Effects of Arginine Vasopressin on Oxygenation and Haemodynamics during One-Lung Ventilation in an Animal Model

In a case of arterial hypotension during one-lung ventilation, haemodynamic support may be required to maintain adequate mean arterial pressure. Arginine vasopressin, a potent systemic vasoconstrictor with limited effects on the pulmonary artery pressure, has not been studied in this setting. Twelve female pigs were anaesthetised and ventilated and arterial, central venous and pulmonary artery catheters were inserted. A left-sided double lumen tube was placed via tracheostomy and one-lung ventilation was initiated. The animals were in the left lateral position, with the left lung ventilated and right lung collapsed. Respiratory and haemodynamic values were recorded before and during a continuous infusion of arginine vasopressin sufficient to double the mean arterial pressure. The arginine vasopressin caused a decrease in cardiac output (3.8±1.1 vs. 2.7±0.7 l/min, P <0.001) and mixed-venous oxygen tension (39.1±5.8 vs. 34.4±5 mmHg, P=0.003). Pulmonary artery pressure was unchanged (24±2 vs. 24±3 mmHg, P=0.682). There was no effect of the arginine vasopressin on arterial oxygen tension (226±106 vs. 231±118 mmHg, P=0.745). However, there was a significant decrease in shunt fraction (28.3±6.2 vs. 24.3±7.8%, P=0.043) and a significant proportional increase in perfusion of the ventilated lung (78.8±9.5 vs. 85.5±7.9%, P=0.036). In our animal model of one-lung ventilation, doubling mean arterial pressure by infusion of arginine vasopressin significantly affected global haemodynamics, but had no influence on systemic arterial oxygen tension.

Loss of the guide wire: mishap or blunder?

We describe four cases of lost guide wires during central venous catheterization. Although percutaneous catheterization of central veins is a routine technique, it is a procedure requiring advanced operating skills, expert supervision, and attention to detail in order to prevent adverse effects.

[The use of the infraclavicular plexus catheter for treatment of perioperative and chronic pain]

OBJECTIVES

The aim of this prospective study was to evaluate the vertical infraclavicular approach to the brachial plexus for the insertion of a catheter to achieve continuous analgesia in postoperative patients and patients with chronic upper limb pain.

METHODS

The brachial plexus was identified using the technique described by Kilka et al. and a flexible catheter (diameter 0.85 mm) was introduced 3-5 cm into the perineural sheath via the punction cannula. Regional analgesia was achieved by intermittent injection of local anaesthetic agent. Placement of the catheter, duration and effectiveness of treatment, complications and reasons for catheter removal were recorded using a standard protocol.

RESULTS

A total number of 226 plexus catheters were placed in 210 patients. Consecutive regional analgesia for at least 48 h was possible in 88%. Analgesia was sufficient in 76% of patients up to the time of catheter removal. The median (minimum-maximum) duration of catheterisation in the whole collective was 7 days (1-240) and 11 days in patients with chronic pain. Almost 30% of the patients were treated for 10 days or longer and 4.4% were treated for 1 month or longer. Major complications occurred in only three cases, while technical problems and minor complications (redness at puncture site) occurred in 10% of cases.

CONCLUSIONS

The placement of an infraclavicular plexus catheter is a suitable method for pain management in the upper limb. This approach may have advantages in patients with severe injuries who cannot abduct the arm. Our results are encouraging in terms of catheterisation time, patient comfort and incidence of complications.

The effects of increasing concentrations of isoflurane and desflurane on pulmonary perfusion and systemic oxygenation during one-lung ventilation in pigs

During one-lung ventilation (OLV), hypoxic pulmonary vasoconstriction (HPV) reduces venous admixture and attenuates the decrease in arterial oxygen tension by diverting blood from the nonventilated lung to the ventilated lung. In vitro, desflurane and isoflurane depress HPV in a dose-dependent manner. Accordingly, we studied the effects of increasing concentrations of desflurane and isoflurane on pulmonary perfusion, shunt fraction, and PaO(2) during OLV in vivo. Fourteen pigs (30-42 kg) were anesthetized, tracheally intubated, and mechanically ventilated. After placement of femoral arterial and thermodilution pulmonary artery catheters, a left-sided double-lumen tube (DLT) was placed via tracheotomy. After DLT placement, FIO(2) was adjusted at 0.8 and anesthesia was continued in random order with 3 concentrations (0.5, 1.0, and 1.5 minimal alveolar concentrations) of either desflurane or isoflurane. Differential lung perfusion was measured with colored microspheres. All measurements were made after stabilization at each concentration. Whereas mixed venous PO(2), mean arterial pressure, cardiac output, nonventilated lung perfusion, and shunt fraction decreased in a dose-dependent manner, PaO(2) remained unchanged with increasing concentrations of desflurane and isoflurane during OLV. In conclusion, increasing concentration of desflurane and isoflurane did not impair oxygenation during OLV in pigs.

