Phrenic nerve stimulation during halothane anesthesia. Effects of atelectasis.
BACKGROUND
Atelectasis formation during anesthesia may be due to loss of respiratory muscle tone, in particular that of the diaphragm. This was tested by tensing the diaphragm by phrenic nerve stimulation (PNS) and observing the effect on atelectasis.


METHODS
Twelve patients (mean age 48 yr) without preexisting lung disease were studied during halothane anesthesia. PNS was executed with an external electrode on the right side of the neck. Chest dimensions and area of atelectasis were studied by computed tomography of the chest.


RESULTS
Right-sided PNS against an occluded airway at functional residual capacity reduced the atelectatic area in the right lung from 5.1 to 3.8 cm2. The atelectasis was reduced to 1.1 cm2 after application of positive end-expiratory pressure (PEEP) of 10 cmH2O and large tidal volumes but increased to 2.5 cm2 within 1 min after discontinuation of PEEP. Commencement of PNS immediately after PEEP prevented the atelectasis from increasing, the mean area being 0.9 cm2. In seven patients, in whom the trachea was intubated with a double-lumen endobronchial catheter the atelectatic area was smaller during PNS with an open airway than during positive pressure inflation of the lung with the same volume as inspired during PNS (3.5 and 5.2 cm2, respectively.


CONCLUSIONS
The findings indicate that contracting the diaphragm in the anesthetized subject reduces the size of atelectasis.
Department of Anesthesia, Huddinge University Hospital, Sweden.
G
G
Hedenstierna
L
L
Tokics
H
H
Lundquist
T
T
Andersson
A
A
Strandberg
B
B
Brismar
D000328:Adult; D000368:Aged; D000758:Anesthesia / Q000009:adverse effects*; D001980:Bronchi; D003964:Diaphragm / Q000294:innervation; D004558:Electric Stimulation; D005260:Female; D006221:Halothane / Q000009:adverse effects*; D006801:Humans; D007442:Intubation, Intratracheal; D008168:Lung / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D010791:Phrenic Nerve / Q000187:drug effects* / Q000502:physiology*; D001261:Pulmonary Atelectasis / Q000139:chemically induced* / Q000503:physiopathology
D006221:Halothane