Safety and efficacy of semi-closed circle ventilation in small infants

The purpose of this clinical trial was to investigate the safety and efficacy of semi-closed circle ventilation of the Dräger anaesthesia ventilators (Cicero, Cato), using a fresh gas flow (FGF) of 600 ml·min^?1. Twenty infants, weighing less than 6000 g, without cardiorespiratory abnormalities who required general anaesthesia of at least 30 min were included. The FGF was reduced to 600 ml·min^?1 after 10 min of denitrogenation with a FGF of 4 to 6 l·min^?1. The composition of the FGF (600ml·min^?1) was calculated as follows: oxygen necessary for consumption (60 ml·min^?1) plus the remaining FGF in a 1:2 relationship for oxygen. The inspiratory nitrogen fraction was calculated to exclude accumulation. Inspiratory fractions of O₂ and N₂O plus inspiratory and endtidal CO₂ partial pressures and noninvasive oxygen saturation were the control parameters. The gas concentrations (O₂ and N₂O) remained within safe limits. Hypoxic gas concentrations were not observed. Neither nitrogen nor CO₂ accumulated in the circle system. In conclusion, low flow anaesthesia can be performed safely in infants under 6000 grams with the Dräger Cicero and Cato anaesthesia ventilators.     

Low and minimal flow inhalational anaesthesia

Purpose

To descnbe the pharmacokinetic behaviour and practical aspects of low (0.5–1l· min^?1) and minimal (0.25–0.5 l · min^?1) flow anaesthesia.

Methods

A Medline search located articles on low flow anaesthesia, and computer simulated anaesthetic uptake models are used.

Principal findings

Most, 85–90%, of anaesthetists use high fresh gas flow rates during inhalational anaesthesia. Low/minimal flow anaesthesia with a circle circuit may avoid the need for in-circuit humidifiers, raise the temperature of inspired gases by up to 6°C, reduce cost by about 25% by reduction of fresh gas flows to 1.51· mm^?1, and reduce environmental pollution with scavenged gas. Knowledge of volatile anaesthetic pharmacokinetic behaviour facilitates the use of minimal/low flow rates. Small amounts of nitrogen or minute amounts of methane, acetone, carbon monoxide, and inert gases in the circuit are of no concern, but the degradation of desflurane (to carbon monoxide by dry absorbent) and sevoflurane (to compound A by using a fresh gas flow of >2 l · min^?1) must be avoided. With modem gas monitoring technology, safety should be no more of a concern than with high flow techniques.

Conclusion

The use of fresh gas flow rates of < 1l · min^?1 for maintenance of anaesthesia has many advantages, and should be encouraged for inhalational anaesthesia with most modem volatile anaesthetics.     

Initial experience of complete switchover to sevoflurane in 1550 children*

A report of our experience with a complete switchover from halothane (HAL) to sevoflurane (SF) in 1550 paediatric cases over a period of 17 months is presented. SF became the sole inhalational anaesthetic in our institution in July 1990. Induction of anaesthesia with SF was performed with the overpressure technique by administering rapid increases of concentration and assisted pulmonary ventilation with a large fresh gas flow (6 l·min^?1 of nitrous oxide and 3 l·min^?1 of oxygen). SF concentration was increased rapidly up to 5 or 7% in increments of 2% in every 2–3 breaths. Induction time as measured in 60 cases (3–6 years) was 50 ± 5 (mean ± SD) sec for loss of eyelash reflex and 119 ± 10 (mean ± SD) sec for loss of movement to venepuncture at 7% SF concentration. No serious complications were observed. Peak serum levels of inorganic fluoride were within a safe range (less than 30 μmol·l^?1) in all 7 cases in which this was studied. The results suggest that SF is a useful anaesthetic agent in paediatric anaesthesia, particularly because of its smooth and rapid inhalation induction.     

