PRE-OPERATIVE ASSESSMENT OF THE RESPIRATORY SYSTEM
INTRODUCTION:
Physicians are often asked to evaluate a patient prior to surgery. The medical consultant
may be seeing the patient at the request of the surgeon, or may be the primary care
physician assessing the patient prior to consideration of a surgical referral.
The goal of this evaluation is to determine the risk to the patient of the proposed procedure
and to minimize known risks.
Postoperative pulmonary complications contribute significantly to overall perioperative
morbidity and mortality. In a study of patients undergoing elective abdominal surgery, as an
example, pulmonary complications occurred significantly more often than cardiac
complications and were associated with significantly longer hospital stays1. The United
States National Surgical Quality Improvement Program (NSQIP) also found that
postoperative pulmonary complications were the most costly of major postoperative medical
complications (including cardiac, thromboembolic, and infectious) and resulted in the longest
length of stay2.
As the impact of pulmonary complications following surgery has become increasingly
apparent, estimation of their risk should be a standard element of all preoperative medical
evaluations.
DEFINITION OF POSTOPERATIVE PULMONARY COMPLICATIONS:
The reported frequency of postoperative pulmonary complications in the literature varies
from 2 to 70 percent. This wide range is due in part to patient selection and procedurerelated risk factors, although differing definitions for postoperative complications account for
much of the variability and make comparison of reported incidences across different studies
difficult.
One proposed definition is a pulmonary abnormality that produces identifiable disease or
dysfunction that is clinically significant and adversely affects the clinical course 3. This would
include:
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Atelectasis
Infection, including bronchitis and pneumonia
Prolonged mechanical ventilation and respiratory failure
Exacerbation of underlying chronic lung disease
Bronchospasm4
EFFECT OF MEDICAL CONSULTATION ON SURGICAL OUTCOMES
Several investigators have studied whether internist care of surgical patients is beneficial.
These studies have shown that internists identify medical conditions that are related to
surgical outcome and often recommend interventions for these conditions 5-7. In addition,
physicians occasionally cancel or delay surgery so that medical conditions can be optimized.
Studies report conflicting findings regarding the effect of medical consultation on length of
stay. Two studies demonstrated a decrease in length of stay when an internist routinely
cared for patients after thoracic surgery8 or hip fracture surgery9, while another showed
similar or increased costs and length of stay for consulted patients, and no improvement in
glucose control, use of perioperative beta blockers, or prophylaxis for venous
thromboembolism10. No study has shown a decrease in perioperative morbidity associated
with medical consultation, although there were fewer minor complications in the group of hip
fracture patients who were cared for by hospitalists9. Nevertheless, the practice of medical
consultation is widespread and, assuming consultants make evidence-based
recommendations that improve surgical outcomes, it is reasonable to infer that consultation
will improve the care of the surgical patient if consultative recommendations are
implemented
GENERAL PRINCIPLES OF CONSULTATION
An effective and satisfactory medical consultation can be performed when some general
principles are followed10
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Determine the question and respond to it.
Establish the urgency of the consultation and provide a timely response.
“Look for yourself”; confirm the history and physical examination and check test
results.
Be as brief as appropriate; be definitive and limit the number of recommendations.
Be specific, including medication details.
Provide contingency plans; anticipate potential problems and questions.
“Honour thy turf”; don't steal other physician's patients.
Teach with tact; consult, don't insult.
Talk is cheap and effective; direct verbal communication is crucial.
Follow-up to ensure that recommendations are followed
In doing a pre-operative assessment, one should seek factors that might put the patient at
higher than average risk and propose plans to reduce this risk. Risks are specific to the
individual patient, the type of procedure proposed, and the type of anesthesia selected. If no
such risks are present, the final statement should be that the patient is at average risk for the
proposed surgery.
Studies that have examined the compliance of referring surgeons with the recommendations
of physicians have found that compliance ranges from 54 to 95 percent depending upon the
setting11.
The following factors or advice have been shown to improve compliance with the physician's
recommendations:
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As discussed previously, the central reason for the consultation request needs to be
clearly stated, understood, and addressed
The physician should respond in a timely fashion. Urgent consultations should be
seen promptly, and elective consultations should be answered so as not to cause a
delay in surgery. In general, all consultations should be done within 24 hours, and
preferably the same day as requested. Any anticipated delays should be
communicated immediately to the referring surgeon.
The physician's recommendations should be definitive, prioritized, and precise.
The number of recommendations should be limited when possible, preferably to five
or fewer. Recommendations identified as "crucial" or "critical" are more likely to be
followed.
The physician should use definitive language and specify relevant recommendations.
