Norbert Zoremba

Comparison of electrical velocimetry and thermodilution techniques for the measurement of cardiac output

Aim:  To compare a new method of non‐invasive determination of cardiac output based on electrical velocimetry (EV‐CO) with invasive thermodilution methods.

Postoperative kognitive Dysfunktion

The incidence of postoperative cognitive dysfunction (POCD) is often underestimated and not intuitively present by many anesthetists. POCD often occurs in the elderly but is also seen in younger patients. The incidence of POCD 1 week after non-cardiac surgery covers a span between 19-41% in patients older than 18 years. An increased POCD rate (10%) 3 months after surgery is only detected in patients older than 60 years. The occurrence of POCD is associated with an increased mortality rate, jet the etiology is mainly unknown despite enormous research efforts. The age of the patient is one of the main risk factors for the development of POCD. Data on how to avoid POCD are limited. However, the maintenance of homoeostasis is an important cornerstone of prophylaxis.

Brain metabolism and diffusion in the rat cerebral cortex during pilocarpine-induced status epilepticus

The real-time iontophoretic method using tetramethylammonium-selective microelectrodes and diffusion-weighted magnetic resonance imaging were used to measure the extracellular space volume fraction alpha, tortuosity lambda and apparent diffusion coefficient of water (ADC(W)) 240 min after the administration of pilocarpine in urethane-anaesthetized rats. The obtained data were correlated with extracellular lactate, glucose, and glutamate concentrations and the lactate/pyruvate-ratio, determined by intracerebral microdialysis. The control values of alpha and lambda were 0.19+/-0.004 and 1.58+/-0.01, respectively. Following pilocarpine application, alpha decreased to 0.134+/-0.012 100 min later. Thereafter alpha increased, reaching 0.176+/-0.009 140 min later. No significant changes in lambda were observed during the entire time course of the experiment. ADC(W) was significantly decreased 100 min after pilocarpine application (549+/-8 microm(2) s(-1)) compared to controls (603+/-11 microm(2) s(-1)); by the end of the experiments, ADC(W) had returned to control values. The basal cortical levels of lactate, the lactate/pyruvate ratio, glucose and glutamate were 0.61+/-0.05 mmol/l, 33.16+/-4.26, 2.42+/-0.13 mmol/l and 6.55+/-1.31 micromol/l. Pilocarpine application led to a rise in lactate, the lactate/pyruvate ratio and glutamate levels, reaching 2.92+/-0.60 mmol/l, 84.80+/-11.72 and 22.39+/-5.85 micromol/l within about 100 min, with a subsequent decrease to control values 140 min later. The time course of changes in glucose levels was different, with maximal levels of 3.49+/-0.24 mmol/l reached 40 min after pilocarpine injection and a subsequent decrease to 1.25+/-0.40 mmol/l observed 200 min later. Pathologically increased neuronal activity induced by pilocarpine causes cell swelling followed by a reduction in the ECS volume fraction, which can contribute to the accumulation of toxic metabolites and lead to the start of epileptic discharges.

Changes in diffusion parameters, energy-related metabolites and glutamate in the rat cortex after transient hypoxia/ischemia

It has been shown that global anoxia leads to dramatic changes in the diffusion properties of the extracellular space (ECS). In this study, we investigated how changes in ECS volume and geometry in the rat somatosensory cortex during and after transient hypoxia/ischemia correlate with extracellular concentrations of energy-related metabolites and glutamate. Adult male Wistar rats (n = 12) were anesthetized and subjected to hypoxia/ischemia for 30 min (ventilation with 10% oxygen and unilateral carotid artery occlusion). The ECS diffusion parameters, volume fraction and tortuosity, were determined from concentration-time profiles of tetramethylammonium applied by iontophoresis. Concentrations of lactate, glucose, pyruvate and glutamate in the extracellular fluid (ECF) were monitored by microdialysis (n = 9). During hypoxia/ischemia, the ECS volume fraction decreased from initial values of 0.19 +/- 0.03 (mean +/- S.E.M.) to 0.07 +/- 0.01 and tortuosity increased from 1.57 +/- 0.01 to 1.88 +/- 0.03. During reperfusion the volume fraction returned to control values within 20 min and then increased to 0.23 +/- 0.01, while tortuosity only returned to original values (1.53 +/- 0.06). The concentrations of lactate and glutamate, and the lactate/pyruvate ratio, substantially increased during hypoxia/ischemia, followed by continuous recovery during reperfusion. The glucose concentration decreased rapidly during hypoxia/ischemia with a subsequent return to control values within 20 min of reperfusion. We conclude that transient hypoxia/ischemia causes similar changes in ECS diffusion parameters as does global anoxia and that the time course of the reduction in ECS volume fraction correlates with the increase of extracellular concentration of glutamate. The decrease in the ECS volume fraction can therefore contribute to an increased accumulation of toxic metabolites, which may aggravate functional deficits and lead to damage of the central nervous system (CNS).

