26
ANESTHESIA AND ANALGESIA . . . Current Researches VOL.56, NO. 1, JAN.-FEB.. 1977
Improved Oxygenation Du ring Thoracotom y with Selective PEEP to the Dependent Lung DAVID R. BROWN, M D * ENID R. KAFER, MD, FRACP, FFARCSt VIRGIL 0. ROBERSON, MDS
BENSON R. WILCOX, MDS GORDON F. MURRAY, M D I I Chapel Hill, North Carolina**
In 22 patients during thoracotomy in the lateral position, the effects of selective positive endexpiratory pressure (PEEP) to the dependent lung while simultaneously ventilating the nondependent lung at zero end-expiratory pressure (ZEEP) on (1) inspired 0, concentration required to maintain adequate Paoz during thoracotomy and (2) alveolar-arterial oxygen difference (AaozD) while breathing 100 percent 0,
at the end of thoracotomy were examined and compared to ventilation of both lungs at ZEEP. Selective PEEP to the dependent lung resulted in adequate Pao, with a lower inspired 0, concentration (44 -C SD 6% versus 70 ? SD 21%), and a smaller Aao,D while breathing 100 percent 0, 189 & SD 31 versus 342 ? SD 69 torr) at the end of thoracotomy.
A
nous shunts. The Aao,D due to shunt is increased when the mixed venous O2 content is reduced in association with an inadequate cardiac output. The majority of studies have shown that during anesthesia pulmonary arteriovenous shunt is the major cause of the increased alveolar-arterial oxygen differences.l.2
oxygenation during thoracotomy in the lateral position may become difficult to maintain due to reduction in the arterial oxygen tension (Pao,). Therefore, it may become necessary to use high inspired 0, concentrations. This not only reduces the choice of anesthetic agents but, if the reduction in Pao, is due to absorption atelectasis of the dependent lung, it may be associated with postoperative hypoxemia. DEQUATE
The reduced Pao, and the associated increased alveolar-arterial 0, differences (Aao,D) are due to venti1ation:blood flow maldistribution and pulmonary arteriove-
During thoracotomy in the lateral position, gravity causes the blood to flow predominantly to the dependent lung. This combined with the following factors which reduce ventilation to the dependent lung results in ventilation: blood flow maldistribution and shunt. First, in association with the
*Associate Professor, Department of Anesthesiology ?Associate Professor, Departments of Anesthesiology and Physiology. $Resident, Department of Anesthesiology. B Professor and Division Chief, Department of Surgery, Division of Cardiothoracic Surgery. //AssociateProfessor, Department of Surgery, Division of Cardiothoracic Surgery. **University of North Carolina School of Medicine, Chapel, Hill, North Carolina 27514. This study was supported in part by Grant HL-17314-01, North Carolina Lung Association and Grant HL-11909-07. Paper received: 2/25/76 Accepted for publication: 6/3/76
Selective PEEP . . . Brown, et a1
27
reduction in the end-expiratory volume, which in the lateral position is most marked in the dependent lung, there is a reduction in the proportion of ventilation going to the dependent l~ng.38~ This is comparable to a person inspiring from below his functional residual capacity (FRC) when the ventilation during tidal breathing goes predominantly to the upper zones.5*6Airway closure in the dependent part of the lung requires greater pressure to ventilate the dependent than the other lung. Second, there is also evidence that during muscle paralysis and controlled ventilation, loss of diaphragmatic force reduces ventilation to the dependent lung.7 Further contributions to pulmonary arteriovenous shunt result from compression of areas of the nondependent lung during surgical manipulation. Theoretically, if loss of the end-expiratory volume of the dependent lung were a major factor in contributing to the maldistribution of ventilation, absorption atelectasis in the dependent lung, and the observed pulmonary arteriovenous shunt, then maintaining the end-expiratory volume of the dependent lung should prevent these changes. We tested this hypothesis by constructing a circuit which, together with a Carlens double-lumen endobronchial tube,xs9 applied 10 cm H,O of positive end-expiratory pressure (PEEP) to the dependent lung and allowed the nondependent lung to be ventilated with the same ventilator but a t zero end-expiratory pressure (ZEEP) . The effect of this circuit on Pao,, Aao,D, and inspired 0%concentration required to maintain safe oxygenation were examined in patients undergoing thoracotomy in the lateral position for pulmonary and esophageal surgery.
