Pulmonary venous admixture during one-lung anaesthesia. The effect of inhaled oxygen tension and respiration rate

Application of CO2 waveform in the alveolar recruitment maneuvers of hypoxemic patients during one-lung ventilation

Deterioration of gas exchange during one-lung ventilation (OLV) is caused by both total collapse of the nondependent lung and partial collapse of the dependent lung. Alveolar recruitment maneuver improves lung function during general anesthesia. The objective of this study was to investigate whether there is an indirect relationship between the changes of CO2 expirogram and the selective lung recruitment. To further improve the oxygenation and gas exchange, we compare adjust setting of ventilated parameters based on CO2 expirogram and a preset setting of ventilated parameters during OLV in patients undergoing right-side thoracic surgery.Thirty patients met the requirements criteria that were studied at 3 time points: during two-lung ventilation (TLV), during OLV with preset ventilation parameters (OLV-PP), and during OLV with adjustable ventilation parameters (OLV-AP) that are in accordance with CO2 expirogram. Adjustable ventilation parameters such as tidal volume (VT), respiratory rate (RR), positive end-expiratory pressure (PEEP), and the ratio of inspiratory to expiratory were adjusted by utilizing the phase III slopes of CO2 expirogram, which together with the relationship between the changes of CO2 expirogram and the selective lung recruitment.During OLV, the phase III slopes of CO2 expirogram in patients with pulse oxymetry (SpO2) decreased less than 93% after the OLV-PP, and were absolutely different from that during TLV. After OLV-AP, the phase III slopes of CO2 expirogram and SpO2 were similar to those during TLV. During OLV, however, parameters of ventilation setting in both OLV-PP and OLV-AP are obviously different.This study indicates that alveolar recruitment by utilizing CO2 expirogram probably improves SpO2 level during one-lung ventilation.

The effects of prolonged inspiratory time during one-lung ventilation: a randomised controlled trial

We evaluated the effects of a prolonged inspiratory time on gas exchange in subjects undergoing one-lung ventilation for thoracic surgery. One hundred patients were randomly assigned to Group I:E = 1:2 or Group I:E = 1:1. Arterial blood gas analysis and respiratory mechanics measurements were performed 10 min after anaesthesia induction, 30 and 60 min after initiation of one-lung ventilation, and 15 min after restoration of conventional two-lung ventilation. The mean (SD) ratio of the partial pressure of arterial oxygen to fraction of inspired oxygen after 60 min of one-lung ventilation was significantly lower in Group I:E = 1:2 compared with Group I:E = 1:1 (27.7 (13.2) kPa vs 35.2 (22.1) kPa, respectively, p = 0.043). Mean (SD) physiological dead space-to-tidal volume ratio after 60 min of one-lung ventilation was significantly higher in Group I:E = 1:2 compared with Group I:E = 1:1 (0.46 (0.04) vs 0.43 (0.04), respectively, p = 0.008). Median (IQR [range]) peak inspiratory pressure was higher in Group I:E = 1:2 compared with Group I:E = 1:1 after 60 min of one-lung ventilation (23 (22-25 [18-29]) cmH2O vs 20 (18-21 [16-27]) cmH2O, respectively, p < 0.001) and median (IQR [range]) mean airway pressure was lower in Group I:E = 1:2 compared with Group I:E = 1:1 (10 (8-11 [5-15]) cmH2O vs 11 (10-13 [5-16]) cmH2O, respectively, p < 0.001). We conclude that, compared with an I:E ratio of 1:2, an I:E ratio of 1:1 resulted in a modest improvement in oxygenation and decreased shunt fraction during one-lung ventilation.

Video-assisted thoracoscopic surgery using single-lumen endotracheal tube anaesthesia in primary spontaneous pneumothorax

BACKGROUND AND OBJECTIVE

Primary spontaneous pneumothorax (PSP) is a common condition that typically affects young adults. With recent advances in techniques, VATS is now a safe and accepted procedure for treating PSP. Lung isolation techniques have been commonly used to facilitate surgical procedures in the past. The purpose of this study was to evaluate the feasibility of using a single-lumen endotracheal tube for thoracoscopic surgery in patients with PSP.

METHODS

A series of 121 consecutive patients with PSP, who underwent VATS using a double-lumen or single-lumen endotracheal tube between January 2000 and December 2002, were assessed retrospectively. The clinical features, operation times, complications, hospital stays and recurrences of PSP in these patients were recorded and analysed.