Recommendations for medications should specify the drug name, dose, frequency,
route of administration, and duration of therapy. Alternatives to a recommended
therapy should be mentioned if available.
Therapeutic recommendations are more likely to be followed than diagnostic
recommendations, but recommendations to start therapy may be less likely to be
followed than those to continue or discontinue therapy.
Direct verbal communication with the requesting surgeon is preferable to
communicating via the chart.
Frequent follow-up visits documented with progress notes are key in improving
compliance with the physician’s recommendations.
How often a physician needs to see a patient will depend upon the patient's medical
problems and type of surgery. When the physician no longer needs to follow the patient, he
should write a note indicating that he is signing off the case. He should also make
arrangements to assure continuity of care for medical problems after the patient is
discharged.
PERIOPERATIVE PULMONARY PHYSIOLOGY
Postoperative pulmonary complications follow logically as an extension of normal
perioperative pulmonary physiology. Reduced lung volume after surgery is a major factor
contributing to the development of postoperative pulmonary complications.
Thoracic and upper abdominal surgery is associated with a reduction in lung volumes in a
restrictive pattern as follows:
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Vital capacity (VC) is reduced by 50 to 60 percent and may remain decreased for up
to one week.
Functional residual capacity (FRC) is reduced by about 30 percent.
Diaphragmatic dysfunction appears to play the most important role in these changes;
postoperative pain and splinting are also factors. Reduction of the FRC below closing
volumes contributes to the risk of atelectasis, pneumonia, and ventilation/perfusion (V/Q)
mismatching. Microatelectasis results in areas of the lung that are perfused but not
ventilated, leading to impaired gas exchange with consequent postoperative hypoxemia.
A decrease in tidal volume, loss of sighing breaths, and increase in respiratory rate occur
after abdominal and thoracic surgery and contribute to the risk of complications. In addition,
residual effects of anesthesia itself and postoperative opioids both depress the respiratory
drive. Inhibition of cough and impairment of mucociliary clearance of respiratory secretions
are factors that contribute to the risk of postoperative infection.
Lower abdominal surgery is associated with similar changes, but to a lesser degree.
Reductions in lung volumes are not seen with surgery on the extremities 12.
PATIENT RELATED RISK FACTORS
Risk factors for pulmonary complications can be divided into patient related and procedure
related risks. The potential patient related risk factors studied include the following:
AGE
The influence of age as an independent predictor of postoperative pulmonary complications
has been questioned. Early studies suggested an increased risk of pulmonary complications
with advanced age. These studies, however, were not adjusted for overall health status or
the presence of known pulmonary disease and subsequent studies did not reliably
demonstrate age as a predictor of postoperative complications. The risk of surgical mortality
was similar across age groups when stratified by American Society of Anesthesiologists
(ASA) class13.
A more recent systematic review prepared for the American College of Physicians estimated
the impact of age on postoperative pulmonary complications among studies that used
multivariable analysis to adjust for age-related comorbidities. This review made the novel
observation that age >50 years was an important independent predictor of risk. When
compared to patients <50 years old, patients aged 50 to 59 years, 60 to 69 years, 70 to 70
years, and ≥ 80 years had odds ratios (OR) of 1.50, 2.28, 3.90 and 5.63, respectively.
Therefore, even healthy older patients carry a substantial risk of pulmonary complications
after surgery.14
CHRONIC LUNG DISEASE
Known chronic lung disease is an important patient-related risk factor for postoperative
pulmonary complications. Unadjusted relative risks of postoperative pulmonary
complications have ranged from 2.7 to 6.0.
An early prospective study assessed pulmonary risk in patients with chronic obstructive
pulmonary disease (COPD) as established by clinical findings and chest radiographs.
Complications occurred in 26 percent of patients compared with 8 percent of controls. In
another report, patients with severe COPD were six times more likely to have a major
postoperative pulmonary complication after abdominal or thoracic surgery than were those
without COPD. Findings of decreased breath sounds, prolonged expiration, rales, wheezes,
or rhonchi correlated with an increased risk for postoperative complications in one case
control study.
A more recent systematic review, however, found that impact of COPD on postoperative
pulmonary complication rates was less than previously estimated. Among studies that used
multivariable analysis to adjust for patient-related confounders, the odds ratio for
postoperative pulmonary complications was 2.3614.
