Principles of artificial ventilation

The application of intermittent positive pressure ventilation (IPPV) during the 1952 Copenhagen polio epidemic led to the development of the world’s first intensive care unit. The requirement for ventilatory support is the most common indication for intensive therapy unit (ITU) admission and is a defining feature of the specialty. Ventilator technology continues to develop and there are many ways to deliver IPPV. The variety of modes of ventilation is increasingly complex and expanding, without evidence that any one mode is associated with improved outcome. Ventilatory support is part of the treatment for a range of conditions including acute respiratory failure, raised intracranial pressure (ICP) and circulatory shock. Ventilator-associated lung injury is reduced by using low tidal volumes and limiting plateau airway pressure to less than 30 cmH₂O. Prolonged artificial ventilation has an associated morbidity and mortality and thus should be reviewed by an expert clinician on a daily basis. Weaning aims to identify those patients who will be able to breathe spontaneously. Protocols exist to facilitate timely extubation without the need for re-intubation.     

Hemodynamic effects of high frequency ventilation superimposed on intermittent positive pressure ventilation in dogs

The hemodynamic effects of high frequency ventilation (HFV) superimposed on intermittent positive pressure ventilation (IPPV) in seven dogs before and after thrombin infusion were investigated. HFV was superimposed on a Servo 900 B ventilator by a Siemens Elema HFV prototype unit. Mean arterial blood pressure, heart rate, central venous pressure, pulmonary artery pressure, cardiac output, right and left ventricular pressures, pleural pressure, arterial blood gases, and right and left ventricular ejection fractions were recorded. Measurements were done during IPPV alone and during HFV superimposed on IPPV. The HFV frequencies were 5, 15, and 20 Hz at a constant minute volume of 5 1. When HFV was started, the IPPV minute volume was reduced to one third of the initial volume. No significant changes in the measured parameters were observed during the different ventilatory modes either before or after thrombin infusion which doubled the pulmonary vascular resistance. It is concluded that high frequency ventilation superimposed on IPPV might be a ventilatory mode that offers cardiovascular stability and reduces the risk of barotrauma.     

CPAP, effective respiratory support in patients with AIDS-related Pneumocystis carinii pneumonia.

Human Immunodeficiency Virus (HIV) related Pneumocystis carinii pneumonia (PCP) associated with severe respiratory failure is an increasingly common problem in major centres and is associated with a high mortality in previous and recent studies. Early in the epidemic, alternatives to invasive intensive care treatment were utilized in our institution and found to be successful. When respiratory failure developed, mask CPAP was used instead of intubation and ventilation. A retrospective review of 175 cases of HIV infected patients with confirmed first presentation PCP was undertaken. Treatment with our protocol resulted in an overall hospital mortality of 9%. Those patients who did not require supplemental oxygen or respiratory support had no in-hospital mortality. The group who required supplemental oxygen had a mortality of 10%. If respiratory failure supervened (severe respiratory distress, PaO2 less than 50 mmHg, SaO2 less than 90% on mask oxygen), CPAP was introduced. The mortality in this group was 22%. Only two patients were admitted to the intensive care unit for respiratory support after failure of CPAP. Both patients were intubated and received intermittent positive pressure ventilation (IPPV). Both patients died.     

Effects of continuous negative extrathoracic pressure ventilation on left ventricular dimensions and hemodynamics in dogs

It has been reported that continuous negative extrathoracic pressure ventilation (CNETPV) depresses cardiac output less than continuous positive pressure ventilation (CPPV) does, and this difference may be related to the different effects of two ventilatory modes on preload. We performed simultaneous measurements of hemodynamics and left ventricular short axis dimensions by transesophageal echocardiography (TEE) to evaluate left ventricular preload and function during CNETPV and CPPV in normal dogs.Hemodynamic measurements and simultaneous TEE recording were performed at 5 successive periods; 1) the first control period of intermittent positive pressure ventilation (IPPV1), 2) CNETPV with negative end-expiratory pressure (NEEP) of –10cmH₂O (CNET10), 3) CNETPV with NEEP of –15cmH₂O (CNET15), 4) the second control period of IPPV (IPPV2), and 5) CPPV with PEEP of 15cmH₂O (CPPV15). Left ventricular end-systolic and end-diastolic dimension (LVESD and LVEDD), ejection fraction (EF) and fractional shortening (FS) were measured from TEE recordings.Both CNET10 and CNET15 induced no significant changes in hemodynamics and left ventricular dimensions, compared with those during IPPV1. However, CPPV15 reduced cardiac output and stroke volume (SV) and increased heart rate significantly, compared with IPPV2. CPPV15 significantly decreased LVEDD compared with IPPV2. Neither EF nor FS showed any significant change throughout the experiment.These results indicate that CNETPV preserved cardiac output because it maintained the preload and the left ventricular function.(Andoh T, Doi H, Kudoh I, et al.: Effects of continuous negative extrathoracic pressure ventilation on left ventricular dimensions and hemodynamics in dogs. J Anesth 7: 308–315, 1993)     