Humidification during low-flow anesthesia in children

Purpose The aim of this study was to compare the effect of low-flow anesthesia with or without a heat and moisture exchanger with high-flow anesthesia on airway gas humidification in children. Methods One hundred twenty children were randomly assigned to one of three groups: low-flow anesthesia with 0.5l·min⁻¹ of total gas flow (LFA,n=40), low-flow anesthesia with 0.5l·min⁻¹ using a heat and moisture exchanger (HME,n=40), and high-flow anesthesia with 6l·min⁻¹ (HFA,n=40). The temperature and relative humidity of the inspired gas were measured throughout anesthesia. Results The relative humidity of the inspired gas in the HME group was increased compared with that of the LFA and HFA groups 20 min after induction (p<0.05). The airway humidification in the LFA group was higher than that in the HFA group 10 min after induction (p<0.05). The temperature of the inspired gas in the HME group was increased compared with that in the LFA and HFA groups after 70 min (P<0.05). Conclusion Low-flow anesthesia is less effective in providing adequate humidification of inspired gas than low-flow anesthesia with a heat and moisture exchanger, but significantly better than high-flow anesthesia in children.     

Comparison of cuffed, uncuffed tracheal tubes and laryngeal mask airways in low flow pressure controlled ventilation in children

Background : The use of low flow circle systems necessitates a ‘leak free’ breathing system which is commonly achieved by using a cuffed tracheal tube (TT). We hypothesized that low flow circle system anesthesia can equally effectively be achieved by using the LMA in pediatric anesthesia. Methods : Following local ethics committee approval we randomly recruited 45 patients scheduled for elective surgery and requiring mechanical ventilation into three groups (cuffed TT, uncuffed TT and LMA group, n = 15). The size of the TT was determined by means of the formula (age/4) + 4.5 for uncuffed and (age/4) + 4 for cuffed TT whereas the size of the LMA size was dependent on weight. Following induction of anesthesia and muscle paralysis patients were ventilated with pressure controlled ventilation through a pediatric circle system and the lowest fresh gas flow (FGF) determined. Results : The FGF achieved were (median and range) 0.20 (0.2–0.25) l·min^?1 for the LMA group, 0.20 (0.2–0.4) l·min^?1 for the cuffed TT group and 1.15 (0.2–4.75) l·min^?1 for the uncuffed group. The differences between the LMA and cuffed TT compared with the uncuffed TT were significant (P < 0.0001 and P = 0.0002, respectively). The difference in FGF between LMA and cuffed TT was not significant. Conclusion : We conclude that pressure controlled ventilation using an LMA is an alternative to a cuffed TT during low flow circle system anesthesia in children. Low FGF is unlikely to be achieved consistently using an uncuffed TT because of a substantial leak.     

Isoflurane anaesthesia (0.6 MAC) and hypoxic ventilatory responses in humans

In order to evaluate the difference between poikilo-capnic (no CO₂ added to inspired gas) and iso-capnic (CO₂ added to keep end-tidal CO₂ constant) hypoxic ventilatory responses (HVR) awake and during 0.6 MAC isoflurane anaesthesia, seven cardio-pulmonary healthy patients were investigated. Pneumotachography and capnography were used before and during hypoxia (end-tidal O₂ tension approx. 7 kPa). In the awake stale, poikilo-capnic hypoxic challenges resulted in an increased HVR as indicated by a V?_E that on average increased by 1.4 ± 1.0 (mean ± s.d.) 1 · min^?1, whereas the iso-capnic hypoxic challenges resulted in a V?_E increase that was 4.7 ± 2.3 1 · min^?1 on average. In the anaesthetized state, the corresponding value during poikilocapnia was 1.3 ± 0.8 1 · min^?1 (88% of the awake responses, n.s.) and during iso-capnia 2.3 ± 1.4 1 · min^?1 (49% of the awake, P < 0.02). Awake HVR was achieved by greater tidal volumes during poikilocapnia as well as during isocapnic challenges, while respiratory rates were unchanged. In the anaesthetized state, during poikilocapnia, however, HVR was mediated by an increased respiratory rate, (from 17.5 ± 1.7 breath · min^?1 to 20.2 ± 2.2) and during isocapnia by a combination of increased rate (from 17.1 ± 1.9 breath · min^?1 to 19.1 ± 1.8) and tidal volume (from 496 ± 80 to 560 ± 83 ml). It is concluded that poikilocapnic HVR is maintained at 0.6 MAC isoflurane whereas iso-capnic HVR is depressed by 50%. In addition, both poikilo- and iso-capnic HVR were accomplished by greater tidal volumes at unchanged respiratory rates in the awake state while the opposite occurred during isoflurane anaesthesia. The more dominating chronotropic HVR during hypoxic challenge under anaesthesia will have to be further clarified in experimental studies.     

