In conclusion, if history and physical examination indicate pulmonary dysfunction, simple pulmonary function tests should be obtained and proper measures taken to reduce morbidity and mortality in surgery patients, especially those with underlying chronic lung disease

Muren, Orhan

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Pulmonary Function Testing for Preoperative Study of Patients for Anesthesia and Surgery* ORHAN MU REN, M. D. Associate Professor of Medicine, Medical College of Virginia , Richmond, Virginia Pulmonary complications are the most prevalent causes of morbidity and mortality in patients who undergo surgical procedures. Simple pulmonary function tests which can detect pulmonary dysfunc-tion may be perfo rmed preoperatively. If prope r measures are taken ( chest physiot herapy, pos-tural drainage, bronchodilating agents , antibio tics, humidification of inspired gases, cessation of c igarette smoking), morbidity and mortality can be reduced significantly. Pulmonary function tests are especially im-portant in patients with borderline pulmonary rese rve who need major surgery. After object ive evaluation , the anesthesiologist and the surgeon ca n prov ide better care for the pat ient. These stud ies may also suggest the patients who are more likely to develop postoperative complications. In many patients, a thorough med ical history and physical examin ation. in addition to a complete blood count with differential, urin alysis, elec trolytes. BUN, and chest x-ray, ofte n will give sa ti sfactory information , and many patients will not need pul-monary function testing prior to anesthes ia and surgery. Should hi story and physical exa min ation show that pulmonary function tes ts are indicated, they will also indicate the type of tests to be carried out. A history of chronic productive cough, dyspnea, pleu-ritic chest pain , occupational respirato ry haza rds, frequent past episodes of pneumoni a, pleurisy, chest colds, and sudden reduction in strength should strongly suggest poss ible pulmonary dysfuncti on. Findings on examination of the chest such as prolonged expiration, diffuse or localized wheezing, absent breath sounds, rales , chest-wall deformities and scars, hypertrophy of scalene muscles, and pul-• Presented a t th e 25th Annual Stoneburner Lecture Series, February 26 , 1972, at the Medica l Co ll ege of Vir-ginia, Richmond. MCV QUARTERLY 8(2) : 13 1-134, 1972 monary osteoarthropathy aga in should suggest possi-ble abnormalities in lung functi on, and proper pul-mon ary function tests should be performed. There are a variety of pulmonary function tests which may be used to detect dysfunction . In gen-eral , they can be divided into two groups: I. Those relating to the ventilatory function of the lungs and thoracic wall. 2. Those relating to pulmonary gas exchange. Ventilatory Function Tests. Ventilatory func-tion is determined by measurement of static lung volumes. These are somewhat indicative of the elastic resistance of the lungs and chest wall and dynamic lung compartments; these tests are mainly a reflec-tion of nonelasticity. Static Lung Volumes. Static lung volumes are assessed by measuring the vital capacity which changes according to height , age, and sex. Full co-operation of the patient during the procedure is essential. Integrity of the entire respiratory system ( respiratory centers, th orax, the connections between these two, chest wall, pleura, lung paranchyma, and airways) is necessary fo r normal vital capacity. If a person has less than predicted normal vital capacity, by definition he has restrictive lung disease. Normal values range ± 15 % of the predicted. As an isolated test, vital capacity is of limited clinical value in differenti al diagnosis of diseases of the chest. However, serial measurements of vital capacity may be helpfu l in assess ing the degree of improvement or worsening in certain conditions such as neuro-muscular disorders, or diffuse interstitial pulmonary fibrosis . Dynamic Lung Volumes. More important infor-mat ion could be obtained by measuring timed vital capacity or forced vital capacity. A young or middle-aged normal person should be able to ex-hale 80% of his vital capacity in one second and 97 % in three seconds. If the ratio between one-131 132 MUREN: PULMONARY FUNCTION TESTING FOR PREOPERATIVE STUDY second fo rced expiratory