Biomedical subjects

L O Jonsson

Publications and source records attributed to L O Jonsson.

14 recordsLinked to original sources

PubMed1990

Predictable PaCO2 with two different flow settings using the Mapleson D system.

Two different settings of fresh gas flow (VFG) and minute ventilation (VE) used with the coaxial Mapleson D system (Bain), were evaluated in 59 adults (ASA I-III) during controlled ventilation and different types of surgical procedures. The two flow settings (alternatives A and B) were VFG of 75 and 110 ml.min-1.kg-1 and VE of 150 and 175 ml.min-1.kg-1, aiming to generate normocapnea and mild hypocapnea, respectively. The PaCO2 obtained with alternative A was 5.5 +/- 0.5 kPa (mean +/- s.d.), with 92% of the patients within the range 4.7-6.1 kPa. With alternative B, the PaCO2 was 4.4 +/- 0.5 kPa, with 82% of the patients within the range 3.5-4.9 kPa. It is concluded that these two flow regimes are suitable for clinical use when either normocapnea or mild hypocapnea is desired.

Adult↗

PubMed1990

Predicted normocapnea in infants and children using the Bain circuit with controlled ventilation.

We have constructed a nomogram for fresh gas flow (VFG) and minute ventilation (VE) for paediatric anaesthesia during controlled ventilation using the Bain coaxial Mapleson D circuit. VFG was based upon the assumption of a high fresh gas utilization because of a low VFG/VE ratio (0.67) and known figures of carbon dioxide elimination. The formulas VFG = 27.8 x VCO2 and VE = 1.5 x VFG were used to calculate the necessary flows to generate normocapnea. The nomogram was evaluated in 59 children (6-62 kg, age 5 months-14 years). PaCO2 (mean +/- s.d.) was 5.0 +/- 0.5 kPa (38 +/- 4 mmHg) with a total range of 3.9-6.3 kPa (29-47 mmHg). Ninety percent of the children had a PaCO2 of 5.7 kPa (43 mmHg) or lower. There was no correlation between body weight and PaCO2. Hence, there was no difference in mean values between children below or above a body weight of 20 kg.

Adolescent↗

PubMed1989

[Tracheal tube obstruction caused by local anesthetic gel].

A case report of tracheal tube obstruction caused by a thin, almost invisible, membrane is presented. It was found probable that the membrane consisted of dried local anaesthetic gel. An experimental study showed that inadvertent application of 0.3 ml of lignocaine or prilocaine gel at the orifice of the tube may result in the formation of such a membrane. After 48 hours, the membrane resisted any pressure that might be generated in a resuscitation bag.

Adhesiveness↗

PubMed1989

Fresh gas flow in the Bain circuit during laparoscopy.

Twenty-two women were studied during laparoscopy with abdominal insufflation of carbon dioxide. A bain anaesthetic breathing circuit was used with a fresh gas flow (VFG) of 110 ml.min-1.kg-1, and controlled ventilation was applied with a minute ventilation (VE) of 175 ml.min-1.kg-1. Arterial blood gases were analysed at the end of the operation. Nineteen of the women (86 per cent) were found to have a PaCO2 within the range for normocapnia (i.e., 4.7-5.9 kPa (35-45 mmHg), two were hypocapnic with a PaCO2 of 4.4 and 4.5 kPa (33 and 34 mmHg) respectively and one was found to have a PaCO2 of 6.2 kPa (46.5 mmHg). It was concluded that the carbon dioxide absorbed from the abdomen during laparoscopy demands fresh gas flows that are higher than normally used in the Bain circuit if a PaCO2 within the normal range is to be obtained. A simultaneous increase in VFG and VE of about 45 per cent is sufficient to achieve normocapnia.

Abdomen↗

PubMed1989

Rebreathing, resistance and external work of breathing in three different coaxial Mapleson D systems.

Using a lung model, rebreathing characteristics, resistance against gas flow and the external work of breathing were tested in three different coaxial Mapleson D systems: the Medicvent D system, the Bain original system and the Coax-II system. The rebreathing characteristics were found to be similar in all systems in both spontaneous and controlled ventilation. The Bain system was found to have the lowest resistance and work of breathing and the Coax-II system the highest. The differences were small and clinically insignificant. Both the resistance and the work of breathing increased with fresh gas flow. The resistance against expiration was found to be in the range 135-160 Pa at a total gas flow of 31 1.min-1, which is well within the acceptable level. The resulting end-expiratory pressure was never above 100 Pa (1 cmH2O) in any system. We concluded that there was no clinically significant difference among the three systems despite differences in design. The coaxial Mapleson D systems can also be used safely with high fresh gas flows with regard to resistance and end-expiratory pressures.

Airway Resistance↗

PubMed1989

Calculation of end-tidal carbon dioxide fractions in the Bain system.

