Effects on respiratory function of the head-down position and the complete covering of the face by drapes during insertion of the monitoring catheters in the cardiosurgical patient

Abstract

) were analysed by a blood gas system. were stable throughout the study. of 0.4).

Background:

) were analysed by a blood gas system.

Results:

were stable throughout the study.

Conclusions:

of 0.4).

Introduction

]. A literature search found no data supporting a negative effect on respiratory function with the drapes covering the face; however, we hypothesized such a negative influence, supposing that the application of the sterile drapes over the face can favour the rebreathing of the expired gases. The aim of this study was to evaluate the effect on respiratory gas exchange of the two combined manoeuvres used during the insertion of monitoring catheters in the cardiosurgical patient before induction of anaesthesia.

Methods

Fifty-four patients scheduled for elective coronary bypass grafting (CABG; 43 coronary patients) and heart transplantation (11 patients with end-stage heart disease) were studied. The study protocol was approved by the local Ethical Committee, and written informed consent was obtained from each patient. Admission criteria for the study were: no history of respiratory disease and no intravenous cardiovascular drugs (for all patients); stable haemodynamic conditions, assessed by clinical examination, and no unstable angina (for patients undergoing CABG); and no rest dyspnoea (for patients undergoing heart transplantation).

Before induction of anaesthesia, all patients were placed in the head-down position (30°) and had their face completely covered by sterile drapes (Foliodrape, Hartmann, Heidenhein, Germany) to position the monitoring catheters. The head-down position was maintained until the internal jugular vein was cannulated, while the sterile drapes were removed after the pulmonary artery catheter was inserted. The coronary patients were randomly divided into four groups:

= 0.4);

=10), coronary patients with preoperative LVEF > 45% breathing room air during the two manoeuvres;

= 0.4);

= 10), coronary patients with preoperative LVEF < 45% breathing room air;

= 0.4).

In all patients, LVEF was assessed by cardiac angiography.

) tension and oxygen saturation (SaO2) were drawn at the following times:

time 1 = in supine position with all patients breathing room air;

time 2 = in supine position only in patients supplied with oxygen by the Venturi mask (groups A1, B1 and C);

time 3 = just before removing the patient from the 30° head-down position;

time 4 = just before removing the drapes covering the face;

time 5 = 5 min after the drapes have been removed.

The analysis of the blood samples was performed by the same operator, using a blood gas system (model 288, Ciba Corning Medfield, Massachusetts, USA) located just outside the operating room. The coronary patients were premedicated with morphine 0.1 mg/kg and scopolamine 0.3–0.5 mg intramuscularly; the patients with end-stage heart disease were premedicated with diazepam 3–5 mg orally. All of these drugs were administered 60 min before entering the operating room. Monitoring of the patients during the study included an electrocardiogram (ECG) (DII-V5), and measurements of the invasive arterial pressure, noninvasive oxygen saturation and respiratory rate. We excluded from the study three coronary patients (two for an anginal episode and one for restlessness) and one patient with end-stage heart disease (for restlessness), as the drapes were temporarily removed in these patients, and nitroglycerin or benzodiazepine were administered.

values < 0.05 were considered statistically significant.

Results

.

returned to the values similar to those recorded at time 2.

at times 3, 4 and 5.

remained stable, without significant change within each group at all times of the study.

].

).

General characteristics of the patients studied

No significant difference was observed among the five groups for age, weight and left ventricular ejection fraction (LVEF). ACE, angiotensin converting enzyme. For definition of groups, please see text.

Duration of the two manoeuvres

No significant difference was observed among the five groups. For definition of groups, please see text.

Arterial respiratory gas modifications at the five times of the study

, arterial carbon dioxide tension. For a definition of the groups and times, please see text.

Discussion

]. The application of the drapes completely covering the face could interfere with respiratory gas exchange by creating a chamber of stagnating air, which might favour the rebreathing of the expired gases through a dead-space effect. This effect was only hypothesized, as we found no such confirmation in the literature. The purpose of this study was to investigate the influence of the two manoeuvres on the respiratory gas exchange in the cardiosurgical patient, and also to find a correlation between the respiratory gas exchange modifications and the preoperative function of the left ventricle.

in patients in these groups.

above the low safety limits.

].

, lower values of PaCO2 and the higher respiratory rate in group C when compared with those of groups A1 and B1 may indicate superior ventilation in the patients with end-stage heart disease.

], but we are unable to conclude this.

was smaller than that observed in patients supplied with oxygen, although the levels of arterial oxygen tension and saturation were still satisfactory.

=0.4.

Respiratory rate at the five times of the study (breaths/min)

<0.05, versus all the other groups; no significant difference was found within each group. For explanation of the groups and times, please see text.

Keywords

• drapes covering the face
• head-down position
• left ventricular ejection fraction
• respiratory gases exchange