Optimizing sedation following major vascular surgery: a double-blind study of midazolam administered by continuous infusion

A randomized, double-blind study was undertaken to determine the dose requirements, recovery characteristics, and pharmacokinetic variables of midazolam given by continuous infusion for sedation in patients following abdominal aortic surgery. Thirty subjects, 50–75 yr, scheduled to undergo aortic reconstructive surgery, entered the study. Following a nitrous oxide-isoflurane-opioid anaesthetic technique, patients were randomly allocated to receive one of three loading doses (0.03, 0.06 or 0.1 mg · kg^?1) and initial infusion rates (0.5, 1.0 or 1.5 μg · kg^?1 · min^?1) of midazolam, corresponding to groups low (L), moderate (M) and high (H). The infusion of midazolam was adjusted to maintain sedation levels of “3, 4 or 5,“ which permitted eye opening in response to either verbal command or a light shoulder tap, using a seven-point scale ranging from “0” (awake, agitated) to “6” (asleep, non-responsive). Additionally, morphine was given in increments of 2.0 mg iv prn for analgesia. On the morning after surgery, midazolam was discontinued, and the tracheas were extubated when patients were awake. Blood samples were taken during, and at increasing intervals for 48 hr following discontinuation of the infusion, and analyzed by gas chromatography. The desired level of sedation was maintained during more than 94% of the infusion period in all three groups, with a maximum of three dose adjustments per patient, for treatment which lasted 16.3 ± 0.6 hr. There was, however, an increase in both the infusion rates and mean plasma concentrations from Group L to Group H (P < 0.05), which corresponded to an inverse relationship of morphine requirements during the period of sedation (P < 0.05, Group H vs Group L). Optimal midazolam infusion rates and resulting plasma concentrations at the times the infusions were discontinued (in parentheses) were as follows — Group L: 0.60 ± 0.18 μg · kg^?1 min^?1 (76 ± 32 ng · mL^?1), Group M: 0.90 ± 0.52 μg · kg^?1 · min^?1 (133 ± 71 ng · mL^?1), and Group H: 1.34 ± 0.69 μg · kg^?1 · min^?1 (206 ± 106 ng · mL^?1). Times to awakening were longer in Group H: 3.1 ± 3.4 hr, than in Group L: 1.1 ± 0.8 h, P < 0.05. Pharmacokinetic variables were found to be dose- independent over the range of infusion rates. Mean values were t_1/2β = 4.4 ± 1.5 hr, CL = 5.94 ± 1.69 mL · min^?1 · kg^?1, Vd = 3.13 ± 1.07 L · kg^?1. It is concluded that midazolam, infused between 0.6–0.9 μg · kg^?1 · min^?1, provides a stable level of sedation, when administered in conjunction with intermittent iv morphine following AAS. This sedation technique, which costs $1.65 ± 0.73 hr^?1 ($Can), is associated with rapid recovery and minimal side effects.     

Contractile force and resting tension in the presence of halothane and increased extracellular potassium or decreased extracellular pH in isolated guinea pig atria