急性呼吸窘迫综合征患者适应性支持通气的效果

目的 评价适应性支持通气（ASV）模式与间歇正压通气（IPPV）模式在急性呼吸窘迫综合征（ARDS）患者中的效果。方法 ARDS患者30例，年龄19—46岁，男18例，女12例，ASAⅢ或Ⅳ级。先应用IPPV模式，吸入氧浓度60％，PEEP为0，潮气量（VT）10ml／kg，吸呼比（I：E）1：2，维持8h后随机选择换用ASV或继续IPPV通气模式，通气时依次按0、5、10cm H2O增加PEEP，每一PEEP水平的通气时间为60min，在同样的分钟通气量的设置下，4h后更换另一种通气模式，仍按0,5、10cm H2O增加PEEP，每一PEEP水平的通气时间为60min。每个PEEP水平通气50min时，用Swan-Ganz导管、心电监测仪、呼吸机监测记录血液动力学、呼吸力学和氧代谢数据。结果 与IPPV模式比较，ASV模式下气道峰值压降低，肺动态顺应性（Cdyn）、动脉氧分压（PaO2）和氧供（DO2）增加（P〈0．05）。两种通气模式的血液动力学参数比较差异无统计学意义（P〉0．05）。结论 ASV模式比IPPV模式更有利于ARDS患者的通气治疗。     

Diaphragmatic dysfunction after pediatric orthotopic liver transplantation

BACKGROUND: Pediatric orthotopic liver transplantation (OLT) has a low mortality. Some children, however, have an adverse outcome defined as a prolonged ventilatory support requirement and protracted pediatric intensive care unit (PICU) stay. The aim of this study was to determine if that adverse outcome related to the child's condition pre-OLT and/or the development of a pleural effusion or diaphragmatic dysfunction. METHODS: The study included 210 children with a median age at transplantation of 45.5 months (range 0.2-252 months). Fourteen had undergone retransplantation. The duration of ventilatory support (intermittent positive pressure ventilation [IPPV]) and PICU admission and development of a pleural effusion and/or diaphragmatic dysfunction were documented for each child. The patients were divided into three groups according to whether they had acute liver failure (ALF), chronic liver disease at home (CHOM), or chronic liver failure sufficiently ill to be in the hospital awaiting transplantation (CHOSP). RESULTS: The 36 children with ALF were of similar age to the 138 CHOM and 36 CHOSP children but required longer IPPV (P<0.0001) and PICU stay (P<0.0001). Overall, 17 children developed diaphragmatic dysfunction and 138 pleural effusions; affected children required longer IPPV and PICU stay (P<0.01). Regression analysis demonstrated that diaphragmatic dysfunction, but not pleural effusion development, was associated with prolonged ventilation (P<0.01) and protracted PICU stay (P<0.05). Other risk factors were ALF (P<0.01), retransplantation (P<0.01), and young age (P<0.05). CONCLUSION: Diaphragmatic dysfunction adversely influences PICU morbidity after OLT. Early assessment of diaphragmatic function, and if necessary aggressive management, might improve outcome.     

Fatal pulmonary haemorrhage during anaesthesia for bronchial artery embolization in cystic fibrosis.

Three children with cystic fibrosis (CF) had significant pulmonary haemorrhage during anaesthetic induction prior to bronchial artery embolization (BAE). Haemorrhage was associated with rapid clinical deterioration and subsequent early death. We believe that the stresses associated with intermittent positive pressure ventilation (IPPV) were the most likely precipitant to rebleeding and that the inability to clear blood through coughing was also an important factor leading to deterioration. Intermittent positive pressure ventilation should be avoided when possible in children with CF with recent significant pulmonary haemorrhage.     

