle paralysis in the isolated forearm was 0.03 mg kg(-1) in 30 ml of 0.9% saline. Muscle paralysis was antagonized in the isolated forearm within 3.2 min in nine of 10 patients; the rest of the patients' bodies remained paralysed. Releasing the tourniquet 15 min later did not affect the train-of-four count in the isolated forearm but significantly increased the train-of-four count in the other arm by 7%.

CONCLUSIONS

Regional antagonization of rocuronium-induced muscle paralysis using a sugammadex dose of 0.03 mg kg(-1) injected into an isolated forearm was feasible and did not have relevant systemic effects.

CLINICAL TRIAL REGISTRATION

The trial was registered at EudraCT (ref. no. 2013-002164-53) before patient enrolment began.

Core and skin surface temperature course after normothermic and hypothermic cardiopulmonary bypass and its impact on extubation time

BACKGROUND AND OBJECTIVE

Cardiopulmonary bypass is associated with temperature pertubations that influence extubation time. Common extubation criteria demand a minimum value of core temperature only. The aim of this prospective study was to test the hypothesis that changes in core and skin surface temperature are related to extubation time in patients following normothermic and hypothermic cardiopulmonary bypass.

METHODS

Forty patients undergoing cardiac surgery were studied; 28 patients had normothermic cardiopulmonary bypass (nasopharyngeal temperature >35.5 degrees C) and 12 had hypothermic cardiopulmonary bypass (28-34 degrees C). In the intensive care unit, urinary bladder temperature and skin surface temperature gradient (forearm temperature minus fingertip temperature: >0 degrees C = vasoconstriction, < or =0 degrees C = vasodilatation) were measured at 30-min intervals for 10 h postoperatively. At the same intervals, the patients were evaluated for extubation according to common extubation criteria.

RESULTS

On arrival in the intensive care unit the mean urinary bladder temperature was 36.8 +/- 0.5 degrees C in the normothermic group and 36.4+/-0.3 degrees C in the hypothermic group (P = 0.014). The skin surface temperature gradient indicated severe vasoconstriction in the both groups. The shift from vasoconstriction to vasodilatation was faster in normothermic cardiopulmonary bypass patients (138+/-65 min) than in patients after hypothermic cardiopulmonary bypass (186+/-61 min, P = 0.034). There was a linear relation between the time to reach a skin surface temperature gradient = 0 degrees C and extubation time (r2 = 0.56, normothermic group; r2 = 0.82, hypothermic group).

CONCLUSIONS

The transition from peripheral vasoconstriction to vasodilatation is related to extubation time in patients following cardiac surgery under normothermic as well as hypothermic cardiopulmonary bypass.

Influence of cumulative number of marginal donor criteria on primary organ dysfunction in liver recipients

BACKGROUND

The aim of this cohort study was to assess the cumulative effect of marginal donor criteria on initial graft function and patient survival after liver transplantation.

METHODS

We included 734 consecutive patients who underwent orthotopic liver transplantation at the Vienna General Hospital between January 1993 and December 2003. We employed the local registry of the Department of Transplant Surgery, where variables of all patients are routinely and prospectively recorded. Primary outcome was initial graft function, secondary outcome was patient survival.

RESULTS

Cumulative number of marginal donor criteria was significantly and linearly associated with an increased rate of primary dysfunction (PDF; p = 0.005). In patients with more than three cumulative marginal donor criteria the rate of PDF was 36%. Patient survival was not influenced by the cumulative number of donor criteria (log-rank test, p = 0.81). Independent marginal donor criteria to predict PDF were cold ischemia time >10 h [odds ratio (OR) 0.56; 95% CI 0.32-0.98] and donor peak serum sodium >155 mEq/L (OR 0.44; 95% CI 0.26-0.77), as assessed in a multivariate regression model.

CONCLUSIONS

The use of marginal liver donors with more than three marginal donor criteria shows deleterious effects on initial graft function. Noteworthy, patient survival was not associated with marginal donor criteria, which may be explained by early and successful retransplantation of liver recipients with primary non-function.

Perspectives for core and skin surface temperature guided extubation in patients after normothermic cardiopulmonary bypass

OBJECTIVE

To investigate the relationship between changes in core and skin surface temperature and extubation time in patients following normothermic cardiopulmonary bypass (CPB).

DESIGN

Prospective observational study.

SETTING

Intensive care unit (ICU) of a university hospital.

