Preoperative and intraoperative factors associated with prolonged mechanical ventilation. A study in patients following major abdominal vascular surgery

Performance of new spirometry reference values in preoperative assessment of lung function

BACKGROUND

Pulmonary function is not routinely assessed in patients without respiratory disease and symptoms before surgery, even if they are smokers. We aimed to check whether the new spirometric reference values of the worldwide Global Lung Initiative (GLI) affected the preoperative assessment of lung function in allegedly lung-healthy patients compared with the still commonly used old predicted values.

METHODS

Two hundred nineteen allegedly lung-healthy non-smokers, past and current smokers were examined by spirometry before elective surgery. The obtained values of forced expiratory volume in 1 second (FEV₁ ), forced vital capacity (FVC) and FEV₁ /FVC were transformed into z-scores according to the GLI guidelines. A comparison between the new and old reference values was performed. FEV₁ was used for the grading of airway obstruction.

RESULTS

One hundred eighty-three subjects performed the ventilation manoeuvre according to the GLI recommendations and were analysed. Most non-smokers and past smokers met the new references ranges for spirometric values. Only z-scores of FEV₁ /FVC distinguished among all three patient groups, FEV₁ between smokers and the other two groups and FVC did not discriminate the groups, irrespective of the reference values used. Airway obstruction was identified in 24% of asymptomatic smokers by z-scores of FEV₁ /FVC but in only 14% by the old predicted values. In elderly smokers (>60 years), the corresponding values rose to 50% and 30%. Old predicted values of FEV₁ underestimated the degree of airway obstruction mainly in middle-aged smokers.

CONCLUSION

Allegedly lung-healthy current smokers showed a higher proportion of preoperatively reduced lung function when z-scores were used, especially in elderly subjects.

Postoperative pulmonary complications

PURPOSE OF REVIEW

Postoperative pulmonary complications, including pneumonia, bronchospasm, respiratory failure and prolonged mechanical ventilation, occur commonly and are a significant source of morbidity and mortality. This review will discuss the etiology of postoperative pulmonary complications and the interventions that reduce their risk.

RECENT FINDINGS

General anesthesia and surgery produce changes in the respiratory system and are responsible, along with underlying conditions, for postoperative pulmonary complications. Risk factors include upper abdominal or thoracic surgery, cigarette smoking, chronic respiratory disease, emergency surgery, anesthetic time of 180 min or more, age greater than 70 years, renal failure, poor nutritional status, and significant intraoperative blood loss. The inhibition of phrenic nerve output results in postoperative diaphragmatic dysfunction. Sleep-disordered breathing occurs after surgery even in patients without obstructive sleep apnea, but patients with obstructive sleep apnea may have a worsening of their disease after surgery. A clear advantage of one anesthetic technique over another in reducing postoperative pulmonary complications has not been demonstrated. Conflicting results have been obtained regarding the value of epidural analgesia in preventing postoperative pulmonary complications. Incentive spirometry decreases rates of postoperative pulmonary complications and hospital lengths of stay.

SUMMARY

Understanding risk factors for the development of postoperative pulmonary complications allows targeted interventions aimed at reducing their frequency and severity. Further research is needed to define the role of regional analgesic and anesthetic techniques in reducing postoperative pulmonary complications, and also to define the nature of risk factors and develop better predictive models of patients at risk of developing postoperative pulmonary complications.

Identifying risk factors for postoperative pulmonary complications

Postoperative pulmonary complications are potentially preventable adverse events that are a major source of postoperative morbidity and mortality. Although these events occur more frequently than cardiac complications, less is known about how to predict their occurrence. This review of the literature identifies significant risk factors for postoperative pulmonary complications. Nurses can be instrumental in preventing postoperative pulmonary complications by identifying patients at risk for their development.

Ion transport in alveolar type I cells

This highlight article summarizes the current published literature of ion channels and ion transport in type I cells. Twenty years ago, the general theory of ion and fluid transport in the lung was that the alveolar type II cells, known to contain ion channels, governed ion transport and that the type I cells, believed to be incapable of ion transport, only allowed passive movement of water. Unable to reconcile the extraordinarily large surface area covered by type I cells (95% of the internal surface area of the lung) with such minimal biological activity, investigators set out to demonstrate that type I cells were capable of ion transport and played a role in regulating lung fluid balance. Various methods were employed to show that type I cells contained ENaC (HSC and NSC channels), CNG and K(+) channels, and CFTR, further necessitating a revision of the current theories of ion and fluid transport in the lung.