Despite the increased risk of postoperative pulmonary complications in patients with
obstructive lung disease, there appears to be no prohibitive level of pulmonary function
below which surgery is absolutely contraindicated. This was illustrated in a study of 12 very
high risk patients as defined by older criteria of inoperability (FEV1 <1 litre), only 3 of 15
surgeries were associated with postoperative complications and there were no deaths. In
another report of surgery in patients with severe COPD (FEV1 <50 percent predicted),
mortality was 5.6 percent (primarily related to a high mortality rate after cardiac surgery) and
severe postoperative pulmonary complications occurred in 6.5 percent. The benefit of
surgery must be weighed against the known risks; even very high risk patients may proceed
to surgery if the indication is sufficiently compelling15
ASTHMA
Despite early reports indicating that patients with asthma had higher than expected rates of
postoperative pulmonary complications, more recent studies have found no link for patients
with well controlled asthma. The largest such report studied 706 patients with asthma
undergoing general surgery. There were no incidents of death, pneumothorax, or pneumonia
in the entire sample. Fourteen minor complications occurred including bronchospasm (12)
and laryngospasm (2). One patient developed postoperative respiratory failure without
sequelae. Patients with asthma who are well controlled and who have a peak flow
measurement of >80 percent of predicted or personal best can proceed to surgery at
average risk.16
SMOKING
Smoking is a risk factor for post operative pulmonary complications, as has been
demonstrated since the first report in 1944. Smoking increase risk even among those without
chronic lung disease. The relative risk of pulmonary complications among smokers as
compared with non-smokers ranges from 1.4 to 4.3. Unfortunately the risk declines only after
eight weeks of preoperative cessation. Warner et al prospectively studied 200 smokers
preparing for coronary artery bypass surgery and found a lower risk of pulmonary
complications among those who had stopped smoking at least eight weeks before surgery
than among current smokers (14.5% vs. 33%). Paradoxically, those who had stopped
smoking less than eight weeks earlier had a higher risk than current smokers17.
OBESITY
Physiologic changes that accompany morbid obesity include:
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Reduction in lung volume
Ventilation/perfusion mismatch
Relative hypoxemia
These findings might be expected to accentuate similar changes seen with anaesthesia and
increase the risk of postoperative pulmonary complications.
However, obesity has not consistently been shown to be a risk factor for postoperative
pulmonary complications.
A systematic review found that, among eight studies using multivariate analysis, only one
study identified obesity as an independent predictor14 and therefore obesity should not affect
patient selection for otherwise high-risk procedures.
OBSTRUCTIVE SLEEP APNOEA
Obstructive sleep apnea (OSA) is an emerging risk factor for postoperative pulmonary
complications. It is well-appreciated in the anesthesia literature that OSA increases the risk
of critical respiratory events immediately after surgery, including early hypoxemia and
unplanned reintubation17.
A subsequent study followed 172 elective surgical patients who had clinical features
suggesting OSA (snoring, excessive daytime somnolence, witnessed apneas, or crowded
oropharynx). Patients underwent home oximetry testing preoperatively, and were stratified
on the basis of the number of oxygen desaturations per hour of at least 4 percent (ODI4%).
Compared to patients with better indices, patients with an ODI4% of >5 were more likely to
have postoperative respiratory (8 versus 1 percent) and cardiac (4 versus 1 percent)
complications. Pulmonary complications included hypoxemia, atelectasis, and pneumonia 18.
While the literature is still emerging, we should consider OSA to be a probable risk factor for
pulmonary complications after surgery. Whether patients without known OSA should be
screened for OSA prior to elective surgery, such as through use of a standardized
questionnaire, are unknown and the subject of current study.
PULMONARY HYPERTENSION
Pulmonary hypertension increases pulmonary complication rates after surgery. This appears
to be true regardless of the underlying etiology of the pulmonary hypertension. As an
illustration, authors studied 145 surgical patients with pulmonary hypertension, excluding
those where the condition was due to left heart disease 19. Complications included respiratory
failure (41), cardiac dysrhythmia (17), congestive heart failure (16), renal insufficiency (10),
and sepsis (10). Risk predictors included:
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History of pulmonary embolus
NYHA functional class ≥ 2
Intermediate or high risk surgery
Duration of anesthesia > 3 hours.
A subsequent study compared 62 patients with pulmonary hypertension of any etiology to
matched controls20. Mortality (10 percent versus 0) and major morbidity (24 versus 3
percent) were both significantly higher among patients with pulmonary hypertension. The
increased risk warrants careful consideration of indications for surgery and discussion of
potential risks with patients with pulmonary hypertension.
HEART FAILURE
The risk of pulmonary complications may be higher in patients with heart failure than in those
with chronic obstructive pulmonary disease. This is suggested by data from the systematic
review that formed the basis of the American College of Physicians guideline, in which the
pooled adjusted odds ratio for pulmonary complications were 2.93 for heart failure patients
and 2.36 for patients with chronic obstructive pulmonary disease14.
