Preserved oxygenation in obese patients receiving protective ventilation during laparoscopic surgery: a randomized controlled study.

BACKGROUND: Venous admixture from atelectasis and airway closure impedes oxygenation during general anaesthesia. We tested the hypothesis that continuous positive airway pressure (CPAP) during pre-oxygenation and reduced fraction of inspiratory oxygen (FIO2 ) during emergence from anaesthesia can improve oxygenation in patients with obesity undergoing laparoscopic surgery. METHODS: In the intervention group (n = 20, median BMI 41.9), a CPAP of 10 cmH2 O was used during pre-oxygenation and induction of anaesthesia, but no CPAP was used in the control group (n = 20, median BMI 38.1). During anaesthesia, all patients were ventilated in volume-controlled mode with an FIO2 of 0.4 and a positive end-expiratory pressure (PEEP) of 10 cmH2 O. During emergence, before extubation, the control group was given an FIO2 of 1.0 and the intervention group was divided into two subgroups, which were given an FIO2 of 1.0 or 0.31. Oxygenation was assessed perioperatively by the estimated venous admixture (EVA). RESULTS: The median EVA before pre-oxygenation was about 8% in both groups. During anaesthesia after intubation, the median EVA was 8.2% in the intervention vs. 13.2% in the control group (P = 0.048). After CO2 pneumoperitoneum, the median EVA was 8.4% in the intervention vs. 9.9% in the control group (P > 0.05). One hour post-operatively, oxygenation had deteriorated in patients given an FIO2 of 1.0 during emergence but not in patients given an FIO2 of 0.31. CONCLUSIONS: A CPAP of 10 cmH2 O during pre-oxygenation and induction, followed by PEEP after intubation, seemed to preserve oxygenation during anaesthesia. Post-operative oxygenation depended on the FIO2 used during emergence.

Cost-effectiveness analysis of local, regional and general anaesthesia for inguinal hernia repair using data from a randomized clinical trial.

BACKGROUND: Inguinal hernia repair is a common operation in general surgery and can be performed under local, regional or general anaesthesia. This multicentre randomized trial was undertaken to compare the costs of the three anaesthetic methods in general surgical practice. METHODS: Between January 1999 and December 2001, 616 patients at ten hospitals who underwent primary inguinal hernia repair were randomized to local, regional or general anaesthesia. The primary endpoints were direct costs. Secondary endpoints were indirect costs and recurrence rates. RESULTS: Total intraoperative, as well as total early postoperative, data showed local anaesthesia to have significant cost advantages over regional and general anaesthesia (P < 0.001). The advantage was also significant for total hospital and total healthcare costs (P < 0.001), whereas there was no significant difference between regional and general anaesthesia. CONCLUSION: The use of local anaesthesia for inguinal hernia repair was significantly less expensive than regional or general anaesthesia.

[An ambulance helicopter in Jamtland. A survival necessity in a county of tourism]. / Ambulanshelikopter i Jämtland. En livsnödvändighet i ett turistlän.

The county of Jämtland is a sparsely populated area in which an ambulance-helicopter has been in use since the middle of the 1970's. A prospective study was undertaken during a six month period with the aim of evaluating the benefits of the helicopter as compared with the use of road-ambulance transport alone. Total number of patients involved was n = 249. Both flight nurses and receiving doctors found that in most cases, patients transported by helicopter manned with a flight nurse were given higher quality care. A follow-up study by specialists from the receiving departments confirmed that for 3% (n = 8), transport by ambulance-helicopter resulted in "probably better prognosis", and that for 2% (n = 6) the result was "lifesaving".

Effects of nitrous oxide/oxygen inhalation on the maternal circulation during vaginal delivery.

The hemodynamic changes occurring during the first stage of labor were studied in 24 healthy pregnant women during inhalation of different nitrous oxide/oxygen (N2O/O2) gas mixtures (intermittent 70/30, 40/60, 0/100 and continuous 40/60). Cardiac output increased (P less than 0.01) from 6.6 +/- 0.2 l/min between uterine contractions to 8.5 +/- 0.3 l/min during contractions. Heart rate, stroke volume, systolic, diastolic and mean arterial pressures were increased (P less than 0.01) and total peripheral vascular resistance was reduced (P less than 0.01) during contractions compared to measurements performed between contractions. The maternal circulation was influenced by the use of N2O/O2. During intermittent inhalation, higher concentrations of N2O were associated with a decrease (P less than 0.01) in heart rate, cardiac output and arterial pressure as well as an increase (P less than 0.01) in stroke volume. The degree of pain relief also increased (P less than 0.01) with increasing concentrations of inhaled nitrous oxide. The circulatory influence of intermittent inhalation given during uterine contractions was also apparent during the interval between contractions when N2O/O2 was not administered. The most obvious effects on both circulation and pain were demonstrated during continuous inhalation of N2O/O2. There was a close association between analgetic and cardiovascular effects indicating that the latter, at least partly, were due to pain relief. However, it was not possible to exclude or confirm possible direct pharmacological effects of N2O/O2 on maternal circulation.