Hemodynamic Changes During Discontinuation of Mechanical Ventilation in Medical Intensive Care Unit Patients

• Background Cardiac dysfunction can prevent successful discontinuation of mechanical ventilation. Critically ill patients may have undetected cardiac disease, and cardiac dysfunction can be produced or exacerbated by underlying pathophysiology.

• Objective To describe and compare hemodynamic function and cardiac rhythm during baseline mechanical ventilation with function and rhythm during a trial of continuous positive airway pressure in medical intensive care patients.

• Methods A convenience sample of 43 patients (53% men; mean age 51.1 years) who required mechanical ventilation were recruited for this pilot study. Cardiac output, stroke volume, arterial blood pressure, heart rate, cardiac rhythm, and plasma catecholamine levels were measured during mechanical ventilation and during a trial of continuous positive airway pressure.

• Results One third of the patients had difficulty discontinuing mechanical ventilation. Successful patients had significantly increased cardiac output and stroke volume without changes in heart rate or arterial pressure during the trial of continuous positive airway pressure. Unsuccessful patients had no significant changes in cardiac output, stroke volume, or heart rate but had a significant increase in mean arterial pressure. The 2 groups of patients also had different patterns in ectopy. Concurrently, catecholamine concentrations decreased in the successful patients and significantly increased in the unsuccessful patients during the trial.

• Conclusions Patterns of cardiac function and plasma catecholamine levels differed between patients who did or did not achieve spontaneous ventilation with a trial of continuous positive airway pressure. Cardiac function must be systematically considered before and during the return to spontaneous ventilation to optimize the likelihood of success.

Increased pulmonary capillary permeability and extravascular lung water after major vascular surgery

INTRODUCTION

We decided to investigate the pathogenesis of pulmonary ventilatory and radiographic abnormalities in patients after major vascular surgery.

PATIENTS AND METHODS

Sixteen mechanically ventilated patients without heart failure were studied, within 3 h after major abdominal surgery. We measured extravascular lung water, intrathoracic, global end-diastolic and pulmonary blood volumes, (67)Ga-transferrin pulmonary leak index and ventilatory and radiographic variables. The latter allowed computation of the lung injury score as a measure of lung injury.

RESULTS

The extravascular lung water was elevated (>7 mL kg(-1)) in 5 of 16 patients, while the pulmonary leak index was elevated in 11 patients and a supranormal extravascular lung water was associated with a high pulmonary leak index and higher extravascular lung water relative to intrathoracic blood volume or pulmonary blood volume. Patients were arbitrarily divided into those with a lung injury score >1 and < or =1, and only differed in the factors composing the score as well as in extravascular lung water divided by pulmonary blood volume. A lung injury score >1 was associated with a longer duration of mechanical ventilation.

CONCLUSION

Our data suggest that mild, subclinical, pulmonary oedema is relatively common after major vascular surgery, mainly caused by increased pulmonary capillary permeability in the absence of overt heart failure. However, permeability oedema only partially contributes to postoperative lung injury score and need for mechanical ventilation, suggesting a major contribution by atelectasis.

Preoperative assessment: pulmonary

Understanding the risk factors for the development of PPCs allows targeted interventions aimed at reducing the frequency and severity of PPCs. The broad categories of what increases the likelihood of developing a PPC are understood but specific understanding of how individual risk factors act to cause PPCs is lacking,and there is little information regarding the interaction or synergy between risk factors. Further research is needed to define the nature of risk factors and develop better predictive models of patients at risk for developing PPCs. It is clear that anesthetic agents produce significant changes in the respiratory system but further information is needed to define how such changes contribute, if at all, to the subsequent development of PPCs. The ongoing controversy regarding the value of regional analgesia or anesthetic techniques, especially epidural analgesia and anesthesia, in reducing or preventing PPCs requires well-done randomized clinical trials. Further research is also needed in the area of postoperative care such as interventions in patients with OSA or the use of inventive spirometric techniques.

