Acta Anaesthesiol Scand 1992: 36: 546-553

Atelectasis and lung function in the postoperative period B. BRISMAR and G . HEDENSTIERNA P. LINDBERG, L. GUNNARSSON, L. TOKICS, E. SECHER,H. LUNDQUIST, Departments of Anaesthesiology, Roentgenology and Surgery, Huddinge University Hospital, Huddinge, and Department of Clinical Physiology, University Hospital, Uppsala, Sweden

Thirteen patients with healthy hearts and lungs, and with a mean age of 68 years, who were scheduled for lower abdominal surgery during isoflurane anaesthesia with muscular paralysis, were investigated with arterial blood gases, spirometry, pulmonary x-ray and computed tomography (CT) of the chest before and during anaesthesia, as well as during the first 4 postoperative days. Before anaesthesia, lung function and gas exchange were normal in all patients. Pulmonary x-ray and C T scans of the lungs were also normal. During anaesthesia, 6 of 13 patients developed atelectasis (mean 1.0% of intrathoracic transverse area in all patients). Two hours postoperatively, 1 I of 13 patients had atelectasis and the mean atelectatic area was 1.8%. Pao, was significantly reduced by 2.1 kPa to 9.8 kPa. On the first postoperative day, the mean atelectasis was unaltered (1.8%). None of the atelectasis found on C T scanning could be detected on standard pulmonary x-ray. Forced vital capacity (FVC) and forced expired volume in 1 s (FEV,) were significantly decreased to 2/3 of preoperative level. Pao, was significantly reduced to less than 80% of the preoperative level (mean 9.4 kPa). There were significant correlations between the atelectatic area and the impairment in FVC, FEV,, and Pao,. Spirometry and blood gases improved during the succeeding postoperative days, and atelectasis decreased. No patient suffered from pulmonary complications, as judged from clinical criteria and pulmonary x-ray, in contrast to the findings of atelectasis in 85% of the patients by computed tomography.

Received 4 September, accepted for publication 30 Dccnnbcr 1991

Kcy words: Anesthesia; atelectasis; complications; computed tomography; isoflurane; lung function; ventilation.

Ventilation and gas exchange are often impaired during and after general anaesthesia and surgery (1-5). A major cause of the impaired gas exchange during anaesthesia is the formation of atelectasis and shunt ( 6 , 7). Other mechanisms such as increased ventilationperfusion mismatch can further impair the arterial oxygenation (7). Residual anaesthesia, pain, immobilisation and reduced sensitivity to hypoxaemia and hypercarbia (1, 3, 8) may contribute to the impaired gas exchange in the postoperative period. Upper abdominal surgery seems to affect diaphragmatic function and to reduce vital capacity by 50% or more (4, 9, 10). Several different approaches to counteract these negative effects have been made, such as breathing with continuous positive airway pressure (CPAP), use of incentive spirometers (1 l ) , chest physiotherapy, early ambulation (12, 13), and use of regional blocks to relieve pain and thus reduce the need for major analgesics (opiates) (14, 15). Efforts have also been made to identify patients who may be susceptible to postoperative respiratory complications and to set criteria for acceptance for surgery (8, 16, 17, 18). Several techniques have been used from standard clinical examination to spirometry ( 19), pulmonary

x-ray (20) and technically sophisticated ventilationperfusion scans (2 1). In the present study we have used computed tomography (CT) of the chest in combination with measurements of forced vital capacity (FVC), arterial blood gases, and pulmonary x-ray to describe the impairment of lung function postoperatively. The findings were correlated to significant pulmonary complications, such as pneumonia and atelectasis. PATIENTS AND METHODS Patients Thirteen patients (7 men and 6 women), with a mean age of 68 years (range 56-78), were investigated before and during anaesthesia, as well as in the postoperative period after abdominal surgery (Table 1). All patients had clinically healthy hearts and lungs and did not show any sign of systemic involvement of their surgical condition. Two of the patients were light smokers, and the others were nonsmokers. Preoperative spirometry and pulmonary x-ray were essentially normal in all subjects. Informed consent was obtained from each patient, and the study was approved by the Ethics Committee of Huddinge University Hospital. Anaesthesia and postoperative analgesia All patients were premedicated with oxycodone 5-10 mg and scopolamine 0.2-0.4 mg, 30 to 60 min before the anaesthesia. After 5 min

547

POSTOPERATIVE ATELECTASIS AND LUNG FUNCTION Table 1 Patient characteristics. Pat.

Age (Yr4

Sex P/M)

Weight (kg)

Height (m)

1 2 3 4 5 6 7 8 9 10 11 12 13 Mean s.d.

