Continuous

Monitoring of Pulmonary Mechanics With the Sidestream Spirometer During Lung Transplantation

Gizella I. Bardoczky,

MD, Philippe

defrancquen,

P

ERIOPERATIVE care of the patient undergoing single-lung transplantation is challenging for the anesthesiologist because of the major hemodynamic and respiratory changes that occur during this procedure. These patients are extensively monitored hemodynamically (invasive direct arterial pressure, multiple-lumen central venous access, pulmonary artery catheter), but their respiratory monitoring is far less complex, restricted to periodic arterial blood gas determinations, end-tidal CO* monitoring, and pulse oximetry. Despite the fact that several commercially available ventilators (Siemens 9OOC,Elmsford, NY; PuritanBennett 7200, Puritan Bennett, Carlsbad, CA), have built-in devices for continuously measuring flow, pressure, and derived respiratory variables, interest in detailed respiratory mechanics during anesthesia has only recently increased.’ Potential problems associated with this technique are attributable to the sampling site (inside the ventilator), and the influence by gas compression, tubing compliance, and leaks. If the flow and volume measuring device is at the level of the endotracheal tube, these errors can be avoided.* With the sidestream spirometer (Datex Instrumentarium, Helsinki, Finland), continuous monitoring of pressure, volume, and flow characteristics of the respiratory system is possible at the endotracheal tube, with a continuous display of the flow-volume and/or pressure-volume curves, and digital display of ventilatory parameters (Fig 1). The D-lite flow sensor and gas sampling tube is the crucial part of the monitor (Fig 2). This two-sided Pitot tube is essentially a pressure-based flowmeter with two fixed resistances interposed into the airstream. Pressure difference caused by the gas flow is measured between the two pressure ports of the D-lite probe. From the measured flows (flow rate, peak flow) and pressure (end-expiratory, plateau, minimum, and maximum pressures), the inspiratory and expiratory tidal and minute volumes, compliance, and resistance are calculated. Two loops are drawn from these values: flow-volume (resistance) and pressure-volume (compliance) loops3 (Fig 1). A case of single-lung transplantation using continuous flow-volume and pressure-volume loop monitoring is reported. CASE REPORT The patient was a 59-year-old woman (60 kg, 163 cm) with advanced pulmonary emphysema of undetermined etiology. She had severe dyspnea on moderate exertion, and received continuous oxygen therapy of 1.5 L/min, on which the PaO? was 67 mmHg and the PaC02 was 51 mmHg. Pulmonary function tests revealed a forced vital capacity of 1.73 L (60% of predicted) and FEVi of 0.58 L (24% of predicted). A lung ventilation/perfusion scan displayed multiple bilateral, heterogenous ventilation and perfusion defects. Radionuclide ventriculogram showed a left ventricular ejection fraction (EF) of 56% and a right ventricular EF of 41%. Cardiac output was 4.7 L/min and pulmonary artery pressure was 41/19 mmHg. Anesthesia was induced with etomidate, fentanyl, and pancuronium for left lung transplantation. A right-sided double-lumen endotracheal tube (DLT) (37 F) was placed, and its position

MD, Edgard Engelman,

MD, and Matte0 Capello,

MD

verified by auscultation and with the aid of fiberoptic bronchoscopy. Positive-pressure ventilation (tidal volume 8 mL/kg at a rate of 15 breaths/min) with air and added oxygen was delivered by a Siemens Elema 900B ventilator. Inspired oxygen concentration was adjusted according to the arterial oxygen saturation values. A pulmonary artery catheter was inserted after induction of anesthesia and revealed values similar to those measured preoperatively. Arterial oxygenation was easily maintained, Pa02 was 186 mmHg on an Ft02 of 0.5. Anesthesia was maintained with a continuous infusion of fentanyl; enflurance was added when it was necessary to deepen anesthesia. Heart rate, ECG, arterial blood pressure, pulmonary artery pressure, and rectal temperature were monitored with a Cardiocap II (Datex, Helsinki, Finland); ventilatory parameters and respiratory gases were monitored with the D-lite probe of the Capnomac Ultima (Datex, Helsinki, Finland) attached to the common adaptor of the DLT. To assess oxygen saturation, the finger probe of the Capnomac Ultima was secured to the thumb. The displayed pressure-volume and flow-volume loops were photographed at each significant point of anesthesia and surgery. Prior to initiation of one-lung ventilation (OLV) for the left pneumonectomy, movement of the correctly positioned DLT was suspected, because of the abnormal configuration of the compliance (Fig 3 A) and resistance (Fig 3 B) loops and the high inflation pressures. No changes in arterial blood gases, SpOz or in hemodynamics were noted. The malposition was confirmed by clamping the left (tracheal) lumen of the DLT, which resulted in a highly aberrant compliance loop (Fig 4) extremely high inflation pressures, and low compliance. Subsequent fiberoptic bronchoscopy proved that the right upper lobe ventilation slot was partially obstructed by the bronchial wall. A slight decrease of the inspiratory pressure and increased compliance were seen on the monitor after repositioning the tube. During the period of OLV, the pulmonary artery systolic pressure increased to 54 to 59 mmHg, systemic arterial pressures did not change, SpOz remained 98% on an FiOz of 0.35, and Pa02 was 120 mmHg. Dopamine, 5 pglkgimin, was continuously infused for renal protection. Omentopexy and cardiopulmonary bypass were not used in this patient. Implantation of the allograft was completed with an ischemic time of 2 hours and 49 minutes. Ventilation of both lungs resumed uneventfully, peak inspiratory pressure and compliance were acceptable, SpO2 was 98%, Pa02 was 229 mmHg on an FiOz 0.35. Flow-volume and pressure-volume curves showed a nearly normal form (Fig 5). Twenty minutes after the onset of the transplanted lung ventilation, right shift of the pressure-volume loop was observed with an enlarged area of the curve, associated with a rise of inspiratoty pressure and reduction of compliance (Fig 6) followed by a decline of SpOz and Pa02. Suctioning of the left lumen of the DLT yielded a large amount