VENTILATORY MANAGEMENT OF NEONATES UNDERGOING SURGERY: A review of the first 3 years' experience in a neonatal surgical intensive care unit

The results of the ventilatory management of babies, obtainedin the first 3 years of a neonatal surgical intensive care unit,are assessed. Overall mortality figures and detailed examinationof the cause of death in individual diagnostic groups supporta selective approach to intermittent positive pressure ventilation(IPPV) based mainly on clinical criteria. The adoption of apolicy of prophylactic IPPV after operation would achieve virtuallyno improvement in mortality. ^* Present address: Anaesthesia Department, St George's Hospital,Hyde Park Corner, London S.W.1     

Cardiac Tamponade and Different Modes of Artifical Ventilation

Cardiac tamponade after open-heart surgery often occurs in a situation when the patient is still mechanically ventilated and needs circulatory support with catecholamines. To evaluate the effects of different modes of artificial ventilation and dopamine on cardiac tamponade, an experimental study was carried out in seven mongrel dogs. In pentobarbital - N₂O anaesthesia, a cardiac tamponade of 20 mmHg was produced by injecting 120–200 ml of normothermic saline into the pericardium. Intermittent positive pressure ventilation (IPPV) and positive end-expiratory pressure (PEEP) ventilation with frequencies of 12 and 20 were tested before and after producing the tamponade. Cardiac tamponade produced a significant fall in arterial pressure and cardiac output, a significant rise in central venous pressure and only a slight increase in pulmonary arterial pressure. PEEP with the slower ventilation frequency of 12 produced additional, significant falls in cardiac output and systemic arterial pressure, which were not noted with the ventilation frequency of 20 and PEEP. Dopamine infusion increased the cardiac output by increasing the heart rate during tamponade. It is concluded that PEEP ventilation with a slow frequency should not be used if cardiac tamponade is suspected after open-heart surgery, and that dopamine has a favourable effect on haemodynamics even in the presence of a severe cardiac tamponade.     

Physiological aspects of intermittent positive pressure ventilation

The mechanical properties of the lungs and chest wall dictate the relationship between tidal volume, flow rate and airway pressure developed during intermittent positive pressure ventilation (IPPV). The increase in intrathoracic pressures associated with IPPV has consequences for the intrapulmonary distribution of ventilation and perfusion (hence gas exchange), cardiac output and regional blood flows. Barotrauma is a potential hazard. IPPV also affects the homeostatic mechanisms that keep the air spaces dry. Strategies to maximise the benefits and minimise the side effects of IPPV include positive end-expiratory pressure, intermittent mandatory ventilation, differential lung ventilation and high frequency ventilation. Understanding the physiological effects of IPPV and associated therapies allows a rational approach to the adjustment of ventilation against pulmonary, cardiovascular and systemic responses so as to optimise gas exchange and peripheral oxygen delivery.     

Intermittent and continuous positive-pressure ventilation in the prophylaxis of endotoxin-induced lung insufficiency. A study in pigs

The effects of intermittent and continuous positive-pressure ventilation (IPPV and CPPV) instituted prophylactically were evaluated in a porcine model of endotoxin-induced pulmonary and cardiovascular failure. Pigs under ketamine anaesthesia were infused i.v. with E. coli endotoxin over 6 h. Twenty animals, breathing air spontaneously, received endotoxin without treatment. Fifteen animals were treated prophylactically with IPPV (normoventilation with air). Nine animals received prophylactic treatment with CPPV (positive end-expiratory pressure 0.8 kPa (8 cmH2O). Endotoxin infusion in spontaneously breathing animals caused profound deterioration of pulmonary gas exchange, a marked rise in pulmonary vascular resistance (PVR) and a moderate increase in extravascular lung water (EVLW). Cardiac output (Qt) and O2 delivery decreased considerably. Metabolic acidosis indicated oxygen deficit. Eleven of 20 animals died during the observation period. IPPV improved arterial oxygenation during endotoxin infusion, and the increase in EVLW tended to be lower. The alterations in pulmonary haemodynamics, Qt and O2 delivery, were of the same magnitude as in spontaneously breathing animals. Survival was improved. CPPV fully prevented the deterioration in pulmonary gas exchange and the development of pulmonary oedema. There was an accentuated increase in PVR. Qt and O2 delivery decreased markedly and a severe metabolic acidosis developed. All animals treated with CPPV died during the observation period. These results indicate that prophylactic IPPV and CPPV may counteract the development of sepsis-induced lung insufficiency in man. However, it must be emphasized that adequate cardiovascular support is essential in optimizing the treatment.     

