Clemens Greim

Sonographic imaging of the sciatic nerve and its division in the popliteal fossa in children

Background:  High resolution ultrasound is a possible option for anesthetists to detect nerves. We tested the possibility of imaging the sciatic nerve and its division into the tibial and peroneal part using high resolution ultrasound in children.

Cardiovascular and metabolic responses to anesthetic-induced malignant hyperthermia in swine

Background Several cardiovascular disturbances, such as tachycardia and hypotension, are observed during human and porcine malignant hyperthermic (MH) crises. However, the pathophysiologic mechanisms responsible for the deterioration of cardiovascular function during MH are not completely known. The purpose of this study was to elucidate the changes in left ventricular (LV) function and metabolism and the systemic and regional hemodynamics during anesthetic-induced MH in swine.

Echocardiographic monitoring during induction of general anesthesia with a miniaturized esophageal probe.

UNLABELLED Standard transesophageal echocardiography (TEE) does not allow cardiac monitoring during the induction of anesthesia because standard probes would limit the oropharyngeal space and impair mask ventilation and tracheal intubation. We hypothesized that a prototype, miniaturized TEE probe could be safely introduced transnasally in awake patients and that mask ventilation and orotracheal intubation could be performed while continuously monitoring left ventricular (LV) function during the induction of anesthesia. Forty-five patients were studied prospectively. The transnasal TEE probe was introduced through one of the nares and advanced until a transverse plane image of the LV at the level of the papillary muscles was seen. Anesthesia was induced, and the patients were ventilated with a mask that had previously been threaded over the TEE probe via a central perforation. Probe insertion was successful in 12 patients under local anesthesia alone and in an additional 31 patients with a combination of local anesthesia and mild sedation. In two cases, probe placement was unsuccessful. Overall, hemodynamic variables did not change significantly during insertion. No case of significant mucosal bleeding was seen. In one patient, regurgitation of gastric contents occurred without affecting the perioperative outcome. The two-dimensional echocardiogram image quality of the LV during the induction of anesthesia was good or acceptable in 95% of patients. We conclude that transnasal TEE can effectively be used for cardiac monitoring during the induction of general anesthesia. IMPLICATIONS This study demonstrates that it is feasible and generally safe to introduce a miniaturized transesophageal echocardiography probe transnasally in awake cardiac risk patients to monitor cardiac performance during the induction of general anesthesia.

The contribution of arterio-venous extracorporeal lung assist to gas exchange in a porcine model of lavage-induced acute lung injury

This prospective large-animal study was performed to evaluate the contribution of arterio-venous extracorporeal lung assist (AV-ECLA) to pulmonary gas exchange in a porcine lavage-induced acute lung injury model. Fifteen healthy female pigs, weighing 50.39±3.8 kg (mean±SD), were included. After induction of general anaesthesia and controlled ventilation, an arterial line and a pulmonary artery catheter were inserted. Saline lung lavage was performed until the PaO2 decreased to 51±16 mmHg. After a stabilization period of 60 min, the femoral artery and vein were cannulated and a low-resistance membrane lung was interposed. Under apnoeic oxygenation, variations of sweep-gas flow were performed every 20 min in order to evaluate the membrane lungs efficacy, in terms of carbon dioxide (CO2) removal and oxygen (O2) uptake. Although AV-ECLA is highly effective in eliminating CO2, if combined with apnoeic oxygenation, normocapnia was not achievable. AV-ECLAs contribution to oxygenation during severe hypoxemia was antagonized by a significant increase in the pulmonary shunt fraction.