From the Departments of Anesthesiology and Thoracic Surgery, Erasmus University Hospital, Free University of Brussels, Brussels, Belgium. Address reprint requests to Gizella I. Bardoczky, MD, Department of Anesthesiology, Erasmus UniversityHospital, Free Universig Hospital, 808 route de Lennik, 1070 Brussels Belgium. Copyright 0 1992 by W.B. Saunders Company 1053-077019210606-0019$03.00/O Key words: monitoring, spirometry, lung mechanics, transplantation

Journalof Cardiothoracic and VascularAnesthesia, Vol6, No 6 (December), 1992: pp 731-734

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Fig 1. Printout of typical flow-volume (left panel) and pressure-volume (right panel) loops obtained during pulmonary surgery, with two-lung ventilation. Far-right panel shows the measured parameters provided by the Capnomac Ultima. On the bottom are the corresponding flow (left) and pressure (right) tracings from the respirator. Left panel: 1. Flow during inspiration 2. Flow during expiration 3. Tidal volume 4. Peak expiratory flow. Right panel: 1. TV: Tidal volume 2. MV: Minute volume 3. Ppeak: Maximum airway pressure (cmHzO) 4. Pplat: End-inspiratory pressure 5. PEEP: End-expiratory pressure 6. VI.0 (%): Volume expired during the first second of expiration 7. I:E: Ratio between inspiratory and expiratory times 8. C: Compliance (mL/cmH,O).

_8: FinI

Tube

From breathing circuit

TO

oatienl

1

C: Sampling PM

Fig 3. Compliance (left panel) and resistance (right panel) loops at the beginning of surgery. Tracings were redrawn from photographs taken from the screen of the Capnomac Ultima. The abnormal shape of the loops raised the suspicion of malposition of the double-lumen tube. insp: 514 mL. exp: 466 mL, Ppeak: 35 cmHZO. Pplat: 25 cmH?O, PEEP: 1 cmH*O, V 1.0: 59% C:18 mL/cmHrO. RR: lG/mlin, SpO,: 98%.

Tolsl PresssuraMrarurcd B-Slavic Pressure Measured C-Hulli-Gas Sampling PDfl

A.

Fig 2. Schematic representation of the D-lite flow sensor and gas sampler. Deadspace of the sensor is 9.5 mL, flow resistance is 0.5 cmH,O/BO L/min. (Reprinted with permission from Datex Instrument Corp, Helsinki, Finland).

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Fig 4. Compliance loop during OLV. Tracing was redrawn from photograph. Note the highly aberrant shape and enlarged area of the curve. Tidal volume inspiratory: 480 mL, tidal volume TV expiratory: 438 mL, Ppeak: 56 cmH*O, Pplat: 45 cmH,O. PEEP: 5 cmH*O, V 1.0: 65%. C: 10 mL/cmHZO, RR: 16/min, SpO,: 97%.

of frothy pink secretions. Reperfusion pulmonary edema was suspected, and furosemide and an increased inspiratory concentration of oxygen were administered. At the conclusion of surgery, SpO2 was 98%, Pa02 93 mmHg on F[Oz of 0.85, compliance of the two lungs slightly improved, but a high inspiratory pressure was still required despite the increased respiratory rate. The DLT was left in place and the patient was transferred to the intensive care unit where her lungs were ventilated independently, with synchronized ventilation. Her oxygenation improved gradually, she was extubated 5 days after the transplantation, and discharged home 5 weeks after surgery. DISCUSSION