PATIENTS

Patients admitted to the ICU after cardiac surgery.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

Thirty-two patients undergoing cardiac surgery with the use of normothermic CPB were studied. In the ICU, urinary bladder temperature and skin surface temperature gradient (forearm temperature minus fingertip temperature) were measured at 30-min intervals for 10 h postoperatively. Every half-hour an anaesthesiologist, blinded to temperature measurements, checked the possibility of extubation. On arrival in the ICU the mean skin surface temperature gradient of the patients was 1.9+/-1.6 degrees C, indicating vasoconstriction of the dermal vessels (>0 degrees C = vasoconstriction, <0 degrees C = vasodilation) while the mean urinary bladder temperature was 36.8+/-0.4 degrees C. The change from thermoregulatory vasoconstriction to vasodilation (skin surface temperature gradient of 0 degrees C) was 137+/-49 min after arrival in the ICU. The mean time until extubation was 135+/-55 min after arrival in the ICU. There was a linear relation between a temperature gradient of 0 degrees C and extubation time, r(2)=0.49. Later, 181+/-67 min after arrival in the ICU, the urinary bladder temperature reached its maximum of 38.2+/-0.6 degrees C.

CONCLUSIONS

This study demonstrates that the transition period from peripheral vasoconstriction to vasodilation provides an opportunity for postoperative extubation.

Assessment of ventricular contractile function during orthotopic liver transplantation

Hemodynamic alterations are a well-known phenomenon that influence the outcome of orthotopic liver transplantation (OLT). Whether or not myocardial dysfunction, which has various causes, contributes to this instability is still debated. Previous transesophageal echocardiography (TEE) studies have presented controversial data, not leading to final clarification. This is mainly because the impact of other contributing factors (inotropic support, alternating preload conditions and temperature) remained unaccounted for. We therefore measured the left ventricular shortening fraction (LVSF), a parameter reflecting myocardial contractility, in 10 consecutive patients undergoing OLT without veno-venous bypass. We measured during preparation (PP), during the anhepatic (AP) phase and the immediate reperfusion phase (RP). During the AP we observed a significant decrease of LVSF which never fell to subnormal levels in the majority of our patients, whereas during the RP, LVSF returned to PP values. These findings support the assumption that myocardial function is influenced by OLT, but that it plays only a minor role in the occurrence of hemodynamic instability, which could mainly be attributed to volume fluctuations.

Acute colonic pseudo-obstruction (Ogilvie’s-syndrome) and Pneumatosis intestinalis in a kidney recipient patient

Acute colonic pseudo-obstruction (Ogilvie's syndrome) is a clinical entity characterized by massive nontoxic dilatation of the colon in the absence of mechanical obstruction and is associated with increased morbidity and mortality in the immunosuppressed patient. We present a case of a kidney transplant recipient developing a life-threatening condition with acute colonic pseudo-obstruction associated with radiologic findings of a linear pneumatosis intestinalis (PI). Urgent laparotomy and resection of the dilated cecum, colon ascendens and transversum was performed because of bowel necrosis with multiple serosal defects. Stool cultures and special stains for microorganisms were all negative, and there was no evidence for viral or fungal infection. The patient was discharged 31 days after transplantation with normal renal function. In conclusion, this steroid-induced ileus (pseudo-obstruction) is a potentially malignant early form of colonic dysmotility rarely reported in transplant recipients. Awareness and early recognition of the condition are critical for a successful outcome. Colonoscopic decompression can achieve reversal of colonic dilatation in most cases, but in some patients prophylactic laparotomy is indicated for prevention of the catastrophic consequences of perforation.

The impact of asymptomatic carotid artery disease on the intraoperative course of coronary artery bypass surgery

Asymptomatic carotid artery stenosis (CAS) may result in neurological injury after coronary artery bypass surgery, but routine preoperative carotid screening is not undisputed. We studied whether routinely determined carotid duplex results, beyond detecting high-risk patients, additionally influence intraoperative course. One hundred and eight patients without new signs of impaired cerebral circulation were investigated. Anesthesiology, perfusionist records, and patient files were reviewed for patient characteristics, intraoperative variables and postoperative neurological sequelae. There was a higher incidence of prior cerebrovascular events and peripheral artery disease in CAS patients (p < 0.05). Pulsatile flow was employed more frequently in this group (p < 0.05). Severe hyperventilation, hyperglycemia, hemodilution, hyperthermia, and lactacidosis were avoided in both groups. However, labile hemodynamics of CAS patients required more corrective interventions (p < 0.05). There was also a tendency toward greater mortality. Stroke and transient ischemic attack (TIA) occurred in two patients without CAS. Since CAS was associated with a greater degree of cardiovascular instability requiring frequent measures to control hemodynamics, positive duplex results should heighten vigilance. Although CAS does not appear to be the major source of cerebral ischemia, it involves significant comorbidity.

