An Unusual Complication With the Administration of a Volatile Anesthetic Agent for Status Asthmaticus in the Pediatric Intensive Care Unit: Case Report and Review of the Literature.

In severe cases of status asthmaticus, when conventional therapies fail, volatile anesthetic agents remain a therapeutic option. When delivered outside of the operating room setting, specialized delivery techniques are needed to ensure the safe and effective use of volatile anesthetic agents. We present a 16-year-old adolescent with status asthmaticus who required the therapeutic administration of the volatile anesthetic agent, sevoflurane, in the pediatric intensive care unit (PICU). Although initially effective in reducing bronchospasm, progressive hypercarbia developed due to defective functioning of the carbon dioxide absorber of the anesthesia machine. This failure occurred as the soda lime compartment filled with water accumulated from circuit humidification and continuous albuterol therapy. The role of volatile anesthetic agents in the treatment of status asthmaticus in the PICU is discussed, options for delivery outside of the operating room presented, and potential problems with delivery reviewed.

Demineralisation of permeable hydroxyapatite with alternating water and acidic buffer: scanning microradiographic study of effect of switching period.

Permeable hydroxyapatite (HAP) blocks were exposed for equal times alternately to pH 4.0 buffer and water for 237 h. Rates of HAP loss with time (determined from changes in X-ray attenuation) were measured as a function of switching period tau (the time for a complete cycle) from 0.5 to 6 h and with a continuous buffer flow. The mean rate of HAP loss decreased markedly as tau increased, and for large tau was about half the rate for continuous buffer flow. We propose that demineralising conditions through the depth of the HAP are influenced by the extent of retention of buffer within its pores which will depend on tau. A mathematical model with parameters R(0) and Deltat was developed, where R(0) is the rate of demineralisation for continuous flow, and Deltat a time added to each tau/2 buffer exposure to account for its retention in the HAP pores. Experimental data fitted the model with Deltat approximately 8 to approximately 10 min and with R(0) close to the rate observed for continuous buffer flow. The model predicts that the rate decreases and approaches R(0)/2 as tau --> infinity, as was found experimentally to be the case. This type of study could potentially give information about subsurface porosity and transport processes during acidic dissolution of permeable solids, for example in dental caries and dental erosion.

Mucoadhesive tablets for buccal administration containing sodium nimesulide.

The possibility of improving the flux of nimesulide across the buccal mucosa using the drug in the form of a sodium salt was investigated in our study. The salt form may increase to flux across buccal membrane, starting from a suspension; its lower permeation coefficient is compensated by a higher concentration gradient. The salt was inserted into a mucoadhesive tablet for buccal administration. The tablets were designed to prevent the loss of the drug into the saliva by means of a protective layer and placed on the area not in contact with the mucosa. Ten volunteers were used. The in vitro release from mucoadhesive tablets was examined through a porcine buccal mucosa, using a standard Franz cell, modified for present purposes. The advantages of a higher concentration gradient for the flux, related to a higher solubility of the salt, and to a sufficiently high permeation coefficient of the drug, despite the ionized form, could not be completely exploited, because the composition of the formulation destroys the chemical form of the drug.

[Interaction of soda lime and halogenated anesthetics]. / Interazioni tra calce sodata ed anestetici alogenati.

The increased use of soda lime for low flow anaesthesia leads to some problems related to the interaction with halogenated agents. These agents may be absorbed by soda lime or degradated according to their water content. Halothane and enflurane, in contact with soda lime, produce some metabolites, but their concentration is low when compared to their own lethal concentration. Sevoflurane degradates to four compounds. Compound A may reach a value between 13.3-42.1 ppm in the inspired fraction: these values are 50-100 times lower than the toxic concentrations. Isoflurane and desflurane are degradable at very low extent. Some case reports of unexpected high carboxyhemoglobin levels during anaesthesia indicate the possibility of CO production from soda lime and baralyme when halogenated agents are used. This reaction occurs only with anaesthetics containing CHF2-moiety (isoflurane, enflurane and desflurane) and when some specific factors make soda lime or baralyme completely dry. Low flow anaesthesia preserves the moisture content of the soda lime and protects from carbon monoxide production, by increasing water content in the circle.

[Halothane absorption by dry soda lime]. / Halothanabsorption durch trockenen Atemkalk.

Humidified soda lime is commonly used to eliminate carbon dioxide from the circulatory system. Little is known about adverse reactions to accidentally dried soda lime. Therefore, a case of unexpected absorption of halothane by dry soda lime is reported. These observations were confirmed by a simulation with relevance to anaesthetic practice. CASE REPORT. A 46-year-old ASA class I patient was scheduled for elective surgery. After induction of general anaesthesia with 500 mg thiopentone, followed by 100 mg suxamethonium, the trachea was intubated. The patient was ventilated with nitrous oxide in oxygen and 1.5 vol% of halothane for several minutes in the induction room. After being connected to a new circulatory system in the operating theatre, the patient was ventilated but, in addition inspiratory and expiratory anaesthetic gas concentrations were measured. Despite a vaporizer position of 1.5 vol% the inspiratory concentration of halothane was below 0.2 vol%. Disconnecting the tube, the typical odour of halothane was missing in the inspiratory line of the circulatory system, but was present in the fresh gas tube. Furthermore, the lower part of the soda lime canister was surprisingly hot. After removing both the absorbers, the inspiratory halothane concentration immediately normalized. The absorbers were replaced by canisters filled with fresh soda lime, and the anaesthesia was terminated without further complications. An absorption of halothane by dried soda lime was suspected. METHODS OF SIMULATION. In the first simulation four circulatory systems with two soda lime canisters each were perfused with 21 of oxygen for 48 h. In the second simulation four soda lime canisters placed in one circulatory system were perfused with 1 l for 120 h. For measurement of halothane absorption each canister was placed in a circulatory system. The canister was perfused with a fresh gas flow of 2 l of oxygen and a vaporizer position up to 1.3 vol% of halothane. By the time an equilibrium was reached, i.e., in- and outflow concentrations of halothane were equal for a 3-min period, further halothane vaporization was stopped. In a 30-s interval the soda lime temperature and the gas concentration entering and leaving the soda lime canister were registered. Subsequently, the humidity of the soda lime was determined. RESULTS. In the first simulation 6 of the 8 canisters showed a humidity of soda lime of 15.5% of 19%, with halothane being absorbed in one case. Normally, the equilibrium between in- and outflow gas concentration was reached after 3.5-4 min. In the remaining two canisters the humidity was 14% and 9%. Only a small amount of halothane vapour was absorbed. The halothane concentrations were in equilibrium after 10 to 13 min. The probes from the second simulation revealed a humidity of soda lime of 2% to 8.7%. Below a humidity of 4% the concentration of halothane leaving the canister was greatly reduced. It took 63 min to reach a steady state in the 2% humidity probe and the temperature rose to 43.1 degrees C. CONCLUSIONS. Accidental perfusion of the circulatory system with dry oxygen can cause a reduction in the humidity of soda lime. Dried soda lime delays the increase of halothane concentration in the inspiratory limb. The absorption of halothane is accompanied by an increase in the temperature of the soda lime. Therefore, in every situation lacking a sufficient anaesthetic level during inhalation anaesthesia, absorption of the vaporized anaesthetic must be excluded. Only dried soda lime can absorb halothane.