[Artificial respiration technics]

In general there are two distinguishable methods of artificial ventilation: assisted spontaneous ventilation and controlled ventilation. Spontaneous ventilation can be supported by CPAP or PEEP, in order to improve oxygenation, and by IMV to improve CO2 elimination. Furthermore, high frequency low pressure ventilation may be used versus low frequency high pressure ventilation. Conventional IPPV may be supported by continuous endexspiratory pressure. In special cases IRV may be applied. High frequency low pressure ventilation methods may be used intra- and postoperatively as well as post-traumatically.

Manipulation of ventilator settings to prevent active expiration against positive pressure inflation

Recent publications have suggested that in infants receiving artificial ventilatory support a particular pattern of interaction between spontaneous breaths and ventilator inflations (active expiration against each ventilator inflation) may be important in the production of pneumothoraces. We have looked at patterns of interaction from 47 preterm infants studied on 51 occasions. We found that active expiration against the ventilator occurred on a total of 16 occasions. This pattern was prevented on 14 occasions by altering the ventilator settings. In two other babies, the pattern persisted but neither baby developed a pneumothorax.

Controversies in the pathophysiology and fluid management of postoperative adult respiratory distress syndrome

Physiologic changes that lead to the development of ARDS begin with the precipitating shock syndrome. Hypovolemia, pulmonary vasoconstriction, reduced myocardial performance, and diminished O2 transport typically precede the development of clinical ARDS after hemorrhage, trauma, postoperative conditions, and sepsis. Since shock lung is a complication of shock, it is not surprising that the antecedent clinical and physiologic events that characterize the shock state may be determinants of both the genesis and the outcome of ARDS. Postoperative ARDS follows unrecognized or inadequately treated hypovolemia and hypoxia during an antecedent period of preoperative or intraoperative shock. Hypovolemia and hypoxia increase cardiac and ventilatory drive and stimulate neurohumoral mechanisms to increase pulmonary vasoconstriction. The last-named, when extensive and uneven, produces maldistribution of flow and reduces DO2 and VO2. Subsequently, mediator-induced pulmonary vasoconstriction increases the problem. When sufficiently extensive, these antecedent physiologic alterations culminate in ARDS. With impaired flow and O2 transport, pathogenic mechanisms of ARDS and acute renal failure may be set in motion; further, the naturally occurring immune mechanisms may be impaired and may lead to associated infection. There are at least six redistributions that are major pathophysiologic influences in ARDS. They are uneven ventilation throughout the lung; redistribution of regional pulmonary blood flow between zones due to gravity; nonuniform pulmonary blood flow between individual metarteriolar-capillary networks because of local vasoconstriction; uneven systemic blood flow between organs; irregular systemic blood flow at the microcirculatory level, producing inadequate nutritional flow to the tissues; and redistribution of body water, leading particularly to fluid accumulation in the extracellular compartment, with expanded interstitial space and contracted plasma volume (hypovolemia). Pathogenic roles have been implicated for capillary leak, surfactant synthesis, erythrocyte and platelet aggregation, leukocyte margination in the pulmonary circulation, complement and kinin cascades, neurohumoral responses, histamine, serotonin, vasoactive peptides, and the metabolic products of arachidonic acid breakdown in pulmonary vessels. However, these potential pathogenic influences have yet to be described in terms of their temporal relationships to the natural physiologic history of ARDS; nor have their roles been evaluated in terms of mechanistic interrelationships.(ABSTRACT TRUNCATED AT 400 WORDS)

Prevention of gastric inflation during mask ventilation in newborn infants

Ten premature infants who had recovered from the respiratory distress syndrome were subjected to cricoid compression during mask ventilation. Each infant was ventilated with an AMBU face mask for 3 min with the nasogastric (NG) tube, without the NG tube, and without the NG tube but applying cricoid pressure during ventilation. The results of the study indicated that, similar to insertion of an NG tube, cricoid compression can prevent gastric inflation during mask ventilation.

[2-frequency artificial respiration--a new therapeutic concept]

A new respiration system is described. The system has been developed for the therapy of very ill newborn and premature infants (RDS stage IV, gestation age less than 28 weeks, severe pneumonia etc.). The special feature of the new respiratory device is an alternating between cycles with low frequencies and relatively high amplitudes, and breathes with low amplitudes and relatively high frequencies.