Can hypocapnia reduce cerebral embolization during cardiopulmonary bypass?

BACKGROUND

Cerebral embolization is a major cause of central nervous dysfunction after cardiopulmonary bypass. Experimental studies demonstrate that reductions in arterial carbon dioxide tension (PaCO2) can reduce cerebral embolization during cardiopulmonary bypass. This study examined the effects of brief PaCO2 manipulations on cerebral embolization in patients undergoing cardiac valve procedures.

METHODS

Patients were prospectively randomized to either hypocapnia (PaCO2 = 30 to 32 mm Hg, n = 30) or normocapnia (PaCO2 = 40 to 42 mm Hg, n = 31) before aortic cross-clamp removal. With removal of the aortic cross-clamp embolic signals were recorded by transcranial Doppler ultrasonography for the next 15 minutes.

RESULTS

Despite significant differences in PaCO2, groups did not differ statistically in total cerebral emboli counts. The mean number of embolic events was 107 +/- 100 (median, 80) in the hypocapnic group and 135 +/- 115 (median, 96) in the normocapnic group, respectively (p = 0.315).

CONCLUSIONS

Due to the high between-patient variability in embolization, reductions in PaCO2 did not result in a statistically significant decrease in cerebral emboli. In contrast to experimental studies, the beneficial effect of hypocapnia on cerebral embolization could not be demonstrated in humans.

[Variants of inborn errors of metabolism with late onset but nevertheless life threatening course]

BACKGROUND

There is a growing number of inborn errors of metabolism (IEM) with late onset but nevertheless life threatening course.

PATIENTS

Patients with late onset variants of urea cycle defects, fatty acid oxidation defects and organic acidurias are demonstrated.

METHODS

Biochemical, enzymatic, molecular methods and especially tandem mass spectrometry (TMS) are used for diagnostic purposes.

RESULTS

IEM variants with late onset are difficult to be detected. TMS has some advantages as the simple sampling of dried blood on filter paper cards and the simultaneous detection of a broad spectrum of disturbances in amino acids and acylcarnitines. This may facilitate a prompt diagnosis. Asymptomatic persons not only carry an unrecognized risk for severe metabolic decompensation but also pass on their mutation of IEM and the associated disease risk to the next generation (Non-disease).

CONCLUSION

TMS, which is used in newborn screening centers is very convenient to establish a prompt diagnosis in some unexpected late onset metabolic crisis following surgeries, infections or other catabolic stress. Furthermore TMS may be a suitable and rapid adjunct method to improve transplantation management.

Multiorgan donation from a donor with unrecognized ornithine transcarbamylase deficiency

Ornithine transcarbamylase (OTC) deficiency, the most common inherited urea cycle disorder, shows a spectrum of severity ranging from severe neonatal hyperammonemic coma to no symptoms among adults. We report on the multiorgan procurement from a donor who died of cerebral edema due to unrecognized late-onset OTC deficiency. The donor's OTC deficiency was diagnosed retrospectively since the liver graft recipient developed cerebral edema postoperatively due to hyperammonemia. Plasma ammonia was extremely elevated (3793 micromol/l), but was not accompanied by general liver dysfunction. Post mortem, the diagnosis of OTC deficiency was established by enzyme and molecular analysis in a biopsy of the transplanted liver. In contrast to the fatal course of the liver graft recipient, the kidney, lung, and heart transplantations were successful. Ten months after transplantation these recipients were alive and showed good graft function. This case demonstrates the importance of careful donor evaluation, particularly if the donor's cause of death is obscure.

