British Journal of Anaesthesia 1993; 71: 747-751 CONTINUOUS SPIROMTRY: AN AID TO MONITORING VNTILATION DURING OPRATION G. I. BARDOCZKY,. NGLMAN AND A. D'HOLLANDR SUMMARY We present six ase-reports of patients who experiened inadequate ventilation as a result of endobronhial or oesophageal intubation, or obstrution to the trahea/ tube or airway and were monitored with on-line spirometry. The ontinuously displayed pressure-volume or flow-volume loops may be ompared with previously reorded baseline loops. The hanging onfiguration of the urves offers additional and instantaneous information about the ause of inreased inspiratory airway pressure, dereased ompliane or inreased airway resistane. Monitoring flow-volume and pressure-volume loops in onjuntion with urrently available tehniques provides a omprehensive method of monitoring ventilation. (Br. J. Anaesth. 1993; 71 : 747-751) KY WORDS Intubation: ompliations. Monitoring: spirometry, flow-volume loop, pressure-volume loop. Routine intraoperative monitoring of the respiratory system inludes tidal volume, inspiratory airway pressure and inspiratory and expiratory gas onentrations. With the development of new, miroproessor-based sensor tehnology, in-line spirometry is inorporated into some monitors, allowing loser evaluation of respiratory physiology during operation. The Ultima SV respiratory monitor (Datex Instrumentarium Corp. Helsinki, Finland) is used for routine intraoperative monitoring in our department. An integral part of the monitor omprises spirometry by a newly developed flow sensor and respiratory gas sampling probe [1]. The flow sensor is plaed between the Y-piee and the traheal tube of the breathing system. It is a bi-diretional, pressurebased flow sensor, with two fixed resistanes interposed in the airflow (fig. 1). The pressure differene aused by gas flow is measured between these two ports during both inspiration and expiration. From the measured flow (flow rate, peakflow)and pressure (end-expiratory, plateau, maximum and minimum) values, the tidal and minute volumes are omputed during both inspiration and expiration. Dynami ompliane of the respiratory system is determined ontinuously using the end-inspiratory plateau pressure. The flow sensor has a deadspae of 9.5 ml, and its resistane is 0.5 m HjO/30 litre min" 1. Two loops are drawn from the measured variables the flow-volume (FV) and the pressure-volume (PV) loop, whih are displayed ontinuously (fig. 2), stored and updated at eah breath. Changes in ompliane and airway resistane or the expiratory flow harateristis of the whole respiratory system (lungs and thorax, traheal tube) are illustrated ontinuously and visually by the hanging form of eah loop and may be ompared with the baseline urves [2,3]. Compromised airway pateny or inorret plaement of the traheal tube may alter the PV and FV urves in a partiular way, whih may help to detet the origin of the problem and its effet on ventilatory mehanis. We report six patients in whom ontinuous spirometry helped to reognize or to onfirm inadequay of ventilation. CAS RPORTS Inadvertently misplaed traheal tubes Patient No. 1: endobronhial intubation. A young woman was undergoing a small proedure on the nek. Her trahea was intubated without diffiulty. Breath sounds were equal bilaterally by ausultation, peak inspiratory airway pressure and ompliane were normal. After the patient's head was turned for surgery, the high pressure alarm sounded and a derease in ompliane aompanied the right shift of the displayed PV urve (fig. 3). Arterial oxygen saturation and end-tidal arbon dioxide onentration were unhanged. On ausultation, no breath sounds were deteted on the left side of the hest and endobronhial displaement of the traheal tube was suspeted. Withdrawing the traheal tube by 3 m resulted in normal PV and FV loops and bilaterally equal breath sounds. Patient No. 2: oesophageal intubation. An 83-yrold woman was undergoing right lobetomy. General anaesthesia was indued and an oral double-lumen endobronhial tube inserted without visualization of the voal ords. The ommon onnetor of the tube was attahed to the flow sensor of the Ultima SV and the ventilator. During routine ausultation of the GIZIXA I. BARDOCZKY, M.D.; DGARD NGLMAN, M.D. ; ALAIN D'HOLLANDR, M.D., PH.D.; Department of Anesthesiology, rasme University Hospital, Free University of Brussels, 808 Route de Lennik, Brussels, Belgium. Aepted for Publiation: April 15, 1993. Correspondene to G. I. B.