volume ( FEY,.,) , over fo rced vital capac ity ( FYC) is less th an 80%, he is considered to have obst ructive lung disease. Diminu-tion in FEY,., to a liter or less ind icates severe impairment of ventilato ry function and a somewhat poor surgical risk. Expiratory fl ow rates can be determined at di ffere nt points during fo rced expi rato ry curve. The fo rces tending to reduce the size of a irways (peri-bronchial pressure and the fo rce generated by con-striction of bronchia l muscles) are balanced by those attempt ing to increase the size of airways (int ra-luminal pressure and radi al traction of elastic fibers). During fo rced exhalation, the alveolar pressure and the intrathoracic pressure are greater than atmo-spheric pressure. The int ramu ral pressure decreases gradu ally from peripheral a irways to atmospheric pressure at the a irway opening. At some distance in the airway, intralumi nal and pleural pressures a re equal. This is ca lled the poin t of equ al pressures. Beyond th is point , int raluminal pressure is less than pleura l pressure; this would tend to narrow airways, thus limiting fl ow. In patients with altered and more coll apsible airways, flow is limited at lower levels of pleural pressure. The max im al fl ow rate produced by fo rced ex halation depends upon the level of lung inflation. At maximum lung inflation, expi ratory flow increases as the pressure increases. At lower lung volumes, expi ratory fl ow increases as pressure increases up to a certain level, afte r which more effort cannot in-crease and may even decrease flow rate. This expl ains why the maximum mid-ex pi ra tory flow rate ( MMFR or F EF 25 %-75%) is the most sensitive test for ex-pi ra tory flow ra te determination since the initi al 25 % of the FYC is primarily effo rt-dependent and the last 25% affected by diminished lung volumes . The MMFR measures the max imum rate of fl ow in the mid portion of F VC curve ( FEF 25% - 75% ) . (The length of time necessary to exhale the middle 50% of the fo rced vital capacity is measured and flow rate is ca lcul ated.) Normal values are 3-4.5 L per second . It should be emph as ized th at small a ir-ways ( 2 mm in diameter ) are only responsible fo r approx im ately 15%-20% of the total a irway re-sistance, so marked increases in peripheral or small airways will not be detected by the convent ional tes ts such as FEV,,, or MMFR. In the ea rl y stages of chronic bronchitis, pul-monary emphysema, and bronchiectas is there is a significant degree of involvement of the small a ir-ways. In the early stages of these conditions , fre-quency-dependent dynamic compliance and alveolar arterial oxygen tension gradient, A-a PO,, may detect pulmonary dysfunction. For clinical purposes, however, simple spirometric studies with measure-ments of FYC, FEY,,,, and MMFR are sati sfactory. Improvements in fl ow rates after administration of bronchodilating agents suggest the presence of par-ti ally reversible obstruction . One-second fo rced ex-pi ratory volume x 30 gives indirec t measurement of max imum voluntary ventilation ( MYY ). If a bedside study of ventilatory function is de-sired, a Wright Respirometer may be used for mea-suring tidal volume and inspiratory capacity. A Peak Flow Meter may also be used for measuring peak flow rates . Failure to blow out a lighted match held six inches away from the wide-open mouth again sug-gests significant reduction in flow rates. In general, patients with obstructive lung disease a re more prone to develop postoperative pulmonary complications such as atelectas is and broncho-pneu-moni a. This is why pulmonary function testing is important fo r determining the type of phys iologic ab-normality present so that proper measures can be taken to improve potentially reversible abnormali-ties. Pulmonary Gas Exchange. One of the most im-portant functions of the lungs is alveola r gas ex-change which involves the following processes: 1. Ventil ation 2. Uniform distribution of inspired ai r 3. Diffusion 4. Pulmonary capillary blood fl ow Normal alveola r gas exchange maintains partial pressures of oxygen and carbon dioxide in the a rteri al blood within normal limits not only at rest, but also during increased physical activity and body metabo lism. Abnorm ality in any of the above proc-esses or in any combinations of the four, results in hypoxemi a o r