O. Norlander

Airway Closure and Distribution of Inspired Gas in the Extremely Obese, Breathing Spontaneously and During Anaesthesia with Intermittent Positive Pressure Ventilation

Airway closure (closing capacity, CC), FRC, total efficiency of ventilation (lung clearance index, LCI) and distribution of inspired gas (nitrogen washout delay percentage, NWOD) were determined by nitrogen washout techniques and arterial Po2 and Pco2 measured by standard electrodes in 10 extremely obese subjects, prior to and during anaesthesia and artificial ventilation. CC was normal, but because of small FRC, airway closure occurred within a tidal breath in 9 out of 10 subjects during spontaneous breathing, when awake. Po2 was reduced, the hypoxaemia correlating to the magnitude of airway closure. LCI was normal, but NWOD was borderline. During anaesthesia, CC was unaltered but FRC was further reduced, so that in nine subjects airway closure occurred above FRC and tidal volume together. A marked increase in relative hypoxaemia was recorded. LCI and NWOD rose, indicating less efficient and less even ventilation. It is concluded that airway closure reasonably explains the marked hypoxaemia in obese subjects during anaesthesia, and that it may also be the reason for the uneven distribution of inspired gas.

PULMONARY FUNCTION IN RELATION TO ANESTHESIA AND SURGERY EVALUATED BY ANALYSIS OF OXYGEN TENSION OF ARTERIAL BLOOD

Major abdominal surgery may in its postoperative course be associated with changes leading to decreased oxygen saturation of arterial blood (L. TROELL (1951)24, A. CAKLSTEN, 0. NORLANDER and L. TROELL (1954)9). There are several possible explanations for this finding, but a more extensive analysis of its cause has not been made. Hypoventilation, postoperatively, due to pain, immobilization and the use of respiratory depressive drugs has been assumed (L. KLOTZ and T. STRAATEN (1931)14), but S. BRATTSTROM ( 1954)8 was not able to demonstrate hypoventilation in any of his 210 patients studied during the postoperative period up to seven days after abdominal surgery. Neither did he find any significant disturbance of gas mixing in the lungs, using the nitrogen elimination method. H. LINDERHOLM and 0. NORLANDER ( 1958)l8 analyzed carbon dioxide tension of arterial blood, and the values indicated sufficient alveolar ventilation 24 hours after anesthesia and surgery, while a few hours after anesthesia there was a slight tendency to hypoventilation in some cases. Shunts in the lungs due to atelectasis is a probable explanation of the arterial hypoxemia, particularly as atelectasis has been observed on chest roentgenograms in the postoperative course. Thus, P. STRINGER (1947)22 reported pulmonary complications in 47 per cent within 24 hours after gastric resection under spinal anesthesia in a series of 55 patients. Similar figures were found by F. KOCH and 0. AXBN (1951)15 on the sixth to seventh postoperative day. L. THORBN ( 1954)23 and S. RRATTSTR~M ( 1954)8 both observed pulmonary complications in 42 to 50 per cent on the fourth postoperative day. Low vmtilationlblood jlow ratios in some parts of the lungs may occur postoperatively and cause decreased oxygen saturation of arterial blood without

Airway Closure During Anaesthesia, and its Prevention by Positive End Expiratory Pressure

Airway closure, functional residual capacity (FRC) and the transpulmonary pressure volume relationship of each lung were studied in the anaesthetized subject in the supine and the left lateral positions. In the supine posture, FRC was of approximately the same size in each lung as was closing capacity (CC). CC exceeded FRC in either lung. In the left lateral position, FRC was increased by 0.91 in the non‐dependent lung and was reduced by 0.2 1 in the dependent lung, while CC was unaltered in either lung. Consequently, FRC exceeded CC in the non‐dependent lung and was further lowered beneath CC in the dependent lung. Airway closure did not occur in the non‐dependent lung until an average of 0.51 of gas had been expelled after the dependent lung had ceased to empty. The addition of positive end‐expiratory pressure (PEEP) in the range 0.5–2 kPa, increased FRC more in the non‐dependent than the dependent lung. The findings suggest that airway closure is evenly distributed in the horizontal level, while it has a discontinuous distribution between the dependent and non‐dependent lung. Moreover, the increase in lung volume caused by PEEP has a distribution that is by no means ideal for the purpose of countering airway closure.