The validity of the Stenqvist-Sonander formula for calculating the end-expiratory fraction of carbon dioxide (FACO2) in the coaxial Mapleson D (Bain) systems was evaluated using a lung model for simulated spontaneous breathing with an optional respiratory wave form. Two different respiratory flow patterns were used, one representing relaxed breathing in a volunteer and one resembling the respiration found in halothane anaesthesia. Each pattern was used with five different fresh gas flows and three different respiratory rates. The formula was found to be quite accurate when the flow pattern of an awake volunteer was simulated, but it underestimated the observed FETCO2 value by about 10% in halothane breathing. It is concluded that the formula can be recommended for use in theoretical and educational situations but that it is too complicated for application in clinical practice.

Anesthesia, Closed-Circuit↗

PubMed1989

Respiratory flow characteristics during isoflurane/nitrous oxide anaesthesia.

Ventilatory characteristics during isoflurane anaesthesia and spontaneous breathing were studied in ten adults during surgery. After premedication with diazepam and induction with thiopental sodium and suxamethonium, 1.2% isoflurane in a 50% mixture of nitrous oxide in oxygen was introduced via a non-rebreathing circuit. Respiratory flow was measured by means of a pneumotachograph, arterial gases were sampled and carbon dioxide elimination and dead-space to tidal volume ratios (VD/VT) calculated. The time axis of one respiratory cycle was divided into 20 equidistant sections and the flow at the end of each section was expressed as a percentage of the maximum flow rate during inspiration and expiration, respectively. In this manner, a relative respiratory flow pattern was constructed. The total ventilation was 5.8 +/- 0.5 1.min-1 (mean +/- s.d.) with a tidal volume of 191 +/- 45 ml and a respiratory rate of 31 +/- 6.min-1. The PaCO2 was 7.2 +/- 0.6 kPa, the carbon dioxide elimination 151 +/- 38 ml (STPD) and VD/VT 0.53 +/- 0.12. The respiratory flow pattern showed early peak flows during both inspiration and expiration. The expiratory flow rate after 90% of the total respiratory cycle time was on average 43% of the maximum expiratory flow rate. The conclusion was that isoflurane seems to have a similar respiratory flow pattern to halothane. The significant hypercarbia that resulted is still acceptable but a lighter anaesthetic level is recommended for routine surgery.

Adult↗

PubMed1988

A new device for administration of nasal continuous positive airway pressure in the newborn: an experimental study.

During treatment with continuous positive airway pressure (CPAP), optimal re-expansion of lung units with minimal work of breathing is best accomplished when the airway pressure (Paw) is kept constant at the desired CPAP level throughout the entire breathing cycle. To achieve this, a new device was constructed in which CPAP was generated by a jet of fresh gas close to the nasal airway. The performance of the new device was investigated experimentally using a lung model which simulated the breathing pattern of a newborn. Paw, flow, and external work of breathing were measured at three CPAP levels, with and without controlled airway leakage. The new device was compared with a traditional continuous-flow CPAP system with standard nasal prongs. Despite a virtually constant pressure within the traditional system, Paw variations and external workload were considerably less with the new device, which was also less sensitive to airway leakage.

Administration, Intranasal↗

PubMed1987

Pressure characteristics of the Ambu CPAP system and the Servo ventilator 900C in CPAP mode.

Spontaneous breathing was stimulated in the Ambu continuous positive airway pressure (CPAP) system and the Servo Ventilator 900C by means of a lung model programmed to mimic the respiratory flow patterns of a healthy volunteer and a patient in severe respiratory distress. Changes in airway pressure, flow and volume were recorded during "breathing" with CPAP at 0.5, 1.0 and 1.5 kPa. In the Ambu system, the airway pressure decreased during inspiration and increased during expiration, while the mean airway pressure was close to the pre-set CPAP value. The pressure changes were minimal when the fresh gas flow was increased from 15 to 25 1 X min-1. The higher fresh gas flow is recommendable during deep or rapid breathing. In the Servo ventilator 900C, there was a short initial inspiratory pressure drop, succeeded by a pressure rise above the CPAP value. The expiratory airway pressure was somewhat higher than CPAP. Both systems were found to be recommendable for clinical use.

Computers↗

PubMed1987

Influence of the respiratory flow pattern on rebreathing in Mapleson A and D circuits.

In a lung model the rebreathing effects of different respiratory flow patterns (RFP) were studied in the coaxial Mapleson A (Lack) and D (Bain, Coax-II) systems during spontaneous breathing. In the Mapleson A system RFP was not found to have any impact. In the D systems FACO2 was higher with an RFP typical of halothane-anaesthetized patients than with an RFP with an exponentially decreasing expiratory flow and an end-expiratory flow pause (FTEP). The difference in FACO2 was 26% with a VF corresponding to 100 ml X min-1 X kg-1 body weight. The RFP in a non-anaesthetized volunteer was intermediate between these two patterns. Rebreathing decreased in the D systems with prolongation of FTEP and when a decelerating expiratory flow was used.

