The Association Between the Initial End-Tidal Carbon Dioxide Difference and the Lowest Arterial Oxygen Tension Value Obtained During One-Lung Anesthesia With Propofol or Sevoflurane

Inhalational versus intravenous anesthetics during one lung ventilation in elective thoracic surgeries: A narrative review

The anesthesia regimen used during one lung ventilation (OLV) carry the potential to affect intra-operative course and post-operative outcomes, by its effects on pulmonary vasculature and alveolar inflammation. This narrative review aims to understand the pathophysiology of acute lung injury during one lung ventilation, and to study the effects of inhalational versus intravenous anaesthetics on intraoperative and post-operative outcomes, following thoracic surgery. For this purpose, we independently searched 'PubMed', 'Google Scholar' and 'Cochrane Central' databases to find out randomized controlled trials (RCTs), in English language, which compared the effects of intravenous versus inhalational anaesthetics on intraoperative and post-operative outcomes, in elective thoracic surgeries, in human beings. In total, 38 RCTs were included in this review. Salient results of the review are- Propofol reduced intraoperative shunt and maintained better intraoperative oxygenation than inhalational agents. However, use of modern inhalational anaesthetics during OLV reduced alveolar inflammation significantly, as compared to propofol. Regarding post-operative complications, the evidence is not conclusive enough but slightly in favour of inhalational anaesthetics. Thus, we conclude that modern inhalational anaesthetics, by their virtue of better anti-inflammatory properties, exhibit lung protective effects and hence, seem to be safe for maintenance of anesthesia during OLV in elective thoracic surgeries. Further research is required to establish the safety of these agents with respect to long term post-operative outcomes like cancer recurrence.

The role of an ambient pressure oxygen source during one-lung ventilation for thoracoscopic surgery

Video-assisted thoracoscopic surgery is facilitated by prompt collapse of the non-ventilated (‘operated’) lung, and interrupted and impeded if there is a need for oxygen (O2) delivery by continuous positive airways pressure in order to manage hypoxaemia. It has been proposed that connecting an ambient pressure O2 source to the airway of the non-ventilated lung at the time one-lung ventilation is initiated and before the chest is opened will, by avoiding entrainment of ambient nitrogen, serve to facilitate lung collapse. It has also been proposed that leaving the O2 source connected will enable, not only ongoing apnoeic oxygenation before the chest is opened, but also the thoracoscopic procedure to commence with the operated lung fully pre-oxygenated (with an inspired oxygen fraction of 1), and apnoeic oxygenation to continue throughout the operative procedure in those patients who exhibit a degree of small airways patency at ambient pressure. In reality, several factors can influence the speed of collapse of the operated lung, and very many factors can influence the incidence of hypoxaemia during one-lung ventilation. It therefore appears unlikely that the necessary evidence to support these proposals will be forthcoming from randomised clinical studies on large numbers of patients. Rather, the necessary evidence may only be provided by specifically designed within-patient clinical measurement studies. Nevertheless, it is argued that, in the meantime, there is already sufficient rationale for an ambient pressure O2 source to be connected to the airway of the non-ventilated lung, and for it to remain connected for the duration of one-lung ventilation.

Hypoxic pulmonary vasoconstriction: physiology and anesthetic implications

Hypoxic pulmonary vasoconstriction (HPV) represents a fundamental difference between the pulmonary and systemic circulations. HPV is active in utero, reducing pulmonary blood flow, and in adults helps to match regional ventilation and perfusion although it has little effect in healthy lungs. Many factors affect HPV including pH or PCO2, cardiac output, and several drugs, including antihypertensives. In patients with lung pathology and any patient having one-lung ventilation, HPV contributes to maintaining oxygenation, so anesthesiologists should be aware of the effects of anesthesia on this protective reflex. Intravenous anesthetic drugs have little effect on HPV, but it is attenuated by inhaled anesthetics, although less so with newer agents. The reflex is biphasic, and once the second phase becomes active after about an hour of hypoxia, this pulmonary vasoconstriction takes hours to reverse when normoxia returns. This has significant clinical implications for repeated periods of one-lung ventilation.