The original Goldman cardiac risk index has been shown to predict postoperative pulmonary
as well as cardiac complications21. Although the Revised Cardiac Risk Index is now more
commonly used to estimate risk for cardiovascular complications, validation studies of the
revised index in predicting pulmonary complications have not been done.
GENERAL HEALTH STATUS
Overall health status is an important determinant of pulmonary risk. Functional dependence
and impaired sensorium each increase postoperative pulmonary risk14.
The commonly used American Society of Anesthesiologists (ASA) classification correlates
well with pulmonary risk and is one of the most important predictors of pulmonary risk. The
criteria for assigning ASA class include the presence of a systemic disease that affects
activity or is a threat to life. Thus, patients with significant preexisting lung disease would be
classified in a higher ASA class. ASA class >2 confers a 4.87 fold increase in risk 14.
Poor exercise capacity also identifies patients at risk. The inability to exercise predicts 79%
of pulmonary complications15.
PROCEDURE RELATED RISK FACTORS
SURGICAL SITE
Surgical site is the single most important factor in predicting the overall risk of postoperative
pulmonary complications. The incidence of complications is inversely related to the distance
of the surgical incision from the diaphragm. Thus, the complication rate is significantly higher
for thoracic and upper abdominal surgery than for lower abdominal and all other
procedures15. In a systematic review of 83 univariate studies, complication rates for upper
abdominal surgery, lower abdominal surgery, and esophagectomy were 19.7, 7.7, and 18.9
percent, respectively14. The higher rates of complications in upper versus lower abdominal
surgery relate to the effect upon respiratory muscles and diaphragmatic function.
Laparoscopic cholecystectomy is associated with shorter recovery times, less postoperative
pain, and less reduction in postoperative lung volumes. Its impact on pulmonary complication
rates is less well established. While the decrease in postoperative pain might be expected to
translate into lower pulmonary complication rates, few studies have evaluated clinically
important pulmonary complications as an endpoint. In a pooled analysis of 12 studies of
laparoscopic versus open colon cancer surgery, there was a nonsignificant trend towards
reduced pulmonary complications14.
DURATION OF SURGERY
Surgical procedures lasting more than three to four hours are associated with a higher risk of
pulmonary complications. As an example, a study of risk factors for postoperative
pneumonia in 520 patients found an incidence of 8 percent for surgeries lasting less than two
hours versus 40 percent for procedures lasting more than four hours. This observation
suggests that, when available, a less ambitious, briefer procedure should be considered in a
very high risk patient14, 15.
TYPE OF ANESTHESIA
There are conflicting data with regard to the pulmonary risk of spinal or epidural anesthesia
when compared with general anesthesia. One study, as an example, found no difference in
the rate of pulmonary complications between patients undergoing transurethral prostate
surgery with spinal anesthesia and those undergoing general surgery with general
anesthesia14.
In contrast, an early retrospective study of 475 men with chronic lung disease undergoing
general surgery revealed a 9 percent incidence of death in the general anesthesia group
compared with no deaths in the spinal anesthesia group22. These findings have been
subsequently supported by others, including a review of high risk patients that found that the
rate of respiratory failure was significantly higher with general anesthesia than with epidural
analgesia and light anesthesia.
Subsequently, investigators conducted the largest systematic review of this literature to
date23. The review evaluated the results of 141 trials that included 9559 patients. They
reported a reduction in risk of pulmonary complications among patients receiving neuraxial
blockade (either epidural or spinal anesthesia) with or without general anesthesia, when
compared to those receiving general anesthesia alone. Patients receiving neuraxial blockade
had an overall 39 percent reduction in the risk of pneumonia and a 59 percent decrease in
the risk of respiratory depression.
Based upon this comprehensive review, it appears likely that general anesthesia leads to a
higher risk of clinically important pulmonary complications than do epidural or spinal
anesthesia, although further studies are required to confirm this observation.
Regional nerve block is associated with lower risk and should be considered when possible
for high risk patients. As an example, an axillary block with conscious sedation could be
used for an upper extremity procedure.
TYPE OF NEUROMUSCULAR BLOCKADE
Pancuronium, a long-acting neuromuscular blocker, leads to a higher incidence of
postoperative residual neuromuscular blockade than do shorter acting agents and a higher
incidence of postoperative pulmonary complications in those patients with residual
neuromuscular blockade24. Residual neuromuscular blockade is also an important risk factor
for critical respiratory events in the immediate postoperative period25.
