PRE-OPERATIVE ASSESSMENT OF THE RESPIRATORY SYSTEM

REGISTRAR: Dr AucampCONSULTANT: Dr Prins

INTRODUCTION

Goal: Determine the risk to the patient

Why:• Contribute significantly to perioperative

morbidity and mortality• Costly • Longest length of stay

Estimation of risk should be a standard element of all preoperative medical evaluations.

DEFINITIONDiffering definitions account for the variability in frequency

Proposed definition by O'Donohue:A pulmonary abnormality that produces identifiable disease or dysfunction

that is clinically significant and adversely affects the clinical course

• Atelectasis • Infection, including bronchitis and pneumonia • Prolonged mechanical ventilation and respiratory failure • Exacerbation of underlying chronic lung disease • Bronchospasm4

O'Donohue, WJ. Postoperative pulmonary complications: When are preventive and therapeutic measures necessary? Postgrad Med 1992; 91:167.

EFFECT OF MEDICAL CONSULTATION ON SURGICAL OUTCOMES

No study has shown a decrease in perioperative morbidity associated with medical consultation9

The practice of medical consultation is widespread

Assuming consultants make evidence-based recommendations, it is reasonable to infer that consultation will improve the care of the surgical patient.....

if consultative recommendations are implemented

Phy, MP, Vanness, DJ, Melton LJ, 3rd, et al. Effects of a hospitalist model on elderly patients with hip fracture. Arch Intern Med 2005; 165:796.

GENERAL PRINCIPLES OF CONSULTATION

• 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

PERIOPERATIVE PULMONARY PHYSIOLOGY

Complications follow logically as an extension of normal perioperative pulmonary physiology

Thoracic and upper abdominal surgery is associated with a reduction in lung volumes: • VC is reduced by 50 to 60 % and may remain decreased for up to one week. • FRC is reduced by about 30%

Important factors:• Diaphragmatic dysfunction• Postoperative pain and splinting

Reduction of the FRC below closing volumes contributes to atelectasis, pneumonia, and V/Q mismatching

Microatelectasis

PERIOPERATIVE PULMONARY PHYSIOLOGY

Decreased TV, loss of sighing breaths, and increase in RR occur after abdominal and thoracic surgery

Residual effects of anesthesia itself and postoperative opioids

Inhibition of cough and impairment of mucociliary clearance

Lower abdominal surgery to a lesser degree.

Reductions in lung volumes are not seen with surgery on the extremities

RISK FACTORSPATIENT RELATED SURGERY RELATED

• Age• Chronic lung disease• Asthma• Smoking• Obesity• Obstructive sleep apnoea• Pulmonary hypertension• Heart failure• General health status

• Surgical site• Duration of surgery• Type of anesthesia• Type of neuromuscular blockade

PATIENT RELATED FACTORS

AGE• ? influence of age as an independent predictor of postoperative pulmonary complications • Early studies were not adjusted for overall health status or known pulmonary disease• ACP review made the novel observation that age >50 years was an important independent

predictor of risk

CHRONIC LUNG DISEASE• Early reports estimated complications at relative risks between 2.7 and 6.0• A more recent systematic review, found the impact less than previously estimated• Among studies that used multivariable analysis to adjust for patient-related confounders, the

odds ratio 2.3614

• There appears to be no prohibitive level of pulmonary function below which surgery is absolutely contraindicated

• Benefit of surgery must be weighed against the known risks

PATIENT RELATED FACTORS

ASTHMA• Well controlled patients with peak flow of >80% of predicted or personal best can proceed

to surgery at average risk16

SMOKING• Risk factor and has been demonstrated since 1944• Increased risk even among those without chronic lung disease• Relative risk 1.4 to 4.3• Risk declines only after eight weeks of preoperative cessation• Paradoxically, those who had stopped smoking less than eight weeks earlier had a higher risk

than current smokers17

OBESITY• Obesity should not affect patient selection for otherwise high-risk procedures

PATIENT RELATED FACTORS

OBSTRUCTIVE SLEEP APNOEA• While the literature is still emerging, we should consider OSA to be a probable risk factor • OSA increases the risk of critical respiratory events immediately after surgery, including early

hypoxemia and unplanned reintubation17

• Patients with an ODI4% of >5 were more likely to have postoperative respiratory (8 versus 1%) complications

PULMONARY HYPERTENSION• Increases pulmonary complication rates after surgery, regardless of the underlying etiology• History of pulmonary embolus• NYHA functional class ≥ 2• Intermediate or high risk surgery• Duration of anesthesia > 3 hours.

