Hypercapnia

Situations requiring specific Rx (other than simply increasing ventilation)

Situations requiring specific Rx (other than simply increasing ventilation)

* Malignant hyperpyrexia
* thyroid storm
* circuit problems (* = increased FiCO2)
exhausted soda lime *
expiratory valve failure *
inadequate fresh gas flow in partial rebreathing circuits *
excessive circuit dead space (i.e. on patient side of Y-piece)

MH ­ Is it?…Isn’t it?…

MH ­ Is it?…Isn’t it?…

* Unfortunately, signs with higher +ve predictive values are not available immediately (e.g. increased CK, myoglobinuria, worsening metabolic acidosis)
* Immediately available clinical signs are non-specific (e.g. increased HR)
* Beware masseter spasm, rigidity of other muscle groups, mottled skin, increased T°C (late sign)
* Keep MH in mind if CO2 continues to rise despite adequate minute ventilation

Management

Management

* Ensure adequate oxygenation
* Ensure adequate ventilation
* Check FiO2
* Blood gases to confirm capnography
* Consider secondary causes, especially those requiring specific Rx (MH, thyroid storm etc.)
* Treat complications of hypercapnia

Ensure adequate ventilation

Ensure adequate ventilation

* Check airway (e.g. is LMA seated well)
* Check circuit (e.g. ventilate manually ­ any obstruction?)
* Check minute ventilation (e.g. ventilator settings or spirometry on ADU if available)

If FiCO2 raised:

If FiCO2 raised:

* Check valves (e.g. expiratory valve stuck open)
* Check if soda lime exhausted
* Check if fresh gas flow inadequate

Complications of hypercapnia

Complications of hypercapnia

* Hypertension, tachycardia
* Pulmonary hypertension
* Arrhythmias

Causes of hypercapnia

Causes of hypercapnia

* Increased CO2 production
* Decreased CO2 excretion
* Increased CO2 delivery to lungs

Increased CO2 production

Increased CO2 production

* Increased temperature (including MH, sepsis)
* Hyperthyroidism (including thyroid storm)
* Exogenous (e.g. CO2 pneumoperitoneum)
* NaHCO3 administration
* Tourniquet release
* Shivering
* Convulsions
* Parenteral nutrition
* Compensation for metabolic alkalosis

Decreased CO2 excretion

Decreased CO2 excretion

* IPPV: inadequate ventilator settings
* Spontaneous ventilation: respiratory depressant drugs
* Partial airway obstruction
* Altered respiratory mechanics (e.g. decreased compliance due to pneumoperitoneum, obesity, Trendelenburg)

Increased CO2 delivery to the lungs

Increased CO2 delivery to the lungs

* Increased cardiac output
* R to L shunt