PREOPERATIVE CLINICAL EVALUATION
A careful history taking and physical examination are the most important parts of
preoperative pulmonary risk assessment. One should seek a history of exercise intolerance,
chronic cough or unexplained dyspnoea.
The physical examination may identify findings suggestive of unrecognized pulmonary
disease. Among such findings,
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Decreased breath sound
dullness to percussion
wheezes
rhonchi
prolonged expiratory phase
predict an increase in the risk of pulmonary complications15.
PREOPERATIVE PULMONARY FUNCTION TESTING
The value of routine preoperative pulmonary function testing remains controversial. There is
consensus that all candidates for lung resection should undergo preoperative pulmonary
function testing. Such testing should be performed selectively in patients undergoing other
surgical procedures. We will subsequently divide the discussion into patients undergoing
lung resection and those for other surgical procedures.
LUNG RESECTION
After determining the anatomic resectability of the disease, it needs to be decided whether
the patient can withstand the planned procedure and can survive the loss of the resected
lung.
Initial evaluation
Detailed medical history, including coexisting disease to ensure the optimal treatment of that
disease. History should include functional capacity and the degree of limitation of activity.
A history of smoking or COPD may lead to preoperative therapeutic interventions such as
bronchodilators and/or steroids. This could lead to some degree of reversal of airway
obstruction and easier weaning of the ventilator postoperatively. The physical examination
should include an evaluation for signs of metastatic spread and the presence of cardiac
failure and pulmonary hypertension. All of these might change the treatment mode and
determine that the patient may not be a suitable surgical candidate.
The pulmonary specific evaluation can be divided into three stages of tests that are
performed in a graded manner to meet the cited goals and help risk-stratify the patients prior
to the anticipated surgery
Stage I assessment
Spirometry:
Spirometry is a simple, inexpensive, standardized and readily available test. Forced
expiratory volume in one second (FEV1), Forced vital capacity (FVC), Forced Expiratory
Flow, mid expiratory phase (FEF25-75%) and Maximum voluntary ventilation (MVV) have been
extensively studied. FVC reflects lung volume, while FEV 1 and FEF25-75% reflects airflow.
MVV reflects muscle strength and correlates with postoperative morbidity. However, it is very
dependent on patient effort. Of all these indexes, FEV 1 is regarded as being the best for
predicting complications of lung resection in the initial assessment26.
Diffusion Capacity
Diffusing capacity of the lung for carbon monoxide (DLCO) reflects alveolar membrane
integrity and pulmonary capillary blood flow in the patient’s lungs. The usefulness of DLCO in
predicting postoperative complications following pulmonary resection has also been
evaluated. Retrospective studies have reported that actual DLCO (as a percent of the
predicted value) and predicted postoperative DLCO are the most important predictors of
mortality and postoperative complications27, 28.
Arterial Blood Gas Levels
Arterial blood gas levels have not been extensively studied as predictor of postoperative
complications. Hypercapnia (PCO2 >45 mmHg) in arterial blood has been a relative
contraindication to lung resection as it indicates chronic respiratory failure. A few studies
however did not find that a PCO2 > 45mmHg was predictive of postoperative complications26.
To summarize, studies on pulmonary function testing in the preoperative evaluation for lung
resection surgery indicate that the following criteria are predictive of increased postoperative
complications and mortality
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For pneumonectomy: FEV1
MVV
DLCO
FEF25-75%
< 2L or < 60% of predicted
< 55% of predicted
< 50% of predicted
< 1.6L/s
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For lobectomy:
< 1L
< 40% of predicted
< 50% of predicted
< 0.6L/s
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For wedge resection : FEV1
DLCO
FEV
MVV
DLCO
FEF25-75%
< 0.6L
< 50% of predicted
These studies suggest that if values more than required for pneumonectomy above are
achieved, no further testing is indicated and that the patient is at low risk for postoperative
complications26.
The current guidelines from the American College of Chest Physicians and the British
Thoracic Society suggest that patients with a preoperative FEV1 in excess of 2 L (or >80
percent predicted) generally tolerate pneumonectomy, whereas those with a preoperative
FEV1 greater than 1.5 L tolerate lobectomy. However, if there is either undue exertional
dyspnea or coexistent interstitial lung disease, then measurement of DLCO should also be
performed. Patients with preoperative results for FEV1 and DLCO that are both >80 percent
predicted do not need further physiological testing29.
They do however concede that most studies used as the basis of current guidelines were
published prior to 1990, and supportive care and perioperative management have improved
substantially since that time. This could result in an overly restrictive approach to surgical
therapy.