hypoxemia and hypercapni a if the person is breathing room air. Arter ial gas studies indicate : I . T he level of oxygenation (P02 in mm of Hg ) 2. The level of ventil ation (PCO, in mm of Hg. ) 3. The hydrogen ion activity (pH) The above dete rminations a re extremely important in all se riously ill patients. MUREN: PULMONARY FUNCTION TESTING FOR PREOPERATIVE STUDY 133 It is often impossible to judge the levels of ventilation and oxygenation by clinical evaluation alone. There is much overlapping between signs and symptoms related to hypoxemia and hypercapnia: nervousness, headache, irritability, confusion, coma, altered blood pressure, tachycardia, etc. Sometimes signs and symptoms related to hypoxemia and hyper-capnia are absent and only by measurements of arterial gas studies can the level of ventilation and oxygenation be determined and appropriate treat-ment initiated. An A-a P02 gradient greater th an IO mm Hg on room-air breathing indicates a defect in blood gas equilibrium. The three primary mechanisms of increased A-a P02 gradient are impaired diffusion , venous-to-arterial shunting of blood, and abnormal ventilation/ perfusion ratios in the lung. The amount of true venous-to-arterial shunt is determined by having the person breathe I 00 % oxygen for 15 to 20 minutes. Normally, arterial PO, will increase to about 600 mm Hg. The observa-tion of increased A-a P02 gradient on breathing room air and of a P02 greater than 550 mm Hg while breathing oxygen indicates that mismatching of the distribution of ventilation and perfusion in the lungs is the cause of hypoxemia. The observation of high A-a P02 gradient on room air in the presence of normal spirometric studies may also suggest peripheral airway disease . Whenever possible, arterial blood gas studies should be obtained at rest, after exercise, and some-times after the administration of I 00 % oxygen for 15 to 20 minutes. The above studies may give valuable information in the evaluation and follow-up of patients with respiratory disease . Normal arterial blood O, at sea level is found in two forms: I. Dissolved 0 2 (0.3 ml per 100 ml per 100 mm Hg) 2. Oxyhemoglobin (Hb O, 19.7 ml per 100 ml) Normally, the total O, content of arterial blood is approximately 20 ml per I 00 ml. The amount of dis-solved 0 2 present is linearly related to arterial 0 2 tension . If partial pressure of 0 2 in arterial blood is 600 mm Hg, there is approximately 1.8 ml of physi-cally dissolved 0 2 per 100 ml blood. On the other hand, the relation between oxy-hemoglobin and partial pressure of 02 is S-shaped. If P02 is 100 mm Hg, oxygen saturation is 96% to 98 %. If P02 is 60 mm Hg, oxygen saturation is approximately 90%. In the flat portion of this curve, a large decrease in 02 tension causes only a small drop in oxygen saturation . However, at the steep portion of this curve, a small reduction in 0 2 tension causes a large diminution of 0 2 saturation. For instance , a drop of O, tension from 40 mm Hg to 27 mm Hg causes a reduction of saturation or O, content of approximately 25 % . A high CO2 tension and increased H ' ion ac tivity shifts this curve to the right. This is called the Bohr effect. In-creased temperature and increased 2-3 DPG (2-3 Diphosphoglycerate) of the red blood cells can also shift this curve to the right. A low PCO,, a high pH, a low temperature, and a low 2-3 DPG causes a shift to the left. Normally, a shift to the left in the lungs helps the loading of O, with hemoglobin. A shift to the right at tissue levels helps unloading of 02 to ti ssues. There are four causes of hypoxemia on breath-ing ambient air at sea level: I. Uneven V /Q 2. Venous-to-arterial shunt 3. Alveolar hypoventilation 4. Impaired diffusion . . In clinical medicine, uneven V /Q is the most common cause of hypoxemia. However, in a given case, there is more than one factor responsible for hypoxemia. Arterial PC02 indicates the balance between CO, produced at the tissue level and CO2 eliminated by alveolar ventilation . vco, PaCO,oo VA Normally, alveolar ventilation is proportional to CO, production which is related to the rate of metabolism. In any given person at any given time, CO2 production is at a certain level and only alveolar venti lation could change arterial PCO,. In conclu-sion, we can say that the level of PC02 indicates the level of ventilation. Hydrogen ion activity is determined by mea-surement of pH. According to the Henderson-Has-selbalch equation: pH PK'+ 1 (HCO,) og PCO, X 0.03 24 pH= 6 .1 + log Ll pH 6.1 + 20 log 1 pH 6. 