Intravenous versus inhalation anaesthesia for one-lung ventilation

BACKGROUND

This is an update of a Cochrane Review first published in The Cochrane Library, Issue 2, 2008.The technique called one-lung ventilation can confine bleeding or infection to one lung, prevent rupture of a lung cyst or, more commonly, facilitate surgical exposure of the unventilated lung. During one-lung ventilation, anaesthesia is maintained either by delivering an inhalation anaesthetic to the ventilated lung or by infusing an intravenous anaesthetic. It is possible that the method chosen to maintain anaesthesia may affect patient outcomes. Inhalation anaesthetics may impair hypoxic pulmonary vasoconstriction (HPV) and increase intrapulmonary shunt and hypoxaemia.

OBJECTIVES

The objective of this review was to evaluate the effectiveness and safety of intravenous versus inhalation anaesthesia for one-lung ventilation.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL); The Cochrane Library (2012, Issue 11); MEDLINE (1966 to November 2012); EMBASE (1980 to November 2012); Literatura Latino-Americana e do Caribe em Ciências da Saúde (LILACS, 1982 to November 2012) and ISI web of Science (1945 to November 2012), reference lists of identified trials and bibliographies of published reviews. We also contacted researchers in the field. No language restrictions were applied. The date of the most recent search was 19 November 2012. The original search was performed in June 2006.

SELECTION CRITERIA

We included randomized controlled trials and quasi-randomized controlled trials of intravenous (e.g. propofol) versus inhalation (e.g. isoflurane, sevoflurane, desflurane) anaesthesia for one-lung ventilation in both surgical and intensive care participants. We excluded studies of participants who had only one lung (i.e. pneumonectomy or congenital absence of one lung).

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data. We contacted study authors for additional information.

MAIN RESULTS

We included in this updated review 20 studies that enrolled 850 participants, all of which assessed surgical participants－no studies investigated one-lung ventilation performed outside the operating theatre. No evidence indicated that the drug used to maintain anaesthesia during one-lung ventilation affected participant outcomes. The methodological quality of the included studies was difficult to assess as it was reported poorly, so the predominant classification of bias was 'unclear'.

AUTHORS' CONCLUSIONS

Very little evidence from randomized controlled trials suggests differences in participant outcomes with anaesthesia maintained by intravenous versus inhalational anaesthesia during one-lung ventilation. If researchers believe that the type of drug used to maintain anaesthesia during one-lung ventilation is important, they should design randomized controlled trials with appropriate participant outcomes, rather than report temporary fluctuations in physiological variables.

One-lung ventilation and arterial oxygenation

PURPOSE OF REVIEW

Hypoxemia during one-lung ventilation (OLV) has become less common; however, it may still occur in about 10% of cases. We review recent developments which may affect the incidence and treatment of hypoxemia during OLV.

RECENT FINDINGS

Changes in surgical techniques are affecting oxygenation during OLV. The increased use of the supine position may adversely affect the prevalence of hypoxemia, whereas the increased application of thoracoscopic techniques is limiting the treatment options. Treatment options such as global or selective recruitment maneuvers and drug effects of dexmedetomidine and epoprostenol on arterial oxygenation during OLV are discussed. Capnometry prior to, or early during OLV, may in fact be able to predict the degree of hypoxemia during OLV. Persistent controversies surrounding the effect of epidural anesthesia, ventilatory modalities and gravity are reviewed.

SUMMARY

Interesting concepts have emerged from case reports and small studies on the treatment and prediction of hypoxemia during OLV. Definitive studies on the most effective ventilatory mode remain elusive. End-organ effects of OLV are an exciting new concept that may shape clinical practice and research going forward.