Mixed venous oxygen saturation during lung transplantation

Mixed Venous Oxygen Saturation

During Lung Transplantation

I.D. Conacher, FRCP (Ed), and M.L. Paes, FRCP

P

conducted in sequence from left lateral thoracotomy, left pneumonectomy, insertion of orthotopic left lung transplant to right lateral thoracotomy, right pneumonectomy, and right orthotopic lung transplant. Cardiopulmonary bypass was not used. The SW& trace is shown in Fig 1 and hemodynamic data is shown in Table 1. The insertion of the left transplant was uneventful apart from the development of an atrial tachycardia, which was stopped with a single DC shock. The transplant functioned adequately to enable progression to right thoracotomy and right pneumonectomy. The gradual decline in SVO2 shown in Fig 1 (No. 6) reflects the increasing strain on the transplant as it bore the load of the total cardiac output. Pulmonary artery hypertension developed. This culminated in the development of pulmonary edema, which was aspiratable from the left side of the double-lumen tube when the pulmonary artery pressure reached and exceeded a mean value of 45 mmHg. SB02 remained about 60% until circulation was restored to the right lung transplant with a consequent decrease in pulmonary artery pressure.

ULSE OXIMETRY, essentially mandatory in modern anesthesiologic practice, still proves of limited value under the circumstances of some major surgery. The sensors, attached to a finger, are subject to artefact from poor contact or displacement, electrical interference, and may become unreliable when the extremities cool and cardiac output falls.‘-” Such situations sometimes occur during lung transplantation4 and a more reliable form of oxygen monitoring would be of value. The most recent systems produced commercially and available to clinicians continuously sense mixed venous oxygen (SOO,) from a fiberoptic catheter with its tip located in a pulmonary artery. Five-lumen, flow-directed, thermodilution pulmonary artery catheters (Oximetrix, Abbot Critical Care Systems, Abbot Laboratories Ltd., Maidenhead, Berkshire, UK) were inserted through percutaneous sheaths into the right internal jugular veins of patients undergoing sequential single-lung transplantation (SSL) or single-lung transplantation. The catheter tip was sited in the main pulmonary artery just distal to the pulmonary valve.5 The proximal end of the catheter was connected to a venous pressure transducer and a signal processor (Oxymetrix 3 SOJCO Computer processor) that displays venous oxygen saturation and

Case 2

A 22-year-old woman who had developed obliterative bronchiolitis in association with long-standing juvenile polyarthritis, underwent a right single-lung transplant. The SVO2tracing is typical of an uneventful operation conducted with a left-sided double-lumen tube, one-lung ventilation in the lateral decubitus position, and without cardiopulmonary bypass. The tracing and data (Fig 2, Table 2) are illustrative, however, of a more advanced stage in the use of this measurement technology. A short trial of one-lung ventilation demonstrated the shunt created by the perfusion of a

thermodilution cardiac output curves, and calculates, from standard formulae, several hemodynamic variables. CASE

REPORTS

Case 1 From the Department of Cardiothoracic Anaesthesia, Freeman Hospitals Trust, Newcastle upon Tyne, England. Address reprint requests to I.D. Conacher, Department ofAnaesthetits, Freeman Hospital, Freeman Rd, Newcastle Upon Tyne, England NE 7 7DN. Copyright o I994 by U! B. Saunders Company 1053-0770194/0806-OQ13$03.00/0 Key words: anesthesia, monitoring surgery

A 44-year-old woman with end-stage bilateral bronchiectasis underwent sequential single-lung transplantation. Preoperative cardiac function was normal as were the simple pulmonary function tests. The accelerated development of incapacitating hypoxemia meant that lung transplantation was the only therapeutic option. Bilateral lung transplantation was indicated because of the septic nature of the basic pathology. A right-sided double-lumen tube was inserted at induction of anesthesia and the operation was

Event 123

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20.

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50

.;.:

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k ”

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30

60

90

120

150

180

2i6

240

Fig 1. Sv02 trace. Case 1: sequential single-lung transplant. Event key: (1) Patient anesthetized. Thoracotomy. Two-lung ventilation. (2) One-lung (right) ventilation. (3) Left PA clamped. (4) First transplant (left) lung operational. (5) Right PA clamped. (6) Pulmonary edema (left transplant). (7) Second transplant operational. Two-lung ventilation.