748 BRITISH JOURNAL OF ANASTHSIA FIG. 1. Setion of the D-lite flow sensor, with the two fixed resistanes and a gas sampling port. <D 600 0 RBW (m H 2 0) rf 30" 5-30-1 600 FIG. 2. Normal pressure volume (left panel) andflow-volume (right panel) urves reorded in a paralysed patient with the trahea intubated undergoing mehanial ventilation.» 600 H 3 7i P&w (m H 2 0) 7 30 <D O it-30 FIG. 3. Patient No. 1: endobronhial intubation. Pressure-volume (left panel) and flow-volume (right panel) urves when the traheal tube was displaed into the right mainstem bronhus (1) and when withdrawn 3 m into the trahea (2). Note the right- and downward shift of the pressure volume urve and the dereased expiratory flow seen on the flow volume urve when the tube was positioned endobronhially. hest, distant breath sounds were reported and a non-ompliant PV loop and distortion of both the inspiratory and expiratory part of the FV loop were displayed (fig. 4), aompanied by small expiratory and inspiratory tidal volumes. The onomitant lak of detetable arbon dioxide suggested oesophageal intubation. A seond laryngosopy onfirmed oesophageal plaement of the double-lumen tube; it was removed and its position orreted. Inreased inspiratory pressure from mehanial auses Patient No. 3: kinking of the traheal tube. A 30-yrold woman underwent general anaesthesia for gynaeologial laparosopy. Shortly after the position of the laparosope was hanged by the surgeon, inreased inspiratory airway pressure and dereased ompliane were noted, with a right shift of the PV loop. On the FV loop, inspiratory and expiratory
AIRWAY MANAGMNT WITH SPIROMTRY 749 30" 600 FIG. 4. Patient No. 2: oesophageal intubation. The area of the pressure-volume loop (left panel) is enlarged; inreased inflation pressure was neessary to deliver a small volume into the non-ompliant oesophagus. The flow-volume loop (right panel) has irregular inspiratory and expiratory parts. 1 itre )W(I IS 600- -30-30- -30-1 - / \ 2 \ : { ^"^ $00 L ^ FIG. 5. Patient No. 3: trahal rube kinking. Pressure-volume (left panel) andflow-volume (right panel) loop reorded after indution of anaesthesia (1) and when the traheal tube was partially kinked (2) during laparosopy. Note the right shift and enlarged area of the PV urve with inreased inspiratory pressure, and the diminished inspiratory and expiratory flow of the FV urve. I 600-. 30 o -30 FIG. 6. Patient No. 4: ompression of the right hemithorax aused by abdominal retrators. The PV urve (left panel) is shifted to the right, its area enlarged, with inreased inspiratory pressure. nd-expiratory pressure was 14 m H,O. On the FV urve (right panel), note that exhalation is not yet omplete at the beginning of the new inspiratory phase. flows were diminished and both limbs beame horizontal, with dereased inspiratory and expiratory tidal volumes (fig. 5). Lifting the drapes from the patient's head revealed partial kinking of the traheal tube, aused by the gynaeologist's elbow. Patient No. 4: hest ompression. A 14-yr-old boy was undergoing exploratory laparotomy under general anaesthesia for removal of an extensive retroperitoneal tumor. During exploration, inreased inspiratory and end-expiratory pressures were aompanied with audible wheezes and abnormal onfiguration of the expiratory parts of the PV and FV loops. The expiratory part of the FV urve did not return to the zero volume axis (fig. 6). On questioning, the surgeon dislosed that the subostally plaed abdominal retrator almost ompletely ompressed the right lung. Repositioning the retrator terminated the wheezing and resulted in normal ventilatory data. Patient No. 5: double-lumen tube dislodgement. A 67-yr-old man's trahea was intubated with a leftsided double-lumen endobronhial tube for a right pneumonetomy. The surgial dissetion was extremely diffiult beause of extensive adhesions. One-lung ventilation was well tolerated. However, the surgeon was asked on several oasions to refrain from exessive strething of the hilum. Suddenly, a ompletely distorted FV urve (fig. 7) was seen, with inspiratory airway pressure greater than 60 m H,O and inability to ventilate the lung. Dislodgement of the double-lumen tube was diagnosed and onfirmed by fibreopti bronhosopy.
750 BRITISH JOURNAL OF ANASTHSIA Paw (m HjO) FIG. 7. Patient No. 5: dislodged double-lumen endobronhial tube. FV urve reorded when the double-lumen endobronhial tube was dislodged from the left mainstem bronhus, and twisted to the other side. Note the highly irregular inspiratory and expiratory limb of the FV loop, the right- and downward shifted PV loop with enlarged area. g 900 i 3 30 O 30-30 FIG. 8. Patient No. 6: inreased inspiratory pressures aused by dereased airway alibre. PV (left panel) and FV (right panel) loops reorded during an episode of bronhospasm (2). Inreased inflation pressure, dereased ompliane and right shift of the PV loop (2) may be observed, in omparison with the loop reorded previously (1). The bowing onfiguration of the expiratory part of the FV loop (2) is harateristi for small airways obstrution. Inreased inspiratory pressure aused by dereased airway alibre Patient No. 6: bronhospasm. A 45-yr-old asthmati male was undergoing heart transplantation. Before termination of ardiopulmonary bypass, pulmonary ventilation was re-established. Hyperinflated lungs were protruded through the sternotomy and ausultation revealed bilateral wheezing. On the sreen of the ventilatory monitor, a right- and downward-shifted PV urve was noted, with a sooped-out expiratory