A. R. Wilkes

Evaluation of Frova, single‐use intubation introducer, in a manikin. Comparison with Eschmann multiple‐use introducer and Portex single‐use introducer*

In a randomised cross‐over study, 48 anaesthetists attempted to place a Frova single‐use introducer, an Eschmann multiple‐use introducer and a Portex single‐use introducer in the trachea of a manikin set up to simulate a grade 3 laryngoscopic view. The anaesthetists were blinded to success (tracheal placement) or failure (oesophageal placement). Successful placement (proportion, 95% confidence interval) of either the Frova introducer (65%, 50–77%) or the Eschmann introducer (60%, 46–73%) was significantly more likely than with the Portex introducer (8%, 3–20%). There were no significant differences between the success rates for the Frova and the Eschmann introducers. A separate experiment revealed that the peak force exerted by the Frova and Portex introducers was two to three times greater than that which could be exerted by the Eschmann introducer, p < 0.0001, indicating that the single‐use introducers are more likely to cause tissue trauma during placement.

The effect of humidification and smoking habit on the incidence of adverse airway events during deepening of anaesthesia with desflurane

The effect of two levels of humidification on the incidence of adverse airway events was studied in 58 adult female patients during deepening of anaesthesia using up to 12% desflurane. Humidification was provided by a breathing system filter with either low moisture‐conserving performance (17.2 mg.l−1 at 0.5 l tidal volume, Group L) or high moisture‐conserving performance (33.5 mg.l−1 at 0.5 l tidal volume, Group H). Forty‐eight per cent of patients smoked and there were more smokers in Group L than in Group H. Adverse airway events consisted of coughing and laryngospasm. For coughing, the dominant explanator was smoking. When both humidity and age were included in the analysis, there was a significant smoking–humidity interaction (p < 0.05), such that high humidity decreased the incidence of coughing in nonsmokers but not in smokers. The incidence of laryngospasm was significantly lower in Group H than in Group L (p < 0.05). We conclude that when patients inspire high concentrations of desflurane during induction of anaesthesia, increasing humidification to the levels achieved in this study decreases the incidence of coughing among nonsmokers and of laryngospasm in both smokers and nonsmokers.

A comparison of the forces exerted during laryngoscopy using disposable and non-disposable laryngoscope blades.

Summary The concern that re‐usable equipment may be a source of cross‐infection has prompted the increased use of disposable laryngoscope blades. We conducted a study investigating the duration of laryngoscopy and the peak force generated using various laryngoscope blades. Five blades were studied: one reusable Macintosh 3 blade, one disposable metal blade and three plastic disposable blades. Sixty anaesthetists performed laryngoscopy on a mannequin using each of the five blades presented in a random order. This was then repeated with a rigid collar applied to the mannequin. The mean force applied with the collar off with the metal blades was 32.8 and 30.8 N, and with the plastic blades 37.3, 39.6 and 41.5 N, respectively (p < 0.0001). The mean force applied with the collar on with the metal blades was 30.5 and 32.5 N, and with the plastic blades 35.5, 34.9 and 31.4 N, respectively (p < 0.0001). The mean duration of laryngoscopy with the collar off for the metal blades was 5.6 and 5.4 s, and with the plastic blades 10, 7.2 and 7.5 s (p < 0.0001). The duration of laryngoscopy with the collar applied for the metal blades was 7.1 and 7.5 s, and with the plastic blades 11.8, 9.7 and 9.0 s (p < 0.0001). The use of plastic blades results in both greater peak force and duration of laryngoscopy.

A comparison of 20 laryngoscope blades using an intubating manikin: visual analogue scores and forces exerted during laryngoscopy.

Fifty anaesthetists were recruited to use 20 different laryngoscope blades (one metal re‐usable blade, five metal single‐use blades and 14 plastic single‐use blades, of which eight were bulb‐type and 12 were fibreoptic‐type) in a manikin to achieve a grade I Cormack and Lehane view. The anaesthetists were asked to provide visual analogue scores (VAS) for: ease of attachment of the blade to the handle; illumination; view of the larynx; and satisfaction for clinical use. The peak force applied and time to achieve the grade I Cormack and Lehane view were also measured. A cluster analysis method was used to group together blades with similar scores or measures.

The bacterial and viral filtration performance of breathing system filters.