Pulmonary complications in anterior-posterior thoracic lumbar fusions

BACKGROUND CONTEXT

Surgery for adult spinal deformity may require both an anterior and posterior approach in order to stabilize the spine and achieve the desired correction. These procedures can be associated with significant pulmonary complications, including atelectasis, pneumonia and respiratory failure. The etiology of some of the respiratory complications is clear: poor inspiratory effort from incision pain and previous pulmonary disease. However, for many patients the direct cause of these complications is not obvious.

PURPOSE

To delineate the incidence, severity and risks associated with pulmonary complications in the setting of major spine surgery.

STUDY DESIGN/SETTING

Retrospective chart review study of adult patients undergoing combined anterior-posterior thoracic, lumbar and sacral fusion spine surgery.

PATIENT SAMPLE

A total of 60 charts were reviewed for this study.

OUTCOME MEASURES

Radiographic abnormalities correlated with clinical findings, postoperative need for ventilation and lengths of hospital stay were used as outcome measures.

METHODS

Perioperative pulmonary complications were assessed for 60 patients with spinal deformities who underwent combined anterior-posterior thoracic, lumbar and sacral fusion over a 2-year period.

RESULTS

One patient was eliminated from analysis because of multiple surgeries during his hospital course. Of the remaining 59 patients, 38 (64%) developed roentgenographic abnormalities. The most common radiographic finding was an effusion found in 66% of these patients, followed by atelectasis in 53%. Twenty-one percent (8 of 38) had infiltrates. Five (5 of 38) or 13% had evidence of partial or complete lobar collapse; in two bronchoscopy was required because of profound hypoxemia. Two patients had pneumonia requiring antibiotic treatment. All but two patients were extubated within 36 hours of surgery. They were kept intubated because of hemodynamic instability. There was no statistically significant difference in the group of patients with and without roentgenographic abnormalities with regard to age, weight, American Society of Anesthesiologists class, smoking history, pulmonary function test results, blood loss, perioperative blood and crystalloid requirement and length of surgery. Patients with radiographic abnormalities were more likely to have had invasion of their thoracic cavity (p=.02) and had a longer mean hospital stay of 13.5 versus 10.2 days (p=.009).

CONCLUSION

Radiographic abnormalities of the lungs are common after major spine surgery involving both an anterior and posterior approach, especially when the thoracic cavity is invaded. In view of the morbidity and longer hospital stay associated with such findings, close monitoring of pulmonary status with aggressive pulmonary toilet are indicated.

Critical care of the vascular surgery patient

Providing effective critical care to vascular surgical patients is challenging to the intensivist. These patients often have multiple significant concurrent diseases that need to be adequately managed. A selective policy for identifying patients that need ICU is recommended. Early and smooth restoration to their preoperative physiological homeostasis is crucial. Optimal pain relief, return to normothermia, and adequate intravascular volume replacement are thus key interventions. Epidurals provide excellent analgesia. Vigilant monitoring and decisive therapy of the wide range of complications that may occur in the postoperative is of paramount importance. The level of monitoring should be an extension of that done intraoperatively. Hemorrhage and thrombosis are dreaded sequelae; cardiac morbidity and mortality is significant. Respiratory complications may necessitate prolonged postoperative mechanical ventilation. Careful clinical evaluation is necessary to detect the various neurological complications that may occur. Renal and gastrointestinal complications are potentially lethal. Graft sepsis may occur later. The development of new techniques, such as endovascular repairs of aneurysms, may minimize the need for ICU.

Relationship between the duration of the preoperative smoke-free period and the incidence of postoperative pulmonary complications after pulmonary surgery

STUDY OBJECTIVE

To examine the relationship between the duration of the preoperative smoke-free period and the development of postoperative pulmonary complications (PPCs) in patients who underwent pulmonary surgery, and the optimal timing of quitting smoking.

DESIGN

Retrospective cohort study.

SETTING

Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka, Japan.

PATIENTS

Two hundred eighty-eight consecutive patients who underwent pulmonary surgery between January 1997 and December 1998.

