Lluis Gallart

Prediction of Postoperative Pulmonary Complications in a Population-based Surgical Cohort

Background:Current knowledge of the risk for postoperative pulmonary complications (PPCs) rests on studies that narrowly selected patients and procedures. Hypothesizing that PPC occurrence could be predicted from a reduced set of perioperative variables, we aimed to develop a predictive index for a broad surgical population. Methods:Patients undergoing surgical procedures given general, neuraxial, or regional anesthesia in 59 hospitals were randomly selected for this prospective, multicenter study. The main outcome was the development of at least one of the following: respiratory infection, respiratory failure, bronchospasm, atelectasis, pleural effusion, pneumothorax, or aspiration pneumonitis. The cohort was randomly divided into a development subsample to construct a logistic regression model and a validation subsample. A PPC predictive index was constructed. Results:Of 2,464 patients studied, 252 events were observed in 123 (5%). Thirty-day mortality was higher in patients with a PPC (19.5%; 95% [CI], 12.5–26.5%) than in those without a PPC (0.5%; 95% CI, 0.2–0.8%). Regression modeling identified seven independent risk factors: low preoperative arterial oxygen saturation, acute respiratory infection during the previous month, age, preoperative anemia, upper abdominal or intrathoracic surgery, surgical duration of at least 2 h, and emergency surgery. The area under the receiver operating characteristic curve was 90% (95% CI, 85–94%) for the development subsample and 88% (95% CI, 84–93%) for the validation subsample. Conclusion:The risk index based on seven objective, easily assessed factors has excellent discriminative ability. The index can be used to assess individual risk of PPC and focus further research on measures to improve patient care.

Permissive Hypercapnia with and without Expiratory Washout in Patients with Severe Acute Respiratory Distress Syndrome

Background: Permissive hypercapnia is a ventilatory strategy aimed at avoiding lung volutrauma in patients with severe acute respiratory distress syndrome (ARDS). Expiratory washout (EWO) is a modality of tracheal gas insufflation that enhances carbon dioxide removal during mechanical ventilation by reducing dead space. The goal of this prospective study was to determine the efficacy of EWO in reducing the partial pressure of carbon dioxide (PaCO2) in patients with severe ARDS treated using permissive hypercapnia. Methods: Seven critically ill patients with severe ARDS (lung injury severity score, 3.1 +/‐ 0.3) and no contraindications for permissive hypercapnia were studied. On the first day, hemodynamic and respiratory parameters were measured and the extent of lung hyperdensities was assessed using computed tomography. A positive end‐expiratory pressure equal to the opening pressure identified on the pressure‐volume curve was applied. Tidal volume was reduced until a plateau airway pressure of 25 cm H2 O was reached. On the second day, after implementation of permissive hypercapnia, EWO was instituted at a flow of 15 l/min administered during the entire expiratory phase into the trachea through the proximal channel of an endotracheal tube using a ventilator equipped with a special flow generator. Cardiorespiratory parameters were studied under three conditions: permissive hypercapnia, permissive hypercapnia with EWO, and permissive hypercapnia. Results: During permissive hypercapnia, EWO decreased PaCO2 from 76 +/‐ 4 mmHg to 53 +/‐ 3 mmHg (‐30%; P < 0.0001), increased pH from 7.20 +/‐ 0.03 to 7.34 +/‐ 0.04 (P < 0.0001), and increased PaO2 from 205 +/‐ 28 to 296 +/‐ 38 mmHg (P < 0.05). The reduction in PaCO sub 2 was accompanied by an increase in end‐inspiratory plateau pressure from 26 +/‐ 1 to 32 +/‐ 2 cm H2 O (P = 0.001). Expiratory washout also decreased cardiac index from 4.6 +/‐ 0.4 to 3.7 +/‐ 0.3 l [center dot] min sup ‐1 [center dot] m sup ‐2 (P < 0.01), mean pulmonary arterial pressure from 28 +/‐ 2 to 25 +/‐ 2 mmHg (P < 0.01), and true pulmonary shunt from 47 +/‐ 2 to 36 +/‐ 3% (P < 0.01). Conclusions: Expiratory washout is an effective and easy‐to‐use ventilatory modality to reduce PaCO2 and increase pH during permissive hypercapnia. However, it significantly increases airway pressures and lung volume through expiratory flow limitation, reexposing some patients to a risk of lung volutrauma if the extrinsic positive end‐expiratory pressure is not substantially reduced.