PATIENT RELATED FACTORS

HEART FAILURE • Higher risk in HF than in COPD• Suggested by data from the ACP review, with odds ratio of 2.93 for HF patients and 2.36 for

patients with COPD14

• The original Goldman cardiac risk index has been shown to predict postoperative pulmonary as well as cardiac complications21

GENERAL HEALTH STATUS • Functional dependence and impaired sensorium each increase risk• ASA classification correlates well with pulmonary risk and is one of the most important

predictors • Patients with significant preexisting lung disease would be classified in a higher ASA class• ASA class >2 confers a 4.87 fold increase in risk14.• The inability to exercise predicts 79% of pulmonary complications15.

PROCEDURE RELATED RISK FACTORS

SURGICAL SITE• Single most important factor in predicting the overall risk of postoperative pulmonary

complications• Significantly higher for thoracic and upper abdominal surgery than for lower abdominal and

all other procedures• The impact of laparoscopic surgery on pulmonary complication rates is not well established• Lower pulmonary complication rates expected but not evaluated as an endpoint

DURATION OF SURGERY • Surgical procedures lasting more than 3-4h are associated with a higher risk • A less ambitious, briefer procedure should be considered in a very high risk patient

PROCEDURE RELATED RISK FACTORS

TYPE OF ANESTHESIA • Conflicting data with regard to spinal or epidural anesthesia vs general anesthesia• A comprehensive review was done and it appears likely that GA leads to a higher risk than do

epidural or spinal anesthesia• 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

TYPE OF NEUROMUSCULAR BLOCKADE • Pancuronium, a long-acting neuromuscular blocker, leads to a higher incidence of

postoperative residual neuromuscular blockade • Higher incidence of postoperative pulmonary complications in those patients with residual

neuromuscular blockade

PREOPERATIVE CLINICAL EVALUATION

A careful history and physical examination are NB! History of:• Exercise intolerance• Chronic cough • Unexplained dyspnoea

The physical examination may identify findings suggestive of unrecognized pulmonary disease:• Decreased breath sound• Dullness to percussion• Wheezes• Rhonchi • Prolonged expiratory phase

Which may predict an increase in the risk of pulmonary complications

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

LUNG RESECTION

INITIAL EVALUATION• Detailed medical history, incl. 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

• The physical examination should include an evaluation for signs of metastatic spread and the presence of HF and PHT

• All of these might change the treatment mode and determine that the patient may not be a suitable surgical candidate.

PULMONARY SPECIFIC EVALUATION

STAGE I ASSESSMENT Spirometry• Spirometry is a simple, inexpensive, standardized and readily available test• FEV1, FVC, FEF mid expiratory phase (FEF25-75%) and MVV have been extensively studied

• FVC reflects lung volume, while FEV1 and FEF25-75% reflects airflow

• MVV reflects muscle strength and correlates with postoperative morbidity• FEV1 is regarded as being the best for predicting complications of lung resection in the initial assessment

Diffusion Capacity• DLCO reflects alveolar membrane integrity and pulmonary capillary blood flow in the patient’s lungs• Retrospective studies have reported that actual DLCO (as % of the predicted value) and predicted

postoperative DLCO are important predictors of mortality and postoperative complications

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

• A few studies however did not find that a PCO2 > 45mmHg was predictive of postoperative complications

PULMONARY SPECIFIC EVALUATION INCREASED POSTOPERATIVE COMPLICATIONS AND MORTALITYFor pneumonectomy: FEV1 < 2L or < 60% of predicted

MVV < 55% of predictedDLCO < 50% of predictedFEF25-75% < 1.6L/s

For lobectomy: FEV < 1L

MVV < 40% of predictedDLCO < 50% of predictedFEF25-75% < 0.6L/s

For wedge resection : FEV1 < 0.6L

DLCO < 50% of predicted

If values more than required for pneumonectomy above are achieved, no further testing is indicated and that the patient is at low risk

Datta, D, Lahiri, B. Preoperative evaluation of patients undergoing lung resection surgery. Chest 2003; 123:2096.

PULMONARY SPECIFIC EVALUATION

STAGE II ASSESSMENTQuantitative ventilation-perfusion scan or Differential lung scan• The percentage of radioactivity contributed by each lung correlates with the contribution to the function • Normally the right lung contributes 55% and the left lung 45% of lung function. • The predicted FEV1 of residual lung following surgery can be calculated

Patients, who undergo a differential lung scan may be allowed to undergo surgery if:• Predicted postoperative FEV1 > 40% of predicted

• Predicted postoperative DLCO > 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

Other tests assessing differential lung function include • Bronchospirometry,• lateral position testing and • total unilateral pulmonary artery occlusion (invasive, special equipment, technical expertise

PULMONARY SPECIFIC EVALUATION STAGE III ASSESSMENTExercise testing stresses the entire cardiopulmonary and oxygen delivery system• Good estimate of cardiopulmonary reserve• HR, BP, ECG and O2 saturation are measured, as well as the measurement of exhaled gasses.• The VO2; VO2max; carbon dioxide output and minute ventilation can be measured• 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• Fixed exercise challenge, in which a sustained level of work is performed• Incremental exercise testing in which the work is sequentially increased to a desired end point

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.