If the above requirements are not met, the patient needs further evaluation.
Stage II assessment
The next stage of assessment consists of tests that measure individual lung function.
Quantitative ventilation-perfusion scan or Differential lung scan
133Xe
is inhaled or 99Tc-labeled macro aggregates are injected IV. The uptake by the lung is
measured by a gamma camera and computer. The percentage of radioactivity contributed by
each lung correlates with the contribution to the function of that lung. Normally the right lung
contributes 55% and the left lung 45% of lung function. Based on the measured radioactive
uptake of the lung that will not be operated on, the predicted FEV1 of residual lung following
surgery can be calculated.
Patients, who undergo a differential lung scan in the course of their preoperative evaluation
for lung resection, may be allowed to undergo surgery if:
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Predicted postoperative FEV1
Predicted postoperative DLCO
> 40% of predicted
> 40% of predicted
Patients whom do not meet these criteria should undergo further evaluation before surgery
can be undertaken.
Patients with a predicted postoperative FEV1 <30 percent predicted are particularly singled
out for their risk of perioperative death and cardiopulmonary complications; they should be
counselled about non-standard surgical options and non-operative treatment modalities in
preference to standard lung resection29.
Other tests assessing differential lung function include bronchospirometry, lateral position
testing and total unilateral pulmonary artery occlusion. These tests are invasive; all require
specialized equipment and a high level of technical expertise for their performance26. They
are no longer performed in the preoperative evaluation of patients who are awaiting lung
resection.
Stage III assessment
Exercise testing stresses the entire cardiopulmonary and oxygen delivery system, and
provides a good estimate of cardiopulmonary reserve. Heart rate, blood pressure, ECG and
oxygen saturation is measured, as well as the measurement of exhaled gasses. The oxygen
uptake (VO2); maximal VO2 (VO2max); carbon dioxide output and minute ventilation can be
measured.
The rate of oxygen uptake increases with exercise until a point at which a plateau is reached
and a further increased in work does not result in a further increase in oxygen uptake. This is
the VO2max. In patients with COPD, dyspnoea or fatigue often interrupts exercise before this
plateau. The VO2 at this stage is called peak VO2. VO2max or peak VO2 indicates whether
the patient has the reserve to counter the multiple physiologic stresses that accompany
surgery.
Two major types of exercise tests have been used in the preoperative evaluation of high risk
patients being considered for lung resection surgery
1. Fixed exercise challenge, in which a sustained level of work is performed
2. Incremental exercise testing in which the work is sequentially increased to a desired
end point.
The maximal end point can be can be defined as exercise that is performed to a plateau at
which further increase in work will not produce an increase in VO2. The sub-maximal end
point can be defined as exercise performed short of achieving the plateau.
Stair climbing: For many years, surgeons have utilized stair climbing as a preoperative
screening tool. Though poorly standardized, this form of testing has been shown to identify
patients at increased risk for lung resection.
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In a prospective series of 640 lobectomy and pneumonectomy candidates, attainment
of a lower altitude (less than 12 meters) on a symptom-limited stair climbing test was
associated with increased cardiopulmonary complications, mortality, and cost,
compared with climbing to a higher altitude (22 meters) 30.
A prospective series of 160 patients studied one day prior to lung resection found that
those who were able to climb more than eight flights of stairs, at their own pace, were
less likely to experience complications than those who could climb fewer than seven
flights of stairs (6.5 versus 50 percent). Patients who climbed between seven and
eight flights of stairs had an intermediate risk of complications (30 percent) 31.
Integrated cardiopulmonary exercise testing: The most important measurement during
cardiopulmonary exercise testing that correlates with postoperative complications is the level
of work achieved, as measured by maximal oxygen consumption (VO2max); invasive
hemodynamic measurements during exercise provide little additional useful data 30. An early
report demonstrated no mortality in patients able to achieve a VO 2max in excess of 1 L/min,
compared with 75 percent mortality in those with a VO2max below 1 L/min31.
Expressing VO2max in terms of mL/kg per min, which takes into account the patient's body
mass, may increase the predictive power of the test. The VO 2max can also be expressed as
a percentage of the predicted value.
Current guidelines from the American College of Chest Physicians considers patients with
VO2max <10 mL/kg per min, or those with VO2max <15 mL/kg per min and both predicted
postoperative FEV1 and DLCO <40 percent predicted, to be at high risk for perioperative
death and cardiopulmonary complications29.
OTHER SURGERY
Pulmonary function testing
There is considerable debate regarding the role of preoperative pulmonary function testing
for risk stratification. These tests simply confirm the clinical impression of disease severity in
most cases, adding little to the clinical estimation of risk. There has also been concern that
preoperative PFTs are overused and a source of wasted health care money32, 33.