Predicting postoperative pulmonary complications in the general population.

Purpose of review Postoperative pulmonary complications (PPCs) are common and lead to longer hospital stays and higher mortality. A wide range of patient, anaesthetic and surgical factors have been associated with risk for PPCs. This review discusses our present understanding of PPC risk factors that can be used to plan preoperative risk reduction strategies. The methodological and statistical basis for building risk scores is also described. Recent findings Studies in specific surgical populations or large patient samples have identified a range of predictors of PPC risk. Factors such as age, types of comorbidity and surgical characteristics have been found to be relevant in most of these studies. Recently, researchers have begun to develop risk scoring systems for a PPC composite outcome or for specific PPCs, especially pneumonia and respiratory failure. Preoperative arterial oxyhaemoglobin saturation is an objective measure that is easy to record and discriminates level of risk for impaired cardiorespiratory function. Preoperative anaemia and recent respiratory infection are factors that have lately been found to confer risk for PPCs. Summary PPC risk prediction scales based on large population studies are being developed. New studies to confirm the validity of these scales in different geographic areas will be needed before we can be sure of their generalizability.

Postoperative respiratory failure: pathogenesis, prediction, and prevention.

Purpose of reviewThis review discusses our present understanding of postoperative respiratory failure (PRF) pathogenesis, risk factors, and perioperative-risk reduction strategies. Recent findingsPRF, the most frequent postoperative pulmonary complication, is defined by impaired blood gas exchange appearing after surgery. PRF leads to longer hospital stays and higher mortality. The time frame for recognizing when respiratory failure is related to the surgical-anesthetic insult remains imprecise, however, and researchers have used different clinical events instead of blood gas measures to define the outcome. Still, studies in specific surgical populations or large patient samples have identified a range of predictors of PRF risk: type of surgery and comorbidity, mechanical ventilation, and multiple hits to the lung have been found to be relevant in most of these studies. Recently, risk-scoring systems for PRF have been developed and are being applied in new controlled trials of PRF-risk reduction measures. Current evidence favors carefully managing intraoperative ventilator use and fluids, reducing surgical aggression, and preventing wound infection and pain. SummaryPRF is a life-threatening event that is challenging for the surgical team. Risk prediction scales based on large population studies are being developed and validated. We need high-quality trials of preventive measures, particularly those related to ventilator use in both high risk and general populations.

Comparative assessment of the anaesthetic and analgesic effects of intramuscular and epidural clonidine in humans

