In vitro suppression of drug-induced methaemoglobin formation by Intralipid(®) in whole human blood: observations relevant to the 'lipid sink theory'.

To provide further evidence for the lipid sink theory, we have developed an in vitro model to assess the effect of Intralipid® 20% on methaemoglobin formation by drugs of varying lipid solubility. Progressively increasing Intralipid concentrations from 4 to 24 mg.ml⁻¹ suppressed methaemoglobin formation by the lipid soluble drug glyceryl trinitrate in a dose-dependent manner (p < 0.001). Both dose and timing of administration of Intralipid to blood previously incubated with glyceryl trinitrate for 10 and 40 min resulted in significant suppression of methaemoglobin formation (p < 0.0001 and p < 0.05, respectively). Mathematical modelling demonstrated that the entire process of methaemoglobin formation by glyceryl trinitrate was slowed down in the presence of Intralipid. Intralipid did not significantly suppress methaemoglobin formation induced by 2-amino-5-hydroxytoluene (partially lipid soluble) or sodium nitrite (lipid insoluble; both p > 0.5). This work may assist determination of the suitability of drugs taken in overdose for which Intralipid might be deployed.

Resuscitation in massive obstetric haemorrhage using an intraosseous needle.

A 38-year-old woman experienced a massive postpartum haemorrhage 30 minutes after emergency caesarean delivery. The patient became severely haemodynamically compromised with an unrecordable blood pressure. Rapid fluid resuscitation was limited by the capacity of the intravenous cannula in place at the time and inability to establish additional vascular access using conventional routes in a timely manner. An intraosseous needle was inserted in the proximal humerus at the first attempt and administration of resuscitation fluid by this route subsequently enabled successful placement of further intravenous lines. Blood and blood products were deployed in conjunction with intra-operative cell salvage and transoesophageal Doppler cardiac output monitoring was used to assess adequacy of volume replacement. Haemorrhage control was finally achieved with the use of recombinant factor VIIa and hysterectomy.

Early treatment of a quetiapine and sertraline overdose with Intralipid.

We describe the initial management and subsequent recovery of a 61 year-old male patient following attempted suicide by oral ingestion of a potentially fatal overdose of quetiapine and sertraline. Intravenous Intralipid was given soon after initiation of basic resuscitation. There was a rapid improvement in the patient's level of consciousness. No other clinical signs of drug toxicity were observed. Intralipid may have reversed the deep coma associated with ingestion and prevented other manifestations of drug toxicity occurring, thus expediting this patient's recovery.

Co-induction of anaesthesia with 0.75 mg kg propofol followed by sevoflurane: a randomized trial in the elderly with cardiovascular risk factors.

BACKGROUND: The induction of general anaesthesia is associated with the greatest cardiovascular changes in elderly patients. Induction can be performed either intravenously or with gaseous induction. Sevoflurane has advantages over propofol for induction of anaesthesia in the elderly, since the lower reduction in mean arterial pressure with sevoflurane is both statistically and clinically significant. This prospective randomized controlled trial investigated the cardiovascular benefits of co-induction of anaesthesia with 0.75 mg kg(-1) propofol and 8% sevoflurane, when compared with 8% sevoflurane alone in patients requiring surgery for fractured neck of femur. METHOD: In total, 38 patients aged 75 or over were allocated into the two groups, receiving either 0.75 mg kg(-1) of propofol followed by 8% sevoflurane or 8% sevoflurane alone. Vital signs were recorded until successful insertion of a laryngeal mask. Induction times, induction events and patient satisfaction scores were also recorded. RESULTS: Results showed that there were no differences in the cardiovascular parameters between the two groups. Induction times were faster in the propofol and sevoflurane group (62 vs. 81 s; P = 0.028). The postoperative questionnaire showed that the majority of patients in both groups were satisfied with the induction process. CONCLUSIONS: We concluded that 0.75 mg kg(-1) of propofol followed by sevoflurane induction is an acceptable alternative to sevoflurane induction. It is associated with similar haemodynamic variables, faster induction times and is very well tolerated.

Sites of vasodilation by inhaled nitric oxide vs. sodium nitroprusside in endothelin-constricted isolated rat lungs.