RESULTS

There were no significant differences in gender, BMI, smoking habits, blebs/bullae on CT, duration of surgery or recurrence of PSP between the two groups. Patients in the single-lumen endotracheal tube group had a shorter duration of anaesthesia (15.4 +/- 2.6 vs 25.6 +/- 3.2 min, P < 0.001), lower early complication rates, lower costs and shorter hospital stays (3.6 +/- 3.0 vs 4.5 +/- 2.8 days, P = 0.02) compared with those in the double-lumen endotracheal tube group. The follow-up period was 40-68 months (mean 54 months). There were two recurrences in each group (3.1% vs 3.4%).

CONCLUSIONS

VATS for the treatment of PSP was easily performed using a single-lumen endotracheal tube, and resulted in lower intubation-related costs, fewer complications and equivalent outcomes, compared with procedures performed using double-lumen endotracheal tube anaesthesia.

[Atelectasis in general anesthesia and alveolar recruitment strategies]

Atelectasis occurs in most patients during general anesthesia and is the main cause of hypoxemia. The objective of this review is to examine the causes and diagnosis of atelectasis and the different strategies for reducing or preventing this complication and improving oxygenation. Pulmonary atelectasis is mainly caused by 3 factors: compression, gas absorption, and lack of surfactant. Compression and gas absorption are, however, the 2 most commonly implicated factors. Lung collapse is accentuated if pure oxygen is inhaled during induction or if the patient is morbidly obese. Laparoscopic, thoracic, and upper abdominal interventions also carry risk of lung collapse. Various techniques may be used to prevent atelectasis or to reopen collapsed lung tissue. These include using positive end-expiratory pressure or a high tidal volume-thus providing a higher airway pressure (vital capacity maneuver)-or both in combination. Alveolar recruitment strategies have been tried in bariatric surgery, single-lung ventilation, laparoscopy, and adult respiratory distress syndrome. Their application has reduced or prevented atelectasis, thereby reducing postoperative pulmonary complications.

Cardiopulmonary effects of positive end-expiratory pressure during one-lung ventilation in anesthetized dogs with a closed thoracic cavity

OBJECTIVE

To evaluate the effects on oxygen delivery (DO2) of 2.5 and 5 cm H2O of positive end-expiratory pressure (PEEP) applied to the dependent lung during one-lung ventilation (OLV) in anesthetized dogs with a closed thoracic cavity.

ANIMALS

7 clinically normal adult Walker Hound dogs.

PROCEDURE

Dogs were anesthetized, and catheters were inserted in a dorsal pedal artery and the pulmonary artery. Dogs were positioned in right lateral recumbency, and data were collected during OLV (baseline), after application of 2.5 cm H2O of PEEP for 15 minutes during OLV, and after application of 5 cm H2O of PEEP for 15 minutes during OLV. Hemodynamic and respiratory variables were analyzed and calculations performed to obtain DO2, and values were compared among the various time points by use of an ANOVA for repeated measures.

RESULTS

PEEP induced a significant decrease in shunt fraction that resulted in a significant increase in arterial oxygen saturation. However, it failed to significantly affect arterial oxygen content (CaO2) or cardiac output. Thus, DO2 was not affected in healthy normoxemic dogs as a net result of the application of PEEP.

CONCLUSIONS AND CLINICAL RELEVANCE

The use of PEEP during OLV in anesthetized dogs with a closed thoracic cavity did not affect DO2. Use of PEEP during OLV in dogs with a closed thoracic cavity is recommended because it does not affect cardiac output and any gain in CaO2 will be beneficial for DO2 in critically ill patients.