PurposeThe aim of the study was to assess and compare in analogous controlled experimental conditions, the anaesthetic sparing and analgesic effects of the same dose of clonidine administered by the intramuscular (im) and epidural (ep) routes.MethodsWe used a randomized, double blind and placebo controlled protocol. Sixty patients undergoing abdominal hysterectomy were distributed into three groups who, 30 min before surgical incision, received: 300 μg ep clonidine plus im saline; ep saline plus 300 μg im clonidine; or ep and im saline (ss). General anaesthesia was maintained with 60% N2O in O2, and isoflurane administered at concentrations to maintain mean arterial pressure (MAP) and heart rate (HR) within 20% of basal values. Isoflurane requirements (mass spectrometry), cardiovascular variables (MAP, HR), and plasma concentrations of glucose, cortisol and prolactin were evaluated at critical time points. In the recovery room (RR), sedation (Ramsay) and pain intensity (VAS) were estimated at the time of analgesia request (TAR).ResultsIntramuscular and ep clonidine decreased isoflurane requirements similarly by about 85% (P < 0.001). Patients in the ep group had lower MAP (P < 0.03) and HR (P < 0.001) than in the im group, but im and ep clonidine similarly blunted the plasma prolactin increase induced by intubation. In RR, ep but not im clonidine (P < 0.01) induced postoperative analgesia demonstrated by a prolonged TAR 80.8 ± 7.3 (ep) 35.9 ± 3.2 (im) and 44.5 ±5.1 (ss) min and a lower VAS (P < 0.05).ConclusionsEpidural and intramuscular clonidine decreased isoflurane requirements similarly, but only the epidural route provided postoperative analgesia, suggesting a spinal site for the analgesic action.RésuméObjectif’Evaluer et comparer dans des conditions expérimentales identiques, l’effet d’épargne anesthésique et analgésique d’une même dose de clonidine administrée par la voie intramusculaire (IM) ou épidurale (Ép).MéthodesUn protcole aléatoire, en double aveugle et contrôlé avec placebo était utilisé. Soixante patientes programmées pour une hystérectomie abdominale étaient réparties en trois groupes qui, 30 min avant l’incision de la peau, recevaient: de la clonodine 300 pg ép et du sol. phys. im; du sol. phys ép et de la clonidine 300 μg im; ou du sol. phys. ép et im (ss). L’anesthésie générale était maintenue avec N2O 60% dans O2 et des concentrations d’isoflurane suffisantes pour maintenir la pression artérielle moyenne (PAM) et la fréquence cardiaque (FC) à 20% des valeurs initiales. Les besoins en isoflurane (spectrornétrie de masse), les paramètres cardiaques (PAM, FC) et la glycémie, la cortisolémie et la prolactinémie étaient évalués au moment des intervalles cruciaux. En salle de réveil, la sédation (Ramsay) et l’intensité de la douleur (EVA) étaient évalués par la durée de l’intervalle précédant la demande d’analgésique (IPDA).RésultatsLa clonidine IM et Ép a diminué également les besoins en isoflurane par environ 85% (P < 0,001). Les patientes du groupe ép avaient des PAM plus basses (P < 0,03) et des FC plus lentes (P < 0,001) que celles du groupe im, mais la clonidine im et ép a diminué également l’augmentation de la concentration plasmatique de prolactine provoquée par l’intubation. À la salle de réveil, la clonidine ép contrairement à la clonidine im (P < 0,01) a induit l’analgésie postopératoire comme le démontrait un IPDA prolongé à 80,8 ± 7,3 (ép), 35,9 ± 3,2 (im) et 44,5 ±5,1 (ss) min et une EVA moins élevée.ConclusionLa clonidine épidurale et intramusculaire diminue les besoins en isoflurane également, mais seule la voie épidurale procure une analgésie postopératoire, ce qui suggère un site d’action rachidien pour l’analgésie.

Effects of Interpleural Bupivacaine on Respiratory Muscle Strength and Pulmonary Function

Background Several reports suggest that interpleural local anesthetics may have deleterious effects on respiratory function. The current study investigated the effects of interpleural bupivacaine on human respiratory muscles and lung function.

factors Influencing the Tracheal Fluctuation of Inhaled Nitric Oxide in Patients with Acute Lung Injury