Anesthesia, Inhalation↗

PubMed1987

Rebreathing and ventilatory response to different fresh gas flows in the Bain and Lack systems. A clinical study.

Thirty-four adults were studied during halothane anaesthesia with spontaneous breathing, while undergoing orthopaedic surgery. They were randomly divided into two groups according to whether the Bain (n = 18) or the Lack (n = 16) system was used. Respiratory flows were recorded and arterial blood gases drawn at different fresh gas flows (VF). The values obtained were compared with those recorded under non-rebreathing conditions (NRC). In the Bain system the proportion of rebreathers was 0.22, 0.25, 0.55 and 0.83 when the VF was 175, 150, 125 and 100 ml X min-1 X kg-1 body weight (b.w.), respectively. In the Lack system these proportions were 0.43, 0.55 and 0.92 at VF of 85, 70 and 55 ml X min-1 kg-1 b.w., respectively. The ventilatory response to rebreathing was an increase in minute ventilation (VE), keeping the partial pressure of arterial carbon dioxide (PACO2) almost unaltered. In the Bain system the VE X kg-1 X b.w. thus increased by 18% and 38% at VF of 125 and 100 ml X min-1 X kg-1 b.w., respectively, when compared to NRC (P less than 0.05). The corresponding increases in the Lack system were 15% and 37% at VF of 70 and 55 ml X min-1 X kg-1 b.w., respectively (P less than 0.01). In the Lack group also the PACO2 increased by 6% when a VF of 55 ml X min-1 X kg-1 b.w. was used compared to the value obtained under NRC (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1986

Fresh gas flow in coaxial Mapleson A and D circuits during spontaneous breathing.

In a lung model simulating spontaneously breathing halothane anaesthesia, the rebreathing characteristics of the coaxial Mapleson A (Lack circuit) and D (Bain circuit) systems were tested. Using decreasing fresh gas flows (VF), the end-tidal carbon dioxide fraction (FACO2) was monitored and the point of rebreathing (R.P.) detected. The effects of changes in minute volume (VE), dead-space to tidal volume ratio (VD/VT) and carbon dioxide elimination (VCO2) were studied. The effect of increased tidal volumes (VT) on FACO2 was investigated for some different fresh gas flows (VF). The VF/VE ratio for R.P. in the Bain circuit was approximately 2 and in the Lack circuit 0.88. In both circuits an increase in VE and a decrease in the VD/VT ratio resulted in higher demands on VF if rebreathing was to be avoided. The latter effect was much more pronounced in the Lack circuit. In neither system did any changes in VCO2 affect the rebreathing characteristics. The conclusion was drawn that the Lack system is a much better choice concerning the fresh gas flows for anaesthesia with spontaneous breathing than the Bain system. It was also concluded that the fresh gas flows recommended by Humphrey for the Lack system (i.e. 51 ml X min-1 X kg b.w.-1) and by the manufacturers for the Bain system (i.e. 100 ml X min-1 X kg b.w.-1) are inadequate and should be increased if a considerable degree of rebreathing is to be avoided.

Anesthesia, Closed-Circuit↗

PubMed1985

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.

Airway Resistance↗

PubMed1985

Flow pattern and respiratory characteristics during halothane anaesthesia.

Using pneumotachography, the flow pattern was analysed in detail and tidal volume, respiratory rate, dead-space to tidal volume ratio (VD/VT) and carbon dioxide output were measured in adults (Group A, n = 12) and 3-8-year-old children (Group B, n = 10) during spontaneous breathing anaesthesia with halothane and surgery. The respiratory cycle was divided by equidistant points into 40 parts and the flow at each point related to peak inspiratory and expiratory flow. Thus a relative flow pattern was derived. This relative flow pattern was almost identical in both groups. Characteristically, the flow curve showed rapid turns from high expiratory to high inspiratory flow rates without any end-expiratory flow pause (except in one adult). The minute ventilation was 6.6 +/- 2.0 1 X min-1 in Group A and 3.4 +/- 0.6 1 X min-1 in Group B, being correlated both to body weight and body surface area in Group A but not in Group B. The tidal volume was 210 +/- 60 ml in Group A and 78 +/- 13 ml in Group B, respiratory rate 31 +/- 4 X min-1 and 44 +/- 10 X min-1, respectively, and the VD/VT ratio 0.40 +/- 0.10 and 0.55 +/- 0.12, respectively. Carbon dioxide output was 173 ml X min-1 (STPD) in the adults and 82 +/- 13 ml X min-1 (STPD) in the children. It was correlated to both body weight and body surface area in the adults but not in the children.

Adult↗