To gain a better understanding of the direct actions of halothane on myocardial function in ischaemia, we studied the effects of increasing extracellular potassium concentration and decreasing extracellular pH (acidosis), alone or in combination with halothane, on the contractile force and resting tension in isolated atria. Guinea pig left atria were superfused with Tyrode’s solution and stimulated at 1 Hz. Isometric contractile force and resting tension were measured using a force displacement transducer. Perfusate potassium concentrations were increased from 5.4 mmol · L⁻¹ to either 8.1 mmol · L⁻¹ or 10.8 mmol · L⁻¹ by adding KCl to the standard Tyrode’s solution, and its pH was decreased from 7.4 to either 7.0 or 6.5 by decreasing bicarbonate. In standard Tyrode’s solution (potassium 5.4 mmol · L⁻¹, pH 7.4), halothane 0.5–2% reduced contractile force in a dose-dependent manner (P < 0.05); the effective concentration of halothane for 50% inhibition of contractile force (IC₅₀) was 1.3%. Both increasing extracellular potassium and decreasing extracellular pH decreased the contractile force in a potassium-or pH-dependent fashion. The negative inotropism of halothane (1%) was not altered by increasing potassium concentrations, whereas 1% halothane caused a greater decrease in contractile force at pH 6.5 than at pH 7.4. Halothane (1%) enhanced the acidosis (pH 6.5)-induced increases in resting tension. Arrhythmias were produced in one of eight preparations during acidosis, while four of eight preparations demonstrated arrhythmias during acidosis in the presence of halothane. These data suggest that acidosis and halothane may have a synergistic interaction on the contractile force and resting tension of the atria. The increase in resting tension observed during acidosis/ halothane conditions suggests than an increase in cytosolic calcium is associated with these synergistic interactions between acidosis and halothane. Pour mieux comprendre l’action direct de l’halothane sur la fonction myocardique pendant l’ischémie, nous avons étudié les effets de l’augmentation du potassium extracellulaire et de la diminution du pH extracellulaire (acidose), seuls ou en association avec l’halothane, sur la force contractile et la tension de repos d’oreillettes isolées. Des oreillettes gauches de cobaye furent perfusées avec une solution de Tyrode et stimulées à 1 Hz. La force contractile isométrique et la tension de repos ont été mesurées avec un transducteur de force de déplacement. Les concentrations de potassium perfusées ont été augmentées de 5,4 mmol · L⁻¹ à 8,1 mmol · L⁻¹ ou à 10,8 mmol · L⁻¹ par l’ajout de KCl à la solution standard de Tyrode, et son pH abaissé de 7,4 à 7,0 ou 6,5 par baisse des bicarbonates. Avec la solution standard de Tyrode (potassium 5,4 mmol · L⁻¹, pH 7,4), l’halothane (0.5–2%) diminue la force contractile proportionnellement à la dose (P < 0,05); la concentration efficace d’halothane requise pour produire une inhibition de 50% de la force contractile (IC_5O) a été de 1,3%. L’augmentation du potassium extracellulaire et la diminution du pH extracellulaire réduisent toutes les deux la force contractile proportionnellement au potassium ou au pH. L’inotropisme négatif de l’halothane (1%) n’est pas modifié par l’augmentation de la concentration de potassium alors que l’halothane produit une diminution plus importante de la force contractile à un pH de 6,5 que de 7,4. L’halothane (1%) exagère l’augmentation de la tension de repos induite par l’acidose (pH 6,5). Des arrythmies sont apparues sur une des huit préparations pendant l’acidose en présence d’halothane. Ces données suggèrent que l’acidose et l’halothane pourraient avoir une activité synergique sur le force contractile et la tension de repos des oreillettes. L’augmentation de la tension de repos observée pendant l’acidose combinée à l’halothane suggère l’association d’une augmentation du calcium cytosolique avec des interactions synergiques entre l’acidose et l’halothane.     

Intrapleural analgesia in a child with a mediastinal tumour

A case is presented of an eight-year-old child with a mediastinal tumour, who had developed acute renal failure following the institution of steroid therapy. Intrapleural analgesia was successfully used for the insertion of a peritoneal dialysis catheter so that the considerable risks of general anaesthesia were avoided. Subsequent dialysis allowed chemotherapy to commence and, as a result of the shrinkage in tumour size, general anaesthesia was administered safely two days later. The purpose of this report is to highlight the use of intrapleural analgesia in children as an alternative to general anaesthesia, when the latter is contraindicated. The mechanism of action of intra-pleural analgesia and the risks of anaesthesia in the presence of a mediastinal tumour are discussed.     

Monitoring during paediatric cardiac anaesthesia

Monitoring of paediatric anaesthesia has become increasingly more complex in recent years and this is particulary true of cardiac anaesthesia. The purpose of this review is to give a comprehensive update of published material related to both routine and specialized cardiac monitoring. Routine monitoring can be particularly affected by the alterations of cardiac rhythm, blood flow, cardiac output and oxygenation which result from the congenital heart abnormalities themselves, the type of surgery undertaken and the effects of cardiopulmonary bypass. The use of specialized monitoring is becoming more widespread, particularly in the areas of cerebral function, mixed venous oxygenation, cardiac output measurement and coagulation. In the last five years, with the development of smaller probes, a great deal has been published on transoesophageal echocardiography. The use of the current monitors of cerebral function still remains controversial despite the need for a monitor of adequate brain perfusion, reflecting the need for a great deal of further research in this area. This review will concentrate on particular areas which have seen the most profound changes and on monitoring that may form the standards of tomorrow. Finally, amongst all the technology, it should not be forgotten that the most important clinical monitor is the bedside clinical monitoring of the physicians themselves. Depuis quelques années, le monitorage de l’anesthésie pédiatrique devient déplus en plus complexe et tout particulièrement en anesthésie cardiaque. L’objectif de ce travail consiste à passer en revue la littérature actuelle qui traite du monitorage usuel et spécialisé. Le monitorage usuel peut être influencé par les modifications de la fréquence cardiaque, du courant sanguin, du débit cardiaque et de l’oxygénation provoqués par les anomalies cardiaques congénitales, du type de chirurgie et des retentissements de la circulation extracorporelle. L’utilisation du monitorage spécialisé est de plus en plus répandu et concerne particulièrement la circulation cérébrale, l’oxygénation du sang veineux mêlé, la mesure du débit cardiaque et la coagulation. Au cours des cinq dernières années, le développement de sondes plus petites a généré de nombreuses publications sur l’échocardiographie transoesophagienne. L’utilisation des moniteurs actuels de la fonction cérébrale demeure sujet à controverse bien qu ’un moniteur de perfusion cérébrale adéquat demeure toujours aussi essentiel, confirmant ainsi le besoin de recherches supplémentaires sur ce sujet. Ce survol se portera spécialement sur les champs d’activités qui ont connu les changements les plus profonds et sur le monitorage qui établira les standards du futur. Finalement, au milieu de cette technologie, il ne faut jamais oublier que le moniteur clinique le plus important se trouve au chevet du malade en la personne du médecin.     