Alternative modes of ventilation. Part I. Disadvantages of controlled mechanical ventilation: intermittent mandatory ventilation

Controlled mechanical ventilation is an accepted therapy for acute respiratory failure but by virtue of the increase in intrathoracic pressure has a large number of disadvantages. It is to overcome these disadvantages that alternative modes of ventilation have been introduced. These aim to reduce the effects of abnormally high airway pressure on the lung whilst recruiting solid alveoli and at the same time maintaining effective blood volume. Intermittent mandatory ventilation is a mode of ventilation first introduced to aid weaning which may reduce the need for sedation, permit better tolerance of high levels of PEEP and maintain urine osmolar output. High frequency ventilation utilising low airway pressures can maintain pulmonary gas exchange whilst reducing the effects of stretch on the lung. Its major role would seem to be in cases of bronchopleural fistula and necrotising pneumonia where a low mean airway pressure is essential. Low frequency positive pressure ventilation with extra corporeal CO2 removal, whilst a very labour intensive technique, has produced a favourable outcome in patients with terminal respiratory failure. Use of PEEP is associated with further deleterious haemodynamic effects which are largely overcome with use of continuous positive airway pressure during spontaneous respiration. PEEP is widely used. Its effect on pulmonary compliance, dead space and oxygen delivery are unpredictable making haemodynamic monitoring mandatory. Inversed ratio ventilation requires further evaluation whereas differential lung ventilation is logical, complicated but very valuable where the time constants for each lung are significantly different.

Use of mechanical ventilation in adults with severe asthma

Asthma severe enough to require intubation and mechanical ventilation is associated with a mortality rate of about 10%. Therapeutic modalities are ever-changing and at times controversial. This paper provides an update on such modalities and presents, in a step-wise fashion, those most appropriate for practical patient care. The timing of intubation and the methods used to control airway patency, arterial pH and gas levels, and hemodynamic status are crucial to the success of therapy. Finally, conventional and disputed methods of bronchodilation are outlined.

Differential ventilation in acute bilateral lung disease. Influence on gas exchange and central haemodynamics

Eight patients with acute respiratory failure (ARF) due to diffuse and rather uniform lung disease were intubated with a double-lumen bronchial tube and ventilated in the lateral decubital position by two synchronized ventilators. Ventilation of each lung was individually adjusted to match the expected regional blood flow (differential ventilation). When ventilation with equal volumes (i.e. 50% of tidal volume to each lung) was performed, a 19% reduction of venous admixture (P less than 0.001) and a 22% increment in arterial oxygen tension (P less than 0.001) were seen. Comcomitantly, the cardiac output increased by 17% (P less than 0.001), to which a reduced pulmonary vascular resistance may have contributed. The net result was a 14% increment of the oxygen availability (P less than 0.001). An attempt to go further, giving 2/3 of the tidal ventilation to the dependent lung, was made on six of the patients. However, this ventilatory pattern did not further improve the gas exchange and also had detrimental effects on the haemodynamics. It is concluded that differential ventilation with equal tidal volumes in the lateral position can substantially improve gas exchange and central haemodynamics in patients with ARF due to diffuse lung disease.

The effect of instrumentation with a telescope during bronchoscopy on arterial oxygen tension and acid-base balance

The effect of instrumentation with a telescope during bronchoscopy on the arterial oxygen tension and acid-base status was studied in 17 unselected, anaesthetized patients using a ventilating technique based on Sanders' method (1). After ventilating the patients with a bronchoscope and a telescope in the trachea, in the left main bronchus or in the right main bronchus, the PaO2 value was always statistically significantly higher than after ventilating only with a bronchoscope. During the course of the bronchoscopy as well as after 1 h in the recovery room, the arterial acid-base status was within normal limits and the mean PaO2 value during bronchoscopy ranged from 175 to 240 mmHg (23.3-31.9 kPa) and was 138 mmHg (18.4 kPa) in the recovery room when the patients breathed about 35% oxygen in air. The present results suggest that instrumentation with a telescope during bronchoscopy ameliorates rather than impairs the ventilation and oxygenation of the patients.