Two reasonable goals that could potentially justify the use of preoperative PFTs:
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Identification of a group of patients for whom the risk of the proposed surgery is not
justified by the benefit.
Identification of a subset of patients at higher risk for whom aggressive perioperative
management is warranted.
A number of measures of pulmonary function have been evaluated. Bedside spirometry is
widely available, and measures of the forced expiratory volume in one second (FEV1) and
forced vital capacity (FVC) have been frequently reported. Early reviews suggested criteria
for increased risk that included the following:
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FEV1
FVC
FEV1/FVC ratio
<70 % predicted
<70 % predicted
<65 %
There is little support from the literature that either of these goals is routinely met other than
for lung resection surgery. As an example, in a study of patients with severe chronic
obstructive lung disease (FEV1 <50 %), preoperative PFTs did not predict the risk of
pulmonary complications, whereas length of surgery, ASA class, and type of procedure were
all significant predictors. Similarly, in a case control study of 164 patients undergoing
abdominal surgery, no component of spirometry predicted pulmonary complications 34.
A critical review of preoperative pulmonary function testing evaluated 14 studies that met
strict methodologic criteria14. Spirometric values were significant risk predictors in three of
four studies that used multivariable analysis. However, other factors conferred higher odds
ratios for pulmonary complications than did abnormal spirometry in two of these studies:
ASA class >3 and chronic mucous hypersecretion.
Two well designed case-control studies have evaluated the benefit of PFTs as risk
predictors. In a study of patients undergoing abdominal surgery, there was no difference in
FEV1, FVC, or FEV1/FVC between patients who had a pulmonary complication and those
who did not. In contrast, factors from the physical examination did predict risk 34.
Recommendation: Based on a systematic review, a 2006 American College of Physicians
guideline recommends that clinicians not use preoperative spirometry routinely for predicting
the risk of postoperative pulmonary complications35.
A reasonable approach to patient selection for preoperative pulmonary function testing
follows:
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Obtain PFTs for patients with COPD or asthma if clinical evaluation cannot determine
if the patient is at their best baseline and that airflow obstruction is optimally reduced.
In this case, PFTs may identify patients who will benefit from more aggressive
preoperative management.
Obtain PFTs for patients with dyspnea or exercise intolerance that remains
unexplained after clinical evaluation. In this case, the differential diagnosis may
include cardiac disease or deconditioning. The results of PFTs may change
preoperative management.
PFTs should not be used as the primary factor to deny surgery
PFTs should not be ordered routinely prior to abdominal surgery or other high risk
surgeries
Arterial blood gas analysis
No data suggest that the finding of hypercapnia identifies high-risk patients who would not
have otherwise been identified based upon established clinical risk factors. Several small
case series have suggested a high risk of postoperative pulmonary complications among
patients with a PaCO2 >45 mmHg, a finding usually seen only in patients with severe chronic
obstructive lung disease. The risk associated with this degree of PaCO 2 elevation is not
necessarily prohibitive, although it should lead to a reassessment of the indication for the
proposed procedure and aggressive preoperative preparation.
Hypoxemia has generally not been identified as a significant independent predictor of
complications after adjustment for potential confounders.
Current data do not support the use of preoperative arterial blood gas analyses to stratify risk
for postoperative pulmonary complications.
Chest radiographs
Abnormal chest x-rays are seen with increasing frequency with age. However, chest x-rays
add little to the clinical evaluation in identifying healthy patients at risk for perioperative
complications. As an example, one study screened 905 surgical admissions for the presence
of clinical factors that were thought to be risk factors for an abnormal preoperative chest xray36. These risk factors were age over 60 years or clinical findings consistent with cardiac or
pulmonary disease. No risk factors were evident in 368 patients; of these, only one (0.3%)
had an abnormal chest x-ray, which did not affect the surgery. On the other hand, 504
patients had identifiable risk factors; of these, 114 (22%) had significant abnormalities on
preoperative chest x-ray.
A meta-analysis of studies of routine preoperative chest x-rays demonstrated a low yield for
abnormalities that actually change preoperative management 37. Of 14,390 preoperative xrays, there were only 140 unexpected abnormalities and only 14 cases where the chest x-ray
was abnormal and influenced management.
The available literature does not allow an evidence-based determination of which patient will
benefit from a preoperative chest x-ray however, it is reasonable to obtain preoperative chest
x-ray in patients with known cardiopulmonary disease and in those over age 50 years
undergoing high risk surgical procedures, including upper abdominal, aortic, esophageal,
and thoracic surgery.