Background: Inhaled nitric oxide (NO) improves arterial oxygenation in patients with acute lung injury (ALI) by selectively dilating pulmonary vessels perfusing ventilated lung areas. It can be hypothesized that NO uptake from the lung decreases with increasing ventilation perfusion mismatch. This study was undertaken to determine the factors influencing the fluctuation of tracheal NO concentration over the respiratory cycle as an index of NO pulmonary uptake in patients with ALI. Methods: By using a prototype system (Opti‐NO) delivering a constant flow of NO only during the inspiratory phase, 3 and 6 ppm of NO were administered during controlled mechanical ventilation into a lung model and to 11 patients with ALI. All patients had a thoracic computed tomography (CT) scan. Based on an analysis of tomographic densities, lungs were divided into three zones: normally aerated (‐1.000 to 500 Hounsfield units [HU]), poorly aerated (‐500 to ‐100 HU), and nonaerated (‐100 to +100 HU), and the volume of each zone was computed. Concentrations of NO in the inspiratory limb and trachea were continuously measured by a fast‐response chemiluminescence apparatus. Results: In the lung model, tracheal NO concentration was stable with minor fluctuation. In contrast, in patients, tracheal NO concentration fluctuated widely during the respiratory cycle (55 +/‐ 10%). Because uptake of NO from the lungs was absent in the lung model but present in the patients, this fluctuation was considered as an index of pulmonary uptake of NO. This was further substantiated by (1) the coincidence of the peak and minimum tracheal NO concentration with the end‐inspiratory and end‐expiratory phases, respectively, and (2) continued decrease of tracheal NO concentration during prolonged expiratory phase. In patients with ALI, the fluctuation of tracheal NO concentration expressed as the difference between inspiratory and expiratory NO concentrations divided by inspiratory NO concentration was greater at 6 ppm than at 3 ppm (P < 0.01), was linearly correlated with normally aerated lung volume, inversely correlated with alveolar dead space and with poorly aerated lung volume. Conclusion: In patients with ALI, fluctuation of tracheal NO concentration over the respiratory cycle can be considered as an index of NO uptake from the lungs that depends on aerated lung volume and perfusion of ventilated lung areas. At bedside, it may be used to follow the evolution of ventilation‐perfusion mismatch.

The dark side of the lung: unveiling regional lung ventilation with electrical impedance tomography.

I N this issue of ANESTHESIOLOGY, we can read the results of a study of the distribution of lung ventilation performed with electrical impedance tomography (EIT). The authors collected data during awake state and during lower limb surgery under general anesthesia in three randomized groups of surgical patients breathing spontaneously or receiving either pressure-support ventilation (PSV) or pressure-controlled ventilation. Two observations of interest emerged from the study. The first concerns the effects of the three ventilatory modes on the distribution of pulmonary ventilation. The second is the potential value of EIT monitoring during anesthesia. The study’s main finding was that when patients breathe spontaneously, gas was distributed similarly in anesthetized and awake states. During pressure-controlled ventilation, on the other hand, the distribution shifted to more ventral regions of the lung, and surprisingly, this shift also occurred in patients assigned to PSV. That atelectasis develops during general anesthesia in dependent zones is well known, and we also know that it leads to ventilation-perfusion mismatching and impaired gas exchange. In the early 1980s, Hedenstierna’s group in Sweden showed that this effect occurs both in patients breathing spontaneously and those under mechanical ventilation. However, Nyrén et al., using single-photon emission computed tomography, recently showed that the distribution of ventilation is similar during inhalational anesthesia in spontaneous breathing and during awake state. In the critical care setting, when patients with acute lung injury are initially allowed to breathe spontaneously with airway pressure release ventilation, better cardiopulmonary function has been observed and patients have required ventilation support for shorter periods. It seems that when diaphragm contraction is preserved at least to some extent, it is able to generate a transpulmonary pressure that exceeds the critical alveolar pressure. This pressure is transmitted to lung regions near the diaphragm, specifically to the more caudal and dorsal zones, where alveolar collapse tends to occur; spontaneous breathing would therefore open lung units where recruitment is most useful, improving aeration. These observations seem to call into question the findings of Radke et al. in patients under general anesthesia and PSV. First, certain design limitations may explain the discrepancy, given that the anesthetic techniques used and the duration of surgery were not entirely homogeneous in the authors’ three patient groups. The differences, though not statistically significant in this small study, may have been clinically significant. We are referring to slight variations in the combination of regional block techniques and general anesthesia, the amount of sufentanil administered, and the depth of anesthesia recorded. As a result, it is possible that automatic ventilator adjustments in the PSV group may have led to enough loss of ventilatory stimulus to diminish diaphragm activity. PSV levels set from 10 to 20 cm H2O are too high to produce enough diaphragm contraction to provide spontaneous ventilation benefits. Second, spontaneous ventilation during airway pressure release ventilation has been shown to be more efficient than PSV in decreasing atelectasis in patients with acute respiratory distress syndrome, even when both ventilator modes are set at the same mean airway pressure. During airway pressure release ventilation, patients