Effect of intermittent mandatory ventilation on respiratory drive and timing

Seven patients receiving chronic ventilatory support were studied to better define the effects of intermittent mandatory ventilation (IMV) on the control and timing of spontaneous breathing between mandatory breaths. Each of these patients could sustain adequate spontaneous ventilation, as reflected by stable end-tidal carbon dioxide concentration (FETCO2), and arterial oxygen saturation (SO2) during periods of unassisted ventilation of sufficient duration to allow study. Inspiratory time (TI), respiratory cycle duration (Ttot), tidal volume (VT), and tracheal occlusion pressure (P0.1) were measured as IMV rate was progressively reduced. Respiratory timing was unaltered by decreasing IMV frequency; however, VT increased progressively. The P0.1 and mean inspiratory flow rate (VT/TI) also increased with each decrease in IMV rate, whereas FETCO2 and arterial SO2 remained constant. Thus, in these stable but ventilator-dependent patients, IMV did not alter respiratory timing or chemical stimuli, but it did alter respiratory drive as measured by VT/TI and P0.1.

Effects of inspiratory pressure oscillation on pulmonary gas exchange and circulatory functions in anesthetized, mechanically ventilated dogs

Anesthetized, mechanically ventilated dogs were used to study the effects of inspiratory pressure oscillation on gas exchange. Respiratory failure was induced in dogs artificially, changing either tidal volume or ventilatory rate. Pressure oscillation of approximately 2 Hz with amplitudes of 2 to 7 cmH2O was applied on the inspiratory phase of mechanical ventilation. PaO2 and PaCO2 were improved consistently by pressure oscillation while minute ventilation was kept fixed. No significant change was observed in AaDO2, cardiac output, heart rate, ECG and both systemic and pulmonary arterial pressures under oscillated ventilation. The oscillated ventilation could be continued for more than 60 minutes without causing any significant change in circulatory function. The ratio of alveolar ventilation to minute ventilation (VA/VE) increased and that of dead space to tidal volume (VD/VT) decreased significantly. The oscillated ventilation while breathing He-O2 and SF6-O2 showed no consistent difference in the effects on gas exchange. It can be concluded that simple pressure oscillation improves gas mixing in the lungs and may be applied to respiratory care. However the mechanism remains to be elucidated.

Occult positive end-expiratory pressure in mechanically ventilated patients with airflow obstruction: the auto-PEEP effect

Alveolar pressure can remain positive throughout the ventilatory cycle of mechanically-ventilated patients with airflow obstruction, even when positive end-expiratory pressure (PEEP) is not applied intentionally. The increase of intrathoracic pressure associated with this "auto-PEEP" phenomenon can severely depress cardiac output as well as elevate the end-expiratory pulmonary artery wedge pressure. Such effects may be exaggerated in patients with chronic obstructive pulmonary disease because abnormally compliant lungs transmit a high fraction of alveolar pressure to intrathoracic vessels. Failure to recognize the hemodynamic consequences of auto-PEEP may lead to inappropriate fluid restriction or unnecessary vasopressor therapy. Although not apparent during normal ventilator operation, the auto-PEEP effect can be detected and quantified by a simple bedside maneuver: expiratory port occlusion at the end of the set exhalation period.

Optimal endexpiratory airway pressure for ventilated patients

In patients ventilated for acute respiratory failure PEEP was changed either by gradual increase and decrease (5 cm H2O/min) or in steps of 5 cm H2O. The effects on gas exchange, pulmonary mechanics and pulmonary and systemic circulation were studied. Total compliance did not change uniformly and cardiac index decreased so much due to PEEP that the increase in PaO2 could not prevent the decrease of arterial oxygen transport. No variable was found helpful to predict the "best PEEP" in a clinical situation.

Does intermittent mandatory ventilation accelerate weaning?

