Effect of positive end-expiratory pressure on the incidence of venous air embolism and on the cardiovascular response to the sitting position during neurosurgery.

We have studied prospectively the effect of 10 cm H2O of PEEP on the incidence of venous air embolism and on the cardiovascular response to change from the supine to the seated position in a large neurosurgical population. Patients were allocated randomly to receive either PEEP (10 cm H2O, n = 45) or conventional (control, n = 44) ventilation. Cardiovascular and respiratory variables were measured in the supine and sitting positions, and monitoring included precordial Doppler probe, pulmonary artery pressure and expiratory carbon dioxide concentration. Venous air embolism was assumed if changes in precordial Doppler sounds occurred, end-tidal carbon dioxide concentration decreased or air could be retrieved from a central venous multi-orifice catheter. The incidence of venous air embolism (26%) did not differ between patients undergoing conventional ventilation and those undergoing ventilation with 10 cm H2O of PEEP. Venous air embolism was always detected first by alterations in Doppler sounds. Cardiac output was significantly higher in patients undergoing conventional ventilation than in those undergoing ventilation with PEEP in the supine but not in the sitting position. Furthermore, pulmonary vascular resistance increased significantly only in the upright position in those undergoing ventilation with PEEP. The pulmonary artery wedge pressure to central venous pressure gradient did not attain negative values with PEEP or with upright positioning. We conclude that the use of PEEP during neurosurgical procedures performed in the sitting position should be abandoned as it does not decrease the incidence of venous air embolism but is associated with significant adverse cardiovascular effects.

[Plethysmechanomyography (PMG). A simple method for monitoring muscle relaxation]. / Die Plethysmo-Mechanomyographie (PMG). Eine einfache Methode zur Erfassung der Muskelrelaxation.

Ideal evaluation of neuromuscular blockade can be done by mechanical or electromyographical registration of muscle contractions evoked by ulnar nerve stimulation. Unfortunately, devices needed for such registration are expensive or complicated to set up, and thus are not often used for routine monitoring in anaesthesia. In this study, we describe a simple and low-priced method permitting intra- and postoperative monitoring of neuromuscular blocking agents. The accuracy of plethysmomechanomyography (PMG) was evaluated by comparing simultaneous electromyographic (EMG) and plethysmographic measurements. METHODS. For plethysmographic registration of muscle response to nerve stimulation a simple infusion system is twisted there to five times around one hand and connected to an anaesthetic monitor via a pressure transducer. The drip chamber is fixed about 20 cm above the hand (Fig. 1). Then, the infusion system is then filled up-with physiologic saline solution and the clamp is nearly closed. Electric stimulation can be carried out using any nerve stimulator. Using this method, PMG mainly records the contractions of abductor digiti minimi muscle, but also partly those of the interossei. Evoked muscle contractions cause stretching of the infusion system, which leads to pressure changes proportional to the strength of contraction. The muscle response to "train-of-four" (TOF) stimulation of the ulnar nerve was recorded simultaneously by EMG and PMG in 11 patients (ASA class I or II) undergoing neurosurgical procedures and therefore requiring muscle relaxation. After induction of anaesthesia by injection of etomidate and fentanyl, supramaximal stimulation and control values (T0) were defined. Anaesthesia was maintained by supplementation with nitrous oxide/oxygen (1:2) and muscle relaxation was carried out with vecuronium. We used the integrated nerve stimulator of a Datex Relaxograph NMT-100 EMG monitor and proceeded to stimulate the ulnar nerve at the forearm with supramaximal strength. The PMG was registered by a Siemens Siredoc 220 printer connected to a Siemens Sirecust 1281 anaesthetic monitor. First twitch ratio (T1/T0) and TOF ratio (T4/T1) were calculated from these recordings. The EMG recordings were made by a Datex Relaxograph NMT-100 monitor, which automatically computes T1/T0 and T4/T1. The comparison of EMG and PMG values was carried out by simple linear regression. Statistical evaluation was performed using analysis of variance. RESULTS. A plethysmographically registered graph of the TOF-evoked muscle response is illustrated in Fig. 2. Simultaneous EMG and PMG recordings of onset and recovery from a nondepolarizing blockade are shown in Fig. 3. A strong positive correlation (P < 0.001) of EMG and PMG was found with correlation coefficients of 0.98 for T1/T0 and of 0.97 for T4/T1. The mean difference between values of both methods was 5%, maximally 18% (T1/T0) and 20% (T4/T1). CONCLUSIONS. Mechanomyography and EMG are well established methods of neuromuscular monitoring. Our data demonstrate that PMG provides a reliable measurement of neuromuscular transmission that correlates well with EMG. Since only materials of daily use in anaesthesia are needed, no substantial costs will arise when the plethysmographic method of measurement is used for routine anesthetic monitoring.

[Hemodynamics and myocardial energy balance in coronary surgery patients during high-dose fentanyl-pancuronium anesthesia and modified neurolept-pancuronium anesthesia]. / Hämodynamik und myokardiale Energiebilanz koronarchirurgischer Patienten unter High Dose Fentanyl-Pancuronium- und unter modifizierter Neurolept-Pancuronium-Anaesthesie.