MEASUREMENTS AND RESULTS

We collected information on the preoperative characteristics, intraoperative conditions, and occurrence of PPCs by reviewing the medical records. Study subjects were classified into four groups based on their smoking status. A current smoker was defined as one who smoked within 2 weeks prior to the operation. Recent smokers and ex-smokers were defined as those whose duration of abstinence from smoking was 2 to 4 weeks and > 4 weeks prior to the operation, respectively. A never-smoker was defined as one who had never smoked. The incidence of PPCs among the current smokers and recent smokers was 43.6% and 53.8%, respectively, and each was higher than that in the never-smokers (23.9%; p < 0.05). The moving average of the incidence of PPCs gradually decreased in patients whose smoke-free period was 5 to 8 weeks or longer. After controlling for sex, age, results of pulmonary function tests, and duration of surgery, the odds ratios for PPCs developing in current smokers, recent smokers, and ex-smokers in comparison with never-smokers were 2.09 (95% confidence interval [CI], 0.83 to 5.25), 2.44 (95% CI, 0.67 to 8.89), and 1.03 (95% CI, 0.47 to 2.26), respectively.

CONCLUSIONS

These findings indicate that preoperative smoking abstinence of at least 4 weeks is necessary for patients who undergo pulmonary surgery, to reduce the incidence of PPCs.

Evaluation and management of patients with pulmonary disease before thoracic and cardiovascular surgery

The risks of respiratory complications after thoracic and cardiovascular surgeries are particularly high for patients with chronic pulmonary disease and are associated with prolonged hospital stays and increased mortality. The primary goals of preoperative management are to identify risk factors and institute interventions likely to reduce subsequent postoperative pulmonary complications. Smoking, symptomatic obstructive lung disease, respiratory infection, obesity, and malnutrition are all potentially modifiable risk factors. Chest physiotherapy is indicated in all patients regardless of risk factor profile. Providing a thoughtfully designed, multifaceted course of preoperative care can result in a clinically significant reduction in postoperative morbidity and mortality, particularly if instituted well in advance of surgery.

Perioperative Ventilation of the Vascular Surgery Patient

Although cardiovascular disease represents the most com mon comorbidity in patients undergoing vascular surgery, perioperative ventilatory issues can also play a vital role in achieving good outcomes. Postoperative respiratory failure is uncommon after carotid endarterectomy or peripheral revascularization procedures, the risk of pulmonary compli cations following intra-abdominal or intrathoracic vascular surgery is high. In addition to primary lung diseases such as chronic obstructive pulmonary disease, associated organ dysfunction syndromes such as stroke, renal failure, and congestive heart failure can also contribute to respiratory morbidity. An approach to minimizing respiratory complica tions begins with a careful preoperative search for ways to maximize pulmonary function and establishment of targets for postoperative weaning. Intraoperative attention should be paid to intraoperative management of bronchospasm, auto-positive end-expiratory pressure, and acid-base status. Postoperative management should strive for rapid extuba tion, continuation of pharmacologic conditioning programs begun preoperatively, and consideration of the use of post operative regional analgesia for patients with severe lung disease.

[Risk factors for mortality in abdominal aortic surgery]

OBJECTIVE

To analyse pre and peroperative variables for predicting mortality after abdominal aortic surgery.

STUDY DESIGN

Prospective study.

PATIENTS

We prospectively included 658 consecutive patients undergoing abdominal aortic surgery from January 1993 to July 1997.

METHODS

Age, gender, hypertension, history of myocardial infarction or coronary revascularization, angina pectoris, diabetes, arrhythmia, cardiac insufficiency, serum creatinine > 150 mumol.L-1, beta-blockers therapy, calcium channel inhibitors, angiotensin converting enzyme inhibitors were preoperative analysed variable. Type of aortic disease (anuerysms versus aortic occlusion), duration of surgery, blood loss, type of laparotomy (medium versus lombotomy) were peroperative analysed variables. Haemoglobinemia was monitored during surgery and patients were transfused if haemoglobinaemia < 80 g.L-1.

RESULTS

Thirty-three patients died after aortic surgery (5%). In multivariate analysis, angina pectoris (OR = 5.47, P < 0.001), chronic obstructive bronchopulmonary disease (OR = 2.27, P = 0.05) and duration of surgery (OR = 1.60, P < 0.001) were the independent predictive factors of mortality. Age, blood loss were predictive factors only in univariate analysis.

CONCLUSION

Angina pectoris and COBP were the two independent preoperative factors of mortality. The duration of surgery was the only peroperative factor. Well monitored blood loss was not a predictive factor.