High frequency oscillatory ventilation and prone positioning in a porcine model of lavage-induced acute lung injury

BackgroundThis animal study was conducted to assess the combined effects of high frequency oscillatory ventilation (HFOV) and prone positioning on pulmonary gas exchange and hemodynamics.MethodsSaline lung lavage was performed in 14 healthy pigs (54 ± 3.1 kg, mean ± SD) until the arterial oxygen partial pressure (PaO2) decreased to 55 ± 7 mmHg. The animals were ventilated in the pressure controlled mode (PCV) with a positive endexpiratory pressure (PEEP) of 5 cmH2O and a tidal volume (VT) of 6 ml/kg body weight. After a stabilisation period of 60 minutes, the animals were randomly assigned to 2 groups. Group 1: HFOV in supine position; group 2: HFOV in prone position. After evaluation of prone positioning in group 2, the mean airway pressure (Pmean) was increased by 3 cmH2O from 16 to 34 cmH2O every 20 minutes in both groups accompanied by measurements of respiratory and hemodynamic variables. Finally all animals were ventilated supine with PCV, PEEP = 5 cm H2O, VT = 6 ml/kg.ResultsCombination of HFOV with prone positioning improves oxygenation and results in normalisation of cardiac output and considerable reduction of pulmonary shunt fraction at a significant (p < 0.05) lower Pmean than HFOV and supine positioning.ConclusionIf ventilator induced lung injury is ameliorated by a lower Pmean, a combined treatment approach using HFOV and prone positioning might result in further lung protection.

Dobutamine induces ineffective work in regional ischaemic myocardium: an experimental strain rate imaging study.

In the present study, we sought to investigate the effects of differing inotropic conditions on regional myocardial function in ischaemic segments. In an experimental pig model ( n =11), the regional deformation parameters peak systolic strain rate [SR(SYS) (peak velocity of thickening)], systolic strain [epsilon(SYS) (systolic wall thickening)] and post-systolic strain [epsilon(PST) (ongoing wall thickening after end of systole)] were measured during normal perfusion and regional ischaemia of the posterior wall. These parameters were compared with global contractility [E(ES) (end-systolic elastance)] measured by a conductance catheter. Ischaemia was induced by an active coronary hypoperfusion in the circumflex coronary artery. Measurements were done at baseline, during dobutamine and during esmolol infusion. In normal perfused hearts, SR(SYS) (4.8+/-0.2 s(-1) at baseline) increased during dobutamine infusion, decreased during esmolol infusion and correlated significantly with global E(ES). In addition, epsilon(SYS) averaged 93+/-3% at baseline and there was almost no epsilon(PST) (4+/-1%) in normal myocardium. In ischaemic myocardium, SR(SYS) and epsilon(SYS) were significantly reduced compared with normal myocardium at baseline (SR(SYS)=2.8+/-0.3 s(-1), and epsilon(SYS)=43+/-6%; P <0.001 compared with normal perfused hearts), whereas global E(ES) was unchanged. In contrast, epsilon(PST) was significantly increased in regional ischaemic segments compared with the non-ischaemic myocardium (15+/-2%; P <0.001). During the dobutamine infusion, SR(SYS) remained unchanged. In contrast, epsilon(SYS) decreased (25+/-5%; P <0.001) and epsilon(PST) increased (25+/-4%; P <0.05) significantly during dobutamine infusion in ischaemic myocardium. In ischaemic segments, an inotropic stimulation with dobutamine resulted in a shift of strain from systole (epsilon(SYS)) to post-systole (epsilon(PST)). Thus dobutamine induced ineffective myocardial work in ischaemic segments.

Abnormal Action Potential Responses to Halothane in Heart Muscle Isolated from Malignant Hyperthermia-susceptible Pigs

