Joel O. Johnson

Intracranial pressure, middle cerebral artery flow velocity, and plasma inorganic fluoride concentrations in neurosurgical patients receiving sevoflurane or isoflurane.

This study examined the concentration-related effects of sevoflurane and isoflurane on cerebral physiology and plasma inorganic fluoride concentrations. Middle cerebral artery flow velocity (Vmca), intracranial pressure (ICP), electroencephalogram (EEG) activity, and jugular bulb venous oxygen saturation were measured, and cerebral perfusion pressure (CPP) and estimated cerebral vascular resistance (CVRe) were calculated at baseline and at 0.5, 1.0, and 1.5 minimum alveolar anesthetic concentration (MAC) sevoflurane (n = 8) or isoflurane (n = 6). Mannitol 0.5-0.75 g/kg was given before dural incision, and blood was sampled for plasma inorganic fluoride during surgery and for up to 72 h postoperatively. Both sevoflurane and isoflurane decreased Vmca (to 31 +/- 12 - 36 +/- 14 cm/s, mean +/- SD), did not significantly alter ICP (13 +/- 9 - 15 +/- 11 mm Hg), and did not cause epileptiform EEG activity. With sevoflurane, decreased Vmca was accompanied by decreased CPP and unchanged CVR (e) at 0.5 MAC, and unchanged CPP and increased CVRe at 1.0 and 1.5 MAC. Plasma inorganic fluoride was 39.0 +/- 12.9 micro M at the end of anesthesia (3.2 +/- 2.0 MAC hours) with sevoflurane, similar to the value (36.2 +/- 3.9 micro M) for 3.7 +/- 0.1 MAC hours sevoflurane in patients not receiving mannitol. Decreased Vmca during sevoflurane presumably results from decreased cerebral metabolic rate, with CVRe changing secondarily in accord with CPP. Plasma inorganic fluoride does not seem to be altered by mannitol-induced diuresis. Implications: In neurosurgical patients, sevoflurane decreased middle cerebral artery flow velocity and caused no epileptiform electroencephalogram activity and no increase of intracranial pressure or plasma inorganic fluoride. These effects are suitable for neurosurgery. Two other possible effects of sevoflurane, i.e., increased cerebrospinal fluid volume and/or intracranial elastance, may not be suitable for neurosurgery and warrant further study. (Anesth Analg 1997;85:587-92)

Venous Air Embolism during Endoscopic Strip Craniectomy for Repair of Craniosynostosis in Infants

Background Various studies have reported an incidence of venous air embolism (VAE) as high as 82.6% during surgical procedures for craniosynostosis. There has been an increase in the use of minimally invasive, endoscopic surgical procedures, including applications for endoscopic strip craniectomy. The current study prospectively evaluated the incidence of VAE during endoscopic strip craniectomy. Methods Continuous, intraoperative monitoring for VAE was performed using precordial Doppler monitoring. A recording was made of the Doppler tones and later reviewed to verify its accuracy. Results The cohort for the study included 50 consecutive neonates and infants ranging in age from 3.5 to 36 weeks and ranging in weight from 3 to 9 kg. Surgical time varied from 31 to 95 min for a total of 2,701 min of operating time, during which precordial Doppler tones were auscultated. In 46 patients, there was no evidence of VAE. In four patients, there was a single episode of VAE. Two of the episodes of VAE were grade I (change in Doppler tones), and two were grade II (change in Doppler tones and decrease in end-tidal carbon dioxide). No grade III (decrease in systolic blood pressure by 20% from baseline) VAE was noted. Conclusion In addition to previously reported benefits of decreased blood loss, decreased surgical time, and improved postoperative recovery time, the authors noted a low incidence of VAE during endoscopic strip craniectomy in neonates and infants.

An effectiveness study of a new piezoelectric sensor for train-of-four measurement

We have developed an easy-to-use, noninvasive piezoelectric sensor for quantitative monitoring of neuromuscular block. In a clinical evaluation with 23 patients, the piezo sensor was objectively compared to a mechanomyogram (MMG) for its ability to measure train-of-four (TOF) ratio from the adductor pollicis. After administration of succinylcholine (120–200 mg intravenously [IV]) to facilitate intubation, neuromuscular block was maintained with vecuronium by either boluses (1–2 mg IV) or an infusion (0.4–1.0 μg·kg−1.min−1 IV). Paired measurements were made of the TOF ratio from both sensors over a complete range of block levels (8%-100%). The difference in the TOF ratio measurement between the sensors showed a bias of 0.018. The SD of the difference between the sensors was ± 0.129. The limits of agreement, which define the range in which 95% of the differences between the sensor measurements lie, were from-0.24 to 0.275. The sensitivity of the piezo sensor for detecting recovery based on a TOF ratio greater than 0.70 was shown to be 0.74 with specificity of 0.91. Under the conditions tested, the piezo sensor was not as accurate as the MMG. However, it was able to predict recovery of neuromuscular block with better accuracy than shown previously by manual evaluation of the TOF ratio, making it a reasonable, convenient alternative for quantitative monitoring of recovery from neuromuscular block.