Cerebral arteriovenous malformations in children

The treatment of cerebral arteriovenous malformations (AVM) or vascular anomalies are challenging neurosurgical procedures for an anaesthetist. Large AVMs are uncommon in children. Only 18% of AVMs become symptomatic before the age of 15 yr. This series reviews the experience at this institution during the period of 1982 to 1992. The symptoms at the time of presentation are varied and include haemorrhage (50%), seizures and hydrocephalus (36%) or congestive cardiac failure (18%). Symptoms of congestive heart failure predominate in the new-born whilst neurological symptoms, such as stroke, seizures or hydrocephalus occur more commonly in infants and older children. Approximately one third of AVMs in childhood present acutely. Radiological investigations, e.g., CT scan, MRI and cerebral angiography are essential to identify the precise location of the lesion. Therapeutic intervention in the acute presentation may involve craniotomy for evacuation of haematoma and treatment of increased intracranial pressure (ICP). Control of seizures and congestive heart failure may take priority and allow time to plan the elective procedures of embolization and surgical excision of the AVM. Operative intervention is hazardous and peroperative complications can be expected in more than 50% of patients. The morbidity and mortality associated with cerebral AVM are high, especially in infants who present in the neonatal period with congestive cardiac failure. The overall mortality in this series was 20%. Children presenting with intracranial arteriovenous malformations require a multidisciplinary approach. The successful management of anaesthesia either for embolization or surgical resection necessitates an understanding of the disciplines of paediatric and neuroanaesthesia. Special care and specific attention to detail may contribute to reduce the high morbidity and mortality encountered in these compromised children.     

A comparison of sevoflurane with halothane,enflurane, and isoflurane on bronchoconstriction caused by histamine

This study was conducted to assess the effect of sevoflurane on lung resistance and compliance, and its responsiveness to histamine. We studied eight dogs to compare the effect of sevoflurane, isoflurane, enflurane, and halothane on bronchoconstriction caused by histamine. Baseline values of pulmonary resistance (R_L) and dynamic pulmonary compliance (C_dyn) were measured prior to administration of histamine. Histamine (2, 4, and 8 μg · kg⁻¹) were administered iv, and the values of R_L and C_dyn at the time of peak effect were recorded. Under 1 or 2 MAC anaesthesia, sevoflurane as well as the other three anaesthetics had no bronchoactive effects. The four anaesthetics, including sevoflurane, demonstrated inhibitory effect on increases in R_L and decreases in C_dyn caused by histamine. At 1 MAC anaesthesia, % changes in R_L caused by 2, 4, or 8 μg · kg⁻¹ of histamine were 38 ± 11, 85 ± 21, or 132 ± 24% (mean ± SE) for halothane, and 65 ± 11, 132 ± 15, or 172 ± 19% for sevoflurane, respectively. Sevoflurane was less effective than halothane in preventing increases in R_L. In preventing decreases in C_dyn, sevoflurane was less effective than halothane only at 8 μg · kg⁻¹ of histamine under 1 and 2 MAC anaesthesia. There was no difference in attenuating effect on changes in R_L and C_dyn between sevoflurane and isoflurane or enflurane. We concluded that sevoflurane was less potent than halothane in attenuating changes in R_L and C_dyn in response to iv histamine. Cette étude a été réalisée dans le but d’évaluer les effets du sévoflurane sur la résistance et la compliance pulmonaires en réponse à l’histamine. Les effets du sévoflurane, de l’isoflurane, de l’enflurane et de l’halothane sur la bronchoconstriction induite par l’histamine sont comparés sur huit chiens. Avant l’administration d’histamine, on mesure les valeurs initiales de la résistance (R_L) et de la compliance dynamique (C_dyn) pulmonaires. L’histamine (2, 4, 8 μg · kg⁻¹) est administrée par la voie veineuse et les valeurs maximales de la R_L et de la C_dyn sont enregistrées. Les quatre anesthésiques, dont le sévoflurane inhibent l’augmentation de la R_L et la diminution de la C_dyn provoquées par l’histamine. A MAC 1 d’anesthésie, les pourcentages de changement de R_L produits par 2, 4, ou 8 μg · kg⁻¹ d’histamine sont respectivement de 38 ± 11, 85 ± 21, ou 132 ± 24% (moyenne + SD) pour l’halothane, et de 65 ± 11, 132 ± 15, ou 172 ± 19% pour le sévoflurane. Le sévoflurane est moins efficace que l’halothane pour prévenir les augmentations de R_L. Le sévoflurane est moins efficace pour prevenir la diminution de C_dyn mais seulement à 8 μg · kg⁻¹ d’histamine sous anesthésie à MAC 1 et 2. Le sévoflurane, l’halothane et l’isoflurane ne sont pas de différents pour amortir les changements de R_L et C_dyn. Nous concluons que le sévoflurane est moins puissant que l’halothane pour diminuer la réponse à l’histamine de la R_L et de la C_dyn.     