Journalof Cardiothorauc and Vascular Anesthesia, Vol8, No 6 (December), 1994: pp 671-674

671

CONACHER AND PAtS

672

Table 1. Case 1 Data: Sequential Single-Lung Transplant

secondary to alplla,-anrltrypsll~ deficiency affected with bullous disease. Preoperativcly

Event (see Fig 1)

1

2

3

4

5

6

7

PO2

0.5

0.5

0.5

0.5

SaOz (%)

100

92

98

98

svoz (%I

81

76

83

80

0.6

1.0

94

1.0

L. The

6.05

anesthesia,

initial

38.0

(mmHg)

285

8.0 60

29 218

16.7 125

10.9

positive-pressure

ventilation

(mmHg)

34

6.0 45

5.7 43

5.6

tional

and minute volume with air and oxygen. was uncomplicated.

10.6

air trapping

79

ventilator

in bullae driving

42

6.3

34

47

7.5 56

Hemodynamics

compromised

at reduced

in the left lung despite

pressure

cardiac

inflation

pressure There

due to a chain of events consequent when

one-lung

massage

and venous Cardiac

was instituted:

on

a reduction

ventilation

hyperinflated.

and could not be enhanced.

and internal

<-rt

tube. conven-

94

58

4.6

double-lumen

residual

induction

81

tuted. The left lung became 4.6

the

81

PC02 (@a)

was X.70 Land

including

65 7.8

82

period,

of a left-sided

introduction

was a rapid deterioration

PO2 (kPa)

rn

was instireturn

was

arrest occurred

the adequacy

of this

can be seen on the SiiOz trace (Fig 3. Table 3). Full cardiopulmo-

CVP (mmHg)

12

15

10

11

13

BP

nary bypass was implemented in the right atrium

SF (mmHg)

100

dia (mmHg)

60

PAP-mean

and her FVC was 2.2 IL. Total lung capacity volume

Blood gases

and both lungs MAIL her FEV! wa\ 0.5s I

(mmHg)

CO (L/min)

115

98

measures. with

29

35

41

25

39

45

25

6.7

Abbreviations: sys, systolic; dia, diastolic; PAP-mean,

venous return

addition

occurred emia.

from

with the venous input from a cannula

and arterial

of large

return

continued volumes

hemorrhage

to the aorta.

Despite

to prove a major problem of fluid

to the

and progressive,

prime.

irreversible

these even Death hypox-

mean pulmo-

nary artery pressure.

DISCUSSION PAP-weary nonventilated lung and the rapid recovery when both lungs were ventilated again (Event 2). In the relatively static phase between recipient pneumonectomy and the transplant coming on-line, steady-state physiologic conditions were achievable and some assessment of the effects of drugs and altering ventilation modes could be made. In this case the effect of a bolus of aminophylline on pulmonary vascular resistance is recorded. The SO02 tracing shows the increase in mixed venous oxygenation (Event S), which reflects the increased cardiac output generated by this stimulant. The consequence of the addition of PEEP on SvOz, through an effect on venous return and cardiac output, is also demonstrated (Event 6).

Case 3 A poor outcome occurred in a 47.year-old woman with emphysema undergoing a right single-lung transplant. Emphysema was

of the end result of the delivery and utilization of oxygen. The assumption has been made that if the oxygen flux is constant, then the value is directly proportional to the cardiac output. This is based on a mathematical derivation of the Fick equation? Physiologically,

the SVO, is an index

S;Oz = Sa02 - 10 (c02.

Hb . 1.36)

The theoretical value in the continuous measurement of SVOZ is that it can be equated with a continuous measurement of cardiac output. In practice, particularly during surgery, each of these variables is a function of several others and these variables. along with dissolved plasma oxygen, have been identified as reasons for poor correlation.*-“’

Event

12

4-l

-1 i-t

Time (min)

30

BO

90

1(20

Fig 2. SvOz trace. Case 2: single-lung transplant. Event key: (1) Patient anesthetized. Thoracotomy. One-lung ventilation. (2) Trial of one-lung ventilation. PA unclamped. (3) One-lung ventilation. PA clamped. (4) Test of aminophyfline (125 mg). (5) Transptant operational. (6) PEEP applied.