Postoperative cognitive dysfunction: Incidence and prophylaxis.

The incidence of postoperative cognitive dysfunction (POCD) is often underestimated and not intuitively present by many anesthetists. POCD often occurs in the elderly but is also seen in younger patients. The incidence of POCD 1 week after non-cardiac surgery covers a span between 19-41% in patients older than 18 years. An increased POCD rate (10%) 3 months after surgery is only detected in patients older than 60 years. The occurrence of POCD is associated with an increased mortality rate, jet the etiology is mainly unknown despite enormous research efforts. The age of the patient is one of the main risk factors for the development of POCD. Data on how to avoid POCD are limited. However, the maintenance of homoeostasis is an important cornerstone of prophylaxis.

Brain metabolism and extracellular space diffusion parameters during and after transient global hypoxia in the rat cortex.

Hypoxia results in both reversible and irreversible changes in the brain extracellular space (ECS). This study utilized microdialysis to monitor changes in the energy-related metabolites lactate, pyruvate, glucose and glutamate in the rat cortex before, during and after 30-min transient global hypoxia, induced in anesthetized rats by reducing inspired oxygen to 6% O(2) in nitrogen. Changes in metabolite levels were compared with ECS diffusion parameters calculated from diffusion curves of tetramethylammonium applied by iontophoresis. Significant increases in lactate concentration and the lactate/pyruvate ratio, as well as decreased glucose levels, were found in the cortex immediately after the induction of hypoxia. Following recovery to ventilation with air, extracellular lactate and glucose levels and the lactate/pyruvate ratio returned to control levels within 40, 20 and 30 min, respectively. Glutamate levels started to increase 20-30 min after the onset of hypoxia and returned to prehypoxic values within 30-40 min of reoxygenation. The ECS volume fraction alpha decreased by about 5% from 0.18+/-0.01 during the first 20-25 min of hypoxia; after 25 min alpha dropped a further 22% to 0.14+/-0.01. Within 10 min of reoxygenation, alpha returned to control values, then increased to 0.20+/-0.01 and remained at this level until the end of the experiment. The observed 22% decrease in alpha markedly influences dialysate levels measured during hypoxia. In our study, the complete posthypoxic recovery of cortical metabolite levels and ECS diffusion properties suggests that metabolic enzymes and related cellular components (e.g., mitochondria) may tolerate prolonged hypoxic periods and recover to prehypoxic values.

Low tidal volume ventilation in a porcine model of acute lung injury improves cerebral tissue oxygenation.

BACKGROUND:In study, we investigated the effects of different tidal volumes on cerebral tissue oxygenation and cerebral metabolism in a porcine model of acute lung injury (ALI). We hypothesized that mechanical ventilation with low tidal (LT) volumes improves cerebral tissue oxygenation and metabolism after experimentally induced ALI. METHODS:After inducing experimental ALI by surfactant depletion, we studied two conditions in 10 female pigs: 1) LT volume ventilation with 6 mL/kg body weight, and 2) high tidal (HT) volume ventilation with 12 mL/kg body weight. Variables of gas exchange, hemodynamic, continuous cerebral tissue oxygen tension (ptiO2), cerebral microdialysis, and systemic cytokines were analyzed. After induction of ALI, data were collected at 2, 4, and 8 h. The primary end point was the change in ptiO2. For group comparisons, a t-test was used. A value of <0.05 was considered to indicate statistical significance. RESULTS:At baseline and after induction of ALI, no differences between groups were found in ptiO2; however, ptiO2 was significantly lower in the HT group after 4 and 8 h. Pao2 and Paco2 showed no significant differences between the groups at all timepoints. Regarding cerebral microdialysis, a significantly higher level of extracellular lactate could be demonstrated after 2, 4, and 8 h in the HT group. The release of cytokines resulted in higher values for interleukin-6 and interleukin-8 in the HT group. CONCLUSION:Protective ventilation with LT yielded a significant improvement in cerebral tissue oxygenation and metabolism compared to HT ventilation in a porcine model of ALI. There was dissociation between arterial and cerebral tissue oxygenation. Cerebral oxygenation and metabolism might have possibly been impaired by a more distinctive inflammatory response in the HT group.

Laypersons can successfully place supraglottic airways with 3 minutes of training. A comparison of four different devices in the manikin