Intermittent mandatory ventilation (IMV) was introduced to facilitate the weaning of patients from mechanical ventilation. The outcome of ventilator management in 116 patients who were treated in the first three months of 1975 was compared retrospectively with that of 135 patients who were treated in the first three months of 1976. All patients who were treated in 1975 received conventional (assisted or controlled) mechanical ventilation. In 1976, seventy-seven patients (57%) were treated with the use of IMV, and 58 (43%) were treated with the use of conventional mechanical ventilation. Sixty-five patients who were treated in 1976 with the use of IMV were matched with patients who were treated in 1975 with the use of conventional ventilation, on the basis of age, sex, race, history of pulmonary disease, smoking history, diagnosis, service, and location of therapy. The average time spent on a ventilator by the IMV patients was 145 hours, whereas the matched control patients spent 142 hours. The length of hospitalization was 36 days for the IMV patients and 30 days for the control patients. These time periods were not significantly different and indicate that IMV did not reduce the length of ventilator management.

[Respiratory training with intermittent positive pressure in acute respiratory disturbances (author's transl)]

In a clinical study the applicability and effectiveness of breathing therapy with intermittent positive pressure in cases of incipient or already established pulmonary complications are evaluated. The case material was divided into four groups: 1. Imminent respiratory complications (haemorrhagic shock, flail chest); 2. acute postoperative pulmonary insufficiency in old patients; 3. postoperative alveolar or interstitial pulmonary oedema; 4. postoperative pneumonia. Individual respiratory training succeeded in all patients in significantly improving the arterial blood gases; prolonged artificial ventilation could be dispensed with. The method and its limitations and indications for its use are reviewed.

Factors contributing to a reduction in anaesthetic mortality

A substantial improvement in anaesthetic mortality has been noted at Coronation Hospital; the reasons for this are discussed. The factors considered include lethal circumstances associated with the use of suxamethonium and fentanyl; improved ventilation monitoring and postanaesthetic surveillance; a technique in the resuscitation of bleeding patients aimed at conserving the intravascular contents; and the management of dehydrated patients. The dangers associated with the induction of anaesthesia in a head-up position are considered and alternated means are suggested.

[Development of a s-IMV-technique for Bird apparatus (author's transl)]

We have developed our IMV-technique described previously to a s-IMV-technique. The principle of this s-IMV-technique is the following: it is necessary to equip two Bird Mark 7 machines with a special system of tubes. Then, an additional inspiratory volume is exactly given with the inspiration, triggered by the patient. for this purpose we constructed an electronic set which is able to recognize the spontaneous breathing of the patient by means of a thermistor and a bedside monitor. Then, more frequency variable inspiration volumes are applied exactly with the breathing of the patient. The adaptation of this apparatus to the patient is reached by impressing of a red stylus (on the left side of the Bird) by an electromagnet according to the inspiration of the patient. With this method it is possible to vary the treatment of patients with respiratory insufficiency, for instance, controlled artificial respiration, s-IMV up to spontaneous breathing. The F.I.O2 of the inspired gas can be chosen and lies between 9,21 and 1,0. CPAP and PEEP are possible.

A follow-up study of very low-birthweight infants receiving ventilatory support by face mask

Recent evidence has suggested that face-mask ventilation of very low birthweight (VLBW) infants may have serious neurological consequences. The 30 surviving VLBW infants from the neonatal intensive care unit at Hammersmith Hospital who had received ventilatory support via face masks over a 25-month period have been reviewed and compared with a control group. Neuropathological findings in the VLBW infants who died during this time have also been reviewed in relation to their ventilatory management. The findings suggest that face-mask treament did not have a major deleterious effect on the surviving infants. The factors which may determine the neurological sequelae of this form of ventilatory support are discussed.

Artificial ventilation of premature newborn rabbits: effects of positive end-expiratory pressure on lung mechanics and lung morphology

44 premature newborn rabbits, removed by hysterotomy on day 27 of gestation, were ventilated with positive pressure under differing standardized conditions, with or without application of positive end-expiratory pressure (PEEP; 5 cm H2O). After 10 min ventilation, compliance of the lung-thorax system was significantly higher in fetuses ventilated with PEEP than in controls. The application of PEEP also resulted in a significantly lower maximal expiratory air flow compared to controls in groups ventilated with standardized tidal volume. Morphometric evaluation revealed bronchiolar epithelial lesions to be less prominent in fetuses treated with PEEP. Our findings show that application of PEEP has a beneficial effect on lung mechanics during artificial ventilation and that it reduces the risk of epithelial damage to the airways, presumably by promoting uniform expansion of the lung parenchyma.