limb of the FV loop (fig. 8). Inreased inspiratory airway pressure, dereased ompliane and dereased tidal volume aompanied the redution in expiratory flow. Beause the patient gave a history of reative airway disease, bronhospasm was onsidered and i.v. bronhodilator therapy was started. Within a few minutes, bronhospasm subsided gradually and ardiopulmonary bypass was disontinued suessfully. DISCUSSION Monitoring lung mehanis (pressure-volume and flow-volume loops) has been used traditionally in the laboratory and intensive are unit [4, 5]. As a result of advanes in omputer tehnology, these measurements have now been introdued into anaestheti pratie [1-3, 6]. The displayed passive FV loop (fig. 2, right) has two omponents: the lower, smoothly urved inspiratory part and the upper, triangular expiratory part, where the apex represents peak expiratory flow [7]. In patients with the trahea intubated, undergoing mehanial ventilation, the shape of the inspiratory limb is influened mainly by the ventilator and does not provide valuable information about the patient's ventilatory system. As exhalation is passive, the expiratory part of the FV loop is determined by the mehanial properties of the ventilatory system (inluding the resistane of the traheal tube). The slightly oval PV loop (fig. 2, left) has an asending lower limb, whih represents the inreasing inspiratory pressure neessary to inflate the lung and a desending upper urve, whih reflets the dereasing pressure during deflation of the lung [8]. The slope of the urve is the dynami ompliane and the area of the urve is mainly a funtion of airway resistane [9]. In patients with the trahea intubated during anaesthesia, resistane of the total ventilatory system is influened mainly by the harateristis of the traheal tube [8]. After orret initial plaement, displaement of the tube may our, its lumen may be obstruted by seretions or kinking and it may be dislodged ompletely, resulting in an inrease in peak airway pressure [8]. Dereasing airway alibre resulting from bronhoonstrition is assoiated with inreased airway resistane and inreased inspiratory pressure. Ausultation and inspetion of the motion of the hest wall an provide important diagnosti lues. However, breath sounds may be diffiult to interpret in
AIRWAY MANAGMNT WITH SPIROMTRY 751 some pathologial onditions or the hest may be inaessible for ausultation. Without additional information, it annot be asertained if the site of inreased resistane is in the traheal tube or the lung. As hanges in airflow resistane and ompliane are illustrated visually by the hanging onfiguration of PV and FV loops, these may be used to differentiate the origin of inreased inspiratory pressure. nlarged areas of the PV urve (inreased resistane) with right- and downward shift of the slope (derease in ompliane) are seen in most of the onditions assoiated with inreased peak airway pressures. Inspeting the expiratory limb of the orresponding FV urve may offer more detailed information: kinking of the traheal tube alters both the inspiratory and expiratory limb to about the same degree and a uniform manner (fig. 5), external obstrution distorts the expiratory limb more (fig. 6) and impingement of the tip against the airway wall or a tidal volume delivered into the non-ompliant oesophagus both result in a grossly distorted FV loop (fig. 4). Bronhoonstrition also is assoiated with inreased airway resistane [4]. The area of the pressure-volume loop is enlarged (fig. 8), with right shift of the slope; greater inspiratory pressure is neessary to deliver a given volume. The flowvolume loop reveals uneven lung emptying with the sooped-out, onvex onfiguration of the expiratory limb. Bronhoonstrition is a dynami phenomenon, and its time ourse may be followed easily by the inreasing or dereasing onvexity of the expiratory limb as suessive FV urves are ompared. There is evidene in the literature that the severity of airway obstrution and response to bronhodilators may be estimated by assessment of ventilatory mehanis [10]. These ases imply that ontinuous monitoring of pressure-volume and flow-volume loops may be useful in deteting and diagnosing airway problems. RFRNCS 1. Bardozky GI, d'hollander A. Continuous monitoring of the flow-volume loops and ompliane during anesthesia. Journal of Clinial Monitoring 1992; 8: 251-252. 2. Simon BA, Hurford W, Alfille PH, Haspel K, Behringer C. An aid in the diagnosis of malpositioned double-lumen tubes. Anesthesiology 1992; 76: 862-863. 3. Bardozky GI, defranquen P, ngelman, Capello M. Continuous monitoring of pulmonary mehanis with the side stream spirometer during lung transplantation. Journal of Cardiothorai and Vasular Anesthesia 1992; 6: 731 734. 4. Bone RC. Diagnosis of auses for aute respiratory distress by pressure-volume urves. Chest 1976; 70: 740-746. 5. Hyatt R, Blak LF. The flow-volume urve: a urrent perspetive. Amerian Review of Respiratory Diseases 1973; X07:191-199. 6. Mili-mili J, Robatto FM, Bates HT. Respiratory mehanis in anaesthesia. British Journal of Anaesthesia 1990; 65: 4-12. 7. Karz JA, Zinn S, Ozanne GM. Pulmonary, hest wall and lung thorax elastanes in aute respiratory failure. Chest 1981; 80: 304-311. 8. Gal TJ. Respiratory Physiology in Anestheti Pratie. Baltimore: Williams & Wilkins, 1991. 9. Nunn JF. Applied Respiratory Physiology, 3rd dn. London: Burterworth, 1983. 10. Hubmayr RF, Gay PC, Tayyab M. Respiratory system mehanis in ventilated patients: tehniques and indiations. Mayo Clini Proeedings 1987; 62: 358-368.