Background During human and porcine malignant hyperthermia (MH), cardiac dysrhythmias and altered myocardial function can be observed. It is unknown whether a primary abnormality in cardiac muscle contributes to the cardiac symptoms during MH. An abnormal response to halothane has recently been demonstrated in action potentials (APs) from MH-susceptible (MHS) human skeletal muscles. We investigated the electrophysiologic properties in trabeculae isolated from the right ventricles of normal (MHN) and MHS pigs. Methods The experiments were performed on electrically stimulated (1 Hz) trabeculae isolated from the right ventricles of MHS and MHN pigs. Resting membrane potentials, APs, and tension were measured with and without the presence of 1% of halothane. In addition, the halothane-equilibrated muscles were exposed to caffeine in increasing doses (1, 2, and 4 mM). Results In the absence of halothane, resting potential and AP characteristics in MHS and MHN muscles did not differ significantly. Halothane did not alter resting potentials but produced different alterations in the APs in MHS and MHN muscles, whereas the decrease in twitch tension was identical. In contrast to reductions in the AP amplitude and duration in MHN muscle, halothane produced an enlargement of the APs in MHS muscle. The addition of caffeine caused nearly identical prolongations of AP duration in MHS and MHN muscles. Conclusions This in vitro study demonstrates that halothane produces abnormal alterations in the dynamic electric properties of the ventricular excitable membrane from MHS pigs. These results suggest a latent defect in the myocardium of MHS pigs that becomes apparent in the presence of MH-triggering agents.

Vertical infraclavicular brachial plexus block in a child with cystic fibrosis

Vertical infraclavicular brachial plexus block (VIP) as described by Kilka et al. in 1995 is becoming increasingly popular in Europe (1,2). It combines easily identifiable landmarks with a high rate of success, rapid onset of plexus blockade, no need for patient cooperation (a nerve stimulator is mandatory), and a good safety margin. Anesthesia of the hand, forearm, elbow, and upper arm, proximally extending almost to the shoulder is achieved. Care must be taken concerning correct needle insertion, as pneumothorax is a specific albeit rare complication (3,4). However, to our knowledge, no reports exist of this approach to the brachial plexus in the pediatric population. We report a case of an 8-year-old, 23-kg girl with cystic fibrosis who was scheduled for open reduction and internal fixation of a supracondylar fracture of her right arm. Her medical history included resection of the right middle and lower pulmonary lobes due to severe bronchiectasis and recurrent pulmonary infections. Auscultation revealed coarse crackles over both lungs but no wheezing. A recent ventilatory function test showed moderately severe restrictive pulmonary disease. After careful consideration and informed consent of the child and her parents, it was decided that because of her pulmonary situation the procedure should be performed under regional anesthesia. VIP was chosen because it was painful for the girl to abduct her arm, which would have been necessary for an axillary block. Moreover, neither the axillary nor the interscalene approach is ideally suited for surgery around the elbow (5). Despite oral premedication with 10 mg of midazolam, the patient reached the holding area in a very anxious state and was crying. Intravenous access was achieved before separation from the parents, and the girl was sedated with propofol before she was taken into the operating room. When routine monitoring was installed, the level of sedation was deepened, and VIP was performed exactly at the midpoint between the sternal notch and the anterior edge of the acromion (length, 12 cm) using the same landmarks as in adults (1,2). Because VIP blockade has been published mainly in adult cases, additional sonography of the infraclavicular region was used (Fig. 1) to verify the relationship between the brachial plexus and the pleura. The patient reacted purposefully to skin infiltration with 2 mL of mepivacaine 1% but did not move during insertion of the 24-gauge short bevel unipolar stimulator needle (Pajunk, Geisingen, Germany) or during actual nerve stimulation. At a depth of 1.5 cm from the skin, a motor response of the thumb and first digit were elicited with a current of 0.35 mA at a stimulus duration of 0.1 ms. Eighteen mL of mepivacaine 1.5% were injected, and complete anesthesia of the arm was achieved within 10 min. Surgery lasted for approximately 1 h and was conducted uneventfully while the girl was kept lightly sedated with incremental IV boluses of propofol. No airway intervention or additional oxygen was required. At the end of the procedure, the patient was fully awake, pain free, and was transferred to the PACU. The postoperative course was uncomplicated, and the girl was discharged home 3 days later. We conclude that brachial plexus blockade using the VIP may be an option for regional anesthesia not only in adults, but also in selected pediatric patients.