The effects of xenon or nitrous oxide supplementation on systemic oxygenation and pulmonary perfusion during one-lung ventilation in pigs

During experimental one-lung ventilation (OLV), the type of anesthesia may alter systemic hemodynamics, lung perfusion, and oxygenation. We studied whether xenon (Xe) or nitrous oxide (N(2)O) added to propofol anesthesia would affect oxygenation, lung perfusion, and systemic and pulmonary hemodynamics during OLV in a pig model. Nine pigs were anesthetized, tracheally intubated, and mechanically ventilated. After placement of arterial and pulmonary artery catheters, a left-sided double-lumen tube was placed via tracheotomy. IV anesthesia with propofol was supplemented in random order with N(2)O/O(2) 60:40 or Xe/O(2) 60:40 or N(2)/O(2) 60:40. All measurements were made after stabilization at each concentration. Differential lung perfusion was measured with colored microspheres. Oxygenation (Pao(2): 90 +/- 17, 95 +/- 20, and 94 +/- 20 mm Hg for N(2)/O(2), N(2)O/O(2), and Xe/O(2)) and left lung perfusion (16% +/- 5%, 14% +/- 6%, and 18.8% for N(2)/O(2), N(2)O/O(2), and Xe/O(2)) during OLV did not differ among the 3 groups. However, mean arterial blood pressure (78 +/- 25, 62 +/- 23, and 66 +/- 23 mm Hg for N(2)/O(2), N(2)O/O(2), and Xe/O(2)) and mixed venous saturation (55% +/- 12%, 48% +/- 12%, and 50% +/- 12% for N(2)/O(2), N(2)O/O(2), and Xe/O(2)) were reduced during N(2)O/O(2) as compared with the control group (N(2)/O(2)). Supplementation of IV anesthesia with Xe or N(2)O does not impair oxygenation nor alter lung perfusion during experimental OLV.

Video-Assisted Thoracoscopic Surgery Using Single-Lumen Endotracheal Tube Anesthesia

BACKGROUND

Most general thoracic surgeons use double-lumen endotracheal tube (DLET) anesthesia for all video-assisted thoracoscopic surgery (VATS). We evaluated a single-lumen endotracheal tube (SLET) for VATS for drainage of pleural effusions and pleural biopsies.

METHODS

A consecutive series of patients with recurrent pleural effusions underwent VATS using an SLET and only one incision. Operations were accomplished via one 2-cm incision using a 5-mm rigid thoracoscope and mediastinoscopic biopsy forceps for directed pleural biopsies. A working area was accomplished with low tidal volumes.

RESULTS

There were 376 patients (191 women). The indications for VATS were a nondiagnosed or benign pleural effusion in 294 patients, and a malignant effusion in 82 patients. Two hundred eight patients underwent biopsy of the parietal pleura, and mean operative time was 17 min. Adequate visibility was obtained in all. When compared to preoperative cytology, VATS was more sensitive (45% compared to 99%, p < 0.001), had a higher negative predictive value (56% compared to 99%, p < 0.001), and was more accurate (67% compared to 99%, p < 0.001). Forty-seven percent of patients with a history of cancer had false-negative preoperative cytology results. Complications occurred in seven patients (2%), and there were three operative deaths (none related to the operative procedure).

CONCLUSION

VATS using SLET and only one incision is possible, and it affords excellent visualization of the pleural space, allowing pleural biopsies and talc insufflation. It avoids the risk, time, and cost of a DLET. It is significantly more sensitive and accurate than preoperative cytology, and it should be considered as the diagnostic and therapeutic procedure of choice in patients with recurrent pleural effusions.

Lung Recruitment Improves the Efficiency of Ventilation and Gas Exchange During One-Lung Ventilation Anesthesia

Atelectasis in the dependent lung during one-lung ventilation (OLV) impairs arterial oxygenation and increases dead space. We studied the effect of an alveolar recruitment strategy (ARS) on gas exchange and lung efficiency during OLV by using the single-breath test of CO(2) (SBT-CO(2)). Twelve patients undergoing thoracic surgery were studied at three points in time: (a) during two-lung ventilation and (b) during OLV before and (c) after an ARS. The ARS was applied selectively to the dependent lung and consisted of an increase in peak inspiratory pressure up to 40 cm H(2)O combined with a peak end-expiratory pressure level of 20 cm H(2)O for 10 consecutive breaths. The ARS took approximately 3 min. Arterial blood gases, SBT-CO(2), and metabolic and hemodynamic variables were recorded at the end of each study period. Arterial oxygenation and dead space were better during two-lung ventilation compared with OLV. PaO(2) increased during OLV after lung recruitment (244 +/- 89 mm Hg) when compared with OLV without recruitment (144 +/- 73 mm Hg; P < 0.001). The SBT-CO(2) analysis showed a significant decrease in dead-space variables and an increase in the variables related to the efficiency of ventilation during OLV after an ARS when compared with OLV alone. In conclusion, ARS improves gas exchange and ventilation efficiency during OLV.