IntroductionSupraglottic airway devices have frequently been shown to facilitate airway management and are implemented in the ILCOR resuscitation algorithm. Limited data exists concerning laypersons without any medical or paramedical background. We hypothesized that even laymen would be able to operate supraglottic airway devices after a brief training session.MethodsFour different supraglottic airway devices: Laryngeal Mask Classic (LMA), Laryngeal Tube (LT), Intubating Laryngeal Mask (FT) and CobraPLA (Cobra) were tested in 141 volunteers recruited in a technical university cafeteria and in a shopping mall. All volunteers received a brief standardized training session. Primary endpoint was the time required to definitive insertion. In a short questionnaire applicants were asked to assess the devices and to answer some general questions about BLS.ResultsThe longest time to insertion was observed for Cobra (31.9 ± 27.9 s, range: 9-120, p < 0.0001; all means ± standard deviation). There was no significant difference between the insertion times of the other three devices. Fewest insertion attempts were needed for the FT (1.07 ± 0.26), followed by the LMA (1.23 ± 0.52, p > 0.05), the LT (1.36 ± 0.61, p < 0.05) and the Cobra (1.45 ± 0.7, p < 0.0001). Ventilation was achieved on the first attempt significantly more often with the FT (p < 0.001) compared to the other devices. Nearly 90% of the participants were in favor of implementing supraglottic airway devices in first aid algorithms and classes.ConclusionLaypersons are able to operate supraglottic airway devices in manikin with minimal instruction. Ventilation was achieved with all devices tested after a reasonable time and with a high success rate of > 95%. The use of supraglottic airway devices in first aid and BLS algorithms should be considered.

The effects of levosimendan on brain metabolism during initial recovery from global transient ischaemia/hypoxia

BackroundNeuroprotective strategies after cardiopulmonary resuscitation are currently the focus of experimental and clinical research. Levosimendan has been proposed as a promising drug candidate because of its cardioprotective properties, improved haemodynamic effects in vivo and reduced traumatic brain injury in vitro. The effects of levosimendan on brain metabolism during and after ischaemia/hypoxia are unknown.MethodsTransient cerebral ischaemia/hypoxia was induced in 30 male Wistar rats by bilateral common carotid artery clamping for 15 min and concomitant ventilation with 6% O2 during general anaesthesia with urethane. After 10 min of global ischaemia/hypoxia, the rats were treated with an i.v. bolus of 24 μg kg-1 levosimendan followed by a continuous infusion of 0.2 μg kg-1 min-1. The changes in the energy-related metabolites lactate, the lactate/pyruvate ratio, glucose and glutamate were monitored by microdialysis. In addition, the effects on global haemodynamics, cerebral perfusion and autoregulation, oedema and expression of proinflammatory genes in the neocortex were assessed.ResultsLevosimendan reduced blood pressure during initial reperfusion (72 ± 14 vs. 109 ± 2 mmHg, p = 0.03) and delayed flow maximum by 5 minutes (p = 0.002). Whereas no effects on time course of lactate, glucose, pyruvate and glutamate concentrations in the dialysate could be observed, the lactate/pyruvate ratio during initial reperfusion (144 ± 31 vs. 77 ± 8, p = 0.017) and the glutamate release during 90 minutes of reperfusion (75 ± 19 vs. 24 ± 28 μmol·L-1) were higher in the levosimendan group. The increased expression of IL-6, IL-1ß TNFα and ICAM-1, extend of cerebral edema and cerebral autoregulation was not influenced by levosimendan.ConclusionAlthough levosimendan has neuroprotective actions in vitro and on the spinal cord in vivo and has been shown to cross the blood–brain barrier, the present results showed that levosimendan did not reduce the initial neuronal injury after transient ischaemia/hypoxia.

Short term non-invasive ventilation post-surgery improves arterial blood-gases in obese subjects compared to supplemental oxygen delivery - a randomized controlled trial

BackgroundIn the immediate postoperative period, obese patients are more likely to exhibit hypoxaemia due to atelectasis and impaired respiratory mechanics, changes which can be attenuated by non-invasive ventilation (NIV). The aim of the study was to evaluate the duration of any effects of early initiation of short term pressure support NIV vs. traditional oxygen delivery via venturi mask in obese patients during their stay in the PACU.MethodsAfter ethics committee approval and informed consent, we prospectively studied 60 obese patients (BMI 30-45) undergoing minor peripheral surgery. Half were randomly assigned to receive short term NIV during their PACU stay, while the others received routine treatment (supplemental oxygen via venturi mask). Premedication, general anaesthesia and respiratory settings were standardized. We measured arterial oxygen saturation by pulse oximetry and blood gas analysis on air breathing. Inspiratory and expiratory lung function was measured preoperatively (baseline) and at 10 min, 1 h, 2 h, 6 h and 24 h after extubation, with the patient supine, in a 30 degrees head-up position. The two groups were compared using repeated-measure analysis of variance (ANOVA) and t-test analysis. Statistical significance was considered to be P < 0.05.ResultsThere were no differences at the first assessment. During the PACU stay, pulmonary function in the NIV group was significantly better than in the controls (p < 0.0001). Blood gases and the alveolar to arterial oxygen partial pressure difference were also better (p < 0.03), but with the addition that overall improvements are of questionable clinical relevance. These effects persisted for at least 24 hours after surgery (p < 0.05).ConclusionEarly initiation of short term NIV during in the PACU promotes more rapid recovery of postoperative lung function and oxygenation in the obese. The effect lasted 24 hours after discontinuation of NIV. Patient selection is necessary in order to establish clinically relevant improvements.Trial Registration#DRKS00000751; http://www.germanctr.de