We localized the sites of vasodilation of inhaled nitric oxide (NO), a selective pulmonary vasodilator, and sodium nitroprusside (SNP) in isolated rat lungs. The sites were determined by analyzing the arterial, venous, and double-occlusion data with a two-resistor (small arteries and veins) three-capacitor (large arteries, large veins, and capillaries) model of the pulmonary vascular bed. Inhaled NO (170 and 670 ppm) and SNP (22.5 and 45.0 micrograms) decreased the small-artery resistance by 7.4 +/- 1.6, 17.2 +/- 2.2, 14.2 +/- 2.8, and 21.4 +/- 3.4% and the small-vein resistance by 13.5 +/- 3.2, 20.3 +/- 3.4 (SNP of 22.5 micrograms not significant), and 9.3 +/- 3.3%, respectively, in blood-perfused lungs (n = 12). Similar results were observed in Krebs-perfused lungs (n = 12). Capillary compliance was unaffected by inhaled NO and SNP. SNP increased the large-artery capacitance by 40.0 +/- 8.6 and 69.3 +/- 9.7%, whereas inhaled NO had no effect. SNP increased the large-vein capacitance by 31.0 +/- 8.7 and 48.0 +/- 10.7%, whereas inhaled NO had no effect in blood-perfused lungs. However, in Krebs-perfused lungs inhaled NO and SNP (45.0 micrograms only) increased the large-vein capacitance by 43.3 +/- 11.9, 41.4 +/- 14.2, and 44.2 +/- 11.0%. In conclusion, in blood-perfused isolated rat lungs inhaled NO and SNP dilate small-resistance arteries and veins, whereas SNP but not inhaled NO dilates larger capacitance arteries and veins. Furthermore, blood appears to prevent the downstream vasodilation by inhaled NO on larger capacitance pulmonary veins.

Sequential drug verification errors resulting in wrong drug administration during caesarean section.

An intravenous bolus of phentolamine was inadvertently given to a parturient during an emergency caesarean section following delivery of her infant when the intention had been to give an intravenous bolus of 5 IU Syntocinon. Root cause analysis identified a series of errors originating in the hospital pharmacy when one drug package was mistakenly issued in place of another. Subsequent checks failed to detect the original mistake. The final and most important check immediately before intravenous administration was also at fault. This case highlights a systems failure that permitted issue, transportation and administration of the wrong drug to a parturient. Robust measures to ensure avoidance of drug administration errors should be evaluated and introduced where possible.

A comparison of keyed and non-keyed vaporizer filling modes and volatile agent wastage.

Two hundred and forty bottles of enflurane were collected after their contents had been emptied into vaporizers equipped with keyed or non-keyed filling ports. The volume of agent remaining, the residual volume, was measured. There was a greater (p < 0.001) residual volume in 'empty' bottles which had been used to fill keyed compared with non-keyed enflurane vaporizers. Five hundred and fifty two bottles of isoflurane were also collected after they had been used to fill keyed vaporizers. There was no significant difference between the residual volume remaining in bottles of isoflurane and enflurane used to fill keyed fillers; however, the difference was statistically significant if the residual volume was expressed as a proportion to the volume of agent contained in the full bottle. The results show that volatile anaesthetic agent wastage is increased by the use of keyed fillers. Isoflurane wastage caused by utilisation of keyed fillers could be reduced by a factor of 2.5 by supplying isoflurane in 250 ml rather than 100 ml bottles.

The effects of needle type, gauge, and tip bend on spinal needle deflection.

Although the use of fine-gauge spinal needles reduces the incidence of postdural puncture headache, they are associated with increased risk of placement failure as a result of deflection and bending. This in vitro study quantifies spinal needle deflection from the axis of insertion with respect to needle type, gauge, and tip bend. In addition to straight-tip needles, those with standardized 5 degrees and 10 degrees tip bends were studied. The purpose was to examine the effect of tip bend, which has been described with small gauge spinal needles after bony contact, on needle path deflection. Needles studied included Quincke (Q), Sprotte (S), and Whitacre (W) in sizes ranging from 18-gauge to 29-gauge. Needles were inserted perpendicularly into porcine paraspinous muscle followed by radiologic investigation. Measurements of needle deflection from the axis of insertion at depths of 20, 40, and 60 mm were performed in a blinded fashion. Straight-tip Q needle deflection, but not W or S, was correlated with gauge and depth of insertion. Although there were differences within needle type groups, needle deflection was generally correlated with the degree of tip bend. We conclude that spinal needle deflection is dependent on the type of needle (W < S < Q), and that the magnitude of deflection is related to gauge (large < small) and tip bend (straight < 5 degrees < 10 degrees).

Regional anaesthesia for repeat Caesarean section in a patient with phantom limb pain.

The triggering of phantom limb pain by subarachnoid or epidural anaesthesia has been well described leading to the suggestion that neuraxial regional anaesthesia is relatively contraindicated in lower limb amputees. We report our experience of the provision of anaesthesia for repeat Caesarean section on two occasions in such a patient. Intrathecal fentanyl and morphine supplementation of bupivacaine successfully abolished peri-operative phantom limb pain, whereas epidural anaesthesia was associated with recurrence of phantom limb pain upon regression of the block.

Comparison of the force required for dural puncture with different spinal needles and subsequent leakage of cerebrospinal fluid.

An in vitro model was used to determine the force required to pierce bovine dura with a range of new spinal needles and to measure the subsequent leakage rate of cerebrospinal fluid (CSF). A significantly greater force was required to pierce the dura with pencil-point style needles compared to Quincke needles of the same size. Quincke needles caused a greater loss of CSF than their pencil-point equivalents. The results suggest that there is not likely to be a significant reduction in postdural puncture headache (PDPH) using a 27-gauge pencil-point needle compared to a 25-gauge needle that may be easier to use. Different makes of the same design and gauge of needle showed significant differences in the amount of CSF leakage, which may influence the clinician's choice of needle.