62 75 72 67 67 66 73 56 74 60 70 61 78 68 6.6

M

114 70 58 52 68 110 62 68

1.80 1.79 1.61 1.67 1.74 1.73 1.72 1.60 1.63 1.57 1.66 I .80 1.69 1.69 0.08

M F F M F M

F F F M

M M 6/7

57 72 64 88 69 73 19.0

Cig./day 15

0 0 0 0 0 0

FVC FEV, % of predicted) 89 93 88 92 102 100 126

0

I10

0 0 5

100 96 131 100 100

0 0

Operation

86 87 100 75 103 100 135 87 90 91 115 100 84 96 15.8

102 13.4

Sigmoid resection Sigmoid resection Hernicolectomy Hemicolectomy Anterior resection Hemicolectomy Hemicolectomy Resection of metastasis, right iliac fossa Hemicolectomy Revision of stoma Sigmoid resection Hernicolectomy Hernicolectorny

F and M: Female and male, respectively; FVC: Forced vital capacity; FEV,: Forced expired volume in I s; Pat: patient; cig.: cigarettes.

of preoxygenation, anaesthesia was induced with thiopental 2 0 M O mg, supplemented with 0.05 mg fentanyl and 2.5-7.5 mg diazepam. Tracheal intubation was performed after muscular relaxation with suxamethonium 75-100 mg. Anaesthesia was maintained with isoflurane 1-1 .5% inspired concentration in oxygen/nitrous oxide, and muscular paralysis was maintained with pancuronium bromide to a total dose of 5-9 mg. Inspired oxygen fraction (FIo,)was 0 . 3 0 . 3 5 and it was checked by mass spectrometry (Centronics, MGA 200). After intubation, the patients were ventilated mechanically at a rate of 12 breathslmin with a Servo 900 C ventilator, equipped with a carbon dioxide analyzer (Siemens). The minute ventilation was adjusted to maintain an end-tidal carbon dioxide concentration of approximately 4%. Postoperatively, conventional parented opioid analgesia was used.

Arterial blood gases Arterial blood gases were taken by direct puncture of the femoral or radial artery. Arterial oxygen and carbon dioxide tensions (Pao,, Paco,) were measured by standard techniques (blood-gas analyzer: ABL-2, Radiometer). The alveolar-arterial oxygen tension difference was calculated as P1o,-Paco,/0.8.-Pao,, PIO, being inspired oxygen tension and 0.8 an assumed respiratory gas exchange ratio. Lung function measurements and pulmonary x-ray Spirometry with determination of forced vital capacity (FVC) and forced expired volume in 1 s (FEV,) (Vitalograph, Vitalograph Ltd) was done in the sitting position(22). Standard chest x-rays in both frontal and lateral projections were obtained in the sitting position. Computed tomography of the chest The transverse lung area and the structure and density of the lungs were studied by CT scanning, with the subject in the supine position on the tomograph table (Siemens Somatom 2). A frontal topogram covering the chest was obtained initially. Two CT scans in the transverse plane were then performed, the lowermost one at a level just above the top of the diaphragm and the other 5 cm cephalad to the first one. Both scan levels were marked with ink on the chest of the patient to enable the same scan level to be used in the succeeding postoperative measurements. Change in diaphragm position caused by, for example, abdominal distension may have influenced the scan position relative to the lung. To minimize these effects, it would have been desirable to obtain a topogram before the scans were made

on each occasion. This would, however, have increased further the radiation to the patient and was not considered justified.The scan time was 5 s at 115 mAs and 125 kV, slice thickness 8 mm and centre/ window settings O/ f 512. The transverse area of the thoracic cavity was calculated from the CT scans, using a computer after manual delineation of the interior border of the thoracic wall; thus the mediastinal organs were included in the analysis. The CT scan was then checked for dense areas in dependent lung regions - such regions were assumed to reflect atelectasis. To calculate the dense area, a magnified image (2 x ) was made of the dorsal portion of the C T scan with an image of both right and left lung. The dorsal border between the thoracic wall and the dense area was identified, and the dense area was encircled as a region of interest (ROI). The atelectatic area was then calculated by the computer as picture elements with an attenuation of between - 100 and + 100 Hounsfield units within the ROI. The amount of atelectasis in the lungs was expressed in per cent of the total transverse area of the thoracic cavity. The variability of the estimation of the atelectatic area, expressed as the coefficient of variation of duplicate measurements of the same scan, was less than 5%.

ABG

n

ABG

ABG

ABG

Spir

Spir

Spir

Spir

X-ray

X-ray

X-ray

X-ray

CT

CT

CT

CT

2h

1

CT

ABG

I

CT

I

Preop Anaesth

2

3

4

Postoperative day Fig. 1. Procedure of the investigation. ABG: Arterial blood gases, Spir: spirometry, x-ray: Pulmonary x-ray. C T CT scanning of the chest. Preop: Awake before induction of anaesthesia, Anaesth: Anaesthesia, 2 h 2 hours postoperatively.

548

P. LINDBERG E T AL.

Awake

Anaesthesia

2 h postoperatively

1" postoperative day

2ndpostoperative day

4" postoperative day

Fig. 2. CT scans of patient no. I 1 awake, during anaesthesia, and in the postoperative period (2 h postoperatively, and on the Ist, 2nd and 4th postoperative day). Note the appearance of dense regions - atelectasis in dependent regions of both lungs. The atelectatic area increased slightly during the first 2 postoperative days. On the last day (4th postoperative day), only a small amount of atelectasis remained.

