Lack of Degradation of Sevoflurane by a New Carbon Dioxide Absorbent in Humans

Background: Potent inhaled anesthetics degrade in the presence of the strong bases (sodium hydroxide or potassium hydroxide) in carbon dioxide (CO2) absorbents. A new absorbent, Amsorb (Armstrong Medical Ltd., Coleraine, Northern Ireland), does not employ these strong bases. This study compared the scavenging efficacy and compound A production of two commercially available absorbents (soda lime and barium hydroxide lime) with Amsorb in humans undergoing general anesthesia.

Methods: Four healthy volunteers were anesthetized on different days with desflurane, sevoflurane, enflurane, and isoflurane. End-tidal carbon dioxide (ETco2) and anesthetic concentrations were measured with infrared spectroscopy; blood pressure and arterial blood gases were obtained from a radial artery catheter. Each anesthetic exposure lasted 3 h, during which the three fresh (normally hydrated) CO2 absorbents were used for a period of 1 h each. Anesthesia was administered with a fresh gas flow rate of 2 l/min of air:oxygen (50:50). Tidal volume was 10 ml/kg; respiratory rate was 8 breaths/min. Arterial blood gases were obtained at baseline and after each hour. Inspired concentrations of compound A were measured after 15, 30, and 60 min of anesthetic administration for each CO2 absorbent.

Results: Arterial blood gases and ETco2 were not different among three CO2 absorbents. During sevoflurane, compound A formed with barium hydroxide lime and soda lime, but not with Amsorb.     

Carbon Dioxide Elimination from Circle Systems

Ten various circle systems were studied in model experiments. All the experiments were performed using a Waters cannister containing 675–685 g of Durasorb. 300 ml of carbon dioxide were supplied to the system per min. The efficacy of these systems was expressed as the time taken to demonstrate a concentration of 0.6% carbon dioxide in the gas mixture supplied to the patient connection during each respiratory cycle. The carbon dioxide elimination was studied at a gas flow of 2, 4 and 6 1 per min. All the systems showed an effective carbon dioxide elimination for 6 h or more at a flow of 2 1. An increasing efficacy was found with increasing flow, but to a varying extent.
A circle system where all the components, including the cannister and directional valves, can be replaced after use is recommended owing to the risk of cross contamination. A soda-lime charge of 600–700 g is advantageous. For anesthetic procedures of less than 1 h, other techniques should be employed as they are more economical.     

Efficacy of Preoxygenation with Tidal Volume Breathing: Comparison of Breathing Systems

Background: Preoxygenation before tracheal intubation is intended to increase oxygen reserves and delay the onset of hypoxemia during apnea. Various systems are used for preoxygenation. Designed specifically for preoxygenation, the NasOral system uses a small nasal mask for inspiration and a mouthpiece for exhalation. One-way valves in the nasal mask and the mouthpiece ensure unidirectional flow. This investigation compares the efficacy of preoxygenation using the standard circle system with the NasOral system and five different resuscitation bags.

Methods: Twenty consenting, healthy volunteers were studied in the supine position for 5-min periods of tidal volume breathing using the circle absorber system, the NasOral system, and five resuscitation bags in a randomized order. Data were collected during room air breathing and at 30-s intervals during 5 min of oxygen administration. Inspired oxygen, end-tidal oxygen, and end-tidal nitrogen were measured by mass spectrometry.

Results: At 2.5 min of oxygenation, end-tidal oxygen plateaued at 88.1 +/- 4.8 and 89.3 +/- 6.4% (mean +/- SD) for the circle absorber and NasOral systems, respectively. This was associated with inverse decreases in end-tidal nitrogen. At no time did these end-tidal oxygen or nitrogen values differ from each other. Three of the resuscitation bags (one disk type and two duck-bill type with one-way exhalation valves) delivered inspired oxygen more than 90%, and the end-tidal oxygen plateaued between 77 and 89% at 2 min of tidal volume breathing. The other two resuscitation bags (both duck-bill bags without exhalation valves) delivered inspired oxygen less than 40%, and the end-tidal oxygen values ranged between 21.8 +/- 5.0 and 31.9 +/- 8.7%.     