There is an increasing experience regarding the anesthetic management for patients undergoing single-lung or double-lung transplantation,4-7 and the authors’ anesthesia protocol is not different from other centers. The continuous display of respiratory parameters and the compliance (pressure-volume) and resistance (flow-volume) curves obtained by the sidestream spirometer were valuable in the management of this patient during singlelung transplantation. Changes in compliance and airflow resistance are visually illustrated by the changing configura-

Fig 6. Pressure-volume curve during two-lung ventilation, at the onset of reimplantation response. Tracing was redrawn from a photograph. Note the rightward shift and enlarged area of the loop. TV insp: 541 mL, TV axp: 558 mL, Ppeak: 31 cmH,O, Pplat: 25 cmH*O, PEEP:O,V 1.0: 67%. C: 21 mL/cmH,O, RR:lB/min. SpO,: 97%.

tion of each loop. In paralyzed patients, changes in compliance can be expected to reflect mainly those in lung compliance, and changes in resistance can be assumed to be representative of those in airway resistance.* In intubated subjects resistance is also influenced by the diameter and length of the endotracheal tube and the resistance of any additional apparatus.* The flow-volume loop is reproducible and characteristic for a given patient,8 consisting of a triangular expiratory limb (the upper part of the curve), with the apex of the triangle representing peak expiratory flow, and a smoothly curved, slightly rectangular inspiratory limb (Fig 1). Elevation of airway resistance and increase or decrease in elastic recoil alter the curve in a particular way, providing a visible estimate of the airway obstruction.lOJ1 Malposition of a DLT is confirmed by diminished expiratory flow rate and a horizontal expiratory limb.12,13 Increased expiratory flow resistance caused by the narrow lumen of the DLT may delay lung deflation, producing incomplete emptying of the lung, seen as an “open” flow-volume curve (Fig 3 B). This pattern is frequently seen during pulmonary surgery with OLV and could be a graphic representation of the persistent end-

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Fig 5. Pressure-volume (left panel) and flow-volume (right panel) loops photographed when transplanted and native lungs were ventilated. TV insp: 510 mL, TV exp: 483 mL, Ppeak: 19 cmH*O, Pplat: 13 cmH1O, PEEP: 1 cmH*O, V 1.0: 59%. C: 39 mL/ cmH,O, RR: 14/min, SpO,: 98%.

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expiratory flow.14 Compliance is a measure of how the pulmonary system complies with a distending pressure. The required pressure and the respired volume are displayed simultaneously to construct the pressure-volume curve.i5 The slope of the curve is the dynamic compliance, calculated from pressure and volume measurements made when there is no gas flow, at end-inspiratory and end-expiratory “no-flow” points. The area of the loop is mainly a function of airway resistance.15 Increased airway resistance due to the malposition of the DLT in this patient was suspected during two-lung ventilation, and became obvious during OLV, due to the highly aberrant contour, and enlarged area of the pressure-volume curve (Fig 4). Because the position of the DLT was corrected immediately after recognition of the abnormal configuration of the pressure-volume and flow-volume loops, oxygen desaturation, or arterial blood pressure changes did not occur. Reimplantation response after lung transplantation occurs frequently, and is characterized by increased capillary permeability, pulmonary edema, and hypoxemia. I6 It is thought to be due to the combined effects of lymphatic interruption, ischemia, and surgical trauma. Functionally, this produces an impairment of transplant ventilation with decreased compliance and a

ET AL

decreased ventilation/perfusion ratio with hypoxemia. In this patient, the configuration of the pressure-volume curve and the compliance were close to normal after ventilation of the transplanted and native lung was started (Fig 5). Later, progressive rightward shift of the curve was observed, with increased width of the pressure-volume loop accompanied by an elevated airway pressure” (Fig 6). Arterial oxygen desaturation, decreased arterial oxygen tension, and increased end-tidal CO2 concentration occurred afterwards, when alveolar flooding was manifested in the form of frothy secretions. To the authors’ knowledge, this is the first reported case in which the reimplantation response was observed by the altered configuration of the pressure-volume curve, and later confirmed by the onset of hypoxemia. In conclusion, continuous monitoring of pressure-volume and flow-volume loops during anesthesia for single-lung transplantation complemented and preceeded detection of abnormalities by other means. However, it requires experience and skill for the interpretation of the curves. Studies are needed to confirm the value of on-line monitoring of compliance and pressure-volume curves during anesthesia. but its potential application seems promising.

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