549

POSTOPERATIVE ATELECTASIS AND LUNG FUNCTION Procedure An arterial blood gas sample was taken when the patient arrived in the x-ray department, and CT scans were recorded (Fig. 1 and 2). Next, the patient was anaesthetised and new C T scans were performed. Then the patient was transferred to the operating theatre for the planned surgical procedure. Approximately 2 h postoperatively, the first postoperative measurement of arterial blood gases and CT scanning were performed. In the morning of the 2 following days and on the fourth postoperative day, new arterial blood gas samples were obtained, and spirometry and CT-scanning as well as pulmonary x-ray were done. Ro, was 0.21 at all measurements of arterial blood gases. Statistics

For each variable, mean value and standard deviation (s.d.) were calculated. The significance of a difference between the investigations was tested by analysis of variance (ANOVA). Newman-Keuls' post hoc test was used for comparisons.

RESULTS Awake and during anaesthesia Preoperative lung function testing showed normal FVC (mean 102% of expected) and FEV, (96% of expected) (22). These values were used as references for the postoperative measurements (Table 2, Fig. 1 and 3). Arterial oxygen tension (Pao,) was 11.9 kPa (Table 2, Fig. 3). Paco, was 4.9 kPa, and the alveolararterial oxygen tension difference (PA-ao,) was 1.8 kPa. Preoperative pulmonary x-ray and awake C T scans were essentially normal in all subjects, thus no atelectasis was seen (Fig. 2-3, Table 2). After induction of isoflurane anaesthesia with muscular paralysis, six of

the 13 patients had developed atelectasis (mean 1.0% (all subjects included) of intrathoracic transverse area in the lower scan) (Table 2, Fig. 2-3). Postoperative period Two hours postoperatively. After the surgery, which lasted on average 2.25 h (range 1-4 h), the patients were transferred to the recovery room. When the patient, according to departmental criteria, was fit to leave the recovery room (approximately 2 h postoperatively), an arterial blood gas sample was taken. The patient had then been without supplementary oxygen for at least 30 min. Compared to the preoperative measurement, Pao, had decreased significantly by 2.1 kPa to 9.8 kPa, while Pacoi was essentially unaltered at 5.2 kPa (Table 2). PA-ao, had doubled compared to the awake measurement and was 3.7 kPa. The C T scans showed that a majority of the patients (1 1 of 13 patients) had developed atelectasis, increasing the mean atelectatic area to l.8%0, compared to the anaesthesia measurements (Table 2, Fig. 2-3). However, only two of the six patients who had atelectasis during anaesthesia increased their atelectatic area further. Postoperative day 1. I n the surgical ward the patient was nursed according to departmental policies, which included standard postoperative physiotherapy and encouragement of early mobilization, but not the use of CPAP or incentive spirometers. The measurement in the morning of the first postoperative day showed significant decreases in both FVC and FEVl to 213 of

Table 2 Ventilation, arterial blood gases and atelectasis awake, during anaesthesia and in the postoperative period. Poatoperative period Preop

Anaesth

2h

day 1

day 2

-

-

68 f 20. 67 & 24*

77 f 15. 73f21*

88 ?: 13**+ 87 k 14**+

9.8 k 2.2* 5.2 +_ 0.7 3.7 f 1.9*

9.4 & 2.1* 4.8 f 0.3

4.4 f 1.9*

9.8 k 1.6* 4.8 k 0.4 4.0 1.6'

10.8 & 1.8**+ 4.7 k 0.4 3.3f 1.7*.+

1.8 f 2.01 9

1.4+ 1.9* 8

0.2 t 0.4' 4

1.3k 1.2* 9

0.9f l.l* 7

0.1 f 0.4+

Ventilation FVC (YOof preop) FEV, (% of preop)

100 f 0 1OOfO

Blood gases Pao, (kPa) Paco, (kPa) PA-ao, (kPa)

11.9* 1.9 4.9 & 0.6 1.8f 1.7

-

Caudal CT scan Atelectasis (%) No. of patients

o*o

l.O+_1.3 6

1.8f 2.2*

0

Cranial CT scan Atelectasis (YO) No. of patients

oto

0.6t 1.0

0

5

1.1 1.1* 11

-

-

11

*

day 4

2

Preop: Awake before anaesthesia, Anaesth: Anaesthesia, FVC, FEV,: Forced vital capacity and forced expired volume in 1 s. Pao,, Paco,: arterial oxygen and carbon dioxide tensions, Pa-ao,: alveolar-arterial oxygen tension difference, Atelectasis: Atelectatic area in per cent of transverse intrathoracic area for all patients. No. of patients: number of patients with atelectasis. ( n = 13, mean k s.d.). * Significantly different from the preoperative measurement, P < 0.05. + Significantly different from postoperative day 1, P