Anaesthetic management of an asthmatic child for appendicectomy

A 13-yr-old boy was scheduled for emergency appendicectomy because of abdominal pain. His preoperative medical history was complicated by a recent hospital admission for management of asthma. He had presented to hospital seven days earlier because of dyspnoea, tachypnoea and oxygen desaturation to 77% on room air. Following admission, he required intensive non-ventilatory management of his asthma, including intravenous salbutamol, methylprednisolone, and aminophylline, as well as use of an ipratroprium bromide inhaler and 100% oxygen by mask. He was discharged to the ward, and continued on prednisone (deltacortisone), beclomethasone inhaler, ipratroprium inhaler, and salbutamol inhaler. During his ICU stay, he complained of nonspecific abdominal pain, interpreted as gastro-oesophageal reflux. After four days, he was discharged to the ward. On his sixth hospital day, he began to experience right-sided lower abdominal pain and right shoulder pain. A surgeon was consulted, and the patient was found to have a very tender right lower quadrant with guarding and rebound pain. He was therefore scheduled for appendicectomy; antibiotic therapy with ampicillin, gentamicin, and metronidazole was initiated.     

Acute airway obstruction following placement of a subclavian Hickman catheter

The purpose of this case report is to describe the events, intervention, and aetiology which led to acute airway obstruction in an adult patient after the placement of a Hickman catheter. Airway obstruction secondary to superior vena cava obstruction occurred after placement of a subclavian vein Hickman catheter. This was felt to occur, in part, to a narrowed superior vena cava as evident by subclavian venography. It resulted in emergency oral tracheal intubation to relieve airway obstruction. Shortly after removal of the Hickman catheter, the signs of superior vena cava obstruction syndrome resolved and the patient was extubated without incidence. It is concluded that, although rare, the serious complication of acute airway obstruction can occur after placement of a Hickman catheter.     

Adjuvant propofol enables better control of nausea and emesis secondary to chemotherapy for breast cancer

We investigated the prophylactic antiemetic effect of added lowdose infusion of propofol in patients exhibiting nausea and vomiting refractory to dexamethasone and serotonin antagonist during non-cisplatin chemotherapy for breast cancer. In a prospective open longitudinal study, 117 patients who had more than five episodes of nausea and vomiting in their first chemotherapy cycle during the first 24 hr completed the study. They received in addition to the usual prophylactic antiemetic regimen a continuous intravenous infusion of 1 mg · kg^?1 · hr^?1 propofol started four hours before chemotherapy and continued up to 24 hr for the two subsequent cycles. The number of vomiting / nausea episodes, level of sedation, patient activity, appetite and preference for future chemotherapy cycles were assessed. In the propofol supplemented cycles 90 and 80% of patients, during the 1st and 2nd propofol-assisted cycle respectively, were free of nausea and vomiting during the first 24 hr after chemotherapy. Patients were more frequently active and had more appetite during the propofol-assisted cycles. No propofol-associated side effects were observed. We conclude that the addition of a subhypnotic infusion of propofol enables better control of nausea and vomiting caused by non-cisplatin chemotherapy in the first 24 hr post-treatment.