Influence of dopexamine hydrochloride on haemodynamics and regulators of circulation in patients undergoing major abdominal surgery

Background: Catecholaminergic support is often used to improve haemodynamics in patients undergoing major abdominal surgery. Dopexamine is a synthetic vasoactive catecholamine with beneficial microcirculatory properties. Methods: The influence of perioperative administration of dopexamine on cardiorespiratory data and important regulators of macro- and microcirculation were studied in 30 patients undergoing Whipple pancreaticduodenectomy. The patients received randomized and blinded either 2 μg · kg^?1 · min^?1 of dopexamine (n=15) or placebo (n=15, control group). The infusion was started after induction of anaesthesia and continued until the morning of the first postoperative day. Endothelin-1 (ET-1), vasopressin, atrial natriuretic peptide (ANP), and catecholamine plasma levels were measured from arterial blood samples. Measurements were carried out after induction of anaesthesia, 2 h after onset of surgery, at the end of surgery, 2 h after surgery, and on the morning of the first postoperative day. Results: Cardiac index (CI) increased significantly in the dopexamine group (from 2.61±0.41 to 4.57±0.78 1 · min^?1 · m^?2) and remained elevated until the morning of the first postoperative day. Oxygen delivery index (DO₂I) and oxygen consumption index (VO₂I) were also significantly increased in the dopexamine group (DO₂I: from 416±91 to 717±110 ml/m² · m²; VO₂I: from 98±25 to 157±22 ml/m² · m²), being significantly higher than in the control group. pHi remained stable only in the dopexamine patients, indicating adequate splanchnic perfusion. Vasopressive regulators of circulation increased significantly only in the untreated control patients (vasopressin: from 4.37±1.1 to 35.9±12.1 pg/ml; ET-1: from 2.88±0.91 to 6.91±1.20 pg/ml). Conclusion: Patients undergoing major abdominal surgery may profit from prophylactic perioperative administration of dopexamine hydrochloride in the form of improved haemodynamics and oxygenation as well as beneficial influence on important regulators of organ blood flow.     

Changes inPetCO2 and pulmonary blood flow after bronchial occlusion in dogs

The use ofPetCO₂ in detecting accidental bronchial intubation was investigated. ThePetCO₂ was measured in six mongrel dogs after occluding the left mainstem bronchus in three conditions; pentobarbital anaesthesia, 0.8% halothane insufflation together withpentobarbital anaesthesia, and simultaneous left pulmonary artery and bronchial airway occlusion with intravenous pentobarbital anaesthesia. An external flow probe measured left pulmonary artery blood flow. ThePetCO₂ decreased after bronchial occlusion during pentobarbital (35 ± 3 vs 30 ± 5 mmHg) and halothane-pentobarbital (30 ± 6 vs 25 ± 6 mmHg) conditions (P < 0.05). However, within three minutes of bronchial occlusion, the values ofPetCO₂ had returned to their pre-occlusion values. After five minutes of bronchial occlusion pulmonary artery blood flow in the non-ventilated lung decreased (P < 0.05) during pentobarbital (770 ± 533 ml · min^?1 vs 575 ± 306 ml · min^?1) and halothane-pentobarbital (495 ± 127 ml · min^?1 vs 387 ± 178ml · min^?1) conditions. Simultaneous bronchial and pulmonary artery occlusion prevented any changes inPetCO₂. It was concluded that accidental one- lung ventilation results in small and transient decreases inPetCO₂. A redistribution of blood flow from the nonventilated to ventilated lung occurs which restoresPetCO₂ to the original values observed with twolung ventilation.     