IMPLICATIONS

In this article, we showed how a pulmonary ventilatory maneuver performed in the dependent lung during one-lung ventilation anesthesia improved arterial oxygenation and dead space.

Alveolar recruitment strategy increases arterial oxygenation during one-lung ventilation

BACKGROUND

Deterioration of gas exchange during one lung ventilation (OLV) is caused by both total collapse of the nondependent lung and partial collapse of the dependent lung. A previous report demonstrated that an alveolar recruitment strategy (ARS) improves lung function during general anesthesia in supine patients. The objective of this article was to study the impact of this ARS on arterial oxygenation in patients undergoing OLV for lobectomies.

METHODS

Ten patients undergoing open lobectomies were studied at three time points: (1) during two-lung ventilation (TLV), (2) during OLV before, and (3) after ARS. The ARS maneuver was done by increasing peak inspiratory pressure to 40 cm H2O, together with a positive end-expiratory pressure (PEEP) of 20 cm H2O for 10 respiratory cycles. After the maneuver, ventilation parameters were returned to the settings before intervention.

RESULTS

During OLV, PaO2 was statistically lower before the recruitment (data as median, first, and third quartile, 217 [range 134 to 325] mm Hg) compared with OLV afterwards (470 [range 396 to 525] mm Hg) and with TLV (515 [range 442 to 532] mm Hg). After ARS, PaO2 values during OLV were similar to those during TLV. During OLV, the degree of pulmonary collapse in the nondependent lung, the hemodynamic status, and the ventilation parameters were similar before and after ARS.

CONCLUSIONS

Alveolar recruitment of the dependent lung augments PaO2 values during one-lung ventilation.

Intrinsic positive end-expiratory pressure during one-lung ventilation of patients with pulmonary hyperinflation. Influence of low respiratory rate with unchanged minute volume

BACKGROUND

We measured lung mechanics and gas exchange during one-lung ventilation (OLV) of patients with chronic obstructive pulmonary disease, using three respiratory rates (RR) and unchanged minute volume.

METHODS

We studied 15 patients about to undergo lung surgery, during anaesthesia, and placed in the lateral position. Ventilation was with constant minute volume, inspiratory flow and FIO2. For periods of 15 min, RR of 5, 10, and 15 bpm were applied in a random sequence and recordings were made of lung mechanics and an arterial blood gas sample was taken. Data were analysed with the repeated measures ANOVA and paired t-test with Bonferroni correction.

RESULTS

PaO2 changes were not significant. At the lowest RR, PaCO2 decreased (from 42 (SD 4) mm Hg at RR 15-41 (4) mm Hg at RR 10 and 39 (4) mm Hg at RR 5, P<0.01), and end-tidal carbon dioxide increased (from 33 (5) mm Hg at RR 15 to 35 (5) mm Hg at RR 10 and 36 (6) mm Hg at RR 5, P<0.01). Intrinsic positive end-expiratory pressure (PEEPi) was reduced even with larger tidal volumes (from 6 (4) cm H2O at RR 15-5 (4) cm H2O at RR 10, and 3 (3) cm H2O at RR 5, P<0.01), most probably caused by increased expiratory time at the lowest RR.

CONCLUSION

A reduction in RR reduces PEEPi and hypercapnia during OLV in anaesthetized patients with chronic obstructive lung disease.

Pathophysiology of one-lung ventilation

The management of some problematic patients having thoracic surgery is among the most difficult challenges for the anesthesiologist. Increasingly complex operations are performed on seriously compromised patients because of the development of new surgical techniques and the anesthesiologists' awareness of surgical needs and requirements to provide a satisfactory and safe surgical field. In order to facilitate thoracic surgery, the single most important and valuable anesthetic technique used actually is one-lung ventilation. This article reviews the complex pathopysiology of one-lung ventilation.

Improvement of arterial oxygenation by selective infusion of prostaglandin E1 to ventilated lung during one-lung ventilation

BACKGROUND

One-lung anesthesia provides a better surgical field for thoracic procedures but also impairs the arterial oxygenation and venous admixture. During one-lung ventilation, pulmonary vasoconstriction is assumed to be present within both ventilated and collapsed lungs. We propose that arterial oxygenation could be optimized by offsetting the vasoconstriction within the microcirculation of ventilated lung.

