Diagnosing and quantifying incomplete expiration in patients with lung disease.
8 Tam NL, Pac-Soo C, Pretomas PM. Epidural haematoma after com-
bined spinal-epidural anaesthetic in a patient treated with clopido-
grel and dalteparin. Br J Anaesth 2006; 96: 262–5
9 Chassot P-G, Delabays A, Spahn DR. Perioperative antiplatelet
therapy: the case for continuing therapy in patients at risk of
myocardial infarction. Br J Anaesth 2007; 99: 316–28
Diagnosing and quantifying incomplete
expiration in patients with lung disease
Editor—Incomplete expiration is common in smokers and
patients with chronic obstructive pulmonary disease
(COPD). This can increase FRC and auto-PEEP. The
increased intrathoracic pressure may compromise venous
return or, if great, could cause a pneumothorax. We report
a simple new method for detecting this, which appears
quick and reliable, and can quantify the increase in lung
During mechanical ventilation of an anaesthetized
subject, we set the APL valve to zero and then discontin-
ued ventilation for approximately 10 s, allowing complete
expiration to occur. Complete expiration was verified by
confirming that the expiratory flow rate shown on the
flow–volume loop was zero. The ventilator was restarted
using the previously set rate and volume and the flow–
volume loop was observed (Fig. 1). With the GE s/5 spi-
rometer (D-lite), which displays successive individual
inspired and expired volumes, the differences between
inspired and expired tidal volumes were added for the next
three respiratory cycles. We have called this the volume of
incomplete expiration, since it represents the volume
retained by the respiratory system when the previous
pattern of mechanical ventilation is resumed.
A female aged 71 yr with a history of 40 pack years of
smoking and symptoms and signs of severe COPD under-
went a total abdominal hysterectomy. The volume of
incomplete expiration was 380 ml. This feature was repro-
ducible, with other measures of incomplete expiration,
resulting in volumes of 310, 400, and 290 ml (mean
345 ml) during the anaesthetic (Fig. 2).
A further patient with a long history of smoking,
although no formal diagnosis of COPD showed incomplete
expiration with a mean total volume of incomplete expira-
tion of 215 ml (200–250 ml) over four trials.
As a control patient, a man of 62 yr with no respiratory
disease and a non-smoker undergoing a hemi-colectomy
had a mean volume of incomplete respiration of 10 ml
(250 to 50 ml) over four trials.
Similarly a man of 65 yr also a non-smoker with no res-
piratory disease undergoing an open right radical nephrect-
omy had a mean volume difference of 40 ml (10–100 ml)
over four trials.
This technique was used in various patients and seems
incomplete expiration. There appears to be a difference
between observed values of our four patients, which corre-
lates with the severity of clinically observed airways
We cannot find previous reports of this manoeuvre, of
volume changes when mechanical ventilation is recom-
menced. This could be particularly useful as most other
methods of detecting incomplete expiration rely on
pressure measurement, as opposed to volume, and do not
quantify the degree of incomplete expiration.
Detecting incomplete expiration is clinically useful.
Various strategies can reduce incomplete expiration, such
as reducing the I:E ratio or the tidal volume. Perhaps, the
Fig 1 Flow–time plot from GE s/5 monitor, with volume measurements
from d-lite spirometer module. There are three breaths on this screen.
Breath 1 is the equilibrium condition as both inspiratory and expiratory
tidal volumes are 450 ml. Ventilation was discontinued after breath
2. The flow rate is zero for a sustained period ensuring complete
expiration. When ventilation was recommenced, with breath 3, the
expiratory tidal volume decreased to 390 ml, despite an inspiratory
volume of 450 ml. Thus, this patient had incomplete expiration of 60 ml.
Plotting breaths 1 and 3 together, one can see the horizontal distance,
which indicates expired volume, is noticeably smaller. Although the
increase in expired volume on prolonged exhalation (breath 2) was
evidence of incomplete expiration, this appeared inconsistent and
Fig 2 Flow–volume loop from case 1. After a prolonged expiration,
ventilation was recommenced and a flow–volume loop created. The
expiratory flow is zero before volume returns to the starting point of the
loop, indicating that the expired volume is less than the inspired volume.
by guest on October 14, 2011
most useful aspect of detecting incomplete expiration is
simply to alert the clinician to the severity of underlying
lung disease, which could influence further management
of the patient.
In conclusion, using a clinically available spirometry
system, we describe how to detect incomplete expiration
in anaesthetized mechanically ventilated patients in a
simple, reliable, and quantifiable way. Equipment to do
this is commonly available in theatres and in ICUs in the
UK. Further studies are needed to validate the method.
G. B. Drummond*
A foam-cushion face mask and a see-through
operation table: a new set-up for face
protection and increased safety in prone
Editor—Positioning the head of patients undergoing
procedures in prone position is crucial and remains a diffi-
cult task for the anaesthesiologist.1Often, it is a compro-
mise between a normal position of the head without
derogating facial and neck tissues on the one hand and
sufficient control over airway devices on the other hand.
Most reported sequelae associated with prone positioning
are due to unnoticed pressure on the head and neck region
and range from mild irritation2 3to disastrous compli-
cations, such as corneal abrasion,4central retinal artery
occlusion leading to impaired vision,5 6or even stroke due
to neck torsion-induced vertebral artery occlusion.1We
believe that the main problem in head positioning is based
on the fact that we, as anaesthetists, try to fit the patient’s
face into the available support cushions and not the
cushion onto the patient’s face, which would allow com-
plete control over head position. Therefore, we developed
a technique using a commercially available foam-based
boxing helmet that is fitted to the patient before turning to
the prone position and guarantees that the face and eyes
are free from pressure (Fig. 1). The helmet also keeps the
neck in a straight line without forcing it into tilting or
turning positions, thus avoiding compression or torsion of
vessels and nerves, although all airway devices remain
accessible and safe. To be able to control pressure on soft
tissue structures and to supervise airway devices, we use
an operating table with a clear plastic window in the head
and neck region. A mirror mounted underneath allows the
anaesthetist to see the position of face and airway devices
at all times (Fig. 2). We believe that the combination of a
face mask and positioning on the see-through table may
be a sensible and cost-effective yet simple approach to
reduce positioning-associated side-effects and increase
safety during prone position procedures.
M. Mo ¨llmann
1 Shermak M, Shoo B, Deune EG. Prone positioning precautions in
plastic surgery. Plast Reconstr Surg 2006; 117: 1584–8
2 Anderton JM, Schady W, Markham DE. An unusual cause of post-
operative brachial plexus palsy. Br J Anaesth 1994; 72: 605–7
3 Jackson L, Keats AS. Mechanism of brachial plexus palsy following
anesthesia. Anesthesiology 1965; 26: 190–4
Fig 1 Side-view of patient in prone position with head supported by face
mask. No pressure is exerted on any facial structures.
Fig 2 The ‘anaesthetist view’: head resting safely on table in the face
mask with control of face and airway with the help of the see-through
plastic table and a mirror fixed underneath.
by guest on October 14, 2011