Comparison of fentanyl,sufentanil and alfentanil during awake craniotomy for epilepsy

Neurolept anaesthesia is used during awake craniotomy for epilepsy surgery. This study compares analgesia, sedation and the side effects of the newer opioids sufentanil and alfentanil, with those of fentanyl in patients undergoing awake craniotomy. Thirty patients were randomized into three groups, each received droperidol, dimenhydrinate and the chosen opioid as a bolus followed by an infusion. The opioid doses used were fentanyl 0.75 μg · kg^?1 plus 0.01 μg · kg^?1 · min^?1; sufentanil 0.075 μg · kg^?1 plus 0.0015 μg · kg^?1 · min^?1, and alfentanil 7.5 μg · kg^?1 plus 0.5 μg · kg^?1 · min^?1. There were no differences in the requirements for droperidol, dimenhydrinate or in the incidence of complications among the three groups. The total doses of the opioids required were fentanyl 4.9 ±1.3 μg · kg^?1, sufentanil 0.6 ±0.2 μg · kg^?1 and alfentanil 149 ±36 μg · kg^?1. Two patients became uncooperative requiring general anaesthesia. The conditions for surgery, electrocorticography and for stimulation testing were satisfactory in all other patients. We conclude that the newer opioids did not offer any benefit over fentanyl.     

Haemodynamic,diuretic and hormonal responses to prostaglandin E1, infusion in halothane anaesthetized dogs: comparison among epidural lidocaine,epidural fentanyl and epidural saline

Deliberate hypotension decreases blood loss and transfusion but it may be accompanied by adverse effects due either to the hypotensive agents themselves or to haemodynamic alterations. Prostaglandin E₁ (PGE₁) has the advantage of a diuretic effect coupled with systemic hypotension. To elucidate the mechanisms by which PGE₁ induces diuresis we compared the haemodynamic, diuretic and hormonal responses to PGE₁ infusion simultaneously with epidural lidocaine (EP-L n = 7), epidural fentanyl (EP-F n = 8) or epidural saline (CONT n = 7) in halothane anaesthetized mongrel dogs. All groups developed a decrease in mean arterial pressure during PGE₁ infusion (from 105 ± 24 to 77 ± 18 mmHg in EP-L; 106 ± 19 to 79 ± 13 mmHg in the EP-F; and 129 ± 14 to 106 ± 18 mmHg in the CONT groups (mean ± SD)) (P < 0.05). In the EP-F and CONT groups urinary output increased during PGE₁ infusion (from 4.31 ± 1.89 to 6.15 ± 2.03 ml · min^?1 and 2.71 ± 1.23 to 4.48 ± 1.66 ml · min^?1 (P < 0.05), respectively) and was accompanied by increases in renal blood flow (from 87.0 ± 40.7 to 111.0 ± 42.8 ml · min^?1 and from 121.6 ± 46.6 to 158.4 ± 64.9 ml · min^?1 (P < 0.05), respectively) and in fractional excretion of sodium (FE_Na) (from 4.78 ± 3.88 to 7.63 ± 5.20% in CONT group). Plasma epinephrine concentration increased after laparotomy in the CONT group (from 0.09 ± 0.08 to 0.17 ± 0.14 pg · min^?1) (P < 0.05) and antidiuretic hormone (ADH) concentration increased after laparotomy (from 6.9 ± 5.2 to 21.0 ± 13.0 pg · ml^?1 in EP-F and from 8.1 ± 6.2 to 45.8 ± 29.9 pg · ml^?1 in CONT groups). Plasma renin activity increased after laparotomy in the EP-L group (from 2.00 ± 1.37 to 4.72 ± 2.73 mg · ml^?1 hr^?1) (P < 0.05). The results suggest that the mechansim of the PGE_1? induced diuretic effect includes increases in renal blood flow while renal sympathetic innervation is maintained and in FE_Na in the presence of elevated plasma ADH concentration.     

