Relation of the static compliance curve and positive end-expiratory pressure to oxygenation during one-lung ventilation.

BACKGROUND: Positive end-expiratory pressure (PEEP) is commonly applied to the ventilated lung to try to improve oxygenation during one-lung ventilation but is an unreliable therapy and occasionally causes arterial oxygen partial pressure (PaO(2)) to decrease further. The current study examined whether the effects of PEEP on oxygenation depend on the static compliance curve of the lung to which it is applied. METHODS: Forty-two adults undergoing thoracic surgery were studied during stable, open-chest, one-lung ventilation. Arterial blood gases were measured during two-lung ventilation and one-lung ventilation before, during, and after the application of 5 cm H(2)O PEEP to the ventilated lung. The plateau end-expiratory pressure and static compliance curve of the ventilated lung were measured with and without applied PEEP, and the lower inflection point was determined from the compliance curve. RESULTS: Mean (+/- SD) PaO(2) values, with a fraction of inspired oxygen of 1.0, were not different during one-lung ventilation before (192 +/- 91 mmHg), during (190 +/- 90), or after ( 205 +/- 79) the addition of 5 cm H(2)O PEEP. The mean plateau end-expiratory pressure increased from 4.2 to 6.8 cm H(2)O with the application of 5 cm H(2)O PEEP and decreased to 4.5 cm H(2)O when 5 cm H(2)O PEEP was removed. Six patients showed a clinically useful (> 20%) increase in PaO(2) with 5 cm H(2)O PEEP, and nine patients had a greater than 20% decrease in PaO(2). The change in PaO(2) with the application of 5 cm H(2)O PEEP correlated in an inverse fashion with the change in the gradient between the end-expiratory pressure and the pressure at the lower inflection point (r = 0.76). The subgroup of patients with a PaO(2) during two-lung ventilation that was less than the mean (365 mmHg) and an end-expiratory pressure during one-lung ventilation without applied PEEP less than the mean were more likely to have an increase in PaO(2) when 5 cm H(2)O PEEP was applied. CONCLUSIONS: The effects of the application of external 5 cm H(2)O PEEP on oxygenation during one-lung ventilation correspond to individual changes in the relation between the plateau end-expiratory pressure and the inflection point of the static compliance curve. When the application of PEEP causes the end-expiratory pressure to increase from a low level toward the inflection point, oxygenation is likely to improve. Conversely, if the addition of PEEP causes an increased inflation of the ventilated lung that raises the equilibrium end-expiratory pressure beyond the inflection point, oxygenation is likely to deteriorate.

Preoperative assessment for pulmonary resection.

Because of recent advances in anesthesia and surgery, almost any patient with a resectable lung malignancy is now an operative candidate, given a full understanding of the risks and provided he or she is investigated appropriately. This progress necessitates a change in the paradigm that one uses for preoperative assessment. Understanding and stratifying the perioperative risks allows the anesthesiologist to develop a systematic focused approach to these patients at the time of the initial contact and immediately before induction, which then can be used to guide anesthetic management (Fig. 7).

The interaction between applied PEEP and auto-PEEP during one-lung ventilation.

OBJECTIVE: To investigate the relationship between applied external positive end-expiratory pressure (PEEP) and auto-PEEP and the resultant total PEEP experienced by the patient during one-lung ventilation (OLV). DESIGN: A prospective clinical study. SETTING: A university hospital. PARTICIPANTS: Ten adult patients undergoing elective thoracotomies. INTERVENTIONS: End-expiratory airway occlusion and measurement of plateau pressure during two-lung ventilation (TLV) and OLV with and without the application of 5 cm H2O of external PEEP via the anesthetic ventilator. The effect of variation of the inspiratory-expiratory ratio on total PEEP with and without applied external PEEP was also studied. MAIN RESULTS: The mean level (+/-SD) of auto-PEEP changing from two-lung to one-lung ventilation rose from 0.9 (+/-0.8) cm H2O to 6.0 (+/-3.0) cm H2O at an inspiratory-expiratory ratio of 1:2. The application of 5 cm H2O external PEEP did not increase the total PEEP (7.3+/-2.0 cm H2O) significantly. The total PEEP increased significantly when the duration of expiration was decreased, and decreased when expiratory time increased. The change in total PEEP caused by the application of external PEEP during OLV correlated inversely with the preexisting level of auto-PEEP (r=-0.84). CONCLUSION: The change in end-expiratory pressure experienced by the ventilated lung during OLV when external PEEP is applied depends on the preexisting level of auto-PEER This may explain some of the inconsistencies in the clinical results of application of external PEEP during OLV. The total PEEP delivered to the patient should be measured whenever external PEEP is applied during OLV.