The bacterial and viral filtration performance of 12 breathing system filters was determined using test methods specified in the draft European standard for breathing system filters, BS EN 13328‐1. All the filters were of two types, either pleated hydrophobic or electrostatic, and these two types differed in their filtration performance. The filtration performance is expressed in terms of the microbial penetration value, defined as the number of microbes passing through the filter per 10 million microbes in the challenge. The geometric mean (95% confidence limits) microbial penetration value was 1.0 (0.5, 3.5) and 2390 (617, 10 000) for the pleated hydrophobic and electrostatic filters, respectively, for the bacterial challenge, and 87 (48, 212) and 32 600 (10 900, 84 900), respectively, for the viral challenge. In general, there was little change in the microbial penetration values following 24 h simulated use. It is concluded that results from the tests specified in the draft standard will allow comparisons to be made between different manufacturers’ products enabling an informed choice to be made.

The ability of breathing system filters to prevent liquid contamination of breathing systems: a laboratory study*

The ability of 29 different breathing system filters (five pleated hydrophobic and 24 electrostatic) to prevent the passage of water was assessed. Five, 10 or 20 ml of water was added on to the patient side of the filter during ventilation of a patient model with the filter layer orientated either horizontally or vertically. Water did not pass through the filter layer during any of the 30 tests on the pleated hydrophobic filters. In contrast, water passed through the filter layer in 39 of the 144 tests on the electrostatic filters (27%; 95% CI for difference between the filter types 14–35%; p = 0.0004). For electrostatic filters, a smaller internal volume, a larger volume of water added, and having the filter layer horizontal rather than vertical all significantly increased the probability of water penetration. Although pleated hydrophobic filters would protect the breathing system against liquid contamination, electrostatic filters can also be used, provided the internal volume is chosen appropriately and the filter layer is vertical.

Sevoflurane (12% and 8%) inhalational induction in children

Background:  Sevoflurane induction of anesthesia is frequently used in children. Rapidly performed inhalational induction may reduce excitation during early anesthesia. Increasing the total anesthetic MAC delivered to patients can be achieved by increasing volatile concentration or adding nitrous oxide. The latter reduces inspired oxygen concentration delivered, which may not be desirable. Even 8% sevoflurane induction is associated with excitation. A system capable of delivering 12% sevoflurane using two tandem vaporizers has been developed.

The moisture-conserving performance of breathing system filters in use with simulated circle anaesthesia breathing systems.

Breathing system filters can be used to humidify gases delivered to patients. Performance can be determined by measuring the net moisture loss (the difference between expired and inspired levels of humidity) from a patient model. The net moisture loss should be decreased by increasing the level of humidity in the breathing system by, for example, using a circle breathing system. The effect of four different filters, three different levels of humidity in the breathing system (7, 13 and 19 g.m−3) and two tidal volumes (0.5 l and 1.0 l) on the net moisture loss from a patient model was measured. The net moisture loss decreased as the humidity in the breathing system increased and was less for the lower tidal volume. Adequate levels of humidity (≥ 20 g.m−3) will be delivered to patients by most filters provided they are used in conjunction with circle breathing systems and low fresh gas flows.

Resistance to gas flow in heat and moisture exchangers

been compared to the control group instead of baseline preoperative scores, the results may have been quite different. Also, in view of the ‘nonsignificant’ differewe between the two groups, perhaps a power function of the test should have been done to see whether the number of patients studied was adequate to reach to any conclusions [3]. Papaveratum may affect psychomotor performance and since there was a difference in the number of patients given papaveratum in the different groups, this may have affected the results. I t also appears (although it is not clear from the results) that those patients who were unable to perform the psychomotor tests have been excluded when giving the median values of the simple reaction time. If indeed this is true, the results may be quite different if these patients were also included when calculating the median values. Besides, since the number of patients who could not perform the test was quite large (up to 36%) at 1 h and in two groups even at 3 h (up to 20%), i t is difficult to conclude either that there was no significant difference from baseline values at 3 h in any group, or that there was no difrerence between the groups! In summary, one must be careful in interpreting results obtained from studies where psychomotor performance is measured using tests associated with ‘learning’. A new test, the perceptive accuracy test, has, in this respect, not been found to have any learning effect [ I , 41 but more studies are needed using this test before any conclusions can be made.

The effect of gas flow on the filtration performance of breathing system filters

When tested according to the European standard, the performance of breathing system filters is determined at a flow of 15 or 30 l.min−1 for filters intended for use with paediatric or adult patients, respectively. However, higher flows of gas may pass through a filter in some circumstances. The penetration of sodium chloride particles through seven different breathing system filters (three pleated hydrophobic and four electrostatic) was measured at five different flows ranging from 15 to 75 l.min−1. Penetration varied from 0.004% to 24.4% for the various filters at the different flows. Penetration increased by between 2 and 40 times for the different filters as the flow increased by a factor of five but this did not markedly alter the rank order of the filters in terms of performance. Testing to the standard provides a useful indication of relative performance at any flow.