A NEW METHOD FOR ANALYSIS OF RESPIRATORY WORK BY MEASUREMENTS OF THE ACTUAL POWER AS A FUNCTION OF GAS FLOW, PRESSURE AND TIME: A Preliminary Report

A method is presented by which it is possible to analyse the respiratory work by measurements of the actual power as a function of gas flow, pressure and time.

A PRECISION METHOD FOR THE DYNAMIC VOLUME-FLOW CALIBRATION DURING PNEUMOTACHOGRAPHY

Pneumotachography, a method introduced by A. FLEISCH~ in 1925, is a valuable tool for measurements of respiratory gas-flows under various conditions. The combination of pneumotachography with pressure-measurements over the lungs and airways gives information of lung-mechanics. Furthermore, the method can with advantage be used for performance analysis of mechanical respirators (0. Norlander ( 1964) 3). Principally the pneumotachograph is a flow-resistive tube, in which the pressure-fall is measured between two points of the tube under conditions of laminar gas-flow. Under those conditions, the pressure-fall is directly proportional to the distance between the measuring points, to the viscosity of the gas and inversely proportional to the fourth power of the radius of the tube, according to the following equation :

Regional Differences in Lung Function during Anaesthesia and Intensive Care: Clinical Implications

Anaesthesia and most frequently acute respiratory failure are accompanied by a lowered functional residual capacity (FRC). This lowering promotes airway closure in dependent lung units and forces ventilation to non‐dependent regions. Perfusion, on the other hand, is forced towards dependent lung units. A ventilalion‐perfusion mismatch is created and hypoxaemia may develop. General PEEP counters airway closure, but impedes cardiac output and forces perfusion further to dependent regions. In addition, barotrauma may occur. Improved matching of ventilation and perfusion can be achieved by: 1 positioning the subject in the lateral posture; 2 ventilating each lung separately in proportion to its perfusion (differential ventilation); and 3 applying PEEP only to the dependent lung (selective PEEP). Because of less overall intrathoracic pressure and lung expansion, interference with the total lung blood How and the danger of barotrauma should be less than with general PEEP. Improved gas exchange with a 50–100% increase in PaO2 has been observed in a limited number of patients with acute bilateral lung disease studied so far during differential ventilation and selective PEEP.

ANESTHESIOLOGICAL EXPERIENCE FROM INTRACARDIAC SURGERY WITH THE CRAFOORD‐SENNING HEART‐LUNG MACHINE

Intracardiac procedures with the aid of cardiopulmonary bypass are nowadays common, especially in the United States. The use of extracorporeal circulation involves many branches of medicine, among which anesthesiology plays an important r81e. However, relatively few publications pertaining to this field of anesthesia have been published, and information on anesthesiological problems related to extracorporeal circulation has mostly been given in the form of personal communications or in occasional reviews (D. MENDELSOHN, T. N. MACKRELL, M. A. MACLACHLAN, F. S. CROSS and E. B. KAY (1957)27; D. E. HALE, P. MORACA and C. E. WASMUTH (1957)19; R. T. PATRICK, R. A. THEYE and E. A. MOFITT (1957y). As the clinical use of heart-lung machines was started in Stockholm in 1954 by c. CRAFOORD and A. SENNING~~, we have thought it may be of interest to give an account of our anesthetic procedures and related investigations on 52 consecutive patients operated upon from November 1957 to July 1958 at the new Thoracic Clinics. I t is also the purpose of this paper to give the results of some investigations on acid-base changes before, during and after bypass.-An important factor in the regulation of the acid-base equilibrium is the adjustment of ventilation, and as we have found controlled respiration with a mechanical, volume-cycled respirator useful during anesthesia as well as postoperatively in many patients who have had extracorporeal circulation, our technique, indications and results from this type of ventilation will also be outlined.