A Circle System Without Carbon Dioxide Absorption

An anaesthetic circle system without a carbon dioxide absorber is described. The efficiency of the circle, i.e., the fraction of alveolar gas in the outflow from the circle, was measured in 15 patients during halothane anaesthesia or neurolept analgesia. The fraction ranged from 0.88 to 0.95 (mean 0.91), while the ratio between the alveolar ventilation and the fresh gas inflow ranged from 0.97 to 1.71. The efficiency was not correlated to this ratio. There was no need for hyperventilation if the fresh gas inflow was 10% higher than the alveolar ventilation required to maintain normal PaCO2. The circle was used in 50 patients manually ventilated by nurse anaesthetists. Mean fresh gas inflow was 60 ml/kg. Mean PaCO2 was 5.47 kPa (41 mmHg). In a similar group of 50 other patients, in which the standard circle used in the department was employed, the mean PaCO2 was 4.80 kPa (36 mmHg). The frequency of hypercapnia was equal in the two groups, but hypocapnia was not seen when the circle without absorber was used.     

Simulated Spontaneous Breathing. A New Model for Testing Anaesthetic Circuits

A carbon-dioxide-producing lung model capable of simulating spontaneous breathing is presented. It consists of a piston in a cylinder, a mixing chamber and a dead space volume. The piston is driven by a direct-current motor controlled by a micro-processor and a servo unit. Respiratory waveform and rate, tidal volume, carbon dioxide production and dead space are easily adjustable within a wide range. The model is easy to handle and accurately mimics a given breathing pattern. It seems suitable for investigations of rebreathing and carbon dioxide elimination in different anaesthetic circuits.     

Control of Carbon Dioxide in Modified Mapleson A and D (Hafnia) Anaesthetic Systems. An Experimental Model

The effects of varying ventilations (V_e) and fresh gas flows (FGF) on end-expiratory CO₂ (F eco ₂) levels were investigated in an experimental model lung, employing the Hafnia modification of the Mapleson A and D anaesthetic systems during CO₂-absorption and CO₂-wash-out (rebreathing). Identical results were found in both systems: F eco ₂ was constant and independent of FGF with CO₂-absorption and constant V_e, whereas rebreathing resulted in increasing F eco ₂ levels as FGF was decreased. As control of F eco ₂ in the rebreathing systems by regulating FGF could only take place within F eco ₂ levels higher than that determined by V_e at complete CO₂-absorption, e. g. for the Hafnia A and D rebreathing systems, control of FGF necessitates relative hyperventilation. F eco ₂ with constant FGF decreased with increasing V_e during CO₂-absorption, as well as during rebreathing, although this decrease was less in the rebreathing systems. Thus a decrease in F eco ₂ with rising V_e can be avoided and hypocapnia prevented. The results agree with those obtained in clinical studies.     

Carbon Dioxide Therapy: Effects on Skin Irregularity and Its Use as a Complement to Liposuction

For a successful conventional or superficial liposuction, it is necessary to consider the competence of the surgeon who is to administer the procedure necessary for this type of surgery as well as the physical and psychological evaluation of the determined patient. A poor result often is related to the persistence of adipose tissue irregularity in the form of fatty tissue accumulation. This complication, common to this type of surgery, has called for research to determine methods for its treatment. Carbon dioxide (CO₂) therapy refers to the transcutaneous and subcutaneous administration of CO₂ for therapeutic purposes. This treatment originated at the Royal Spas of France in 1932 with the treatment of patients affected by obliteration of arteriopathies. Recent studies have demonstrated the effect of subcutaneous CO₂ therapy performed to improve local parameters of circulation (performed by Doppler, laser–Doppler, and trans-cutaneous partial pressure of oxygen determination), and to reduce localized adiposities (verified reporting variations in maximum circumference and performing histologic studies). With these results, the absence of toxicity, and the relevant side effects related to this treatment taken into consideration, the Plastic Surgery Unit of Siena has been committed to researching the role that CO₂ therapy can play in the treatment of skin irregularity and as a complement to liposuction. The authors report their experience using Carbomed programmable automatic CO₂ therapy apparatus and 30GA1/2 0,3X13 microlance needles for the treatment of patients with adipose tissue accumulations located on the thighs and knees. In their study, 42 patients were divided into three groups: A, B, and C. In Group A, only liposuction was performed. In group B 3 weeks after liposuction CO₂ therapy was administered in two weekly subcutaneous applications of CO₂ for 10 consecutive weeks. In group C, CO₂ therapy alone was administered with the same contingencies used for group B (two weekly subcutaneous applications of CO₂ for 10 consecutive weeks). The objective was to assess the effectiveness of CO₂ therapy for skin irregularity and as a complement to liposuction for adipose tissue accumulation by reporting variations in circumference and skin elasticity monitored by the Cutometer SEM 474 in all treated areas. The data obtained were analyzed statistically. Values of p less than 0.05 were considered significant. The authors report their experience and the results achieved from the study.