Smoking and postoperative pulmonary complications. An evidence-based review of the recent literature

Postoperative pulmonary complications (PPC) lead to significant morbidity after both thoracic and non-thoracic surgical procedures. The role of smoking as an independent risk factor is controversial, though recent level III and IV studies suggest that it may indeed be significant. In addition, the role and timing of pre-operative smoking cessation is not clear. Although some studies suggest that abstinence too soon prior to operation may actually increase the risk of PPC, it still appears that aggressive counseling for smoking cessation prior to any elective procedure is the best overall course of action.

Preoperative evaluation of the pulmonary patient undergoing nonpulmonary surgery

As the human population continues to live longer, patients with chronic pulmonary disease are increasingly presenting for surgical treatment. The influences of general anesthesia and an operative procedure are well known to negatively impact pulmonary gas exchange. Pulmonary-compromised patients are at high risk for the development of perioperative complications as a consequence of not only their pulmonary disease but of associated comorbid disease processes. Certain risk factors associated with preexisting pulmonary conditions are known to increase the likelihood of intraoperative or postoperative complications. Essential components in the comprehensive care of these patients are the identification of these high-risk patients and the implementation of an inclusive perianesthetic care regimen designed to decrease pulmonary complications. This article will familiarize the perianesthetic nurse with pertinent skills required to effectively assess and prepare patients with pulmonary disease for their upcoming surgery.

[Repercussion of postoperative pain, benefits attending to treatment]

Physiological responses to postoperative acute pain may impede organ functions (cardiovascular, pulmonary, coagulation, endocrine, gastrointestinal, central nervous system, etc). Pain alleviation improves patient's comfort, but also may minimise perioperative stress response, physiological responses and postoperative organ dysfunction, assist postoperative nursing and physiotherapy, enhance clinical outcome, and potentially shorten the hospital stay. Potent postoperative analgesia, especially by epidural route, may be associated with reduction in incidence and severity of many perioperative dysfunctions. Peridural analgesia using local anaesthetics is the best technique for decreasing postoperative stress after lower abdominal or lower limb surgery. Analgesia using either epidural or high doses of morphine may improve some cardiac variables such as tachycardia and ischaemia, but does not change the incidence of severe cardiac complications. For patients undergoing vascular or orthopaedic surgery, epidural analgesia can improve clinical outcome by preventing the development of arterial or venous thromboembolic complications. However, in comparative studies, the control groups did not receive adequate prophylactic treatment for thromboembolic complications. Epidural analgesia can hasten the return of gastrointestinal motility and shorten the hospital stay. Postoperative mental dysfunction is decreased using intravenous PCA morphine in the elderly. Epidural analgesia with local anaesthetics improves postoperative respiratory function but, for unknown reasons, these benefits are not associated with a decrease in respiratory complications. On balance, the mode of acute pain relief decreases adverse physiological responses and many intermediate outcome variables; however, there is inconclusive evidence that it affects clinical outcome. Major advances in postoperative recovery can be achieved by early aggressive perioperative care, including potent analgesia, early mobilisation and oral nutrition. As a result, the hospital stay may be shortened.

Preoperative smoking habits and postoperative pulmonary complications

OBJECTIVE

To examine the effect of preoperative smoking behavior on postoperative pulmonary complications.

DESIGN

Prospective cohort study.

SETTING

The Veterans Administration Medical Center, Syracuse, NY.

PARTICIPANTS

Patients scheduled for noncardiac elective surgery (n=410).

MEASUREMENTS AND RESULTS

Smoking status was determined by self-report. Postoperative pulmonary complications were determined by systematic extraction of medical record data. Postoperative pulmonary complications occurred in 31 of 141 (22.0%) current smokers, 24 of 187 (12.8%) past smokers, and 4 of 82 (4.9%) never smokers. The odds ratio (OR) for developing a postoperative pulmonary complication for current smokers vs never smokers was 5.5 (95% confidence interval [CI], 1.9 to 16.2) and 4.2 (95% CI, 1.2 to 14.8) after adjustment for type of surgery, type of anesthesia, abnormal chest radiograph, chronic cough, history of pulmonary disease, history of cardiac disease, history of COPD, education level, pulmonary function, body mass index, and age. Current smokers who reported reducing cigarette consumption prior to surgery were more likely to develop a complication compared with those who did not (adjusted OR=6.7, 95% CI, 2.6 to 17.1).