METHODS The circuit (figure) consists of a common inspiratory path for both lungs and for expiration of the nondependent lung, a C K U S*mM L VENTIUTW
TO NONDEPENDENT LUNG
ONE W N VNVE 10 LXPENDENT LUNG
FIGURE. Schematic of circuit used to apply selective PEEP to dependent lung while ventilating nondependent lung with ZEEP.
TABLE 1 Physical Characteristics of Patients and Duration of Operation Group I
PEEP to dependent lung Mean and SD
Age, years Weight, kg
56
(-C 7.8)
73.9 (-+ 11.4)
FEV1/VC, percent
61 ( k 1 5 )
Duration of surgery hours
6.4 (21.25)
Group II ZEEP to both lungs Mean and SD
54 (? 8.0) 66.9 ( & 7.7) 67 (ell)
5.75 ( & 1.1)
one-way valve separating expiratory flow of each lung, and a 10 cm H,O “dead weight” PEEP.” The circuit was used with a Carlens double-lumen endobronchial tube,n,g and a standard circle system with C 0 2 absorber and a ventilator.? The circuit for each lung was tested by ventilating a Manley test lung$ having ranges of compliance and resistance, and at ranges of flow and volume encountered in adult thoracic surgery. The circuit was reliable. The volume of the circuit is 50 ml; it does not cause any significant increase in dead space, and the resistance to air flow of the common inspiratory and expiratory limb of nondependent lung is negligible. During clinical use, insertion of the circuit into the anesthesia breathing circuit and onto the Carlens catheter did not cause any increase in the inflating pressures. Twenty-two patients were studied during thoracotomy in the lateral position for resective pulmonary surgery (20) and Belsey hiatal hernia repairs ( 2 ) . The patients were randomly divided into 2 groups: group I, experimental, and group 11, controls. Groups were similar in age, weight, preoperative spirometry, and duration of the surgical procedure (table 1 ) . Group I patients were intubated with a Carlens double-lumen endobronchial tube (39 or 41), and during the lateral thoracotomy both lungs were ventilated and selective PEEP was applied to the dependent lung with ZEEP to the nondependent lung. Group I1 patients were intubated with a cuffed endotracheal tube and both lungs were ventilated with ZEEP. *Model 4801, Boehringer Laboratories, Wynnewood, Pennsylvania. iventimeter, Air Shields, Inc, Hatboro, Pennsylvania. SBlease Medical Equipment Ltd, Deansway, Chesham, United Kingdom.
28
ANESTHESIA AND ANALGESIA . . . Current Researches VOL.56,No. 1,JAN.-FEB., 1977
Both groups were premedicated with diazepam (0.2 mg/kg) and the anesthetic agents for the 2 groups were similar, 5 patients in each group receiving either halothane or enflurane in N20-0, and the remainder receiving narcotic-relaxant drugs with N,O-0,. Both groups were ventilated with a similar pattern of large tidal volumes (10 to 15 ml/kg), slow respiratory frequency (8 to 10/min), and with sufficient minute ventilation to maintain a normal Paco,. Throughout operation, temperature, acidbase balance, and electrolytes were normal, blood loss was replaced as required, and the arterial and central venous pressures remained within the patients’ normal range. The urine flow, which was maintained by volume replacement, was > 50 ml/m2 of body surface area. Arterial pressure was monitored by a pressure transducer and arterial blood gases were taken from an indwelling radial artery catheter. Both groups were initially ventilated with 30 to 50 percent 0, (table 21, and arterial blood gases were measured 10 minutes after the thoracotomy. During thoracotomy, arterial samples were taken every 15 minutes and the inspired 0, concentration was adjusted to maintain a Pao., greater than 100 torr. After closure of the thoracotomy, establishment of underwater drainage, and while still in the lateral position, all patients breathed 100 percent O2for 10 minutes: then arterial blood gases were again measured.