METHOD

In an anesthetized dog model, incremental doses of prostaglandin E1 (PGE1) were selectively infused into the main trunk of the pulmonary artery of the ventilated lung after one-lung ventilation for 60 min (PGE1 group, n = 9). Arterial oxygenation and calculated venous admixture (Qs/Qt) was also assessed in a time-course control group (Control group, n = 5). During two-lung ventilation (FIO2: 0.66), arterial PO2 and venous admixture was 44.2 +/- 3.5 kPa and 10.7 +/- 2.3%, respectively. One-lung ventilation (FIO2: 0.66) with left lung collapsed reduced arterial PO2 to 11.6 +/- 1.7 kPa and increased venous admixture to 40.7 +/- 5.8% (P<0.001). Venous O2 tension also decreased from 6.3 +/- 0.7 kPa to 5.0 +/- 0.6 kPa with a slight increase in mean pulmonary artery pressure and pulmonary vascular resistance (P<0.05).

RESULTS

During selective infusion of PGE1 at a dose of 0.04 to 0.2 mu g kg-1 min-1, there was a dose-dependent improvement in arterial PO2 with a parallel reduction of venous admixture during one-lung ventilation. Arterial PO2 increased to a maximum of 23.0 +/- 4.3 kPa, and the venous admixture decreased significantly to a minimum of 27.4 +/- 4.2% by PGE1 at a dose of 0.04-0.4 mu g kg-1 min-1 (P<0.01). PGE1 resulted in a small increase in cardiac output and decreases of pulmonary pressure and pulmonary vascular resistance at a relatively high dose of 0.4 mu g kg-1 min-1 during selective infusion (P<0.05).

CONCLUSIONS

These results suggest that a selective pulmonary artery infusion of PGE1 to the ventilated lung within the dose range of 0.04-0.4 mu g kg-1 min-1 is practical and effective to improve arterial oxygenation and reduce venous admixture during one-lung ventilation.

Differential lung ventilation as an alternative to one-lung ventilation during thoracotomy. Report of three cases

Investigation was carried out on three elderly patients undergoing thoracotomy. During one-lung ventilation using a Robertshaw double-lumen tube, the PaO2 decreased below 11.7 kPa despite ventilation of the dependent lung with 100% oxygen. Differential lung ventilation was then initiated by partial occlusion of the adapter limb to the nondependent lung, whilst maintaining unrestricted ventilation of the dependent lung. In the three patients, differential lung ventilation increased the PaO2 to 15-37.2 kPa. The increased PaO2 may be attributed to diffusion oxygenation via the partially inflated, nondependent lung. Differential lung ventilation can be used during thoracotomy whenever one-lung ventilation is followed by hypoxaemia, despite adequate ventilation of the dependent lung with 100% oxygen.

High-frequency jet ventilation vs continuous positive airway pressure for differential lung ventilation in patients undergoing resection of thoracoabdominal aortic aneurysm

Twenty patients, scheduled for surgical resection of thoracoabdominal aortic aneurysm were divided into two groups according to the type of differential lung ventilation used during graft replacement of the descending thoracic aorta. In the high-frequency jet ventilation (HFJV) group of ten patients, HFJV was applied to the left lung once collapsed and retracted by the surgeon, the patient lying in the right lateral decubitus and being intubated by a Carlens' tube. In the continuous positive airway pressure (CPAP) group of ten patients, CPAP was applied to the left lung at the same mean airway pressure as HFJV (1 kPa). Before anaesthetic induction, an arterial and a Swan-Ganz catheter were inserted for cardiovascular monitoring. The same anaesthetic technique using fentanyl 6 micrograms.kg-1, flunitrazepam 0.02 mg.kg-1 and pancuronium 0.1 mg.kg-1 was used for each patient. Haemodynamic and respiratory measurements were made; 15 min after positioning the patients in the right lateral decubitus using two-lung ventilation; 15 min after collapse and retraction of the left lung using one-lung ventilation and 15 min after using differential lung ventilation with CPAP or HFJV. Left lung collapse with conventional one-lung ventilation induced a dramatic decrease in arterial oxygenation: PaO2/FIO2 ratio decreased from 43 +/- 6 kPa to 20 +/- 8 kPa, alveolo-arterial oxygen difference increased from 24 +/- 7 kPa to 72 +/- 11 kPa and pulmonary shunt increased from 17 +/- 2% to 37 +/- 3%. Whereas differential lung ventilation with CPAP did not improve any of the respiratory parameters measured, differential lung ventilation with HFJV, significantly increased PaO2/FIO2 ratio to 41 +/- 14 kPa.(ABSTRACT TRUNCATED AT 250 WORDS)