Comparing Doppler ultrasonography and cerebral oximetry as indicators for shunting in carotid endarterectomy

To determine the thresholds of selective shunting in carotid endarterectomy during general anesthesia, we compared transcranial Doppler ultrasonography and cerebral oximetry (RSO2). During carotid cross-clamping, RSO2 and mean blood flow velocity in the middle cerebral artery (Vm,mca) was simultaneously monitored in 55 of 59 patients. A relative decrease in Vm,mca to <20% of preclamp velocity was the indication for selective shunting. Three patients were shunted, two because of criteria of Vm,mca and one in which Vm,mca measurements were impossible. No postoperative neurological deficits occurred. During cross-clamping, both Vm,mca (42+/-16 vs. 26+/-12 cm/s; P<0.001) and RSO2 (68+/-7% vs. 62+/-8%; P<0.01) decreased and a significant correlation between %Vm,mca and DeltaRSO2 was found (R(2) = 0.40; P = 0.003). Decreases in RSO2 >13% identified two patients later shunted; however, this threshold would have indicated unnecessary shunting in seven patients (false positives = 17%). Transcranial Doppler ultrasonography identified patients at risk for ischemia more accurately than RSO2. Relying on RSO2 alone would increase the number of unnecessary shunts because of the low specificity. Accepting higher decreases in RSO2 does not appear reasonable because it bears the risk of a low sensitivity.

Intrathoracic fluid volumes and pulmonary function during orthotopic liver transplantation

BACKGROUND

Impaired pulmonary function is a frequent finding in patients undergoing orthotopic liver transplantation (OLT). Experimental data suggest an essential contribution of splanchnic ischemia and reperfusion as a result of intraoperative volume shifts, i.e., the accumulation of extravascular lung water (EVLW). Increases of intrathoracic blood volume (ITBV) and pulmonary blood volume (PBV) might additionally influence pulmonary capillary fluid filtration. The main objective of this study was to determine the intrathoracic volume changes during OLT and to test whether there were any relationships between intra- and extravascular volume shifts and pulmonary function, as determined by the calculation of venous admixture (QS/QT) and alveolar-arterial oxygen gradient (AaDO2).

METHODS

Twenty-five patients undergoing OLT were studied. Using the transpulmonary double indicator dilution method, ITBV, PBV, and EVLW were determined from the mean transit times and exponential decay times of the indocyanine green and the thermal indicator curves recorded simultaneously with a fiberoptic catheter in the descending aorta. Recordings were made after induction of anesthesia, at the end of the anhepatic stage, immediately after reperfusion, and 1 and 4 h postoperatively.

RESULTS

Significant increases in QS/QT related to changes of ITBV were observed after reperfusion. Only a minor impact on AaDO2 was perceived. EVLW remained constant during the study period.

CONCLUSIONS

Postreperfusion increases of ITBV influence pulmonary function, as demonstrated by the increase in QS/QT. However, they need not be associated with greater EVLW levels, and impact on oxygenation is less severe than assumed. Hence, sufficient mechanisms protecting oxygenation and stalling increased EVLW seem to be present during uncomplicated human OLT.

S(+)-ketamine for caudal block in paediatric anaesthesia

We have evaluated the intra- and postoperative analgesic efficacy of preservative-free S(+)-ketamine compared with bupivacaine for caudal block in paediatric hernia repair. After induction of general anaesthesia, 49 children undergoing hernia repair were given a caudal injection (0.75 ml kg-1) of S(+)-ketamine 0.5 mg kg-1 (group K1), S(+)-ketamine 1.0 mg kg-1 (group K2) or 0.25% bupivacaine with epinephrine 1:200,000 (group B). No additional analgesic drugs were required during operation in any of the groups. Haemodynamic and respiratory variables remained stable during the observation period. Mean duration of analgesia was significantly longer in groups B and K2 compared with group K1 (300 (SD 96) min and 273 (123) min vs 203 (117) min; P < 0.05). Groups B and K2 required less analgesics in the postoperative period compared with group K1 (30% and 33% vs 72%; P < 0.05). Postoperative sedation scores were comparable between the three groups. We conclude that S(+)-ketamine 1.0 mg kg-1 for caudal block in children produced surgical and postoperative analgesia equivalent to that of bupivacaine.

Effect of temperature and PaCO2 on cerebral embolization during cardiopulmonary bypass in swine

BACKGROUND

Patients experience cerebral embolization during cardiopulmonary bypass (CPB). This study determined if alterations in temperature and/or PaCO2 can reduce cerebral and ocular embolization.

METHODS AND RESULTS

Forty-four pigs underwent CPB: 24 animals at 28 degrees C, and 20 at 38 degrees C. The two temperature groups were randomized to undergo embolization (67-microm fluorescent microspheres) at either hypercarbia or hypocarbia. Before and after embolization, cerebral and ocular blood flow were determined at normocarbia. Reducing temperature or PaCO2 reduced cerebral and ocular embolization. Hypocarbia reduced cerebral embolization by 60% and 45% in normothermic and hypothermic groups, respectively (p < 0.0001 and p < 0.05). Relative to normothermic animals, hypothermia reduced cerebral embolization by 37% under an elevated CO2 condition (p < 0.05), but not under hypocarbic conditions. Similarly, regardless of temperature, fewer emboli were delivered to the eye in hypocarbic animals (p < 0.05), but hypothermia did not reduce ocular embolization.