IMPLICATIONS

In an animal model of one-lung ventilation, increasing concentrations of desflurane and isoflurane dose-dependently decreased shunt fraction and perfusion of the nonventilated lung and did not impair oxygenation. The decreases in shunt fraction are likely the result of anesthetic-induced marked decreases in cardiac output and mixed venous saturation.

Lung perfusion affects preload assessment and lung water calculation with the transpulmonary double indicator method

OBJECTIVES

The transpulmonary double indicator method uses intra- and extravascular indicators to calculate cardiac output, intrathoracic blood volume, global end-diastolic volume, and extravascular lung water content. Since lung perfusion may be of importance during these measurements, we studied the effects of pulmonary blood flow occlusion on measurements obtained with this method.

SETTING

Experimental animal facility of a University department.

METHODS AND INTERVENTIONS

In seven pigs, the branch of the pulmonary artery perfusing the lower and middle lobe of the right lung was occluded. Measurements before, during, and after the occlusion were made with a pulmonary artery catheter and a commonly used transpulmonary double indicator catheter and device.

MEASUREMENTS AND RESULTS

Occlusion of the right lower and middle lobe branch of the pulmonary artery increased mean pulmonary pressure (before occlusion: 24+/-1, during occlusion: 32+/-2, after reopening 25+/-1 mmHg; P<0.05), increased right ventricular end-diastolic volume (172+/-34, 209+/-21, 174+/-32 ml, respectively; P<0.05), decreased intrathoracic blood volume (998+/-39, 894+/-48, 1006+/-49 ml, respectively; P<0.05), and decreased extravascular lung water (7.2+/-0.5, 4.2+/-0.4, 6.9+/-0.4 ml/kg, respectively; P<0.05) without causing significant changes in cardiac output. All changes were reversible upon reopening the vessel.

CONCLUSIONS

These data show that the transpulmonary double indicator method may underestimate extravascular lung water and right ventricular preload when the perfusion to parts of the lung is obstructed.

Effect of ketamine on the neuromagnetic mismatch field in healthy humans

Mismatch negativity (MMN) is a component of the auditory evoked event-related potentials (ERP) that assesses automatic sound change detection and is disturbed in schizophrenic patients. Animal experimental evidence has linked the generation of MMN to the N-methyl-D-aspartate (NMDA) receptor. We investigated the neuromagnetic mismatch field (MMF) in healthy volunteers before and after intravenous application of a subanesthetic dose of the NMDA receptor antagonist ketamine (0.3 mg/kg). Ketamine had a significant influence on latency and dipole moment of the MMF, whereas the N100m latency of the standard tone was not prolonged and its dipole moment remained stable. Our results suggest that ketamine interferes with aspects of preattentive information processing and is in line with the view that disturbed NMDA receptor function may mediate the deficient auditory mismatch response in patients with schizophrenia.

Cardiovascular function and brain metabolites in normal weight and intrauterine growth restricted newborn piglets--effect of mild hypoxia