Propofol does not inhibit hypoxic pulmonary vasoconstriction in humans

The influence of increasing doses of propofol (from 6 to 12 mg/kg/h by continuous infusion) on hypoxic pulmonary vasoconstriction was studied in 10 patients prior to thoracic surgery. All patients were intubated with a left-sided double-lumen endobronchial tube. Initial anesthesia and muscle relaxation were accomplished by administering fentanyl, droperidol, and pancuronium. After 100% oxygen ventilation of both lungs for 20 min in a lateral decubitus position, the nondependent lung was deflated and one-lung ventilation was started. The dependent lung was continuously ventilated with 100% oxygen. Twenty minutes after the start of one-lung ventilation, propofol at an IV infusion rate of 6 mg/kg/h was added to the anesthetic technique. Thirty minutes later it was increased to 10 mg/kg/h and another 15 min later to 12 mg/kg/h. Then the propofol infusion was stopped. Thirty minutes later, two-lung ventilation was restarted to compare initial values. No changes in venous admixture or PaO2 were observed during propofol infusion. There was no change in any respiratory or circulatory variables except systemic vascular resistance, which decreased significantly immediately after the propofol infusion commenced but returned to control values 15 min later for the rest of the observation period. After reestablishing two-lung ventilation, all variables did not differ from control values. In all patients, the hypoxic pulmonary vasoconstriction reflex was present after institution of one-lung ventilation and was not abolished after administration of propofol in doses from 6 to 12 mg/kg/h.

Unilateral high-frequency jet ventilation during one-lung ventilation for thoracotomy

One-lung ventilation is indicated during thoracic operations for bronchopleural fistula, pulmonary abscess, and pulmonary hemorrhage in spite of the possibility of the development of severe hypoxemia. To evaluate methods for improving oxygen transport during one-lung ventilation, we applied high-frequency jet ventilation (HFJV) and continuous positive airway pressure (CPAP) to the nondependent lung following deflation to atmospheric pressure in each procedure, and measured the effects on cardiac output and arterial oxygenation. In each case, the dependent lung was ventilated with conventional intermittent positive pressure ventilation (IPPV). Eight patients were studied during posterolateral thoracotomy using double-lumen endobronchial tubes. HFJV or CPAP to the nondependent lung improved arterial oxygenation significantly during both closed and open stages of the surgical procedures (p less than 0.008). When the chest was open, HFJV maintained satisfactory cardiac output, whereas CPAP usually decreased cardiac output (p less than 0.008). There were no significant differences in mean partial pressure of arterial carbon dioxide between HFJV, CPAP, and deflation to atmospheric pressure. In conclusion, HFJV to the nondependent lung provides not only satisfactory oxygenation but also good cardiac output, thereby maintaining better oxygen transport than CPAP or deflation to atmospheric pressure, while the dependent lung is ventilated with IPPV during one-lung ventilation for thoracotomy.

Oxygenation and hemodynamic changes during one-lung ventilation: effects of CPAP10, PEEP10, and CPAP10/PEEP10

The effects of 10 cm H2O positive end-expiratory pressure (PEEP10), 10 cm H2O continuous positive airway pressure (CPAP10), and their combination (CPAP10/PEEP10) on oxygenation and hemodynamics were studied in 20 patients undergoing one-lung ventilation (OLV) with 50% nitrous oxide, isoflurane, and oxygen. Compared to OLV alone, CPAP10 and CPAP10/PEEP10 significantly increased PaO2 (from 80 +/- 6 to 125 +/- 11 and 137 +/- 17 mmHg, respectively); increased SaO2 (from 93.9 +/- 0.8 to 97.1 +/- 0.5 and 97.0 +/- 0.6%, respectively); and decreased Qs/Qt% (from 36.4 +/- 1.6 to 26.2 +/- 2.0 and 23.2 +/- 2.0%, respectively). Although not statistically significant, PEEP10 caused an increase in PaO2 (to 105 +/- 12 mmHg) and a decrease in Qs/Qt% (to 27.6 +/- 2.1%), which are of clinical significance. However, CPAP10/PEEP10 caused a significant decrease in cardiac output (from 4.50 +/- 0.26 to 3.83 +/- 0.22 L/min), stroke volume (58.6 +/- 3.0 to 52.8 +/- 2.9 mL/beat), and oxygen delivery (653 +/- 39 to 590 +/- 38 mL/min). Application of CPAP10, PEEP10 or their combination had no significant effect on heart rate, arterial, pulmonary arterial, mean pulmonary capillary wedge or central venous pressures, systemic or pulmonary vascular resistances, or mixed venous oxygen saturation. Overall, CPAP10 had the most beneficial effect on oxygenation and hemodynamics during OLV with 50% N2O, isoflurane and oxygen.