CONCLUSIONS

Cerebral embolization is determined by both temperature and PaCO2 at the time of embolization. In CPB practice, reductions in temperature and/or PaCO2 during periods of embolic risk may reduce brain injury.

Supralaryngeal tubeless combined high-frequency jet ventilation for laser surgery of the larynx and trachea

We have developed a new technique of combined high-frequency jet ventilation (HFJV), characterized by simultaneous application of a low-frequency (LF) and a high-frequency (HF) jet stream. Tubeless supralaryngeal jet ventilation was delivered via a modified Kleinsasser laryngoscope. We studied 44 adults undergoing 45 elective surgical procedures of the larynx and trachea using a carbon dioxide laser during HFJV. Applied inspiratory oxygen ratios ranged from 0.4 to 1.0. Mean driving pressures of the HF and LF jet streams were 1.5 bar and 1.8 bar in adults, respectively. Mean duration of HFJV was 41 (range 10-180) min. HFJV resulted in mean PaO2 and PaCO2 values of 16.6 (range 9.8-26.9) kPa and 5.7 (3.0-7.6) kPa, respectively. Tubeless supralaryngeal HFJV was safe and effective in maintaining gas exchange in the presence of laryngeal or tracheal stenoses, providing optimal visibility of anatomical structures, offering maximum space for surgical manipulation, and avoiding the use of combustible material inside the larynx or trachea.

Relationship between cardiopulmonary bypass flow rate and cerebral embolization in dogs

BACKGROUND

Cerebral embolization is a primary cause of cardiac surgical neurologic morbidity. During cardiopulmonary bypass (CPB), there are well-defined periods of embolic risk. In theory, cerebral embolization might be reduced by an increase in pump flow during these periods. The purpose of this study was to determine the CPB flow-embolization relation in a canine model.

METHODS

Twenty mongrel dogs underwent CPB at 35 degrees C with alpha-stat management and a fentanyl-midazolam anesthetic. In each animal, CPB flow was adjusted to achieve a mean arterial pressure of 65-75 mmHg. During CPB, an embolic load of 1.2 x 10(5) 67 microm fluorescent microspheres was injected into the arterial inflow line. Before and after embolization, cerebral blood flow was determined using 15-microm microspheres. Tissue was taken from 12 brain regions and microspheres were recovered. The relation between pump flow and embolization/g of brain was determined.

RESULTS

The mean arterial pressure at embolization was 67 +/-4 mmHg, and the range of pump flow was 0.9-3.5 l x min(-1)x m(-2). Cerebral blood flow was independent of pump flow. At lower pump flow, the percentage of that flow delivered to the brain increased. There was a strong inverse relation between pump flow and cerebral embolization (r = -0.708, P < 0.000 by Spearman rank order correlation).

CONCLUSIONS

Cerebral embolization is determined by the CPB flow. At an unchanged mean arterial pressure, as pump flow is reduced, a progressively greater proportion of that flow is delivered to the brain.

Support of mean arterial pressure during tepid cardiopulmonary bypass: effects of phenylephrine and pump flow on systemic oxygen supply and demand

OBJECTIVE

To examine the effects of phenylephrine infusion and increases in pump flow on systemic oxygen supply and demand when they are used to support mean arterial pressure (MAP) during cardiopulmonary bypass (CPB).

DESIGN

Prospective, unblinded study.

SETTING

The animal cardiopulmonary laboratory at the Mayo Foundation (Rochester, MN).

PARTICIPANTS

Twelve pigs.

INTERVENTIONS

Twelve pigs had systemic oxygen delivery (DO2) and consumption (VO2) measured before CPB and then underwent CPB at 35 degrees C. During CPB, measurements of DO2 and VO2 were obtained at an MAP of approximately 50 mmHg and a pump flow of 2.2 L/min/m2. Thereafter, MAP was elevated to 70 mmHg either by increases in pump flow or by a phenylephrine infusion, and the balance between systemic oxygen supply and demand was reassessed.