Effect of positive-end-expiratory-pressure on right ventricular output in lambs with hyaline membrane disease

Right and left ventricular outputs, pulmonary and systemic blood flows, and blood flows in both directions through the ductus arteriosus were measured before and during positive-end-expiratory-pressure in 5 premature lambs with induced hyaline membrane disease. During positive-end-expiratory-pressure, right ventricular output increased in all lambs without any significant change in left ventricular output or pulmonary vascular resistance. Left-to-right ductus flow decreased in lambs which initially had large left-to-right ductus shunts. significant right-to-left ductus flow did not occur before or during positive-end-expiratory-pressure.

Treatment of acute respiratory failure with low-frequency positive-pressure ventilation and extracorporeal removal of CO2

Terminal respiratory failure was reversed in three patients with a combination of extra-corporeal CO2 removal through a membrane lung and oxygen diffusion into the diseased lungs between mechanical breaths induced at a frequency of 2-3/min. The technique seems to prevent the pulmonary barotrauma and extrapulmonary derangements caused by conventional mechanical ventilation.

Cardiorespiratory effects of high frequency intermittent positive pressure ventilation in the dog

The cardiorespiratory effects of increasing respiratory frequency were investigated in two groups of dogs ventilated mechanically with a system which minimized apparatus and anatomical deadspace. In one group minute volume was constant whilst frequency was increased; in the second group minute volume was increased to maintain normal PaCO2. The reduction in tidal volume with increasing frequency was accompanied by a reduction in physiological deadspace. However, the reduction in deadspace was proportionally less than the decrease in tidal volume, so that the deadspace/tidal volume ratio increased. The peak airway pressures were minimal at a frequency of 45 b.p.m. At frequencies of 60 b.p.m. and more, the lung failed to empty so that peak airway pressures were increased and cardiac output decreased.

Evaluation of mechanical ventilation in newborn infants. II. Pulmonary and neuro-developmental sequelae in relation to original diagnosis

The incidence of bronchopulmonary dysplasia (BPD) and neuro-developmental sequelae in 135 infants surviving intermittent positive pressure ventilation (IPPV) in the newborn period were studied in relation to primary disorders requiring IPPV. The rate of BPD increased over the 6-year study period in hyaline membrane disease survivors from 14% to 28%, but decreased in infants with apnoea repetens from 38% to 13%. Immaturity seemed to be one important factor for development of BPD. The incidence of neuro-developmental sequelae in IPPV treated infants fell from 22% to 13% over the years. In infants with birth weight below 1501 g the rate of neurological handicaps was 11%.

Evaluation of mechanical ventilation in newborn infants. I. Techniques and survival rates

The short-term outcome with survival rate, causes of death and neonatal complications in a 6-year material comprising 253 infants treated with intermittent positive pressure ventilation (IPPV) in the neonatal period has been analyzed in relation to different primary disorders necessitating IPPV treatment. The total survival rate was 53%. For the different diagnoses the survival rates were: hyaline membrane disease (HMD) 41%, apnoea repetens of immaturity 85%, severe birth asphyxia 46% and septicemia 59%. The total rate of pneumothorax during IPPV was 15% but occurred more often in the HMD group (28%). Trends in survival rates over the study period are discussed as are measurements for improvements.

Intermittent mandatory ventilation and weaning

Oxygen, PEEP, and mechanical ventilatory therapy should be administered to patients in varying amounts and should be removed gradually and independently. The method of determining optimal PEEP, oxygen, and ventilation is not unlike that recommended for many other therapies. Nine years of prospective evaluation have demonstrated the numerous clinical advantages of this technique, and relatively few complications have been associated with it. Reduced FIO2 may promote resistance to atelectasis and allow rapid discontinuation of mechanical ventilation and PEEP. Similarly, optimal levels of PEEP may improve matching of ventilation and perfusion and assist lung mechanics so that FIO2 and mechanical ventilation may be reduced. Minimal mechanical ventilatory support eliminates iatrogenic respiratory alkalosis, and weaning from ventilatory support may be initiated early. This, in turn, minimizes the detrimental effects of mechanical ventilation on acid-base balance and cardiovascular function, as well as lessening barotrauma. We think that this approach has simplified the clinical management of patients with compromised repiratory function and decreased their mortality.