• Attainment of a lower altitude (less than 12m) on a symptom-limited stair climbing test was associated with increased cardiopulmonary complications, mortality, and cost, compared with climbing to a higher altitude (22m)

• Those who were able to climb > 8 flights of stairs, at their own pace, were less likely to experience complications than those who could climb < 7 flights of stairs

• Patients who climbed between 7-8 flights of stairs had an intermediate risk of complications (30%)

PULMONARY SPECIFIC EVALUATION

Integrated cardiopulmonary exercise testing: • The most important measurement during cardiopulmonary exercise testing that correlates with

postoperative complications is the level of work achieved• Measured by VO2max

• An early report demonstrated no mortality in patients able to achieve a VO2max 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

Current guidelines from the ACCP considers patients with: • VO2max <10 mL/kg per min

• VO2max <15 mL/kg per min predicted postoperative FEV1 and DLCO <40% predicted, to be at high risk for perioperative death and cardiopulmonary complications

6 min walk test

OTHER SURGERYPULMONARY FUNCTION TESTING

There is considerable debate regarding the role of preoperative pulmonary function testing for risk stratification

Two reasonable goals that could potentially justify the use of preoperative PFTs: • ID of a group of patients for whom the risk of the proposed surgery is not justified by the benefit• ID of a subset of patients at higher risk for whom aggressive perioperative management is warranted

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.

Increased risk:• FEV1 <70 % predicted • FVC <70 % predicted • FEV1/FVC ratio <65 %

There is little support from the literature that any of these goals is routinely met other than for lung resection surgeryOther factors conferred higher odds ratios for pulmonary complications than did abnormal spirometry• ASA class >3 and chronic mucous hypersecretion.

OTHER SURGERYRECOMMENDATION: 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 complications

A reasonable approach to patient selection for preoperative pulmonary function testing follows:

• 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

• Obtain PFTs for patients with dyspnea or exercise intolerance that remains unexplained after clinical evaluation

• 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

OTHER SURGERYARTERIAL BLOOD GAS ANALYSIS• No data suggest that the finding of PCO2 >45mmHg identifies high-risk

patients who would not have otherwise been identified based upon established clinical risk factors

• The risk associated with this degree of PaCO2 elevation is not necessarily prohibitive, although it should lead to a reassessment of the indication

• 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

EXERCISE TESTING• There are no data to support its routine use in the evaluation of patients

prior to general surgery.

OTHER SURGERYCHEST RADIOGRAPHS • Abnormal CXR are seen with increasing frequency with age• CXR add little to the clinical evaluation in identifying healthy patients at risk

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 CXR • No risk factors in 368 patients; of these, only one (0.3%) had an abnormal CXR, which did not affect

the surgery• 504 patients had identifiable risk factors; of these, 114 (22%) had significant abnormalities on

preoperative CXR

A meta-analysis of studies of routine preoperative CXR • Of 14,390 preoperative x-rays, 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 CXR however, it is reasonable to obtain preoperative CXR:• 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.

PULMONARY RISK INDICES

CARDIOPULMONARY RISK INDEX A combined CPRI was proposed based upon the Goldman criteria for cardiac risk, adding:

• 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

Results of this scoring system have been mixed

Limitation of this index is the requirement for PFT and ABG

PULMONARY RISK INDICESBROOKS-BRUNN RISK INDEX A different set of proposed criteria for a risk index

Six factors were independently associated with increased pulmonary risk after abdominal surgery:

• 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 other factors emerged as significant

PULMONARY RISK INDICESMULTIFACTORIAL RISK INDEX FOR POSTOPERATIVE RESPIRATORY FAILURE

• Investigators have more recently published the most ambitious multifactorial risk index to predict postoperative respiratory failure

• This index is modelled after the widely used cardiac risk indices• 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• Metabolic factors

as risk factors • Investigators have also reported a similar index to predict postoperative pneumonia.

• 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.

SUMMARY

Postoperative pulmonary complications are an important source of perioperative morbidity and mortality

A careful history and physical examination are the most important tools for preoperative risk assessment in evaluating patients for potential postoperative pulmonary complications

No role for preoperative ABG analyses to identify high risk patients or to deny surgery

CXR should be obtained in patients undergoing high risk surgery who are > 50 years, or if cardiac or pulmonary disease is suggested by the clinical evaluation

PFT 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

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