Propofol anaesthesia reduces early post-operative emesis after paediatric strabismus surgery

Propofol anaesthesia may reduce postoperative emesis. The purpose of this study was to compare the incidence of emesis after propofol anaesthesia with and without nitrous oxide, compared with thiopentone and halothane anaesthesia, in hospital and up to 24 hr postoperatively, in outpatient paediatric patients after strabismus surgery. Seventy-five ASA class I or II, unpremedicated patients, aged 2–12 yr were randomly assigned to one of three groups: Thiopentone, 6.0 mg · kg^{? 1} iv induction followed by halothane and N₂O/O₂ for maintenance (T/H); propofol for induction, followed by propofol and oxygen for maintenance (P/O₂); and propofol for iv induction, followed by propofol infusion and N₂O/O₂ for maintenance (P/N₂O). All received vecuronium, controlled ventilation, and acetaminophen pr. Morphine was given as needed for postoperative analgesia. There were no differences in age, weight, number of eye muscles operated upon, duration of anaesthesia or surgery. The P/N₂O group (255 ± 80 μg· kg^{? 1}· min^{? 1}) received less propofol than the P/O₂ group (344 ± 60 μg · kg^{? 1}· min^{? 1}) (P ≤ 0.0001) and had shorter extubation (P < 0.001) and recovery (P < 0.01) times. Emesis in the hospital, in both the P/N₂O (4.0%) and P/O₂ group (4.0%) was less than in the T/H group (32%) (P < 0.01). Antiemetics were required in four patients in the T/H group (16.0%). Overall emesis after surgery was not different among the groups: T/H (48%), P/O₂ (28%) and P/N₂O (42%). The use of propofol anaesthesia with and without N₂O decreased only early emesis. This supports the concept of a short-acting, specific antiemetic effect of propofol.     

Réponse ventilatoire à l'hypercapnie et à l'hypoxie hypocapnique du chien sous différents niveaux d'anesthésie à l'Alfatésine

The authors have studied the response to hypercapnia and hypocapnic hypoxia in nine dogs anesthetised with Althesin, in correlation with three levels of anaesthesia defined by three different anaesthetic flow rates (A = 6.57 ± 2.00 μl . kg^?1 . min^?1; B = 13.88 ± 2.87 μl . kg^?1 . min^?1; C = 19.53 ± 5.34 μl . kg^?1 . min^?1). The animals were intubated. Ventilation was measured by means of a pneumotachograph. Arterial blood gases (pHa, PaCO₂, PaO₂) were measured before and at the end of each hypercapnia and hypocapnic hypoxia test. The results were compared with data in the literature concerning the dog awake. Increasing depth of anaesthesia leads to worsening hypoventilation and hypercapnia. As with other anaesthetic agents, the response to hypercapnia is more depressed the deeper the anaesthesia. On the other hand, unlike what has been described with other anaesthetic agents, hypoxia stimulates ventilation; the response to hypoxia is not abolished by the deeper states of anaesthesia. The possible mechanisms of this difference are discussed.     

Morphine does not affect the awakening concentration of sevoflurane

This study was designed to determine whether morphine 0.1 mg·kg^?1 iv given intraoperatively altered the end-tidal concentration of sevoflurane which is associated with eye opening to verbal command. We studied 24 healthy ASA physical status I patients to determine whether morphine, or placebo administered about 60 min before the end of surgery affected recovery from sevoflurane/oxygen anaesthesia. During anaesthesia no other anaesthetics or drugs were given. After surgery, end-tidal sevoflurane concentration was reduced gradually at the rate of less than 0.01% · min^?1. The end-tidal concentration at the time patients could respond to verbal command was recorded as MACawake. The MACawake was 0.58 ± 0.12% (mean ±SD) for the control group to whom placebo had been administered, and 0.57 ± 0.11% for morphine group to whom morphine had been administered. In both groups, the MACawake decreased with age, and the ratio to age-adjusted sevoflurane MAC was 0.31 ± 0.04 (mean ± SD) for the control group and 0.30 ± 0.04 for the morphine group. The ratio had no correlation with age. It is concluded that the awakening concentration of sevoflurane during recovery from anaesthesia is not affected by analgesic doses of morphine 0.1 mg · kg^?1 iv administered intraoperatively.     