Pharmacy savings generated by preoperative administration of clonidine

STUDY OBJECTIVE To evaluate the effects of the preoperative administration of clonidine by the oral, intramuscular (i.m.), or epidural routes, on isoflurane expense during total abdominal hysterectomy. DESIGN Randomized, double-blind, placebo-controlled study. SETTING University hospital. PATIENTS 80 ASA physical status I and II patients scheduled for total abdominal hysterectomy. INTERVENTIONS Patients were distributed into four groups of treatment: oral, i.m., epidural, and control. Each group received 300 microg clonidine according to the treatment group, plus placebo by the other routes. The control group received placebo by all three routes. Depth of anesthesia was evaluated by changes in blood pressure and heart rate over baseline values. Cost evaluation was based on three components: expense of isoflurane, cost of 300 microg of clonidine (tablets or ampoules), and the disposable material required to dispense clonidine to each group. MEASUREMENTS AND MAIN RESULTS Groups were comparable regarding demographic data, duration of surgery, and time to discharge from recovery room. Postoperatively, none of the patients had recall of intraoperative events. Clonidine reduced isoflurane pharmacy cost by approximately 45%, regardless of the route of administration. However, when cost of clonidine and the disposable equipment used for its administration were taken into account, the cost of the epidural kit surmounted the savings in isoflurane expense. CONCLUSION In the patient population studied, premedication with 300 microg oral, i.m., or epidural clonidine, similarly and significantly reduced the expense of isoflurane during general anesthesia of an approximate duration of two hours. However, the cost of the epidural kit offsets the savings in isoflurane.

Almitrine Fails to Improve Oxygenation During One-Lung Ventilation With Sevoflurane Anesthesia

OBJECTIVE Almitrine enhances hypoxic pulmonary vasoconstriction (HPV) and can improve hypoxemia related to one-lung ventilation (OLV). Studies using almitrine have been conducted without inhaled anesthetics because they could inhibit HPV, counteracting the effect of almitrine. This hypothesis, however, has not been confirmed. This studys aim was to evaluate whether almitrine could improve oxygenation when administered during OLV with sevoflurane anesthesia. DESIGN A prospective, randomized, double-blind, placebo-controlled trial. SETTING A tertiary care, university teaching hospital. PARTICIPANTS Thirty adult patients undergoing open-chest thoracic surgery. INTERVENTIONS Patients were assigned randomly to receive almitrine or placebo during OLV. Respiratory and hemodynamic variables were recorded continuously. Anesthesia was maintained with sevoflurane and remifentanil. Intraoperative techniques and medical teams were the same all over the study. MEASUREMENTS AND MAIN RESULTS Respiratory and hemodynamic variables were measured during two-lung ventilation and during open-chest OLV. Two-way repeated-measures analysis of variance was used to compare the effects of almitrine and placebo. During OLV, PaO2 and shunt fraction worsened in all patients without significant differences between groups. At 30-minutes of OLV, PaO2 was 184±67 mmHg in the almitrine group and 145±56 mmHg in the placebo group, while shunt fraction were 31%±6% and 36%±13%, respectively. Mean pulmonary artery pressure was higher in the almitrine group (31±5 v 24±5 mmHg, p<0.001). CONCLUSIONS During anesthesia with sevoflurane for open-chest OLV, almitrine failed to improve oxygenation and increased pulmonary artery pressure. The combination of sevoflurane and almitrine should, therefore, be avoided.