Asian Cardiovasc Thorac Ann 2003;11:289-292
© 2003 Asia Publishing EXchange Ltd
Ultrasonography and Lung Mechanics Can Diagnose Diaphragmatic Paralysis Quickly
Takahiro Manabe, MD,
Masahide Ohtsuka, MD,
Yutaka Usuda, MD,
Kiyotaka Imoto, MD,
Michio Tobe, MD,
Yoshinori Takanashi, MD
First Department of Surgery, Yokohama City University School of Medicine, Yokohama, Japan
For reprint information contact: Takahiro Manabe, MD Tel: 81 45 787 2645 Fax: 81 45 786 0226 email: manaberu{at}aol.com 3-9 Fuku-ura, Kanazawa-ku, Yokohama 236-0004, Japan.
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ABSTRACT
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Diaphragmatic paralysis after cardiovascular surgery requires early diagnosis prior to extubation. The effectiveness of ultrasonography and a lung mechanics assessment was evaluated. Paralysis of the diaphragm was diagnosed when the diaphragm failed to move or moved in a cephalad direction during inspiration. It was diagnosed in 3 of 40 patients (7.5%) who underwent cardiovascular surgery from 1998 to 1999. Patients were extubated when all parameters met the extubation criteria, irrespective of the presence or absence of diaphragmatic paralysis. One patient required prolonged assisted ventilation and died from mediastinitis on the 35th postoperative day. The other 2 patients required assisted ventilation for an additional 1–3 days. Ultrasonography and a lung mechanics assessment are effective tools for the early diagnosis of diaphragmatic paralysis and assessment of respiratory function after cardiovascular surgery.
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INTRODUCTION
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Diaphragmatic paralysis due to phrenic nerve injury may complicate as many as 2.3% to 36% of surgical procedures for cardiovascular diseases.1–5 In such cases, the other respiratory muscles cannot always compensate for the decrease in respiratory mechanics because cardiac operations have an adverse effect on respiratory function.6 Respiratory failure after extubation may be fatal due to the development of lung complications such as secondary pneumonia.7,8 Therefore, diaphragmatic paralysis after cardiovascular surgery requires accurate and early diagnosis prior to removal of the tracheal tube. We investigated whether ultrasonography and a lung mechanics assessment were beneficial in the diagnosis of diaphragmatic paralysis and evaluation of ventilatory performance early after cardiovascular surgery.
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PATIENTS AND METHODS
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Forty patients (28 males and 12 females; age range, 7 to 75 years; mean age, 55 ± 20 years) underwent surgery for cardiovascular disease at Yokohama City University Hospital between June 1, 1998 and June 1, 1999. Table 1
shows the surgical procedures performed on these patients. No ice slush was used for myocardial protection during surgery. The ultrasonographic assessment was performed using a SSH-160A ultrasound scanner (Toshiba Medical Systems, Tokyo, Japan) with 3.5-MHz mechanical sector scanheads. Intercostal views with the transducer from the 6th or 7th intercostal space at the midaxillary line were obtained on each side. To evaluate unassisted ventilatory performance, the ventilator was removed and the patient was connected to a Jackson-Rees circuit during each examination. Paralysis was diagnosed when the diaphragm failed to move or moved in a cephalad direction during inspiration. Ventilatory parameters (minute volume, respiratory rate, tidal volume, vital capacity, maximum inspiratory pressure, and maximum expiratory pressure) were assessed simultaneously in the supine position. Patients were extubated when all parameters met the extubation criteria (Table 2), irrespective of whether diaphragmatic paralysis was present or absent.
Data are expressed as the mean ± standard error. Differences between the ventilatory parameters of patients and controls were determined by a one-way factorial analysis of variance with Fisher’s post-hoc test. Statistical significance was established when p < 0.05.