Inhibition of cerebral metabolic and circulatory responses to nitrous oxide by 6-hydroxydopamine in dogs

Purpose

To determine whether cerebral metabolic and circulatory consequences of N₂O result from activation of the sympathoadrenal system. The effects of pretreatment with intracistemal injection of 6-OHDA, which produces chemical sympathectomy, were studied in dogs.

Method

Seven days before measurement dogs were pretreated with intracisternal injection of either saline vehicle (sham-group) or 100 μg· kg^?1 6-hydroxydopamine (6-OHDA group). Cerebral blood flow (CBF) was measured using an electromagnetic flow-meter probe and cerebral metabolic rate for oxygen (CMRO₂) was calculated as the product of CBF and arterial-sagittal sinus blood oxygen content difference [C(a-v)O₂].

Results

In the sham group, N₂O (60%) increased CMRO₂ from 6.11 ± 0.21 ml· 100 g^?1· min^?1 to 7.10 ± 0.39 ml· 100g^?1· min^?1 and CBF from 63 ± 5 ml· 100 g^?1 · min^?1 to 173 ± 26 ml· 100 g^?1· min^?1. In the 6-OHDA group, CMRO₂ did not change during N₂O exposure, whereas CBF increased from 61 ± 3 ml· 100 g^?1· min^?1 to 135 ±19 ml· 100 g^?1· min^?1 but less then in the sham group. The 6-OHDA group displayed a reduction in cortical noradrenaline (NA) concentration from 263.2 ± 35.6 ng·g^?1 to 102.7 ± 16.5 ng· g^?1. Cortical dopamine (DA) concentration was not affected by 6-OHDA administration.

Conclusion

These results suggest that most of the increase in CMRO₂ and, at least a part of, the increase in CBF during N₂O exposure in the sham-group are related to sympathoadrenal-stimulating effects of N₂O.     

Nasal midazolam in children, plasma concentrations and the effect on respiration

Twenty ASA 1 children, one to six years old, weighing 10–20 kg, scheduled for a combination of general and caudal anaesthesia received at random midazolam 0.2, 0.4, or 0.6 mg·kg^?1 or NaCl 0.9% (control group) intranasally. Drug or NaCl 0.9% were administered in one nostril, after inhalation induction of anaesthesia, intubation without relaxant and caudal anaesthesia. Spontaneous respiration was via a circle system and fresh gas flow of 61·min^?1 (N₂O/O₂= 2:1), PEEP 5 cm H₂O, endtidal halothane 0.4%. Immediately before and 2, 5, 8, 12, 16, 20, 30, 60 and 120 min after application of the drug 2.5 ml blood was sampled for plasma levels of midazolam. Endtidal CO₂, respiratory rate, and oxygen saturation were recorded as long as the children were intubated. Endtidal CO₂ and respiratory rate showed no statistical difference between the groups at any time, however, in the group receiving 0.6 mg·kg^?1, -endtidal CO₂ increased significantly from 5.3 kPa (41 mm Hg) at the start to 5.9 kPa (45.5 mm Hg) after 30 min. Plasma levels of midazolam were detected 2 min after application in 10 of 15 patients. Median peak levels were found between 12 and 16 min. Medians of peak plasma levels showed no statistical difference between the three groups (0.2 mg·kg^?1:111 ng·ml^?1, 0.4 mg·kg^?1:136 ng·ml^?1, 0.6 mg·kg^?1:277 ng·ml^?1). After 30, 60 and 120 min medians of midazolam plasma concentration were significantly higher in the group 0.6 mg·kg^?1.     