Flow resistances of disposable double-lumen, single-lumen, and Univent tubes.

OBJECTIVE: To compare the airflow resistances of modern double-lumen, single-lumen, and Univent (Fuji Systems Corp; Tokyo, Japan) tubes. DESIGN: A laboratory bench study. SETTING: A university hospital laboratory. MEASUREMENTS: Pressure differentials (Pd) were measured across study tubes at 10 L/min airflow (V) increments from 0 to 60 L/min in a tracheal model. Coefficients of resistance k1 (linear) and k2 (nonlinear) were calculated for each tube by the method of least squares using the Rohrer equation Pd/V = k1 + k2V. Data were assessed by analysis of variance (ANOVA) for the effects of tube design, circumference, and manufacturer on k1 and k2. MAIN RESULTS: Calculated combined mean k1 and k2 were significantly lower for single-lumen tubes compared with double-lumen or Univent tubes. There were no significant differences for k1 values between double-lumen or Univent tubes. The values for k2 were significantly lower for double-lumen tubes compared with Univent tubes. The k2 values were significantly lower for Rusch (Duluth, GA) or Sheridan (Argyle, NY) double-lumen tubes compared with Mallinckrodt (St Louis, MO) double-lumen tubes. This difference was because of the Y-connectors of the Mallinckrodt tubes. CONCLUSIONS: Flow resistances of modern disposable double-lumen tubes are lower than commonly perceived. In most clinical situations, there will be no decrease in flow resistance when a Rusch or Sheridan double-lumen tube is replaced by a single-lumen tube.

A comparison of the effects of propofol-alfentanil versus isoflurane anesthesia on arterial oxygenation during one-lung ventilation.

OBJECTIVE: To determine whether intravenous propofol-alfentanil anesthesia provides superior arterial oxygenation (Pao2) during one-lung ventilation (OLV) compared with isoflurane inhalation anesthesia. DESIGN: A prospective, randomized, cross-over study. SETTING: Tertiary-care university hospital. PARTICIPANTS: Thirty adults having either thoracoscopic pulmonary surgery or esophageal surgery. INTERVENTIONS: Patients received either propofol-alfentanil infusion anesthesia or one minimum alveolar concentration (MAC) of isoflurane during the initial period of two-lung ventilation and the first 30 minutes of OLV and then were switched to the other anesthetic for the duration of OLV. MEASUREMENTS AND MAIN RESULTS: Arterial blood gases and hemodynamics were recorded during two-lung ventilation and after 20 and 30 minutes of OLV with each anesthetic technique. The mean values (+/- SD) for Pao2 during propofol-alfentanil anesthesia after 20 minutes (222 +/- 100) and 30 minutes (228 +/- 102 mmHg) of one-lung ventilation were not significantly different than after 20 minutes (213 +/- 99) or 30 minutes (214 +/- 96 mmHg) of isoflurane; beta error less than 0.1. Mean heart rate was lower during intravenous (78 +/- 15 min) than inhalation (85 +/- 17 min) anesthesia (rho = 0.03). CONCLUSION: This study does not support the theory that total intravenous anesthesia will decrease the risk of hypoxemia during OLV.

A clinical comparison of bronchial cuff pressures in three different designs of left double-lumen tubes.

This study compared the bronchial cuff pressures and volumes required by three different designs of disposable left double-lumen tubes during clinical one-lung ventilation in 48 patients having right thoracotomies. Mallinckrodt, Rusch, and Sheridan design tubes (n = 16 for each) were studied in a randomized fashion using Fr# 35, 37, 39, and 41 sizes (n = 12 for each size). There were no pressure/volume differences between brands during bronchial cuff inflation before endotracheal intubation. Intraoperatively, the Sheridan design required significantly higher mean bronchial cuff pressures: [27.9 cm H2O +/- 17 cm H2O (SD)] than either the Mallinckrodt [17.6 cm H2O +/- 8.5 cm H2O (P = 0.012)] or Rusch [14.1 cm H2O +/- 8.6 cm H2O (P = 0.010)] to achieve one-lung isolation. During prolonged one-lung ventilation, the potential for trauma to the bronchus may be reduced with a Mallinckrodt or Rusch design of left double-lumen tube.