1 + 1.3 = 7.40 134 MUREN: PULMONARY FUNCTION TESTING FOR PREOPERATIVE STUDY The ratio of HCO:i and dissolved CO2 determine the pH. As long as this ratio is 20, the pH should be normal. There are four prim ary o r s imple ac id-base disturbances as we ll as combined or mi xed acid-b,1s~ disturbances. Primary increase or decrease in PC02 indicates respiratory ac idosis or alk alos is respec-tively. Primary increase or decrease in HCO:i in-dicates metabolic alkalosis or ac idosis respec tive ly. The fo llowing a re some indica tions for pu lmo-nary function testing: I . To determine the type of physiologic altera-tion present. 2. To quantitate the degree of functi onal im-pairment. 3. To initiate therapy on a more rati onal phys iological basis and objectively fo llow the efficacy of therapy. 4. Preopera tive ri sks evalu ati on. R e : anesthes ia and surge ry. The fo llowing arte ri al gas studies were obtai ned on room ai r in a 60-year-old man with chronic ob-structive pu lmonary disease (COPD ): P0, :60 mm Hg PC0, :55 mm Hg p H: 7.34 HC0, :30 m Eq/ L The above studies indicate mild hypoxemia and partially compensated respiratory ac idosis. Spirometric stud ies revealed moderately severe airway obstructive disease. One day afte r admi ss ion, elect ive cholecystectomy was performed . One day after surgery , arte rial gas studies on ambient a ir were obta ined. P0, :45 mm Hg PC0, :80 mm Hg p H: 7.26 HC0":35 m Eq/ L The above stud ies indicate severe hypoxemi a and partially compensated severe respiratory acidos is. It took approximately 12 days to correct arteria l gas studies and acid-base disturbance . On the other hand , in another patient wit h COPD and more or less the sa me arte ri al gas ab-no rmaliti es, elec ti ve ga ll bladder surgery was post-poned for seven days and the patient was given chest phys iotherapy, postural drainage, bronchod ilating agents. ant ibio tics. and humidified inspired air. He stopped smok ing. Postopera ti ve status was entirely unremarkable. In conc lusion , if hi story and physical examina-tion indicate pulmon ary dysfunc tion, simple pulmo-nary funct ion tests should be obtai ned and proper measures taken to reduce morbidity and mortality in surge ry pat ients, espec ially those with underlying chronic lung d isease. REFERENCES BHES. D . Y .. M AC l·ILl~ I . P. T .. AND C HRISTIE , R. V . R es-piratory F1111uio 11 in Disease. Phil adelphia : W. B. Saunders, 197 1. CA MPBELL. E. J . M .. AGOSTON I . E .. AND D AVIS , J . N. The Rejpiratory Muscle.r. M echanics and Neuro l. Control. Philw ade lphi a: W . B. Saunders. 1970. CHERN IAC K . R . M . AN D C HERN IACK, L. R espiration in H ealth ond Diseosc. Phi lade lphia: W. B. Saunders, 196 1. C0'1ROE. J . H .. FOR STER. R. E. , D U BOIS, A. B. , BRISCOE, W . A .. AN D CAR I SEN . E .. JR . Th e L1111g. C hicago: Yearbook Meclica l Publica tions. 1962. F ENN. W. 0. AND R AHN. H . H andbook of Physio logy, Sec-lion J: R cspira1ion. Vo l. I and 2. Baltimore: Waverly Press, 1965. ME AD, J. Mec hani ca l propert ies of lun gs. Phvsiol. R ev. 4 1 : 28 1, 196 1. M EAD. J.. T URN [R, J . M .. M ACKLEM, P. T .. AND Lll,LE, J. I! . Significa nce of the re lat ionship between lung recoil ancl maximum ex pirator y fl ow. / . Appl. Phvsiol. 22:95 , 1967. SCURR . C. AND F ELDMAN. S. Scientific Fo1111datio11s of An <'.,-,hl'sio. Philade lphi a : F. A . Davis Company, 1970. S1 ONO' I. N. B. AND H AM IL TON , L. H. R espirator/ Ph ysiol-og_,·. Saint Louis : The C. V. Mosby Company. 197 1. SYKlcS, M. K .. M c N 1co1.. M . W .. AN D CAMPB ELL. E. J . M. Rl'spirator_,. Failure. Oxfo rd: Blac kwell Scientific, 1969. W1-s-r . J. B. 1/('IJtilation / Blood Flo ll' and Gas Exchange. Ph ilade lphi a: F. A. Davis Company. 1970. Woo 1c-oc K. A. V .. Y ENCE NT, N. J .. AND MACHLEM. P. T. Frequ ency cl cpendence of compli ance as a test for ob-struc ti o n in the sma ll a irways . / . Clin. In vest. 48: 1097. 1969. 

Pulmonary Function Testing for Preoperative Study of Patients for Anesthesia and Surgery

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Pulmonary Function Testing for Preoperative Study of Patients for Anesthesia and Surgery

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