Argon does not affect cerebral circulation or metabolism in male humans.

OBJECTIVE: Accumulating data have recently underlined argon´s neuroprotective potential. However, to the best of our knowledge, no data are available on the cerebrovascular effects of argon (Ar) in humans. We hypothesized that argon inhalation does not affect mean blood flow velocity of the middle cerebral artery (Vmca), cerebral flow index (FI), zero flow pressure (ZFP), effective cerebral perfusion pressure (CPPe), resistance area product (RAP) and the arterio-jugular venous content differences of oxygen (AJVDO2), glucose (AJVDG), and lactate (AJVDL) in anesthetized patients. MATERIALS AND METHODS: In a secondary analysis of an earlier controlled cross-over trial we compared parameters of the cerebral circulation under 15 minutes exposure to 70%Ar/30%O2 versus 70%N2/30%O2 in 29 male patients under fentanyl-midazolam anaesthesia before coronary surgery. Vmca was measured by transcranial Doppler sonography. ZFP and RAP were estimated by linear regression analysis of pressure-flow velocity relationships of the middle cerebral artery. CPPe was calculated as the difference between mean arterial pressure and ZFP. AJVDO2, AJVDG and AJVDL were calculated as the differences in contents between arterial and jugular-venous blood of oxygen, glucose, and lactate. Statistical analysis was done by t-tests and ANOVA. RESULTS: Mechanical ventilation with 70% Ar did not cause any significant changes in mean arterial pressure, Vmca, FI, ZFP, CPPe, RAP, AJVDO2, AJVDG, and AJVDL. DISCUSSION: Short-term inhalation of 70% Ar does not affect global cerebral circulation or metabolism in male humans under general anaesthesia.

Asphyxia due to laryngeal spasm as a severe complication of awake deep brain stimulation for Parkinson's disease: a case report.

BACKGROUND: In accordance with German neurosurgical and neurological consensus recommendations, lead placements for deep brain stimulation (DBS) in patients with Parkinson's disease (PD) are usually performed with the patient awake and in "medication off" state. This allows for optimal lead position adjustment according to the clinical response to intraoperative test stimulation. However, exacerbation of Parkinsonian symptoms after withdrawal of dopaminergic medication may endanger the patient by inducing severe "off" state motor phenomena. In particular, this can be a problem in awake craniotomies utilizing intraoperative airway management and resuscitation. CASE PRESENTATION: We report the case of a PD patient with progressive orofacial and neck muscle dystonia resulting in laryngeal spasm during DBS lead placement. This led to upper airway compromise and asphyxia, requiring resuscitation. CONCLUSIONS: Laryngeal spasms may occur as a rare "off" state motor complication in patients with PD. Other potential causes of intraoperative difficulties breathing include bilateral vocal cord palsy, positional asphyxia, and silent aspiration. In our practice, we have adjusted our medication regimen and now allow patients to receive their standard dopaminergic medication until the morning of surgery. Neurologists and neurosurgeons performing lead placement procedures for PD should be aware of this rare but unsafe condition to most optimized treatment.

Influence of isoflurane on the diastolic pressure-flow relationship and critical occlusion pressure during arterial CABG surgery: a randomized controlled trial.

The effects of isoflurane on the determinants of blood flow during Coronary Artery Bypass Graft (CABG) surgery are not completely understood. This study characterized the influence of isoflurane on the diastolic Pressure-Flow (P-F) relationship and Critical Occlusion Pressure (COP) during CABG surgery. Twenty patients undergoing CABG surgery were studied. Patients were assigned to an isoflurane or control group. Hemodynamic and flow measurements during CABG surgery were performed twice (15 minutes after the discontinuation of extracorporeal circulation (T15) and again 15 minutes later (T30)). The zero flow pressure intercept (a measure of COP) was extrapolated from a linear regression analysis of the instantaneous diastolic P-F relationship. In the isoflurane group, the application of isoflurane significantly increased the slope of the diastolic P-F relationship by 215% indicating a mean reduction of Coronary Vascular Resistance (CVR) by 46%. Simultaneously, the Mean Diastolic Aortic Pressure (MDAP) decreased by 19% mainly due to a decrease in the systemic vascular resistance index by 21%. The COP, cardiac index, heart rate, Left Ventricular End-Diastolic Pressure (LVEDP) and Coronary Sinus Pressure (CSP) did not change significantly. In the control group, the parameters remained unchanged. In both groups, COP significantly exceeded the CSP and LVEDP at both time points. We conclude that short-term application of isoflurane at a sedative concentration markedly increases the slope of the instantaneous diastolic P-F relationship during CABG surgery implying a distinct decrease with CVR in patients undergoing CABG surgery.