Regional anaesthesia for hernia repair in children: local vs caudal anaesthesia

The purpose of this study was to compare the effect of local anaesthesia (LA) with that of caudal anaesthesia (CA) on postoperative care of children undergoing inguinal hernia repair. This was a randomized, single-blind investigation of 202 children aged 1–13 yr. Anaesthesia was induced with N₂O/O₂ and halothane or propofol and maintained with N₂O/O₂/halothane. Local anaesthesia included ilioinguinal and iliohypogastric nerve block plus subcutaneous injection by the surgeon of up to 0.3 ml · kg^?1 bupivacaine 0.25% with 5 μg · kg^?1 adrenaline. The dose for caudal anaesthesia was 1 ml · kg^?1 up to 20 ml bupivacaine 0.2% with 5 μg · kg^?1 adrenaline. Postoperative pain was assessed with mCHEOPS in the anaesthesia recovery room, with postoperative usage of opioid and acetaminophen in the hospital, and with parental assessment of pain with a VAS. Vomiting, time to first ambulation and first urination were recorded. The postoperative pain scores and opioid usage were similar; however, the LA-group required more acetaminophen in the Day Care Surgical Unit. The incidence of vomiting and the times to first ambulation and first urination were similar. The LA-patients had a shorter recovery room stay (40 ± 9 vs 45 ± 15 min, P < 0.02). The postoperative stay was prolonged in the CA group (176 ± 32 vs 165 ± 26 min, P = 0.02). We conclude that LA and CA have similar effects on postoperative care with only slight differences.     

Deep sedation with propofol in preschool children undergoing radiation therapy

Immobilization of children undergoing radiation therapy always requires anaesthesia. Deep sedation with continuous infusion of propofol and spontaneous breathing, (we call it ‘sedative anaesthesia’), may be an alternative to general anaesthesia with intubation and controlled ventilation. This clinical report deals with 155 anaesthetics performed in 11 consecutive paediatric oncology patients, mean age 30 months (range 19–42), who required radiation therapy for from seven to 33 consecutive days. Mean duration of anaesthesia was 18 (±11) mins. For induction, a loading dose of 3.6 (SD±0.59) mg·kg^?1 propofol was administered immediately followed by a continuous infusion of 7.4 (±2.2) mg·kg^?1.h^?1 for maintenance of anaesthesia. There were no complications of clinical importance involving respiration, circulation or neurology, except for one short episode of transient desaturation, which was managed by suctioning and changing head position. Children opened their eyes spontaneously four (±3.7) min after discontinuing the propofol infusion and could be discharged about 30 mins later. Tachyphylaxis or unpleasant side effects during and after anesthesia have not been observed. Sedative anaesthesia with propofol seems to be an excellent method to immobilize paediatric patients during radiotherapeutic procedures.     

Thoracic epidural block attenuates cardiovascular response to apnea in rabbits

Purpose

Apnea is one of the potential complications during anaesthesia. If sympathetic nerve activity is blocked by epidural anaesthesia, circulatory responses to apnea might change. Our objective was to assess the potential modifying effects of epidural anaesthesia on the cardiovascular responses to apnea in the animals.

Methods

Twenty rabbits anaesthetised with pentobarbital (25 mg·kg^?1 iv, 8 mg·kg^?1·hr^?1) and pacuronium bromide (0.2 mg·kg^?1·hr^?1 iv) were randomly assigned to one of two groups: control (n = 10) and epidural (n = 10). In the control group, 0.6 ml saline, and in the epidural group, 0.6 ml lidocaine 1% was injected into the epidural space respectively. After mechanical ventilation with FIO₂ 0.4, apnea was induced by disconnecting the anaesthetic circuit from the endotracheal tube, and mean arterial pressure (MAP), heart rate (HR), and time to cardiac arrest were measured.

Results

Before apnea MAP was lower in the epidural than in the control group (73 ± 10vs 91 ± 10 mmHg,P < 0.05). Heart rate was not different between groups (264 ± 36vs 266 ± 24 bpm). Mean arterial pressure increased in the control group after apnea, but not in the epidural group. The time to cardiac arrest was less in the epidural group than in the control group (420 ± 67vs 520 ± 61 sec,P < 0.05). Heart rate decreased markedly after apnea in the control group whereas it decreased gradually in the epidural group.

Conclusion

Thoracic epidural anaesthesia attenuated cardiovascular response to apnea and reduced the time to cardiac arrest.     