Endotracheal Tube Cuff Pressure Increases Significantly During Anterior Cervical Fusion with the Caspar Instrumentation System

&NA; To determine whether endotracheal tube cuff pressure increases significantly with surgical retraction and cervical spine distraction during anterior cervical spine surgery with Caspar instrumentation, we prospectively studied 10 patients undergoing this procedure. The tracheas of all patients were intubated with a Mallinckrodt Hi‐Lo® endotracheal tube. Tracheal tube cuff pressures measured with a transducer system were 42.4 mm Hg ± 7.0 mm Hg (SEM) after intubation and cuff inflation. Air was removed from the endotracheal tube cuff until the trachea was just barely sealed at a cuff pressure of 15.2 mm Hg ± 1.6 mm Hg. The endotracheal tube cuff pressure was readjusted to “just‐seal” pressure before the surgeons introduced the Caspar instrumentation. The cuff pressure with traction and distraction was 43.2 mm Hg ± 5.0 mm Hg. This pressure was significantly increased from the “just‐seal” pressure, and from the cuff pressure after instrumentation was discontinued (9.8 mm Hg ± 2.3 mm Hg). We conclude that anterior cervical spine surgery with Caspar instrumentation is associated with a significant increase in endotracheal tube cuff pressure. (Anes Analg 1993;76:1318‐21)

Rapacuronium administration to two children with Duchenne's muscular dystrophy

Children with Duchennes muscular dystrophy should not be exposed to succinylcholine because of the risk of hyperkalemic cardiac arrest and rhabdomyolysis. This report describes the response to rapacuronium bromide in two patients with Duchennes muscular dystrophy. Both patients had a recovery index 2 times longer than that reported in children with normal neuromuscular function.

Fuzzy logic for model adaptation of a pharmacokinetic-based closed loop delivery system for pancuronium

In this paper, we investigate the ability of fuzzy to adapt the parameters of a pharmacokinetic and pharmacodynamic model-based controller for the delivery of the muscle relaxant pancuronium. The system uses the model to control the rate of drug delivery and uses feedback from a sensor which measures muscle relaxation level to adapt the model using fuzzy logic. The control strategy administers mini-bolus doses of pancuronium and modulates the magnitude and time interval between the bolus doses to maintain a patients muscle relaxation within an allowable range specified by the user. Before each new dose is given, the fuzzy logic adaptation scheme uses the error between the predicted patient response and the measured response to adapt the model. The system was tested using computer simulation by varying the parameters of the model by 50% from their nominal values. It was also evaluated in a clinical trial of five patients undergoing surgical procedures lasting 5 h or longer.

Measurement of central venous pressure from a peripheral vein in infants and children.

Background Previous studies in adults have demonstrated a clinically useful correlation between central venous pressure (CVP) measured from a peripheral intravenous catheter and that measured from a central venous catheter. The current study prospectively compares CVP measurements from a central catheter and a peripheral catheter in infants and children. Methods The study cohort included patients younger than 12 years presenting for a surgical procedure for which central venous access was necessary. CVP was measured simultaneously every 15 minutes for a total of 10 measurements from the central venous catheter and the peripheral IV catheter using standard pressure transducers, which were zeroed at the phlebostatic axis. Results The cohort for the study included 30 infants and children ranging in age from 1 to 12 years. The peripheral IV catheter from which the CVP was measured ranged from a 24 to an 18 gauge. In 5 of the patients, there was no increase in the CVP value from the peripheral IV catheter in response to a sustained inspiratory breath or occlusion of the extremity above the catheter. In these 5 cases, the difference between the CVP measured from the central and peripheral catheter was 16 ± 5 mm Hg versus 5 ± 3 mm Hg in the other 25 patients (P < 0.0001). In the remaining 25 patients, the difference between the CVP measured from the peripheral and the central site was 5 ± 3 mm Hg. There was no difference in the central versus peripheral CVP measurement depending on the size of the IV cannula, its location (upper versus lower extremity), or the patient’s position. Conclusion CVP can be measured from a peripheral IV catheter in infants and children provided that there is continuity with the central venous compartment demonstrated by showing an increase in the CVP from the peripheral IV catheter in response to a sustained inspiratory effort and by occlusion of the extremity above the site of the catheter.

Anesthetic implications in stiff-person syndrome.