Carbon dioxide induced changes in cerebral blood flow and flow velocity: role of cerebrovascular resistance and effective cerebral perfusion pressure.

In addition to cerebrovascular resistance (CVR) zero flow pressure (ZFP), effective cerebral perfusion pressure (CPPe) and the resistance area product (RAP) are supplemental determinants of cerebral blood flow (CBF). Until now, the interrelationship of PaCO2-induced changes in CBF, CVR, CPPe, ZFP, and RAP is not fully understood. In a controlled crossover trial, we investigated 10 anesthetized patients aiming at PaCO2 levels of 30, 37, 43, and 50 mm Hg. Cerebral blood flow was measured with a modified Kety-Schmidt-technique. Zero flow pressure and RAP was estimated by linear regression analysis of pressure-flow velocity relationships of the middle cerebral artery. Effective cerebral perfusion pressure was calculated as the difference between mean arterial pressure and ZFP, CVR as the ratio CPPe/CBF. Statistical analysis was performed by one-way RM-ANOVA. When comparing hypocapnia with hypercapnia, CBF showed a significant exponential reduction by 55% and mean VMCA by 41%. Effective cerebral perfusion pressure linearly decreased by 17% while ZFP increased from 14 to 29 mm Hg. Cerebrovascular resistance increased by 96% and RAP by 39%; despite these concordant changes in mean CVR and Doppler-derived RAP correlation between these variables was weak (r=0.43). In conclusion, under general anesthesia hypocapnia-induced reduction in CBF is caused by both an increase in CVR and a decrease in CPPe, as a consequence of an increase in ZFP.

Moderate hyperventilation during intravenous anesthesia increases net cerebral lactate efflux.

BACKGROUND: Hyperventilation is known to decrease cerebral blood flow (CBF) and to impair cerebral metabolism, but the threshold in patients undergoing intravenous anesthesia is unknown. The authors hypothesized that reduced CBF associated with moderate hyperventilation might impair cerebral aerobic metabolism in patients undergoing intravenous anesthesia. METHODS: Thirty male patients scheduled for coronary surgery were included in a prospective, controlled crossover trial. Measurements were performed under fentanyl-midazolam anesthesia in a randomized sequence aiming at partial pressures of carbon dioxide of 30 and 50 mmHg. Endpoints were CBF, blood flow velocity in the middle cerebral artery, and cerebral metabolic rates for oxygen, glucose, and lactate. Global CBF was measured using a modified Kety-Schmidt technique with argon as inert gas tracer. CBF velocity of the middle cerebral artery was recorded by transcranial Doppler sonography. Data were presented as mean (SD). Two-sided paired t tests and one-way ANOVA for repeated measures were used for statistical analysis. RESULTS: Moderate hyperventilation significantly decreased CBF by 60%, blood flow velocity by 41%, cerebral oxygen delivery by 58%, and partial pressure of oxygen of the jugular venous bulb by 45%. Cerebral metabolic rates for oxygen and glucose remained unchanged; however, net cerebral lactate efflux significantly increased from -0.38 (2.18) to -2.41(2.43) µmol min 100 g. CONCLUSIONS: Moderate hyperventilation, when compared with moderate hypoventilation, in patients with cardiovascular disease undergoing intravenous anesthesia increased net cerebral lactate efflux and markedly reduced CBF and partial pressure of oxygen of the jugular venous bulb, suggesting partial impairment of cerebral aerobic metabolism at clinically relevant levels of hypocapnia.

Reduced sevoflurane loss during cardiopulmonary bypass when using a polymethylpentane versus a polypropylene oxygenator.

PURPOSE: The goal of this investigation was to examine the influence of two oxygenators with different membranes, made of either polypropylene (PPL) or polymethylpentane (PMP), on the plasma concentration of sevoflurane during cardiopulmonary bypass. METHODS: The concentrations of sevoflurane during cardiopulmonary bypass were examined in patient plasma, endotracheal tubes, cardiotomy reservoirs and the outlets of the heart-lung oxygenators in twenty patients who underwent elective heart surgery. RESULTS: The sevoflurane losses are smaller in cardiopulmonary bypass when using a polymethylpentane versus a polypropylene oxygenator. Ten minutes after beginning cardiopulmonary bypass, the sevoflurane plasma concentration in the PPL oxygenator group compared to the PMP oxygenator group fell significantly (PPL 0.48-1.79 (0.93) vs. PMP 0.80-2.15 (1.56) µL × 100 mL-1, p = 0.02). This difference persisted until ten minutes after the termination of cardiopulmonary bypass. CONCLUSION: The results of this study show that using a polymethylpentane membrane oxygenator rather than a polypropylene oxygenator significantly reduces the losses of sevoflurane, resulting in higher plasma concentrations and greater depth of anesthesia.