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RESULTS
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Satisfactory ultrasonographic intracostal scans of the diaphragm were obtained for all patients. Paralysis of the diaphragm was diagnosed in 3 patients (7.5%) and their ventilatory parameters are shown in Table 3. The first patient was a 36-year-old man who had undergone ascending aortic replacement for acute aortic dissection 1 year previously. He underwent aortic arch replacement for an aneurysm along the aortic arch. He was fully awake and fully conscious with stable hemodynamics on the 13th postoperative day. Ultrasonography and assessment of lung mechanics revealed a respiratory rate of 49 breaths per minute and paralysis of the left diaphragm. The patient required prolonged assisted ventilation and died from mediastinitis on the 35th postoperative day. The second patient was a 67-year-old woman who underwent aortic valve replacement for aortic stenosis. The postoperative course was uneventful. On the first postoperative day, ultrasonography and a lung mechanics assessment revealed paralysis of the right diaphragm (Figure 1) and a vital capacity of 9.4 mL•kg-1. She required assisted ventilation for an additional 3 days until her vital capacity increased to 10.0 mL•kg-1 and all parameters met the extubation criteria. She was weaned from the ventilator easily and did not require reintubation. At follow-up 1.5 years postoperatively, she had not recovered from diaphragmatic paralysis; M-mode ultrasonography revealed paradoxical movement during inspiration (Figure 2). The third patient was a 25-year-old woman who had undergone right ventricular outflow tract reconstruction for congenital pulmonary stenosis at 5 and 15 years of age, and underwent a third operation due to restenosis. The postoperative course was uneventful and she had stable hemodynamics. Ultrasonography and a lung mechanics assessment were performed on the first postoperative day, revealing paralysis of the left diaphragm and a maximum inspiratory pressure of 18 cm H2O. She required assisted ventilation for an additional day. The following day, ultrasound revealed satisfactory movement of the left diaphragm and all parameters met the extubation criteria (maximum inspiratory pressure of 20 cm H2O). She was extubated easily and did not require reintubation. None of the other 37 patients without diaphragmatic paralysis required reintubation. Patients who underwent repeat surgery tended to experience a higher incidence of diaphragmatic paralysis complications (p = 0.024).
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Figure 1. Satisfactory ultrasound imaging in the intracostal position showing an absence of movement during inspiration (left, inspiration; right, expiration).
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DISCUSSION
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Haber and colleagues9 described the effectiveness of ultrasonography when visualizing diaphragmatic motion in a study of 110 adults with intraabdominal abnormalities. Studies by other groups demonstrated the effectiveness of bedside ultrasonography in the diagnosis of diaphragmatic paralysis after surgery for congenital heart disease.10,11 The diagnosis was confirmed by fluoroscopy in all patients, and there were no false positive or false negative diagnoses. Fluoroscopy remains the standard method of assessing diaphragmatic motion although it has disadvantages.12 The patient and staff are exposed to risks from radiation, and the patient, often still on ventilatory support, must be transferred to the fluoroscopy screening room with hemodynamic monitoring and infusion lines in place. This is potentially hazardous as well as time consuming and labour intensive. On the other hand, ultrasound equipment is available in all units that regularly provide patient care after cardiovascular surgery, and it can be easily brought to the patient’s bedside. Ultrasonography is not known to have any dangerous side-effects and it enables clinicians to assess the presence or absence of diaphragmatic palsy promptly, which we recommend particularly prior to extubation. Unless the clinician is cognizant of the phases of respiration, bilateral palsy can be missed by fluoroscopy because the two sides move in harmony, even when moving paradoxically.10 This error is less likely to occur using ultrasonography because the diaphragm and thoracic movement can be directly observed at the bedside.
The measurement of lung mechanical parameters is important when determining the timing of extubation, because a patient who has diaphragmatic paralysis but meets the extubation criteria can be weaned easily and safely from the ventilator. This is possible because the other respiratory muscles compensate for the decrease in muscle power caused by the diaphragmatic paralysis. We speculate that a patient without diaphragmatic paralysis who is on the borderline of the extubation criteria can be extubated with no complications. However, we recommend that a patient who manifests complications of diaphragmatic paralysis and is also on the borderline of the extubation criteria, such as the last 2 cases described herein, should not be extubated until the diaphragmatic paralysis has been compensated for or improved adequately. The daily measurement of lung mechanical parameters can also be performed at the bedside easily without causing adverse side-effects.
We advocate that once respiratory function has improved, mechanical respiratory support can be withdrawn, irrespective of whether the patient has diaphragmatic paralysis or not. In the first patient, we considered further surgery such as phrenic pacing or diaphragmatic plication, but treatment for infection was started prior to surgical intervention. In the other 2 patients, we expected their diaphragmatic paralysis would improve or be readily compensated. Direct phrenic nerve injury might have occurred while opening the pericardium, particularly upon repeat surgery, because the anatomy was distorted.8 Occasionally, thermal injury of the phrenic nerve may occur during cauterization of pericardial bleeding to promote hemostasis. Therefore, surgeons should exercise extreme caution during cauterization in order to prevent this avoidable complication.
This study is limited by the lack of preoperative ultrasonography, nonrandomized protocol, small number of patients, and the fact that ultrasound imaging is operator-dependent. Despite these limitations, it was concluded that ultrasonography and a lung mechanics assessment are beneficial in the early diagnosis of diaphragmatic paralysis and evaluation of respiratory function after cardiovascular surgery.
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ABSTRACT
INTRODUCTION