In order to clarify the influence of intrauterine growth restriction on systemic hemodynamics, catecholamine response, and regional distribution of brain energy metabolites per se and during mild hypoxic episodes a study was performed in thirty newborns with a well-characterized state of intrauterine and intra-natal development. Thirty animals were divided into fifteen normal weight piglets (NW) and fifteen intrauterine growth restricted (IUGR) piglets according to their birth weight. Category "NW" covered animals with a birth weight of > 40th percentile; IUGR category covered animals with a birth weight of > 5th and < 10th percentiles. Animals were anesthetized with halothane in 70% nitrous oxide and 30% oxygen and after immobilization artificially ventilated. The acid-base balance and blood gas values at baseline conditions were similar within the different groups investigated and consistent with other data obtained from anesthetized and artificially ventilated newborn piglets. Mild hypoxic hypoxia which was induced by lowering the FiO2 from 0.35 to 0.15 resulted in reduced arterial pO2 (NW: from 115 +/- 37 mmHg to 39 +/- 7 mmHg; IUGR: from 117 +/- 23 mmHg to 39 +/- 3 mmHg; p < 0.05), but arterial pH and pCO2 remained unchanged. Under baseline conditions arterial blood pressure, cardiac output, and myocardial contractility, expressed as dp/dt(max) and plasma catecholamine values were similar in all groups studied. Heart rate was slightly increased in IUGR (p < 0.05). Mild hypoxia led to a strong increase of myocardial contractility in NW as well as IUGR piglets to 2.4 and 2.7 fold and remained increased during recovery (p < 0.05). Moreover, total peripheral resistance was enhanced at the end of recovery period in IUGR animals (p < 0.05). There was a significant increase of epinephrine (E) in NW animals in comparison to sham-operated animals (p < 0.05). Interestingly, during reoxygenation the further increase in E and norepinephrine (NE) levels were enhanced in the animals which suffered from mild hypoxia (p < 0.05). Regional distribution of brain tissue metabolites was partly affected by intrauterine growth restriction. In particular, brain tissue glucose content was strongly reduced by 65 to 72 per cent in all brain regions investigated. Mild hypoxia led to an increase of about 30 percent in NW animals (p < 0.05). In IUGR piglets the percentage increase of brain glucose content was on an average more pronounced but with considerably higher variance. Also, a strong increase of brain lactate content appeared here (p < 0.05). In contrast, brain tissue ATP was quite similar in all groups studied, but brain creatine phosphate was significantly reduced in some forebrain structures of IUGR piglets after mild hypoxia (figure 2, p < 0.05). In summary, this investigation provides information on cardiovascular functions and brain metabolites of normal weight and naturally occurring growth restricted newborn piglets. Mild hypoxemia was well-tolerated from both animal groups. It is suggested that lactate may play a significant role as a source for brain energy production in the newborn IUGR piglets.

Body weight distribution and organ size in newborn swine (sus scrofa domestica) -- a study describing an animal model for asymmetrical intrauterine growth retardation

Normal growth is the expression of the genetic potential to growth which is neither abnormally constrained nor promoted by internal or external factors. Restricted fetal growth is common in human pregnancy and is associated with increased perinatal morbidity and mortality. Because of ethical restrictions, pathogenetical studies are necessarily dependent on appropriate animal models. In the studies presented, evidence will be provided that the naturally occurring distribution of body weight in newborn piglets, obtained from n = 512 newborn piglets (about 12 hours old) in 50 consecutive deliveries in the breed cohort of the mixed German domestic breed - "Deutsches Land-/Edelschwein" gives an appropriate sampling for providing a statistically reliable basis with which to determine different degrees of fetal growth for further pathophysiological studies intended. A strong inverse correlation (r = -0.66, p < 0.05) was found between the mean weight of the litter and the number of piglets per litter, and an inverse correlation (r = -0.64, p < 0.05) was found between the lowest weight of the littermate and the number of piglets per litter. Moreover, gravimetric investigations were made into an additional 53 one-day-old newborn piglets reflecting the naturally occurring birth weight distribution determined. A marked linear correlation between body weights and various organ weights was found (values of the correlation coefficient amounted to between 0.45 and 0.98; p < 0.05). The lowest variation of organ weights was found in the CNS structures (0.68-1.33). Skeleton and heart exhibited similar ranges of weight variation (0.35-1.81 and 0.38-2.00 of the means) to body weight (0.38-1.77 of the means). This was also expressed in the regression analysis, because the slope values were 0.99 and 0.97 respectively. The hormonal glands investigated, the kidneys, and the abdominal parenchymal organs exhibited the largest ranges of weight variation. Moreover, regression analysis gives evidence that the weight restriction was more pronounced than expected concerning respective body weight. This is indicated by slope values > 1 in almost all of those organs. Plasma concentration of IGF-1 showed an inverse correlation with body weight (r = -0.42; p < 0.05, fig 4). IGF-1 concentration of intrauterine growth retarded (IUGR) newborn piglets was in the mean nearly double that of normal weight animals (p < 0.05) and the brain weight to liver weight ratio was increased more than 2.5 times in IUGR newborn (fig 5 A, p < 0.05). This investigation provides information on the naturally occurring body weight distribution of one-day-old piglets, which was obviously a result of epigenetic factors. Gravimetrical estimation showed clearly that body weight variety is most probably caused by alterations of placental functioning. Severe alterations resulted in asymmetrical growth retardation, which was proved by a significantly increased brain to liver ratio in animals with a body weight < 10th centile. Thus, evidence is provided that naturally occurring asymmetrical intrauterine growth restricted newborn piglets can be identified simply by body weight measurement, so that convenient conditions are given for pathogenetically motivated studies on intrauterine compromised newborns.