Relation between renal dysfunction requiring renal replacement therapy and promoter polymorphism of the erythropoietin gene in cardiac surgery.

Several genetic polymorphisms have been identified to play a role in the occurrence and progression of renal dysfunction after cardiac surgery with cardiopulmonary bypass (CPB). Recently, it was demonstrated that the T allele of SNP rs1617640 in the promoter of the erythropoetin (EPO) gene is significantly associated with proliferative diabetic retinopathy (PDR) and end-stage renal disease (ESRD) due to increased EPO expression. This disease risk-associated gene and its potential pathway mediating severe microvascular complications in T-allele carriers could also play a role on renal dysfunction in patients who underwent cardiac surgery with CPB. We hypothesized that the patients' ability to produce increased EPO concentrations will affect morbidity and mortality after CPB. We conducted a prospective single center study between April 2006 and May 2007. In 481 patients who underwent cardiac surgery with CPB we prospectively examined the SNP rs1617640 in the promoter of the EPO gene by DNA sequencing. The patients were grouped according to their genotype (GG, GT, and TT). The genotype distribution of SNP rs1617640 in the promoter of the EPO gene was 36% (TT), 49% (TG), and 15% (GG). There was no difference in age, body mass index, gender, CPB time, or length of stay in intensive care unit. The hospitalization was irrespective of the patients' genotypes. The baseline creatinine in the TT group was 0.2 points higher than in the other groups; however this was without statistical significance in the multivariate analysis. No significant difference was shown in Euroscore, the Simplified Acute Physiology Score II, the Acute Physiology and Chronic Health Evaluation Score II, Acute Renal Failure Score, or the Risk, Injury, Failure, Loss of Kidney Function Score. The mortality was equal across the genotypes. However, an association between the TT genotype and acute renal replacement therapy (P=0.03), intra-aortic balloon pump usage (P=0.02), and serum creatine phosphokinase-MB increase (P=0.03) were observed after cardiac surgery. Our analysis suggests that the risk allele (T) of rs1617640 plays a role in the development of renal dysfunction after cardiac surgery with CPB. Patients with the TT risk allele required more frequent acute renal replacement therapy. Since our result is close to the border of significance, this hypothesis should be investigated in larger prospective studies with long-term follow-up to emphasize this polymorphism as a potential risk factor.

Prospective clinical and fiberoptic evaluation of the Supreme laryngeal mask airway.

BACKGROUND: In March 2007, a new disposable laryngeal mask airway (LMA) became available. The LMA Supreme (The Laryngeal Mask Company Limited, St. Helier, Jersey, Channel Islands) aims to combine the LMA Fastrach feature of easy insertion with the gastric access and high oropharyngeal leak pressures of the LMA ProSeal. METHODS: The authors performed an evaluative study with the LMA Supreme, size 4, on 100 women to measure the ease of insertion, determinate the laryngeal fit by fiberoptic classification, evaluate the oropharyngeal leak pressure, and report adverse events. RESULTS: Insertion of the LMA Supreme was possible in 94 patients (94%) during the first attempt, and in 5 patients (5%) during the second attempt. In one small patient, the LMA Supreme could not be inserted because of limited pharyngeal space. This patient was excluded from further analysis. Insertion of a gastric tube was possible in all patients at the first attempt. The median time for LMA Supreme insertion was 10.0 s (+/-4.7 s; range, 8-30 s). Laryngeal fit, evaluated by fiberscopic view, was rated as optimal in all patients, both immediately after insertion of the LMA Supreme and at the end of surgery. After equalization to room pressure, the mean cuff volume needed to achieve 60 cm H2O cuff pressure was 18.4 ml (+/-3.8 ml; range, 8-31 ml). The mean oropharyngeal leak pressure at the level of 60 cm H2O cuff pressure was 28.1 cm H2O (+/-3.8 cm H2O, range, 21-35 cm H2O). Eight patients (8.1%) complained of a mild sore throat. No patient reported dysphagia or dysphonia. CONCLUSIONS: Clinical evaluation of the LMA Supreme showed easy insertion, optimal laryngeal fit, and low airway morbidity. Oropharyngeal leak pressure results were comparable to earlier data from the LMA ProSeal.

Off-pump supraarterial decompression myotomy for myocardial bridging.