MIXED VENOUS OXYGEN SATURATION

673

Table 2. Case 2 Data: Single-Lung Transplant

Table 3. Case 3 Data: Single-Lung Transplant

Event

Event

(see Fig 2)

1

2

3

1.0

0.8

5

(see Fig 3)

Blood gases

2

3

0.6

0.6

Blood gases 0.4

FIOZ SaOz (%)

73

s30* (%)

87

97

51

0.5

1.0

99

FIOZ SaOZ (%)

99

93

75

svo,

69

a2

PO2

(%)

a3

PO* 39.5

&Pa)

296

(mmHg) PCO,

6.5

Wa) (mmHg) Hemodynamic CVP (mmHg)

6.5 49 7.5

17.7 132

34.3

5.1

60.2

Wa)

257

451

(mmHg) PCO*

6.8

7.2

kPe)

49

56

38

51

(mmHg) Hemodynamic

54

16

15

16

12

CVP (mmHg)

10

SBP

11.6 a7

16.5 124

7.1

a.1

53

61

SBP

SYS (mmHg) dia (mmHg)

119

98

a2

62

SF (mmH9) dia (mmHg)

31

38

54

SVR

1682

932

921

1147

PVR

291

150

278

109

PAP-mean

1

(mmHg)

PAP-mean

CO (L/min)

2.5

5.3

4.6

4.4

Cl (L/min/mz)

1.7

3.7

3.2

3.1

All the advantages of pulmonary artery catheters are achievable. Cardiac output and intravascular pressures can be measured with the same apparatus and several other hemodynamic parameters of use to monitor the progress of lung transplant operations can easily be computed. Earlier experience4 suggests that management and therapeutic decisions during lung transplantation are made on arterial blood gas changes and systemic and pulmonary artery changes. Therefore, there is little apparent justification for incurring the extra cost of measuring SVO, except that it can be used as an indicator for the need for cardiopulmonary bypass6 However, it is a useful measure for tracking the operations because of the continuous nature of the information (both real time and hard copy). The unique advantage would seem to be evidence of

Event

Fig 3. SvOz trace. Case 3: single-lung transplant. Event key: (1) Patient anesthetized. Thoracotomy. Two-lung ventilation. (2) Thoracotomy. Trial of one-lung ventilation. PAclamped. (2a) Cardiac arrest and massage. (3) Institution of cardiopulmonary bypass. (4) Problems with venous return. (5) Death.

1

Time (min)

(mmtlg)

CO (L/min)

113

100

75 23

62 42

44

3.9

circulatory efficiency provided in rare situations when peripheral transducing devices such as pulse oximeter sensors, arterial cannulae, and ECG electrodes become unreliable. A measure of SVOz rarely helps define causes of changes in oxygen flux during the non-steady-state conditions that prevail in lung transplantation, but it is of particular value in alerting clinicians to the development of potential problems because a decrease in SV02 is an early indicator of pathophysiology. It is concluded that a peculiar value that justifies the use of fiberoptic catheters and mixed venous oxygen measuring systems is the sense: of security that goes with achieving values in the normal range that are indicative of good supply, optimum delivery, and efficient use of provided oxygen under difficult clinical conditions and circumstances.

2a

3

30

4

5

674

CONACHER AND PAES

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New York. NY. (‘hurchill

Livingstone.

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7. Sekela ME. Noon GP, Holland VA, Lawrence EC: Ditferential perfusion: Potential complication of femoral-femoral bypass during single lung transplantation. J Heart Lung Transplant 10:322-324. 1991 8. Boylan JF, Teasdale SJ: Con: Perioperative continuous monitoring of mixed venous oxygen should not be routine in high-risk cardiac surgery. J Cardiothorac Anesth 4:651-654.1990 9. Nelson LD: Monitoring oxygen delivery. Proceedings of the Royal College of Physicians of Edinburgh. 21:401-408. 1991 10. Birman H, Haq A, Hew E, Aberman A: Continuous monitoring of mixed venous oxygen saturation in hemodynamically unstable patients. Chest 86:753-7X 1984