In 8 patients with coronary artery disease (CAD) classed as NYHA II or III, anesthesia was induced with high-dose fentanyl (0.05 mg/kg) and pancuronium (0.1 mg/kg). The patients were ventilated normally with the aid of a mask (O2: air 1:1, tidal volume 10 ml/kg with a rate of 10/min) for 5 min and then intubated. In 8 further patients with CAD NYHA class II or III, anesthesia was induced with 0.02 mg/kg flunitrazepam, N2O/O2 1:1 and isoflurane 0.5 vol%; they were relaxed with pancuronium (0.1 mg/kg) in combination with a bolus of 0.005 mg/kg fentanyl. These patients were also ventilated normally for 5 min and then intubated. Measurements of cardiovascular dynamics included cardiac output (CO), heart rate (HR), arterial pressure (AP), pulmonary artery pressure (PAP), pulmonary capillary wedge pressure (PCWP), right atrial pressure (RAP), myocardial blood flow (MBF), and arterial and coronary sinus oxygen and lactate contents. Cardiac index (CI), stroke volume index (SVI), total peripheral resistance (TPR), myocardial oxygen consumption (MVO2), coronary vascular resistance (CVR), coronary perfusion pressure (CPP), myocardial oxygen content difference (AVDO2cor) and myocardial lactate extraction rate (LE) were calculated from standard formulas. Measurements and an electrocardiogram were taken before anesthesia, after induction of anesthesia and after intubation. The hemodynamic parameters HR, AP, CI, CPP were relatively stable in patients anesthetized with high-dose fentanyl and pancuronium, whereas we found greater decreases in these parameters with the balanced anesthesia technique. Determinants of myocardial oxygen demand were higher in the high-dose fentanyl group; therefore, myocardial blood flow and oxygen consumption did not decrease to the same extent as in the balanced anesthesia group.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of pancuronium and vecuronium combined with balanced anaesthesia on haemodynamics and myocardial oxygen balance.

The effects of the non-depolarizing muscle relaxants pancuronium (Pancuronium) and vecuronium (Norcuron) (0.1 mg/kg) on myocardial blood flow, myocardial oxygen consumption, myocardial lactate balance, cardiovascular dynamics and electrocardiogram were studied in two groups of eight patients undergoing coronary artery bypass surgery. After induction of anaesthesia with 0.015-0.02 mg/kg flunitrazepam, isoflurane (0.5 vol%) and N2O/O2 (l/l), neuromuscular blockade was induced with pancuronium or vecuronium (0.1 mg/kg) combined with a single dose of 0.005 mg/kg fentanyl. Haemodynamic measurements were performed and the electrocardiogram was recorded before anaesthesia, in steady-state anaesthesia, after relaxation with pancuronium or vecuronium combined with fentanyl, and after intubation. The haemodynamic data consisted of heart rate, cardiac index, stroke volume index, mean arterial pressure, total peripheral resistance, pulmonary arterial pressure, pulmonary capillary wedge pressure, right atrial pressure, myocardial blood flow, coronary vascular resistance, myocardial oxygen consumption, coronary aterio-mixed venous content difference, myocardial lactate extraction and rate pressure product. In the vecuronium group, heart rate decreased significantly more (21%) than in the pancuronium group (9%). Therefore myocardial oxygen consumption (48% resp. 35%) and coronary blood flow (31% resp. 18%) decreased more in the vecuronium than in the pancuronium group. The higher metabolic demand in the pancuronium group induced a significantly lower coronary vascular resistance, because the decrease in coronary perfusion pressure was similar in both groups. None of the other haemodynamic parameters differed significantly in either patient group. We did not observe ST-segment depressions or elevations in the ECG, increases in PCWP or myocardial lactate production. Therefore extended myocardial ischaemia can be excluded in our patients who received pancuronium or vecuronium for neuromuscular blockade.

[The effect of pancuronium and norcuron on hemodynamics, coronary circulation and myocardial oxygen consumption in coronary surgery patients]. / Der Einfluss von Pancuronium und Norcuron auf die Hämodynamik, die Koronardurchblutung und den myokardialen Sauerstoffverbrauch bei koronarchirurgischen Patienten.