Exercise testing
Exercise testing has been studied most extensively in preparation for lung resection surgery.
There are no data to support its routine use in the evaluation of patients prior to general
surgery.
PULMONARY RISK INDICES
Three recent studies have proposed pulmonary risk indices.
Cardiopulmonary risk index
A combined Cardiopulmonary Risk Index (CPRI) was proposed in a study of patients
undergoing pulmonary resection based upon the Goldman criteria for cardiac risk 38. The
pulmonary risk factors added to the cardiac risk index include the following:
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Obesity (BMI >27 kg/m2)
Cigarette smoking within eight weeks of surgery
Productive cough within five days of surgery
Diffuse wheezing or rhonchi within five days of surgery
FEV1/FVC <70%
PaCO2
>45 mmHg
The results of this scoring system have been mixed. Patients with a combined score greater
than 4 (of a total of 10 possible points) in the original series were 17 times more likely to
develop postoperative pulmonary complications than those with a score less than 4; no
complications occurred in patients with a score of 2 or less. However, this study included
only patients undergoing lung resection. A subsequent trial reported that, of 43 patients
undergoing thoracic and upper abdominal surgery, the 8 with a CPRI >3 all experienced
pulmonary complications39. In contrast, another review found that the CPRI did not predict
complications in a cohort of 180 patients undergoing thoracic surgery40. In addition to the
discrepancy between these studies, a limitation of this index is the requirement for PFTs and
arterial blood gas analysis in all patients as part of the index.
Brooks-Brunn risk index
A separate study of 400 patients undergoing abdominal surgery identified a different set of
proposed criteria for a risk index34. Six factors were independently associated with increased
pulmonary risk after abdominal surgery:
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Age >60
Obesity (BMI >27 kg/m2)
Impaired cognitive function
History of cancer
Smoking history in past eight weeks
Upper abdominal incision
In a subsequent validation cohort by the same author, the original model validated relatively
well, but when a new model was developed different factors emerged as significant41.
Multifactorial risk index for postoperative respiratory failure
Using a prospective cohort model that included both derivation and validation cohorts from a
large Veterans Administration database, investigators have more recently published the
most ambitious multifactorial risk index to predict postoperative respiratory failure42. This
index is modelled after the widely used cardiac risk indices. The authors evaluated those
factors that predicted postoperative respiratory failure, assigned each points based on their
strength in the multivariate analysis, and developed a risk score. Procedure-related risk
factors dominate the index with type of surgery and emergency surgery being the most
important predictors. New observations in this study included the importance of abdominal
aortic aneurysm repair, emergency surgery, and metabolic factors as risk factors. The same
investigators have also reported a similar index to predict postoperative pneumonia 43.
These indices significantly advance the field of preoperative pulmonary risk assessment.
They rely upon readily available clinical information. A limitation is that most of the factors
are not modifiable.
RISK REDUCTION STRATEGIES
Preoperative
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Encourage cessation of cigarette smoking for at least 8 weeks
Treat airflow obstruction in patients with COPD or asthma
Administer antibiotics and delay surgery if respiratory infection is present
Begin patient education regarding lung-expansion maneuvres
Intra-operative
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Limit duration of surgery to less than 3 hours
Use spinal or epidural anesthesia
Avoid use of Pancuronium
Use laparoscopic procedures when possible
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Substitute to less ambitious procedure for upper abdominal or thoracic surgery when
possible
Post operative
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Use deep-breathing exercises
Use continuous positive airway pressure
Use epidural analgesia
Use intercostals nerve blocks15
SUMMARY
Postoperative pulmonary complications are an important source of perioperative morbidity
and mortality. They represent an extension of the normal physiologic changes in the lung
that occur with anesthesia.
A careful history and physical examination are the most important tools for preoperative risk
assessment in evaluating patients for potential postoperative pulmonary complications.
Attention should be paid to symptoms that suggest the possibility of occult underlying lung
disease, including exercise intolerance, cough, and unexplained dyspnea
In addition to the history and physical examination, a chest x-ray should be obtained in
patients undergoing high risk surgery who are over age 50 years, or if cardiac or pulmonary
disease is suggested by the clinical evaluation, unless one has been obtained in the past six
months. Pulmonary function tests should be reserved for patients with uncharacterized
dyspnea or exercise intolerance and for those with COPD or asthma where clinical
evaluation cannot determine if airflow obstruction has been optimally reduced. The benefit of
PFTs in other situations is unproved. There is no role for preoperative arterial blood gas
analyses to identify high risk patients or to deny surgery.