CONCLUSIONS

Current smoking was associated with a nearly sixfold increase in risk for a postoperative pulmonary complication. Reduction in smoking within 1 month of surgery was not associated with a decreased risk of postoperative pulmonary complications.

Acute lung injury after aortic surgery: the relation between lung and leg microvascular permeability to 111indium-labelled transferrin and circulating mediators

BACKGROUND

Aortic surgery is a risk factor for acute lung injury and this may relate to ischaemia/reperfusion (I/R) of the lower body and release of inflammatory mediators. The aim of this study was to define the changes in microvascular protein permeability and circulating inflammatory mediators after aortic surgery.

METHODS

In 11 consecutive patients who underwent elective aortic surgery microvascular permeability in lung and leg was measured before and a median of 2.8 hours after completion of surgery using 111indium (In)-labelled transferrin and 99mtechnetium (Tc)-labelled red blood cells, yielding a protein leak index (PLI) that is specific for protein permeability. Circulating leucocyte counts and levels of inflammatory mediators were determined.

RESULTS

In the lung the PLI rose from a median of 0.6 (range -0.5 to 2.2) x 10(-3)/min before surgery to 5.4 (-2.3 to 33.5) x 10(-3)/min after surgery, and in the leg from 0.3 (-1.6 to 1.7) x 10(-3)/min to 5.0 (1.0 to 27.8) x 10(-3)/min. The increase in PLI in the lung was related to that in the leg. Levels of activated complement C3a and tumour necrosis factor-alpha did not change, but levels of interleukin (IL)-6, IL-8 and elastase-alpha 1-antitrypsin increased. After surgery there was slight neutrophilia and the leucocyte counts were inversely related to the IL-8 level. The rise in lung but not in leg PLI was greatest in patients with the highest IL-8 levels and the lowest leucocyte counts.

CONCLUSIONS

Early after aortic surgery microvascular protein permeability increases in the leg and lung. Leg I/R injury may result in neutrophil activation and release of IL-8, which may induce neutrophil sequestration and subsequently increased pulmonary microvascular permeability. These findings may help to explain the occurrence of acute lung injury after I/R in man.

Assessment of operative risk for patients with advanced lung disease

Increasingly, patients with advanced lung disease are being offered operative procedures. The assessment of the perioperative risk of these patients must include not only the assessment of their lung disease, but the assessment of the patient's cardiovascular disease, their age, and their other medical problems. Knowledge of the stress of particular surgical procedures is also of importance in risk assessment, and is addressed in this article.

Analyzing intensive care unit length of stay data: problems and possible solutions

OBJECTIVES

To explore methods of evaluating the length of stay patterns of intensive care unit (ICU) patients. It was hypothesized that the mean does not adequately describe the typical length of stay (central tendency) because distribution patterns are often markedly skewed by patients with extended stays. Therefore, other descriptors are needed. In addition, ways are needed to identify outliers-patients with stays longer or shorter than the bulk of the data.

DESIGN

Review of retrospective data.

SETTING

University hospital surgical ICU.

PATIENTS

Representative data included all (4,499) patients admitted over a 6-yr period. Each was assigned to a diagnostic group that represented either a frequently performed surgical procedure (e.g., thymectomy) or in cases where there was no predominant procedure, a surgical discipline (e.g., otolaryngology).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The frequency distributions were usually skewed to the right and included two populations of interest: The portion with the majority of observations ("body"), which described "typical" behavior, and the "tail", which provided information on outliers. The average of the mean lengths of stay of all diagnostic groups was higher than the average of the medians (3.9 +/- 1.8 [SD] vs. 2.7 +/- 1.1 days, p < .001) and modes (2.1 +/- 1.2 days, p < .001), reflecting the rightward skewness of the length of stay frequency distributions. The median +/- 1 day included 75 +/- 13% of the patients, thus confirming that the median was the most useful descriptor of central tendency. Various methods were used to identify outliers. Histograms of the frequency distributions were examined and outliers visually identified. Conventional outlier analysis labeled as outliers patients staying greater than two standard deviations from the mean stay. This method underestimated the number of outliers when the distributions were skewed to the right. Another method involved designating a specific length of stay (e.g., 7 or 10 days) or percentage of patients as the outlier threshold. Each method designated different numbers of patients as outliers.