Cardiopulmonary resuscitation: effect of CPAP on gas exchange during chest compressions

BACKGROUND: Conventional cardiopulmonary resuscitation (CPR) includes 80-100/min precordial compressions with intermittent positive pressure ventilation (IPPV) after every fifth compression. To prevent gastric insufflation, chest compressions are held during IPPV if the patient is not intubated. Elimination of IPPV would simplify CPR and might offer physiologic advantages, but compression-induced ventilation without IPPV has been shown to result in hypercapnia. The authors hypothesized that application of continuous positive airway pressure (CPAP) might increase CO2 elimination during chest compressions. METHODS: After appropriate instrumentation and measurement of baseline data, ventricular fibrillation was induced in 18 pigs. Conventional CPR was performed as a control (CPR(C)) for 5 min. Pauses were then discontinued, and animals were assigned randomly to receive alternate trials of uninterrupted chest compressions at a rate of 80/min without IPPV, either at atmospheric airway pressure (CPR(ATM)) or with CPAP (CPR(CPAP)). CPAP was adjusted to produce a minute ventilation of 75% of the animal's baseline ventilation. Data were summarized as mean +/- SD and compared with Student t test for paired observations. RESULTS: During CPR without IPPV, CPAP decreased PaCO2 (55+/-28 vs. 100+/-16 mmHg) and increased SaO2 (0.86+/-0.19 vs. 0.50+/-0.18%; P < 0.001). CPAP also increased arteriovenous oxygen content difference (10.7+/-3.1 vs. 5.5+/-2.3 ml/dl blood) and CO2 elimination (120+/-20 vs. 12+/-20 ml/min; P < 0.01). Differences between CPR(CPAP) and CPR(ATM) in aortic blood pressure, cardiac output, and stroke volume were not significant. CONCLUSIONS: Mechanical ventilation may not be necessary during CPR as long as CPAP is applied. Discontinuation of IPPV will simplify CPR and may offer physiologic advantage.     

Nasal ventilation to facilitate weaning in patients with chronic respiratory insufficiency.

BACKGROUND: The non-invasive technique of nasal intermittent positive pressure ventilation (NIPPV) has an established role in providing domiciliary nocturnal ventilatory support in patients with chest wall disorders, neuromuscular disease, and chronic obstructive lung disease. NIPPV was used to simplify ventilatory management and assist the return of spontaneous breathing in patients with chronic respiratory insufficiency who had failed to wean from conventional intermittent positive pressure ventilation (IPPV). METHODS: A trial of NIPPV was carried out in 22 patients with weaning difficulties. Nine patients had chest wall disorders or primary lung disease, six had neuromuscular conditions, and seven had cardiac disorders with additional pulmonary disease. Conventional IPPV via an endotracheal tube or tracheostomy had been continued postoperatively in nine patients and 13 had been ventilated after acute cardiorespiratory decompensation. RESULTS: Conventional IPPV had been continued for a median of 31 days (range 2-219). Eighteen patients were successfully transferred to NIPPV and discharged home a median of 11 days (range 8-13) after starting this type of ventilation. Sixteen patients remain well 1-50 months after hospital discharge and 10 of these continue on domiciliary nocturnal NIPPV. Seven patients have returned to work. CONCLUSION: NIPPV can be used to facilitate the return of spontaneous breathing and to reduce the need for intensive care accommodation in patients with an acute exacerbation of chronic respiratory insufficiency that requires intubation and IPPV.     

The decreasing incidence of diaphragmatic dysfunction in liver transplantation: A probable advantage of the piggy-back liver transplant technique

Background. Pediatric orthotopic liver transplantation (OLT) has a low mortality. Some children, however, have an adverse outcome defined as a prolonged ventilatory support requirement and protracted pediatric intensive care unit (PICU) stay. The aim of this study was to determine if that adverse outcome related to the child's condition pre-OLT and/or the development of a pleural effusion or diaphragmatic dysfunction. Methods. The study included 210 children with a median age at transplantation of 45.5 months (range 0.2-252 months). Fourteen had undergone retransplantation. The duration of ventilatory support (intermittent positive pressure ventilation [IPPV]) and PICU admission and development of a pleural effusion and/or diaphragmatic dysfunction were documented for each child. The patients were divided into three groups according to whether they had acute liver failure (ALF), chronic liver disease at home (CHOM), or chronic liver failure sufficiently ill to be in the hospital awaiting transplantation (CHOSP). Results. The 36 children with ALF were of similar age to the 138 CHOM and 36 CHOSP children but required longer IPPV (P < 0.0001) and PICU stay (P < 0.0001). Overall, 17 children developed diaphragmatic dysfunction and 138 pleural effusions; affected children required longer IPPV and PICU stay (P <0.01). Regression analysis demonstrated that diaphragmatic dysfunction, but not pleural effusion development, was associated with prolonged ventilation (P <0.01) and protracted PICU stay (P <0.05). Other risk factors were ALF (P <0.01), retransplantation (P <0.01), and young age (P <0.05). Conclusion. Diaphragmatic dysfunction adversely influences PICU morbidity after OLT. Early assessment of diaphragmatic function, and if necessary aggressive management, might improve outcome.     