BACKGROUND: Myocardial bridging of the left anterior descending (LAD) artery may result in clinical symptoms. Surgery with cardiopulmonary bypass (CPB) is a therapeutic option with considerable risk. We hypothesized that off-pump supraarterial myotomy could be an effective treatment modality. METHODS: Between October 1998 and May 2000, 13 patients were referred for surgery. All were symptomatic despite medical therapy. Anteroseptal ischemia had been proven by thallium scintigraphy in all 13 patients, exercise testing was positive in 11. All patients were operated on with an off-pump approach after median sternotomy. RESULTS: Mean patient age was 61 +/- 8 years (range, 43-71 years). Coronary artery disease mandating additional bypasses was present in 3 patients. The bypasses were done off pump in 2 patients. Conversion to on-pump surgery was necessary in 3 of 13 patients (23%) because of hemodynamic compromise (1 patient), opening of the right ventricle (1 patient), and injury to the LAD (1 patient). Supraarterial myotomy was performed in all patients. One patient who underwent surgery with CPB developed postoperative anteroseptal myocardial infarction. Postoperative exercise testing was performed in all patients and did not reveal any persistent ischemia. Mortality was 0%. All patients were free from symptoms and had not undergone repeat interventions after an average of 51 +/- 7 months of follow-up. CONCLUSIONS: Off-pump supraarterial myotomy effectively relieves coronary obstruction but has a certain periprocedural risk as evidenced by 1 myocardial infarction, 1 right ventricular injury, and 1 LAD injury. Long-term freedom from symptoms and from reintervention favor further investigation of this surgical therapy.

Efficacy of postoperative rewarming after cardiac surgery.

OBJECTIVE: To compare the efficacy of forced-air warmers and radiant heaters on rewarming after cardiac surgery in a prospective randomized study. METHODS: Fifty male patients who had undergone coronary artery bypass graft surgery were studied. The control group (Gr. C, n=10) was nursed under a standard hospital blanket. Two groups were treated with forced-air warmers: WarmTouch 5700 (Gr. WT, n=10) and Bair Hugger 500 (Gr. BH, n=10). Two other groups were treated by radiant heaters: the Aragona Thermal Ceilings CTC X radiant heater (Gr. TC, n=10) and a self assembled radiant heater of 4 Hydrosun 500 infrared lamps (Gr. HY, n=10). Changes of oesophageal temperature, mean skin temperature, mean body temperature and relative heat balance were calculated from oesophageal temperature, 4 skin temperatures and oxygen consumption (VO(2)). RESULTS: All actively treated groups with exception of the TC group showed significantly faster oesophageal warming than the control group. The mean body temperature increased 1.1 (0.7-1.7) degrees Ch(-1) in Gr. WT, 1.3 (0.7-1.5) degrees Ch(-1) in Gr. BH, 0.8 (0.5-1.4) degrees Ch(-1) in Gr. TC and 0.7 (0.4-1.0) degrees Ch(-1) in Gr. HY compared to Gr. C with 0.4 (0.2-0.7) degrees Ch(-1). The mean VO(2) and the maxima of the VO(2) during the study period did not differ significantly between the groups. CONCLUSION: In the current setting active warming, forced-air warming more than radiant warming, increased speed of rewarming two- to threefold in comparison to insulation with a blanket.

Evaluation of heated humidifiers for use on intubated patients: a comparative study of humidifying efficiency, flow resistance, and alarm functions using a lung model.

OBJECTIVE: Evaluation of humidification efficiency, flow resistance, and alarm functions of heated humidifiers (HH;(Kendall-Aerodyne-delta, Fisher&Paykel-MR 730; Dräger-Aquapor; Puritan-Bennett-Cascade II) in accordance with ISO/EN-8185:1997 and on a ventilated lung model in accordance with ISO/EN-9360:2000. METHODS: Humidification efficiency was evaluated by (a) measuring the water content of the inspiratory air on perfusion with different gas flows, (b) measuring the water loss of a lung model, and (c) simultaneous measurement of the in- and expiratory water content with a capacitive hybrid sensor. The resistance characteristics were measured, the data were compared with a mathematical approximation. The alarm functions were determined. RESULTS: The humidification efficiency of HHs is a function of gas flow and design characteristics. In HHs with tube heating it is possible to make settings at which the inspiratory humidity falls below the minimal value of 33 mgH(2)O/l stipulated by ISO/EN-8185:1997. The inspiratory resistances extend from 0.5 to 4.4 cmH(2)O l(-1) s(-1); the expiratory flow resistances of the devices are low. The alarm functions of HHs with tube heating are inadequate for cases involving both "dry start" and "running dry." CONCLUSIONS: Efficiency data that allow a direct comparison with heat and moisture exchangers data according to ISO/EN-9360:2000 can also be determined for HH. HH do not prevent pulmonary water losses in intubated patients. These losses can exceed the physiological range. The airway resistance of the Cascade II prohibits its use in spontaneously breathing patients. The warning and shut-off features of HH are unacceptable and hazardous.