CONCLUSIONS

When analyzing length of stay data it is important to visually examine the frequency distribution because it is often skewed to the right. This skewness renders traditional parameters such as the mean and standard deviation less useful for describing the typical length of stay. Instead, the median, mode, and harmonic mean should be used. When reporting length of stay, some indication of the characteristics of the data should be presented. A graph of the frequency distribution rapidly allows the reader to determine its shape. A simple method is to report the mean, median, and range.

Respiratory insufficiency after abdominal surgery

The objective of this study was to define the relationship between respiratory insufficiency (RI) and various putative risk factors for patients undergoing abdominal surgery. A review of 1332 adults undergoing abdominal surgery was undertaken. Information was collected in a unbiased, prospective and uniform manner with regard to baseline characteristics, perioperative events and adverse outcomes after surgery. Respiratory Insufficiency was defined as either: a PO2 < 60 mm Hg, the performance of a tracheotomy, or endotracheal intubation for more than 24 h. The incidence of RI was 3% (40/1332). A logistic regression analysis only identified an American Society of Anesthesia (ASA) classification > 2 (P < 0.001) and the presence of chronic bronchitis (P (P < 0.05) as significant risk factors. In addition, 33% (8/24) of the patients who developed postoperative intraperitoneal sepsis and 30% (14/47) of the patients who underwent a reoperation developed RI. It was concluded that patients with a significant systemic disease (ASA > 2), as well as patients with chronic bronchitis, should be the recipients of intense efforts to prevent pulmonary complications after abdominal surgery.

[Prevention of respiratory complications after abdominal surgery]

Abdominal surgery, especially upper abdominal surgical procedures are known to adversely affect pulmonary function. Pulmonary complications are the most frequent cause of postoperative morbidity and mortality. This review article aimed to analyse the incidence and risk factors for postoperative pulmonary morbidity and their prevention. The most important means for preoperative assessment is the clinical examination; pulmonary function tests (spirometry) are not reliably predictive for postoperative pulmonary complications. Age, type of surgical procedure, smoking and nutritional state have all been identified as potential predictors for postoperative complications. However, usually there is not enough preoperative time available to obtain beneficial effects of stopping smoking and improvement of nutritional state. In patients with COPD, a preoperative multidisciplinary evaluation including the primary care physician, pulmonologist/intensivist, anesthesiologist and surgeon is required. Consensus as to preoperative physiologic state, therapeutic preparation, and postoperative management is essential. Simple spirometry and arterial blood gas analysis are indicated in patients exhibiting symptoms of obstructive airway disease. There are no values that contra-indicate an essential surgical procedure. Smoking should stop at least 8 weeks preoperatively. Preoperative therapy for elective surgery with antibiotics, beta2-agonist, or anticholinergic bronchodilator aerosols, as well as training in cough and lung expansion techniques should begin at least 24 to 48 hours preoperatively. Postoperative therapy should be continued for 3 to 5 days. Usually, anaesthesia is responsible for early complications, whereas surgical procedures are often associated with delayed morbidity. Laparoscopic procedures are recommended, as postoperative morbidity and hospital stay seem reduced in patients without COPD. Regional anaesthesia is given as having less adverse effects on pulmonary function than general anaesthesia. However, for unknown reasons these benefits are not associated with a decrease in postoperative respiratory complications. Moreover, the quality or the type of postoperative analgesia does not influence postoperative respiratory morbidity. Postoperatively, oxygen administration increases SaO2, but cannot abolish desaturation due to obstructive apnea. The various techniques of physiotherapy (chest physiotherapy, incentive spirometry, continuous positive airway pressure breathing) seem to be equivalent in efficacy; but intermittent positive pressure breathing has no advantages, compared with the other treatments and could even be deleterious. Chest physiotherapy and incentive spirometry are the most practical methods available for decreasing secretion contents of airways, whereas continuous positive airway pressure breathing is efficient on atelectasis. In stage II or III COPD patients, admission in a intensive therapy unit and prolonged mechanical ventilation may be required.