Effects of fresh gas flow,tidal volume,and charcoal filters on the washout of sevoflurane from the Datex Ohmeda® (GE) Aisys®, Aestiva®/5, and Excel 210 SE Anesthesia Workstations

Purpose

We investigated the effects of tidal volume (V_T), fresh gas flow (FGF), and a charcoal filter in the inspiratory limb on the washout of sevoflurane from the following Datex Ohmeda^® (GE) Anesthesia Workstations (AWSs): Aisys^®, Aestiva^®/5, and Excel 210SE.

Methods

After equilibrating the AWSs with 2% sevoflurane, the anesthetic was discontinued, and the absorbent anesthesia breathing circuit (ABC), reservoir bag, and test lung were changed. The lung was ventilated with 350 or 200 mL·breath^?1, 15 breaths·min^?1, and a FGF of 10 L·min^?1 while the washout of sevoflurane was performed in triplicate using a calibrated Datex Ohmeda Capnomac Ultima? and a calibrated MIRAN SapphIRe XL ambient air analyzer until the concentration was ≤ 10 parts per million (ppm). The effects of decreasing the FGF to 5 and 2 L·min^?1 after the initial washout and of a charcoal filter in the ABC were recorded separately.

Results

The median washout times with the Aisys AWS (14 min, P < 0.01) and the Aestiva/5 (17 min, P < 0.001) with V_T 350 mL·breath^?1 were significantly less than that with the Excel 210SE (32 min). The mean (95% confidence interval) washout time with the Aisys increased to 23.5 (21.5 to 25.5) min with V_T 200 mL·breath^?1 (P < 0.01). Decreasing the FGF from 10 to 5 and 2 L·min^?1 with the Aisys caused a rebound in sevoflurane concentration to ≥ 50 ppm. Placement of a charcoal filter in the inspiratory limb reduced the sevoflurane concentration to < 2 ppm in the Aisys and Aestiva/5 AWSs within two minutes.

Conclusion

The GE AWSs should be purged with large FGFs and V_Ts ~350 mL·breath^?1 for ~25 min to achieve 10 ppm sevoflurane. The FGF should be maintained to avoid a rebound in anesthetic concentration. Charcoal filters rapidly decrease the anesthetic concentration to < 2 ppm.     

Atropine-induced heart rate changes: a comparison between midazolam-fentanyl-propofol-N2O and midazolam-fentanyl-thiopentone-enflurane-N2O anaesthesia

Atropine-induced heart rate (HR) changes were studied in 19 patients (ASA physical status I) during anaesthesia maintained predominantly with propofol-N₂O or thiopentone-enflurane-N₂O. Ten patients (Group A) received midazolam (0.07 mg · kg^?1), fentanyl (1 μg · kg^?1), propofol (2 mg · kg^?1) and succinylcholine (1 mg · kg^?1). Following tracheal intubation, anaesthesia was maintained with propofol (6 mg · kg^?1 · hr^?1), N₂O (67 per cent) and O₂ (33 per cent). In nine patients (Group B) thiopentone (4 mg · kg^?1) was substituted for propofol and anaesthesia maintained with N₂O (67 per cent) O₂ (33 per cent), and enflurane (0.5 per cent inspired concentration). The study was non-randomised because Group B patients were only included if HR before administration of atropine < 90 beats · min^?1. IPPV was performed in all patients using a Manley ventilator (minute vol. 85 ml · kg^?1; tidal vol. 7 ml · kg^?1). Ten minutes after tracheal intubation, incremental doses of atropine (equivalent cumulative doses: 1.8, 3.6, 7.2, 14.4, 28.8 μg · kg^?1) were administered at two-minute intervals and HR responses calculated during the last 45 sec of each intervening period. No differences were observed between the groups following 1.8 and 3.6 μg · kg^?1 atropine, but propofol-N₂O anaesthesia was associated with reduced responses (P < 0.01) following 7.2, 14.4 and 28.8 μg · kg^?1 atropine. These results suggest that there is a predominance of parasympathetic influences during propofol-N₂O anaesthesia compared with thiopentone-enflurane-N₂O anaesthesia.