Changed systemic and cerebral hemodynamics and oxygen supply due to gradual hemorrhagic hypotension induced by an external PID-controller in newborn swine

An experimental design including an external closed-loop PID-(proportional-integral-differential-)controller is presented which enables the induction of gradual hemorrhagic hypotension at different stages of blood flow reduction up to stages of critically disturbed systemic and regional hemodynamics and oxygen supply. For this purpose nine newborn piglets (12-26 hours old, body weight 1626+/-160 g) were anesthetized and artificially ventilated. Gradual hemorrhagic hypotension was induced at four different steady state stages (stage 1 = 60 mmHg; stage 2 = 50 mmHg; stage 3 = 40 mmHg; stage 4 = 35 mmHg) every 30 minutes by gradual blood withdrawal using external PID controller equipment. Cardiac output and brain regional blood flows were measured by the colored microsphere technique. Systemic and brain regional hemodynamics and O2 supply, metabolic parameters and blood catecholamine concentrations were obtained under baseline conditions and at every 25th minute of the four different steady state stages. About 35 percent of the calculated total blood volume (cTBV) was withdrawn in order to reach the first stage of hemorrhagic hypotension. Further blood withdrawal of about 10 percent of the cTBV, about 5 percent of the cTBV, and about 3 percent of the cTBV were necessary to reach the other respective hypotensive stages. Gradual hemorrhagic hypotension led to an increasing reduction of the cardiac output at every hypotensive stage up to about 20 percent of the baseline value (p<0.05). This was accompanied by a concomitant increase of the total peripheral resistance to about 2.5 fold (p<0.05) and a huge increase in the blood catecholamine concentrations (epinephrine: about 64 fold; norepinephrine: about 35 fold). The induced redistribution of the circulating blood volume was shunted to the vital organs. Therefore, brain cortical blood flow was slightly increased at stage 1 and stage 2. A significant reduction of rCBF did not occur until stage 4 (p<0.05). Regional cerebrovascular resistance was concomitantly reduced at stage 1 and stage 2 (p<0.05) and thereafter again slightly elevated. Brain cortical oxygen consumption was maintained up to stage 2, reduced by about 20% at the next stage of hemorrhagic hypotension (p<0.05) and reached the lowest level of about 50% from baseline at stage 4 (p<0.05). Excellent accuracy and stability was shown at each stage for the external PID controller equipment, so that each given setpoint of the instantaneous mean arterial blood pressure was reached and stabilized even at the lowest hypotensive stage (stage 1: 59.53+/-0.23; stage 2: 50.03+/-0.56; stage 3: 39.18+/-1.75; stage 4: 35.28+/-0.45 mmHg (mean+/-SD)). We conclude that the experimental design presented, with an external PID controller to induce gradual hemorrhagic hypotension in newborn piglets is sufficient for producing functional states with changed systemic and cerebral features with high stability and accuracy, enabling a systematic study of disturbed regional hemodynamics and energy metabolism under steady state conditions even under critically changed states of the systemic cardiovascular regulation.

Validation of the multiple colored microsphere technique for regional blood flow measurements in newborn piglets

The use of multiple colored microspheres (CMS) for the measurement of regional blood flow (RBF) in almost all organs and tissues of newborn piglets was validated. For this purpose mixtures of different CMS and/or radio-labeled microspheres (RMS) were injected into the left ventricle of eight newborn piglets. Regional blood flows (RBF) were quantified using the reference sample method. Flow rates estimated by RMS and CMS were compared for each tissue sample. An excellent correlation (r = 0.995-0.999) between CMS and RMS flow rates was found even for organs with low perfusion and tissue samples containing 400-750 CMS. We conclude that the CMS technique is a valid alternative for RBF measurement in newborn piglets, and that all disadvantages arising from radioactive labeling are thereby avoided.