Sublingual buprenorphine as postoperative analgesic: a double-blind comparison with pethidine.

Buprenorphine and pethidine as postoperative analgesics were compared in 96 women having gynaecological operations by lower laparotomy. A fixed dose of the respective drug was given in a double-blind and double-dummy manner, initially intramuscularly and thereafter by sublingual buprenorphine (0.4 mg) or intramuscular pethidine (75 mg) at the request of the patient during the first 24 h postoperatively. Patients receiving buprenorphine had longer dose intervals and thus needed fewer doses. The analgesic effect, as assessed by a visual analog scale, was similar with both drugs. There were no significant differences between the groups regarding respiratory depression and nausea. It appears that sublingual buprenorphine is as effective and safe as intramuscular pethidine in the postoperative period.

[Tracheal tube obstruction caused by local anesthetic gel]. / Trakealtubestop forårsaget af lokalanalgesi-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.

A slide-rule for assessment of venous admixture.

Determination of venous admixture (physiological shunt, Qva/Qt) requires analysis of both arterial and mixed venous blood. When a pulmonary arterial catheter is not in use, the pulmonary oxygenating capacity may be assessed from arterial blood gas data, the fraction of inspired oxygen (FIO2) and an assumed value of the arterial-mixed venous oxygen content difference. To facilitate this process, a slide-rule based on the "virtual shunt" concept is presented. It permits rapid assessment of Qva/Qt from known values of arterial oxygen tension (PaO2) or saturation (SaO2) and FIO2 and may promote the choice of appropriate FIO2. The limitations of the slide-rule were studied theoretically and its validity was tested by comparing 100 determinations of virtual shunt with the corresponding Qva/Qt values. The slide-rule was found to estimate Qva/Qt more accurately than commonly used oxygenation indices such as the PaO2/FIO2 ratio.

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.

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.

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.

Assessment of the efficiency of pulmonary oxygenation. The choice of oxygenation index.

Oxygen-derived indices are often used as alternatives to determination of venous admixture (Qva/Qt) when a pulmonary arterial catheter is not in use, but the question of which more accurately indicates the efficiency of oxygenation is controversial. The theoretical relationships between six measures of oxygenation (PaO2, SaO2, P(A-a)O2, PaO2/FIO2, P(A-a)O2/PaO2, PaO2/PAO2) and venous admixture were analyzed with special reference to the influence of the concentration of inspired oxygen (FIO2). In addition, the predictability of Qva/Qt was evaluated on the basis of 100 authentic sets of arterial and mixed venous blood gas data. Of the above six indices, PaO2/FIO2 was most accurate (r = 0.88), but was far from independent of the FIO2 used. However, a direct Estimate of Venous Admixture (EVA) - based on arterial blood analysis and with C(a-v)O2 assigned a value of 50 ml.l-1 - predicted Qva/Qt still better (r = 0.95). It is concluded that when mixed venous blood gas data are lacking, EVA is the preferable measure of oxygenation.

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.

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)

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.

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.

A new nomogram facilitating adequate haemodilution.

When using deliberate haemodilution to a certain haematocrit value (Hct), the appropriate preoperative blood volume of the patient must be determined and matched with the transfusion volume at a certain blood loss. In order to facilitate such calculations a nomogram was constructed, aiming for a final Hct of 33%. Preoperative Hct, height, weight and sex of the patient are input variables. After drawing three straight lines, the nomogram yields the normal blood volume and the acceptable pre-transfusion blood loss (BL). This nomogram was used during surgery when the preoperative Hct exceeded 35%. Protocols from 100 patients bleeding more than 50% of their BL were studied. Blood loss was 1.1 +/- 0.6 1 (mean +/- s.d.) ranging from 0.4 to 4.0 1. Fifty-one of the patients received blood transfusion. This program resulted in a decrease of Hct (mean +/- s.d.) from 41 +/- 3% preoperatively to 33 +/- 4% during the first 30 min postoperatively. Sixty-three of the patients had a final Hct of 30-35%, 13 had 27-29% and one had 26%. The low values were most likely due to underestimation and consequent unsubstituted blood loss. In summary, the nomogram makes time-consuming mathematical operations unnecessary. It was easy to use and the postoperative Hct was close to that desired in most patients.