A 46-yr-old female presented to the operating room for repair of an intrathecal baclofen pump. Her diagnosis of SPS was based on clinical presentation and the presence of an autoantibody against the central nervous system enzyme glutamic acid decarboxylase (GAD). The syndrome began as muscle stiffness in her lower extremities and insidiously progressed to a state of constant stiffness resulting in permanent contractures of her lower extremities and moderate rigidity of her upper extremities. The patient’s facial, cervical, and extraocular muscles were spared. When startled by a loud noise, the patient experienced a painful brisk spasm resulting in opisthotonic posturing. These acute exacerbations were treated with a 50-mg dose of diazepam administered intramuscular. Other pharmacologic therapies included intrathecal baclofen and 100 mg of diazepam orally per day. Past surgical history was significant for a 2-day history of prolonged postoperative weakness after the baclofen pump was inserted, and an overdose of baclofen was suggested as the cause. A review of the previous anesthetic record revealed that propofol and succinylcholine followed by desflurane was used for induction of anesthesia, tracheal intubation, and maintenance of anesthesia, respectively. Anesthesia was induced with sufentanil 10 pg, thiopental 375 mg (5.8 mg/kg), and vecuronium 8 mg (0.12 mg/kg) administered intravenously (IV). It was inferred from the slow and inadequate induction of anesthesia that the IV catheter had infiltrated subcutaneously although visual inspection was equivocal. A facial nerve train-of-four twitch monitor indicated an absence of all four twitches 10 min after induction of anesthesia. Inhalation anesthesia via a

Effects of rapacuronium on respiratory function during general anesthesia. A comparison with cis-atracurium

BackgroundWith its introduction for widespread clinical use, there has been an increase in reports of bronchospasm related to the administration of rapacuronium. As it is commonly used for rapid sequence intubation, it has been suggested that these effects may be related to an inadequate depth of anesthesia. The current study examines the airway effects of rapacuronium in tracheally intubated, anesthetized adults. MethodsEndotracheal intubation was accomplished without the use of neuromuscular blocking agents. Dynamic compliance, tidal volume, peak inspiratory flow rate, peak expiratory flow rate, and peak inflating pressure were measured after administration of either rapacuronium (1.5 mg/kg) or cis-atracurium (0.2 mg/kg) to 20 adult patients (10 received rapacuronium and 10 received cis-atracurium) anesthetized with propofol–remifentanil. ResultsStatistically significant increases in peak inflating pressure (22 ± 6 to 28 ± 9 cm H2O, P = 0.0012) and decreases in dynamic compliance (108 ± 43 to 77 ± 41 ml/cm H2O, P = 0.0001), peak inspiratory flow rate (0.43 ± 0.11 to 0.39 ± 0.09 l/s, P = 0.0062), peak expiratory flow rate (0.67 ± 0.10 to 0.59 ± 0.09 l/s, P =0.0015), and tidal volume (744 ± 152 to 647 ± 135 ml, P = 0.0293) occurred after administration of rapacuronium. No changes were seen after administration of cis-atracurium. ConclusionThese data demonstrate that rapacuronium, but not cis-atracurium, has significant airway effects in intubated, mechanically ventilated adults.

Measurement of central venous pressure from a peripheral intravenous catheter in the lower extremity

Objectives: The measurement of central venous pressure (CVP) is used to assess intravascular status. Although this is usually accomplished by placement of a central venous catheter (CVC), there are circumstances when placement of a CVC may be technically difficult or impossible. The current study investigates the feasibility of measuring CVP from a peripheral intravenous catheter. Methods: CVP was simultaneously measured from a CVC and from a peripheral intravenous site. The continuity of the peripheral intravenous catheter with the central venous system was evaluated by noting the change in the pressure measured from the peripheral catheter during a sustained inspiratory effort and during occlusion of the extremity (arm or leg) above the catheter. Results: The cohort for the study included 37 adult patients. In 8 of the 37 patients (22%), there was no increase in the peripheral venous pressure (PVP) in response to a Valsalva maneuver or occlusion of the extremity above the intravenous site. For the upper extremity intravenous sites without a PVP increase, the PVP-CVP difference was 11.2 ± 6.2 mm Hg versus 2.7 ± 2.2 mm Hg in the patients in whom the PVP increased with these maneuvers (P < 0.0001). For the lower extremity intravenous sites without a PVP increase, the PVP-CVP difference was 7.6 ± 4.0 mm Hg versus 2.6 ± 1.9 mm Hg in the patients in whom the PVP increased (P < 0.0001). No variation in the accuracy of the technique was noted, depending on the size of the intravenous cannula, its location (upper versus lower extremity), CVP value, or patient positioning (supine, prone, lateral). Conclusions: Provided that the PVP increases to a sustained inspiratory breath and occlusion above the intravenous site, there is a clinically useful correlation between the PVP and the CVP.