Perioperative respiratory assessment and management.

There have been many recent advances in the understanding and therapy of respiratory diseases. This review has attempted to cover some of the relevant new information about those disorders most likely to be encountered by anaesthetists.

Perioperative respiratory assessment and management.

There have been many recent advances in the understanding and therapy of respiratory diseases. This review has attempted to cover some of the relevant new information about those disorders most likely to be encountered by anaesthetists.RéSUMé: Il y a de nombreux progrès récents dans la compréhension et la thérapie des maladies respiratoires. Cette revue a tenté de revoir l'information nouvelle et pertinente concernant les maladies les plus susceptibles d'être rencontrées par les anesthésistes.

Anaesthesia for lung resection.

Management options to consider in the high-risk patient for pulmonary resection include: 1. The use of EAA plus a postoperative pain management scheme to optimize pulmonary function in the critical two to four days after surgery. 2. The use of a "step-down" or intermediate care area, with a level of monitoring between that of the intensive care unit and the regular postoperative ward, for the initial three to four days. 3. Preoperative optimization of concurrent medical conditions with aggressive physical and medical therapy. 4. Careful titration of intra-operative fluids with early recourse to invasive monitoring, vasopressors and inotropes. Perioperative digitalization of patients with a history of cardiovascular disease for pneumonectomy. 5. Avoidance of N2O. Ventilate intraoperatively with an air/oxygen mixture, during both two- and one-lung ventilation, titrated against the arterial oxygen saturation. Avoidance of complete intraoperative atelectasis of the ND-lung with a low level of air/oxygen CPAP. 6. Surgical alternatives. The use of a median sternotomy or limited resection. A simple cost/benefit analysis tells us that not every recent advance in thoracic anaesthesia is indicated for every patient. It is now part of the anaesthetist's responsibility to identify the high-risk patient and to develop an appropriately stratified management plan.

Intraoperative awareness due to malfunction of a Siemens 900B ventilator.

A case of intraoperative awareness during a thoracotomy is described. The patient's recall coincided with an intraoperative period during which a Siemens 900B ventilator and a Siemens 952 isoflurane vaporiser were used. Subsequent assessment of this equipment with an anaesthetic agent analyzer revealed that, at the ventilator settings which had been used, the delivered anaesthetic vapour concentration varied greatly from the vaporizer settings. This problem eventually was traced to a malfunctioning inlet control valve on the ventilator. This complication may have been prevented if the end-tidal anaesthetic concentration had been monitored intraoperatively.

Fiberoptic bronchoscopic positioning of double-lumen tubes.

This article has attempted to familiarize the anesthesiologist with the bronchoscopic appearance of normally and abnormally positioned double-lumen endobronchial tubes. Double-lumen tubes are being used in an increasing proportion of thoracic surgical cases in major centers. Double-lumen tubes are also being used more frequently in intensive care units for independent lung ventilation, bronchopleural fistula, massive hemoptysis, and other asymmetrical pulmonary disorders. Obstruction of the left or right upper lobe bronchus is the most common significant malposition with these tubes. If it occurs after the start of surgery it can be extremely difficult to diagnose clinically and can lead to dangerous levels of hypoxemia during one-lung ventilation. The risk/benefit ratio of fiberoptic bronchoscopy before the initiation of one-lung ventilation is extremely small. Due to variations in bronchial anatomy and intrathoracic pathology there will always be a certain percentage of cases in which the current designs of double-lumen tubes cannot be adequately positioned. The anesthesiologist's index of suspicion in these cases may be raised by examining the preoperative chest x-ray. Fiberoptic bronchoscopy is the most efficient and reliable method to position a double-lumen tube when the anatomy is distorted. When used as described, the FOB is a monitor. Like all new monitors it will take some time before there is a general consensus whether it is to be used routinely or only for certain indications. Whatever the final consensus on the indications for the FOB in double-lumen tube positioning, it is certain that all anesthesiologists involved in managing thoracic cases should be familiar with this technique.