RESULTS Throughout the thoracotomy, the patients given selective PEEP to the dependent lung (group I) were ventilated with the same inspired 0, concentration. There was no significant decrease in the Pao, (p>0.05) or increase in Aao,D (p>0.05) (table 2 ) . The inspired 0, concentration was 30 to 50 percent (mean 44 2 SD 6%) and the mean Pao, during thoracotomy was 162 2 SD 37.9. By contrast, of the patients who did not receive selective PEEP to the dependent lung, 8/11 required an increase in the inspired 0, concentration to maintain an adequate Pao,. Despite this increase in inspired O2 concentration, there was a significant decrease in the Pao, (p
ANESTHESIA AND ANALGESIA . . . Current Researches VOL.56, NO. 1, JAN.-FEB.. 1977
Improved Oxygenation Du ring Thoracotom y with Selective PEEP to the Dependent Lung DAVID R. BROWN, M D * ENID R. KAFER, MD, FRACP, FFARCSt VIRGIL 0. ROBERSON, MDS
BENSON R. WILCOX, MDS GORDON F. MURRAY, M D I I Chapel Hill, North Carolina**
In 22 patients during thoracotomy in the lateral position, the effects of selective positive endexpiratory pressure (PEEP) to the dependent lung while simultaneously ventilating the nondependent lung at zero end-expiratory pressure (ZEEP) on (1) inspired 0, concentration required to maintain adequate Paoz during thoracotomy and (2) alveolar-arterial oxygen difference (AaozD) while breathing 100 percent 0,
at the end of thoracotomy were examined and compared to ventilation of both lungs at ZEEP. Selective PEEP to the dependent lung resulted in adequate Pao, with a lower inspired 0, concentration (44 -C SD 6% versus 70 ? SD 21%), and a smaller Aao,D while breathing 100 percent 0, 189 & SD 31 versus 342 ? SD 69 torr) at the end of thoracotomy.
A
nous shunts. The Aao,D due to shunt is increased when the mixed venous O2 content is reduced in association with an inadequate cardiac output. The majority of studies have shown that during anesthesia pulmonary arteriovenous shunt is the major cause of the increased alveolar-arterial oxygen differences.l.2
oxygenation during thoracotomy in the lateral position may become difficult to maintain due to reduction in the arterial oxygen tension (Pao,). Therefore, it may become necessary to use high inspired 0, concentrations. This not only reduces the choice of anesthetic agents but, if the reduction in Pao, is due to absorption atelectasis of the dependent lung, it may be associated with postoperative hypoxemia. DEQUATE
The reduced Pao, and the associated increased alveolar-arterial 0, differences (Aao,D) are due to venti1ation:blood flow maldistribution and pulmonary arteriove-
During thoracotomy in the lateral position, gravity causes the blood to flow predominantly to the dependent lung. This combined with the following factors which reduce ventilation to the dependent lung results in ventilation: blood flow maldistribution and shunt. First, in association with the
*Associate Professor, Department of Anesthesiology ?Associate Professor, Departments of Anesthesiology and Physiology. $Resident, Department of Anesthesiology. B Professor and Division Chief, Department of Surgery, Division of Cardiothoracic Surgery. //AssociateProfessor, Department of Surgery, Division of Cardiothoracic Surgery. **University of North Carolina School of Medicine, Chapel, Hill, North Carolina 27514. This study was supported in part by Grant HL-17314-01, North Carolina Lung Association and Grant HL-11909-07. Paper received: 2/25/76 Accepted for publication: 6/3/76
Selective PEEP . . . Brown, et a1
27
reduction in the end-expiratory volume, which in the lateral position is most marked in the dependent lung, there is a reduction in the proportion of ventilation going to the dependent l~ng.38~ This is comparable to a person inspiring from below his functional residual capacity (FRC) when the ventilation during tidal breathing goes predominantly to the upper zones.5*6Airway closure in the dependent part of the lung requires greater pressure to ventilate the dependent than the other lung. Second, there is also evidence that during muscle paralysis and controlled ventilation, loss of diaphragmatic force reduces ventilation to the dependent lung.7 Further contributions to pulmonary arteriovenous shunt result from compression of areas of the nondependent lung during surgical manipulation. Theoretically, if loss of the end-expiratory volume of the dependent lung were a major factor in contributing to the maldistribution of ventilation, absorption atelectasis in the dependent lung, and the observed pulmonary arteriovenous shunt, then maintaining the end-expiratory volume of the dependent lung should prevent these changes. We tested this hypothesis by constructing a circuit which, together with a Carlens double-lumen endobronchial tube,xs9 applied 10 cm H,O of positive end-expiratory pressure (PEEP) to the dependent lung and allowed the nondependent lung to be ventilated with the same ventilator but a t zero end-expiratory pressure (ZEEP) . The effect of this circuit on Pao,, Aao,D, and inspired 0%concentration required to maintain safe oxygenation were examined in patients undergoing thoracotomy in the lateral position for pulmonary and esophageal surgery.