A comparative study of conventional versus high-frequency jet ventilation with relation to the incidence of postoperative morbidity in thoracic surgery

Sixty-five patients undergoing a thoracic procedure were randomly allocated to one of two groups. The first group received a conventional method of ventilation (double-lumen endobronchial tube and collapse of one lung) and the second, high-frequency jet ventilation (HFJV). The incidence of postoperative chest infections (clinical and bacteriological), the chest drain volumes, and the length of postoperative stay in the hospital were recorded. Results showed the jet ventilator group had a significantly reduced mean hospital stay (p less than 0.01), which could be attributed to a lower incidence of postoperative chest infections (p less than 0.001) and significantly improved arterial blood O2 tensions at 4 hours (p less than 0.05), 24 hours, and 7 days postoperatively (p less than 0.001).

One lung anaesthesia. Cardiovascular and respiratory function compared during conventional ventilation and high frequency jet ventilation

Ten patients about to undergo left-sided thoracotomy for carcinoma of the lung were entered into a crossover trial to compare cardiovascular and respiratory function during high frequency jet ventilation and conventional mechanical ventilation for one lung anaesthesia. All patients were anaesthetised with a standard technique using double lumen tubes and placed in the lateral position with the left chest open. The results showed no significant differences with regard to ventilation sequence but one lung high frequency jet ventilation gave higher values than one lung conventional ventilation for shunt (p less than 0.01) and positive end expiratory pressure (p less than 0.05) and lower peak inflation pressure values (p less than 0.01). There were no significant differences in cardiac output, pulmonary capillary wedge pressure, arterial carbon dioxide or available oxygen. Surgical conditions were satisfactory during both methods of ventilation and satisfactory gas exchange occurred. It was, however, more difficult to assess adequacy of ventilation during high frequency jet ventilation and the routine use of this method of ventilation is not recommended during one lung anaesthesia.

One-lung ventilation. The effect of positive end expiratory pressure to the nondependent and dependent lung

We applied positive end expiratory pressure to the nondependent, nonventilated lung, or both nondependent and dependent, ventilated lung during one lung anaesthesia, and compared the results to those obtained by other techniques, such as increasing the inspired oxygen concentration in the dependent lung, or insufflating with oxygen using positive end expiratory pressure in the nondependent lung. Our study suggests that arterial oxygenation and intrapulmonary shunt can be lessened during one lung ventilation by continuous oxygen insufflation of the nondependent lung at 0.98 kPa positive end expiratory pressure while the dependent lung is ventilated with 0.49 kPa positive end expiratory pressure.

Selective bronchial intubation for one lung anaesthesia in thoracic surgery. A new method

A new method for one lung anaesthesia in thoracic surgery is described. Separate lung ventilation is obtained with selective main bronchus intubation, by means of an appropriate cuffed tube inserted through a standard orotracheal tube. Ventilation is carried out separately through the bronchial tube on one side and the residual tracheal tube lumen on the other side. This method greatly simplifies the technique of bronchial intubation and offers many advantages over commercially available double-lumen tubes.