Dexmedetomidine facilitates induction of noninvasive positive pressure ventilation for acute respiratory failure in patients with severe asthma

Noninvasive positive pressure ventilation (NPPV) has been reported to be effective for acute respiratory failure in patients with severe asthma. Although NPPV requires less sedative than invasive mechanical ventilation, agitated patients with severe asthma should be given the minimum sedation necessary to facilitate the induction of NPPV. Two asthmatic patients (a 65-year-old man and a 32-year-old woman) separately presented to the intensive care unit with exacerbating respiratory failure. We initiated NPPV using bilevel positive airway pressure (PAP) ventilation. The ventilation was initially set as an inspiratory PAP of 15 cmH₂O and an expiratory PAP of 4 cmH2O. Because they seemed too agitated to tolerate the mask ventilation, dexmedetomidine was administered intravenously, at 3 μg·kg⁻¹·min⁻¹ for 10 min, followed by a continuous infusion at 0.2–0.6 μg·kg⁻¹·min⁻¹. One hour after the institution of NPPV, the patients were well cooperative with the mask ventilation and the respiratory symptoms had markedly improved. While the Ramsay sedation scale was maintained at 2 or 3 during the continuous dexmedetomidine infusion, we successfully weaned the patients from NPPV by reducing the inspiratory PAP. Dexmedetomidine helped the agitated patients cooperate with mask ventilation without inducing respiratory depression. We conclude that dexmedetomidine may be a valuable sedative to facilitate the induction of NPPV. This case report was presented in part at the 81st clinical and scientific congress of the International Anesthesia Research Society, Orlando, Florida, March 23–27, 2007.     

Pressure support ventilation vs spontaneous ventilation via ProSeal™ laryngeal mask airway in pediatric patients undergoing ambulatory surgery: a randomized controlled trial

Aim: To investigate the advantages of using pressure support ventilation (PSV) vs spontaneous ventilation via ProSeal? laryngeal mask airway in children undergoing ambulatory surgery. Background: In our ambulatory surgical unit, the use of unassisted spontaneous breathing via laryngeal mask airway is a common anesthetic technique during general anesthesia. However, this may be associated with inadequate ventilation. PSV is a ventilatory mode that is synchronized with the patient’s respiratory effort and may improve gaseous exchange under general anesthesia. Materials and methods: After the approval from the ethics committee, a randomized controlled trial involving 24 pediatric patients was conducted in our ambulatory surgical unit. They were randomized into two groups, namely Group PSV (receiving PSV) and Group SV (unassisted spontaneous ventilation). Outcome measures included intraoperative respiratory and hemodynamic parameters as well as recovery room data. Results: There were no significant differences in baseline characteristics between the two groups. Patients in Group PSV had lower ETCO₂ (42.8 ± 5.8 vs 50.4 ± 4.0, P = 0.001) and higher expiratory tidal volume per kg bodyweight (8.3 ± 1.8 ml kg^?1 vs 5.8 ± 0.8 ml kg^?1, P = 0.001) compared with patients in Group SV. There were no significant differences in other respiratory and hemodynamic parameters or recovery room data between the two groups. Conclusion: Pressure support ventilation via ProSeal? laryngeal mask airway during general anesthesia improves ventilation in pediatric patients undergoing ambulatory surgery. However, this did not translate to a difference in clinical outcome among our study patients.     

THE EFFECTS OF INTERMITTENT POSITIVE PRESSURE VENTILATION ON LUNG FUNCTION IN HYALINE MEMBRANE DISEASE

Fifty-eight infants with hyaline membrane disease were admittedto an intensive care unit. Twenty of these developed respiratoryfailure despite bicarbonate and oxygen therapy. They were thentreated by intermittent positive pressure ventilation and 13of the 20 survived. The mechanism of IPPV was determined in12 of these by the measurement of lung function and blood-gastensions. Results indicated that a normal alveolar ventilationcould be produced in these infants by a 50 per cent increasein their original minute volume. An adequate tidal volume (20ml) could only be obtained by a high peak transpulmonary pressure(35 cm H²O) and this volume had to be delivered at a mean rateof 56 cycles per minute. A reduction in either transpulmonarypressure or the rate of cycling resulted in an inadequate alveolarventilation and a precipitious fall in Pa_o2. Assisted breathingappeared to be more effective than passive ventilation overa short period of time. Measurements were made within 4 minutesof paralyzing the respiratory muscles, and must therefore beaccepted with reserve.     