The effects of the non-depolarizing muscle relaxants pancuronium (Pancuronium) and vecuronium (Norcuron) (0.1 mg/kg) on myocardial blood flow, myocardial oxygen consumption, myocardial lactate balance, cardiovascular dynamics and electrocardiogram were studied in two groups of eight patients undergoing coronary artery bypass surgery. After an introduction of anaesthesia with 0.015-0.02 mg/kg rohypnol, isoflurane (0.5 Vol%) and N2O/O2 neuromuscular blockade was induced with pancuronium or vecuronium combined with a single dose of 0.005 mg/kg fentanyl. Measurements and electrocardiogram were performed before anaesthesia, in steady state of anaesthesia and after relaxation with pancuronium or vecuronium, combined with fentanyl. The measurements consisted of heart rate (HR), cardiac index (CI), stroke volume index (SVI), mean arterial pressure (AP), total peripheral resistance (TPR), pulmonary arterial pressure (PAP), pulmonary capillary wedge pressure (PCWP), right atrium pressure (RAP), myocardial blood flow (MBF), coronary vascular resistance (CVR), myocardial oxygen consumption (MVO2), coronary ateriomixed venous oxygen content difference (AVDO2cor), myocardial lactate extraction (LE) and rate pressure product (RPP). In the vecuronium group heart rate (HR) decreased significantly greater (21%) than in the pancuronium group (9%). Therefore myocardial oxygen consumption (MVO2) and coronary blood flow (CBF) diminished more in the vecuronium (48% resp. 35%) than in the pancuronium group (31% resp. 18%). The higher metabolic demand in the pancuronium group induced a significantly lower coronary vascular resistance (CVR). All the other hemodynamic parameters did not differ significantly in both patients groups. In all the patients we could not observe ST-segment depressions or elevations in the ECG, increases of PCWP or myocardial lactate productions.(ABSTRACT TRUNCATED AT 250 WORDS)

[Validity of the electroencephalogram and evoked potentials in the diagnosis of brain death]. / Zur Validität von Elektroenzephalogramm (EEG) und evozierten Potentialen in der Hirntoddiagnostik.

Alterations of electroencephalogramm and evoked potentials in brain dead patients are known. We are going to discuss the value of the various parameters as well as their comparison with the clinical symptoms. Newer guidelines recommend the brain-stem acoustic evoked responses, too. So we analysed those comatose patients requiring for artificial respiration in whom brain stem acoustic responses could not be evoked. We found 21 patients out of 103 unselected consecutive patients with primary cerebral disease. All patients with isoelectric EEG were brain dead. Absence of acoustic response was not sure combined with clinical symptoms of brain death. Earlier SSEP components were frequent, deformed flash evoked potentials were found in all brain dead patients. In all brain dead patients there was an absence of early acoustic evoked responses and an isoelectric electroencephalogramm. The longer the symptoms of brain death lasted, the more complete the disappearance of evoked potentials was. The investigations demonstrate the value of clinical examination and electroencephalogramm in the diagnosis of brain death, but also point to the value of evoked potentials as additional parameter, esp. in order to get informations of the pathophysiological mechanisms leading to death.

[Evoked potentials in intracranial operations: current status and our experiences]. / Evozierte Potentiale bei intrakraniellen Eingriffen: Gegenwärtiger Stand und eigene Erfahrungen.

Intraoperative neuromonitoring, especially evoked potential monitoring, has gained interest in recent years for both the anesthesiologist evaluating cerebral function and the neurosurgeon wishing to avoid neuronal lesions during intracranial operations. Before evoked potential monitoring can be introduced as a routine method of intraoperative management, experience with this method particularly in intensive care units, is imperative. We recorded evoked potentials with the Compact Four (Nicolet) and Basis 8000 (Schwarzer Picker International) computer systems. Preoperative derivations should be done with the same apparatus used intraoperatively and parameters of peri- and intraoperative derivations should not be changed. The patient's head must be fixed in a Mayfield clamp in order to avoid artefacts during trepanation. The possible artefacts due to apparatus, patient, or anesthesia are summarized in the tables. The derivations of evoked potentials should be supervised by a person who is not involved in the anesthesia or the surgical procedure; this condition may change in the future with full automatization of the recording technique and alarms. Good communication between surgeon, anesthesiologist, and neurophysiological assistant is a prerequisite. The modality is chosen in accordance with the affected neuronal system: visual-evoked potential (VEP) monitoring in the management of processes affecting the visual pathway, brain stem auditory-(BAER) and somatosensory-evoked potential (SSEP) monitoring in lesions affecting these pathways, in particular space-occupying lesions of the posterior fossa. VEP monitoring may be useful, but we observed alterations of the responses without changes in the level of anesthesia or manipulation of the visual pathways. In space-occupying processes of the cerebellopontine angle, BAER could not be developed in nearly all cases because the large underlying tumor had caused the disappearance of waves II-V. In these cases SSEP monitoring could be carried out. Despite these difficulties, evoked potential monitoring seems useful. We believe, however, that it is not routinely used in operating rooms at present because alterations of the responses can be due to different causes; for the neurosurgeon, the problem as to which interdependent degrees of alteration in evoked potentials are related to neuronal disturbances remains unsolved.

[Reaction of hemodynamic parameters to coronary angiography with two different age groups (author's transl)]. / Verhalten hämodynamischer Parameter während Koronarangiographie bei zwei verschiedenen Altersgruppen.

Two groups of patients (A = 19 less than 50 a; B = 21 greater than 50 a) were supervised during coronary injection as to cardiac and pulmonary pressure. In both groups there is an equivalent increase of the cardiac index by 20%, the initial value being lower in groups B. The increase lasts for more than 2 Min. During 5 Min the pulmonary pressure is increased by 25%. The reaction is based on an intracellular calcium flow induced by contrast medium.