MEASUREMENTS AND MAIN RESULTS

Before CPB, DO2 was 375 +/- 83 mL/min/m2 and decreased with the onset of CPB mainly because of the effects of hemodilution. During CPB, with a pump flow of 2.2 L/min/m2 and an MAP of 53 mmHg, DO2 was 218 +/- 40 mL/min/m2. Increasing perfusion pressure to an MAP of 72 mmHg with phenylephrine and maintaining pump flow constant (2.2 L/min/m2) did not change DO2 (222 +/- 37 mL/min/m2), and the oxygen extraction ratio (OER) was increased relative to pre-CPB levels. In contrast, increasing MAP to 71 mmHg by increasing pump flow to 3.2 L/min/m2 resulted in a significantly greater DO2, and the OER normalized to the pre-CPB value.

CONCLUSIONS

During CPB with conventional flow rates, DO2 is decreased. Supporting MAP with increases in pump flow better maintains DO2 than the administration of an alpha-agonist.

[Difference between gastric mucosal pCO2 and arterio-intramucosal pCO2 during orthotopic liver transplantation]

Tonometry is a clinically accepted method to monitor blood flow of the splanchnic region, which is of particular interest in orthotopic liver transplantation (OLT). We investigated the hemodynamic changes and the tonometrically registered perioperative course of the difference between gastric mucosal pCO2 (prCO2) and arterial mucosal CO2 (CO2 gap) in 23 patients undergoing OLT without veno-venous bypass. Gastric mucosal pH (pHi) was additionally calculated. Despite significant changes in systemic hemodynamics during the anhepatic stage and after reperfusion and a significant drop in pHi during anhepacy, the difference between prCO2 and CO2 was constant. These contrasting findings of tonometry, i.e. solely a drop in pHi is, in our opinion, a consequence of the poor metabolic capacity of the liver in the perioperative OLT period, which influenced the calculation of the pHi with the Henderson-Hasselbalch equation. We conclude that, due to methodical problems, calculated pHi is not a reliable indicator of splanchnic blood flow and oxygenation during OLT. We therefore suggest that the prCO2 and the CO2 gap be used to monitor the splanchnic region. These parameters, obtained perioperatively, do not indicate a further reduction in splanchnic oxygenation despite profound changes in systemic hemodynamics during OLT without veno-venous bypass.

The use of the antioxidant tirilazad mesylate in human liver transplantation: is there a therapeutic benefit?

OBJECTIVES

To test the hypothesis whether in patients undergoing liver transplantation the antioxidant tirilazad mesylate can reduce hepatic ischaemia-reperfusion injury and improve postoperative outcome.

DESIGN

Prospective, randomised, placebo controlled trial.

SETTING

University hospital.

PATIENTS

20 patients were randomised to receive either tirilazad mesylate or placebo (saline).

INTERVENTIONS

Patients in the tirilazad group (n = 10) received four intravenous infusions of tirilazad at 6-h intervals (men 3 mg/kg, women 3.75 mg/kg) after the induction of anaesthesia. The other patients (n = 10) served as controls.

MEASUREMENTS AND RESULTS

Plasma levels of malonaldehyde (MDA) were determined after the induction of anaesthesia prior to the infusion of tirilazad (baseline), during the anhepatic period, and 5 min and 24 h after reperfusion. Postoperatively, alanine aminotransferase, aspartate aminotransferase, prothrombin time, and serum cholinesterase were determined daily for 1 week. Compared to baseline, plasma MDA levels did not significantly change during the anhepatic period and after reperfusion and they did not differ between groups. Postoperative liver enzymes and prothrombin time did not differ between groups, but on the first (p = 0.03) and second (p = 0.01) postoperative day cholinesterase levels were significantly higher in tirilazad-treated patients than in control patients. For neither length of stay in the intensive care unit nor hospital stay were any differences observed between groups.

CONCLUSIONS

In patients undergoing liver transplantation, tirilazad does not improve overall outcome. Whether the higher cholinesterase levels on the first 2 postoperative days in tirilazad treated patients indicates an earlier recovery of liver function remains to be tested.