METHODS The circuit (figure) consists of a common inspiratory path for both lungs and for expiration of the nondependent lung, a C K U S*mM L VENTIUTW
TO NONDEPENDENT LUNG
ONE W N VNVE 10 LXPENDENT LUNG
FIGURE. Schematic of circuit used to apply selective PEEP to dependent lung while ventilating nondependent lung with ZEEP.
TABLE 1 Physical Characteristics of Patients and Duration of Operation Group I
PEEP to dependent lung Mean and SD
Age, years Weight, kg
56
(-C 7.8)
73.9 (-+ 11.4)
FEV1/VC, percent
61 ( k 1 5 )
Duration of surgery hours
6.4 (21.25)
Group II ZEEP to both lungs Mean and SD
54 (? 8.0) 66.9 ( & 7.7) 67 (ell)
5.75 ( & 1.1)
one-way valve separating expiratory flow of each lung, and a 10 cm H,O “dead weight” PEEP.” The circuit was used with a Carlens double-lumen endobronchial tube,n,g and a standard circle system with C 0 2 absorber and a ventilator.? The circuit for each lung was tested by ventilating a Manley test lung$ having ranges of compliance and resistance, and at ranges of flow and volume encountered in adult thoracic surgery. The circuit was reliable. The volume of the circuit is 50 ml; it does not cause any significant increase in dead space, and the resistance to air flow of the common inspiratory and expiratory limb of nondependent lung is negligible. During clinical use, insertion of the circuit into the anesthesia breathing circuit and onto the Carlens catheter did not cause any increase in the inflating pressures. Twenty-two patients were studied during thoracotomy in the lateral position for resective pulmonary surgery (20) and Belsey hiatal hernia repairs ( 2 ) . The patients were randomly divided into 2 groups: group I, experimental, and group 11, controls. Groups were similar in age, weight, preoperative spirometry, and duration of the surgical procedure (table 1 ) . Group I patients were intubated with a Carlens double-lumen endobronchial tube (39 or 41), and during the lateral thoracotomy both lungs were ventilated and selective PEEP was applied to the dependent lung with ZEEP to the nondependent lung. Group I1 patients were intubated with a cuffed endotracheal tube and both lungs were ventilated with ZEEP. *Model 4801, Boehringer Laboratories, Wynnewood, Pennsylvania. iventimeter, Air Shields, Inc, Hatboro, Pennsylvania. SBlease Medical Equipment Ltd, Deansway, Chesham, United Kingdom.
28
ANESTHESIA AND ANALGESIA . . . Current Researches VOL.56,No. 1,JAN.-FEB., 1977
Both groups were premedicated with diazepam (0.2 mg/kg) and the anesthetic agents for the 2 groups were similar, 5 patients in each group receiving either halothane or enflurane in N20-0, and the remainder receiving narcotic-relaxant drugs with N,O-0,. Both groups were ventilated with a similar pattern of large tidal volumes (10 to 15 ml/kg), slow respiratory frequency (8 to 10/min), and with sufficient minute ventilation to maintain a normal Paco,. Throughout operation, temperature, acidbase balance, and electrolytes were normal, blood loss was replaced as required, and the arterial and central venous pressures remained within the patients’ normal range. The urine flow, which was maintained by volume replacement, was > 50 ml/m2 of body surface area. Arterial pressure was monitored by a pressure transducer and arterial blood gases were taken from an indwelling radial artery catheter. Both groups were initially ventilated with 30 to 50 percent 0, (table 21, and arterial blood gases were measured 10 minutes after the thoracotomy. During thoracotomy, arterial samples were taken every 15 minutes and the inspired 0, concentration was adjusted to maintain a Pao., greater than 100 torr. After closure of the thoracotomy, establishment of underwater drainage, and while still in the lateral position, all patients breathed 100 percent O2for 10 minutes: then arterial blood gases were again measured.
RESULTS Throughout the thoracotomy, the patients given selective PEEP to the dependent lung (group I) were ventilated with the same inspired 0, concentration. There was no significant decrease in the Pao, (p>0.05) or increase in Aao,D (p>0.05) (table 2 ) . The inspired 0, concentration was 30 to 50 percent (mean 44 2 SD 6%) and the mean Pao, during thoracotomy was 162 2 SD 37.9. By contrast, of the patients who did not receive selective PEEP to the dependent lung, 8/11 required an increase in the inspired 0, concentration to maintain an adequate Pao,. Despite this increase in inspired O2 concentration, there was a significant decrease in the Pao, (p
