Peri-operative pulmonary dysfunction and protection.

Pulmonary complications are a major cause of peri-operative morbidity and mortality, but have been researched less thoroughly than cardiac complications. It is important to try and predict which patients are at risk of peri-operative pulmonary complications and to intervene to reduce this risk. Anaesthetists are in a unique position to do this during the whole peri-operative period. Pre-operative training, smoking cessation and lung ventilation with tidal volumes of 6-8 ml.kg(-1) and low positive end-expiratory pressure probably reduce postoperative pulmonary complications.

A randomised controlled trial comparing the GlideScope(®) and the Macintosh laryngoscope for double-lumen endobronchial intubation.

Double-lumen endobronchial tubes are the most common method of achieving lung isolation and one-lung ventilation during thoracic anaesthesia and surgery. We compared the clinical performance of the Macintosh laryngoscope and the GlideScope(®) during endobronchial intubation with a double-lumen tube. Seventy patients with no predictors for difficult laryngoscopy were allocated randomly to the Macintosh laryngoscope or GlideScope. The time taken for endobronchial intubation with the Macintosh laryngoscope was significantly shorter compared with that taken for the GlideScope, median (IQR [range]) 33 (22-52 [11-438]) s vs 70 (39-129 [21-242]) s, respectively, p = 0.0013. There was no statistical difference in the rate of success at the first attempt (91% vs 83%, respectively). On a numerical rating scale (scored from 0 to 10), the 30 anaesthetists who took part in the study rated endobronchial intubation overall as easier using the Macintosh compared with the GlideScope, 2 (1-3 [0-8]) vs 3 (2-6 [0-10]), respectively, p = 0.003. Postoperative voice changes were also less common in the Macintosh group (8 (22%) vs 17 (58%), p = 0.045). Anaesthetists found the GlideScope more difficult to use than the Macintosh laryngoscope and endobronchial intubation took longer; therefore, we cannot recommend its routine use with double-lumen tubes in patients who are predicted to have a normal airway.

Lung protective strategies in anaesthesia.

Patients are at risk for several types of lung injury in the perioperative period including atelectasis, pneumonia, pneumothorax, acute lung injury, and acute respiratory distress syndrome. Anaesthetic management can cause, exacerbate, or ameliorate these injuries. This review examines the effects of perioperative mechanical ventilation and its role in ventilator-induced lung injury. Lung protective ventilatory strategies to specific clinical situations such as cardiopulmonary bypass and one-lung ventilation along with newer novel lung protective strategies are discussed.

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).

Post-pneumonectomy pulmonary edema: is anesthesia to blame?

Post-pneumonectomy pulmonary edema is a major cause of early mortality following lung resection surgery. It is not clear whether this complication is caused by excessive perioperative intravenous fluid as was previously thought. The recent demonstration of increased pulmonary capillary permeability of the lung following a pneumonectomy suggests measures to try and decrease the incidence of this highly lethal syndrome. These measures include the judicious use of intravenous crystalloids, avoidance of lung hyperinflation and efforts to minimize the pulmonary artery pressure.

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.