Outcome and costs of intensive care. A follow-up study on patients requiring prolonged mechanical ventilation

This historically prospective study analysed hospital costs and long-term outcome in 249 consecutive patients who required intensive care including intermittent positive pressure ventilation (IPPV) for 48 h or more. The mean age of the patients was 46.7 years and the mean duration on IPPV was 9.1 days. Mortality in hospital was 43%, increasing to 54.6% five years after admission. The mean cost per patient treated was 22,823 US dollars (USD (1980 value]. The mean cost to yield one survivor was 40,035 USD. The mean cost per survivor was 26,056 USD, whereas that of a non-survivor was 18,500 USD. The cost-benefit ratio, i.e. calculated cost per year of extended life until the age of 75 years, averaged 1420 USD (range 360-7980 USD). With the exception of patients suffering from cancerous diseases, the cost-benefit ratio found in this study was favourable in comparison to other high-cost medical care. This is further emphasized by the fact that for the years saved, the quality of life was mostly good.     

Non-invasive ventilation in surgical patients in a district general hospital

We have retrospectively audited the use of non-invasive ventilation (NIV) in surgical patients. We analysed the case notes of 38 surgical patients who received NIV over a 9-month period. Twenty-three patients received NIV following emergency surgery, eight after elective surgery, and seven did not have an operation. Co-morbidity was common. The commonest reasons for starting NIV were chest infection, acute respiratory distress syndrome and pulmonary oedema. NIV was often only one aspect of treatment in surgical patients with complex medical problems. With intensive support from the critical care outreach team, NIV can be safely delivered on a surgical ward, and may sometimes prevent intensive care unit admission. Use of NIV on the intensive care unit may obviate the need for tracheal intubation in some patients. In very ill surgical patients with a poor prognosis, NIV was frequently used as the ceiling of respiratory support.     

Continuous Flow Apneic Ventilation

A study was designed to evaluate the adequacy of gas exchange during continuous flow apneic ventilation (CFAV) in dogs. Seventeen dogs (average weight 22.9 kg) were divided into three experimental groups. Group I (n = 7) was anesthetized, paralyzed and ventilated with air using intermittent positive pressure ventilation (IPPV) through a tracheal tube. The tube was removed and each main stem bronchus was cannulated with a 2.5 mm i.d., 4 mm o.d. polyethylene catheter using a fiberoptic bronchoscope. The tracheal tube was replaced to hold the catheters in place. Heated, humidified air was continuously delivered equally to each catheter. Total flows ranged from 8 to 28 1/min (0.4—1.4 1 + kg^-1 min-^-1). Airway pressure (P_aw) in the trachea did not exceed 2 mmHg (0.27 kPa). Adequate gas exchange in terms of arterial oxygen and arterial carbon dioxide tension (Pao₂ and Paco₂) was found after 30 min at flows greater than 16 l · min_-1. Group II (n = 7) was managed similarly to the first group, insufflating endobronchial air using the optimal flow of 1.0 1 · kg ¹ · min^-1 obtained from Group I. CFAV continued for 5 h in all animals. Blood gas samples and measurements of systemic blood pressure, heart rate (HR), pulmonary artery blood pressure, pulmonary artery wedge pressure, cardiac output (Qt), and temperature were taken every 30 min. Group III (n = 3) was anesthetized similarly to the other groups. Pulmonary gas distribution was evaluated in relation to catheter placement using Xe¹³³. Results showed significant differences between Paoj values during CFAV and IPPV; however, all animals were adequately oxygenated. During 5 h of CFAV, adequate CO₂ elimination was achieved in all animals. There was no difference in PaO₂, Paco₂ and shunt fraction (Qs/C}t) with CFAV at 30 min and 5 h. Differences in HR, Qt, and systemic vascular resistance at 30 min and 5 h were related to the hypothermia during the developing course of experimentation. With the catheters above the carina, gas distribution studies demonstrated gas limited to the large airways with no peripheral distribution, resulting in low Pao₂ levels and elevated Paco₂ levels. Endobronchial catheters permitted gas distribution to the peripheral airways, and oxygenation and ventilation were normal.