Cerebral response to haemodilution during cardiopulmonary bypass in dogs: the role of nitric oxide synthase

During cardiopulmonary bypass, haemodilution is standard practice and is accompanied by increases in cerebral blood flow (CBF). We investigated if changes in cerebral vascular resistance (CVR) during cardiopulmonary bypass-haemodilution are dependent on nitric oxide synthase. The cerebral response to haemodilution in nine dogs treated with the nitric oxide synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME), was compared with a control group (n = 8). Both groups underwent serial isovolaemic haemodilution (target packed cell volumes 0.39, 0.26, 0.19 and 0.14) using 6% dextran 70. CBF, CVR and cerebral metabolic rate for oxygen (CMRO2) were measured. While initial CVR was different in the two groups, haemodilution-dependent reductions in CVR were equivalent and the curves describing the packed cell volume-CVR relationship were parallel in control and nitric oxide synthase inhibition groups. Our data indicate that nitric oxide synthase does not play a primary role in the cerebral response to haemodilution.

Quantification and distribution of cerebral emboli during cardiopulmonary bypass in the swine: the impact of PaCO2

BACKGROUND

Patients undergoing cardiac surgery have a substantial incidence of neurologic complications related to cerebral embolization during cardiopulmonary bypass. The purpose of this study was to determine if adjustments in the arterial carbon dioxide (PaCO2) level can reduce cerebral and ocular embolization.

METHODS

Twenty pigs underwent cardiopulmonary bypass at 38 degrees C. At either hypercarbia (PaCO2 = 50-55 mmHg, group H, n = 10) or hypocarbia (PaCO2 = 25-30 mmHg, group L, n = 10), an embolic load of 1.2 x 10(50 67-microm orange fluorescent microspheres was injected into the aortic cannula. Before and after embolization, cerebral and ocular blood flows were determined at normocapnia using 15-microm fluorescent microspheres. After cardiopulmonary bypass was completed, the eyes were enucleated and brain tissue samples were collected. Microspheres were isolated and the fluorescence was measured.

RESULTS

In groups H and L, the mean PaCO2 values at embolization were 52+/-3 mmHg and 27+/-2 mmHg, respectively (P < 0.0001). Total and regional embolization were significantly less in hypocapnia than in hypercapnic animals: 142% more emboli were detected in the brain in group H than in group L (P < 0.0001). Cerebral blood flow after embolization was unchanged in both groups. Similarly, fewer ocular emboli occurred in hypocapnic animals than in hypercapnic animals (P = 0.044), but in contrast to the brain, ocular blood flow decreased significantly in both groups after embolization.

CONCLUSIONS

Cerebral embolization is determined by the PaCO2 at the time of embolization. In cardiopulmonary bypass practice, reductions in PaCO2 during periods of embolic risk may reduce the risk for brain injury.

Critical cerebral perfusion pressure during tepid heart operations in dogs

BACKGROUND

The management of blood pressure during cardiopulmonary bypass varies widely. This may be particularly relevant with the trend to warmer bypass temperatures and an older patient population. Therefore, we examined the minimal perfusion pressure that maintains cerebral oxygen delivery during cardiopulmonary bypass at 33 degrees C.

METHODS

Ten dogs were placed on bypass and body temperature was reduced to 33 degrees C (alpha-stat pH management). At six randomly ordered mean arterial blood pressures (35, 40, 45, 50, 60, and 70 mm Hg), cerebral blood flow, oxygen delivery, and metabolic rate were determined.

RESULTS

Cerebral oxygen delivery was stable if the mean arterial pressure was greater than or equal to 60 mm Hg. If mean arterial pressure was less than or equal to 50 mm Hg, cerebral oxygen delivery decreased, and at less than 45 mm Hg cerebral ischemia was seen.

CONCLUSIONS

In a dog without vascular disease, the brain becomes perfusion pressure-dependent at a mean arterial pressure of approximately 50 mm Hg. There is no leftward shift of the cerebral autoregulatory curve during bypass at 33 degrees C. Greater support of mean arterial pressure during "tepid" cardiopulmonary bypass is indicated in the current adult surgical population that is older and has vascular comorbidity.

[Protein catabolism after lung transplantation and heart transplantation]

