Gas embolism caused by surgery

- During neurosurgery in a sitting position

A variety of techniques have been proposed to detect gas bubbles: oesophageal stethoscope44; capnography44'52'81; continuous monitoring of mixed venous oxygen saturation93; continuous monitoring of the partial pressure of expired nitrogen94; Doppler ultrasonography in the precordial

51,82 51 93,95

area ' or by oesophageal route ; trans-oesophageal echocardiography ' ; transcutaneous oxygen and CO2 pressure monitoring93'96; and right atrial catheterisation79'80'87. Their relative sensitivities have been compared with ultrasounds (i.e.' trans-oesophageal echocardiography; precordial Doppler ultrasonography) being the most sensitive' followed by capnography and transcutaneous oxygen pressure monitoring96'97 (Table 2.2.2-4). Preventing GE involves maintaining a high venous blood pressure (vascular filling' jugular compression)98' and providing controlled ventilation at continuous positive pressures99.

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D. Mathieu, S. Tissier and M. Boulo

Table 2.2.2-4. Sensitivity of the various methods for detecting age (from Glenski et al.)93

Sensitivity

Monitoring methods

Mean quantity of air (in ml/kg) required

to reach detection threshold (+ SD)

Greatest

Trans-oesophageal

0.19 + 0.25

echocardiography

Precordial Doppler

0.24 + 0.33

ultrasonography

Intermediate

PAP

0.61 + 0.37

petc├╝2

0.63 + 0.23

PaO2

0.71 + 0.54

PtcO2

0.76 + 0.58

Least

PaCO2

1.15 + 0.76

MAP

1.16 + 0.76

PtcCO2

1.54 + 0.70

PAP : pulmonary artery pressure PaCO2 : arterial pressure of CO2

PETCO2 : end Tidal expired pressure of CO2 MAP : mean arterial pressure PaO2 : arterial pressure of O2 PtcCO2: transcutaneous pressure of CO2

PtcO2: transcutaneous pressure of O2

PAP : pulmonary artery pressure PaCO2 : arterial pressure of CO2

PETCO2 : end Tidal expired pressure of CO2 MAP : mean arterial pressure PaO2 : arterial pressure of O2 PtcCO2: transcutaneous pressure of CO2

PtcO2: transcutaneous pressure of O2

Nitrous oxide has a worsening effect on the consequences of GE and it must therefore be avoided in such situations. From a surgical point of view, all bone edges must be filled with wax and, in the case of vascular injuries, the operating area must be flooded with physiological saline solution. The sitting position should actually be avoided unless is it absolutely necessary for technical reasons. - During heart surgery

Continuous EEG and monitoring by spectral analysis (for years considered to be the best method for detection) is now being replaced by transcranial Doppler100.

Preventing GE caused by the ECC circuit involves careful de-airing of the circuit and heart chamber. However the passage of microbubbles cannot be completely avoided and have been associated with post-operative neurological injuries.

Preventing GE caused by opening the heart chambers involves a number of well-known methods: clamping the descending thoracic aorta; inducing cardiac arrest via electrical ventricular fibrillation or hypothermia; and mostly careful de-airing procedures that are essential and are to be carried out on the heart chambers, pulmonary veins, left atrium and auricle, left ventricle, aortic root, and the pulmonary infundibulum.

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