[Technics for artificial ventilation of a single lung during thoracotomy]

Different means of limiting the fall in arterial PO2 produced by single artificial ventilation were studied in 60 patients during thoracotomy. Changing from ventilating both lungs to the one healthy lung in the lateral recumbent position, without modifying tidal volume and frequency, brought about a fall in arterial PO2 from 180 +/- 56 to 67 +/- 40 mmHg. The alveolar to arterial oxygen gradient increased to 110 +/- 45 mmHg (the alveolar oxygen pressure being calculated). Reducing the tidal volume so as to keep the inflation pressure at its initial level did not improve the arterial PO2 but slightly increased the arterial PCO2 (2.3 mmHg). The use of 6 to 8 cm H2O positive end-expiratory pressure did not significantly modify the arterial PO2 or PCO2. Increasing the inspired oxygen fraction from 0.5 to 0.7 increased the arterial PO2 from 100 +/- 89 mmHg to 165 +/- 59 mmHg, whilst the alveolar to arterial oxygen gradient increased to 118 +/- 60 mmHg. Clamping the pulmonary artery increased the arterial PO2 and dual lung ventilation restored it to its initial value. Therefore, the only effective means of increasing oxygenation was to increase the inspired oxygen fraction. Unilateral continuous positive airway pressure was not used so as not to impair surgery. Dual lung ventilation may be necessary if the arterial PO2 remains low.

Continuous ketamine infusion for one-lung anaesthesia

The mechanism which normally affects distribution of blood flow through unventilated areas of the lung is hypoxic pulmonary vasoconstriction; this acts to divert the blood to well ventilated alveoli, resulting in a better ratio of ventilation to perfusion. Several reports have focused attention on the reduction or abolition of this reflex in the unventilated lung by most of the volatile anaesthetic agents used in clinical practice. This response was not abolished by the intravenous anaesthetic agents. One hundred and ten patients undergoing elective pulmonary resection were studied to evaluate the effect of a continuous infusion of ketamine during one-lung anaesthesia, by observing the changes in PaO2 as a reflection of shunt. Ketamine was chosen as the intravenous agent for its positive inotropic and chronotropic action. Additionally, by providing both analgesia and hypnosis, we were able to administer inspired oxygen concentrations of 50-100 per cent without concern that the patient might have recall for events during operation. We have demonstrated that in all cases a PaO2 in excess of 9.31 kPa (70 torr) was achieved with ketamine and FIO2 1.0 as well as an increase in shunt fraction from 25.9 per cent (FIO2 0.5) to 36.0 per cent (FIO2 1.0). We feel that ketamine provides a satisfactory alternative to the volatile agents for one-lung anaesthesia in patients where relative hypoxaemia might be unacceptable during operation.

Foetal hypoxia--an anaesthetist's approach to classification and prevention

Nearly one third of perinatal deaths are due to hypoxia occurring during pregnancy and labour. Many factors contribute to foetal hypoxia and in order to group these into orderly categories a classification of hypoxia, which is familiar to anaesthetists, has been applied to the maternal and foetal circulations. This theoretical approach forms a logical guide to our understanding the cause, prevention and treatment of foetal hypoxia.

Prospective study of the Robertshaw endobronchial catheter in thoracic surgery

One hundred three men undergoing thoracotomy on a general thoracic surgery service received endobronchial anesthesia with 100% oxygen using the Robertshaw tube. Bronchial intubation was accomplished in all. However, cross-leak or difficulty with deflation necessitated discontinuance in 8, while Pao2 values of 41 and 45 mm Hg caused abandonment in 2. There were no operative deaths. Surprisingly, hypoxemia in these patients related more to insufficient alveolar ventilation than to the venoarterial shunt.

Cardiorespiratory function during thoracic anaesthesia: a comparison of two-lung ventilation and one-lung ventilation with and without PEEP5

Previous studies have shown that, in patients undergoing thoracic surgery, a relatively high positive end-expiratory pressure (PEEP of 10 cmH2O = PEEP10) has no beneficial effect on oxygenation during one-lung ventilation (OLV). In the present investigation, cardiorespiratory function was examined in 11 patients intubated endobronchially and undergoing thoracotomy. Comparison was made between two-lung ventilation (TLV) and OLV and between zero end-expiratory pressure and PEEP5 during OLV. Cardiac output was determined to obtain information of the total oxygen delivery (cardiac output times arterial O2 content. The change from TLV to OLV was accompanied by a marked fall in PaO2 and a marked rise in shunt, whereas no significant change was observed in mean cardiac output. Oxygen delivery also remained unchanged due to relatively small decrease in SaO2 (arterial oxygen saturation) and maintenance of cardiac output. The application of PEEP5 during OLV produced no significant changes in these parameters. The findings in individual patients demonstrated the relative importance of cardiac output in determining oxygen delivery during OLV. A significant negative correlation was found between inspiratory airway pressure and cardiac index during OLV.