Page 322 - ACCCN's Critical Care Nursing

Cardiac Surgery and Transplantation 299

TABLE 12.1 Postoperative ventilation settings

Nominal or generally
acceptable settings Alternatives to nominal settings and reasons for variation
SIMV with volume control ventilation Pressure control suitable. Generally used only if there is significant hypoxaemia or the
need to exert greater control on pulmonary pressure. Hybrid modes such as Autoflow,
pressure-regulated volume control or volume control plus (VC+) are also suitable,
generally for same indications as pressure control.
Tidal volume 8–10 mL/kg Lower tidal volumes (6–8 mL/kg) when there is known compliance disorder (atelectasis,
pulmonary oedema, fibrosis) or unexplained high plateau pressures.
Mandatory rate 10 L/min Faster rates may be necessary if low tidal volume strategies become necessary. Lower rates
if gas trapping risk due to airways disease.
Inspiratory flow 30–50 L/min to provide I : E Slower flows to prolong the inspiratory time may be necessary if there is atelectasis and
ratio of 1 : 2 to 1 : 4 acceptable hypoxaemia, or if there is a desire to lessen inspiratory pressures. Faster flows to enhance
expiratory time necessary only if gas-trapping risk.
PEEP minimum levels of 5 cmH 2 O Higher levels of PEEP according to severity of hypoxaemia.
Pressure support 5–10 cmH 2 O Automated pressure support modes such as automatic tube compensation (autoadjusted
pressure support according to overcome flow resistance of tracheal tubes) or volume
support (autoadjusted pressure support to achieve target tidal volume on spontaneous
breaths) exist. There is no pressing indication for their use in uncomplicated cardiac
surgical patients.
Permissive hypercapnoea rarely necessary Particularly important to avoid if existing pulmonary hypertension, as may worsen acutely
with respiratory acidosis.
FiO 2 initially 1.0 then wean down according According to PaO 2 /SaO 2.
to PaO 2 /SaO 2

rates of bleeding, the cardiac surgical unit must be Chest drainage should be monitored closely, and while
equipped to institute rapid volume replacement, and bleeding is active, volumes should be assessed every 5
have access to adequate blood and blood product minutes and patency of drains ensured to avert tampon-
stores, blood warmers, and all necessary procoagulant ade. Sudden cessation of drainage should always raise the
therapies. In addition, dedicated equipment should be possibility of the loss of tube patency and risk of tam-
available to facilitate emergency resternotomy to control ponade, but tamponade may also occur while drainage
haemorrhage. continues, as collections and compression may occur at
sites isolated from drains, or losses may simply be occur-
One or more chest drains are inserted to remove and ring faster than that able to be removed by patent drains.
monitor blood loss, but the positioning of drains is vari-
able, depending in part on the procedure performed, the Chest drains should also be observed for bubbling, to
surgical route taken, and surgeon preference. Regardless assess for air leaks originating from either system faults
of these considerations there will always be a retrosternal/ or patient leaks. When bubbling can be attributed to the
anterior mediastinal drain, as the sternum is generally the patient, the patency of tubes becomes additionally impor-
major source of bleeding in the absence of complications. tant to avert tension pneumothorax, which may accumu-
Additional drains may be inserted in the pericardial or late rapidly, even over the course of a few breaths in the
pleural spaces. Pericardial drains are more likely to be ventilated patient.
inserted following aortic valve surgery, while pleural Blood transfusions are not aimed at restoring haemoglo-
drains become necessary following mammary artery har- bin to normal levels, and, despite variations in acceptable
vesting or when the pleura is opened for any other reason. levels, relative anaemia is almost universally tolerated.
Pleural drains may be anterior, posterior, or ‘wrap-around’ Haemoglobin levels are thus not routinely treated unless
configurations in which they project over the anterior below 80 g/L, except in the elderly or when there are
lung, following the pleural space first from midline, to significant comorbidities. 19,32 From these levels patients
lateral and then finally the posterior pleural space.
return to normal haemoglobin status within 1 month
Reportable postoperative blood losses vary, but greater postoperatively. 32
than 100 mL/h, or greater than 400 mL in the first 4
hours, would generally be regarded as excessive and
worthy of surgeon notification. Importantly, excessive Contributors to impaired haemostatic capability
bleeding does not always represent a surgical defect that Many factors may contribute to postoperative bleeding by
reoperation might correct, as there are many contributors their influence on coagulation and haemostatic ability.
to impaired haemostatic capability in the cardiac surgical CPB is used in the majority of cardiac surgical cases and
patient (see below). exerts many influences on coagulation, as do additional