Effects Of Carbon Dioxide And Halothane On Compliance And Pulmonary Resistance During Cardio-Pulmonary Bypass

Lung-mechanics during and at the end of cardio-pulmonary bypass were studied in seventeen patients operated upon for acquired or congenital heart disease. Pulmonary resistance to gasflow, volume-pressure ratios and work of breathing were continuously measured with the aid of a respiratory analogue computer. A special calibrating device was used for frequent calibrations with the patients respiratory gas. Measurements were made at constant blood gas tensions but with varying fractions of inspired carbon dioxide. The effect of halothane as well as the influence of the patients circulatory situation were analysed. Hypocapnia of the airways resulted in an increase in pulmonary resistance, while ventilation with a 6.5% carbon dioxide mixture in air-oxygen caused a decrease in resistance with 19 to 71% as compared to hypocapnic conditions. An increase of compliance occurred in the majority of the patients with carbon dioxide. Compliance was generally relatively uninfluenced during the operative and postoperat...

VENTILATORY AND CIRCULATORY EFFECTS OF ANAESTHESIA AND CARDIOPULMONARY BYPASS

Sixteen patients scheduled for open‐heart surgery were studied before, during and after cardiopulmonary bypass. Measurements were made of oxygen uptake, cardiac output, physiological dead space, blood‐gas tension, acid balance, peripheral vascular resistance and lung‐chest compliance. Anaesthesia was maintained with fentanyl and small concentrations of halothane. Oxygen uptake was higher than predicted values and was not influenced by anaesthesia and controlled ventilation. The uptake after cardiopulmonary bypass did not show any significant changes in comparison with preperfusion values. However, there was a significant increase at the end of anaesthesia and surgery. This can probably be attributed to the anaesthetic technique used with the light level of analgesia at the end of the procedures. Cardiac output showed only minor variations with no significant changes associated with the surgical procedures. Arterial mean blood pressure was stable with only minor variations within the range of 64‐80 mm Hg as measured before, during and after bypass. Blood gases showed only small variations and buffer‐base did not undergo any important changes. Alveolo‐arterial oxygen tension differences varied between 370‐439 mm Hg, corresponding to a venous admixture of 18‐24 per cent. There were no significant changes between the different periods of investigation. When calculating alveolar ventilation, physiological dead space and VD/VT ratios, an equation for the correction of the influence of venous admixture on Pcoa was taken into account. Significantly lower Pcog levels for all periods of determinations as compared with actually measured values were obtained. The values for VA, VD and VD/VT were significantly lower immediately before and after bypass as compared with non‐corrected values. The VD/VT ratios were virtually constant, varying between 0.47 and 0.5. Peripheral resistance did not change before and after bypass. During bypass there was a significant increase in peripheral resistance in the hypothermia group. Volume‐pressure changes of the lungs and chest varied between 27 and 39 ml/cm H20 with the highest values when the chest was open. At the end of anaesthesia there was a significant decrease in compliance. This decrease was not associated with an increase in alveolo‐arterial oxygen‐tension differences or on an increased venous admixture. In two patients, the decrease was probably due to left‐heart failure. In the other patients, the decrease might be explained by increased muscular tonus, where a contributory factor might have been the use of fentanyl. In comparison with our earlier experience of anaesthesia, where halodiane was the principal agent, the use of more analgesics and less halothane seems to have certain clinical advantages as regard a more stable circulation. However, there were no differences of major importance as compared with our previous findings. It is our opinion that low concentrations of inspired halothane provide a smooth and balanced anaesthesia level, counteracting to a certain extent peripheral vasoconstriction, as demonstrated in this series. The increased oxygen uptake observed at the end of the procedures in this series may be a disadvantage, as it is associated with a higher demand on circulatory and respiratory reserves.

CLINICAL EXPERIENCE OF A DISC OXYGENATOR WITH AUTOMATIC BLOOD LEVEL REGULATION

Three hundred and sixty-one cases of open-heart surgery undergoing perfusion with the AGA-Bjork disc oxygenator and 22 cases with a disposable bubble oxygenator have been analysed regarding blood trauma and oxygenating performance. The haemolysis reached a level of 61 mg% plasma haemoglobin after more than 4 hours of perfusion with the disc oxygenator. The bubble oxygenator caused a haemolysis of a significantly higher degree. No oxygen debt was found in the patients at the end of perfusion with the disc oxygenator. Blood gas values and acid base data were within normal and expected ranges for the disc oxygenator.