Any surgical intervention is associated with an activation of protein catabolism, the extent of which is dependent on the severity of surgical trauma. There is a paucity of reports on protein catabolism after transplantation of chest organs (lung transplantation (LTX) and heart transplantation (HTX)). The aim of the present study was to quantify and compare the extent of postoperative protein catabolism and associated metabolic perturbations in patients after LTX and HTX. Eighteen consecutive patients after LTX and 15 consecutive patients after HTX who required postoperative intensive care for more than 4 days, constituted the study population. The nitrogen balance (assessed on the basis of the urea nitrogen production rate and nitrogen intake) was assessed retrospectively and correlated with insulin requirements, immunosuppression and the clinical course. Within the first 5 days the nitrogen balance became progressively negative in both groups, reaching a maximum on the 5th day. Thereafter the nitrogen balance of patients following LTX remained negative, whereas the nitrogen balance of patients following HTX tended to improve. The evolution of nitrogen balance significantly differed between both groups (p < 0.01). The mean nitrogen loss was -0.29 +/- 0.17g/kg BW/day after LTX versus -0.22 +/- 0.12g/kg BW/day after HTX. Smaller amounts of glucocorticoids were used for immunosuppression in patients after HTX than in patients after LTX; nevertheless, heart transplant recipients required higher doses of insulin to maintain normoglycemia. A regression analysis revealed that the duration of stay at the intensive care unit (p < 0.001) and the amount of glucocorticoids (p < 0.01) negatively affected the nitrogen balance, whereas an increased protein intake (p < 0.001) exerted a positive effect. Compared to other major surgical procedures, protein catabolism is excessively elevated in patients after thoracic transplantation. Immunosuppressive therapy with glucocorticoids contributes to protein degradation; the nitrogen balance after LTX is more negative than that after HTX because of higher glucocorticoid requirements following LTX. More aggressive nutritional intervention and especially an increased nitrogen intake might help to reduce protein losses in these patients.

Hemodilution and whole body oxygen balance during normothermic cardiopulmonary bypass in dogs

OBJECTIVE

The purpose of this study was to determine the minimum hematocrit value that can support whole body oxygen consumption during normothermic cardiopulmonary bypass. The effect of hemodilution on peripheral resistance, whole body oxygen delivery, and oxygen consumption was determined over a range of hematocrit values.

METHODS

Measurements were obtained during 38 degrees C cardiopulmonary bypass with progressive normovolemic hemodilution (hematocrit value 40% to 9%) in nine dogs. Dextran 70 (6%) was used as a diluent. Anesthesia consisted of high-dose fentanyl and midazolam. A mean arterial pressure of 60 mm Hg was maintained throughout cardiopulmonary bypass via increases in pump flow.

RESULTS

Progressive hemodilution was associated with a decreasing total peripheral resistance. During normothermic cardiopulmonary bypass with a whole blood prime, the whole body oxygen consumption approximated values previously reported in dogs under nonbypass conditions. Oxygen delivery and whole body oxygen uptake were maintained between a hematocrit value of 39% and 25%. Significant decreases for both were seen when the hematocrit value was reduced to 18% and below.

CONCLUSIONS

A hematocrit level greater than 18% was needed to maintain systemic oxygen delivery and consumption during warm cardiopulmonary bypass. The critical hematocrit value may be higher under bypass than nonbypass conditions because the flow increases that are practical during cardiopulmonary bypass do not approximate those seen in response to hemodilution of the intact circulation. Finally, the critical hematocrit value for the body may be higher than that required for the brain during warm cardiopulmonary bypass.

Nutritional status, ICU duration and ICU mortality in lung transplant recipients

OBJECTIVE

To determine the relation of malnutrition and underlying diagnosis to the length of stay in the Intensive Care Unit (ICU) and to mortality after lung transplantation (LTX).

DESIGN

Retrospective ICU chart review.

SETTING

Cardiothoracic ICU in a University hospital.

PATIENTS

Fifty-one consecutive patients who suffered from end-stage lung disease from April 1992 to January 1994.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

The median time spent in the ICU was 5 days (range, 2-123 days). Patients with an underlying diagnosis of obstructive lung disease had significantly shorter ICU stays (median 4 days; range, 2-28 days) than those with restrictive lung disease (median 7 days; range, 2-123 days) (p = 0.005) or pulmonary hypertension (median 10 days' range, 2-38 days) (p = 0.041). Significant differences in ICU duration were observed between patients after double lung transplantation (median 10 days; range, 2-123 days) and those after single lung transplantation (median 4 days; range, 2-36 days) (p = 0.004). No statistically significant difference in ICU duration was found between patients with different nutritional statuses. In those patients who could not be discharged from the ICU before the 5th day, a body mass index (BMI) below the 25th percentile was a statistically significant risk factor for ICU mortality (p = 0.05).

CONCLUSIONS

We conclude that the type of transplant procedure and the underlying diagnosis are important predictive indicators of ICU duration. A poor nutritional status (BMI below the 25th percentile) is a risk factor for ICU mortality in cases of patients who stay for 5 days or longer in the ICU.