* Negative-pressure
pulmonary edema: A phenomenon unique to the postextubation
period and thus pertinent to the PACU is negative-pressure pulmonary edema. As
with other causes of pulmonary edema, findings include coarse breath sounds and
production of pink frothy sputum. Typically in the PACU setting hypoxia and
hypertension precede the telltale physical signs.
·
Recruitment
maneuver, Also known as a vital
capacity (VC) maneuver, the technique consists of giving multiple
manual positive-pressure "sigh" breaths and maintaining pressure at
40 cm H2O for 5-10 seconds in an effort to open, or "recruit," atelectatic alveoli. Nearly all patients experience atelectasis under general anesthesia. A VC maneuver
resolves this atelectasis, but it will recur within 5
minutes or so of breathing 100% oxygen. Atelectasis
recurs more slowly if a lower fraction of inspired oxygen (FiO2) is used (e.g.,
> 45 minutes for FiO2 of 0.30).
·
Diffusion hypoxia
is a decrease in PO2 usually observed as the patient is emerging from an
inhalational anesthetic where nitrous oxide (N2O) was a component. The rapid
outpouring of insoluble N2O can displace alveolar oxygen, resulting in
hypoxia. All patients should receive supplemental O2 at the end of an
anesthetic and during the immediate recovery period.
·
Commonly cited
criteria for intubation and mechanical ventilation in adults include the
following:
PaO2/FiO2 ratio < 300 mmHg
PaCO2 > 50 mmHg in the absence
of metabolic alkalosis (also consider chronicity)
Dead space to tidal volume ratio (Vd/Vt) > 0.6
Respiratory rate > 35
Insufficient negative inspiratory force (NIF) > -20 mm H2O
Tidal volume < 5 mL/kg
Vital capacity
·
Methylmethacrylate,
a cement used in joint
replacement, undergoes an exothermic reaction that causes it to adhere to
imperfections in the bony surface. Hypotension
usually occurs 30-60 seconds after placement of the cement but can occur up to
10 minutes later. Postulated mechanisms include tissue damage from the
reaction, release of vasoactive substances when it is
hydrolyzed to methacrylate acid, embolization,
and vasodilation caused by absorption of the volatile
monomer.
·
DIFFERENTIAL
DIAGNOSIS FOR A NARROW COMPLEX TACHYCARDIA
Sinus tachycardia
Atrial
flutter
Atrial
fibrillation
Multifocal atrial
tachycardia
Atrial
tachycardia
Atrioventricular
nodal reentrant tachycardia (AVNRT)
Atrioventricular
reentrant tachycardia (AVRT)
Junctional
tachycardia
·
Despite its short half-life, adenosine can provoke severe exacerbations of bronchospasm,
and it should be used with caution in patients with a history of asthma or
reactive chronic obstructive pulmonary disease.
·
DIFFERENTIAL
DIAGNOSIS FOR A WIDE COMPLEX TACHYCARDIA
- Ventricular tachycardia
- Supraventricular tachycardia with aberrant conduction, such as with a bundle branch block
- Tachycardia with activation of the ventricles via an accessory pathway (Wolff-Parkinson-White syndrome)
·
Monomorphic ventricular tachycardia is common in patients
with structural heart disease (such as a previous Q wave myocardial
infarction), but it is generally not due to acute ischemia. Polymorphic VT may be seen in a variety of
settings. Patients may have a long QT interval associated with polymorphic
ventricular tachycardia, commonly referred to as torsades
de pointes. This may arise from medications, electrolyte derangements, a
congenital predisposition (long QT syndrome), severe bradycardia,
or myocardial ischemia.
·
TEMPERATURE
DISTURBANCES
- Hypothermia is an extremely common event in the operating room because the environment and the effects of anesthetics increase heat loss. Anesthetics also decrease the ability to generate a response to hypothermia (shivering and vasoconstriction).
- Even mild hypothermia has a negative influence on patient outcome, increasing wound infection rates, delaying healing, increasing blood loss, and increasing cardiac morbidity threefold.
- The best method to treat hypothermia is use of forced air warming blankets. Warm all fluids and blood products. Cover all body surfaces possible, including the head, to further reduce heat loss.
·
A phenomenon unique to the postextubation
period and thus pertinent to the PACU is negative-pressure
pulmonary edema. As with other causes of pulmonary edema, findings
include coarse breath sounds and production of pink frothy sputum. Typically in
the PACU setting hypoxia and hypertension precede the telltale physical signs.
The cause of the edema is the patient's vigorous ventilatory
effort against a partially closed glottis or occasionally a small endotracheal tube. The clinical presentation follows a
rapid emergence, often when the patient has been intoxicated at the time of
induction. This phenomenon should be anticipated in young muscular individuals
but may occur in any patient with some degree of laryngospasm
after extubation.
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